Papers by Author: Zhi Jian Wang

Abstract: As an important element of the index in room acoustics, the reverberation time has been considered as an objective parameter with clear concept and had good correlation with the subjective perceptions in the field of psycho-acoustic criteria. Through the computer acoustic simulation software EASE and the electro-acoustic test system CLIO, this paper conducts research on the reverberation time of the car speaker sound field, which in the domestic car of a certain type, studies show that EASE is accurate and reliable in the simulation of the car speaker sound field, the reverberation time is greater than 0.4s when the frequency less than 500 HZ and less than 0.1s when the frequency greater than 1000 HZ, when reaches to 500 HZ, the reverberation time reaches the maximum 1.103s.

Abstract: The three-Dimensional model of 40BZ6-15 centrifugal pump is built by the Solidworks software. This paper employs three-D Navier-Stokes equation and standard equation, and uses MRF and STMPLE algorithm to simulate the internal flowing of the 40BZ6 centrifugal pump. The velocity field and pressure field are gained. Through a further analysis, the rule of the internal flow of the centrifugal pump is unveiled, and then the simulative results are compared with the experimental ones, which can provide the base for the further improvement of the centrifugal pump.

Abstract: On many occasions, the wired communications technologies can not meet the actual needs, such as in the operating in the wild or harsh environment. If using communication module built by radio frequency communication chip to achieve the data transmission of two regions of space, take MCU as a control component to achieve the freely data communication docking. This will be a good way to solve the wireless communications problems.

Abstract: Studying how and how much the factors affect on the cooling rate of workpieces is very significant to improve the ability of vacuum high pressure gas quenching furnace. From changing the structure and technology of nozzle-type vacuum high pressure gas quenching furnace, by a large number of computer simulation, this paper discusses some factors affecting the cooling rate. By changing the number and distance of nozzles on each wind pipe, we can better control the cooling rate and uniformity of workpieces. From the perspective of improved process, the number, shape, size and placement of the workpieces have certain effects on cooling rate, in which the placement of the workpiece is very significant and significant. The simulation results for the further development of new high-pressure gas quenching vacuum device provide a theoretical basis.

Abstract: In the process of metal powder laser rapid forming, various defects may be caused in forming parts on account of technical parameters, equipment performance, material characteristics and other factors. While dimensional accuracy error and surface sticky powder caused by powder factor are the two major defects of forming parts. The experimental analysis finds that less or over accumulation resulting from powder feed delay is the main reason for affecting the dimensional accuracy of cladding and the main reason which affects the appearance of surface sticky powder is specific energy.

Abstract: Taking Silicon tetrachloride (SiCl4) and hydrogen (H2) as the reaction gas, by the method of plasma-enhanced chemical vapor deposition (PECVD), this paper simulates the deposition process of polycrystalline silicon thin film on the glass substrates in the software FLUENT. Three dimensional physical model and mathematics model of the simulated area are established. The reaction mechanism including main reaction equation and several side equations is given during the simulation process. The simulation results predict the velocity field, temperature distribution, and concentration profiles in the PECVD reactor. The simulation results show that the deposition rate of silicon distribution is even along the circumference direction, and gradually reduced along the radius direction. The deposition rate is about 0.005kg/(m2•s) at the center. The simulated result is basically consistent with the practical one. It means that numerical simulation method to predict deposition process is feasible and the results are reliable in PECVD system.

Abstract: In order to learn gas flow state in the vacuum high pressure gas quenching furnace, this paper simulates and tests the gas flow under the no-loaded and cold state. Hot wire anemometer is used to measure the speeds of some feature points, on the one hand to provide boundary conditions for the numerical simulation, and on the other hand to compare with the numerical simulation results. FLUENT software is used to simulate the gas flow of nozzle-type vacuum high-pressure gas quenching furnace. The results show that at the center of the furnace appears high-pressure low-speed zone in which is resulted by the gas collision there, and the vortex also appears in the area around the furnace. The results mean that the cooling rate of works will be slow there. Different exit velocities of five nozzles cause the uneven flow distribution, which will affect the cooling uniformity of works. The comparison between the simulation results and the measured results shows that the error is within 10%. It means that numerical simulation method to predict gas flow is feasible and the results are reliable in high pressure gas quenching furnace.

Abstract: Coaxial powder delivery nozzle plays an important role in metal part direct and rapid prototyping technology and the reasonable structure can ensure uniform and stable flow of metal powder. Gas-solid two-phase flow theory is considered to simulate outside flow field of carrying gas-type coaxial powder delivery nozzle. The physical and mathematical models are erected. FLUENT software is used to simulate the velocity distribution of gas and solid particle, the volume fraction distribution of particle and the focusing properties. The simulative results indicate that both the structure of coaxial powder delivery nozzle and inlet velocity affect the convergence of powder. When the metal powder is only driven by the carrying gas without the shield gas flow, the powder appears focusing and the focus is 8mm far from the nozzle exit, but the volume fraction at the focus is only 2.6 percent, which shows the convergence of powder is not good and the usage rate is not high. In the optimized structure the simulative results show that the powder flow is affected by the flow of shield gas. When the velocity of shield gas is 6m/s, the powder shows good convergence and the volume fraction of powder at the focus reaches 3.3 percent. The higher the velocity of shield gas is, the more uniformly the powder flows, but the volume fraction at the focus is slightly lower. It is obvious that the numerical simulation will benefit for coaxial nozzle designing and performance improving.

Abstract: High-pressure gas quenching is the heat treatment technology which quenches the works by use of high-pressure and high-speed flow gas. FLUENT software is used to simulate the process of gas-solid coupling flow and heat transfer in the nozzle-type vacuum high-pressure gas quenching furnace. The hot wire anemometer is used to measure the inlet velocities of nozzles, which provides the boundary conditions for computer simulation. By the computer simulation, the gas flow fields, work temperature fields and work cooling curves are attained. The results show that the big eddy current occurs at the corner of the furnace and the cooling rate of the work is slow there. Contrasting the simulating result of work cooling rate at the center of furnace with the actual measured one by the thermocouple, we find when work is cooled to the temperature of 430K, the simulating result is faster than the actual one about 50 seconds. The simulating results basically correspond with the actual trend of the gas quenching.

Abstract: At present, laser processing has been widely used, but the traditional laser processing can not rapidly adapt to current market demands, so the virtual prototyping technology based on laser processing is put forward. In this paper, the research status of the virtual prototyping technology based on laser processing is summarized and the structure figure of laser processing virtual prototyping system is established. Then the virtual prototyping technology based on metal part direct rapid prototyping is studied, which includes the structure parameterization designs of coaxial powder feeding device and powder nozzle and the simulation of the gas-solid two-phase flow in the coaxial powder feeding device and the temperature distribution during the deposition process of metal powder.