Jon C. Yingling

Routing for a Just-in-Time Supply Pickup and Delivery System

An optimization-based approach is developed for routing a just-in-time (JIT) supply pickup and delivery system. The approach defines routes among suppliers serving a large JIT assembly plant, the timing of these routes, and the frequency that they are run (implicitly defining parts quantities picked up each visit). The solutions satisfy various operational constraints at the JIT facility, including requirements for high-frequency/small-quantity deliveries and limits on space for parts storage. The solution space we consider here is restricted by an operational discipline that the industry calls common frequency routing. Under this system we only consider routing designs where each part source is being served by a single route run at a fixed daily frequency instead of designs where multiple routes visit that supplier, each potentially run at a different frequency. This dramatically reduces dimensionality of the problem and is also known to provide both management and operational advantages in practice. In solving the formulation, column generation and tabu search strategies have been developed, the latter suitable for realistic-sized problems. The utility of the approach is illustrated through a number of examples.

A review of computer-based truck dispatching strategies for surface mining operations

ABSTRACT Computer-based truck dispatching systems are becoming a widely used means for improving equipment utilization and productivity at surface mining operations and for helping to insure that extraction operations at these mines meet additional performance requirements such as maintenance of stripping ratios and ore grade standards. This paper classifies existing truck dispatching strategies and examines their underlying mathematical formulations in detail. Strengths and weaknesses of the alternative approaches are identified and information on their expected performance in the field is summarized.

Parameter and configuration optimization of flotation circuits, part I. A review of prior work

Abstract Prior work in configuration and parameter optimization of flotation circuits is reviewed. The papers are split into two groups on the basis of problem formulation and solution strategies. Both groups employ a structural parameters approach to represent circuit configuration alternatives, which, without care, may result in solutions involving complicated circuit configurations. The group I authors have found an effective way to deal with problem nonlinearities in a direct search optimization approach, and the latter work of this group appears to have overcome earlier problems with configuration complexity. The group II authors have dealt with the nonlinearity by a two-stage optimization approach that first determines optimum configuration, then optimum component flows. However, the optimality of the resulting configurations is questionable since individual species flows and product grade have not been considered. Moreover, there are questions as to whether the separation behavior of the flotation cells can be accurately represented in their procedure.

Circuit analysis: optimizing mineral processing flowsheet layouts and steady state control specifications

Abstract Process optimization aims to extend flowsheet simulation technology with techniques for determining plant control strategies and, ideally, circuit structural layout that result in optimum performance of the circuit in economic terms. Such an endeavor is confronted with problems of model scale, nonlinearity, and the general difficulties of mixed discrete/continuous optimization. This paper shows how the structure of the flowsheet models for mineral processing circuits facilitates overcoming these difficulties in many applications. Specifically, the same structural features used in the development of circuit analysis (Meloy, 1983) are employed here with the addition that a formal probabilistic interpretation is given to the unit partition coefficients. Original optimization algorithms, extensions of the techniques of stochastic dynamic programming, are reported. These algorithms have capability to determine control settings for the unit operations that maximize the net value of the circuit yield. Moreover, they can select the best of a number of discrete circuit layout options posed by the system designer, considering fully the scope of control adjustments for all candidate vessels in the system. The algorithms are computationally efficient and are readily applied to full-scale models. Several issues relevant to application of the algorithms are discussed.

AN MILP FORMULATION FOR LOAD-SIDE DEMAND CONTROL

ABSTRACT This paper presents a mixed integer linear programming formulation for load-side control of electrical energy demand. The formulation utilizes demand prediction to determine if control actions are necessary, and it schedules both shedding and restoration times based on an optimization model that minimizes the net cost of load shedding. Operational constraints are satisfied through the use of minimum/maximum uptimes/downtimes, which depend upon the current state of the system. The algorithm is evaluated using a simulation model of an underground coal mining operation where, (i) its performance is compared with a traditional static, priority-based, load-shedding schedule, and, (ii) its potential is established for producing net savings through demand control.

Parameter and configuration optimization of flotation circuits, part II. A new approach

Abstract This paper extends the flowsheet optimization algorithm given by Yingling (Int. J. Miner. Process., 29: 149–174) for application to parameter and configuration optimization of froth flotation circuits. The procedure uses individual cell models and optimizes bank interconnection configuration, number of cells per bank, and cell design and control parameters. The designer has flexibility in whether to consider split stream interconnections among the banks or whether to restrict the design to single stream interconnections. Experience with the procedure suggests that if the designer formulates an initial network superstructure that provides for adequate residence time in the various banks of the circuit, solutions involving split stream interconnections will seldom be optimum.

On-line control strategies to minimize peak loads on mine conveyor networks using surge units with variable discharging capability

Earlier work has shown how differences in material transit times from surge units to transfer points in a mine conveyor network enable precise forecasts of load levels that will be intersected by the discharge of a controlled surge unit over future time intervals. Using these forecasts, control policies can be determined that specify the units discharge rates over a planning horizon in a manner that prevents peaks in the combined flow at the transfer point from exceeding belt capacity limits while simultaneously insuring adequate unit through-flow to prevent it from becoming a production bottleneck. This paper first extends this control approach to the case where the differences in transit times between surge units are small. It is shown that multiple units should be considered simultaneously when determining control actions, and a dynamic programming approach is given for determining the optimal control policy in such a situation. Subsequently the application of this approach is considered for longwall mines where flow from the longwall is not controlled but the discharge rates of continuous miner section feeders are adjusted in real time to prevent belt overloading while minimizing any production constraint from the continuous miner units. This application requires special treatment for the highly variable material flow pattern produced by longwalls. The practical utility of these approaches is evaluated through detailed simulation studies.<<ETX>>

A NEW FRAMEWORK FOR SIMULATION OF MATERIAL FLOWS ON MINE CONVEYOR NETWORKS

A number of state variables important to bulk material conveyor simulation models vary continuously with time, e.g. the position of material along the beltline or the level of material in a feeder, bunker, or discharging/receiving vehicle. Ostensibly, the generation of time histories of these state variables requires continuous simulation, and most belt simulation packages execute what is essentially a continuous simulation using various discretization approaches. However, since it is reasonable to assume that the derivatives of these continuous variables change at discrete points in time, one alternatively can model the system using a higher-order discrete approach. Such an approach is developed in this paper. Advantages offered by the new framework include (1) improved accuracy, (2) faster execution, (3) the ability to realistically interface with models of production or loadout operations, and (4) the ability to study the performance of a wide array of real-time control systems. The framework has been implemented using the event-scheduling interface to the SIMAN simulation language, but it could readily be employed with other discrete-event simulation languages. The framework is demonstrated in examples involving an integrated track/belt haulage system and a system for reduction of peak loads on gathering belts that involves real-time control of feeder discharge rates.

Algorithms to control coal segregation under non-stationary conditions: Part II: Time series based methods

Abstract In this paper, procedures involving the use of time series models are developed for coal segregation control. In contrast to the methods of Part I of this paper, time series models directly accommodate the auto-correlated nature of the coal quality levels when estimating parameters to characterize the process. Moreover, they also provide forecasting capability that is useful in segregation control. Special attention is given in the paper to development of viable parameter updating strategies in order to deal with non-stationary applications. Performance of the time series methods is evaluated, and it compares favorably to the methods developed in Part I. Although more complicated to implement than the Part I methods, time series methods have the potential to be extended to applications where quality targets are to be maintained over small batches of coal (homogeneity control), whereas the other methods only apply to large batch quality targeting.

Analysis of the twisting department at Superior Cable Corporation: A case study

Abstract The production of communication cables involves four major serial operations, namely tandem, twisting, stranding, and jacketing. Superior Cable Corporation manufactures such communications cables at the Elizabethtown, Kentucky, plant. The bottleneck operation in this facility is the twisting department. In this paper, we used simulation to analyze the operations in the twisting department and provide several recommendations to improve the production capacity of this department. Several of our recommendations are successfully implemented.