The literature on the two-machine flowshop scheduling problem reveals that the problem has been addressed with bicriteria of either makespan and mean flowtime or makespan and maximum tardiness (lateness). This paper extends the problem to all the three criteria (tricriteria) where the objective is to minimize a weighted sum of makespan, mean flowtime, and maximum lateness. A dominance relation and a lower bound are established. The dominance relation and the lower bound are used to develop a branch-and-bound algorithm. The dominance relation is also used to develop several heuristics. An extensive computational analysis is conducted to evaluate the performance of the dominance relation and the heuristics. The analysis shows that the dominance relation is effective. The analysis also shows that the heuristics are quite efficient, and some heuristics have an error of less than 1%. Moreover, these heuristics have the desirable property that the error does not increase by the number of jobs. 相似文献
Apart from in-plant water recovery, inter-plant water integration (IPWI) offers another promising mean for the reduction of fresh water and wastewater flowrates for process plants. This paper extends the automated targeting technique that was developed for single water network into IPWI. This optimisation-based technique is based on the concept of pinch analysis, which enables the setting of various network targets prior to detailed design. The automated targeting technique is formulated as a linear programming model for which global optimum is guaranteed. The proposed technique is demonstrated using several industrial and literature examples. 相似文献
Many biological and thermochemical processing options exist for the conversion of biomass to fuels.
Commercially, these options are assessed in terms of fuel product yield and quality. However, attention must also be paid to the environmental aspects of each technology so that any commercial plant can meet the increasingly stringent environmental legislation in the world today.
The environmental aspects of biological conversion (biogasification and bioliquefaction) and thermal conversion (high pressure liquefaction, flash pyrolysis, and gasification) are reviewed. Biological conversion processes are likely to generate waste streams which are more treatable than those from thermal conversion processes but the available data for thermal liquefaction are very limited. Close attention to waste minimisation is recommended and processing options that greatly reduce or eliminate waste streams have been identified. Product upgrading and it's effect on wastewater quality also requires attention. Emphasis in further research studies needs to be placed on providing authentic waste streams for environmental assessment. 相似文献
This paper presents a simulation based analysis of a service robot operating in a robot-centered FMC, in which the robot is located at the approximate center of the cell and the machines are arranged in a partial circle around it. The robot's function is to locate and service the parts which require a series of unloading, moving, and loading operations. The main purpose of the study is to determine the best movement decision for the robot when it becomes to be free in the robot-centered FMC where multiple products with different but similar operation sequences are processed. The results from the study, based on both statistical and nonstatistical analyses, suggest the best policy for the robot movement that holds promise for application to the robot-centered FMC. 相似文献
The paper deals with the problem of minimizing the expected makespan in a two-machine flow shop with blocking and random job
processing times. It is well known that it reduces to an instance of the traveling salesman problem (TSP). Assuming that the
job processing times can be stochastically ordered on both machines, we show that the problem under study is equivalent to
TSP on a permuted Monge matrix. This allows us to prove that it is NP-hard for the independently and exponentially distributed
job processing times, and identify a new class of efficiently solvable special cases. 相似文献
Modular reconfigurable machines offer the possibility to efficiently produce a family of different parts. This paper formalises a cost optimisation problem for flow lines equipped with reconfigurable machines which carry turrets, machining modules and single spindles. The proposed models take into account constraints related to: (i) design of machining modules, turrets, and machines, (ii) part locations, and (iii) precedence relations among operations. The goal is to minimise equipment cost while reaching a given output and satisfying all the constraints. A mixed integer programming model is developed for the considered optimisation problem. The approach is validated through an industrial case study and extensive numerical experiments. 相似文献
This paper describes a torque ripple reduction technique with constant switching frequency for direct torque control (DTC) of an induction motor (IM). This method enables a minimum torque ripple control. In order to obtain a constant switching frequency and hence a torque ripple reduction, we propose a control technique for IM. It consists of controlling directly the electromagnetic torque by using a modulated hysteresis controller. The design methodology is based on space vector modulation (SVM) of electrical machines with digital vector control. MATLAB simulations supported with experimental study are used. The simulation and experimental results of this proposed algorithm show an adequate dynamic to IM; however, the research can be extended to include synchronous motors as well. The implementation of the proposed algorithm is described. It doesn’t require any PI controller in the torque control loop. The hardware inverter is controlled digitally using a Texas Instruments TMS320F240 digital signal processor (DSP) with composed C codes for generating the required references. The results obtained from simulation and experiments confirmed the feasibility of the proposed strategy compared to the conventional one. 相似文献