SIMULATION

Xu, Xing-Yuan; Song, Xiao-Na; Cai, Yuan-Li

doi: 10.1177/0037549715588839pmid: N/A

As the maneuverability of targets has been further increased in recent years, it is highly desirable to improve the performance of an interceptor’s guidance law. The “hit-to-kill” scenarios of a kinetic kill vehicle (KKV) require a centimeter-level miss distance, and control of impact angle can considerably increase the KKV’s lethality. Two forms of linear quadratic differential game (LQDG) guidance laws for the KKV are proposed in this paper. The first can achieve only zero terminal miss distance, and the second can achieve a specified impact angle as well as zero terminal miss distance. The LQDG guidance laws are obtained by solving a two-sided linear quadratic optimization problem. In game theory, the adversaries are considered as two independent controlled objects. A major advantage is that the LQDG guidance laws make no assumption of the target’s future maneuver strategy. Simulation results show that the two guidance laws can meet the requirements of the KKV and that the centimeter-level miss distance does not lead to a large guidance command near the terminal time.

Yu, Bin; Feng, Tao

doi: 10.1177/0037549719863213pmid: N/A

Korkmaz Tan, Rabia; Bora, Şebnem

doi: 10.1177/0037549719846366pmid: N/A

The purpose of this study was to solve the parameter-tuning problem of complex systems modeled in an agent-based modeling and simulation environment. As a good set of parameters is necessary to demonstrate the target behavior in a realistic way, modeling a complex system constitutes an optimization problem that must be solved for systems with large parameter spaces. This study presents a three-step hybrid parameter-tuning approach for agent-based models and simulations. In the first step, the problem is defined; in the second step, a parameter-tuning process is performed using the following meta-heuristic algorithms: the Genetic Algorithm, the Firefly Algorithm, the Particle Swarm Optimization algorithm, and the Artificial Bee Colony algorithm. The critical parameters of the meta-heuristic algorithms used in the second step are tuned using the adaptive parameter-tuning method. Thus, new meta-heuristic algorithms are developed, namely, the Adaptive Genetic Algorithm, the Adaptive Firefly Algorithm, the Adaptive Particle Swarm Optimization algorithm, and the Adaptive Artificial Bee Colony algorithm. In the third step, the control phase, the algorithm parameters obtained via the adaptive parameter-tuning method and the parameter values of the model obtained from the meta-heuristic algorithms are manually provided to the developed tool performing the parameter-tuning process and they are tested. The best results are achieved when the meta-heuristic algorithms that were successful in the optimization process are used with their critical parameters adjusted for optimum results. The proposed approach is tested by using the Predator–Prey model, the Eight Queens model, and the Flow Zombies model, and the results are compared.

Wang, Huaizhu; Zhang, Mengjie; Chen, Chao; Yao, Baozhen

doi: 10.1177/0037549717738336pmid: N/A

This paper proposes a selection model of candidate nodes and an air parcel network hub location model to estimate the efficiency of the parcel network when adding pure freighters. Using the data on real demands among airports in practice, this article analyzes the hub location problem of the parcel network for DHL Express in the Asia-Pacific region. We find that Beijing, Hong Kong, Singapore, and Mascot are potential choices to be hub airports. The four hubs have parcel production of 10.1, 5.36, 2.75 and 0.84 million tons in the planning horizon, respectively. A sensitivity analysis is conducted to analyze the influence of different numbers of pure freighters on the air parcel network and the results indicate that the number of pure freighters can alleviate parcel pressure.

Wang, Wensi; Tian, Zhihui; Jiang, Yonglei; Wu, Lan; Gao, Jianqiao

doi: 10.1177/0037549717742508pmid: N/A

Real-time control strategies are important methods for high-frequency transit to counteract the effects of bus bunching in passenger waiting time. This paper extends previous literature with the development of an optimization model for multiple lines in a corridor capable of executing a dynamic control strategy based on passenger choice behavior with real-time information. The bi-level model integrates “passenger perceptions,”“service selection,” and “control strategy” effectively. The upper level model is a control model with the objective of minimizing the total waiting time of passengers in the system composed of common lines to decide whether a bus arriving at the hub should be held and its holding time. The lower level model is an allocation model with the utilization of a Nested Logit model to study passenger choice behavior. In addition, a heuristic algorithm is introduced to solve the problem. The effectiveness of the model is evaluated with the data of two lines in Dalian city of China. The results show that the control strategy proposed in this paper outperforms the simple control strategy without passenger choice behavior, where the waiting time of passengers, the number of buses that need to hold, and bus holding time are all reduced.

Abdelghany, Ahmed; Mahmassani, Hani; Abdelghany, Khaled; Al-Ahmadi, Hasan; Alhalabi, Wael

doi: 10.1177/0037549718794882pmid: N/A

This paper presents the main findings of a simulation-based study to evaluate incidents in pedestrian/crowd tunnels and similar elongated confined facilities, with high-volume heterogeneous traffic. These incidents, when occur, imposes hazardous conditions that always result in significant number of fatalities. The aim of this study is to understand how these facilities perform under different irregular scenarios and possibly identify potential causes of accidents. The problem of studying incidents in large-scale high-volume pedestrian facilities is that these incidents are difficult to expect or replicate. Thus, studying these facilities through real-life scenarios is almost impossible. Accordingly, a micro-simulation assignment model for multidirectional pedestrian movement is used for this purpose. The model adopts a Cellular Automata (CA) discrete system, which allows detailed representation of the pedestrians’ walkways in the tunnel. The modeling approach captures crowd dynamics through representation of behavioral decisions of heterogeneous pedestrians at the individual level. Several experiments are conducted to study the pedestrian flow in the proposed tunnel considering different operational scenarios including demand levels, heterogeneous traffic, evacuation scenario, and tunnel blockage. Results show that flow of large pedestrian volumes through a long confined linear structure, such as a tunnel, are subject to the same flow dynamics as we observe with vehicular traffic. In particular, they are subject to the formation of “clumps” and shock waves that can rapidly propagate and lead to inefficient operation, including flow breakdown with stop-and-go waves.

Zanj, A.; He, F.

doi: 10.1177/0037549718797410pmid: N/A

In this paper, a feasibility study on modeling the multi-physical dynamic behaviors of the start period of hydro-mechanical control devices is presented. Using a novel multi-model Bond graph approach, a nonlinear, variable degree-of-freedom, state-space model is developed for a typical pressure regulator during its start period. Simulation studies demonstrate the essential physical behavior of the regulator during the transient period, and confirm the integrity of the resulting nonlinear model of the system.

Xiao, Yong; Guo, Jianchun; Wang, Hehua; Lu, Lize; Chen, Mengting

doi: 10.1177/0037549718793216pmid: N/A

Geothermal energy is renewable, clean and green energy generated and stored in the Earth’s crust. The most important consideration for geothermal energy development in non-hydrothermal scenarios is the use of hydraulic fracturing technology to establish an effective network pathway to conduct fluid from injectors to producers. Hydraulic fracturing in geothermal wells is referred to as hydro-shearing and the aim is to improve the conductivity of natural fractures. In this paper, linear elastic constitutive relationships and shear strength of discontinuities in the pre-peak region are initially considered. Based on the dynamic frictional weakening, a proved conductive aperture and the post-peak elastoplastic constitutive models are proposed to analyze the deformation and conductivity of the natural fracture. Simulation research has shown that the joint compressive strength (JCS) mainly affects the shear displacement and hardly affects the dilation. The joint roughness coefficient (JRC) is more important for decreasing the shear strength and improves the dilation aperture. To no one’s surprise, reducing the effective normal stress is the best way for increasing the shear displacement, dilation and conductivity of the natural fracture. Almost 90% of the slip displacement and dilation occurs after fracture shear failure. This displacement not only increases the hydraulic conductivity of the fracture, but also reduces the required surface pumping pressure.

Yu, Xuhui; Tang, Guolei; Guo, Zijian; Song, Xiangqun

doi: 10.1177/0037549718815969pmid: N/A

The ever-increasing worldwide container throughput and the intensified port competition have demanded better terminal operational performance, which is usually measured by the gross crane rate (GCR). In this paper, a multiagent-based simulation model is proposed to investigate how the block length of the storage yard and the tactical-level stacking policy affect the operational performance of non-transshipment container terminals over the long term. Experiments consider seven block lengths, two yard truck fleet sizes and two stacking policies. The results demonstrate that the best block length yielding the highest GCR is dependent on the stacking policy and the yard truck fleet size, and the separate stacking policy is essentially superior to the scattered stacking policy. Specifically, only when 9-yard trucks are deployed per quay crane under the separate stacking policy, can the typical 42-slot block length achieve the highest GCR. Although the experiments are not exhaustive, they do provide the first fundamental insights, with respect to the effects of block lengths and stacking policies, on the long-term performance at a manually controlled non-transshipment container terminal.