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551.
Structure-borne sound attenuation at corner interface of two plates with dynamic vibration absorber attached is investigated by wave approach. Equations governing transmission and reflection coefficients are deduced by introducing some non-dimensional coefficients, which help to reveal the physical sense inside and to simplify the analysis. Numerical investigation on vibration energy transmission of bending wave is carried out as well. The results from measurement and prediction show almost the same trends in the simplified experiment. It is found that energy transmission at corner interface depends greatly on whether the dynamic vibration absorber attached acts at resonance and is relatively lower right after the nature frequency of dynamic vibration absorber. Furthermore, the dynamic vibration absorber attached provides less energy transmission of bending wave than blocking mass at the end of “passing band”.  相似文献   
552.
The biomechanical relationship between the articular cartilage defect and knee osteoarthritis (OA) has not been clearly defined. This study presents a 3D knee finite element model (FEM) to determine the effect of cartilage defects on the stress distribution around the defect rim. The complete knee FEM, which includes bones, articular cartilages, menisci and ligaments, is developed from computed tomography and magnetic resonance images. This FEM then is validated and used to simulate femoral cartilage defects. Based on the obtained results, it is confirmed that the 3D knee FEM is reconstructed with high-fidelity level and can faithfully predict the knee contact behavior. Cartilage defects drastically affect the stress distribution on articular cartilages. When the defect size was smaller than 1.00 cm2, the stress elevation and redistribution were found undistinguishable. However, significant stress elevation and redistribution were detected due to the large defect sizes (⩾1.00 cm2). This alteration of stress distribution has important implications relating to the progression of cartilage defect to OA in the human knee joint.  相似文献   
553.
The simulation of injection molding process requires a stable algorithm to model the molten polymer with non-isothermal non-Newtonian property. In this paper, a staggered and iterative scheme is particularly designed to solve the velocity-pressure-temperature variables. In consideration of the polymer characteristic of high viscosity and low thermal conductivity, the non-Newtonian momentum-mass conservation equations are solved by the Crank-Nicolson method based split (CNBS) scheme, and the energy conservation equation with convective character is discretized by the characteristic Galerkin (CG) method. In addition, an arbitrary Lagrangian Eulerian (ALE) free surface tracking and mesh generation method is introduced to catch the front of the fluid flow. The efficiency of the proposed scheme is demonstrated by numerical experiments including a lid-driven cavity flow problem and an injection molding problem.  相似文献   
554.
Rolling force and temperature field are important parameters in the hot rolling process of plate steel. Most researchers use ANSYS/LS-DYNA and MSC.Marc to simulate the hot rolling process, however, software DEFORM-3D is not used widely in this field. Therefore, in this study, the commercially available finite element analysis software DEFORM-3D is used to simulate the distribution of rolling force, stress-effective, strain-effective and temperature field during the hot rolling process of plate steel with the size of 0.220m×2.070m×1.904m. Both the simulated rolling force and temperature of the multi-pass are compared with the measured results. It is shown that the simulated values by the finite element method are approximate to the measured values in the hot rolling of plate steel. So the simulation can provide an important reference and optimization to make rolling process and parameters in steel factory.  相似文献   
555.
The metallurgical structure and composition of ingots which depend critically on the fluid motion within the molten pool during the vacuum arc remelting (VAR) process have important effect on the subsequent mechanical processes like forging, rolling and welding. In order to determine the fluid motion of molten pool, a 2D finite element model is established using ANSYS10.0 software, combined with the turbulent fluid flow and heat transfer. The fluid motion caused by thermo buoyancy forces is investigated at different VAR processes in the present study. The results indicate that the fluid flows symmetrically along the axis of the molten pool and clockwisely along the circle at the right pool’s profile. It is also shown that the maximum velocity increases with increasing melting rate and a direct proportional relationship exists.  相似文献   
556.
HAVAL is a hash function proposed by Zheng et al. in 1992, including 3-, 4- and 5-pass versions. We improve pseudo-preimage and preimage attacks on 3-pass HAVAL at the complexity of 2172 and 2209.6, respectively, as compared to the previous best known results: 2192 and 2225 by Sasaki et al. in 2008. We extend the skip interval for partial-patching and apply the initial structure technique to find the better message chunks, and combine the indirect-partial-matching, partial-fixing and multi-neutral-word partial-fixing techniques to improve the attacks based on the meet-in-the-middle method. These are the best pseudo-preimage and preimage attacks on 3-pass HAVAL.  相似文献   
557.
Problems related to fault detection of networked control systems (NCSs) with both uncertain timevarying delay and quantization error are studied in this paper. A novel model with the form of polytopic uncertainty is given to represent the influences of both the time-varying delay and the quantization error, and then the reference model based method is used to design the residual generator that is robust to both unknown network-induced delay and unknown inputs. A numerical example is also given to illustrate the merits of the presented method. The proposed method can be regarded as an extension of the authors’ former work, which can only deal with time-varying delay.  相似文献   
558.
To give concurrent consideration both the efficiency and the security (intensity of intractable problem) in the standard model, a chosen ciphertext secure identity-based broadcast encryption is proposed. Against the chosen ciphertext security model, by using identity (ID) sequence and adding additional information in ciphertext, the self-adaptive chosen identity security (the full security) and the chosen ciphertext security are gained simultaneously. The reduction of scheme’s security is the decisional bilinear Diffie-Hellman (BDH) intractable assumption, and the proof of security shows that the proposed scheme is indistinguishable against adaptive chosen ciphertext attacks in the standard model under the decisional BDH intractable assumption. So the security level is improved, and it is suitable for higher security environment.  相似文献   
559.
The optical rays that form the image of an object and propagate a supersonic flow over a vehicle are refracted by the density variations. A numerical analysis of the aero-optical characteristics of supersonic flow over blunt wedge with a cavity window is carried out. A hybrid method of Reynold averaged Navier-Stokes and direct simulation Monte Carlo (RANS/DSMC) is employed to simulate the flowfield. Refraction factor is introduced to evaluate the flowfield’s aero-optical characteristic. The results show that mean flow’s aero-optical effects are mainly caused by the shock wave, the expansion wave and the turbulent boundary layer. Fluctuation flow’s aero-optical effects are mainly caused by the turbulent boundary layer and the shock wave induced by the cavity window. The aero-optical effects at the leading side of window are caused by the mean density variations, while the effects at the trailing side are caused by the density fluctuations. Different draft angles of the cavity window are investigated. The airborne optical devices of supersonic vehicle should be mounted in the middle of the cavity window with a large draft angle.  相似文献   
560.
The present study is aimed at determining the confidence limits of design wave parameters derived from numerical modeling—for both extremes and operational conditions—over the Central and Western Mediterranean Sea. The paper presents the methodology and results of an extensive validation activity conducted on a chain of medium-resolution third-generation wave models used for hindcast purposes. The stringent requirements of state-of-the-art coastal and offshore engineering applications over this area make the adoption of medium- or high-resolution hindcast wave and wind models almost mandatory because of the complex coastal geometry, bathymetry, and orography that in turn lead to large variations of the design wave parameters even within small regions. The chains of nested meteorological and wave models used in this hindcast study belong to the ETA and WaveWatch III families, respectively. In this study the wind and wave numerical models have been run over the past 20 years, with increasing resolutions of the wave models from 0.2° up to 0.04°. The results presented herein have 0.1° resolution for both wind and wave models. The wave data obtained are compared with available measurements from 14 wave buoys in coastal zones in the Central and Western Mediterranean Sea.  相似文献   
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