模糊解耦控制器设计及应用

针对串联解耦控制鲁棒性较差的问题,提出了模糊解耦控制方案,并将此方法应用于青霉素结晶过程的控制中,仿真结果表明该方案简单、易行,鲁棒性得到了提高。     

Dynamische Berechnung der Stromgestehungskosten von Energiespeichern für die Energiesystemmodellierung und -einsatzplanung

Due to the transition in energy supply from fossil to renewable energy sources, energy storage systems are getting more and more important for the security of power supply. Therefore also the modeling of those storage systems in energy system modeling needs to be further discussed. This paper focuses on the levelized costs of energy storage. In the beginning, the existing approaches of calculating those costs are analyzed in a literature review. It will be shown that all of the approaches calculate the levelized costs on the basis of the energy storages’ lifetime. For the usage in energy system modeling it is mandatory that the calculation can be done for variable and shorter time periods. Therefore this work’s approach calculates the costs based on the time of operation in any period chosen. Additionally, the model can be used for any type of storage system. After introducing the mathematical model, the levelized costs of energy storage will be calculated to illustrate the models properties and then verified with reference load profiles for five different energy storage types. Following this, particular input parameters are varied and sensitivities are pointed out. Most of the programs for power plant dispatch calculations use linear or mixed integer linear programing algorithms. As the calculation of levelized costs of electricity is non-linear, most programs use fixed values during the whole time of simulation. In this article the integration of the presented approach into a linear optimization program via recursive and shifted calculation is elaborated. Results are presented and discussed.     

Excess Returns, Inflation and the Efficiency of the Housing Market

This paper examines the influence that unexpected inflation has on the reported time pattern in housing returns. Two alternative models of expected inflation are used to study its effect: a rational expectations model and an adaptive expectations model. Findings indicate that both estimates of unexpected inflation are positively correlated with excess returns to housing. If inflation expectations are assumed to have been adaptive during the 1970s and early 1980s, serial correlation in the excess returns is shown to be greatly diminished when adjusted to control for unexpected inflation. However, substantial inertia in the pattern of the adjusted return series remains.     

Depth and breadth of external knowledge search and performance: The mediating role of absorptive capacity

Nowadays it is commonly accepted that exploiting external knowledge sources is important for firms' innovation and performance. However, it is still not clear how this effect takes place and what internal capabilities are involved in the process. We propose to open the black box between external knowledge search strategies, and innovation and performance by proposing absorptive capacity (AC) as the mediating variable. A sample of 102 biotechnology firms from Spain is used to test the proposed theoretical model through structural equation modeling taking the partial least squares approach. Results suggest that AC acts as a full mediator in the relationship between the depth of external knowledge search and the innovation and business performance of the firm. Finally, some suggestions for managers and future lines of research are highlighted.     

Evaluating shop floor input control using rapid modeling

A simple, spreadsheet-based rapid modeling approach to analysis of input control is developed. This approach uses relationships which allow decomposition of a job shop queuing network. Order release is based on a minimum release time interval, dictated by the bottleneck machine utilization. The objectives are to develop insights into how input control affects work flow and how rapid models can help in achieving this. The rapid model performs well and the order release mechanism is shown to be robust. Economic analysis based on throughput, inventory and lead time tradeoffs is provided. The value of input control is shown to be dependent on the cost structure. The impact on profitability is small, however, relative to the impact of operating at the optimal utilization level.     

Order release planning with clearing functions: A queueing-theoretical analysis of the clearing function concept

We consider the problem of planning future order releases in hierarchical production planning and control systems. An established research direction is the clearing function concept: the planned material flow through a production unit is modelled by inventory balance equations for WIP and final products, and the consequences of the stochastic properties of the material flow are modelled by clearing functions, which is the functional relationship between the level of WIP and the maximum output of a work centre in a period.Using a transient M/M/1 model, our paper shows that the usual definition of a nonlinear clearing function suffers from substantial shortcomings concerning both the definition of the function and empirical estimation of its parameters. We propose an alternative transient clearing function and derive a procedure for its parameterization.     

A robustness study of a multi-echelon inventory model via simulation

This paper examines the robustness of a standard model of multi-echelon inventory systems, specifically the models discussed in Axsäter (Oper. Res. 48(5) (2000) 686). A simulation model was developed to explore the model's ability to predict system performance for a two-echelon one-warehouse, multiple retailer system using (R,Q) inventory policies under conditions that violate the model's fundamental modeling assumptions. In particular, the impact of non-stationary demand on this stationary demand inventory model was examined. The model performs well at the low demand and large retailer order batch size situations, but our testing of the model indicated that care must be taken when applying this model to situations that violate its fundamental assumption. These results should help practitioners to better understand the assumptions of these models and to determine when or when not to apply these models in practice.     

基于系统动力学与DEA的企业技术创新项目效率评价方法研究

本文综合考虑项目层和企业组织层影响因素,提出企业技术创新项目效率综合评价方法。首先分析组织层与项目层的影响因素;然后,构建涵盖项目层和组织层影响因素的两层次系统动力学仿真模型,为所建立的数据包络分析模型提供仿真值,有效解决数据包络分析模型中定性变量的量化;最后,以国内纺织业某大型集团公司多项技改项目为例,验证建模思路与方法的正确性。研究成果对于企业技术创新项目的有效管理具有指导意义。     

Derivation of confidence intervals of service measures in a base-stock inventory control system with low-frequent demand

We explore a base-stock system with backlogging where the demand process is a compound renewal process and the compound element is a delayed geometric distribution. For this setting it holds that the long-run average service measures order fill rate (OFR) and volume fill rate (VFR) are equal in values. However, though equal ex ante one will ex post observe differences as actual sample paths are different. By including a low-frequency assumption in the model, we are able to derive mathematical expressions of the confidence intervals one will get if OFR and VFR are estimated in a simulation using the regenerative method. Through numerical examples we show that of the two service measures it is OFR that in general can be estimated most accurately. However, simulation results show that the opposite conclusion holds if we instead consider finite-horizon service measures, namely per-cycle variants of OFR and VFR.     

A hybrid simulation optimization method for production planning of dedicated remanufacturing

This paper presents a hybrid cell evaluated genetic algorithm (CEGA) for optimization of the dedicated remanufacturing system with simulation. The paper first summarizes the special characteristics and problems of the dedicated remanufacturing. The paper then proposes a simulation model with a prioritized stochastic batch arrival mechanism, considering factors that affect the total profit. Based on the simulation model, the CEGA algorithm is developed to optimize the production planning and control policies for dedicated remanufacturing. A case study is provided based on the remanufacturing facility located at Austin, USA     

基于CFX的典型差压式流量计流场数值模拟研究

基于CFX商业软件,对典型差压式流量计的内部流场进行数值模拟研究。详细研究了关于孔板流量计及V锥流量计的流出系数影响因素,得到了不同模拟工况下的内部流场变化规律。将数值模拟与经验公式计算值进行对比验证,两者吻合度高,误差基本控制在5%以内。借助CFX数值模拟进行孔板、V锥流量计的压降及耗能定量分析,结果表明V锥流量计具有明显的节能效果,同时探讨了孔板流量计的沉积、冲蚀问题。研究表明数值模拟可作为一种差压式流量计设计及标定的辅助方法。     

醋酸丁酯合成工艺设计及控制

为了对醋酸丁酯的合成工艺过程进行优化控制,在Aspen Plus稳态模拟的基础上,利用Aspen Dynamics软件对醋酸丁酯的合成进行动态模拟,建立了醋酸丁酯合成工艺流程模型。在Aspen Dynamics软件中设定不同的控制结构,并引入进料流量干扰,通过改变醋酸丁酯的纯度和灵敏板的温度来检验不同控制结构的性能。结果表明,通过CS4控制,可以很好地解决产品纯度的波动问题。     

Customer retention: A source of value for serial acquirers

Customer retention, in most cases, is regarded as an indicator of acquisition performance, but factors influencing it have rarely been studied in the serial acquirer context. As a consequence, this paper presents a model of the linkage between serial acquirers and customer retention by drawing on serial acquirer and customer relationship marketing and management literature. The paper proposes that the serial acquirers' focus on retaining acquired firms' business customers per acquisition deals may enhance the post-acquisition value. Furthermore, serial acquirers' acquisition experience (skills), managerial overconfidence/hubris, own customers' behaviour and technological context are identified to impact the customer retention of the acquired firm. Moreover, two dual-purpose variables—acquired firms' customer experience and acquired firms' customer relationships—are proposed to moderate the effects of serial acquirers' acquisition experience (skills), managerial overconfidence/hubris, own customers' behaviour and technological context on acquired firm customer retention and also to autonomously influence acquired firms' customer retention. The implications for serial acquirers and practice are discussed.     

基于Solidworks & SimMechanics的机构运动分析与仿真

介绍了几种常用机构运动分析的方法及特点,重点阐述了以Solidworks和SimMechanics 为工具,通过机构的实体造型、建立机构模型、设置各模块参数及仿真参数等环节,对摆动导杆机构和曲柄摇块机构在给定驱动力下的运动性能进行分析与仿真,绘制了机构关键点的运动特性曲线,得到了机构运动的仿真动画。指出这种机构运动分析...     

基于Matlab的离网光伏单相全桥 逆变器控制策略

为了解决离网光伏发电系统为负载供电时逆变器输出电压存在谐波畸变率高的问题,提出一种改进的逆变器控制策略。首先,根据离网光伏发电系统的结构建立了单相全桥逆变器的数学模型;其次,基于数学模型分析,在接线性负载和投切线性负载时对逆变器采用电压电流双闭环控制策略,而在接非线性负载时引入输出电流反馈量,提出了由电感电流内环、输出电压外环、输出电流负反馈组成的逆变器多环稳压控制策略;最后,基于Matlab进行仿真,通过河北科技大学直流微电网系统进行试验验证,并将试验结果与仿真结果进行了对比分析。结果表明,上述3种工况下的逆变器电压谐波畸变率分别为1.8%,2.7%和2.3%,均满足小于5%的要求。研究结果对于改善逆变器的性能,提高离网光伏发电效率,以及发展新能源发电具有参考价值。     

Approximation approach for the performance analysis of production lines under a kanban discipline

In a JIT production environment, pull-type control systems are usually implemented to reduce the lead time and to synchronize the production rate with the demand rate. The design of an effective production control system requires easy and reliable approaches for evaluating the effect of the major system parameters on its performance.In this paper we model the kanban control system of a manufacturing line as a Markov process. In addition, we develop an approximation approach to the model that permits reliable evaluation of manufacturing system performance in terms of throughput time and work-in-process. The validation of the approach is implemented by comparing the exact results (based on discrete event simulation) and the approximated results.A good approximation is observed for a large range of conditions.     

基于AMESim的防抱死制动系统控制研究

为了提高ABS制动模型的准确性,提出液压数值模拟的方法,并结合Simulink软件环境,建立车辆单车轮ABS动力学模型。采用PID控制和有限状态机相结合的控制方法,实现对ABS液压系统的制动控制。应用AMESim与Simulink对系统进行联合仿真,分析不同动力黏度的液压油对ABS的影响。结果表明,所采用的控制策略能使车轮滑移率稳定在最佳滑移率0.2附近,实现了对ABS的有效控制;随着液压油动力黏度由0.725 Pa·s增加到1.425 Pa·s,制动距离由24.28 m增加到25.51 m,说明油液黏度增加会使制动距离加长。因此,所建立的车辆单车轮ABS动力学模型比线性化制动模型更能体现参数的特性变化,研究方法可应用于ABS液压系统设计中的参数选择与匹配。     

Eliminating drift in inventory and order based production control systems

An Inventory and Order Based Production Control System lies at the heart of many commercial and bespoke ordering systems based on periodic review of stock and production targets. This simple and elegant control system works well, even when dealing with scenarios in which there are many competing value streams. However, such “interferences” inevitably cause some uncertainty in pipeline delivery times. We show via linear z-transform analysis that the consequences may include the possibility of inventory drift and instability. In this paper we establish the stability boundaries for such systems, and demonstrate an innovative method of eliminating inventory drift due to lead-time effect. This new principle is confirmed by simulation results.