Sheikh Ahmad Zaki

Geometric Dependence of the Scalar Transfer Efficiency over Rough Surfaces

We performed a series of wind-tunnel experiments under neutral conditions in order to create a comprehensive database of scalar transfer coefficients for street surfaces using regular block arrays representing an urban environment. The objective is to clarify the geometric dependence of scalar transfer phenomena on rough surfaces. In addition, the datasets we have obtained are necessary to improve the modelling of scalar transfer used for computational simulations of urban environments; further, we can validate the results obtained by numerical simulations. We estimated the scalar transfer coefficients using the salinity method. The various configurations of the block arrays were designed to be similar to those used in a previous experiment to determine the total drag force acting on arrays. Our results are summarized as follows: first, the results for cubical arrays showed that the transfer coefficients for staggered and square layouts varied with the roughness packing density. The results for the staggered layout showed the possibility that the mixing effect of air can be enhanced for the mid-range values of the packing density. Secondly, the transfer coefficients for arrays with blocks of non-uniform heights were smaller than those for arrays with blocks of uniform height under conditions of low packing density; however, as the packing density increased, the opposite tendency was observed. Thirdly, the randomness of rotation angles of the blocks in the array led to increasing values of the transfer coefficients under sparse packing density conditions when compared with those for cubical arrays.

Determination of aerodynamic parameters of urban surfaces: methods and results revisited

Estimates of aerodynamic parameters, in particular roughness length z0 and displacement height d, are important for the analysis of the roughness of an urban surface, which affects processes that occur within the urban boundary layer such as pollutant dispersion and urban ventilation. Findings regarding the aerodynamic effects of various configurations of urban arrays were compiled from various studies. Several experimental, numerical and semi-empirical studies to estimate z0 and d were reviewed and compared with each other. The results can be summarized as follows: (1) the influence of the frontal area index (λf) on z0 is significant and their relationship has been confirmed by both experimental and numerical data; (2) compared to one-parameter and two-parameter fitting methods, the three-parameter fitting method is the least accurate; (3) the physical meaning of d remains vague because its definition as the height where surface drag acts may not be accurate for sharp-edged roughness blocks and (4) the peak values of z0 for uniform and heterogeneous block heights indicate presence of skimming or wake-interference flow effects, which may influence surface roughness. Finally, the semi-empirical models were found to be limited to cases derived from available experimental data, which normally involve uniform arrays of cubes.

Large eddy simulation of natural ventilation for idealized terrace houses due to the effect of setback distance

Similar to most tropical countries, Malaysia have low wind speed and airflow characteristics to provide an effective natural ventilation system for comfortable living especially in terrace houses. Even so, by designing them with suitable threshold height/width, H/W, ratio may help reduce heat sink, or even the accumulation of contaminants within the setback distance. Through this study, the downstream building of these terrace houses will be investigated due to the effects from an upstream building. With the use of Large-Eddy Simulation (LES) method, the formation of the vortex within the threshold H/W ratio will be clearly simulated and allow the observation of flow regimes developed by each model. With increasing threshold H/W ratios the models will exhibit some wake interference flow and skimming flow which will determine the negative or positive effect of ventilation from the upstream building towards the downstream building. The airflow characteristics of the downstream house will also be analysed and the most effective layout in providing a better air circulation may be determined. Improving the natural ventilation of such houses could significantly reduce these negative effects such as the accumulation of dust, smoke or bacteria. In turn, with the alarming rate of depletion in natural resources and its effects to the environment, this study can significantly reduce energy usage for ventilation and space cooling.

Mean Wind Flow Field around Idealized Block Arrays with Various Aspect Ratios

This study investigates the characteristic of spatially averaged mean velocity profile and the flow pattern within urban canopy layer especially in pedestrian level using CFD technique. Large eddies simulation (LES) was used to perform a series of simulation of the flow around block arrays with staggered arrangement under various conditions of aspect ratio, αp (roof-to-frontal area ratio) from 0.33 to 3.0. The spatially-average profiles of both mean wind speed and streamwise velocity over various block arrays were compared with each other. The analysis clarified the following two facts. 1) The vertical mean flow structure inside the canyon change due to change a plan area ratio and block aspect ratio. 2) The horizontal mean flow structure around the block change if pedestrian level change form z = 0.05h to z = 0.25h. This can be translated to the effect of high-rise building to the flow around the building.

Progress in Wind Environment and Outdoor Air Ventilation at Pedestrian Level in Urban Area

This paper reviews the progress made in outdoor wind environment and outdoor ventilation at pedestrian level in urban area for the past few decades until today. The focus is on the effect of wind on people at pedestrian level and how the urban geometry can influence the flow field around the building. Section 1 explains the effect of natural wind environment on comfort and safety of the pedestrian. Section 2 describes the characteristic of pedestrian wind and flow pattern around the building due to the building geometry arrangement.

Enhancing vehicle ride comfort through intelligent based control

The research presented in this paper is carried out to investigate the performance of a suspension systems either an active or passive type. Controllers that are used in this study are proposed fuzzy logic controller and proportional integral derivative controller as a benchmarking comparison. The simulations in this research have been carried out using Simulink of MATLAB. The parameters in the simulation model for the suspension system under study include car body mass, wheel mass, spring and damping elements of shock absorber, and tire. The block model of the suspension system has been designed to represent the equation of motion of the sedan car suspension system. The road disturbance for the active suspension system is modelled in two different ways, namely, unit step input signal and sine wave input signal. The simulation results indicate that fuzzy logic control of an active car suspension system has better performance compared to the passive system.

Time series data analysis of household electricity usage during el-nino in Malaysia

The aim of this research is to investigate the occupant’s total electricity consumption as well as air conditioner usage behaviour in residential building located in Kuala Lumpur. The field survey was conducted between March to May, 2016 which is the hottest period during the year due to El Nino phenomenon. The results obviously show the heterogeneity of occupant’s behaviour of energy usage. The total energy consumption is in the range of 9 kWh/d to 29 kWh/d. The measured energy consumption was compared with the outdoor air temperature.

Investigation of the PMV and TSV Models of Thermal Comfort in Air-Conditioned University Classrooms in Malaysia

A field study was done on the thermal comfort of seven air-conditioned university classrooms in the hot and humid climate of Malaysia. The aims of this paper are to investigate the perceptions of thermal comfort and the adaptation method of students in air-conditioned classrooms. In total, 189 respondents from the classrooms completed the questionnaire. A comparison was made between the Predicted Mean Vote (PMV) and the Thermal Sensation Vote (TSV) and it was found that the TSV values tended to be more sensitive than the PMV values. A variety of adaptation methods of the occupants in the classrooms are also presented. It was found that most of the occupants preferred to change the air-conditioning thermostat, probably because all the occupants had the opportunity to control the thermostat.

A Verification and Validation Study of CFD Simulation of Wind-Induced Ventilation on Building with Single-Sided Opening

Wind-induced ventilation is widely acknowledged as one of the best approaches for inducing natural ventilation. Computational fluid dynamics (CFD) technique is gaining popularity among researchers as an alternative for experimental methods to investigate the behavior of wind-driven ventilation in building. In this present paper, Reynolds averaged Navier-Stokes equation (RANS) k-ε model approach is considered to simulate the airflow on a simplified cubic building with an opening on a single façade. Preliminary simulation using models from previous experiment indicates the reliability of OpenFOAM, the open source software that will be used in this study. The results obtained in this study will better define options for our future study which aims to explore how different buildings arrays modify the airflow inside and around a naturally ventilated building.

A Validation Study for CFD Simulation of a Simplified Urban Model

A proper setting of boundary conditions is a standard upon which simulation results are justified. This study is specifically designed to simulate airflow over a repeating unit of simplified urban models with the application of periodic boundary condition. Similar setting of boundary conditions is used for all models which are of square layout with 25% packing density. The models are constructed with such that the initial velocity field is uniform throughout its internal domain. The results show that different domain heights of 4h and 5h (h as the building height) do not affect the spatial averaging of velocity profiles. In terms of the number of grids per building height, a finer meshing of 32 grids produce more accurate results of velocities and turbulence intensities compared with those of 25 grids when validated against the previous direct numerical simulation (DNS) data. Nevertheless, these criteria depend upon longer averaging period for better estimation of flow statistics. The boundary condition setting used in this preliminary study is nevertheless capable of producing current results comparable to past data although future works should focus on optimizing the important criteria in a simulation such as domain height, grid numbers, and averaging time.