Imposing rigidity constraints on immersed objects in unsteady fluid flows

Imposing rigidity constraints of an immersed elastic body in a transient flow field is not trivial. It requires solution stability and accuracy. In this paper, we present an efficient and accurate algorithm implemented to enforce fluid–structure interface constraints used in the immersed finite element method (IFEM). This interface treatment is a constraint applied onto the rigid bodies based on the fluid structure interaction force evaluated from the immersed solid object. It requires no ad hoc constants or adjustments, thus providing numerical stability and avoiding unnecessary trial-and-error procedures in defining the stiffness of the elastic body. This force term can be evaluated for both uniform and nonuniform fluid grids based on the higher order interpolation function adopted in the IFEM. The ability in handling nonuniform interpolations offers the convenience in modeling arbitrary geometrical shapes and provides solution refinements around interfaces. The results we obtained from flow past a rigid cylinder demonstrate that this convenient way of constraining the interface is a reliable and robust numerical approach to solve unsteady fluid flow interacting with immersed rigid bodies.     

Scheduling assembly tasks with caterpillar precedence constraints on dedicated machines

In this work, we address the problem of scheduling a set of n non-preemptive tasks on m dedicated machines in order to minimise the makespan. For each task deterministic processing times and a specific processing machine are given, moreover a set of precedence constraints among the tasks are known. We present a heuristic and some lower bounds on the minimum makespan for a relevant case in manufacturing applications, namely when the precedence constraints form a caterpillar graph. A caterpillar is a directed tree consisting of a single directed path and leaf nodes each of which is incident to the directed path by exactly one incoming arc. A number of computational experiments are also performed in order to test the performance of the proposed solution algorithm.     

Minimising makespan on parallel machines with precedence constraints and machine eligibility restrictions

The block erection problem is defined as a parallel machine scheduling problem with precedence constraints and machine eligibility restrictions. A heuristic algorithm combined of the largest total amount of processing first rule (LTAP) and the enhanced smallest machine load first rule (ESML) is proposed to minimise makespan for the block erection in a shipyard. Finally, four lower bounds and the percentage of the reduced makespan compared with the current solutions are defined to evaluate the performance of the proposed algorithm. The experiments are performed on data selected from a shipbuilding company, and the results demonstrate that the presented algorithm can effectively find a good solution to minimise the makespan of the block erection problem.     

Tool design problems in a punch press flexible manufacturing system

In this paper, we study tool design problems encountered in using a punch press Flexible Manufacturing System (FMS) for producing flat sheet-metal parts. We consider the problem of designing the minimum number of tools needed to punch a given set of holes in the parts. Holes described by a single attribute as well as two attributes are considered. We model the tool design problems as graph theoretic problems. Such an approach is believed to be new for the problem studied. We have made the following major contributions: First, we show that the two-attribute tool design problem is equivalent to the minimum clique cover problem on the intersection graph of rectangles, which is a well known NP-complete problem. Second, we develop a fast algorithm to construct a set-covering formulation from the underlying graph model. In addition, we show that our approach has applications beyond the tool design problem (e.g., location problems).     

Product batching and batch sequencing for NC punch presses

This paper proposes a two-stage practical product batching and batch sequencing algorithm for NC punch presses used in the production of precision sheet metal electronics components. The first stage of the algorithm batches a given set of products in order to maximize the number of products in a batch as well as the tool magazine utilization. In this stage, tool magazine constraints such as number of available slots, size of slots, tool configurations and tool locations are taken into consideration. The resulting batches are passed to the second stage of the algorithm which sequences these batches. The sequencing is done by using the ‘ nearest neighbour’ heuristic for the ‘ travelling salesman problem’ Comparison of the new method with the procedure previously used by a manufacturer of such components demonstrated a significant reduction in setup times.     

Advanced planning and scheduling based on precedence and resource constraints for e-plant chains

The e-plant chain is an extension of the integration beyond a production site by means of improved distribution management, electronic data interchange and coordination of multiple plants. The present paper proposes an advanced planning and scheduling model for the e-plant chain. The advanced planning and scheduling is the most important function when supporting flexible planning and scheduling in the e-plant chain. The problem is formulated as a mixed integer-programming model. The model includes the main features of the system including flexible operations’?sequences, resource requirements and alternative schedules. Since the problem is NP-hard, an intelligent search approach based on a genetic algorithm is developed. Numerical experiments show the proposed approach is satisfactory in its accuracy and efficiency.     

A batching-move iterated local search algorithm for the bin packing problem with generalized precedence constraints

In this paper, we propose a generalisation of the bin packing problem, obtained by adding precedences between items that can assume heterogeneous non-negative integer values. Such generalisation also models the well-known Simple Assembly Line Balancing Problem of type I. To solve the problem, we propose a simple and effective iterated local search algorithm that integrates in an innovative way of constructive procedures and neighbourhood structures to guide the search to local optimal solutions. Moreover, we apply some preprocessing procedures and adapt classical lower bounds from the literature. Extensive computational experiments on benchmark instances suggest that the developed algorithm is able to generate good quality solutions in a reasonable computational time.     

Design of high-performing hybrid meta-heuristics for unrelated parallel machine scheduling with machine eligibility and precedence constraints

This study involves an unrelated parallel machine scheduling problem in which sequence-dependent set-up times, different release dates, machine eligibility and precedence constraints are considered to minimize total late works. A new mixed-integer programming model is presented and two efficient hybrid meta-heuristics, genetic algorithm and ant colony optimization, combined with the acceptance strategy of the simulated annealing algorithm (Metropolis acceptance rule), are proposed to solve this problem. Manifestly, the precedence constraints greatly increase the complexity of the scheduling problem to generate feasible solutions, especially in a parallel machine environment. In this research, a new corrective algorithm is proposed to obtain the feasibility in all stages of the algorithms. The performance of the proposed algorithms is evaluated in numerical examples. The results indicate that the suggested hybrid ant colony optimization statistically outperformed the proposed hybrid genetic algorithm in solving large-size test problems.     

冲头形状对液压冲孔塌陷的影响

为了研究管材液压冲孔中冲头形状对塌陷的影响规律,采用7种不同形状的冲头进行了液压冲孔实验,分析了冲头形状对液压冲孔质量的影响.实验结果表明:塌陷深度随着冲头端面倾斜角度的增大而减小,随着冲头圆角的增大而增大.提高内压能够降低塌陷深度,塌陷深度随着管内压力的增大而减小.不同形状冲头对塌陷的影响不同,斜冲头冲孔后塌陷较小,圆角冲头冲孔后塌陷较大.     

Moving punch on a highly orthotropic elastic layer

Summary An analytical solution was given to the problem of a long rigid punch moving rapidly on a strip of a highly orthotropic material. This elastic layer rests in turn on a rigid frictionless foundation. Obviously, the problem presents a lot of interest from the view-point both of geophysical and mechanical sciences. The solution was effected by means of integral transforms and the Wiener-Hopf technique. Asymptotic results were obtained valid near the edge of the moving punch.With 3 Figures     

模具型面工艺孔对面畸变的影响

为了研究成形凸模工艺孔对面畸变形态及大小的影响,以矩形双曲面扁壳为模型,采用拉深成形工艺方法获得了不同成形条件下的拉深件,利用油砂轮研磨双曲面扁壳拉深件表面,局部的畸变呈圆形暗坑,取暗坑直径(D)与工艺孔径(d)之比作为面畸变的评价指标,研究成形条件对面畸变的影响规律.研究结果表明:凸模型面工艺孔可以诱发双曲面扁壳拉深件面畸变;屈服强度越大、板料厚度越大、凸模型面弦高越小、压边力越小,面畸变越小.     

3D numerical study on wrinkling characteristics in NC bending of aluminum alloy thin-walled tubes with large diameters under multi-die constraints

With an increase in the diameters of aluminum alloy thin-walled tubes (AATTs) and a decrease in their bending radii, wrinkling characteristics and its prediction under multi-die constraints have become a key problem urgently to be solved for improving the forming quality in numerical control (NC) bending of AATTs with large diameters. Thus in this paper, considering the characteristics of the bending processes, based on the ABAQUS software environment, a 3D elastic–plastic finite element model and a wrinkling energy prediction model under multi-die constraints are established and their reliabilities are validated, respectively, in which, the appropriate choosing of forming parameters is achieved to guarantee no excessive thinning and flattening in the processes even if wrinkling borders on occurring. By combining the two models, variation relationships of the maximum wrinkling factor with different compressed deformation zones and forming ratios, and effects of clearances and friction between different dies and tubes on the maximum wrinkling factor are obtained, and then an investigation into the wrinkling characteristics is carried out for the processes. It is found that the larger the diameters of AATTs, the larger the wrinkling sensitive zones (WSZs), and there is a larger possibility of wrinkling in the bending segments of WSZs than in the straight ones; the larger the effects of clearances and friction between different dies and tubes on wrinkling.     

Flat punch of arbitrary shape on an elastic half-space

A new method is proposed for the analysis of elastic contact problems for a flat punch of arbitrary planform under the action of a normal centrally applied force. The method is based on an integral representation for the reciprocal distance between two points obtained by the author earlier. A simple yet accurate relationship is established between the punch settlement and the applied force for an arbitrary flat punch. Specific formulae are derived for a punch whose planform has a shape of a polygon, a triangle, a rectangle, a rhombus, a circular sector and a circular segment. All the formulae are checked against the solutions known in the literature, and a good accuracy is confirmed.     

Finite element analysis of punch height effect on V-bending angle

Considering the advantages of the V-bending die, the economical set-up time and the fabrication of a wide range of part size and complex shape, the V-bending die is generally used, especially in the Press Brake machine. However, the punch heights in the partial V-bending die affected the bending angle. In this study, the finite element method (FEM) was used to investigate the effects of punch height. The FEM simulation results revealed that the effects of punch height on the bending angle were clearly theoretically clarified based on the material flow analysis and stress distribution. The punch height affected the gap between the workpiece and the die, as well as the reversed bending zone, which resulted in a non-required bending angle. Therefore, applying a suitable punch height created a balance of compensating the gap between the workpiece and the die, and the stress distribution on the bending allowance and the reversed bending zone. This resulted in achieving the required bending angle.     

Sound localization in reverberant environment based on the model ofthe precedence effect

This paper presents a model-based method for sound localization of concurrent and continuous speech sources in reverberant environment. A new algorithm adopted from the echo-avoidance model of the precedence effect was used to detect the echo-free onsets by specifying a generalized pattern of impulse response. Fine structure time differences were calculated from the zero-crossing points in different microphones. They were integrated into an azimuth histogram by the restrictions between them. Two sound sources were localized in both an anechoic chamber and a normal room which has walls, floor, and ceiling made of concrete. The time segment needed for localization was 0.5-2 s and the accuracy was a few degrees in both environments     

Annular punch on an elastic layer overlying an elastic foundation

The problem solved here is the axisymmetric mixed boundary value problem of the isotropic homogeneous theory of elasticity, in which the normal displacement is specified inside an annular area $\text{a ≤ r ≤ b}$, the normal stress is zero in $\text{r < a, r \# b}$ and the shearing stress is zero on the whole face $\text{z = ?h}$, the upper face of the elastic layer; the continuity of the normal and radial displacements and the normal and shearing stresses is assumed at the interface $\text{z = 0}$ between the elastic layer and the elastic foundation having different elastic constants. The problem is reduced to the solution of a Fredholm integral equation of the first kind. The Fredholm integral equation is further put in terms of four simultaneous Fredholm integral equations of the second kind in four unknown functions. The iterative solution of these integral equations has been obtained for $\text{epsi = b/h ? 1}$, and $\text{λ = a/b ? 1}$ for the case of an annular cylindrical punch. The expressions for the normal stress $\text{σ}{}_{\mathrm{zz}}\text{(r, ?h)}$ for $\text{a ≤ r ≤ b}$ and the total load $\text{P}$ on the punch have been obtained.     

The problem of a circular punch on a micropolar elastic solid

The problem of a rigid circular punch in a linear, micropolar, elastic half-space is reduced to the solution of dual integral equations, and ultimately to a pair of Fredholm integral equations of the second kind. These are solved numerically. The distribution of stresses and couple stresses due to the punch have been calculated.