Discrete-continuous Simulation Research Articles

Efficient computation of safe, fast charging protocols for multiphase lithium-ion batteries: A lithium iron phosphate case study

Fast charging is a desirable feature for lithium-ion batteries. Charging at high currents, however, can damage the battery and accelerate aging processes. Fast charging protocols are typically computed by solving an optimization in which the cost function and constraints encode the conflicting requirements of safety and speed. A key element of the optimization is the choice of the dynamic model of the battery, with an inherent tradeoff between model accuracy and computational complexity. An oversimplified model may result in unreliable protocols, whereas a complex model may result in an optimization that is too computationally expensive to be suitable for real-time applications. This article describes an approach for embedding a complex battery model into charging optimization while having low computational cost. Multiphase Porous Electrode Theory is used to provide an accurate description of batteries characterized by multiphase materials, and the optimization is solved by transformation into mixed discrete-continuous simulation of a set of Differential–Algebraic Equations. The methodology is applied to an MPET model of commercially available Lithium Iron Phosphate batteries. Protocols based on a variety of operational constraints are computed to assess both the effectiveness of the approach, and the advantages and disadvantages of the charging protocols.

Long-Term Impact Evaluation of Advanced Under Frequency Load Shedding Schemes on Distribution Systems With DG Islanded Operation

This paper presents a long-term impact evaluation algorithm to assess advanced under frequency load shedding (UFLS) schemes on distribution systems with intentional islanding of distributed generation (DG). The algorithm is based on a combined discrete-continuous simulation model which is utilized to verify the effect of the schemes on reliability indices such as the system average interruption frequency index, system average interruption duration index, and energy not supplied. Moreover, a polynomial neural network-based approach to advanced load shedding is implemented to support DG islanding in order to illustrate the applicability of the evaluation. Simulation results highlight the long-term effect of employing UFLS to support intentional islanding of DG using an actual network from the South of Brazil.

Simulation of Discrete-Continuous Process via E-Network

This paper denotes approaches to discrete-continuous process simulation via E-network. It covers principals of discrete-continuous process simulation via E-networks using the scheme of the interaction of static and dynamic components modeling. The construction of discrete-continuous process dynamic models is based on the state space method and is implemented by using E-network.

A hybrid simulation approach for quantitatively analyzing the impact of facility size on construction projects

Abstract Sizing temporary facilities is a crucial task in construction site layout planning due to its significant impact on project productivity and cost. This paper describes a simulation-based approach for modeling the size of facilities that temporarily contain materials in construction projects. Different methods have been introduced for estimating the required size of this kind of facility; however, space limitations, particularly on congested sites, may not allow the planner to allocate the estimated space to the facilities. This study aims at quantitatively analyzing the impact of facility size on the project and modeling the managerial corrective actions to remedy the space shortage in facilities. To this end, a hybrid discrete-continuous simulation technique is adopted. Simulation is superior in modeling dynamic interactions between variables as well as modeling construction processes with inherent uncertainties. The combination of discrete and continuous simulation is used to enhance accuracy and model the project at both operational level (i.e., activity level with higher level of detail) to estimate production rate, and strategic level (i.e., macro level with lower level of detail) to account for some construction planning decisions such as material management variables. The novelty of this study is analyzing the impact of facility size on the project time and cost, while managerial actions taken to resolve space shortages are modeled, and interdependent influencing parameters of the different disciplines, such as site layout, material management, logistics, and construction process planning are integrated in a unified model. The applicability and suitability of the proposed approach is demonstrated in layout planning of a tunneling project site.

An Analysis of Out-of-home Non-work Activity Time Use and Timing Behaviour Based on Work Schedule and Trip Time

This paper attempts to integrate the discrete of activity timing and the continuous data of time allocation based on the concept of utility. The analysis combines the concept of discrete-continuous simulation equations framework to represent the interactions between activity timing and time allocation behaviour during the day. Activity timing choice was modelled as a discrete choice variable involving three alternatives broad periods: home-to-work period, work-based period and post home period. For fixed time workers, it was found that the model in which activity time allocation is assumed to be determined first influence activity timing show statistical measure of fit. Significant parameter of trip characteristics and social economic variables also influence activity timing choice. Activity timing choice model based on time-allocation data can be used to estimate the number of induced and reduce trips and evaluate the impacts of alternative transportation improvement projects to decision to carry out the activities and trips.

Joint production and setup control policies: an extensive study addressing implementation issues via quantitative and qualitative criteria

This paper addresses the production and setup control problem in unreliable multiproducts manufacturing system. Several decision criteria are considered in order to conduct an exhaustive comparative study of the two most complete control policies in the literature. The objective is to propose a production and setup control policy for the system under review. The first part of this work consists in analyzing the effect of the system parameters variation on the difference between the total costs of the two control policies studied. The best control policy in terms of cost will then be determined using a numerical example in the case of two identical product types and without the loss of generality of the problem. In the second part, two key performance indicators (KPIs): the cost and the customer satisfaction rate are simultaneously considered. The goal is to optimize the parameters of the policies studied, which minimize the total cost incurred while respecting customer satisfaction constraint. A discussion on the best control policy is conducted based on cost and customer satisfaction. An experimental resolution approach is used. It integrates combined discrete-continuous simulation models with statistical techniques of optimization such as design of experiments, analysis of variance, and response surface methodology. Finally, a discussion is conducted on the effects of other quantitative and qualitative criteria in order to determine the best control policy and to reach the best concerns of the company’s decision makers. These decision criteria are generally related to the storage space required constraint, the setups complexity, the implementation issue, and the complexity of the optimal control problem.

Modeling of Simultaneously Continuous and Stochastic Construction Activities for Simulation

Construction operations have been modeled and simulated using discrete-event simulations with effectiveness and fidelity that have continuously increased over the past four decades. Today, it is possible to model construction operations so that its discrete components are represented very faithfully. However, construction operations often include activities that are simultaneously continuous and stochastic in nature. These continuous activities have typically been modeled by discretization and in some cases using combined discrete-continuous simulation. The current literature does not discuss the series of important statistical issues, such as divisibility of fitted distributions and a significant possibility of the discretized activities not being independent and identically distributed, which are brought along by discretization and can significantly impact the results of the simulation study. Combined discrete-continuous simulations have treated the continuous portion dynamically (i.e., based on differential equations of rate change) but either deterministically or disrespecting statistical properties of the underlying continuous stochastic process and its interactions with the discrete portion. These approaches can seriously affect the accuracy of the model in representing the system behavior, grossly impact the simulation results, and can be detrimental to the acceptance of the model due to difficulties in verification and validation. A clear understanding of the underlying problems is thus required when modeling simultaneously continuous and stochastic activities. This paper investigates the major issues associated with modeling continuous stochastic construction activities that have been traditionally modeled using discrete-event methods. This paper contributes to the body of knowledge by identifying the issues pertaining to and impacts of discretization of continuous activities. The paper improves awareness of these issues that have been ignored or not understood by previous studies and help future researchers in building valid and credible simulation models. The paper also demonstrates the effect of discretization on the behavior of the model and the simulation results using a case study of a road-paving operation.

Adequacy and Security Evaluation of Distribution Systems With Distributed Generation

This paper presents an adequacy and security evaluation of electric power distribution systems with distributed generation. For this accomplishment, bulk power system adequacy and security evaluation concepts are adapted to distribution system applications. The evaluation is supported by a combined discrete-continuous simulation model which emulates the distribution system operation. This model generates a sequence of operation states which are evaluated from a steady-state perspective using AC power flow computations. Frequency and voltage stability are also assessed using dynamic simulation in order to verify the feasibility of islanded operation. Simulation results are presented for the RBTS-BUS2-F1 as well as an actual feeder from the South of Brazil. The results emphasize the need to consider adequacy and security aspects in the distribution system assessments, mainly due to the ongoing integration of distributed energy resources.

7102 離散系・連続系混合モデルによるサプライ・チェーン・シミュレーション(OS7 学生研究課題発表)

7102 離散系・連続系混合モデルによるサプライ・チェーン・シミュレーション(OS7 学生研究課題発表)

A hybrid systems approach toward modeling and dynamical simulation of dextrous manipulation

This paper presents an approach toward comprehensive discrete-continuous modeling and accurate dynamical simulation of dextrous manipulation. The resulting hybrid-state model integrates time-driven mechanical features of manipulation systems as well as their discrete-event aspects resulting from varying contact situations. It can easily be embedded into sophisticated simulation environments. A MATLAB implementation serves us as a tool for mechatronic control design for grasping systems. Results from dynamical simulations of a four-fingered hand grasping and manipulating an object demonstrate the efficiency and high accuracy of our approach.

The Winter Simulation Conference

The Winter Simulation Conference (WSC) is the premier international forum for disseminating recent advances in the field of system simulation, with the principal focus being discrete-event simulation and combined discrete-continuous simulation. In addition to a technical program of unsurpassed scope and quality, WSC provides the central meeting place for simulation practitioners, researchers, and vendors drawn from all disciplines and from the industrial, governmental, and academic sectors.

An analysis of SIMAN as a general-purpose simulation language for mining systems

ABSTRACT The SIMAN computer language is a general-purpose, discrete-continuous simulation analysis language for modeling a variety of systems. The language has been extensively used for modeling manufacturing systems but has many features that are advantageous in the modeling of mining materials handling systems. The authors have evaluated the language by applying it to an open pit truck/shovel materials handling system. This paper summarizes the results of the application of the model, compares its features with other simulation languages and evaluates its usefulness for simulation of mining systems.

Modeling noncoventional sampling schemes with a combined discrete-continuous language

Combined discrete-continuous simulation languages can pro vide a convenient and flexible structure for modeling a wide variety of nonconventional sampled-data control problems. Using the language SIMAN, it is shown how to model fixed, random, and signal-dependent nonconventional sampling schemes in cluding a nonsynchronous multirate system with a PID controller.

A simulation study of energy consumption by elevators in tall buildings

The problem of estimating the energy requirements of elevators in tall buildings is shown to be dependent on the integration of functions of random variables. In addition, the period of integration is also random. Hence, a discrete-continuous simulation language, GASP IV, is employed as a method of solving the equations which describe the model. The model is applied to estimating the energy requirements of a building which contains both apartments and commercial facilities. Amongst the topics studied are the effects of elevator speeds and counterweight values on energy consumption, and also the amount of energy available for regeneration. Although the prediction of energy consumption is not considered to be an Industrial Engineering function, Industrial Engineering concepts and tools are used in modelling the problem.