Numerical optimization study to install air curtain in a subway tunnel by using design of experiment

Subways are a major mode of public transportation in metropolitan cities. A proper ventilation system is required to maintain indoor air quality in subway tunnels. Platform screen doors improve the platform environment but degrade air quality in subway tunnels. Trains transport fine particles from the tunnel into the platform. An air curtain installation in the subway tunnel permits traffic and reduces the transfer of bacteria and fine particles. The existing tunnel of Seoul subway was investigated by using computational fluid dynamics and design of experiment method for optimum air curtain installations. The flow field of the subway tunnel was computed by using ANSYS CFX software. Minitab software was used to generate the design process and to analyze the computational results. The computational domain of the existing tunnel included two natural ventilation shafts, one mechanical shaft, and the twin tracks. The height, width, and length of each track were 6, 4, and 400 m, respectively. The air curtain installation area was located between the natural and the mechanical ventilation shafts of Rrack 1. The design variables for the optimization study were the width, velocity, and installation location of the air curtain. The object function for optimization was mass flow rate at the natural ventilation shaft. The length of the air curtain was fixed at 4 m. The predicted mass flow rates were analyzed with the design variables by using the response surface method (RSM). The optimum values of the design variables, i.e., velocity, width, and installation location were 25 m/s, 0.2 m, and 5.8195 m, respectively. The maximum mass flow rate with the optimum design values was 114.4447 kg/s. The optimum values of the design variables were validated by computing the tunnel with the optimum values from RSM. The mass flow rate in the natural ventilation shaft 1 was 114.2 kg/s, as predicted. The optimization study can be helpful to set the optimum design conditions for the subway ventilation system.     

A computational analysis of the airflow in a twin-track subway tunnel with a sliding-curtain to improve ventilation performance

A computational model of an actual Seoul subway tunnel was analyzed in this study. The computational model was comprised of one natural ventilation shaft, two mechanical ventilation shafts, one mechanical air supply, a twin-track tunnel and a train. The natural ventilation shaft discharges and supplies air due to the train’s movement. The mechanical ventilation shaft and the mechanical air supply discharges and supplies, respectively, the airflow from the axial flow fans in the middle of the ducts of the shafts. A sliding-curtain was installed in the tunnel. The objective of this study was to numerically investigate train-induced airflow in the twin-track subway tunnel with natural and mechanical ventilation shafts and an installed curtain. The numerical analysis characterized the aerodynamic behavior and performance of the ventilation system by solving three-dimensional turbulent Reynolds-averaged Navier-Stokes equations. ANSYS CFX software was used for the computations. The airflow velocity from the computational results was validated by experimental results. Understanding the flow pattern of the train-induced airflow in the tunnel is necessary to improve ventilation performance. The ventilation and aerodynamic characteristics in the tunnel, including train-induced airflow, were investigated by analyzing the volume flowrate at the exits of the ventilation shafts and the velocity in the tunnel. The computational results were compared to cases with and without a curtain installed in the twin-track tunnel. As the train passed the mechanical ventilation shafts, the quantity of discharged-air in the ventilation shafts decreased rapidly. The flowrate at the exits of the ventilation shafts was gradually recovered with time, after the train passed the ventilation shafts. The airflow at the natural shaft and mechanical ventilation shaft 2, which was closest to the curtain, was increased. The computational results showed that the installed curtain can improve ventilation performance in the tunnel.     

Lightweight material for the speed reducer housing of a car chassis

Lightweight materials improve the fuel efficiency and carbon emissions of vehicles. The purpose of this study is to develop a light-weight, injectable, high-stiffness plastic composite material to replace aluminum in the housing of the speed reducer of a car chassis. The material was tested computationally and experimentally by analyzing the physical properties of specimens with different amounts of reinforcement in the base materials. POM, PA, PEI, PES, PPS and PPA were used as the base materials, while Glass fiber (GF) and Carbon fiber (CF) were used as reinforcement material. The computations were carried out using Moldflow insight software to simulate the injection molding process. The volumetric shrinkage and shear rate of the PA66+GF70 % specimen were 5.3 % and 2985.25 1/s, respectively. The mold material must withstand this shear rate. This sample had the most suitable properties, and the tensile strength, elongation, flexural strength, and thermal expansion coefficient were 312.15 MPa, 1.5 %, 329.2 MPa and 0.022 (10^-5/°C), respectively. As a result of this study, a patent was received for this lightweight material technology.     

A computational analysis of the train-wind to identify the best position for the air-curtain installation

This study focuses on computational analysis for the improvement of the tunnel ventilation and the environmental control system of the subway by solving Reynold-averaged Navier-Stokes equations for train-induced unsteady flow. The two-equation turbulence model can predict velocity and pressure field at the tunnel. The sharp interface method is used for the moving boundary of an immersed solid. The flow rate through the natural ventilation-shaft and the features of the train-wind in the subway tunnel help to find better installation locations for the air-curtain. The air-curtain separates two adjacent environments and reduces the transfers of bacteria and radioactive particles. The ANSYS CFX software is used to perform unsteady computations of the flow field at the subway tunnel.     

Computational optimization approach to design a water-jet nozzle for a water-jet loom using the design of experiment method

Journal of Mechanical Science and Technology - A water-jet nozzle is widely used on a water-jet loom to carry thread from one side of the loom to the other. The nozzle performance is important for...     

Synthesis of Nanostructured Erbium Oxides and Investigation of Influence Oxides on the Immune System and of Some Animal Tissues

Nanostructured erbium oxides （Er2O3） with coherent scattering length 26, 31, 62 and 65 nm were obtained using as a precursor of erbium chloride and erbium oleate. The influences of Er203 on the immune system and some animal tissues were carried out. The experiments have been made on white mouse＇s and outbred rats. Complex pharmaco-toxicological research presented erbium oxide nanostructure size of coherent scattering regions 26, 31, 56 and 65 nm showed that when administered orally no acute toxicity, no effect on the immune system of the body, has no effect on blood cells. But, long-term （30 day） intragastric administration shows toxicities on the internal organs of experimental animals, which lead to structural changes and functional impairment due to tissue accumulation of nanoparticles.