International Journal of Modeling, Simulation, and Scientific Computing

Simulation has become an essential way and sometimes the only way to study complex systems (e.g., system of systems, SoS). Simulation is the model-based activity. How to build a high-quality model is the first consideration in simulation. Fidelity and credibility are the two mostly used metrics to evaluate the quality of a model. However, the definitions and evaluation methods of fidelity and credibility vary from one research to another and it’s hard to evaluate the metrics precisely. More importantly, the evolution process of a model in use cannot be directly reflected by the two metrics. Therefore, this paper introduces the model maturity to track the status of a model during its life cycle, especially in the use and management phases, which will be an important supplement to the quality evaluation system of models. The concept of model maturity is given and a framework of index system for model maturity evaluation is established. Then, a hierarchical evaluation method based on qualitative and quantitative analysis (HEQQ) for model maturity is proposed. Finally, a case study is used to validate the feasibility and effectiveness of the proposed method.

The central pattern generator (CPG) is an important functional unit in the spinal cord which can produce rhythmic signals to control locomotion. Recently, there has been a growing interest in programmable central pattern generators (PCPG). In this paper, a new PCPG oscillator and a generic PCPG model based on the Matsuoka oscillator are presented. The perturbation method is used to determine the convergence of the generic PCPG model. The sine signal, the mix signal and chaotic signals are provided as inputs to the model, and the simulation results show that the generic PCPG can learn arbitrary periodic signals. In this paper, the generic PCPGs are allocated at each joint of the compass-like and the three-link robots and their outputs are chosen as joint position commands. The simulations show that the generic PCPG can be used to control robot locomotion effectively. The contributions of this paper are as follows: (1) A new PCPG oscillator based on the Matsuoka oscillator is presented as a beneficial enhancement to the PCPG oscillators. (2) A generic PCPG model is built comprising three PCPG oscillators. It can learn any periodic input signal. These findings are a significant contribution to generic PCPG research.

Non-commercial Land Ports of Entry (LPOEs) are unique transportation facilities controlling the ingress and egress of passenger vehicles from Mexico to the United States and vice versa. The calibration of microscopic traffic simulation models of non-commercial LPOEs requires a deep understanding of operational processes and driving behavior at these facilities. This paper provides a methodology to guide modelers in calibrating microscopic traffic simulation models of non-commercial LPOEs. The methodology establishes a common framework for modeling operational processes and traffic operations. Moreover, the methodology includes the value of four state variables that characterizes operations of passenger vehicles at non-commercial LPOEs. These variables are speed, acceleration, deceleration, and headway. The authors evaluated this methodology using the Otay Mesa non-commercial LPOE as a case study. Results showed that this methodology could be potentially used to model non-commercial LPOEs along the US–Mexico border and other border regions worldwide.

Electronic packages that are used these days are exposed to different types of vibration loadings in their usage environment. This vibration exposure can be categorized as harmonic and random vibrations. When reliability assessment of modern electronic systems is considered, vibration loading has an important role to play. One of the biggest challenges facing today is the accurate and rapid assessment of fatigue life under the vibration loading. Conventional solder joints were made of lead-tin alloy. According to many environment legislations and rules, lead is prohibited as an ingredient in the solder alloy. The reason for the prohibition of the usage of the lead is that it poisons the environment. In this study, Sn-0.5Cu-3Bi-1Ag is used as the lead-free solder alloy. Fatigue life prediction of electronic package containing SAC405 is conducted with the aid of vibration testing and Finite element analysis under harmonic vibration loading. A specially designed Plastic Ball Grid Array Package (PBGA) component is mounted on Printed Circuit Board (PCB). It is taken as a test vehicle for the vibration test. The test vehicle is excited by a sinusoidal vibration. The frequency of this excitation equals the fundamental frequency of the test vehicle and it is continued till the component fails. Since the solder balls are very small for direct measurement, Finite Element analysis (FEA) is used for noting down the stresses. The stress versus failures cycles (S-N) curve is made by relating both the stresses on the solder balls obtained and the number of failure cycles from vibration analysis. The fatigue life of the component can be estimated from the generated S-N curve. It is analyzed that the methodology is effective in predicting the component’s life. Hence, the reliability of electronic package can be improved.

This paper analyzes Bernoulli’s binary sequences in the representation of empirical nonlinear events, analyzing the distribution of natural resources, population sizes and other variables that influence the possible outcomes of resource’s usage. Consider the event as a nonlinear system and the metrics of analysis consisting of two dependent random variables 0 and 1, with memory and probabilities in maximum finite or infinite lengths, constant and equal to 1/2 for both variables (stationary process). The expressions of the possible trajectories of metric space represented by each binary parameter remain constant in sequences that are repeated alternating the presence or absence of one of the binary variables at each iteration (symmetric or asymmetric). It was observed that the binary variables $X_1$ and $X_2$ assume on time $T_k\to \infty$ specific behaviors (geometric variable) that can be used as management tools in discrete and continuous nonlinear systems aiming at the optimization of resource’s usage, nonlinearity analysis and probabilistic distribution of trajectories occurring about random events. In this way, the paper presents a model of detecting fixed-point attractions and its probabilistic distributions at a given population-resource dynamic. This means that coupling oscillations in the event occur when the binary variables $X_1$ and $X_2$ are limited as a function of time $Y$.

It is proposed to use the spectral form of mathematical description of control systems for modeling continuous-time Markov random processes described by linear stochastic differential equations with additive or multiplicative noise. The obtained results are applied to solve the output process analysis problem and the optimal estimation problem.

Driving behavior is heterogeneous for various drivers due to the different influencing factors as reaction time, gender, driving years and so on. Some existing works tried to reproduce some of the complex characteristics of real traffic flow by taking into account the heterogeneous driving behavior, and the drivers are generally divided into two classes (including aggressive drivers and careful drivers) or three classes (including aggressive drivers, normal drivers and careful drivers). Nevertheless, the classification approaches have not been verified, and the rationality of the classifications has not been confirmed as well. In this study, the trajectory data of drivers is extracted from the NGSIM datasets. By combining the K-Means method and Silhouette measure index, the drivers are classified into four clusters (named as clusters A, B, C and D, respectively) in accordance with the acceleration and time headway. The two-dimensional approach is applied to analyze the characteristics of different clusters. Here, one dimension consists of “Cautious” and “Aggressive” behaviors in terms of velocity and acceleration, and the other dimension consists of “Sensitive” and “Insensitive” behaviors in terms of reaction time. Finally, the fuel consumption and emissions for different clusters are calculated by using the VT-Micro model. A surprising result indicates that overly “cautious” and “sensitive” behaviors may result in more fuel consumption and emissions. Therefore, it is necessary to find the balance between the driving characteristics.

The effect of investigation results on viscoelastic properties of the material and bases on vibration fatigue of a pipeline conveying pulsating fluid flow is given in the paper. A mathematical model of viscoelastic pipeline vibrations based on the theory of beams was developed when a pulsating fluid flows through it. A computational algorithm has been developed to solve vibration problems of composite pipelines conveying pulsating fluid. Stability and amplitude-time characteristics of vibrations of composite pipelines conveying pulsating fluid were studied at wide range of parameters variation of deformable systems and fluid flow.

Viscous heating has a substantial influence on the extrusion forming process and product quality of powder materials. This study selected the MUZL420 ring die pellet mill as the research object, from which a 3D flow physical model was established. The numerical simulation of 3D nonisothermal flow in the extrusion pelletizing process of granulated alfalfa was performed with POLYFLOW. The distribution laws of pressure, velocity, shear rate, viscosity, viscous heating and temperature in the flow field were revealed to thoroughly investigate the pelletizing process and provide a reference for structural optimization and process control. The results showed that two extrusion zones in the pelleting chamber were symmetrical with respect to the center, and the significant pressure gradient along the rotating direction of the ring die and the roller caused the material to flow back in the opposite direction. There were larger velocity gradients, shear rates and viscous heating levels in the deformation and compaction zone, the negative pressure zone behind the extrusion zone and the die holes. The distribution of viscosity was opposite to that of the shear rate. The temperature increase area caused by viscous heating gradually expanded from the material inlet to the bottom of the extrusion chamber along the $Z$-axis direction, and the temperature increased accordingly. The extrusion force and the forming temperature in the extrusion forming zone were captured in the numerical simulation. The extrusion forming density was calculated with the regression prediction model established through the simulation experiment of pelletizing with a ring die. Through a comparison with the results of mean alfalfa pellet density from the ring die pellet mill experiment, the relative error was less than 5%, which indicated that the numerical simulation method was reliable.

Nonlinear differential equations with moving singular points require emergence and development of new approximate methods of solution. In this paper, we give a solution to one of the problems of the analytical approximate method for solving nonlinear differential equations with moving singular points, and study the influence of the perturbation of the initial conditions on the analytical approximate solution in the analytic domain. Theoretical material was tested using a numerical experiment confirming its reliability. The theoretical material presented in this paper allows researchers to use nonlinear differential equations with moving singular points when designing mathematical models of building structures.