Short-term hydrothermal optimisation with congestion and quality of service constraints

In short-term hydrothermal coordination (STHC), the transmission network is typically modelled through a DC power flow. However, this modelling can lead to inoperable solutions when verifying with AC power flow. A methodology that includes an AC power flow model to overcome the problem applied to STHC is presented. The approach takes into account issues such as congestion management and control of quality of service, which are often present in large and weakly meshed networks - the typical pattern of Latin American electrical power systems. Generalised Benders- decomposition together with more traditional and well-known optimisation techniques, is used for this problem. The master problem stage defines the generation levels by considering the inter-temporal constraints, whereas the sub-problem stage determines both the active and reactive economical dispatches for each step of the load curve. It meets the electrical constraints (nodal balance, transmission limits and voltage levels) through a modified AC optimal power flow. The methodology was proved over a nine-busbar hydrothermal system and the solution found was validated with a quasi-exhaustive enumeration procedure to prove the optimality of the solution. Also proved over large system was the feasibility to realistic systems.     

A multiperiod stochastic production planning and sourcing problem with service level constraints

We study a stochastic multiperiod production planning and sourcing problem of a manufacturer with a number of plants and/or subcontractors. Each source, i.e. each plant and subcontractor, has a different production cost, capacity, and lead time. The manufacturer has to meet the demand for different products according to the service level requirements set by its customers. The demand for each product in each period is random. We present a methodology that a manufacturer can utilize to make its production and sourcing decisions, i.e., to decide how much to produce, when to produce, where to produce, how much inventory to carry, etc. This methodology is based on a mathematical programming approach. The randomness in demand and related probabilistic service level constraints are integrated in a deterministic mathematical program by adding a number of additional linear constraints. Using a rolling horizon approach that solves the deterministic equivalent problem based on the available data at each time period yields an approximate solution to the original dynamic problem. We show that this approach yields the same result as the base stock policy for a single plant with stationary demand. For a system with dual sources, we show that the results obtained from solving the deterministic equivalent model on a rolling horizon gives similar results to a threshold subcontracting policy. Correspondence to: Fikri KaraesmenThe authors are grateful to Yves Dallery for his ideas, comments and suggestions on the earlier versions of this paper.     

Pre-positioning inventory and service outsourcing of relief material supply chain

Service outsourcing is very common in a commercial supply chain, and in humanitarian relief area, the transportation service is usually outsourced. To practice relief supply more effectively, it seems essential to enlarge outsourcing from shipping to more areas, and private enterprises could play a vital role. This paper examines the optimal pre-disaster order quantity of a certain relief commodity, based on a two-stage coordinated approach. Our findings show that the delay cost, shortage penalty cost, risk of supply shortage, salvage value, expected perishable rate, unit inventory cost and reactive price have significant impacts on the optimal amount of propositioned inventory. Moreover, the outsourcing strategies differ by types of relief commodities. For perishable supplies, proactive or reactive outsourcing would improve the benefits of buyer and supplier simultaneously. As for imperishable supplies, it is better to combine proactive insourcing approach and reactive outsourcing strategy. In view of some supplies whose monitoring cost is high, the insourcing approach is much better than the outsourcing approach.     

A cost minimisation model for joint production and maintenance planning under quality constraints

In this paper, integrated planning of production, imperfect maintenance and process inspections in a multi-machine system is investigated. This system consists of parallel machines which deteriorate with time and they may shift from a primarily in-control state to a degraded state with a higher defective rate or to a failed state. Maintenance scheduling corresponds to a discrete time age-based imperfect maintenance with a large number of maintenance alternatives. Process inspections are considered to detect the current state of the system. Detecting a deteriorated condition initiates the quality check of the related sub-lots, rework of defective items and a process adjustment that brings the machine in its normal conditions. Production planning includes a capacitated lot-sizing problem with multiple products. We propose a joint approach that coordinates the decisions of the three functions, where the objective function minimises the total cost. Evaluation of costs and interacting factors is presented and two heuristic methods are proposed to solve the problem. The results of the joint model are compared to a non-integrated method and a sensitivity analysis is conducted.     

Measurement planning for quality assurance with allowance for systematic error

We present a procedure for choosing optimal measurement plans for quality assurance with allowance for systematic error in the measurements. Translated from Izmeritel'naya Tekhnika, No. 8, pp. 3–9, August, 1998.     

Trajectory planning for multiple unmanned vehicles under reciprocal constraints

In this article, a special class of trajectory optimization problems is formalized and solved. It involves the optimization of different unmanned vehicle (UMV) trajectories that are coupled through reciprocal constraints. It is shown in the article that searching for a solution to the problem at hand may stipulate not just planning a longer than the shortest possible path for each UMV, but also choosing slower travel speeds in order to co-ordinate between the UMVs. Although it seems that solving the problem possesses merits, it has been only partially treated before. Here it is solved by utilizing an evolutionary approach which involves a new algorithmic feature that allows striving towards the desired optimality. The approach is demonstrated and studied through solving and simulating several trajectory planning problems. It is shown that a wide range of problems might be related to that class of problems.     

Capacity planning of serial and batch machines with capability constraints for wafer fabrication plants

Capacity planning is crucial to the investment and performance of wafer fabs. This research proposes a practical procedure to calculate the required number of machines with serial and batch processing characteristics, respectively. Several formulae are first presented. Five heuristic algorithms are then proposed to determine the lower bound, the upper bound, and the near-optimal of the number of machines of the type with capability constraint. Data from real foundry fabs are used in a case study to determine the required number of 64 types of equipment and to evaluate the performance of the proposed procedure. The algorithm using the best ratio of production efficiency and equipment cost to select the machine type with capability constraint results in the least required number of machines, the highest machine utilisation, and the lowest equipment investment. An AutoSched AP simulation model is used to evaluate if a wafer fab using the calculated number of machines of each type can result in a preset monthly output rate. Simulation results indicate that the proposed procedure can quickly and accurately calculate the required number of machines leading to the required monthly production target. Fab managers can use this tool to conduct what-if analysis for equipment investment alternatives.     

Benefits of considering inventory in service parts logistics network design problems with time-based service constraints

We study the integrated logistics network design and inventory stocking problem as characterized by the interdependency of the design and stocking decisions in service parts logistics. These two sets of decisions are usually considered sequentially in practice, and the associated problems are tackled separately in the research literature. The overall problem is typically further complicated due to time-based service constraints that provide lower limits on the percentage of demand satisfied within specified time windows. We introduce an optimization model that explicitly captures the interdependency between network design (location of facilities, and allocation of demands to facilities) and inventory stocking decisions (stock levels and their corresponding stochastic fill rates), and present computational results from our extensive experiments that investigate the effects of several factors including demand levels, time-based service levels and costs. We show that the integrated approach can provide significant cost savings over the decoupled approach (solving the network design first and inventory stocking next), shifting the whole efficient frontier curve between cost and service level to superior regions. We also show that the decoupled and integrated approaches may generate totally different solutions, even in the number of located facilities and in their locations, magnifying the importance of considering inventory as part of the network design models.     

Production control policy for tandem workstations with constant service times and queue time constraints

Queue time constraints are commonly imposed to ensure product quality in contemporary production systems. We study the performance of two single stations with deterministic service times and a predetermined time window in between, where both stations suffer time-based pre-emptive breakdowns. To improve productivity, achieving higher capacity and lower rework rate are the two main objectives. While higher capacity requires a higher work-in-process (WIP)-level threshold, a lower rework rate requires a smaller one. To quantify the trade-off between the two objectives, an analytical model is derived. The model is then used to derive the WIP-level threshold control policy for a time-constrained system. We also show that system capacity diminishes with the decrease in WIP-level thresholds.     

Models and algorithms for solving combined vehicle and crew scheduling problems with rest constraints : an application to road feeder service planning in air cargo transportation

We present a mathematical model and two algorithms for solving a complex combined vehicle and crew scheduling problem. The problem arises in the area of road feeder service (RFS) for air cargo transportation where cargo airlines engage specifically equipped RFS-carriers to serve so-called lines, i.e. regular weekly patterns of trips starting and ending at the central hub, respectively. The complexity of the problem stems from the time windows, the rest regulations for drivers and the highly heterogenous requirements with respect to the fleet. The model can be applied to different planning scenarios at the RFS-carrier as well as the airline. The model and method has been incorporated into a decision support system called block.buster where sequences of single trips are combined to feasible blocks starting and ending at the hub and then combined to feasible vehicle round trips.     

Rolling horizon,multi-product production planning with chance constraints and forecast evolution for wafer fabs

In this paper, we study production planning models for semiconductor wafer fabrication facilities (wafer fabs) that consider both safety stocks at the finished goods inventory level and workload-dependent lead times. The evolution of demand forecasts over time follows the multiplicative Martingale Model of Forecast Evolution (MMFE) for multiple products and is incorporated into the planning models via shortfall-based chance constraints, permitting the simultaneous determination of production quantities and safety stocks. We study two variants of this formulation, one that considers forecast updates and one that does not. A planning model with workload-dependent lead times that does not consider safety stocks is used for comparison. The performance of the planning models is assessed in a rolling horizon environment using a simulation model of a scaled-down wafer fab. We find that the chance-constrained model with forecast updates outperforms the one without forecast updates with respect to expected service level and profit. Both chance-constrained models outperform the model without safety stocks. These results indicate that considering forecast evolution in production planning models can lead to improved performance by exploiting the advance demand information provided by the forecast updates.     

Component commonality in a multiple-period inventory model with service level constraints

It has been clearly demonstrated in the literature that introducing a common component that replaces a number of unique components reduces the level of safety stock required to meet service level requirements. It is not clear, however, that overall costs are reduced when the common component is more expensive than the components it would replace. Most recent work has used single-period models to investigate the cost savings (or losses) from commonality. This paper will develop a simple multiple-period model with service level constraints to compare the effect of commonality in the single-period and multiple-period case. Interestingly, the results are drastically different for these two cases. When the common component is more expensive than the components it replaces, commonality is often still beneficial in the single-period model, but almost never in the multiple-period model.     

An approach for deriving emergency planning zones for chemical munitions emergencies

The selection of an emergency planning zone (EPZ) for hazardous materials is often a difficult technical as well as a political task. This paper descri     

Multimaterial topology design for optimal elastic and thermal response with material-specific temperature constraints

We present an original method for multimaterial topology optimization with elastic and thermal response considerations. The material distribution is represented parametrically using a formulation in which finite element–style shape functions are used to determine the local material properties within each finite element. We optimize a multifunctional structure that is designed for a combination of structural stiffness and thermal insulation. We conduct parallel uncoupled finite element analyses to simulate the elastic and thermal response of the structure by solving the two-dimensional Poisson problem. We explore multiple optimization problem formulations, including structural design for minimum compliance subject to local temperature constraints so that the optimized design serves as both a support structure and a thermal insulator. We also derive and implement an original multimaterial aggregation function that allows the designer to simultaneously enforce separate maximum temperature thresholds based upon the melting point of the various design materials. The nonlinear programming problem is solved using gradient-based optimization with adjoint sensitivity analysis. We present results for a series of two-dimensional example problems. The results demonstrate that the proposed algorithm consistently converges to feasible multimaterial designs with the desired elastic and thermal performance.     

Quality decision of the logistics service supply chain with service quality guarantee

In the logistics service supply chain (LSSC), quality supervision and coordination is an important approach that can ensure the effective operation of LSSC and obtain more customers. This paper aims to study the quality decisions of the functional logistics service provider (FLSP) and the logistics service integrator (LSI) when a service quality defect guarantee is promised by the FLSP. Assuming that customer demand is a function of the quality defect guarantee of the FLSP, the optimal quality decisions of the LSI and FLSP are presented under three typical game modes: Nash game, Stackelberg game, and centralised decision. Numerical analysis is conducted to show how the quality parameters of the customer affect the optimal quality decision-making behaviour of the LSI and FLSP. The research results indicate that, under all three game modes, the optimal quality defect guarantee of the FLSP increases as the customer punishment increases, and decreases as the elasticity of the customer demand for the quality defect guarantee increases. In addition, under all three game modes, the optimal quality supervision effort of the LSI is an increasing function of both customer punishment and elasticity of the customer demand for the quality defect guarantee.     

Multi-product selective newsvendor problem with service level constraints and market selection flexibility

We consider a multi-product multi-market newsvendor problem where the decision-maker could select some markets to serve. The considered problem involves the integration of procurement and market selection decisions. The products are procured from an external supplier. We assume that the realised demand for each product should be satisfied. In the case of shortages, the firm procures items at a higher cost. The paper considers the case where the selling prices, market entry costs, and product demand distributions are market dependent. Specifically, we discuss three cases of the Multi-Product Selective Newsvendor Problem: flexible market entry case, full market entry case and partial market entry case. The mathematical models of the above cases result in binary nonlinear programmes. We develop solution algorithms for solving the resulting combinatorial problems. Some managerial insights are provided.     

Two-echelon multi-item spare parts systems with emergency supply flexibility and waiting time constraints

We consider a two-echelon multi-item spare parts inventory system in which supply flexibility through both lateral transshipments and direct deliveries are used in response to stock-outs. We develop a simple heuristic to determine the stocking levels for each type of spare part at the central warehouse and local warehouses minimizing the expected total system cost subject to a target level for the average waiting time across items at each local warehouse. Numerical comparisons between the heuristic's objective function values and lower bounds obtained by applying Lagrangian relaxation techniques show that the heuristic performs well. A study to evaluate the relative merits of a two-echelon system as opposed to a single-echelon system is also presented. We find that the presence of lateral transhipment improves the performance of the single-echelon system considerably. A two-echelon system is only worth implementing when lateral transhipments are not possible.     

An Improved formula for inventory decisions under service and safety stock constraints

This paper solves the reorder point inventory model under two constraints: safety stock is nonnegative, and the fraction of backorders does not exceed a given limit. The solution procedure modifies a noniterative approach due to Simpson in order to achieve better accuracy and wider applicability of the results. A formula for the implied cost of a fixed service level is also developed.     

Integrated planning of spare parts and service engineers with partial backlogging

OR Spectrum - In this paper, we consider the integrated planning of resources in a service maintenance logistics system in which spare parts supply and service engineers deployment are considered...