Applied Mechanics and Materials Vols. 105-107

Abstract: Stability of the large thin-walled absorption tower is essential to its safe operation. The large finite-element analysis software is adopted for parameterized modeling of the tower. It requires the internal pressure of the tower tube to be the load form of the partial yield on the tower, respectively considering the structural model displacement and the actual dent on the tower surface as the initial defect, and performing the nonlinear buckling analysis of the reinforced absorption tower structure. As is indicated, the yield load produces lesser effect on the initial defect. Meanwhile, when the structure yields critically, plastic deformation takes place in some part of the tower tube due to potentiation of the stiffening ribs. Moreover, stiffening ribs and wall thickness improve the stable load. With the increase of wall thickness, the load of critical stable internal pressure on the tower grows constantly but the critical stable load increases more slowly.

Abstract: The RNG turbulence model is used to carry out the 3D steady turbulent calculation on the runner and draft tube of the Francis turbine. And the prototype of the Francis turbine is HLA351. Under 8 typical operating conditions, numerical simulation on how the runner outlet urge the vortex rope in draft tube are accomplished in this paper, and the calculation models are long blade model and mixed blade model. The results show that the runner outlet of the mixed model can lead the vortex rope location to the downstream relatively, reduce the circumfluence and cushion area and the probability of the second-vortex. What’s more, the flow pattern in mixed model is superior to the long model and that benefits the operation stability and economy of the unit.

Abstract: On the basis of the rotor dynamic balancing theory, the rotor balancing least squares influence coefficient method has been discussed in detail in this paper. In order to solve the problem that the residual vibration in some of the measuring point and the balancing weight are comparatively large in the balance process with least squares influence coefficient method, particle swarm optimization algorithm with cross-factor, which is an improved swarm intelligence algorithm, is introduced into rotor balancing least squares influence coefficient method. Theoretical analysis and numerical examples show that the algorithm has a good convergence, with reducing the balancing weight and residual vibration effectively compared with basic least squares influence coefficient method. The result can achieve better balance effect in the rotor balancing process.

Abstract: The nonlinear dynamic model of Ravingneaux compound planetary gear sets has been built. The model includes time-varying mesh stiffness of gears, backlash as well as comprehensive mesh errors nonlinearities. By introducing relative displacements of components as the new generalized coordinates, uniform nonlinear differential equations of compound planetary gear sets are built. Then the nondimensional dynamic differential equations are derived. The nonlinear differential equations have been solved utilizing ariable step size Gill method. By changing system nondimensional excitation frequency, monocycle anharmonic response, multiply periodic subharmonic response, quasi-periodic response and chaotic response are obtained. By means of time histories, phase-plane diagram, Poincare maps and power spectrum, various responses are compared and analyzed in detail.

Abstract: The geometric nonlinear dimensionless dynamical equations of suspension spring cushioning packaging system were established and a new concept of damage boundary curves of the system was developed under the action of rectangular pulse. Considering the angle of the suspension spring ,a three-dimension damage boundary curve is obtained.The mathematic results of the equation are calculated by using the four steps Runge-Kutta method. Studies have shown that the dimensionless pulse peak, the angle of suspension spring and the damping ratio of the system can affect the safe region, and that increasing damping can enlarge the safe region of the system. The shock of the packed product can reduce by adjusting the parameters of the system properly. These results have important application value in design of the suspension cushioning system.

Abstract: As cars become quieter the sound quality of components becomes more critical in the customer perception of car quality. This requires a need of new evaluation method for the specification of component sounds. Considering that high frequency noise plays an important roll for internal noise, the noise signals in the range from 7000Hz to 8000Hz are specially emphasized. Then the acoustic evaluation parameters, such as Sound Pressure Level, Sharpness and Steadiness have been evaluated. Judged from experiences and measuring results, an abnormal noise comes from Generator, through the exchange of Generator, Sound Pressure Level and sharpness were greatly improved. At the same time, subjective evaluation also indicated that there was no complaint any more in passenger compartment. Low Sound Pressure Level, sharpness can lead to perceived high product quality.

Abstract: Detection and classification of buried objects is of great importance in underwater counterterrorism and archaeology. To penetrate the sediment, a low frequency intensive acoustic source is needed. Underwater plasma acoustic source (UPAS) with high voltage discharge has the advantage of adjustable pulse length, high source level output and no pollution to the environment, which can satisfy these needs. In this paper, we introduced the UPAS, including its basic mechanism, structure and pressure output. Then we build up an elastic wave propagation model, solved it with finite difference and staggered grid methods, and combined with certain source and boundary condition, we simulated and analyzed the pressure wave propagation in time domain with an aluminum cylinder buried in sediment, from the results we validated the effectiveness of UPAS in the application of buried object detection.

Abstract: An acoustic similarity due to two geometrically similar structures which are vibrating in heavy flow, such as in water, is investigated. The acoustic similarity states that for two geometrically similar structures, if a group of dimensionless similarity numbers are constant, the dimensionless acoustic pressure coefficient keep constant at the corresponding acoustic field points for the two flow–loaded vibrating structure systems. Numerical simulations and experiment results are presented to validate the acoustic similarity. This acoustic similarity may be useful when a small structure is employed to investigate the acoustic performance of large scale structure.

Abstract: In order to properly simulate bolted joints and make the numerical modes as accurate as possible, this paper is focused on modeling methods for dealing with bolt connection structures composed of two sheets. Six methods are presented to establish the FE models using different element types(8-node brick elements and 4-node shell elements) and different constraints (such as contact interaction and coupling constraint). The models are solved in ABAQUS software and natural frequencies and vibration shapes are obtained. Then, the experiments of bolt fastening structures are performed and FE simulation results are compared with the experimental ones. Moreover, the methods which agree well with the experiments are selected as the FE model of bolted connection. Finally, the element layers in the through-thickness direction are discussed. FE models built in this paper can reflect the real situation of bolted joints and provide significant reference to FE analysis for the complex system connected by bolts.

Abstract: Viscous dampers are widely used in vibration energy dissipation project. The researches on viscous dampers used in energy dissipation project at present are more, and one of the main research contents is about how to improve energy dissipation efficiency. In the current study, the effect of the supporting stiffness in dampers is neglected, and only its strength and stiffness is verified. Based on the research on the principle and mechanical model of viscous damper, the influence of supporting stiffness on various energy dissipation working parameters has been analyzed in this paper. The results showed that, supporting stiffness has great influence on the energy dissipation efficiency, then with energy dissipation efficiency as the index, this paper derived the generality support stiffness design formula for energy consumption optimizing, which provide scientific basis for similar design.