The Economic Design of ―x Charts: A Proactive Approach

It has long been recognized that poor quality can only result in higher costs. Yet, the idea of reducing cost through better quality is not fully realized. Current models for the economic design of control charts provide strategies to maintain existing quality levels. In this research, a comprehensive cost model is developed to incorporate two cost functions. A reactive function, which accounts for all quality related costs incurred while maintaining a stable level of the process, and a proactive function, which accounts for the cost of process improvement. Using incremental economics, the two cost functions are assembled to allow an evaluation of process improvement alternatives based on their economic worth. Procedures for obtaining economically optimum designs for controlling the process mean are developed and designed experiments are utilized to investigate model performance over a wide range of input parameters. The results indicate that the model is sensitive to changes in 13 parameters, especially when the magnitude of the process shift is small. Copyright © 2004 John Wiley & Sons, Ltd.     

An integrated approach to the retrofitting of mass exchange networks

 The synthesis of optimal mass exchange networks (MENs) deals with the identification of a cost-effective network of mass exchangers that preferentially transfer certain species from rich streams to lean streams. To date, MEN synthesis has dealt with grass-root design where the emphasis is on the maximization of process lean streams usage and the minimization of operating cost. Another important class of problems is the retrofit of MENs in which mass-exchange units already exist in the plant and the focus is to maximize the usage of the process units so as to minimize capital cost of newly added units and trade it off with operating cost. In this paper, we develop a systematic procedure for the retrofitting of MENs. First, we identify alternative structural configurations of interest through heuristics. Series and parallel structures are addressed. Next, we focus on two primary retrofitting strategies: those restricted by no capital constraints and those involving capital expenditure. The no-capital alternatives include enhancing performance of a current system as well as solvent substitution. The capital-based alternatives include the addition of new equipment. A new type of mass-pinch analysis is developed to maximize the utilization of existing capital while reconciling added capital with operating cost. The main concept in this novel pinch diagram is identifying maximum performance as dictated not only by thermodynamic limitations but also by physical size limitations. Different process alternatives are considered and screened to attain the optimum design. A case study is presented to demonstrate the broad applicability and potential benefits of the novel approach. Received: 30 July 2000 / Accepted: 11 October 2000     

An optimization approach for the synthesis of recycle and reuse water integration networks

This paper presents a convex mathematical programming model for the global optimization of recycle/reuse water networks. The model is based on a general superstructure that includes the major configurations of interest such as segregation, mixing, recycle, bypass, and treatment of streams needed to satisfy the process and environmental constraints. The basic idea of the model formulation is to consider component balances, treating as optimization variables the individual flowrates. This formulation avoids the bilinear terms that appear when the compositions and total flowrates are considered as optimization variables. The objective function consists in the minimization of the total annual cost including the fresh sources costs, the treatment units costs (which are reformulated as convex functions) and the piping costs. Four examples problems are solved to show the applicability of the proposed model.     

Determination of optimal lot sizing parameters and a controllable process mean for a production system

Several mathematical models have been developed separately for determining production and recycled lot quantities to minimize total production cost and the determination of optimal process mean setting to minimize total quality cost. For a single stage discrete part production system, this paper presents a mathematical model that combines these two inter-related aspects. The production process has a controllable parameter, the process mean, which determines the output lot quality. One-sided tolerance is used to decide the quality of finished goods. Bad units are reworked before they can be reprocessed with the fresh input. For such a situation, the model determines production lot size, recycling lot quantity, and a process mean while minimizing total system cost. The model has been validated using sample data from a pharmaceutical company. Results indicate that the production lot size and the recycled quantity have an inverse relationship with process mean and, a direct relationship with process variance.     

A New Method for Siting Hazardous Units in Chemical Process Facilities Which Minimizes Risk at Least Cost: RIDIMPUS

A new method, RIsk and DIstance Minimization in Process Units Siting (RIDIMPUS), is presented with which hazardous units can be sited in a chemical process facility in a manner that the risk of accidents involving the hazardous units as also the cost of spacing the units is minimized. To achieve this, safety and cost factors were modeled using various governing parameters and then expressions were designed to integrate the safety and the economic concerns to form model equations, inequalities and disjunctions. The resulting nonlinear programming model is solvable by using algorithms and solvers on any common desktop computer, thereby providing an optimal and prompt solution.     

一体式托架缓冲防护结构设计与有限元分析

目的 为解决快递末端配送中存在的回收体系不完善,快递的不安全性,快递员与消费者沟通少,快递员拒绝上门配送等问题。方法 通过层次分析法建立快递末端配送体系的模型,并通过模糊综合评价,得出消费者对于目前快递末端配送的评分。结果 环境效益的权重为0.665,表明消费者较为重视,然而经济效益的权重为0.104,表明消费者较易忽视。同时,建立了快递末端配送综合效益与指标体系的关系式,时间成本的权重最高为0.619,运输成本的权重最低为0.097,表明消费者较为注重时间成本,较易忽视运输成本。综合评价得出消费者对现有快递末端配送的评分结果为75.09分,满意度为中等。结论 提出了快递市场规范化,制定了快递回收机制,合理分配快递末端配送投入方式以及给出了一些APP或小程序的优化建议,为我国快递末端配送提供借鉴。     

Optimal design of distributed treatment systems for the effluents discharged to the rivers

This paper presents a methodology for the optimal synthesis of distributed treatment systems of effluents discharged into a main river to meet water discharge quality constraints. The methodology is based on a new superstructure that is formulated and solved as a multi-objective mixed-integer nonlinear programming model. A material flow analysis technique is used to track the pollutants through the watershed considering the combined effects of the inputs, outputs (i.e., agricultural, residential, industrial, and so on) and the chemical transformations. A disjunctive programming model is implemented for selecting the optimal location of the distributed treatment system. Prior to the optimization and based on the pollutants considered, a discretization approach is implemented to determine from simulation the removal efficiency and the unit cost of given configurations and operating conditions of the selected treatment units. Therefore, the optimization process determines the removal efficiency used to treat the effluents and the flow rate treated. Simultaneous minimization of the total annual cost of the distributed treatment system and the contaminant concentration of the discharge to the catchment of the watershed are considered as two objective functions. Three case studies (one in Mexico and two in Egypt) have been selected to illustrate the methodology. Results show that significant savings can be obtained when the distributed treatment system is implemented. Finally, the proposed methodology can be used for supporting governmental decisions (i.e., it provides the investment required for a specific water quality).     

Process integration techniques for optimizing seawater cooling systems and biocide discharge

This work addresses the problem of using seawater for cooling and the associated environmental problems caused by the usage and discharge of biocides. The discharged biocide and its byproducts are toxic to aquatic lives and must be decreased below certain discharge limits on load prior to discharge. The conventional approach has been to add biocide removal units as an end-of-pipe treatment. This work introduces an integrated approach to reducing biocide discharge though a set of coordinated strategies for in-plant modifications and biocide removal. In particular, process integration tools are used to reduce heating and cooling requirements through the synthesis of a heat-exchange network. Heat integration among process hot and cold streams is pursued economically by reconciling cost reduction in utilities versus any additional capital investment of the heat exchangers. Other strategies include maximization of the temperature range for seawater through the process and optimization of biocide dosage. This new approach has the advantage of providing cost savings while reducing the usage and discharge of biocides. A case study is used to illustrate the usefulness of this new approach and the accompanying design techniques.     

On- and offshore prepositioning and delivery mechanism for humanitarian relief operations

Traditionally, international humanitarian organisations have used on-demand dispatch of disaster relief goods from regional logistics units (RLUs) for sudden onset disaster response. This paper investigates the improvements in efficiency and resilience of disaster relief operations by combining the existing method of onshore prepositioning of relief items in RLUs with offshore prepositioning of relief items on-board vessels and at seaport terminals. The problem is formulated as a linear programming model that incorporates different logistical costs, including inventory cost, replenishment cost, and transportation cost, to find the best combination of disaster relief methods. At the tactical level, the model determines how much and where disaster relief items need to be prepositioned. At the operational level, the model addresses how much and by which mode of transport the disaster relief items need to be transported to disaster points. The model is tested on 16 major disasters in Southeast Asia. The main finding is that offshore prepositioning can contribute to cost reduction and resilience without compromising on the speed or the scale of the response. The results also suggest that the benefits depend on the duration of the disaster emergency period and the ratio of offshore storage cost to onshore storage cost.     

Condition, safety and cost profiles for deteriorating structures with emphasis on bridges

After an enormous investment in construction of highway networks undertaken in the second half of the 20th century, the highway networks of most European and North American countries are now completed or close to completion. As a result, the need in funding changed from building new highway structures to repair, rehabilitation, and replacement the existing ones. In this paper, a model for analyzing the evolution in time of probabilistic performance indicators of existing structures, in terms of condition, safety, and cost under no maintenance, preventive maintenance, and essential maintenance, is presented. This model integrates the current practice in bridge management systems based on visual inspections (condition index) with structural assessment (safety index) during the lifetime of existing structures. The proposed model allows the consideration of uncertainties in the performance deterioration process, times of application of maintenance actions, and in the effects of maintenance actions on the condition, safety, and life-cycle cost of structures by defining all parameters involved in the model as random variables. Interaction between condition and safety profiles is defined through probabilistic and deterministic relations. The probabilistic characteristics of the condition, safety, and cost profiles of deteriorating structures are computed by Monte-Carlo simulation. Several realistic examples, based on data on highway bridge components gathered in the United Kingdom, are presented.     

On the hazard rate process for imperfectly monitored multi-unit systems

The aim of this paper is to present a stochastic model to characterize the failure distribution of multi-unit systems when the current units state is imperfectly monitored. The definition of the hazard rate process existing with perfect monitoring is extended to the realistic case where the units failure time are not always detected (non-detection events). The so defined observed hazard rate process gives a better representation of the system behavior than the classical failure rate calculated without any information on the units state and than the hazard rate process based on perfect monitoring information. The quality of this representation is, however, conditioned by the monotony property of the process. This problem is mainly discussed and illustrated on a practical example (two parallel units). The results obtained motivate the use of the observed hazard rate process to characterize the stochastic behavior of the multi-unit systems and to optimize for example preventive maintenance policies.     

X-bar charts or pre-control: an economic evaluation using alternative cost models

The on-line monitoring techniques of pre-control and X-bar control charts are compared, using two cost models that differ in the treatment of process variation cost. The first cost model assumes that process variation results in increased costs only when out-of-tolerance parts are made, while the second cost model uses Taguchi's loss function to quantify the cost of process variation. An example shows that the least-cost alternative depends on the cost model used. The sensitivity of the two techniques to changes in a number of process parameters is analysed for the loss function-based model. The results indicate that the most important consideration in choosing the process monitoring procedure is the assumption regarding the cost of process variation.     

Stress test optimization using an integrated production test and field reliability model

Numerous papers and texts have been written in the reliability literature regarding the determination of the optimum test duration for a production stress or a burn‐in test. The techniques presented have largely been based on the identification of the change point at which infant mortality has largely been removed from the units. The time‐on‐test is typically the only factor that influences this decision. Few of these models have attempted to integrate the field performance or the influence of warranty costs into this decision. This paper proposes and validates a methodology that integrates the influence of the production test failures and the field performance including their respective costs into a single unified model. The objective is to identify a production test duration that minimizes the overall cost. A Weibull model is initially developed for the production test that incorporates the failure observations in different time segments of the test based on the ability to detect latent defects in the product. A separate Weibull model is then developed for the product's performance in the field that includes the lifetime of the unit. This paper identifies how both these Weibull models can be combined into a single model including both test and field costs with the objective of minimizing the overall cost. The advantage of the proposed technique is that it does not require one to track individual units from production through to the field in order to develop an integrated test and field cost model. Copyright © 2009 John Wiley & Sons, Ltd.     

Simultaneous tolerance synthesis for manufacturing and quality

Tolerance allocation affects product design, manufacturing, and quality. No existing technique has been found by the authors that takes product design, manufacturing, and quality into account simultaneously. This paper introduces a new concurrent engineering method for tolerance allocation. A nonlinear optimization model was constructed to implement the method. The model minimizes the combination of quality loss and manufacturing cost simultaneously in a single objective function by setting both process tolerances and design tolerances simultaneously. The purpose of the model is to balance manufacturing cost and quality loss to achieve near-optimal design and process tolerances simultaneously for minimum combined manufacturing cost and quality loss over the life of the product. Compared to other models, this model shows significant improvements. Electronic Publication     

Optimal degradation processes control by two-level policies

Two-level control policies are applied to various types of Markov processes describing degrading parameters of system units. To estimate the system operation cost an expectation of losses per unit time is evaluated. It is assumed that the degradation process is observable, and a monitoring system can signal about future failures. Firstly, semi-Markov processes are considered. A death process is proposed for a unit subjected to corrosion. A Markov chain are used for the problem of fatigue crack growth. The control problem is studied mainly in a steady-state regime for units of multiple use when the cost function is performed as the ratio of expectations. The cost function as the expectation of losses per unit time for single units is also studied, and the majorizing property of this cost function is shown.     

International perspectives on plant life assessment

Abstract

To satisfy the ever-increasing global demands for power, efficient generation and use of electricity should be integrated with economic, social and environmental considerations. However, it is apparent that in many parts of the world cost and continuity of fuel supplies are considered critical factors. A significant increase in the percentage of electricity generated using combined cycle gas turbines is taking place and further installation of units of this type is planned. However, this increase requires substantial investment in the infrastructure needed to handle and distribute gas and is expected to result in upward pressures on gas prices. Existing coal fired and nuclear stations will be required to operate for some time to minimise the amount of new capacity needed. Evaluation of the useful operating lives of the existing stations will be an on-going process, which will utilise technical and analytical tools developed through collaborative research and development projects. Increasingly, the financial investments required to introduce new generating technologies are beyond the resources of individual companies so international partnerships have been established to evaluate options. In view of the significant known reserves, advanced coal-generating units, which include minimum emissions, are being investigated for the long-term. It is apparent that the global challenges faced by the energy sector can only be met by worldwide collaboration with the broadest possible cross-section of public and private stakeholders.     

基于故障树映射的产品族保证成本分析

针对当前制造企业的产品通常以产品族而不是单一产品的形式存在的现实,对现有的基于单一产品的保证成本计算模型进行了改进,并指出产品族保证成本计算取决于配置产品的元件的可靠性。通过逆向搜索的方法,元件可靠性可以根据故障树模型向BOM模型映射得到。作者通过一个笔记本电脑的案例说明文中方法的操作过程,并比较了企业采用FRW和PRW两种策略时保证成本的差异。     

A noninvasive system-level model order reduction scheme for flexible multibody simulation

This paper presents a novel system-level model order reduction scheme for flexible multibody simulation, namely the system-level affine projection (SLAP). Contrary to existing system-level model order reduction approaches for multibody systems simulation, this methodology allows to obtain a constant reduced order basis which can be obtained in a noninvasive fashion with respect to the original flexible multibody model. It is shown that this scheme enables an automatic joint constraint elimination which can be obtained at low computational cost through exploitation of the component level modes typically employed in flexible multibody simulation. The equations of motion are derived such that the computational cost of the resulting SLAP model is independent of the original model size. This approach results in a set of ordinary differential equations with a constant mass matrix and nonlinear internal forces. This structure makes the resulting model suitable for a range of estimation, control, and design applications. The proposed approach is validated numerically on a flexible four-bar mechanism and shows good accuracy for a very low-order SLAP model.     

Minimum Cost Quality Control Tests

An expected cost model of a process whose mean is controlled by an X chart is developed. A two-stage numerical procedure is used to calculate the sample size, the number of units produced between samples, and the control limits of optimal control charts. Optimal plans are tabulated for three values of the a priori distribution parameter and three values of each of the three cost coefficients.     

机械压缩式湿垃圾处理装置设计

针对现有湿垃圾就近处理装置存在成本高、占地面积大以及垃圾处理后仍达不到排放标准等问题,研制了一款新型机械压缩式湿垃圾处理装置.首先,介绍了机械压缩式湿垃圾处理装置的功能和技术特点.然后,对机械压缩式湿垃圾处理装置进行模块化设计,主要包括提升装置、传送带分拣装置、破碎脱水装置、污水处理装置以及压块装置等.最后,对机械压缩...