International Journal of Modeling, Simulation, and Scientific Computing

In this paper, a two-dimensional axisymmetric thermal model using finite element method (FEM) has been established for predicting the temperature distribution profile on the work piece during electro discharge machining (EDM) and obtained material removal rate (MRR) from the temperature isotherm. For prediction of MRR, the model utilizes some important features viz. size and shape of the heat source (Gaussian heat distribution), thermal properties of workpiece, amount of heat distribution among the dielectric fluid, workpiece and tool, material flushing efficiency and pulse off/on time, etc. ANSYS software was used for developing the thermal model for the single spark operation. For this investigation, AISI 304 stainless steel and tungsten carbide was used as workpiece and electrode material, respectively. A comparison study has been carried out for theoretical and experimental MRR for the effect of each process parameter viz. gap voltage, pulse on time and peak current. The temperature distribution along the radial and depth direction of the workpiece has been reported. The model was validated by comparing the theoretical MRR with the experimental MRR and found a good correlation between them.

With the increasing advances in technology, ubiquitous computing services have been able to satisfy users by providing high quality services. Such services can be found in different areas such as healthcare, social networks, urban transportation, and multimedia. Nowadays, there are a wide variety of services with similar functionalities in each of the abovementioned areas. Ranking these services based on quality of service (QoS) criteria can help the users to choose the most appropriate services that meet their preferences. The aim of this research is to create a comprehensive framework based on QoS criteria in ubiquitous environment to rank services. At first by extending the previous research, this paper gathers and classifies the QoS criteria into four classes of architecture, usability, ubiquity, and security. This classification organizes QoS criteria in a hierarchical structure. Afterward, Analytic Hierarchy Process (AHP) is used to propose a customized service ranking framework according to the values of each criterion. To utilize the opinions of experts of the subject, a questionnaire is designed to evaluate the proposed structure of QoS criteria and to determine the weight of each criterion. Finally, comparing the proposed framework with previous approaches indicates that this framework includes a complete set of criteria, which leads to a deep perception of QoS in a ubiquitous computing environment. Moreover, the computed inconsistency ratio indicates that the performed decision-making process has a reasonable consistency.

Today, a large number of information and communication technologies (ICT) and networking technologies are being used in industrial control systems. Thus, networked industrial control systems (NICS) are exposed to many security threats. Moreover, new technologies for NICS also need to be tested. This paper presents a cloud-based experimental platform for NICS to test new technologies and security threats. A cloud platform is used to emulate network devices and Simulink is used to simulate the physical layer. To build this testbed, we modify the cloud platform and add three modules to the testbed. One module is used so that the cloud platform can connect to real devices. By using this module, real devices can be added to the networks in the cloud platform. The second module is used for network connection configurations in the testbed. By using this module, the bandwidth, delay and packet loss rate for networks in the testbed can all be set. The third module is used to connect the Simulink to the testbed. The main features of the proposed platform are high flexibility, high authenticity, and low cost. Advanced persistent threat (APT) attacks are a common threat for NICS nowadays. In order to prove the feasibility of the proposed testbed, a common NICS is established and an APT attack is executed on it.

The implementation of numerical methods to solve and study equations for cardiac wave propagation in realistic geometries is very costly, in terms of computational resources. The aim of this work is to show the improvement that can be obtained with Chebyshev polynomials-based methods over the classical finite difference schemes to obtain numerical solutions of cardiac models. To this end, we present a Chebyshev multidomain (CMD) Pseudospectral method to solve a simple two variable cardiac models on three-dimensional anisotropic media and we show the usefulness of the method over the traditional finite differences scheme widely used in the literature.

In the present worldwide scenario, plenty of problems arising in science and engineering which can be modeled as differential equations and out of these, autonomous system has become a subject of great interest. Several laws of physics in which time is considered as an independent variable are expressed as autonomous systems. In this paper, Runge–Kutta (RK) three-stage geometric mean method is used to solve the initial value problem arises in autonomous systems. The method is discussed in detail, convergence of method is discussed, the accuracy and efficiency of the method are proved by considering a numerical example. The result is compared to some other methods and proposed method is found to be more efficient. The detailed analysis of error estimation confirms that proposed method is more efficient as compared to other methods.

The detection of the low-altitude acoustic target is an important way to compensate for the weakness of radar. Removing the noise mixed in acoustic signal as much as possible to retain the useful information is a challenging task. Inspired by the wavelet threshold, the de-noising method for low-altitude battlefield acoustic signal based on threshold empirical mode decomposition (EMD-T) is proposed in this paper. Firstly, the noisy signal is decomposed by empirical mode decomposition (EMD) to get the intrinsic mode functions (IMFs). Then the IMFs, whose actual energy exceeds its estimated energy, are processed by the EMD threshold. Finally, the processed IMFs are summed to reconstruct the de-noised signal. To evaluate the performance of the proposed method, extensive simulations are performed using helicopter sound corrupted with four types of typical low-altitude ambient noise under different signal-to-noise ratio (SNR) input values. The performance is evaluated in terms of SNR, root mean square error (RMSE) and smoothness index (SI). The simulations results reveal that the proposed method de-noising method has the perspective of the highest SNR, smallest RMSE and SI in de-noising low-altitude ambient noise compared to other methods, including the wavelet transform (WT) and conventional EMD.

Crowds of people are often found in enclosed or constricted spaces. Evacuation in such situations is usually conducted calmly, but real or perceived danger may trigger panic. In panicked crowds, the interpersonal distance crowd members normally observe is often overwhelmed by the physical pressure of crowd members pushing against each other. That pressure can both slow evacuation and lead to injury or death. Models have been developed to study crowd evacuation in a range of situations. This paper describes the implementation, testing, and validation of a crowd evacuation model using Unity, a commercial computer game engine. A realistic physics-based model of crowd movement that calculates and considers the physical pressure crowd members exert on each other was implemented in Unity. The implemented model was tested under both nonpanicked and panicked scenarios; those tests exhibited known qualitative characteristics of such scenarios. The model was then quantitatively validated by comparing its results to the outcome of an actual evacuation event, the 2003 fire at The Station nightclub in Rhode Island. The implementation and validation show that Unity can be an effective tool for evacuation modeling.

Airborne passive electronic reconnaissance equipment has developed rapidly during recent years. However, because of its expensive and unavailable military features, the simulation realization of these equipment needs to be solved. And the smaller the simulation particle is, the better the simulation system will be. In this study, a signal-level airborne electronic reconnaissance simulation system was built. Mathematical model and simulation realization of each part are introduced in this study. Focusing on the shortness of traditional signal sorting methods, we creatively proposed a presorting method based on the Euclidean distance inside signal flows. Simulation results show that the presorting method based on Euclidean distance successfully reduced the pressure on main sorting and appeared good for signal sorting. Simulation test results of each model built in this study are also shown in the study. This study provides a new thought on the realization of airborne electronic reconnaissance equipment and benefits the development of electronic countermeasure.

In this paper, we introduce a bipartite matching model for matching markets with dynamic arrivals and departures. Different from classical models with a finite-time horizon, our model has a long-time horizon with infinite vertices. In our model, the matching goal is to maximize the ratio of matched vertices, i.e., matched ratio. We define two types of online algorithms, i.e., Greedy and Patient, analyze their performance with evaluation metrics of both upper bounds and competitive ratios, and conduct extensive simulations to validate our analysis. To further simulate the real situation, we extend our model with the user’s strategic behavior and prove the existence of a specific Nash equilibrium under a differentiated matching mechanism.

The development of micro-grid renewable energy system in China has achieved rapid growth in recent years, and the micro-grid renewable energy system has been drawing more and more attention by its flexible operation. Due to the randomness, fluctuation, uncertainty of the wind and photovoltaic renewable generation, abundant flexibility is required to meet the needs of safe, reliable and independent operation of the micro-grid energy system. We need to connect large energy systems to accept outside assistance when the micro-grid renewable energy system is short of adjustment capability. Independent operation and network operation will affect the economic benefit of the micro-grid energy system, so it is practically meaningful to study on the economic benefit evaluation of the micro-grid renewable energy system. This paper proposes a micro-grid energy system operation simulation model about wind and photovoltaic generation, the uncertainty of which is tackled based on the scenario generation and extraction techniques. Based on the proposed indices, the economic benefit could be evaluated by simulating the micro-grid energy system operation. The proposed method is validated by a real micro-grid energy system.

In this paper, we present splitting schemes for the two-level Bloch model. After proposing two ways to split the Bloch equation, we show that it is possible in each case to generate exact numerical solutions of the obtained sub-equations. These exact solutions involve matrix exponentials which can be expensive to compute. Here, for $2\times 2$ matrices we develop equivalent formulations which reduce the computational cost. These splitting schemes are nonstandard ones and conserve all the physical properties (Hermicity, positiveness and trace) of Bloch equations. In addition, they are explicit, making effective their implementation when coupled with the Maxwell’s equations.

This paper proposes the Trasfugen method for traffic assignment aimed at solving the user equilibrium problem. To this end, the method makes use of a genetic algorithm. A fuzzy system is proposed for controlling the mutation and crossover rates of the genetic algorithm, and the corrective strategy is exploited for handling the equilibrium problem constraints. In the model, an approximation algorithm is proposed for obtaining the paths between the origin–destination pairs in the demand matrix. Unlike the traditional deterministic algorithm that has exponential time complexity, this approximation algorithm has polynomial time complexity and is executed much faster. Afterward, the Trasfugen method is applied to the urban network of Tehran metropolitan and the efficiency is investigated. Upon comparing the results obtained from the proposed model with those obtained from the conventional traffic assignment method, namely, the Frank–Wolfe method; it is shown that the proposed algorithm, while acting worse during the initial iterations, achieves better results in the subsequent iterations. Moreover, it prevents the occurrence of local optimal points as well as early/premature convergence, thus producing better results than the Frank–Wolfe algorithm.

In practice, we experience low efficiency of search and rescue (SAR) frequently in disaster relief. Here, we will optimize the SAR through agent-based simulation. In the kind of cases described here, rescue teams are characterized by different capabilities, and the tasks often require different capabilities to complete. To this end, a combinatorial auction-based task allocation scheme is used to develop a cooperative rescue plan for the heterogeneous rescue teams. Then, we illustrate the proposed cooperative rescue plan in different scenarios with the case of landslide disaster relief. The simulation results indicate that the combinatorial auction-based cooperative rescue plan would increase victims’ relative survival probability by 13.8–16.3%, increase the ratio of survivors getting rescued by 10.7–12.7%, and decrease the average elapsed time for one site getting rescued by 19.0–26.6%. The proposed rescue plan outperforms the rescue plan based on the F-Max-Sum a little bit. The robustness analysis shows that the proposed rescue plan is relatively reliable on condition that both the search radius and scope of cooperation are larger than thresholds. Furthermore, we have investigated how the number of rescue teams influences the rescue efficiency.