New finite element results for the square cavity

New results for the recirculating flow inside a square cavity obtained by a finite element method are presented. The full Navier-Stokes equations in the form of a single, fourth order equation for stremfunction is recast into arestricted variational principles, which form finite element discretization. A triangular element with Hermitian interpolation is used, such that the velocities are continuous and the incompressibility is satisfied exactly. The resulting nonlinear system is solved by Newton-Raphson iteration. Calculations are carried out with several gridworks of progressive show: (1) the convergence of solutions with refinement for fixed Reynolds number $\text{R}$; and (2) the loss of accuracy with $\text{R}$ for fixed gridwork. The range of $\text{R}$ covered is from $\text{10}{}^{\mathrm{?4}}$ to 3450. The features illustrated include the enlargement of the inviscid core of rigid rotation, the intensification of primary and secondary vortices and the appearance of a third secondary vortex near the upper upstream corner at $\text{R =1500}$.     

Buffer-assisted on-demand multicast for VOD applications

Multicast communications is widely used by streaming video applications to reduce both server load and network bandwidth. However, receivers in a multicast group must access the multicast stream simultaneously, and this restriction on synchronous access diminishes the benefit of multicast because users in a video-on-demand service usually issue requests asynchronously, i.e., at anytime. In this paper, we not only formulate this streaming problem but also propose a new multicast infrastructure, called buffer-assisted on-demand multicast, to allow receivers accessing a multicast stream asynchronously. A timing control mechanism is integrated on intermediate routing nodes (e.g., routers, proxies, or peer nodes in a peer-to-peer network) to branch time-variant multicast sub-streams to corresponding receivers. Besides, an optimal routing path and the corresponding buffer allocations for each request must be carefully determined to maximize the throughput of the multicast stream. We prove that the time complexity to solve this routing problem over general graph networks is NP-complete, and then propose a routing algorithm for overlay networks to minimize server load. Simulation results demonstrate that buffer-assisted on-demand multicast outperforms many popular streaming methods.     

A simple and efficient block motion estimation algorithm based on full-search array architecture

This paper first presents an array structure using ±1 full-search (FS) architecture as the search engine of block motion estimation which takes advantage of the design regularity of FS. An efficient algorithm named modified gradient-descent search (MGDS) is then introduced based on the proposed architecture. MGDS utilizes an adaptive computation distribution mechanism to efficiently allocate computation of the employed ±1 FS array to blocks or frames of video sequences. Experimental results indicate that MGDS uniformly achieves a higher quality than FS by an amount that is dependent on motion activities of sequences.     

Fatigue of Yttria-Stabilized Zirconia: I, Fatigue Damage, Fracture Origins, and Lifetime Prediction

Uniaxial tension–compression fatigue behavior of 3-mol%-yttria-stabilized tetragonal zirconia polycrystals was investigated. Hysteresis in the stress–plastic strain curve featured cumulative plastic strain and weakened elastic stiffness. Fracture statistics in terms of cycle-to-failure depends strongly on the maximum stress and less on the stress amplitude. Preexisting processing flaws were identified as the fracture origins in all cases. We suggest that microcracking is the dominant mechanism of fatigue damage, that nucleation of fatigue crack is usually not necessary, and that fatigue lifetime is primarily controlled by crack propagation, which is most sensitive to the maximum stress.     

Plasticity-Induced Fatigue Damage in Ceria-Stabilized Tetragonal Zirconia Polycrystals

Current studies on the fatigue lifetime of ceramics are mostly focused on the relation between the stress amplitude (or maximum Stress) and cycles to failure. For a more compliant and plastic ceramic which has a pronounced nonlinear stress–strain relation, the role of plastic strain in the fatigue damage is investigated for the first time in this study using a 12 mol% Ce-TZP. By testing at different temperatures, we were able to vary the amount of transformation plasticity with the same microstructure. The Coffin–Manson relationship, which suggests that fatigue lifetime in the low cycle fatigue regime is best correlated with the plastic strain range, was confirmed for the tough ceramic. Fatigue damage is found to be a bulk process which continuously degrades flaw tolerance by microcracking. Evidence for the latter mechanism was also provided by uniaxial cyclic tension–compression stress–strain response and by TEM examination. Despite such damage, the possibility of plasticity-induced surface-crack nucleation in fatiguing ceramics, unlike in metals, appears unimportant.     

Lyapunov stability analysis of second-order sliding-mode control and its application to chattering reduction design

This paper proposes a new sliding mode control design with reduced control chattering. The proposed new design inherits the design concept from dynamic sliding mode control, in which the first-order time derivative of the control input is treated as the control variable for a chattering control design. Previous dynamic sliding mode designs require an extra uncertainty observer or uncertainty estimator to construct the sliding surface. This paper is able to waive such observer or estimator.     

A formability index for the deep drawing of stainless steel rectangular cups

The effects of process parameters on the formability of the deep drawing of rectangular cups made of SUS304 stainless steel were investigated by both the finite element analysis method and the experimental approach. A statistical analysis was employed to construct an orthogonal chart which reflects the effects of the process parameters and their interactions on the formability of rectangular cup drawing. The material properties and the forming limit diagram (FLD) of SUS304 stainless steel were obtained from the experiments conducted in the present study and were employed by the finite element simulations. In the finite element analysis, the strain path that led to fracture in the drawing process was examined and the failure modes caused by different process parameters were also identified. With the help of statistical analysis, a formability index for the deep drawing of SUS304 stainless steel rectangular cups was constructed and the critical value of the formability index was determined from the finite element simulation results. The actual drawing processes of rectangular cups were also performed in the present study. The validity of the finite element simulations and the formability index were confirmed by the good agreement between the simulation results and the experimental data. The formability index proposed in the present study provides a convenient design rule for the deep drawing of SUS304 stainless steel rectangular cups.     

A cascading MRVQ-DCT scheme for the compression of sequence images

In this correspondence, a mean residual vector quantizer (MRVQ) is superimposed on the motion estimator for improving the intraframe coding quality of MPEG. The proposed scheme performs an MRVQ before executing the discrete cosine transformation (DCT) for the purpose of curing the DCT intrinsic trouble of blocking effect at low bit rate.     

Filtering and Searching Vector Quantization

Under the consideration of computational complexity and design regularity, in this paper, a FASVQ (filtering and searching vector quantization) is presented to compress images. FASVQ utilizes a heuristic to filter codevectors with small costs and then employs full-search VQ within the surviving codevectors. We have proven that the proposed heuristic can easily be implemented by a table lookup technique and over 95% codevectors can be filtered. Although, the quantized codevector of FASVQ wouldn't be optimal, the experimental results show that the PSNR degradation between full-search VQ and FASVQ is only 0.24 dB on the average.