Magnetic pulse spot welding of bimetals

One of the main parameters in magnetic pulse welding (MPW) is the requirement of certain distance/spacing called “air gap” between the two sheets or tubes to be welded. This work presents means to alleviate this constraint through stamped humps in one of the sheets. The sheets remain in contact all over except at humps where a local air gap is sufficient to generate impact velocity required to produce spot welds using electromagnetic energy. The developed approach has been validated on the heterogeneous assembly of AA1199 aluminum to EN 355 steel. The microstructural analysis revealed that the weld interface is wavy and the waves are in two opposite directions from the center. Quasi-static tension–shear tests validated the joint efficiency of spot welds.     

Dynamic modeling and optimal control of goethite process based on the rate-controlling step

The iron removal process is an important technology in zinc hydrometallurgy. Due to its complicated reaction mechanism, it is difficult to highly control the performance of process solely relying on manual experience. Therefore, this paper focuses on the dynamic modeling for the goethite process and its optimal control method. In different reactors, different operating conditions will influence the rate-controlling step of process reactions, as well as the kinetic model. We determine the rate-controlling step of reactions in each reactor according to the reaction conditions, and subsequently the dynamic model has been developed based on the rate-controlling step. Then an optimal control method for the goethite process has been proposed, which satisfies the technical requirements with minimal process consumption. The proposed optimal control includes pre-setting of descent gradient of outlet ferrous ion concentration and optimal control of oxygen and zinc oxide. The simulation results demonstrate that the proposed dynamic model exhibits greater performance comparing with the process model without considering rate-controlling step, and the proposed control strategy has a higher satisfactory than the nonlinear model predictive control. Then, the proposed optimal control is validated by the industrial experiment, which the average oxygen and zinc oxide consumptions decreased by 568 m³/day (6.22%) and 3.09 t/day (5.16%) and the qualified rate of outlet ferrous ion concentrations increased by 5.5%, compared with the manual control.     

Analysis of microbending of CuZn37 brass foils based on strain gradient hardening models

Microbending experiments of brass foils were conducted and demonstrated clear size effects, i.e., the normalized bending moment increased with the reduction of foil thickness. The experiments were modeled using the classical plasticity model and three strain-gradient plasticity models. A modified Nix-Gao model was proposed to consider the number of twins across the thickness direction in strain hardening. It was found that the proposed model could better predict the normalized bending moment for both fine-grain and coarse-grain foils and the proposed equation for material intrinsic length could better capture the physics of material deformation. Furthermore, micro-hardness distributions in the bending area were measured and obvious lower-hardness region was found in the middle layer of fine-grain foils instead of coarse-grain foils. This indicates that the modified Nix-Gao model and the assumption of fully plastic bending worked better for coarse-grain foils than for fine-grain foils.     

A robust weakly compressible SPH method and its comparison with an incompressible SPH

This paper presents a comparative study for the weakly compressible (WCSPH) and incompressible (ISPH) smoothed particle hydrodynamics methods by providing numerical solutions for fluid flows over an airfoil and a square obstacle. Improved WCSPH and ISPH techniques are used to solve these two bluff body flow problems. It is shown that both approaches can handle complex geometries using the multiple boundary tangents (MBT) method, and eliminate particle clustering‐induced instabilities with the implementation of a particle fracture repair procedure as well as the corrected SPH discretization scheme. WCSPH and ISPH simulation results are compared and validated with those of a finite element method (FEM). The quantitative comparisons of WCSPH, ISPH and FEM results in terms of Strouhal number for the square obstacle test case, and the pressure envelope, surface traction forces, and velocity gradients on the airfoil boundaries as well as the lift and drag values for the airfoil geometry indicate that the WCSPH method with the suggested implementation produces numerical results as accurate and reliable as those of the ISPH and FEM methods. Copyright © 2011 John Wiley & Sons, Ltd.     

基于块方向图的指纹中心点定位

提出了一种基于块方向图的指纹中心点定位方法,该方法先利用灰度梯度法得到指纹块方向,再利用块搜索得到指纹的大致中心点位置,最后根据块的Poincare index算法得到指纹确定的中心点位置,该算法简单、快速、鲁棒性好。     

Steady and transient inflow dynamics with actuator disk vortex theory

The actuator disk is a well‐known and widely used theoretical tool in wind engineering. This work proposes a new theory based on an actuator surface, capable of treating time‐varying vectorial load distributions and yaw/pitch misalignment. A simplified representation of vortex motion is used to arrive at a tractable problem. The theory is not restricted to disks; arbitrary coplanar (optionally disjoint) actuator surfaces may be modeled. Some of the theoretical novelties used in the modeling includes use of the fractional Laplacian and extensive use of the Fourier transform on . Promising experimental validation based on pitch‐step experiments at the Tjæreborg turbine is furnished. Comparisons are also made to existing methodologies. Analysis and numerical work shows that the model encapsulates Coleman's vortex theory.     

Investigation of coalesced droplet vertical jumping and horizontal moving on textured surface using the lattice Boltzmann method

The coalesced droplet vertical jumping and horizontal moving on conical posts textured surface are numerically studied using the three-dimensional (3D) multi-relaxation-time (MRT) pseudopotential lattice Boltzmann model. The influences of wettability gradient and roughness gradient are investigated systematically. It is found that the coalesced droplet on the flat and conical posts textured surfaces can move horizontally from superhydrophobic bend to hydrophobic bend without the roughness gradient. Moreover, the coalesced droplet is able to spontaneously move from lower conical post density region to higher conical post density region without the wettability gradient. Specifically, the in-line array textured surface is more beneficial to the coalesced droplet horizontal moving than the staggered array at the same wettability parameter. However, the staggered array textured surface is more beneficial to the coalesced droplet vertical jumping than the in-line array. The hybrid effect of wettability gradient and roughness gradient plays critical roles in coalesced droplet vertical jumping and horizontal moving. The present work demonstrates that the dropwise condensation heat transfer can be enhanced in a self-sustained manner if the wettability and roughness of the textured surface are properly designed. It is also confirmed that the 3D MRT pseudopotential lattice Boltzmann model is of potential to simulate coalesced droplet behaviors on textured surface.     

Experimental analysis of the air velocity and contaminant dispersion of human exhalation flows

Human exhalation flow is a potential source of pathogens that can constitute a cross‐infection risk to people in indoor environments. Thus, it is important to investigate the characteristics of this flow, its development, area of influence, and the diffusion of the exhaled contaminants. This paper uses phase‐averaged particle image velocimetry together with a tracer gas (CO₂) to study two different exhalation flows over time: the exhalation of an average male (test M) and an average female (test F), using a life‐sized thermal manikin in a supine position. The exhalation jets generated for both tests are similar in terms of symmetrical geometry, vorticity values, jet opening angles, and velocity and concentration decays. However, there is a difference in the penetration length of the two flows throughout the whole exhalation process. There is also a time difference in reaching maximum velocity between the two tests. It is also possible to see that the tracer gas dispersion depends on the momentum of the jet so the test with the highest velocity decay shows the lowest concentration decay. All these results are of interest to better understand cross‐infection risk.     

Boundary detection of internal defect based on discontinuity of second-order gradient of out-of-plane displacement in phase-shifting digital speckle pattern interferometry

A new method for detecting the boundary of an internal defect is proposed in this paper. The proposed method can be used in phase-shifting digital speckle pattern interferometry to detect accurately the boundary of an internal defect based on discontinuity of the second-order gradient of out-of-plane displacement in the direction perpendicular to the defect boundary. Both theoretical analysis and experimental result are presented in this paper.     

A simulation‐based algorithm for optimal pricing policy under demand uncertainty

We propose a simulation‐based algorithm for computing the optimal pricing policy for a product under uncertain demand dynamics. We consider a parameterized stochastic differential equation (SDE) model for the uncertain demand dynamics of the product over the planning horizon. In particular, we consider a dynamic model that is an extension of the Bass model. The performance of our algorithm is compared to that of a myopic pricing policy and is shown to give better results. Two significant advantages with our algorithm are as follows: (a) it does not require information on the system model parameters if the SDE system state is known via either a simulation device or real data, and (b) as it works efficiently even for high‐dimensional parameters, it uses the efficient smoothed functional gradient estimator.