Applied Mechanics and Materials Vols. 29-32

Abstract: When the gas accumulation position, volume and concentration are basically determined, the gas explosion is ignited with the minimum ignition power. The main task is to study the damage effects by explosion shock wave on the roadway structures or barriers within the roadway. That the roadway and its ventilation structures are damaged will have an important impact on some lanes, mine ventilation system as well as the whole mine, which will influence the decision-making during disasters relief. As the experimental studies of damage effect by gas explosion is more difficult, therefore, the numerical simulation and analysis is important and useful. In conclusion, simulation can not only use low-cost way to reproduce gas explosion shock wave propagation and the damage of roadway structures, but also obtain the relationship between explosion damage effect and the volume and concentration.

Abstract: In most cases, high gas concentration and oxygen consumption result in severe hypoxia after explosion. When the ventilation system is damaged, the air volume will be re-distributed so that explosion region is lack of oxygen. However, under mechanical ventilation and self-diffusion, the high temperature and toxic and harmful gases will constantly spread downwind of the roadway or certain areas, which threatens substations, winch room and workers’ escape. If the hot gas meets with gas concentration overrun areas or the coal dust explosion hazardous area, secondary disasters such as fire or explosion may be caused. Numerical simulation shows that high temperature, toxic and harmful gas will be disseminated. In conclusion, measures must be taken to withdraw the workers and to restore ventilation to prevent secondary disasters. If the gas explosion power is increased, the safety nearby working face would be threatened. To control and reduce the extent of gas explosion hazards and losses, a reasonable gas explosion disaster prevention and treatment plan should be established.

Abstract: Flower baffle heat exchanger’s structure and design idea is introduced. Flower baffle heat exchanger has unique support structure. It can both enhance the efficiency of the heat transfer and reduce the pressure drop. Through the experimental study, under the same shell side flow, the heat transfer coefficient K which the distance between two flower baffles is 134mm is higher 3%~9% than the one of which the distances between two flower baffles are 163mm,123mm. The heat transfer coefficient K which the distance between two flower baffles is 147mm is close to the one of which the distances between two flower baffles is 134mm. The shell volume flow V is higher, the incremental quantity of heat transfer coefficient K is more. The integrated performance K/Δp of flower baffle heat exchanger which the distance between two flower baffles is 134mm is higher 3%~9% than the one of which the distances between two flower baffles are 163mm,123mm. Therefore, the best distance between two flower baffles exists between 134mm~147mm this experiment.

Abstract: The spray cleaning method is important and universal in many industrial processes and other occasion. Because the size of the waterdrop is one of key factors for cleaning, this paper not only studied the relationship between the size of waterdrop and other influencing factors, but also researched the forecasted method for the size of waterdrop. In lab, by measuring the size of the waterdrop, jetted by one kind of nozzle, data were acquired and were used to train the Back Propagation Neural Network ( BPNN ). Through comparing those diameters, between measured in lab and calculated by BPNN after trained. It was acquired that the maximum errors was smaller than 1.62%, between the computed results and the factual measured ones. The experimental results showed that BPNN is an effective tool to predict the variation of the non-linear waterdrop diameter.

Abstract: The aim of the study was to develop a numerical model to reproduce the bubbly flow field created by ventilated cavity which includes three different regions. The model was established based on the Eulerian-Eulerian two-fluid model coupled with a population balance approach which is solved by the Homogeneous Multiple-Size-Group (MUSIG) model to predict bubble size distribution. Base on the model, the simulation was carried out at the experimental condition of Su et al. (1995). Firstly three regions were successfully captured proved by the spatial voidage distribution and streamline shape. Then distributions of void fraction and Sauter mean bubble diameter at various sections below the cavity corresponding to three regions respectively were plotted against experimental data. A close agreement was observed in the void fraction distribution which indicates that qualitative details of the structure of the two-phase flow field below the cavity was successfully produced. The Sauter mean bubble diameter in the pipe flow region was under-predicted for about 10%. In conclusion, the proposed model was validated in predicting the multi-region flow field below the ventilated cavity which will provide a valuable insight in designing and controlling of the two phase systems with the detailed flow field information obtained.

Abstract: The purpose of this paper is to study the shear behavior of rock specimens containing joints with various distribution forms. Two sets of specimens are simulated by the rock failure process analysis code (RFPA2D). The friction-sliding failure pattern occurs with the lower undulation angle specimen, and the failure pattern turns to be tensile-shear failure mode gradually with the increase of undulation angle. The specimen possesses the highest peak shear load when the undulation angle is about 30º. And joint rock shear character also deteriorates with the increase of weak interlayer thickness. In the intermittent joint model, the unified connection ratio specimen’s peak shear load increases with rock bridge amount, and the multi-joint mode is beneficial to keep rock mass shear stiffness. This study comes to meaningful results to the expansion of joint rock strength evolution law with various joint distribution forms.

Abstract: In order to solve the electro-hydraulic system position tracking control problem, which caused by the nonlinear system friction torque disturbance, a model-free algorithm for the friction torque adaptive identification and compensation was put forward. The algorithm is based on the application mathematics knowledge and matching & following principle. It can accommodate to all situations with the friction torque (force) variety. The simulation result indicates that the algorithm can restrains the interference of the friction torque (force) effectively, and the system’s low speed character and tracking performance were been improved.

Abstract: Gemini surfactant flooding is a promising technique to enhance oil recovery from medium-high permeability oil reservoirs. The screening of the surfactants is mainly based on their capability of lowering the surface tension between oil and water. However, gemini surfactants with high capability of lowering the surface tension do not necessarily enhance oil recovery from low-permeability oil reservoirs. Based on the fractal analyses of low-permeability cores and molecular spacer group, the fluid mechanics of gemini surfactant flooding in low-permeability oil reservoir is discovered. The fractal dimensions of the spacer group of gemini surfactants should match the fractal dimensions of the pore structures of low-permeability oil reservoirs.

Abstract: Low permeability oil reservoirs were usually considered low quality reserves. However, low permeability oil reservoirs account for more and more percent of the proven reserves year by year in China. Conventional methods for analyzing medium-hign permeability cores are not suitable to low-permeability cores. Based on fractal method and the mercury injection curve data, the fractal dimensions of the pore structures of low permeability oil reservoirs are different from those of medium-high permeability oil reservoirs. The fractal dimensions of the pore structures of low permeability oil reservoirs are less than 2. Low permeability oil reservoirs which were not able to be developed are able to be developed by gemini surfactant flooding. This helps more and more low quality reserves be turned into producing reserves.

Abstract: Consider the imperfectness of mass partition coefficient for a whole car in automotive theories, a vehicle physical model with fourteen degree of freedoms under vertical and lateral road excitations is adopted as research background in this paper. With the help of force analysis of sprung mass in three dimensional space and investigations on vertical, lateral, pitch, roll and yaw motions, the ration relations of dynamical coupling between a whole suspension and four quarter suspensions are deduced and achieved. The analytical results obtained in this paper develop the theoretical content of mass partition coefficient. It will be utilized to analyze, test and control among different car suspensions in the fields of vibration, handling and steering systems in future.