A numerical model for the jet flow generated by water impact

In this paper a numerical model is developed aimed at describing the jet flow caused by water impact. The study, carried out in the framework of a potential-flow assumption, exploits the shallowness of the jet region to significantly simplify the local representation of the velocity field. This numerical model is incorporated into a fully nonlinear boundary-element solver that describes the flow generated by the water entry of two-dimensional bodies. Attention is focused on the evaluation of the capability of the model to provide accurate free-surface shape and pressure distribution along the wetted part of the body contour, with particular regard to the jet region. After a careful verification, the proposed model is validated through comparisons with the similarity solution of the wedge impact with constant entry velocity. This similarity solution is derived with the help of an iterative procedure which solves the governing boundary-value problem written in self-similar variables.     

三维宽浅河道水流数学模型研究

针对宽浅河道水流的特点,建立了一个基于分层积分降维数值解法的三维浅水紊流数值模型。通过对弯道水流的验证计算,其计算成果和试验值能较好地吻合。笔者等建立的数学摸型特别适合用来解决宽浅河道及河口水流问题。     

A model of vacancy flux induced segregation to grain-boundaries during cooling

A recently developed method of analysis provided a direct measure of grain-boundary solute enrichment in slowly cooled Zn-Cd alloys as a function of holding temperature. These experimental data are here compared with the change of boundary solute enrichment computed from a model based on the vacancy flux generated uphill diffusion of solute to boundaries. The agreement between experiment and theory is satisfactory. This agreement is considered to be a direct proof that previously reported grain-boundary hardening of slowly cooled dilute alloys is a consequence of non-equilibrium solute adsorption.     

A cellular automaton for segregation during granular avalanches

Segregation is a complex and poorly understood phenomenon that is prevalent in many industrial and natural granular flows. When grains flow down a slope [1–5], are spun in a rotating drum [6–8] or shaken in a box [9], we observe those grains organising into intriguing patterns. Kinetic sieving is the dominant mode of segregation in granular avalanches, where separation of particles occurs according to size. Using a cellular automaton we have modelled kinetic sieving as the swapping of particles in a one-dimensional system. From the cellular automaton we have deduced a continuum model to describe the segregation.     

A semi-analytical model for predicting the flow into a wellbore completed by inflow control devices

A method to predict the detailed flow into horizontal wellbores completed by inflow control devices is presented. In this work, the inflow control device (ICD) is a sequence of pipes lining the wellbore and perforated by many holes to enable the inflow of hydrocarbons. The reservoir is assumed to be infinite in the radial and axial directions and its permeability is assumed to be uniform. The pore pressure at infinity and inside the wellbore, is constant. To solve the problem of the flow into a single hole, we first treat it as if the pressure field is singular at the hole acting like an unknown point source. In this way we produce an outer approximation of the problem. We then examine the region where the singularity occurs and find a regular solution for this region only. Finally we match the two asymptotic solutions in the overlap zone, where they are both valid. Beginning with the problem of a single hole on the ICD, we use the superposition principle to add the pressure produced by the flow from the other holes at position i. We are left with a linear system of N equations relating the N unknown point sources of the N holes, with the given pressure drawdown. This system is inverted to give the strength of the point sources. This method is potentially very CPU demanding and an approximate method is also developed to deal with a lot of holes. The two methods are compared and the performance of a realistic ICD is compared against an open-hole.     

干式空心电抗器模型结构减震控制试验及数值分析

基于压电陶瓷驱动器的工作原理以及形状记忆合金(shape memory alloy,SMA)丝的力学性能特点,研发一种SMA压电混合减震装置,对其进行电-力学试验,并在试验数据的基础上建立以速率符号、电压和位移为神经元输入的混合装置BP网络预测模型。最后将其安装到一个相似比1∶2的10 kV干式空心电抗器结构模型中,其中压电驱动器的激励电压采用T-S模糊逻辑输出,对其进行无控、被动控制和混合控制时的模拟地震振动台试验和数值模拟,进而分析模型结构的动力特性变化规律和不同地震波时的地震响应抑制效果。结果表明:文中研制的SMA-压电摩擦混合减震装置性能稳定、构造合理,可以有效地降低电抗器结构的动力反应。一般地,被动控制时位移和加速度的减震率可达40%,混合控制时可达50%,且震后未见电抗器结构薄弱部位发生地震破坏,说明智能材料减震系统提高了电抗器结构的抗震可靠性,为电气设备系统的减震控制保护提供了新途径。另外,试验与数值模拟结果吻合较好,表明BP神经网络可以较好地跟踪压电SMA混合减震装置的输出力。     

Comparison of three computational models for predicting pressurization characteristics of cryogenic tank during discharge

In order to select an effective approach to predict the pressurization characteristics of cryogenic tank during rocket launching, three computational models, defined as 0-D, 1-D and CFD models, are used to obtain the pressure evolution and thermal performance of a cryogenic tank during pressurized discharge period. Several pressurization cases are computed by all of the three models to evaluate their predictive abilities and effects, respectively. The comparative study shows that for the case with a diffuser-type injector at the tank inlet, the consistent results by the three models are obtained in the most of period, except that 1-D model has a peak departure prediction of pressure value at the beginning of process. All of the three models can be used to predict the pressurization performance, and their predictive abilities could be validated with one another. The CFD model is the unique suitable model to display the pressurization performance including physical distribution in radial direction especially for the system with no-diffuser-type injector. Based on the analysis, the application selection of three models for different cases is accomplished. The 0-D model is the priority selection for a simple pressure prediction of tank ullage, even for the situation that severe temperature distribution exists in the ullage range. The 1-D model is the optimal selection as considering both the convenience and the time consumption for the constant-pressure cases. But it is not recommended in a constant-inlet flux cases for its distinct predicting deviation at the beginning of the process. When the detailed distributions within the tank are concerned, the CFD model is the unique selection. The results of this paper may be beneficial to the model selection and optimization analysis of a pressurization system.     

The random crack core model for predicting the longitudinal tensile strengths of unidirectional composites

A perfect evolvement process of random crack cores is presented and a random crack core model for predicting the longitudinal tensile strengths of unidirectional composites is built in this paper. Based on the crack propagation rules, the numerical relationship of the number of random crack cores, evolvement probability of a random crack core evolving to critical size, and failure probability of a unidirectional composite are deduced. With considering some fibers breaks simultaneously and the influenced-length of the random crack cores increasing with the number of broken fibers, evolvement probability algorithms of a random crack core are developed based on the perfect evolvement process. At last, the longitudinal tensile strengths of unidirectional composites are predicted by the random crack core model, and the result shows that the random crack core model is more accurate than the classical theoretical models.     

A hybrid model for prismatic solids

A finite prism approach for the approximate analysis of three-dimensional solids is proposed. The approach is based on a semi-algebraic assumed stress hybrid model, according to Pian's scheme. Prismatic solids with various end conditions can be analysed with a traditional matrix-displacement procedure, thus enlarging the possibilities offered by analogous compatible models.     

A mathematical model for the density-augmented spreading of a particle-laden discharge in a turbulent shallow-water flow

A two-dimensional horizontal dispersion equation is derived for the many ways that buoyancy modifies the spreading of a mono-disperse discharge of particles in a shallow-water flow. The particle-induced lateral density gradient gives rise to a secondary transverse flow which tends to carry particles outwards. Stratification with the consequent reduced mixing, changes the local vertical profile of the original flow and gives rise to a Burgers nonlinearity (slowing down of sinking particles or a speeding up of buoyant particles). Stratification also modifies the non-local horizontal distribution of the current, with an inflow towards particle-laden regions where the drag is reduced. A simple eddy-diffusivity turbulence model is used which permits explicit evaluation of most of the linear and nonlinear coefficients. Nonlinear effects are shown to be significant for particle volume concentrations of only 10 parts per million.     

Two-dimensional numerical model for the analysis of macrosegregation during solidification

This paper presents a 2D extension of a one-dimensional model proposed initially for the analysis of macrosegregation of multicomponent alloys. Some simulations were carried out to compare the performance of an explicit/implicit time integration scheme for coupling thermal-solutal fields with a fully implicit one. Simulations carried out for the analysis of a two-dimensional solidification problem has fitted the unidirectional and two-dimensional experimental data very well.     

Improvement of three-phase flow numerical simulations by means of novel hybrid methods

Numerical simulations of three-phase flows are facing the challenge that their mathematical models include a lot of assumptions and the equation systems often deliver controversial solutions. The object of this study is the improvement of numerical simulations of a three-phase (solid, gas, liquid) flow according to the four-way coupling Eulerian-Eulerian frame. Following the strategy of incorporating a priori knowledge in a system, initial velocity information achieved by several experimental and numerical techniques is implemented in the numerical simulations. Particle image velocimetry (PIV) data are employed in a numeroexperimental hybrid and artificial neural network (ANN) data in numeroneuronal and neuroexperimental hybrids, where the ANNs are trained with numerical or PIV data, respectively. The employment of the three presented hybrid methods affords better convergence of the numerical simulations, delivers more accurate numerical results and enables saving of computational time, thus, more precise information about the behaviour of the fluid mechanical system is faster achieved.     

A hybrid optimisation model for pallet loading

This study adopts a hybrid approach that integrates the genetic algorithm (GA) and fuzzy logic in order to assist in the generation of an optimal pallet loading plan. The proposed model enables the maximisation of profits for freight forwarders through the most efficient use of space and weight in pallet loading. The model uses fuzzy controllers to determine the numbers and size of cargo units on a pallet as well as the mutation rate in the GA approach within the optimisation process and enables the capture of tacit knowledge vested in industry practitioners. The pragmatic use of the model is illustrated using a freight-forwarding scenario that demonstrates the inherent limitations of the standard GA method, followed by the application of the proposed fuzzy GA model. To further demonstrate the benefits of the hybrid model, simulated annealing and Tabu search are used to benchmark the results achieved using various approaches; the proposed hybrid model is demonstrated to exceed these other approaches in overall performance. The application of the proposed hybrid approach across a range of scenarios is also discussed.     

A hybrid rigid body rotation model for predicting a response of a temporary soil-filled wall subjected to blast loading

This study is aimed to provide an efficient analytical model to calculate a time history of response for a free-standing soil-filled HESCO Bastion concertainer^® wall subjected to air blast loading. The model is formulated based on the observations of the wall response to air blast loading in the experiments and on the deformation of a finite element model. This hybrid rigid body rotation model combines both a reverse Winkler foundation to model the distribution of pressure at the base of the wall and perfectly plastic shear resistance to model the shear deformation at the corner. The time histories of horizontal and vertical displacements calculated from the proposed analytical model are validated with displacements from both full-scale blast testing of free-standing simple straight walls and calculations using a finite element model.     

A BEM approach to model heat flow during crystallization

In most polymer processing applications such as injection moulding, fibre spinning and extrusion, crystallization plays an important role. The energy flow at the solid-liquid interface during crystallization controls the kinetics and subsequently influences the morphology of the transforming material. Our approach is based on the classical phase-change problem. The governing transient heat conduction equations in the liquid and the solid domains are solved using a boundary element method (BEM) with a time dependent fundamental solution to determine the temperature distribution. The boundary energy equation is used to predict the movement of the front. The crystallization kinetics are introduced through a mathematical model based on the cooling rate of a hypothetical control volume in the solid (crystalline) domain and the changes in the crystallinity are expressed in terms of the varying interface temperature. First, we verified the BEM formulation and implementation by comparing the results of two examples with an analytical and a finite difference method in one-dimension. Next, we investigated the effects of the crystallization kinetics by allowing the interface temperature to vary during the crystallization process. The results show that the crystallization front movement is slowed considerably when the kinetics are taken into account. Also, depending on the cooling rate and the parameters in the kinetics model, there may be undercooling during the process.     

A hybrid water flow algorithm for multi-objective flexible flow shop scheduling problems

In this article, the multi-objective flexible flow shop scheduling problem with limited intermediate buffers is addressed. The objectives considered in this problem consist of minimizing the completion time of jobs and minimizing the total tardiness time of jobs. A hybrid water flow algorithm for solving this problem is proposed. Landscape analysis is performed to determine the weights of objective functions, which guide the exploration of feasible regions and movement towards the optimal Pareto solution set. Local and global neighbourhood structures are integrated in the erosion process of the algorithm, while evaporation and precipitation processes are included to enhance the solution exploitation capability of the algorithm in unexplored neighbouring regions. An improvement process is used to reinforce the final Pareto solution set obtained. The performance of the proposed algorithm is tested with benchmark and randomly generated instances. The computational results and comparisons demonstrate the effectiveness and efficiency of the proposed algorithm.     

Axial collapse of hybrid square sandwich composite tubular components with corrugated core: numerical modelling

The present paper is dealing with the implementation of the explicit FE Code LS-DYNA to the simulation of the crash behaviour and energy absorption characteristics of thick-walled square tubular crashworthy components made of hybrid sandwich material with corrugated core subjected to axial compressive loading. The obtained numerical results are compared with actual experimental data from small-scale models in terms of deformation modes, energy absorption capability, load/deflection history and crush zone characteristics, showing very good agreement.     

A hybrid BEM model

The hybrid stress method is very successful for stress concentration problems.^1–7 Especially for problems of fracture mechanics, procedures can be found that work efficiently for two- and three-dimensional problems. The rate of convergence with this method, evidently, is higher than that with conventional FE models. The BEM procedure, too, works more efficiently, but shows some essential disadvantages against the FEM, such as that for the direct method no symmetric positive definite matrix can be found and that there occur numerical problems at corners.^8,9 This happens also when BEM and FEM are even coupled commonly.^10–12. In the following, a hybrid BEM model will be described which combines the advantages of both the FEM and the BEM. It will be shown in this paper that BEM is very successful in formulating finite element functions for the hybrid assumed stress method.