فصلنامه مدل سازی در مهندسی
پیاپی 60 (بهار 1399)

Urea, as the most widely used fertilizer, has the highest nitrogen loss in aqueous media. Urea-modified lignin matrix as a biodegradable and inexpensive bio-polymer can become a controlled-release fertilizer with commercial capability; Therefore, release models investigate is very important. Two-dimensional partial differential equation was solved analytically considering time and radius as two independent variables in spherical coordinates for infinite volume and compared to the results for finite volume of liquid. In order to validate the model’s results, equal amounts of melted urea and lignin acetylated were mixed for preparation of matrix using spherical frame. The amount of nitrogen release from the matrix of lignin in water was measured by Kjeldahl method at different time intervals. Presented models were able to predict release of urea for the infinite and finite fluid volume with R2 equivalent to 9967/0 and 9946/0, respectively. Moreover, empirical models were applied to predict the release pattern including: Power, Modified Schwartz and Suggested Modified hyperbolic model. Among the models used in this research, obtained analytical model for infinite volumes, finite and modified hyperbolic model had the highest accuracy, respectively.

In this paper the effects of increasing the wall temperature and the amount of liquid charge on the oscillating flow in a U-shaped miniature tube, with a simple bend of diameter 1.5 mm and closed end investigated. The governing equations are obtained by applying the conservation of mass, momentum and energy for the liquid slug and the vapor plugs. A complete numerical simulation has been performed to investigate the effects of wall temperature and the amount of liquid charge on the heat pipe performance using explicit method. The obtained results show that by increasing the walls temperature difference, amplitude of oscillations of the liquid slug, sensible and latent heat transfer will be increased, as the temperature difference is increased by only ,oscillation amplitude of the liquid slug about 8 mm, the sensible heat transfer 4 watts and the latent heat transfer watts increases. Additionally, by increasing the charge rate, the oscillation amplitude and the sensible heat transfer are significantly reduced, for example, increasing the charge rate from 30 to 50% reduces the oscillation amplitude by about 65 mm as well as the sensible heat transfer by 87 watts reduces. In the charging ratio 90%, the heat pipe operation is stopped.

An experimental study was made to determine the effect of angle of attack on Hydraulic- Thermal Performance from a cam-shaped tube with constant heat flux in cross flow. Reynolds numbers based on an equivalent diameter are within 15500 < Re_(D_eq ) < 42000. Angle of attack is between 0 < α < 180 using air as fluid for cross flow. Results indicate that with increasing the angle of attack from 0˚ to 90˚ the mean nusselt number and drag coefficient increases about 7-13 and 114-122%, respectively. Drag coefficient and mean Nusselt number have been studied and the results demonstrate that in all Reynolds numbers the angles of 0˚ and 150˚ results in lowest and 90˚ results in the highest amount. A Hydraulic-Thermal comparison of the tube was made and the results show that the angles of 0˚ and 150˚ have the best performance comparing to other angles and the difference is about 31-125 %. Also angles of 0˚ and 150˚ are about 36-82 % better than a circular tube with equivalent diameter.

This paper focuses on identification of bearing failure mechanisms in double sided bolted joints whith GLARE construction meanwhile to get a comprehensive analysis for bolted joint including GLARE type laminates. The GLARE laminate is designed and introduced in accordance with standard geometry and dimensions from standard methods for test procedures to be inserted into the bolted joint. By simulating the test mechanisms in ABAQUS FE Software, the effects of the important parametrs such as distance to the edge(DTE) and bolt diameter on the Bearing Strength of Bolted Joints are described and investigated. FE models are evaluated and validated by convergency process and comparing with a sample case. The results, explain the degree of the dependcy of bearing mechanical behaviour and strength of the bolted joint to number of layers, laminate type and construction in introduced bolt diameters and the GLARE. The reults also represent, considerable delay in failure of the GLARE laminates for a limited region.

Compound channels are consisting of two hydraulic sections namely main channel and floodplain. In meandering rivers, with the passage of time and lateral movement of the meanders, the external bending progression and the sinusoidal or curvature is increased. The curvature of meandering sections can be defined by a dimensionless parameter as the sinusoidal number which is the ratio of meandering length of main channel to the floodplain length. In this research work, the hydraulic characteristics of flow including the velocity magnitude, boundary shear stress, turbulence intensity and turbulence energy of the main channel along the meandering compound channel have been investigated numerically, regarding changes in the sinusoidal ratio for six types of channels with different sinusoidal ratios. In order to investigate the effect of sinusoidal ratio in meandering compound channels on the hydraulic characteristics of the flow, the FLOW3D software is applied. Numerical simulation results show that by increasing the channel sinusoidal number from 1 to 1.641, the velocity and bed shear stress decrease and the turbulence intensity and energy increases. So that the maximum value of the above parameters occurs in the inner arc.

Inverters as one of the most important elements of power systems have been profoundly developed in recent decades and their performance has attracted researches in control and structure point of view. In this paper, a novel bidirectional structure is proposed for multilevel converter in order to reduction the switch count and total converter cost. This structure contains DC sources, power switches and power diodes. The proposed structure is presented for symmetrical mode and the number of power electronic devices is decreased in comparison with similar works. Considering recent proposed symmetrical structures, the proposed structure has superior condition in terms of semiconductor switches as well as converter cost. The performance of the proposed single phase symmetrical eleven-level converter is analyzed and simulated in MATLAB/Simulink for both PWM and selective harmonic elimination switching methods. Not only the results are desirable, but also the experimental results of laboratory prototype validate the simulation results.

In this paper, a hybrid model of fuzzy multi-criteria decision making is presented for the cases a large number of criteria, relationships or affiliation exists are between them. In this model, the DEMATEL method is used to determine the relationships between criteria and analytic network process (ANP) method to identify the weight of each criteria and the VIKOR method for optimizing the multi-criteria of ranking the best supplier. In this study, in order to cover the cases of decisions with ambiguous scenarios, rather than using absolute numbers, the linguistic variables are used. The proposed hybrid model can direct managers and experts organizations In order to improve their choices, especially when there are numerous criteria and there is dependence between them under conditions of uncertainty.The proposed method, reduces number of pairwise comparison matrix and volume of calculations and also increases calculation speed and the complexity of the problem is reduced. In order to showing the solving process a numerical example is presented. The computational results show that proposed hybrid method, in addition to ranking alternatives calculates the final weight of each criterion.

In this study, an optimized mathematical model for a multi-product supply chain with the possibility of supplier disruption under sanctions is presented. A supply chain involves the alignment of companies that market products or services. In order to manage the multi-product supply chain, there is a need for supplies and raw materials to be used in the processes and the supply of these items is subject to uncertainty so that suppliers may meet part of the ordered demand at the required time. Not to be provided to the customer. There are two types of suppliers to deal with this form of uncertainty. The first category is low-cost but unreliable suppliers, and in the second, there are suppliers that are reliable but more expensive than the first. Items received from suppliers are used in the manufacturing or repair process and a model for managing this process must be provided. To integrate these decisions into an integrated model, a stochastic two-stage decision model has been used and the approximation of mean sampling method has been used to solve the proposed problem. The results show that using the random two-step model results in an improvement of 6.84% in the outputs of the problem and also the use of suppliers along with the cheap supplier leads to the improvement of the model outputs. It was 14.9%.

Given the cost reduction of power switching devices, 2/3level hybrid inverters have been recently presented with the voltage generation capability close to the sinusoidal voltage. The hybrid inverter, while having the benefits of the conventional three-level inverters, has fewer switching devices, which will reduce the cost, size, and total weight of the inverter. In this paper, a 2/3 hybrid inverter containing eight switches and two diodes is used to control the speed of a three-phase asynchronous motor, which has four switches and two diodes less than the conventional three-level inverter. The indirect rotor‐flux oriented vector control is proposed for speed control, the control loops of the system are designed, and a proper and efficient carrier wave based switching technique is proposed for the hybrid inverter. In order to verify the efficiency of the proposed inverter and its control, a variety of simulations are performed in the MATLAB/Simulink software and the speed control results in motor mode and step changes in load torque are presented.

In this article, a novel observer has been designed for the online estimation of time delay in SISO-LTI continuous time systems with uncertain and time variant delay in the control input. It is obvious that Laplace transfer function of a delayed system includes a time delay factor. In this paper, it is assumed that the only uncertain and time variant parameter in the system is the very system’s time delay parameter. The main idea used in designing the proposed observer is based on the establishment of duality principle between controller and observer, such that a direct adaptive controller structure (MRAS) is indirectly used for designing an estimator. For this, the main sections in an MRAS control system are organized the way that designing the controller will lead to designing the delay estimator in dual problem. In fact, adaptation rule in designing the controller will express the same estimator mechanism in the dual problem. Also, in computing the estimation mechanism, the two methods, one based on Lyapunov Theory and the other based on MIT rule, are used. Eventually, simulation results are indicative of the rather desirable performance of the proposed estimator in dealing with uncertain and time varying delays.

The accurate and fast localization in the Internet of Things is an essential requirement in expanding the use of applications for these networks. Due to limited computing power of sensor nodes and the limited power capacity of these nodes, reducing computational complexity and reducing communication overhead in localization algorithms is critical. In this paper, a particle swarm optimization based algorithm is proposed for localization of sensor nodes in IoT. In general, trapping in local optima and the slow convergence rate are two main weaknesses of the classic PSO. In the proposed algorithm, using the chaos theory, trapping in local optima is prevented and convergence of the algorithm is improved. In addition, using the fractional derivatives, the particles convergence rate accelerates to the optimal solution. The performance evaluation of the algorithm is performed by its implementation on specific test functions. Simulation results exhibit the effectiveness of the proposed algorithm in localization of sensor nodes in IoT.

Due to the increase in wind power production and the increasing development of wind farms its impact on power systems cannot be neglected and modeling of wind farms has been converted to an important topic in power engineering. When studying the effects of a wind farm on the power system, Instead of modeling the wind farm in detail, the performance of the wind farm at the point of the common coupling can be considered as an equivalent model includes an equivalent generator and an equivalent turbine. This approach in addition to simplify the system analysis would considerably reduce the simulations burden. In order to improve the accuracy of this equivalent model the mechanical parts of the wind turbines can be replaced with more than one equivalent turbine using clustering algorithms. Traditionally these algorithms consider the wind speed as the feature for clustering. In this paper it is proposed to classify the wind turbines by power coefficient of each turbine instead of the wind speed. The simulation results obtained using this approach is verified against the conventional approach and also the detailed model. Simulations are done in MATLAB. The results indicate that the accuracy of the equivalent model obtained using proposed approach, is considerably improved.

Breakwater is a coastal-offshore structure which is used to protect the harbors and shores from waves and coastal streams. Breakwaters decrease the height of the waves and reduce the energy of the waves before reaching the harbors. The height of the streams near harbors with shallow waters is very high in comparison to deep waters situation. Due to the time consuming and high cost of experimental study of a typical breakwater, the present study was conducted via the Star CCM Software. To this end, the composite semi-circular breakwater was modeled under three different water line conditions. The simulation space for all the three conditions was the RANS equations. The results were compared and verified by the numerical and experimental results. It was found that the simulation results are in acceptable agreement with the reported experimental and numerical results. Therefore, the physical modeling and simulation field of the studied structure can be employed for simulation of the static coastal-offshore structures. The use of semi-circular breakers in deep waters encounter with problems such as required space and construction materials. Therefore, a composite semi-circular breaker was modeled and investigated to tackle these problems. Based to the results, the drag on composite semi-circular breaker increases in comparison with the original structure; however, due to the design specifications of the structure, the semi-circular breaker occupies less space and is suitable for application in deep waters.

Interlinking converter topology on bipolar hybrid microgrid is gaining increasing attention during last years. The heart of bipolar hybrid microgrid structure is the interlinking converter that plays the primary role in this structure. This interlinking converter has decisive tasks in the microgrid control system and controlling the dc-bus is one of the critical ones. This paper investigates application of a 10 switch inverter as an interlinking converter for a bipolar hybrid microgrid and aims to increase the power quality on both AC and DC side, and enhance efficiency in such systems. The 10 switch converter costs less in comparison to other multilevel converters and also diminishes volume and application costs. A modified modulation method and a novel control system is proposed for this converter which results in reducing computations for modulation, and adds the ability to control the dc-bus independently in unbalance dc bus conditions. Unlike conventional converters used for these microgrid types, this converter does not need any additional DC/DC converter to act as a balancer converter to balance dc-link pole voltages. The superiority of the proposed modulation and control strategy of 10 switch converter is studied in a simulation system, and the 10 switch converter results are compared to conventional topologies. The costs and semiconductor power loss of studied interlinking converters are evaluated and compared to prove the advantages of the proposed interlinking converter.

In the present study, the performance of the palladium-silver membrane reactor during the cyclohexane dehydrogenation (DCH) reaction is modeled and simulated based on the computational fluid dynamics (CFD) method. In recent years, hydrogen production has been important due to its industrial applications and clean energy. Therefore, the dehydrogenation process of cyclohexane has been considered due to the production of crude dioxide and crane monoxide-free hydrogen as well as high hydrogen capacity. For this purpose, a symmetric two-dimensional model is proposed for the palladium membrane reactor. In this regard, after modeling and simulating the performance of the fixed bed reactor and comparing its results with the laboratory data, a good agreement (4% error) was obtained between theoretical and laboratory results. In order to better understand the performance of the membrane reactor during the DCH reaction, the influence of various operating parameters (reaction temperature, reaction pressure, adsorption factor and flow arrangement) on the concepts of cyclohexane conversion percentage and hydrogen recovery percentage have been investigated. As a general result in all operating conditions, the PdC membrane reactor (MRC) showed better performance than the synchronous flow membrane reactor (MR) and conventional fixed bed reactor (TR). For example, the cyclohexane conversion rate increased with increasing temperature from 430 to 490 K, for MRC reactor from 28.4 to 100%, MR reactor from 10.1 to 77.75 and TR reactor from 7.42 to 46.29.

Two important issues in the modern transmission lines protection are the speed and accuracy of the fault type classification, which have a great impact on the duration of fault clearing time and the accuracy of fault detection by the distance relay. The purpose of this study was to use the phase space analysis and decision tree-learning algorithm to classify the fault type in single circuit transmission lines. Accordingly, an algorithm is developed in which the three-phase current and voltage signals are measured and sampled on one side of the transmission line, firstly. Then, after the phase space analyzing of the current and voltage samples, the statistical feature vector of the output of the analysis is calculated. In the end, the feature vector is fed to the pre-trained intelligent model, to determine the type of fault occurred. The proposed algorithm has been investigated and tested on the sample network in different fault conditions, including different values of fault resistance, fault inception time, the amount of the transferred power on the transmission line, and the fault location. The results show that the proposed algorithm can determine the fault type with a length of post-fault data window less than 2 ms and accuracy of 100 percent.

Flameless combustion is a leading way to increase combustion efficiency and reduce pollutant production. The investigation of the properties of flameless combustion in industrial furnaces needs further study.The purpose of this study is to numerically investigate the effect of geometric parameters including distance between the fuel and air injection nozzles and number of fuel nozzles on flameless combustion performance in a semi-industrial furnace.Standard k-ɛ and the eddy dissipation concept models are used to model turbulence and combustion, respectively, and the WSGGM model is used to calculate the absorption and emission coefficients. Comparison of preliminary simulation results with experimental data on temperature and velocity distribution at different cross sections shows good compatibility. The accuracy of the radiative model has been evaluated by examining the states without applying the radiative model,P1 model and DO model and based on results P1 model has been selected.The results show that changing the distance of the fuel and oxidizer nozzles is more effective in the upstream area of the combustion chamber.By removing the fuel nozzle from the center of the chamber, the effect of the return combustion products on the reaction zone intensifies and the peak temperature of the chamber decreases. Also,with the increase in the number of fuel injectors,more temperature gradient is created in the chamber and combustion from the flameless state leads to the unstable flame.Increasing the distance between the nozzles with fewer fuel nozzles improves the accessing to flameless combustion state in industrial furnaces and reduces the amount of nitrogen oxide emissions produced.

In the present study, an inverse model was used to identify the location and functions of the intensity of unknown point sources in the river. In this research, the inverse solution of the advection-dispersion equation is carried out using a mathematical approach. The main objectives of this model are to identify the location of the pollutant in the presence of several sources in the river without any prior information from the sources in the entire mathematical framework. The strength point of the inverse model is that, by measuring the concentration-time curve from a few points, the source location can be obtained with the highest accuracy. Also, after finding the source location in the river, the functions of the intensity of the pollutant sources are restored. Verification of the inverse model provided by numerous hypothetical examples. In hypothetical examples, the location and intensity functions of the pollutant sources were considered differently so that the efficiency of the method is observed in different forms of intensity functions. Since in real mode, Measurements have errors, Error percent added to data. Finally, the verification was done between the exact state and the results of the inverse model. In all cases, the results of the inverse model were accurately acceptable.