An indoor environment in a hospital building requires a high indoor air quality (IAQ) to overcome patients’ risks of getting wound infections without interrupting the recovery process. However, several problems arose in obtaining a satisfactory IAQ, such as poor ventilation design strategies, insufficient air exchange, improper medical equipment placement and high door opening frequency. This paper presents an overview of various methods used for assessing the IAQ in hospital facilities, especially in an operating room, isolation room, anteroom, postoperative room, inpatient room and dentistry room. This review shows that both experimental and numerical methods demonstrated their advantages in the IAQ assessment. It was revealed that both airflow and particle tracking models could result in different particle dispersion predictions. The model selection should depend on the compatibility of the simulated result with the experimental measurement data. The primary and secondary forces affecting the characteristics of particle dispersion were also discussed in detail. The main contributing forces to the trajectory characteristics of a particle could be attributed to the gravitational force and drag force regardless of particle size. Meanwhile, the additional forces could be considered when there involves temperature gradient, intense light source, submicron particle, etc. The particle size concerned in a healthcare facility should be less than 20 μm as this particle size range showed a closer relationship with the virus load and a higher tendency to remain airborne. Also, further research opportunities that reflect a more realistic approach and improvement in the current assessment approach were proposed.
Ultrasonic irradiation approach has become one of the most popular methods applied in chemical processing including lignocellulosic biomass pretreatment and industrial cleansing. The phenomenon of ultrasonic cavitation can be indeed delineated via the Rayleigh-Plesset equation (RPE), which governs the transient radius of the bubble. Nonetheless, the time marching in the numerical solutions for RPE is highly unstable, which cannot be assured using von Neumann analysis. High sensitivity of RPE to time step may lead to extremely long computational time. The lack of numerical investigation into the time stepping issue of RPE has hindered in-depth simulation of ultrasonic cavitation. Therefore, the purpose of this paper is to investigate the stability criterion of time stepping for RPE in different time progression schemes, namely Euler explicit, 2nd order Taylor’s method, 4th order Runge-Kutta, Runge-Kutta Fehlberg and Cash-Karp Runge-Kutta method. A simple modified adaptive time step method and α independence study has been introduced in this paper for fast, stable and accurate computation of RPE. Compared with the traditional constant time marching method, the new model is able to improve the computational cost significantly without affecting the time marching stability and resolution of the results. Among the investigated method, Runge-Kutta family solvers have higher computational accuracy, with the cost of higher critical α value. The model is also applied to compute the pressure and temperature hike during bubble collapse due to different sonication power. The simulation results show that the ultrasonic irradiation with higher sonication power could produce a higher energy to break the lignocellulose wall.
Abstract. In the study, the vortex-induced vibration (VIV) of a cylinder fitted with and without helical strakes is investigated using fluid-structure interaction (FSI) software. The purpose is to predict the VIV characteristic of cylinder fitted with and without helical strakes. Fluid and structural solvers in commercial computational fluid dynamic (CFD) software were implemented as two-way FSI solvers to develop the simulation. A flexible circular cylinder of diameter, D = 0.018 m was tested. The pitch and height of the helical strakes were 10D and 0.10D, respectively. Existing experiment outputs of bare cylinder were used as benchmark to verify the simulated results. In overall, the simulation was able to predict the trend of the amplitude response and the mean drag coefficient. However, a slight over-prediction was noticed. It was also found that the helical strakes was able to reduce up to 60% of the VIV in water.
An experimental study was carried out to identify the effect of angle of attack on flow-induced vibration (FIV) of square cylinders. The experiment was conducted at the Aeronautical and Wind Engineering Laboratory (AEROLAB), UTM Kuala Lumpur using a wind tunnel that was free from external wind conditions. A supporting structure was designed and fabricated to conduct this experiment. The importance of this support structure was to enable the rigid cylinder to suspend and vibrate freely upon excitation of wind speed. The results were analysed through the response of amplitude and frequency of the rigid cylinder over a velocity range of 0.5m/s to 4.0m/s. The results showed that for a square cylinder of ?=0°, vortex-induced vibration (VIV) occurred at low reduced velocity (UR) in range of 5 ? UR ? 10 and galloping occurred at higher reduced velocity which started at UR=15. A tranquil zone was found between VIV and galloping in the reduced velocity range of 10 ? UR ? 15. As for ?=22.5° and 45°, only VIV response was found at low reduced velocity in range of 4? UR ? 9. ABSTRAK: Satu kajian eksperimentasi telah dilakukan bagi mengenal pasti pengaruh sudut serangan oleh getaran cetusan-aliran (FIV) dalam silinder persegi. Eksperimen ini dijalankan di Makmal Kejuruteraan Aeronautika dan Angin (AEROLAB), UTM Kuala Lumpur dengan menggunakan terowong angin yang bebas dari pengaruh angin luar. Struktur sokongan telah direka dan difabrikasi bagi tujuan eksperimen ini. Ini penting bagi membolehkan silinder pegun tergantung dan bergetar dengan bebas semasa ujian kelajuan angin. Dapatan kajian dianalisis melalui tindak balas amplitud dan frekuensi silinder pegun pada kadar halaju 0.5m/s sehingga 4.0m/s. Hasil kajian menunjukkan bahawa bagi silinder persegi ? = 0 °, getaran pengaruh-vorteks (VIV) berlaku pada halaju rendah (UR) dalam julat 5 ? UR ? 10 dan getaran lebih teruk telah ketara berlaku pada kadar halaju berkurang iaitu bermula pada UR = 15. Zon tenang dijumpai antara VIV dan getaran teruk pada kadar halaju berkurang 10 ? UR ? 15. Adapun pada ? = 22.5° dan 45°, hanya tindak balas VIV dijumpai pada halaju rendah dalam kadar 4? UR ? 9.
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