Advanced Materials Research Vol. 625

Abstract: Water management plays a significant role in enhancing performance of proton exchange membrane fuel cell (PEMFC). Successful water management requires effective removal of liquid water produced by electrochemical reactions. Therefore, it is a critical challenge to understand liquid water movements in flow channels. In the present study, a three-dimensional unsteady two-phase model for the cathode side of PEMFC consisting of gas channel (GC), gas diffusion layer (GDL) and catalyst layer (CL) is developed using FLUENT software with a volume-of-fluid (VOF) method and user-defined-function (UDF). When fuel cells are assembled, the cross sections of gas channel change, resulting in different water droplet movements. The effects of GDL deformations on water droplet movements are discussed.

Abstract: Shear-thinning power-law fluid is a kind of non-Newtonian fluid in which the viscosity is a function of shear rate. Impinging jets system is used to study the breakup characteristics of power-law liquid sheets formed by two symmetrical round jets in this study. High quality images are obtained from the experiment with a high speed camera and breakup length is extracted from the images. Closed-rim sheet, web-like sheet and ligaments sheet are observed with the increase of jet velocity. A series of images show that the wave length on the surface of sheets tends to decline as the jet velocity increases. At a low We number, the breakup length increases with an increasing We number. However, it first increases and then decreases when the liquid sheet breaks up at a high We number. The liquid jets with larger diameter collide to each other and lead to a liquid sheet with a smaller breakup length.

Abstract: Dynamic behavior of the 1100kV porcelain arresters with and without the new type lead dampers and are investigated，based on theoretical analysis and finite element analysis. The results of theoretical analysis show that the dynamic response of 1100kv porcelain arrester can be decreased by damping measures, which can change the dynamic behavior of equipment. The results of finite element analysis show that the primary frequencies of these two structures are between 1Hz and 10Hz and the differences between them is not obvious, which indicated that the overall stiffness of the two structures is low and the frequency and vibration mode of these two structures have hardly been changed by the lead dampers. The level modes dominated the equipment, while vertical modes and torsional modes are not obvious. Owning to an effect of increment of damping device with the new type lead dampers, there is a reduction by 40% above in the maximum root stress of porcelain bushing. In the meantime, the new type lead dampers can also decrease the relative displacement at the top of equipment.

Abstract: Thin-walled structure absorbs most impact kinetic energy during collision accident,and they are widely used as energy-absorbing element. In order to improve crashworthiness of them, regular pyramidal ripple is added on the thin-walled square tube’s surface. Explicit finite element technology is applied to simulate the behavior of the tube under axial impact load. Simulation data was delt with by Response Surface Method to form a function of variables and response,and the new structure was optimized. Research results show that, the thin-walled square tube with pyramidal ripples can improve controllable of structure deformation obviously and Optimized structure can absorb and dissipate much more impact kinetic energy.

Abstract: Hydraulic transmission has a wide range of applications and attains rapid development. As the traditional methods of mathematic modeling in the design of the electro-hydraulic control system are very complex, making the design and debugging cycle of the hydraulic system longer. Thus in this paper, using the AMESim which is a senior modeling software facing engineering task design, does the modeling and simulation calculations for one kind of digital hydraulic cylinder. We get its simulation in the application of the actual working condition. At the same time, we optimize the simulation parameters and analyze the simulation results. The simulation results and analysis can provide certain reference value for the design, debugging and subsequent improvement of the digital hydraulic cylinder. According to the simulation results, it can meet different operational requirements by making appropriate compensation and adjustment in practical applications.

Abstract: A simple type of structure with two different fortification intensities was chosen to calculate, and the costs between the low intensity structure after reinforcement and the high intensity structure were compared. The possible economic losses of structures in different seismic fortification intensity was also compared in order to analysis the affect of intensity on the building economic effect. The result showed that the economic benefit of high intensity structure was 1.07, and the reinforced low intensity structure was 0.58. So the economic benefit of structure with reasonable seismic input was evident.

Abstract: The vertical launch of the gas curtain is a new underwater launch technology. The gravity effect of the launch speed on hydrodynamic characteristics of the underwater vehicle vertical launching by using the gas curtain has been studied by adopting the multiphase VOF model and the standardturbulence model. The relationship between the launch speed and the shape of the underwater vehicle has been achieved by using the numerical simulation. The relationships between the launch speed and the hydrodynamic characteristics of the underwater vehicle vertically launching from the tube, navigating in water and exiting water have been investigated by using numerical simulation. The hydrodynamic characteristics of underwater vehicle vertical launching by using the gas curtain method are small. The effects of the launch speed on the hydrodynamic characteristics of the underwater vehicle vertical launching in the gas curtain are small.

Abstract: Based on the analysis to the geometric relations of eccentric slider-crank mechanism (ESCM) at two limiting positions, a new and simple graphic method for design of ESCM was proposed in the paper. The method has the characteristics of legible concept, concise operation and good practicality. Utilizing the new method, the ESCM could be designed quickly under given conditions (slider stroke H, coefficient of travel speed variation K, the auxiliary conditions such as the length of crank a, length of connecting rod b and deflection distance e) without any calculation. Meanwhile, under given conditions (H, K) the alternative region of crank fixed center A, the possible feasible regions of crank length a and deflection distance e were discussed.

Abstract: The vibration absorption is the principle factor which influences the working reliability, operating comfort, noise and parts service life of vibratory roller. This paper made a test on the performance of a new type of single drum vibratory roller with a national brand and found the problem of polarization and shimmy; set up a physical model of the roller for simulation analysis, seeking the reasons of polarization and shimmy, as well as proposing the improvement program so that the performance of Level-I vibration absorption of the sample was improved while each indicator of vibration severity can be above the permissible level.

Abstract: For the lunar return mission, a concern of the entry guidance requirement is the full flight envelope applicability and landing accuracy control. A concise numeric predictor-corrector (NPC) entry guidance (NPCEG) algorithm is developed for this requirement. It plans a real-time trajectory on-line by modulating the linear parameterized bank profile. To meet the path constraint, we propose an integrated guidance strategy which combines NPC method with an analytical constant drag acceleration method. Monte Carlo analysis shows that the algorithm is sufficiently robust to allow precision landing with a delivery error of less than 2.0 km for the entire between 2,500 km and 10,000 km range.