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1.
This paper describes a practical method for setting safety lead-times for purchased components in assembly systems with uncertainty in the supply process. The approach is specifically designed to be used in an MRP procurement environment. A two-stage production model in which suppliers were uncapacitated with stochastic lead times was developed. Then, a combinatorial optimization method that took advantage of structural properties was developed to produce an optimal integer solution of safety lead-times. In addition to yielding a practical lead-time setting tool, the model led to some interesting policy insights: (1) the flexibility achieved by bringing parts in early may have value even in situations with ideal suppliers; (2) purchasing components in batches offers some of the same protection as does safety lead time, but is less precise and subsequently more expensive; and (3) ignoring the complicating issues of MRP procurement results in far from optimal results.  相似文献   

2.
A new partitioned solution procedure for the direct time integration of second order coupled-field systems is presented and it is applied to the problem of soil–pore fluid interaction. The necessary convergence analysis for the iterative method is carried out and the fulfilment of the convergence condition is achieved with the introduction of two suitable auxiliary matrices in the basic equations governing the dynamic phenomena. Numerical examples are presented to demonstrate the effectiveness and the versatility of the proposed solution procedure.  相似文献   

3.
This paper considers a stochastic assembly system operating on a make-to-order basis with complex product structure and resource constraints. The problem is to find the optimal planned job release times by minimizing the expected sum of the work-in-progress holding cost, product earliness cost and product tardiness cost. A perturbation analysis algorithm is developed to derive the gradient estimate of the cost function with respect to the job release times. This gradient estimate is shown to be unbiased and may lead to the optimal solution by using a stochastic approximation method. Moreover, a procedure is presented to adjust planned job release times to meet service level constraint for each individual job. Numerical examples, which use manufacturing and assembly data from a capital goods company, are given to demonstrate the results.  相似文献   

4.
A hybrid method is presented for the design of inspection stations in serial production systems. The hybrid method combines a constrained bottleneck shortest path algorithm and discrete event simulation. The network method determines the allocation of the inspection stations and the simulation helps the decision maker estimate accurately the possible outcome of the allocation. A computational study with the method is performed based on a practical problem. Other aspects related to the application of the method to real problems are also discussed.  相似文献   

5.
The form of the eigenvector solution for a general corner or finite opening crack is examined for both real and complex eigenvalues using a complex potential approach. An overdetermined collocation algorithm to calculate the coefficients associated with eigenvectors for both the real and complex eigenvalues is presented. The algorithm is tested on a problem of known solution.  相似文献   

6.
This paper considers the problem of determining safety stocks in multi-item multi-stage inventory systems that face demand uncertainties. Safety stocks are necessary to make the supply chain, which is driven by forecasts of customer orders, responsive to (demand) uncertainties and to achieve predefined target service levels. Although there exists a large body of literature on determining safety stock levels, this literature does not provide an effective methodology that can address complex multi-constrained supply chains. In this paper, the problem of determining safety stocks is addressed by a simulation based approach, where the simulation studies are based on solving the supply chain planning problem (formulated as a mathematical programming model) in a rolling horizon setting. To demonstrate the utility of the proposed approach, an application of the approach at Organon, a worldwide operating biopharmaceutical company, will be discussed.  相似文献   

7.
A mixed-model assembly line is a type of production line which is used to assemble a variety of product models with a certain level of similarity in operational characteristics. This variety causes workload variance among other problems resulting in low efficiency and line stops. To cope with these problems, a hierarchical design procedure for line balancing and model sequencing is proposed. It is structured in terms of an amelioration procedure. On the basis of our evolutionary algorithm, a genetic encoding procedure entitled priority-based multi-chromosome (PMC) is proposed. It features a multi-functional chromosome and provides efficient representation of task assignment to workstations and model sequencing. The lean production perspective recognises the U-shape assembly line system as more advanced and beneficial compared to the traditional straight line system. To assure the effectiveness of the proposed procedure, both straight and U-shape assembly lines are examined under two major performance criteria, i.e., number of workstations (or line efficiency) as static criterion and variance of workload (line and models) as dynamic criterion. The results of simulation experiments suggest that the proposed procedure is an effective management tool of a mixed-model assembly line system.  相似文献   

8.
This paper reports on the development of an efficient and accurate means for the direct computation of crack surface weight functions for two dimensional fracture mechanics analysis. Weight functions are mathematical representations which can be used to efficiently calculate stress intensity factors for a variety of crack loading and boundary conditions. The method is inherently capable of handling mixed-mode problems. The weight function capability is especially important for problems of fatigue crack growth modeling where the efficient calculation of stress intensity factors is crucial.The basis of the new formulation and numerical solution method is the boundary element method (BEM), as implemented for two dimensional fracture mechanics analysis. The paper will review the analytical formulation of the new BEM, the numerical solution algorithm, and a limited number of validation examples.  相似文献   

9.
Semi-Markov models for systems undergoing periodic test and maintenance are developed. In particular, systems undergoing specific changes of state at predetermined instances of time and transiting to states with generally distributed sojourn times are considered. Problems addressed by the models are those concerned with optimum assessment of test intervals, and allowable outage times. Equivalent Markovian models allowing for the decomposition of a system of dimensionality N+M into two smaller problems of dimensionality N and M, respectively are developed. The general model is also specialized to systems with instantaneously testable components, unmonitored components undergoing tests (repair, maintenance) of fixed duration, and systems containing components characterized by limited allowable outage time (under test, or repair). Approximate equivalent Markov models are derived in these cases. Simple numerical examples are also presented.  相似文献   

10.
11.
In this paper the two-dimensional problem of a bolt loaded-hole in an infinite piezoelectric laminate is considered in terms of the complex variable method. Firstly, an explicit form Green function for a generalized point load acted at an arbitrary point outside the hole is derived. Secondly, the Green function for a generalized point load acted at the rim of the hole, as a special case, is obtained, and then a general solution for the case of arbitrarily distributed mechanical and electric loading on the hole surface is presented based on the superposition principle. In general, the solution is in the form of series, but its novel feature is that the coefficients involved in the solution can be easily written out once the distributed loading is specified. Finally, several examples useful for engineering are given.  相似文献   

12.
In this paper we explore the reuse of components of known good schedules in new scheduling problems. This involves accumulating a case-base of good quality schedules, retrieving a case (or cases) similar to a new scheduling problem and building a new schedule from components of the retrieved cases. We start by introducing the components of 'case-based reasoning' (CB R) and we describe a CB R solution to a 'travelling salesman problem' in order to illustrate the use of CB R in optimization problems. Two CB R solutions to a single machine scheduling problem with sequence dependent setup times are described. These are evaluated by comparing them with two more conventional alternative techniques simulated annealed and myopic search. Both CB R techniques are shown to provide good quality solutions quickly.  相似文献   

13.
In this paper we study the problem of scheduling the fabrication and assembly of components in a two-machine flowshop so as to minimize the makespan. Each job consists of a component unique to that job and a component common to all jobs. Both the unique and the common components are processed on the first machine. While the unique components are processed individually, the common components are processed in batches and a setup is needed to form each batch. The assembly operations of a job is performed on the second machine, and can only begin when both components for the job are available. We first show that the problem is NP-complete with either batch availability or item availability for the common components. We identify several properties of an optimal solution to the problem, and some polynomially solvable special cases.  相似文献   

14.
15.
Research on strategic planning in manufacturing has tended to focus on two themes: (1) integrating manufacturing strategy with business strategy; and (2) aggregate capacity planning and allocation. This paper introduces a new planning problem that provides a bridge from strategy to capacity by focusing on the configuration of key manufacturing resources. The problem is introduced in the context of consumer electronics. As a first step toward developing planning tools, a single period approximation is formulated. The single period model provides some analytical insights and leads to two solution approaches. Specific algorithms are developed and computationally tested. Directions for future research are described.  相似文献   

16.
Generation of the alternating strong and almost zero homogeneous magnetic field that the magnetocaloric material has to be exposed to is a major challenge in magnetic refrigeration. With this paper we start a series of publications considering designing of Halbach cylinder based magnet assemblies for non simultaneous cycles. In present, for the first part we define a designing procedure which, applied to the Halbach cylinder, allows creation of two or higher pole number magnet assemblies. We consider here two and four pole cases in great details. Each designing procedure step is accompanied by 3D finite element simulation. The achieved final magnet designs fulfill the predefined requirements of particular field distribution in the air gap, maximized ratio of high field volume to the permanent magnet volume, best utilization of magnets and magnetocaloric materials and constructional simplicity. A short comparison of two and four pole arrangements is given.  相似文献   

17.
Multi-level lot sizing problems are difficult to solve optimally when the product structure contains more than a few items. This paper identifies conditions on the cost parameters which, when applicable, allow items to be combined for purpose of optimization, thereby reducing the size of the problem.  相似文献   

18.
A general, well-structured and efficient method is advanced for the solution of-a large class of dynamic interaction problems including a non-linear dynamic system running at a prescribed time-dependent speed on a linear track or guideway. The method uses an extended state-space vector approach in conjunction with a complex modal superposition. It allows for the analysis of structures containing both physical and modal components. The physical components studied here are vehicles modelled as linear or non-linear discrete mass–spring–damper systems. The modal component studied is a linear continuous model of a track structure containing beam elements which can be generally damped and which can be embedded in a three-parameter damped Winkler-type foundation. The complex modal parameters of the track structure are solved for. Algebraic equations are established which impose constraints on the transverse forces and accelerations at the interfaces between the moving dynamic systems and the track. An irregularity function modelling a given non-straight profile of the non-loaded track or a non-circular periphery of the wheels is also accounted for. Loss of contact and recovered contact between a vehicle and the track can be treated. The system of coupled first-order differential equations governing the motion of the vehicles and the track and the set of algebraic constraint equations are together compactly expressed in one unified matrix format. A time-variant initial-value problem is thereby formulated such that its solution can be found in a straightforward way by use of standard time-stepping methods implemented in existing subroutine libraries. Examples for verification and application of the proposed method are given. The present study should be of particular value in railway engineering.  相似文献   

19.
We study the problem of selecting components for redundancy in coherent systems to maximize system reliability. For this optimization problem most of the previous results are obtained under the assumption that the values of component reliabilities are known, or at least an ordering of them must be known in advance. However, in many practical situations such information about component reliabilities is unobtainable. In this paper we propose selection criteria based solely on structural information, and show that the resulting selections from the criteria are optimal when certain conditions are satisfied. Some numerical examples illustrate that the selection methods we propose are easy to apply and perform quite well in practical structures.  相似文献   

20.
The possibility of approximate modeling of a stationary reactor with mixing by a system of differential equations is examined.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 36, No. 6, pp. 1052–1058, June, 1979.  相似文献   

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