فصلنامه مدل سازی در مهندسی
پیاپی 66 (پاییز 1400)

System of systems is a collection of independent systems that pool their resources and capabilities together to create a new, more functional system. One of the basic features of any system of systems is emergent behavior that arises out of the interactions between components of a system and cannot easily be predicted or extrapolated from the behavior of those individual components. The purpose of this study is to provide an analysis of reliability-emergent behavior in the system of systems involving energy hubs. Based on this, the effect of the electrical interaction of energy hubs is examined, in order to improve reliability and economic indices in the management of the microgrid system. In order to evaluate the proposed model, the method has been implemented on IEEE 33-bus 12.66 kV test system. Numerical experiments confirm the performance and effectiveness of the proposed method. Keywords: Systems of systems, Emergent behavior, Microgrid operation scheduling, Smart energy hubs, Reliability

High step-up DC-DC converters are widely used in various applications such as renewable energy sources. The voltage gain of the conventional boost converter is limited by high voltage stress, high current ripple and low efficiency due to the high duty cycle ratio. In order to solve these problems, a step-up DC-DC converter based on active switched capacitor (ASC) network is proposed. In the proposed structure, both active switched capacitor (ASC) and active switched inductor (ASL) techniques are combined together with the switch and diode array to achieve high voltage gain. Employing three switches with two different duty cycles and increasing the voltage gain by adding only one extra diode and capacitor are the main advantages of this converter. Beside these advantages, unlike other voltage-boosting structures that utilized switched capacitor, the proposed converter avoids the extreme instantaneous currents of capacitor. The operational principles of the proposed converter in the continuous conduction mode (CCM), inductor and capacitor design and comparison of the proposed converter with other similar structures are presented in this article. Also, the parasitic elements are assumed to calculate the DC-voltage gain and the efficiency of the converter accurately. Finally, simulation results are presented in PSIM software to validate the feasibility of the proposed converter.

Multi-level inverters (MLIs) have made great strides in the use of renewable and industrial energy compared to conventional two-level inverters in terms of output voltage quality, filters and high efficiency requirements. This paper describes a new topology for single-phase multi-level invereter. This topology is presented with the aim of reducing the number of isolated voltage sources, switches and drivers that are able to modularly increase the number of output levels. The proposed structure has been improved to achieve a higher number of output voltage levels relative to the number of switches, drivers and DC voltage source. To confirm the superiority of the proposed structure, a detailed comparison has been performed with other multi-level inverter topologies. In this paper, the Nearest Level Modulation (NLM) is used to generate the output voltage and is simulated in Matlab/Simulink environment. The performance of the designed structure is comprehensively evaluated in symmetric and asymmetric topologies.

Induction motor is one of the most widely used electric motors in the industry and even in everyday life. Various controllers are provided for this motor, one of which is the predictive control method. The main problem with this new method is the inaccuracy of the motor parameters and the lack of access to accurate system information. This inaccuracy can lead to errors in the controller operation. In this paper, the predictive control of induction motors is considered. To improve the performance of this controller, a super twisting sliding observer is used to reduce the effect of uncertainties in the structure of the induction motor. A model reference adaptive estimator has also been used to improve speed estimation in sensor-less control and online estimation of stator resistance. Finally, by adding a fuzzy controller, improvements in the performance of this estimator have been achieved. The simulation results indicate the optimal performance of this method in eliminating the uncertain effect and optimal control of the induction motor.

After a comprehensive study of voltage unbalance issue, this ‎paper presents the defects of some unbalance factors and ‎concentrates on the importance of considering the angle of ‎complex voltage unbalance factor (CVUF) in order to ‎unbalanced condition assessment. Then, for the sake of precise ‎analyzing of the steady state performance of the induction ‎motor (IM) under unbalanced condition, the paper concentrates ‎on the complex current unbalance factor (CCUF) that consists of ‎complex voltage unbalance factor and impedance unbalance ‎factor (IUF). Therefore, the method considers the effects of ‎induction motor parameters as well. Because, the induction ‎machine parameters affect the performance of the induction ‎motor under unbalanced condition, complex current unbalance ‎factor gives a precise estimation of the electromagnetic torque ‎and the output power of the motor. In this paper, the ‎improvement of the steady state performance of an induction ‎motor under unbalanced condition by coupling small sized ‎induction motors instead of a large one is proved.‎

The use of multi-unit cubic satellite (CubeSats), designed nowadays, in accordance with a certain standard, have made any research aimed towards their optimization, quite significant. In the present paper, studies one such common satellite design structure known as “1U”. Our study is carried out with a focus on the structure subsystem, which is of high consequence, due to the direct relationship, it would establish with other subsystems. Informed by the conditions, such satellite structure is exposed to, the present paper, defines the dynamic equations governing its motion, as well as relevant heat, modal and static equations, and utilizes the finite element method (FEM), in several separate portions to solve them. To attain a higher accuracy, our study takes into account, the standards and design specifications for such satellites. Analysis indicate temperature variations on the outer structure of the satellite is in a range from −19.79°C up to 18.85. Moreover, the highest stress value taken by the satellite structure is 45.42 MPa, demonstrating structural resilience versus stress excreted. The first mode of satellite structural resonance is 467.647 Hz. reliability factor was obtained as well, from an investigation of stress values inside the structure. Put together, the results from the analyses have allowed us to conclude that the structure, is in fact resilient, against the excreted stress. Supplementary output from the present study is also valuable, in provision of various prerequisites to an optimal design of the structure subsystem, as well as several other subsystems.

Recently, the most common tool to compensate for various organ defects is tissue transplantation with several problems involved. These problems have led to the rapid growth of tissue engineering with a designed tissue approach or organ substitute in the last decade. For this purpose, it is important to determine the tissue mechanical properties. In this study, to obtain the cartilage structural parameters, isotropic Pro-Hyper-Viscoelastic Mooney-Rivlin and Neo-Hooke are used. These model coefficients are obtained by reverse engineering methods and using a coupled finite element-optimization algorithm utilized unconfined stress relaxation tests with root-mean-square error (RMSE)) less than 0.036, 0.033 for Neo-Hooke and Mooney-Rivlin respectively. Using Neo-Hooke and Mooney-Rivlin models, the modulus of elasticity was 0.47 MPa and 0.44 MPa, and the shear modulus was 0.188 MPa and 0.184 MPa, respectively. The predicted tissue mechanical response obtained by the finite element model showed that the Mooney-Rivlin model is more consistent with the stress relaxation experiments than Neo-Hooke one. The results showed that during the stress relaxation test, by applying a compressing load on the sample, initially the fluid pressurization in the matrix pores has the most contribution in the load-bearing (total stress). When time elapses, the fluid contribution in the load-bearing decreases, and the solid matrix contribution increases.

The main purpose of the reliability theory of structural systems is the optimal design based on the reliability concept. Trusses and space structures are widely used, and cost and safety both are important in these structures. Therefore the weight optimization of these structures based on the theory of reliability (probabilistic optimization) using Genetic Algorithms was studied in this paper. The objective function was weight of structure and the constraints were based on the failure probability of elements or nodes or the system. To increase the accuracy of structural safety calculations, the probabilistic form of buckling is presented in this research. The results of this study show that increasing the system allowable failure probability decreases the optimum weight of structure. The process of this weight loss occurred at first with a very fast slope and then with a gentle slope and finally tended to a constant value. Optimum weight was very sensitive to coefficient of variation comparison of allowable failure probability. In the probabilistic optimization, if the system allowable failure probability and coefficient of variation of load and yield stress are considered near zero, and if results are compared to the deterministic optimization, the difference in optimum weight is less than 9%. In this case, convergence for deterministic optimization was very fast and occurred in less than 20 generations but convergence in probabilistic optimization occurred slowly after 85 generations.

Each variation in public transportation system has a direct effect on passengers travel time. It’s due to the integrated, direct and continuous relationship between passengers and public transportation system. In addition to, reduction in travel and waiting time for passengers will increase the use of public transport systems in a metropolitan. On the other hand, now a days, using simulation software, is one of the strongest and most acceptable tools for traffic analysis. In this study the AIMSUN (Advanced Interactive Microscopic Simulator for Urban and non-urban) and Legion software has been used for simulation of pedestrian travel time between a group of urban subway stations from Gheitarieh to Shahid Haqqani. The pedestrian flow in each station, waiting time, boarding, alight and travel time inside the vehicle has been considered too. According to the current schedule of trains, sum of the waiting time for pedestrian will be 15% more than the schedule with 5 minutes headway. Also the 4 minutes headway will cause the 45% decrease in passengers waiting time.

Voice coil motors (VCM) are used in very small equipment such as mobile phone cameras and the use of a robust control feature as sliding mode control (SMC) is inevitable in them. The most important property of SMC is its invariant against matched disturbances and uncertainties which is due to the using of Sign function in input control signal. The invariant property is stronger than robustness. But, this method is not invariant with respect to the mismatched uncertainties i.e. is variant and sensitive. This is the challenge of SMC in VCM because of existents mismatched uncertainty in their models. To solve this problem in this paper, input control signal is calculated at first via SMC and then, coefficients of the sliding surface are determined in such a way that the effect of mismatched uncertainties or disturbances is removed in closed loop system and invariant property is retained. The proposed approach is simple in concept and realization. Moreover, due to the inaccessible system states, a new nonlinear observer is proposed for system model identification. In simulation, the electro-mechanical model of motor has been used which has both matched and mismatched uncertainties. Simulation results show the effectiveness of this approach.

In liquid-liquid extraction processes, the hydrodynamic characteristics of the system are important parameters in mass transfer. In this research, the effect of continuous and dispersed phases speed, and pulsation intensity on the hydrodynamic characteristics of the system has been investigated. The results showed that the pulsation intensity is an influential parameter. As the pulsation intensity increases, the droplet diameter decreases and the hold-up in the system increases. Then, the effect of nanoparticle and surfactant on the hydrodynamic characteristics of the system was investigated. The results showed that by adding nanoparticle and surfactant, the droplet size decreased and the hold-up increased. A semi-empirical correlation is proposed to predict droplet diameter in terms of operating parameters and system properties and nanoparticle concentration. The results showed that with increasing nanoparticle concentration, the droplet diameter decreases and the predominant mechanism of mass transfer is molecular diffusion. In this case, by using nanoparticles, the extraction efficiency increases from 46 to 78%. By adding a surfactant to the system, the extraction efficiency increases from 70 to 91%. The mechanism of mass transfer in the system without the presence of nanoparticle and surfactant was investigated in their presence. The results show that in this system with the presence of nanoparticle and surfactant Newman theory is a suitable model for predicting mass transfer coefficient.

Hubs are special facilities used as switching, transferring, and sorting points in many distribution systems. Instead of serving each origin-destination pair directly, the hub facility concentrates flow to take advantage of the resulting economic savings. Flows from the same source combine with different destinations on their path to a hub and combine with flows that have different sources but have the same destination. The accumulation of flows takes place in the path from the origin to the hub and from the hub to the destination, as well as between the hubs. These types of systems, commonly known as hub-and-spoke, are studied in the form of hub location problems. In this paper, we develop the single allocation hub location problem with uncertain zero-one demands, in which the amount of demand between each origin-destination pair is considered as a Bernoulli random variable with a definite probability p. Due to the fact that this problem has not been studied in the literature so far, a new mathematical model of mixed integer programming type is developed for the problem and is solved using GAMS software. Also, the results of solving different test problems from the CAB data set are examined and the effect of different parameters on the optimal solution of the problem is examined.