Cost Minimization Objective Research Articles

Decomposition approaches for solving the integer one-dimensional cutting stock problem with different types of standard lengths

This paper considers the integer one-dimensional cutting stock problem with different types of standard lengths and the objective of cost minimization. Decomposition approaches based on the well-known column-generation technique for exactly solving the continuous relaxation of the problem and specific methods for separately solving the arising residual problems are proposed. For evaluating the performance of the different approaches, more than 12,000 randomly generated test problems have been solved. The computational experiments prove the effectiveness of one of the proposed decomposition procedures with respect to the computing effort and the quality of the solutions obtained.

A module-oriented tool for optimum design of stiffened structures—Part I

The development of the LBR-5 “Stiffened Panels Software” is included in the development of a new design methodology to ease and to improve preliminary studies of naval structures and floating hydraulic structures. The ultimate target is to link standard design tools (steel structure CAD, hull form, hydrostatic curves, floating stability, weight estimation, etc.) with a rational optimization design module and a minimum construction cost (or minimum weight) objective function. This paper is the first part of a series of two articles. It focuses on the ‘ Module-Oriented Optimization’ methodology and on the rational constraints. The second paper presents the optimization technique using convex linearization and a dual approach, and the optimization of an FSO unit as an example (Rigo and Fleury, Marine Stuructures, 2001). LBR-5 allows, as of the first draft, an optimization of the scantling of the structure's constituent elements. Relevant limit states of the structure are taken into account thanks to a 3D rational analysis of the structure based on the general rules of solid-mechanics and structure behaviour. The optimization module is composed of 3 basic modules (OPTI, CONSTRAINT and COST) and a group of sub-modules (in external databases). Among these the user selects a set of relevant sub-modules (i.e. geometrical and structural constraints). Since the present optimization deals with least construction costs (as objective function), and uses an explicit objective function (not empirical), the user must specify labor costs (unitary material costs, welding, cutting, etc.).

Scantling optimization based on convex linearizations and a dual approach—Part II

The development of the LBR-5 “Stiffened Panels Software” is included in the development of a new design methodology to ease and to improve preliminary studies of naval structures and floating hydraulic structures. It allows, as of the first draft, an optimization of the scantling of the structure's constituent elements. The ultimate target is to link standard design tools (steel structure CAD, hull form, hydrostatic curves, floating stability, weight estimation, etc.) with a rational optimization design module and a minimum construction cost (or minimum weight) objective function. It is developed to be a user-oriented tool. The optimization module is composed of three basic modules (OPTI, CONSTRAINT and COST) and a group of sub-modules (in external databases). Among these the user selects a set of relevant sub-modules (i.e. geometrical and structural constraints). Since the present optimization deals with least construction costs (as objective function), and uses an explicit objective function (not empirical), the user must specify labor costs (unitary material costs, welding, cutting, etc.). This paper is the second part of a series of two articles. The previous paper focused on the ‘Module-Oriented Optimization’ methodology and on the rational constraints (Rigo, Marine Structures 2001). This paper presents the optimization algorithm based on convex linearization and a dual approach (OPTI module). It also includes the optimization of a FSO unit as a detailed example.

A cast-off replacement policy for a component demanded by two parallel units

Sometimes a component is removed and thrown away from a unit when it is not working satisfactorily: this could be wasteful in many cases. Some components after removal from a unit may work satisfactorily in another less demanding parallel unit, for a reasonable length of time. Therefore, in this paper we present a cast-off replacement policy that makes maximum utilization of a component that is non-repairable and demanded by two parallel units. A minimum total cost objective function is assumed.

Tabu search in audit scheduling

The problem of audit staff scheduling normally involves auditors with varying efficiencies, and several audit engagements with varying requirements and at different locations. The task of scheduling auditors to the audit tasks becomes more complicated if the scheduler has to accommodate the many real life considerations. The problem, regardless of its size or complexity, has been formulated as a (0–1) integer program. However, the large number of variables and constraints in such a formulation makes the use of exact optimization methods impractical. In this paper, we present a heuristic procedure based on tabu search (TS) and intelligent memory structures for solving this problem. The TS method starts with a feasible schedule generated by a greedy forward dispatching procedure, then through a series of intensification and diversification steps it improves on the initial schedule. The improvement in the value of the objective function is observed interactively. The search can be terminated as the improvement in the value of the objective function stabilizes. Application of the TS method to different audit scheduling problems has led to a consistent and significant improvement in the value of the cost minimization objective function.

Combined active and reactive dispatch with multiple objectives using an analytic hierarchical process

A fully coupled active and reactive dispatch using linear programming and an analytic hierarchical process is developed. The purpose of combined active and reactive dispatch (CARD) is to achieve the overall objective of minimum generation cost and to improve the distribution of reactive power and voltage, subject to constraints which ensure system security. Security is defined as the maintenance of individual circuit flows, generator reactive power output and system voltages within limits under normal system conditions and contingency cases. The weighting factors of different kinds of objective functions are determined by an analytic hierarchical process (AHP), considering the relative importance of these objective functions. The developed method is demonstrated through its application to determine the combined active and reactive dispatch of a 713-node network representing a practical power system, provided by the National Grid Company plc (NGC). The calculation results show that a good balance can be achieved among the various objectives and a satisfactory generation pattern is obtained from the enhanced CARD program.

An introduction to the segmented flow approach for discrete material flow systems

Due to increases in versatility and the complexity of demands in modern manufacturing systems a growing need has evolved t0 simplify the control of these systems while maintaining a high degree of efficiency and flexibility in operation. The segmented flow approach (SFT) suggested in this paper is a possible solution to these needs. This structure simplifies the control task by reducing the need for dispatching and by eliminating the need for routeing material handling devices and scheduling traffic at intersections. Each task involves only one material handling device and one possible route. This structure maintains a high degree of efficiency by operating material handling devices in a bidirectional mode and eliminates congestion and blocking by operating them on mutually exclusive tracks. This paper introduces a design procedure for an SFT implemented system using a minimum cost objective, and compares the throughput and time in system performance of this system to a conventional system and a tandem ty...

Integrated computer-aided optimal design and finite element analysis of a plain milling cutter

This paper presents the computer-aided integration of solid modelling, optimization, and finite element analysis. Interactive (three-dimensional) solid modelling is used in the development of relatively efficient and fast solutions to the many constraints and/or limitations encountered in the design process. The study also addresses the fatigue analysis using 3D finite element analysis on a workstation. Throughout the study, interactive 3D solid modelling is used in the development of a practical and economical design procedure. The research highlights the interactive and integrated nature of the design tasks. An optimal formulation of an automatic design algorithm is also carried out. The cost minimization objective function along with design constraints and behavior constraints are developed. The optimal design parameters thus obtained are tested for stresses at the tip of the tool and at the fillets. Interactive application of optimization, solid modelling, and finite element techniques produce the acceptable optimal design. The design methodology presented in this paper is general and generic in nature. This has been illustrated through an example of design of a plain milling cutter.

Combined active and reactive despatch. I. Problem formulation and solution algorithm

A fully coupled active-reactive despatch using linear programming is presented. The purpose of combined active and reactive despatch (CARD) is to achieve the overall objective of minimum generation cost and/or to improve other system parameters, subject to constraints that ensure system security. CARD allows a series of time steps to be considered. The duration of each time stage may be chosen so that despatching points occur at any critical points of the predicted load curve within the despatch period. The problem is expanded such that the linear program variables include the output at the end of each time step, with the objective function value integrated over all stages. System constraints are replicated at each time stage. Dynamic rate limits are also included. The reactive power despatch is regarded as static within each step, but is influenced by the generator active power rate of change limitations.

Machining economics with machine interference considerations

Abstract We present solution methods to the problem of synchronizing parallel machining operations in order to avoid overlapping tool changes. The proposed algorithm utilizes results from the economic lot scheduling problem and modifies the machining speeds of the various operations in accordance with the minimum machining cost objective. The procedure is demonstrated through a numerical example.

OPF incorporating load models maximizing net revenue

Previous studies have shown that the incorporation of load models in optimal power flow (OPF) solutions using a minimum cost objective reduces fuel cost by lowering the power demand of the modeled loads. It is shown that the reason for the decrease is due to misuse of the objective. An objective that avoids the tendency to lower the total power demand, total revenue and net revenue for OPF neglecting contingencies (normal OPF) as well as for security-constrained OPF is proposed. The minimum cost objective is modified by subtracting the total power demand from the total fuel cost. This is equivalent to maximizing the net revenue. >

Indian urban solid waste management systems—Jaded systems in need of resource augmentation

In India, the systems of urban solid waste management are becoming increasingly expensive and complex because of continuous and unplanned growth of urban centres. The difficulties in providing the desired level of public service through them is often attributed to poor financial status of the managing municipal corporations. The systems, in practice, have to meet several objectives. Therefore, they cannot be analysed effectively by optimising models using the single objective of cost minimisation. To study the problems of resource gaps within the frame work of these conflicting objectives, an interactive goal programming model for multi-objective planning of the system is proposed. The model is applied to plane the solid waste operations for a typical Indian city. Initially, the model considers existing resource levels and methods of estimation. The results indicate that these resource levels are far too inadequate for achievement of even the primary goal of the system. The model is reapplied with augmented resources so that optimal resource requirements for the system to attain the desired objective are determined, and the resource planning gaps are identified.

Optimal Update Policies for Distributed Materialized Views

In this paper we present an analysis of the problem of determining optimal policies for updating distributed materialized views. We demonstrate the general application of materialized views, and define the concept of materialized view currency and allow a query to specify its currency requirement. We also allow a materialized view to be updated from either a base relation or another materialized view. This flexibility provides an opportunity for further reduction in the cost of maintaining distributed materialized views. We model the problem of optimal update policies to capture currency and policy constraints, replicated data, and various view update policies. The optimization incorporates a minimum-cost objective function as well as user's response time constraints.

Radial bus networks with multi‐period and many‐to‐many demand

AbstractMathematical models are developed for optimizing radial bus networks with time dependent demand and supply characteristics. These models can deal with many‐to‐many demand distribution in heterogeneous rather than idealized geographic environments. With some approximations, closed‐form solutions for the optimal route angle, headways for different time periods, and stop spacings for various locations are obtained for a total cost minimization objective. The relations between the decision variables and system parameters are identified analytically. The optimality of a constant ratio between headways and route angle is found to hold with a time related factor. The optimized wait cost, operator cost, and lateral access cost are found to be equal. A numerical example is given for a case with three service periods. It illustrates the applicability of the analytic model to irregular demand patterns that may be directionally imbalanced during some periods.

Searching for New Manufacturing Plant Locations: A Study of Location Decisions in Central Appalachia

WALKER R. and CALZONETTI F. (1989) Searching for new manufacturing plant locations: a study of location decisions in Central Appalachia, Reg. Studies 23, 15–30. This paper analyses the search behaviour of manufacturers in Central Appalachia and develops a model of hierarchical decision-making under imperfect information. Using data collected from interview surveys of plant managers, regional and local search processes are evaluated. It is shown that the set of factors influencing the decision to undergo a regional search is different from the set of factors influencing the local search. Further, branch plant search behaviour may be described by cost minimization objectives whereas the behaviour of single-plant establishments is more idiosyncratic. The analysis shows that the comparative advantage of Central Appalachia consists, in part, of low cost electricity. WALKER R. et CALZONETTI F. (1989) A la recherche de nouveaux emplacements: une etude en Appalachia central des decisions portant sur la localisati...

A Multiobjective Hierarchical Covering Model for the Essential Air Services Program

This paper presents the development of a mathematical programming model for evaluating options for the continuance of the Essential Air Services (EAS) program, a provision of the Airline Deregulation Act of 1978. The EAS program was established to guarantee continued air service to small communities that suffered air service losses as a result of carrier withdrawals permitted by the Deregulation Act. The model has been designed to aid decision makers in allocating subsidized air services to communities in a region, given the goal of maximizing access to the air transportation system. In order to provide information on optimal service locations, service characteristics, and patterns of access, the authors have utilized a maximal covering formulation and incorporated elements of hierarchical and weighted benefit models. In addition, a stopover service option has been included in the model to permit evaluation of potential gains in economic efficiency that may be realized by utilizing stopover service, when appropriate, in place of more costly nonstop service. In addition to the coverage objective, a second objective of systemwide cost minimization is employed. By using a multiobjective approach, the trade-offs between the conflicting objectives of coverage and cost can be explored and the spatial patterns of service associated with each combination of coverage level and cost can be examined. The model is applied to a sample study of small community air service in North and South Dakota.

Optimal cooling towers management for zero discharge

In order to operate the cooling tower system as a zero discharge unit, the blowdown should be treated and recycled or used in other processes within the industrial plant limits. A mathematical model, applicable to wet cooling towers, was developed. The basic assumptions of the model were: • . Cooling tower blowdown and makeup might be treated in the same plant (Alternative I) or in different plants (Alternative II). • . Average removal efficiencies were used as basis for determining the feasibility of each one of the selected treatment techniques ((FILTRATION, SOFTENING, REVERSE OSMOSIS, ELECTRODIALYSIS, ION EXCHANGE, VAPOR COMPRESSION EVAPOPATION), to reduce the concentration of the limiting chemical compounds. • . Water Quality Guidelines for circulating cooling water, were uses as constraints to be satisfied in the cooling circuit. • . Three types of outflows: evaporation, drift and brine or sludge, were considered leaving the cooling system. • . The composition and temperature of the cooling water and drift streams were equal. • . The system was under steady-state conditions. • . All treatment plants had to be constructed . The Model's statement was: Objective Function: Minimize Total Cooling Tower Makeup and Blowdown Treatment Costs. Subject to: 1. (1) Flow constraints 2. (2) Water Quality constraints Costs functions were developed for the selected treatment techniques in order to be used as the objective functions of the Model. The optimization algorithm was based on the searching of a minimum cost objective function by varying the flow rates of the treated makeup and blowdown in an iterative way. Five computer programs were developed and the corresponding printouts show the feasibility region and the optimal basis. The Model was applied to three cooling towers scale levels (Equivalent reject heat loads: 20 MW, 150 MW, and 500 MW) and using two makeup sources of different quality.

A focussed review of scheduling in services

The paper first outlines the special characteristics of services, as compared to those of the manufacturing systems. The second section stresses that each of the service systems has its own major primary objective/objectives, but such primary objectives are invariably in conflict with the well-known cost-minimization objective of manufacturing systems. The paper also discusses the variety of legal, union, and budgetary constraints which must not be violated by the service-system managers under any circumstances. Finally, the paper lists eleven different types of service systems, showing for each the unique constraints, the special sets of conflicting objectives as designated by their respective managements, and the commonly used techniques, methods and procedures. The most important and the most frequently referenced articles related to each type of system are indicated.

Locating New Facilities with Respect to Existing Facilities

Abstract An efficient algorithm is presented for optimally locating new facilities with respect to existing facilities when movements between facilities are rectilinear. A cost-minimization objective is assumed. The algorithm has been programmed for a digital computer and large problems (500 existing and 100 new facilities) have been solved that illustrate the efficiency of the algorithm. An example problem is presented. Upper and lower bounds on the optimal value for direct (straight-line) movements are derived. Experience has shown that these bounds are relatively close.