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Guam YN and Fadeyi MO (2020). Optimisation of sheltered walkways performance to mitigate wind-driven rain in Singapore. Built Environment Applied Research Sharing #03, ISSUU Digital Publishing Platform.

Š BEARS reserves the right to this applied research article

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Optimisation of sheltered walkways performance to mitigate winddriven rain in Singapore Yi-Ting Natalyn Guam and Moshood Olawale Fadeyi,* Sustainable Infrastructure Engineering (Building Services) Programme, Singapore Institute of Technology, 10, Dover Drive, Singapore 138683, Singapore *Corresponding author’s email: fadeyi.moshood@singaporetech.edu.sg

ABSTRACT Sheltered walkways are common urban features in Singapore as pedestrians utilise them as pathways to public transportation locations in Singapore. In a tropical environment like Singapore, with high solar intensity and frequent and heavy rains, the walkways provide essential benefits in reducing users’ thermal discomfort and wetness. Of particular concern in the design of sheltered walkways in Singapore is the need for protection from wind-driven rain. This part of the pedestrian’s comfort is often neglected. Sheltered walkways are built with vertical, and 30° angled rainfall in mind. The considerations of the influence of wind are often neglected in the design of sheltered walkways, which results in a larger area of walkways receiving a high amount of rain penetration. To better evaluate the design of sheltered walkways, it is crucial to understand the pedestrian’s perspective and the correlation between wind and rain, and its effects on sheltered walkway design. Findings from the use of 3Dimensional Computational Fluid Dynamics (CFD) simulations of wind flow and wind-driven rain for sheltered walkway designs are presented in this study. Additionally, a proposed microcontroller prototype, Arduino UNO, is built to validate the feasibility of the design solution. This study demonstrates the importance of considering wind-driven rain during the sheltered walkway design process.

Keywords: Shelter walkways, Wind-driven rain, Land Transport Authority, Computation fluid dynamics, Prototype design, Walk2Ride

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1. INTRODUCTION A Walk2Ride programme is promoted by the Land Transport Authority (LTA), which provides a network of sheltered walkways to allow pedestrians to enjoy convenient connections to public transportation locations, no matter rain or shine. Given the tropical climate of Singapore, weather protection is one of the crucial factors for the considerations in the design of sheltered walkways. However, the existing sheltered walkways designed by LTA, are built with vertical and 30° angled rainfall in mind. The considerations of the influence of wind are neglected in the design of a sheltered walkway, which results in a larger area of the walkway receiving a high amount of rain penetration, and cause discomfort to pedestrians. With the advancement in technologies, the use of CFD simulations to study the interaction between both wind and rain has been widely adopted in many environmentally sustainable design (ESD) firms. The aerodynamics effects on buildings have also been widely studied using full-scale experiments (Pabiou et al., 2015), wind tunnel experiments (Duthinh and Simiu, 2011), and numerical models (Foroushani et al., 2014). However, there is minimal knowledge on the airflow behaviour of sheltered walkways in tropical climates. Subramanian et al. (2019) conducted subjective and objective comfort measurements to improve the performance of sheltered walkways in Singapore. Yet, the focus of the study is on the influence of solar heat gain on sheltered walkways. As the influence of rain is also an important aspect of pedestrian comfort in tropical environment like Singapore, 3D CFD studies on sheltered walkways are required for a detailed analysis of the wind flow and wind-driven rain patterns. As LTA has standardised the design of sheltered walkways across Singapore, similar wind-flow patterns and wind-driven rain distributions can be predicted by performing CFD simulations. This study aims to optimise the performance of sheltered walkways in Singapore, by providing a solution to mitigate the effects of wind-driven rain on pedestrians utilising the sheltered walkways. As an initial step, a literature review and survey are conducted to understand better the background of sheltered walkways and the pedestrian’s perspective. A 3D steady-state CFD Simulation is applied to a standalone sheltered walkway to investigate the effects of wind-driven rain under various wind and rain conditions. The flow field is modelled using the ReynoldsAveraged Navier-Stokes (RANS) equation together with the đ?‘˜ − đ?œ€ turbulence model; where đ?‘˜ represents the turbulent kinetic viscosity and đ?œ€ represents the turbulent dissipation (Chiu et al., 3


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2017). The choice of the turbulence model is based on the existing CFD Methodology for Singapore’s Building and Construction Authority Green Mark, which is further explained in Section 3.2. Eulerian particle tracking is adopted for wind-driven rain CFD simulation to obtain raindrop trajectories on sheltered walkways. The performance of the different mitigation methods is evaluated based on a decision matrix, as explained in Section 3.3. Last, a prototype of a sheltered walkway is designed to conduct experiments and of showcasing the mitigation methods. This study is also intended to support future sheltered walkway research and design. According to the ministry of transport Singapore, more than 60 new mass rapid transit (MRT) stations are being built. Hence, 100km of the new sheltered walkway will be constructed by 2029, to serve the extensive public transportation network. Consequently, research on sheltered walkways is expected to increase significantly due to the increasing numbers of new sheltered walkways planned. It is also crucial to recognise that rain penetration on pedestrians provides a severe level of discomfort; which is generally not considered in pedestrian comfort studies for sheltered walkways. This study is conducted in the context of Singapore. Singapore is located at the southern tip of Malay Peninsula, at 1.29° North and 103.85° East; and is classified under a tropical rainforest climate with no distinctive seasons. Its climate has a uniform temperature, high humidity, and abundance of rainfall of about 2165.9mm. At the same time, the wind speed experiences significant variances due to the monsoon seasons over a year. The climatic data used in the study were obtained from meteoblue.

(a): Front View of Sheltered Walkway

(b): Side View of Sheltered Walkway

Figure 1: Modelled Sheltered Walkway Configuration

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The sheltered walkway configuration used in this study is based on the LTA and Urban Redevelopment Agency (URA) Walking and Cycling Design Guide for Covered Linkway (Figure 1a and 1b). A typical sheltered walkway has a dimension of 2.4m or 3m width and standing at 2.4m height (Figure 1a). Besides, it has a sloped roof with an inclination of 3° (Figure 1b). The height and width ratio is designed to protect pedestrians from light rain, while the downward sloped roof is designed to direct rainfall into the pavement drainage system.

2. SURVEY As part of the research to assess the existing sheltered walkway design to the general public, a survey was conducted. The general public of all age groups, living in Singapore was involved in the survey study. Respondents were asked to answer the effectiveness of the sheltered walkway, during a heavy downpour, based on their daily routine. 2.1

Methodology for Survey Administration

A preliminary survey was carried out with five random participants to assess the practicability and ease of understanding for each question. Based on the feedbacks retrieved from the five respondents, the questionnaires were adjusted and distributed to the general public. The questionnaire includes a prologue, which describes the purpose, background, and problem statement of this study. The prologue ensures that respondents understand the context of the survey before attempting it. During the conduct of the survey, a total of eight questions were asked to the general public. The flow chart of the survey questionnaire is given in Figure 2, while the survey questions and their answer options are as listed in Table 1. The questions in Table 1a were designed to get an overview of the respondent’s general feedback with regards to their daily routine. Respondents are questioned on their daily utilisation of sheltered walkways and the efficiency of the existing sheltered walkway design to determine the practical use of sheltered walkways in Singapore. This is carried out to understand better respondent’s present impression of the existing sheltered walkway design. It is important to note the respondent’s frequent means of transportation as well, as Sheltered Walkways are not only positioned near bus stops and MRT stations. Those travelling via private or personal transportation, likewise, use these sheltered walkways at other locations.

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Figure 2: Flow Chart of Survey

The questions in Table 1b were designed to get an overview of the feedback from respondents who frequently travel around Singapore by public transportation. It is crucial to consider their feedbacks as sheltered walkways are provided primarily for pedestrians traveling to bus stops or MRT stations. Since the primary intention of the study is to evaluate the design of existing sheltered walkways to mitigate wind-driven rain, respondents were given a scenario-based question to comprehend their decision making in times of heavy downpour. Besides the scenario-based questions, respondents were questioned with an open-ended response on their decision in utilising the sheltered walkways during times of heavy rain. The questions in Table

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1c were designed to get a comprehensive understanding of the respondent’s viewpoint of the efficiency of the existing sheltered walkways during times of heavy downpour. Respondents are posed with other scenario-based questions, and the questions are provided with on-site photographs. The photographs are provided to ensure that respondents understand the situation and answer the questions accordingly. The questions in Table 1d were designed to get an understanding of the respondent’s viewpoint of the new sheltered walkways design. Therefore, it is crucial to question their thoughts on the advantages of the existing sheltered walkways design. By recognising the advantages of existing sheltered walkways design, certain features of the existing sheltered walkways can be incorporated into the new design. Since sheltered walkways are ultimately designed for the pedestrians living in Singapore, the design should appeal to these pedestrians. Thus, respondents were questioned on the type of designs they would appreciate, for the new sheltered walkways. The answer options provided are the existing passive design for rain shade in the residential areas and other facilities. In addition, respondents were given the opportunity to provide interesting designs for the new sheltered walkways, via an open-ended answer option. Table 1: Survey Questionnaire 1a: Section One – General Feedback Question

Answer Options More than Twice a day (Everyday)

1

How often do you utilize the

Once a day (Everyday)

sheltered walkways?

Three Days a week One Day a week

2

Do you think sheltered walkways

Yes

are designed efficiently?

No a. Public Transportation (Bus, MRT, LRT)

3

What is your frequent means of transportation on a weekly basis?

b. Private Transportation (Grab, Gojek, Taxi) c. Personal Transportation (Car, Van, Motorcycle)

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1b: Section Two – Public Transportation Question 4

Answer Options

In this scenario, which will you

i. Still Walk to take Public Transportation

prefer?

ii. Just book Private Transportation

Provide some reasons on the 5

willingness to take Public

Open Ended Paragraph Answer

Transportation in such a weather

1c: Section Three – Efficiency of Sheltered Walkways Question 6

Answer Options

In this scenario, would you prefer a

i. Yes

more efficient sheltered walkway?

ii. No

1d: Section Four - Sheltered Walkway Design Question 7

What is the advantage of existing sheltered walkway design?

Answer Options Open Ended Paragraph Answer Retractable Roller Shade at the side

What kind of designs would you 8

love to see for the new sheltered walkways?

Louvres at the side Extended Width of the Sheltered Walkways Others: Open ended Answer

2.2

Respondents

The survey was conducted for one month, from the 9th of September 2019 to the 9th of October 2019. The survey reached out to 208 participants. The survey is distributed via different modes of social media, such as WhatsApp and Telegram. Respondents can click the provided link in the text message and attempt the survey through an online platform, Google Forms. The return ratio of the survey was 89.4%, which is a total of 186 respondents. 2.3

Results and Discussion

Figure 3a shows the respondent’s average usage of sheltered walkways, based on a week. Most of the respondents (60.8%) stated they use of sheltered walkways for more than twice a day, 8


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while 22% of the respondents utilise sheltered walkways once a day, both daily. A minority of respondents (7%) stated they use sheltered walkways for about three days a week, while 10.2% of the respondents utilise sheltered walkways one day a week. Supplementary to the survey results, one of the respondents explained that the lack of use is as a result of absence of sheltered walkways in the vicinity. The impression of the efficiency of the existing sheltered walkway design is dependent on the pedestrians, who utilise these sheltered walkways. From Figure 3b, more than half of the respondents (65.6%) agreed that the existing sheltered walkways are efficient, while 34.4% of the respondents disagreed. This impression of an efficient sheltered walkway could be forged as a result of respondents utilising sheltered walkways, particularly during non-rainy periods. The most common mode of transportation is by public transport such as buses, MRTs, and light rail transit (LRT). To be specific, respondents who travel via public transportation accounts for 78.5%, while those that travel via private and personal transportation accounts for 2.7% and 18.8%, respectively (Figure 3c). Considering the cost of owning a personal vehicle and the surge in private transportation prices in Singapore, it is reasonable that most respondents travel via the cheapest form of transportation. Based on Figure 3c, a total of 146 respondents declared that they travel via public transportation. However, when respondents are faced with a heavy downpour scenario in sheltered walkways, 17.8% of respondents are more willing to book private transportation to travel to their destination (Figure 3d). The remaining 82.2% of respondents are still inclined to commuting via public transportation, despite the physical discomfort from the rain. Based on the openended answers, the majority responded that they are not willing to pay extra for transportation as private transportation prices usually are hiked during periods of heavy downpour in Singapore. Although 65.6% of the total respondents (Figure 3b) agree that the existing sheltered walkways are efficient, the numbers drastically fell after respondents are placed in scenarios-based questions. As shown in Figure 4e, the majority of the respondents (95.7%) want to have a more efficient sheltered walkway, while 4.3% of the respondents disapprove. The impression of respondents could have changed based on the heavy downpour scenario, provided in some of 9


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the questions. Before the survey questionnaire comes to a closure, respondents were requested to select the types of design they would appreciate, for the new sheltered walkway. Since there are about 246km of existing sheltered walkways in Singapore, it is impractical to design entirely new sheltered walkways. Therefore, the types of designs to mitigate wind-driven rain should be easily installed on existing sheltered walkways. As sheltered walkways are designed for the use of pedestrians, respondents must be involved in the design process of the sheltered walkways, ensuring that they benefit from the new sheltered walkways.

Figure 3a

Figure 3b

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Figure 3c

Figure 3d

Figure 3e Figure 3: Survey results 11


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3. COMPUTATIONAL FLUID DYNAMICS SIMULATIONS In recent years, the development of computer simulations enables large-scale simulations to be conducted to understand fluid flows, which allows a virtual analysis of the performance and effectiveness of the existing or intended design. Raman et al. (2018) explain the concept of CFD application, which includes a combination of physics, mathematics, computer technology, and flow fields. CFD is capable of predicting the behaviour of fluids by solving the NavierStokes equation by satisfying three conservation laws, which are mass, momentum, and energy. 3.1

Methodology of Simulation Study

To further understand how wind-driven rain affects the sheltered walkways, CFD simulations were conducted on a 3D modelled sheltered walkway. The type and methodology of the simulations to be conducted is based on Singapore’s Building and Construction Authority (BCA) Green Mark Criteria, Technical Guide, and Requirements. Table 2 shows the atmospheric boundary conditions, which provides an estimation of the suitable wind speed for wind-driven rain simulation, based on National Environmental Agency’s (NEA) 32-year weather data at a reference height of 15m. Furthermore, BCA states the four different raindrop sizes to be analysed, 0.5mm, 1.0mm, 2.0mm, and 5.0mm. With that, wind-driven rain simulation was carried out in accordance with BCA’s standards for a strict identification process of the severity of rain penetration in a sheltered walkway. Table 2: Wind-Driven Rain – Atmospheric Boundary Conditions (Source: www.bca.gov.sg)

To simulate a sheltered walkway with accurate estate and climatic details requires a large amount 12


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of simulation time. As it would be biased to simulate specific wind directions according to specific estates, the wind direction and speed will not be accurately simulated as per current environmental conditions. With that, to determine the best and worst-case wind-driven rain scenario, the lowest and highest wind speed from Table 2, is used as the simulation parameter (Table 3a). The wind direction is decided based on the most impactful wind-driven rain scenario, as seen in Figure 4a. The sheltered walkway is designed as a control model for all four simulations to ensure the accuracy of results. Sheltered walkways are designed to allow pedestrians to enjoy convenient connections to public transportation locations, no matter rain or shine. Hence, simulation must be performed on a model that includes both a sheltered walkway and a human to mimic the real-life experience. From this, simulation results will exhibit the severity of wind-driven rain, on both the human and sheltered walkway’s footpath. The simulation parameters for the human model simulation (Table 3b) is determined by the worst-case wind-driven rain scenario, which is 8.4m/s. Table 3: Computational Fluid Dynamics Simulation Parameters 3a: Existing Sheltered Walkway Model Wind Speed

Wind Directions

2.9 m/s

North

South

8.4 m/s

North

South

3b: Human with Sheltered Walkway Model

Wind Speed 8.4 m/s

Wind Directions North

South

The new sheltered walkway should be designed efficiently to mitigate wind-driven rain on pedestrians. Based on the survey results (Figure 3), each design solution is simulated to identify the most desirable sheltered walkway to mitigate wind-driven rain. The simulations performed for all design solutions ought to have the same control parameters, such as the wind speed and wind direction. From the earlier two groups of simulation mentioned, the wind speed and wind direction adopted is 8.4m/s and South Wind, respectively. In addition, a fair evaluation is conducted by performing the simulation consistently on the same base model, which includes

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both sheltered walkways and a human. Figure 4c shows the illustration of four design solutions implemented on an existing sheltered walkway.

Figure 4a: Basic Simulation Model

Figure 4b: Human Simulation Model

Figure 4c: Sheltered Walkway Design Simulation Model Figure 4: Simulation Models

3.2

Methodology of CFD Simulation

To assess the naturally ventilated building designs in Singapore, BCA launched a CFD Ventilation Simulation Methodology and Requirement in 2008. According to Poh et al. (2019), the CFD Ventilation Simulation Methodology takes reference from different international standards, to enhance the limited guidelines on natural ventilation in Singapore. Therefore, by integrating the BCA Green Mark Scheme into the CFD simulations of a sheltered walkway, a guided process is engaged to ensure the accuracy and quality of simulation results. An opensource CFD Solver, OpenFOAM, solve the performed numerical CFD simulation. The preprocessing of the numerical CFD simulations is achieved by using graphical interface software, BIM HVACTool, designed by Tian Building Engineering. 14


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3.2.1 Computational Geometry and Grid The geometry of the sheltered walkway itself has a dimension of 2.5m height and width. The length of the sheltered walkway is insignificant as the study is focused on the depth of rain penetration on the width of the sheltered walkway’s footpath. To ensure that the CFD numerical simulation is performed accurately, it requires a computational domain that satisfies the direction blockage ratio as required by BCA CFD Ventilation Simulation Requirements. A computational domain is defined as a region in space in which numerical equations of fluid flows are solved by CFD (Çengel and Cimbala 2006). Tominaga et al. (2008) pointed out that the frontal blockage ratio should be below 3% to avoid any artificial acceleration of the fluid flow during the conduct of the CFD Simulation. The frontal, lateral, and vertical blockage ratio equations are provided by BCA, as shown below. The existing sheltered walkway design has a computational domain dimension of 700m x 200m x 30m (L x B x H), while the human simulation model has a dimension of 250m x 100m x 15m. Table 4 shows the blockage ratio of the sheltered walkway simulations.

Frontal Blockage Ratio Measured from the direction of the wind flow

đ??ľđ?‘… =

đ??š đ??š

< 3%

Lateral Blockage Ratio

Vertical Blockage Ratio

Measured from the lateral direction of

Measured from the tallest building in

the wind flow

the domain

đ??ľđ?&#x2018;&#x2026; =

đ??ż đ??ż

< 17%

đ??ľđ?&#x2018;&#x2026; =

đ??ť

,

đ??ť

< 17%

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Table 4: Blockage Ratio of CFD Simulation Study

Simulation

Blockage Ratio Frontal

Lateral

Vertical

Existing Sheltered Walkway

2.86%

1.25%

8.33%

Sheltered Walkway with Human Geometry and Design

2.8%

2.5%

16.67%

With only the computational domain, it is impossible to solve the complicated Navier-Stokes equation. Hence, OpenFOAM is essential to assist in the discretisation process of the computation domain. Discretisation approximates the complex equations allowing them to be easily solved by computers (Sosnowski, 2018). Therefore, the discretisation process generates computational grids with a multiblock mesh generator (blockMesh) provided by OpenFOAM (Soner and Ozturan 2015). However, for complex geometries like sheltered walkways, it requires a new process known as the snappyHexMesh. It refines the existing mesh iteratively and integrates the mesh to the surface of the geometry. To ensure the quality of the simulation results, BCA has provided a computational grid size guideline (Table 5). The computational grid of the existing sheltered walkways and the sheltered walkway with human geometry can be observed in Figure 5. Table 5: Recommended Computational Grid Size (source: www.bca.gov.com.sg)

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Figure 5: Computational Grid â&#x20AC;&#x201C; Existing Sheltered Walkway (Top), Human Geometry (Bottom)

3.2.2 Boundary Conditions, Turbulence Models and Solver Settings This section intends to provide information about the specific boundary conditions, turbulence models, and solver settings required to perform the numerical CFD simulations. To perform a wind-driven rain case, 3D CFD wind flow simulation should be performed beforehand to capture the realistic wind flow patterns over the modelled sheltered walkway. Thereafter, a Eulerian multiphase model is performed to calculate the specific catch ratio distribution on the human body and footpaths of sheltered walkways. The specific catch ratio is determined by three factors, the referenced wind speed, referenced rain intensity, and the horizontal distribution of 17 different rain droplets sizes (Blocken et al., 2005). 3.2.2.1 Wind flow case Majority of the 3D CFD wind flow studies are performed with a steady-state simulation approach. The CFD code, OpenFOAM, is used to solve the 3D RANS equation together with the realizable đ?&#x2018;&#x2DC; â&#x2C6;&#x2019; đ?&#x153;&#x20AC; turbulence model. Van Hooff et al. (2011) explained the use of the realisable đ?&#x2018;&#x2DC; â&#x2C6;&#x2019; đ?&#x153;&#x20AC; turbulence model to be directly relatable to the accuracy of the CFD wind17


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driven rain simulation when compared to a full-scale measurement. Therefore, the use of the realisable đ?&#x2018;&#x2DC; â&#x2C6;&#x2019; đ?&#x153;&#x20AC; turbulence model is adopted for this study. The parameters of the realizable đ?&#x2018;&#x2DC; â&#x2C6;&#x2019; đ?&#x153;&#x20AC; turbulence model can be easily modified through the boundary conditions of the computational domain, according to the simulation requirements. The computational domain is bounded by six faces, where five boundary conditions are applied to each face. The computational domain and its individual faces are shown in Figure 6, while Table 6 shows the computational domainâ&#x20AC;&#x2122;s boundary condition, provided by a local company in Singapore called Tian Building Engineering Pte Ltd.

Figure 6: Computational Domain Table 6: Boundary Conditions of Computational Domain

At the inlet of the computational domain, it imposes a neutral Atmospheric Boundary Layer (ABL) to establish an environment that is similar to the natural environment that pedestrians experience. As stated by Poh et al. (2019), ABL is represented in the CFD simulation by an inbound vertical wind profile that is based on a Logarithmic Law with a reference height of 15m. Furthermore, the logarithmic wind profile determines the vertical distribution of the

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average wind speed at different heights. The two equations provided below shows the derivation of the vertical wind profile (Figure 7). Equation two is applied to derive the wind speed at the specified height. Equation 1:

đ?&#x2018;&#x2C6;â&#x2C6;&#x2014;

Equation 2: đ?&#x2018;&#x2C6;(đ?&#x2018;§) =

=

đ?&#x2018;&#x2C6; â&#x201E;&#x17D;+đ?&#x2018;§ ln đ?&#x2018;§

đ?&#x2018;&#x2C6;â&#x2C6;&#x2014; đ?&#x2018;§+đ?&#x2018;§ ln đ?&#x153;&#x2026; đ?&#x2018;§

Where,

đ?&#x2018;&#x2C6; â&#x2C6;&#x2014; : ABL friction velocity đ?&#x153;&#x2026; : von Karman constant (0.42) đ?&#x2018;§ : Aerodynamic roughness length đ?&#x2018;&#x2C6; : Specified velocity at reference height h đ?&#x2018;§ : Specified Height

Figure 7: Vertical Wind Profile â&#x20AC;&#x201C; 2.9m/s (Left), 8.4m/s (Right)

Since wind is significantly influenced in the presence of nearby walls, such as the bottom and solid geometry boundaries, a near wall treatment is applied using the standard wall-function method. The wall-function method models the velocity profile from the first point to the wall. Thus, the near wall boundary conditions are provided by bridging the inner regions between walls and developed turbulence regions (Launder and Spalding, 1974). 3.2.2.2 Wind-driven rain case Following the completed 3D CFD wind flow simulation study, the evaluation of wind-driven rain on the sheltered walkway is performed by a numerical CFD simulation that is presented based on the Eulerian multiphase model. The Eulerian multiphase model is applied instead of the Lagrangian multiphase model, as rain droplets in the Eulerian approach are regarded as a 19


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continuum like wind, instead of individual rain droplets. Huang and Li (2010) justified that the Eulerian multiphase model reduces the complexity of evaluating wind-driven rain parameters. Furthermore, wind-driven rain simulations based on the Eulerian Multiphase model are verified to be reliable and accurate when compared with the available numerical and experimental data (Blocken and Carmeliet, 2007). For a wind-driven rain simulation, only the Top and Front is specified as an inlet while the rest are specified as a wall. At the inlet of the computational domain, the specification of the rainfall intensity, rain droplets sizes, and velocity are required. The volume of water per hour can express rainfall intensity (mm/hr) in a unit area. For the study, a rainfall intensity of 25mm/hr is applied for each wind-driven rain simulation study. The rainfall intensity is selected based on the highest rainfall intensity, as shown in the pre-processing graphical interface software, BIM HVACTool. To determine the severity of wind-driven rain on sheltered walkways, 17 different rain droplets sizes are injected into the computational domain. Kubilay (2014) explains that rain droplets with a diameter of smaller than 0.3mm are of nearly perfect spheres and also known as a drizzle. Hence, rain droplet sizes smaller than 0.3mm are not considered in this simulation study. In addition, considering that any rain droplets larger than 6.0mm is known to break apart when they fall, the upper limit for the largest rain droplet diameter is set at 6.0mm. As the study focuses on wind-driven rain, an oblique rain intensity vector is formed as a result of the occurrence of wind and rain. Rain droplets motions for wind-driven rain is governed by gravity and drag forces, where the horizontal component shows the wind intensity on rain droplets based on drag. In contrast, the vertical component shows the horizontal rainfall intensity based on gravity. By adopting the Eulerian multiphase method, each class of rain droplet sizes is regarded as a different phase since similar rain droplet sizes interact with the wind flow in a similar manner (Kubilay, 2014). Once the governing equations for the rain phases are solved, the specific catch ratio distribution for each rain droplet size can be calculated. The specific catch ratio locates the catchment of rain trajectories on the sheltered walkway. Thus, the specific catch ratio is capable of determining the severity of wind-driven rain on sheltered walkways. . 3.3

Simulation Results and Discussion

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As the sheltered walkways designs are evaluated using the BCA CFD Ventilation Simulation Methodology and Requirements Technical Guide, it requires the analysis of only four different rain droplet sizes and their respective terminal velocity. In this section, three different groups of simulation results are evaluated. The three groups are existing sheltered walkways, a sheltered walkway with human geometry, and lastly, the different sheltered walkway design solutions. The three groups are evaluated based on the specific catch ratio of the different rain droplets size analysed. 3.3.1 Wind Flow Analysis Figure 8 shows the wind-flow patterns of all three groups on a horizontal plane at the height of 1.2m above ground level. From Figure 8a, due to the two different wind speed simulated, it utilises a different velocity magnitude scale during the comparison. Based on the observed wind velocity vectors, the columns of the sheltered walkway alter the wind flow patterns, resulting in an increase in wind velocity in the areas between the columns. The wind flow pattern is similar across all four simulations of the basic simulation model as they are simulated with the same geometry. However, human geometry may change the wind-flow patterns in the sheltered walkways. To test the effectiveness of the sheltered walkways that LTA designed, the sheltered walkway is also simulated with a human geometry (Figure 8b). The addition of human geometry in the simulation drastically changes the wind-flow pattern around the columns. As the north wind comes into contact with the columns first, wind speed is decelerated before reaching human geometry. Subsequently, wind velocity is further decelerated. However, for the south wind direction, the area between the sheltered walkway roof and human geometry is significantly reduced. Based on the principals of fluid mechanics, a smaller area results in a higher velocity. Hence, the wind velocity above human geometry increased. Furthermore, the edge of the sheltered walkway created a cornering effect, which increases the wind velocity as well. After testing the effectiveness of the sheltered walkways, the developed design solutions should mitigate wind-driven rain. Although the solution should be able to mitigate wind-driven rain, the design solution must also provide thermal comfort to the pedestrians. From Figure 8c, the thermal comfort for the Louvres is the highest, as compared to the rest of

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the design solutions. The sheltered walkway designed with the louvres shows similar wind-flow patterns when compared to the existing sheltered walkway. Therefore, there is a likelihood that the sheltered walkways will be affected heavily by wind-driven rain, due to the similarities in wind-flow patterns. However, when Roller Rain Shade is implemented, the wind-flow pattern significantly changed due to the blockage of wind, from the rain shade. A cornering effect is noticed on the corners of the rain shade, which increases wind speed as more wind enters the sheltered walkway. This results in the thermal comfort of humans, not being compromised. Other than the three-design solution mentioned above, the other solutions that have similar windflow patterns are the angled rain shade with louvres. As both the rain shades are designed the same, it is evident that the wind-flow patterns would be similar. However, as both the slanted rain shade is constructed with different angles, the wind speed experienced can differ slightly.

Figure 8a: Wind Flow of Existing Sheltered Walkway

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Figure 8b: Wind Flow of Existing Sheltered Walkway with Human Geometry

Wind Direction

Wind Direction

Figure 8c: Wind Flow of Sheltered Walkway Design Figure 8: Wind Flow Analysis

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3.3.2 Depth of Rain Penetration Figure 9 shows the various simulation results graph, where the depth of rain penetration is plotted against the rain droplet size. The values provided are estimated based on the wind-driven rain simulations performed. The depth of rain penetration (Figure 9a) differs greatly based on the two wind speeds simulated. For the North Wind Simulation, at 2.9m/s wind speed, the depth of rain penetration is noticed to decrease gradually from 0.5mm to 6.0mm. Hence, with higher wind speed, wind-driven rain intensity increases, which results in the rain droplets travelling further. For the South Wind Simulation, based on the depth of rain penetration values, it can be deduced that rain penetrates fully on the footpath due to the lack of columns placed at the exterior edge of the sheltered walkway. The placement of columns in sheltered walkways is very important as it alters the wind-flow patterns to reduce the depth of rain penetration into the footpaths of sheltered walkways. The graph in Figure 9b shows the depth of rain penetration against the rain droplet diameter of the five different design solutions. The values provided are estimated based on the wind-driven rain simulations performed. Based on the depth of rain penetration results, the Roller Rain Shade proved to be the most effective solution out of the five design solutions. Considering that the Roller Rain Shade encloses the entire sheltered walkway, it is natural that wind-driven rain is eliminated from the sheltered walkways. Based on the simulation results, the louvres are deemed to be an ineffective solution as the depth of rain penetration is the highest amongst all five design solutions. From on-site observations, one side of the sheltered walkway is blocked by the development. Hence, a Roller Rain Shade fixed with louvres is simulated. From the results, it shows that the louvres mitigate wind-driven rain better when installed with roller rain shade. Simulation results might differ if the simulation is performed with the prevailing wind direction facing the louvres. From the survey results, one of the design solutions is to extend the width of the sheltered walkways. Therefore, a slanted rain shade is suggested. However, there are two different angles used to perform the simulation. This is done to analyse the level of rain penetration when the rain shade is slanted at different angles. Although the depth of rain penetration is similar for the smaller rain droplet sizes, the 45° slanted rain shade prevents further rain penetration from larger droplet sizes.

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Figure 9a: Depth of Rain Penetration for Existing Sheltered Walkway Design

Figure 9b: Depth of Rain Penetration for Sheltered Walkway Design Solutions Figure 9: Depth of Rain Penetration VS Rain Droplet Diameter graph

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3.3.3 Sheltered Walkway Wind Drive Rain Simulation Results According to BCA, four rain droplets diameter is required for analysis. Hence, based on Figure 10, a comparison of the four rain droplet diameter is made for each scenario. From Figure 10a, although each wind speed and direction demonstrate different severity of wind-driven rain, rain droplet of diameter 0.5mm shows a significant impact of wind driven rain on all scenarios. Considering that the horizontal rainfall intensity decreases as the rain droplet diameter decreases, with the same amount of wind-driven rain intensity applied; the rain droplet is capable of travelling a further distance. Additionally, it can be observed that the South Wind with a wind speed of 8.4m/s is the worst-case scenario, based on the four rain droplet sizes compared. Hence, similar to the graph above, the worst-case scenario is determined to be the south wind, at 8.4m/s. Sheltered walkways are designed for safe and comfortable use for pedestrians. Hence, it is important to observe the severity of wind-driven rain on human geometry itself. Figure 10b shows the comparison based on the individual scenario to determine the severity of wind-driven rain. For both the north and south wind scenarios, although the severity of wind-driven rain decreases as the rain droplet size increases, the full body is still affected by wind-driven rain. However, the north wind scenario is observed to be the worst-case scenario. This might be caused by the position of human geometry, which is situated nearer to the edge of the sheltered walkway. Hence, it directly impacts human geometry, which causes it to be fully wet, regardless of the rain droplet size. Figure 10c shows the severity of wind-driven rain on the five design solutions. The louvres manage to mitigate wind-driven rain by reducing the severity of it on the human body. Yet, the rain droplets of diameter 0.3mm to 2.0mm affects more than half of the entire human body. However, when the louvres are simulated with the Roller Rain Shade, it is seen to be very effective in mitigating wind-driven rain. In addition, a close comparison between the 30° and 45° slanted rain shade is observed. Both slanted rain shade is capable of mitigating wind-driven rain effectively as the human geometry on both simulations is observed to be dry. However, the rain droplet of diameter 0.5mm affects human geometry at the calf area, at a negligible extent. Although the calf area is affected, survey results proved that pedestrians do not mind unless their full body is drenched from the cause of wind-driven rain. 26


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All in all, based on the depth of rain penetration into the sheltered walkway and the wind-driven rain impact on human geometry, the design solutions that are the most effective are the Roller Rain Shade and the 45° slanted Rain Shade with Louvres. In addition, based on the simulation results for Louvres with Roller Rain Shade, it is evident that if the sheltered walkways are designed with both the 45° slanted Rain Shade and Roller Rain Shade, it would still mitigate wind-driven rain efficiently. Considering that not all sheltered walkways are obstructed at the North and Southside, it is essential to also develop a passive design solution, instead of only an active design solution, which is the automated roller rain shade. Hence, both the Roller Rain Shade and 45° slanted Rain Shade with Louvres can be installed at all types of sheltered walkways in Singapore.

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Blue Area represents a heavier rain penetration (Wet) while Grey areas represents relatively little or no rain penetration (Dry) Red Arrow shows the wind direction

North Wind, 2.9m/s

North Wind, 8.4m/s

South Wind, 2.9m/s

South Wind, 8.4m/s Figure 10a: Severity of wind-driven rain for existing sheltered walkway

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Blue Area represents a heavier rain penetration (Wet) while Grey areas represents relatively little or no rain penetration (Dry) Red Arrow shows the wind direction

South Wind, 8.4m/s

North Wind, 8.4m/s

South Wind, human geometry

North Wind, human geometry

Figure 10b: Severity of wind-driven rain for human geometry model 29


BEARS #03 Blue Area represents a heavier rain penetration (Wet) while Grey areas represents relatively little or no rain penetration (Dry)

30° Slanted Rain Shade with Louvres

Louvres

Louvres with Roller Rain Shade

45° Slanted Rain Shade with Louvres

Roller Rain Shade

Figure 10c: Severity of wind-driven rain on sheltered walkway design solution Figure 10: Comparison of the severity of wind-driven rain based on depth of rain penetration

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4. PROTOTYPE DEVELOPMENT The development of a prototype is crucial as it is directly related to the effectiveness of the design solution. The effectiveness of the prototype is deemed by performing an actual scaleddown experiment in the natural environment, along with the completed computer simulations. The prototype is constructed based on the simulation results (Section 3.3), where the final design solutions are determined to be preferable to mitigate wind-driven rain on pedestrians. 4.1

Physical Prototype

This section is intended to highlight the development of the physical prototype. As mentioned in the earlier part of the study, solutions should be designed to be conveniently installed on the existing sheltered walkways. As the design solution consists of both passive and active design solutions, the two prototypes will be fixed on to the same main body to ensure consistency during the experiment. However, the automated roller rain shade also requires the use of an Arduino system, which is an open-source electronic prototyping platform. The Arduino prototype controls the automated roller rain shade, to allow the plastic sheet to roll down when rain is detected. The Arduino prototype and its functions will be further explained in section 4.2.

45° slanted rain shade with louvre – Front (Left), Side (Right)

Automated Roller Rain Shade – Front (Left), Side (Right) Figure 11: Physical Prototype

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4.2

Arduino Prototype

Automatic rain-sensing rolling shades are introduced in this section of the study. Incoming rain is detected via the Arduino system, where the roller shade can be engaged when a heavy downpour is detected. The Arduino system consists of a raindrop sensor module that detects the intensity of the rainfall and acts as required. Rainfall intensity data is sent to the main Arduino UNO board, which engages the roller shade once requirements are satisfied. The 5V DC Stepper Motor controls the roller rain shade. 4.2.1 Required Hardware Components The hardware components used in this design are as listed below. 

Arduino UNO

Raindrop Sensor

Raindrop Sensor Module

5V DC Stepper Motor

ULN2003 Driver Module

LED Indicator

Buzzer

4.2.2 Automated Roller Rain Shade System The system block diagram, flow chart, and overall circuitry of the Automated Roller Rain Shade are shown in Figure 12. The raindrop sensor detects the rain intensity while it’s sensor module acts as a resistor, which changes its resistance when the raindrop sensor circuit is wet or dry. The Arduino UNO microcontroller receives these data from the raindrop sensor module and transmits it to the ULN2003 Driver Module. The data retrieved by the ULN2003 driver module controls the turning direction of the 5V DC stepper motor, which is used to rotate the physical roller rain shades. When the 5V DC Stepper Motor is activated, the LED Indicator and Buzzer is activated at the same time as well. The LED Indicator and Buzzer ensures that all pedestrians notice that the roller rain shade is activated and moving.

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Figure 12a: System Block Diagram of Automatic Rain sensing Roller Shade

Figure 12b: Overall Arduino Circuit

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Figure 12c: Flow Chart of the overall Arduino System Figure 12: Overall Arduino system

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4.2.3 Operation of the System In this Arduino prototype, the Arduino UNO microcontroller is the main brain that controls the ULN2003 Driver Module and the Raindrop Sensor Module. The main requirement for this system is the initialization of the raindrop sensor module and the ULN2003 Driver Module. Once the requirements are appropriately set, the system can operate to get the ideal results. The raindrop sensor detects the rain intensity and sends the data collected to the raindrop sensor module. Thereafter, the retrieved data is transmitted to the Arduino UNO microcontroller. A set of codes is written to the Arduino UNO microcontroller to recognise the data received from the raindrop sensor module. Considering that the Raindrop Sensor Module outputs the data in an analog voltage, the analog-to-digital converter in the Arduino UNO microcontroller reads the changing voltage and converts it to numbers for better visualisation. The numbers indicate the level of resistance of the raindrop sensor, ranging from 0 to 1024, where 0 represents the minimum limit, and 1024 represents the maximum limit that the sensor can detect. To ensure that the raindrop sensor works efficiently and accurately, it is programmed to detect rain droplets on the raindrop sensor continuously. Therefore, the raindrop sensor automatically sends data to the raindrop sensor module even when there is no rain droplet detected. However, in cases where the raindrop sensor detects rainfall, the Arduino UNO microcontroller will send the required data to the ULN2003 Driver module to activate the 5V DC Stepper Motor. Another set of codes is written to the Arduino UNO microcontroller, for the ULN2003 Driver Module and 5V DC Stepper Motor, as they read a different library from the raindrop sensor module. The set of codes allows the Arduino UNO microcontroller to input a set of instructions into the ULN2003 Driver Module, to activate the 5V DC Stepper Motor. The ULN2003 receives steps and directional signals from the Arduino UNO microcontroller and converts the information into electrical signals to activate the 5V DC Stepper Motor. The activated 5V DC Stepper Motor will rotate the rotor based on the number of revolutions specified in the codes. One revolution of the rotor is equivalent to 2048 steps. Since the Roller Rain Shade is fixed to the rotor, as the rotor rotates, the Roller Rain Shade is operated. Additionally, once the 5V DC Stepper Motor is activated, the buzzer and LED indicator will be activated simultaneously.

5. EXPERIMENT

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Based on the physical prototype developed, a physical experiment is conducted to determine the effectiveness of the active and passive design, in mitigating wind-driven rain. To prevent any interference of the experiment from the different design solutions, the experiment for the automated roller rain shade prototype is conducted before the construction of the 45° Slanted Rain Shade with Louvres. Thereafter, the 45° Slanted Rain Shade with Louvres is constructed onto the sheltered walkway prototype, where the experiment proceeds. The experiment is conducted in a natural environment where a kestrel device is utilised to measure the wind speed, while a handheld fan is utilised to blow wind to the prototype. Rain is simulated by using a Handheld Pressure Sprayer to spray water onto the prototype. Similar wind speed reading is achieved to prove that the experiment is conducted similarly and accurately for the comparison of results.

Both the automated roller rain shade and 45° Slanted Rain Shade with Louvres experiment are conducted via the same process as well. This is to ensure that the experiment is done similarly and accurately for the comparison of results. The process is as described: 1) Place the prototype at the same location that is blocked by natural wind 2) Stand about 1m away from the prototype 3) Hold the Handheld Pressure Sprayer at chest level 4) Spray the prototype for about 5 seconds The first experiment conducted with the automated roller rain shade is to test the efficiency of the active design and, at the same time, the efficiency of the Arduino prototype. All of the hardware components and devices are connected and fixed on the physical prototype. The total number of revolutions required is calculated at 3.5 revolutions to ensure that the roller rain shade can cover the height of the sheltered walkway. This is done based on the height of the sheltered walkway and the revolutions of the rotor. As the rain sensor is required to be placed at a position that detects rain droplets easily, it is placed on top of the roof of the sheltered walkway. The second experiment is conducted with the 45° Slanted Rain Shade with Louvres, to test the effectiveness of the passive design, in mitigating wind-driven rain. Figure 13a shows the overall experimental setup for the experiment conducted with the automated roller rain shade and 45° Slanted Rain Shade with Louvres.

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Figure 13: Experimental Set up: Automated Roller Rain Shade (Left), 45° Slanted Rain Shade with Louvres (Right)

The experimental process for both experiments can be seen in Figure 14. As the raindrop sensor detects rain, the 5V DC Stepper Motor is engaged in extending the rain shades. Thereafter, when the simulated rain is stopped, the rain sensor senses no rain, the 5V DC Stepper Motor is activated, and the rain shade is retracted to its original position. On the other hand, the experiment conducted for the 45° Slanted Rain Shade with Louvres is simple, as there is no automation required for it.

Simulating Rain

Roller rolling down once rain is detected

Plastic Sheet

Roller at maximum

Roller roll up once rain is not detected

Figure 14a: Automated Roller Rain Shade Experiment

Tiny Water Droplets

Wet Surface

Figure 14b: 45° Slanted Rain Shade with Louvres Experiment Figure 14: Experimental Process

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Figure 15 shows the wind-driven rain effects on the footpath of the sheltered walkway after the experiment. Based on Figure 15, a small amount of tiny droplets are noticed on the footpath of the sheltered walkway. Since the rain is simulated before the rain shade is activated, tiny droplets from the rain are expected. However, for the 45° Slanted Rain Shade with Louvres, it is seen that there are small droplets of water at the bottom of the louvres. Considering that the rain shade is constructed at a 45° angle, water droplets might have flowed down the rain shade to the footpath of the sheltered walkway. Furthermore, based on the simulation results, the area below the louvres are seen to be wet as well. Hence, both the experimental results resonate with the simulation results, as explained in section 3.3.3.

Rain Droplets

Rain Droplets

Automated Roller Rain Shade (Left), 45 Slanted Rain Shade with Louvres (Right) Figure 15: Experimental Results – Footpath of Sheltered Walkway

6. DISCUSSION This section is intended to discuss the outcomes gathered from the survey, CFD simulations, and lastly, the experiments. Based on the overall study, wind-driven rain is successfully mitigated from the different passive and active design solutions constructed. This can be seen from the simulations and experiments conducted. Other than the explanations and outcomes of the study, some limitations and recommendations will be addressed as well. 6.1

Survey

The survey results provide an overall evaluation of the significance of sheltered walkways in Singapore. From the survey results, the eight questions have provided substantial evidence and raw data on sheltered walkways, in this study. Based on the statistical analytical results, an indepth understanding of the pedestrian’s perspective is provided. Furthermore, it proved that

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there is a need to tackle the issues of wind-driven rain on sheltered walkways to ensure that pedestrians travel comfortably and safely. Hence, the survey results justify the problem statement, as pedestrians prefer a more efficient sheltered walkway during rainy days. Although five participants have practically assessed the survey questionnaire, the conducted survey questionnaire can be further improved. This is to ensure that all respondents have an in-depth understanding of each question, which lowers the probability of respondents answering incorrectly. Hence, a clearer explanation had to be provided to those respondents before they can continue attempting the questionnaire. To help respondents answer the questions accurately, answer options provided should be clear and precise. One limitation of the survey results would be the open-ended answers that respondents have provided for the few questions that require a long text answer. Since respondents can freely pen down their thoughts, their answers might not be relatable to the question. Thus, this affected the accuracy of selecting the main design to focus on. With that, the decision-making process was difficult, and simulations had to be conducted for all three different answer options to deem the most efficient sheltered walkway design. One recommendation to prevent this limitation would be to remove the open-ended answer option, where respondents are fixed to only three answer options. Thus, this would provide an accurate representation of which sheltered walkway design the respondents would appreciate. 6.2

Computational Fluid Dynamics Simulation

The study uses CFD Simulations to assess the distribution of wind-driven rain on the sheltered walkway. The simulation study uses a steady-state solver, which therefore represents an average value of the wind-flow. However, it provides a general guide of the influence of wind-flow on the sheltered walkway during the rainy period. From the simulation study performed, it proved that the existing sheltered walkway design by LTA and URA are not up to standard as the sheltered walkways are strongly influenced by wind-driven rain. In addition, the study also showed that the passive design of the sheltered walkway roof could significantly affect the 3D wind-flow pattern, which results in a different influence in the simulation results of wind-driven rain. Based on the design solutions as proposed in Section 5.3, the designs are evaluated by a decision matrix that consists of six components. Table 7 shows the overview of the wetted sheltered walkway area, while Table 8 shows the decision matrix and its components. The simulation results of the sheltered walkway designs have been explained earlier in Section 3.3.3.

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BEARS #03 Table 7: Overview of wetted Sheltered Walkway Area Sheltered Walkway

Side View

Droplet Diameter: 0.5mm

Droplet Diameter: 1.0mm

Droplet Diameter: 2.0mm

Droplet Diameter: 5.0mm

Louvres

Louvres and Roller Rain Shade

30ยบ Rain Shade and Louvres

45ยบ Rain Shade and Louvres

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Table 8 shows the criteria and weightage of the decision matrix. As each criterion has a different level of importance, with relevance to the sheltered walkways, a weighing column is implemented to consider the importance of specific criteria. The criteria weighting uses a simple scale from 1 to 6, where 1 is the least important, and 6 is the most important. In addition, the scores of each sheltered walkway are on a scale of 1 to 5, where 1 is the unfavorable solution, and 5 is the best solution. Therefore, the sheltered walkway design with the highest score is the most favorable design solution. From Table 8, the most favorable design solution is the Roller Rain Shade, followed by the 45° Slanted Rain Shade with louvres. The most important criterion is listed as the “impact of rain on pedestrians”. Since the focus of the study is the impact of wind-driven rain, the “impact of rain on pedestrians” should be ranked first, and the “depth of rain penetration” is ranked next. Based on both criteria, the Roller Rain Shade scored the highest score while the louvres design scored the lowest, as the Roller Rain Shade design can mitigate wind-driven rain efficiently. The louvres, on the other hand, proved to be ineffective as the pedestrians are still primarily affected by winddriven rain. However, when the design solutions are compared to the Thermal Comfort criterion, the louvres design appears to have the highest score. The Thermal Comfort of each design is shown by the wind-flow patterns seen in Section 3.3.1. Due to the lack of obstructions, the louvres design brings in more wind to the sheltered walkway. However, what is surprising would be the Roller Rain Shade design. Despite it being concealed, the wind is consistently entering the sheltered walkway, ensuring the comfort of the pedestrians. Besides the comfort of the pedestrians, cost and ease of implementation are important in determining the feasibility of design solutions. As the Roller Rain Shade uses an active design solution, the cost of implementation would be more expensive, as compared to the other passive design. Hence, the Roller Rain Shade scored the lowest as compared to the louvre design. In addition, the Roller Rain Shade with louvres scored the lowest in the maintenance and ease of implementation, as it requires two different design solutions. With that, various parties are needed to fix and maintain the design solutions, which is a tedious job, as compared to the other design solutions that require only one party. For both the 30º and 45° Slanted Rain Shade with louvres, they are ranked equally as the materials and cost are the same, with the exception that they are constructed differently.

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BEARS #03 Table 8: Decision Matrix of Sheltered Walkway Design

Sheltered Walkway Designs Louvres Criteria

Roller Rain Shade

Louvres and Roller Rain Shade

30ยบ Rain Shade and Louvres

45ยบ Rain Shade and Louvres

Weighting

Score

Total

Score

Total

Score

Total

Score

Total

Score

Total

Impact of Rain on Pedestrian

6

1

6

5

30

4

24

2

12

3

18

Depth of Rain Penetration

5

1

5

5

25

4

20

2

10

3

15

Thermal Comfort

4

5

20

4

16

1

4

2

8

3

12

Cost

3

5

15

1

3

2

6

4

12

4

12

Maintenance

2

5

10

2

4

1

2

4

8

4

8

Ease of Implementation

1

5

5

2

2

1

1

4

4

4

4

Total Points

61

80

57

54

69

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Although the CFD simulation results proved the efficiency of the Roller Rain Shade and 45° Slanted Rain Shade with louvres, in mitigating wind-driven rain, the CFD simulations for winddriven rain were conducted for only one reference wind speed (8.4m/s) and one wind direction (South). Due to the different varying parameters, such as the different wind speed and wind direction in Singapore, to determine the effectiveness of a sheltered walkway design would have resulted in an excessive amount of computations and results. However, the limitation of having simulated one wind speed and wind direction would affect the estimated wind-driven rain results. As the aim of the study was to understand the effects of wind-driven rain on sheltered walkways in Singapore, further insights of the sheltered walkway design solutions should be obtained by comparing simulations with different wind speed and wind directions. With that, a complete set of simulations with varying wind direction and speed would provide an estimate of the impact of wind-driven rain on pedestrians. 6.3

Experiments

The experimental results provide an overall evaluation of the effectiveness of the two sheltered walkway design solutions. From the experiment conducted in Section 5, the two sheltered walkway design solutions have provided substantial evidence on the effectiveness in mitigating wind-driven rain, in this study. Based on the experiment, both design solutions are conducted with the same control parameters to ensure the accuracy of the experimental results. With that, the experiments conducted can be easily compared, as they are completed under the same parameters. However, what was unexpected about the experimental results is that it was quite similar to what is seen for the CFD simulation results. This proved that the physical prototype was constructed in accordance with the 3D model, which ensured the accuracy of the experiment as well. Although the experiments were performed similarly, there are several limitations that should be considered. To achieve an experiment that has added accuracy, the experiment should be conducted in a control environment. A controlled environment can include an acrylic box that is covering the physical prototype. With that, no additional natural wind will affect the experimental results, resulting in a greater extent of accuracy. In addition, the experiment can be performed with a count-down timer to time the length of spray. As the experiment was conducted based on the ability of the user to count, it might not be as accurate as the countdown timer.

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7. CONCLUSION Although some studies on sheltered walkways in Singapore were performed in the past, 3D CFD Simulation studies of wind-driven rain have not been performed. A full comfort study is conducted on sheltered walkways, to assess the severity of wind-driven rain on the footpaths of sheltered walkways and the pedestrians. The purpose of this study is, therefore, to provide insights into the wind-flow patterns and wind-driven rain distribution on the sheltered walkways. With that, government agencies such as LTA and URA can design sheltered walkways that provide comfort to us, pedestrians. Since sheltered walkways are designed for pedestrians, they must play a part in deciding if the existing sheltered walkway is efficient enough. According to the results of the existing sheltered walkway design, 95.7% of the respondents wish to see a change in the current design. Based on the survey results, a series of new sheltered walkway designs are modelled, to ensure that it efficiently mitigates wind-driven rain. The new sheltered walkways design in the study were evaluated based on their ability to mitigate wind-driven rain through a CFD simulation. However, the best-sheltered walkway design is determined by different design criteria, which are evaluated based on a decision matrix. From the high wind speed and wind direction proposed in the study, the approved sheltered walkways designs are the Roller Rain Shade and the 45° Slanted Rain Shade with louvres. Both of the designs performed the best in mitigating wind-driven rain while ensuring that the cost and maintenance of the installation are affordable. In addition to that, the physical experiment is performed to test the abilities of the actual product. Unexpectedly, the results of the experiment coincide with the CFD simulations results. Therefore, it proved that both the active and passive sheltered walkway design could mitigate wind-driven rain efficiently by ensuring a safe and comfortable commute for pedestrians.

ACKNOWLEDGEMENT The support of the Singapore Institute of Technology in carrying out this applied research study is gratefully acknowledged. Ms. Yi-Ting Natalyn Guam did the work and contents of this paper as part of her BEng final year design project in the Sustainable Infrastructure Engineering (Building Services) programme. Dr. Moshood Olawale Fadeyi guided the development of the prototype solution and experimental design to test the effectiveness of the developed solution. Dr. Fadeyi also contributed to the development of this article.

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REFERENCES Blocken, B., and Carmeliet, J. (2007). On the errors associated with the use of hourly data in wind-driven rain calculations on building facades. Atmospheric Environment, 41(11), 23352343. Blocken, B., Carmeliet, J., and Poesen, J. (2005). Numerical simulation of the wind-driven rainfall distribution over small-scale topography in space and time. Journal of Hydrology, 315(14), 252-273. Ă&#x2021;engel, Y.A., and Cimbala, J.M. (2006). Introduction to Computational Fluid Dynamics. In Fluid Mechanics: Fundamentals and Applications, First ed., New York, McGraw-Hill. Chiu, P. H., Raghavan, V. S., Poh, H. J., Tan, E., Gabriela, O., Wong, N. H., ... and Leong-Kok, S. M. (2017). CFD methodology development for Singapore Green Mark Building application. Procedia engineering, 180, 1596-1602. Duthinh, D., and Simiu, E. (2011). The Use of Wind Tunnel Measurements in Building Design. Wind Tunnels and Experimental Fluid Dynamics Research, 282-300. Foroushani, S. S. M., Ge, H., and Naylor, D. (2014). Effects of roof overhangs on wind-driven rain wetting of a low-rise cubic building: A numerical study. Journal of wind engineering and industrial aerodynamics, 125, 38-51. Huang, S. H., and Li, Q. S. (2010). Numerical simulations of wind-driven rain on building envelopes based on Eulerian multiphase model. Journal of Wind Engineering and Industrial Aerodynamics, 98(12), 843-857. Kubilay, A. (2014). Numerical simulations and field experiments of wetting of building facades due to wind-driven rain in urban areas (Doctoral dissertation, ETH Zurich). Launder, B. E., & Spalding, D. B. (1983). The numerical computation of turbulent flows. In Numerical prediction of flow, heat transfer, turbulence and combustion (pp. 96-116). Pergamon.

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Pabiou, H., Salort, J., Ménézo, C., and Chillà, F. (2015). Natural cross-ventilation of buildings, an experimental study. Energy Procedia, 78, 2911-2916. Poh, H. J., Chiu, P. H., Ooi, C. C., Raghavan, V., Wan, S., Xu, G. ... and Ming, L. K. S. (2019). Development of GM2015 Computational Fluid Dynamics (CFD) Methodology for Naturallyventilated Non-residential Buildings (NRB) in Singapore. In IOP Conference Series: Earth and Environmental Science (Vol. 238, No. 1, p. 012079). IOP Publishing. Raman, R.K., Dewang, Y., and Raghuwanshi, J. (2018). A review on applications of computational fluid dynamics. International Journal of LNCT, 2(6), 137-143. Soner, S., and Ozturan, C. (2015). Generating multibillion element unstructured meshes on distributed memory parallel machines. Scientific Programming, 2015. Article ID 437480. Sosnowski, M. (2018). The influence of computational domain discretization on CFD results concerning aerodynamics of a vehicle. Journal of Applied Mathematics and Computational Mechanics, 17(1), 79-88. Subramanian, R., Tunçer, B., and Binder, A. (2019). Thermal Comfort Based Performance Appraisal of Covered Walkways in Singapore. CAADRIA 2019, Victoria University of Wellington, Wellington, New Zealand. Tominaga, Y., Mochida, A., Yoshie, R., Kataoka, H., Nozu, T., Yoshikawa, M., & Shirasawa, T. (2008). AIJ guidelines for practical applications of CFD to pedestrian wind environment around buildings. Journal of wind engineering and industrial aerodynamics, 96(10-11), 17491761. Van Hooff, T., Blocken, B., & Van Harten, M. (2011). 3D CFD simulations of wind flow and wind-driven rain shelter in sports stadia: influence of stadium geometry. Building and Environment, 46(1), 22-37.

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Optimisation of sheltered walkways performance to mitigate wind-driven rain in Singapore  

Guam YN and Fadeyi MO (2020). Optimisation of sheltered walkways performance to mitigate wind-driven rain in Singapore. Built Environment Ap...

Optimisation of sheltered walkways performance to mitigate wind-driven rain in Singapore  

Guam YN and Fadeyi MO (2020). Optimisation of sheltered walkways performance to mitigate wind-driven rain in Singapore. Built Environment Ap...

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