فصلنامه مدل سازی در مهندسی
پیاپی 65 (تابستان 1400)

The stability of the roll motion of crafts is of great importance because of its significant impact on safety, ease of travel, overall performance and potential capsizing of the system. It is important to study this motion and to investigate its dynamic stability, which is completely nonlinear and highly sensitive to atmospheric conditions, asymmetric loads and the presence of water on the deck. In this research, it was tried to study the stability of the roll motion under the pointed conditions and random white-noise waves analytically. To do this, the probability density function of response was obtained using the Fokker Planck Kolmogorov (FPK) method and the stationary solution of the corresponding partial differential equation. Then, the effect of water on the deck, deviation moment due to the asymmetric load or crossing winds, the damping coefficient and the intensity of the random wave was investigated. Introducing non-dimensional parameters, the equation of roll motion was derived so that it could be applied to a wide range types of crafts. The results, as expected, indicate a significant qualitative change i.e. a bifurcation in the behavior when we have water on the deck. The stability of three types of the crafts is also studied and it is shown that in the presence of water on the deck, the type of craft can completely effect on instability phenomenon.

In recent years, inertial microfluidics (the use of inertial forces in microchannels) have attracted much attention aiming particle separation. The advantage of this method over other methods of separation and enrichment is its high-throughput performance and inexpensiveness. In the present study, the purpose of enriching the fluid with particles greater than 15 microns in diameter accomplished by designing a rectangular microchannel with an array of contraction-expansion regions in which expansion regions (reservoirs) had the task of trapping larger particles. By using the finite element method and by solving the Navier-Stokes equations, streamlines and vortex shapes are obtained. It was observed that for inlet flow rates in the range of 0.25 to 0.5 milliliters per minute, the highest capture efficiency for particles larger than 10 microns in diameter occurred near 0.35 milliliters per minute. The effect of parameters such as channel height, number of reservoirs and the initial length of the contraction region on the capture efficiency was also measured. Finally, in order to approach the practical applications, the effect of viscosity change due to replacement of blood (Non-Newtonian fluid) instead of water was also investigated, which resulted in the formation of vortices at higher flow rates. In general, vortices created in the expansion region, whose intensity depends on the parameters mentioned above, play a dominant role in particle separation, while inertial lift forces appear as an initial guide

The CUSTOM 450 gas turbine compressor blades are corroded in chlorine environments. The initiation and growth of pits and cracks lead to failure. In this paper, prediction of the pitting corrosion behavior of the alloy is studied. In this regard, in the laboratory section, two-point bending specimen is first subjected to different potentials in a 3.5 wt.% sodium chloride solution to cause pitting corrosion and finally leads to failure at the maximum bending region. According to different potentiostatic tests, an equation is proposed to predict the pitting and life time of stressed sample at different potentials. In the numerical section, the strain in the grown pits is calculated by using digital image correlation method and also the COMSOL Multiphysics software. The location of the localized maximum strain obtained from these two methods is in good agreement with growth of the corrosion pits in the electrochemical experiments. Thus, without needs of experiments, the growth direction of the pit can be simulated.

The potential capabilities of Autonomous Underwater Vehicle (AUV) compared to traditional tools and equipment have led to increased attention and use of underwater vehicles in various commercial, military, and research fields. The manufacture and development of an offshore operational platform require the design of a complete and expensive system of a maritime laboratory in order for evaluating and validating the characteristics and performance of the integrated system and its subsystems. Modeling can be a cost-effective tool for conducting tests, verifying and certifying components and performance of hardware and software, performing missions, and thus reducing potential errors in marine tests and missions. These goals can be achieved through a relatively accurate dynamic simulation and modeling of equipment and environmental conditions inside the hardware in the loop (HIL) laboratory. The purpose of this paper is to provide real-time modeling and implement a physics-based depth environmental simulator for an AUV to equip the HIL laboratory. Validation of the performance of the depth environmental simulator in the dynamic bed of six degrees of freedom of an Autonomous Underwater Vehicle crawler has been done in real-time. The results indicate that the output of the depth environmental mechanism matches the measured depth of the field experiment at sea and there is no delay and bias between the real and simulated signal.

With reduction in the mineral grade due to thedevelopment of the mining area to the depths and to ensure the economic efficiencyof mining operations, it is necessary to increase the annual productioncapacity, therefore scheduling problems optimization in mines requires moreprecise designing.  Among the undergroundmining methods, the block caving method is one of the largest and most widespreadmethods is used in the world. In the operation of such mines, drawing controlis the most critical element. In the current study, a mathematical model basedon MILP has been modeled the dilution controlling constraint (BDC) in theproduction scheduling problems. The BDC by reduction of the waste and ore mixingin the draw column presents a real optimization plan. TheMILP formulation for a block-cave production schedule was developed,implemented, and tested in the CPLEX/IBM environment. The resultsof the implementation of the models using 325 drawpoints over 15 periods show that the NPVincreased by 7.47% about 12.2M$. Moreover was prevented of extraction of 3.5Mtwaste. BDC while increasing the average annual production-grade, reduce the stripping costs and increase the life of equipment involved inmining operations

The purpose of the present study is to predict the transient response of the human cornea via a structural model appropriately representing its biomechanical behavior. Load bearing characteristics of the cornea remain poorly understood due to the complexity of its constitutive model. A constitutive model that captures the response of cornea over the whole experimental time and incorporates all included nonlinearities is necessary. In the current study, parameters of the structural anisotropic fiber-reinforced hyper-viscoelastic model have been obtained using coupled finite element-optimization analysis and the uniaxial tensile test for three different strain rates. The utilized model accounts for the dispersion of the fibers along with their reorientation during loading, the nonlinear behavior of finite tissue deformation, and the intrinsic viscoelastic property of the matrix. Results show that the higher the strain rate the higher the stiffness of tested samples. Samples showed stiffening behavior specially at the end section of the tissue response for slower tensile rates. Eventually, the model behavior and its connection with its micro structures such as the collagen fibers, have been investigated. Examining the results shows that the numerical simulations performed for the prediction of the cornea tissue behavior are in agreement with the experimental results.

This paper uses circuit and field models incorporated into the finite element analysis to detect and locate partial discharges (PDs) in winding insulation of high voltage electric machines. Locating PDs with KHz-MHz frequency components is enabled by fast transient models. For this purpose, a PD current pulse with MHz frequency component is injected into each winding turn of the very fast transient model of a squirrel cage induction machine 6KV/250KW. To detect the PD pulse, all field and circuit equations are presented and solved to obtain the system final matrix. In addition, to investigate the model accuracy, the induction machine windings are also simulated using the multi conductor transmission line circuit model. After injecting the PD pulse, the discharge locations are estimated using current analysis. The results are then compared with the proposed model, confirming the reasonable accuracy of the model in estimating the location of PD with high frequency components.

Due to the complexity and large size on the one hand and addition of new equipment and technologies on the other hand, power systems may be subject to uneven or uncoordinated development. That is, development and addition of new technologies are mostly done locally, and then their effect on the whole system is observed in future. Such an approach endangers the long-term integrity and security of the power system. From economical point of view, it can also lead to waste of investment and poor asset management. Grid architecture is a topic that has been of interest in recent years to address these problems. Output of the grid architecture usually includes models and roadmaps that are aligned with the goals and requirements of the power system and coordinate downstream activities with upstream ones in the system. This paper presents the concepts, steps, notes and challenges of the grid architecture. A general view of the topic is presented that could be useful for researchers and those who are involved in the electricity industry.

Rate of penetration (ROP) estimation in a drilling process is very important because it leads to the optimal selection of drilling parameters and reduction of the operating costs. The main purpose of this paper is to modeling and estimating ROP using optimized multilayer perceptron neural network with whale optimization algorithm (WOA-MLPNN), optimized multilayer perceptron neural network with ant colony optimization algorithm (ACO-MLPNN), back propagation multilayer perceptron neural network (BP-MLPNN) and two mathematical models including Bourgoyne and Young model (BYM) and Bingham model. The data required for development of the models were collected from the mud logging unit and the final reports of three drilled wells in an oil field located in southwestern Iran, which were first pre-processed to remove outliers and reduce noise. In the following, 12.25” hole-section information of two wells containing a similar sequence of drilled formations was used to train and test the models, and then the generated models were validated by the third well information. In the end, the performance of models was evaluated by statistical indicators and various graphical tools. The results of this study showed that the machine learning methods are much more accurate than conventional mathematical models. Also, more detailed studies showed that the WOA-MLPNN model with AAPRE values of 3.19, 5.48 and 9.31 for the three sections of training, testing and validation, respectively, has the highest performance compared to other models.

With the high penetration of renewable energy, especially wind power generation with probabilistic nature, the power system is faced with multiple challenges from planning and operation point of view. The need for highly flexible emerging sources like energy storage systems for the integration of renewable energy is essential. Furthermore, the natural gas network as a clean and low-cost energy carrier has an impressive role in the long-term energy perspective. The emergence of new technologies like Power-to-Gas (P2G) and compressed air energy storage (CAES) technologies cause the interdependency between electricity and natural gas networks. An optimal bidding strategy of the hybrid wind farms, CAES and P2G facilities to participate in the day-ahead market is investigated in this paper. The hybrid robust-stochastic approach is implemented to handle the system uncertainties including wind power generation, as well as power market prices to maximize profit. The power generated by the wind farm is modeled by a scenario-based stochastic approach, while day-ahead power price uncertainty to find bidding/ offering curves is modeled by a robust optimization approach. Numerical results indicate an increase in profit, as well as maximum utilization of wind power capacity in the presence of P2G and CAES, simultaneously.

Lack of accurate knowledge of pavement behavior under moving loads is the one of the most important disadvantages in calculation of Equivalent Axle Load Factor (EALF) in roads pavement. Among the many researches, the most comprehensive method is based on the AASHTO road test. As the main weakness of this method, the results are limited to the experimented axles, which makes it impossible to determine the EALF for all existing axles, hence reducing the accuracy of the results, causing premature failure, and leading to higher maintenance costs. Today, although numerous software packages are available for EALF calculation, they require various parameters, are time-consuming, and can only simulate one section at a time . On the other hand, artificial neural networks, as an artificial intelligence subcategory, have many advantages such as reduced input data, increased modeling process speed, ability of parallel modeling of several pavements with different conditions, etc. In this paper, after verifying the simulation of flexible pavements in ABAQUS, a model based on Artificial Neural Network (ANN) was presented to calculate EALF using the back-propagation architecture. Finally, from among the reviewed ANN configurations, the network with the 7-13-1 architecture incorporating the sigmoid function was selected as the optimum network.

Parameters of meta-heuristic algorithms are very effective in their performance and are usually done experimentally, which is very time-consuming. In this research, a hybrid method for selecting the optimal parameters of meta-heuristic algorithms is presented. The proposed method is a combination of data envelopment analysis methods and response surface methodology and is called DSM. In fact, this method can be used to optimize multi-objective problems and its main advantage is to create and optimize one performance response procedure instead of optimizing multiple output response procedures. In addition to optimizing parameters, it also simultaneously maximizes efficiency. In this research, the proposed DSM method has been used to adjust the parameters of the cuckoo optimization algorithm to optimize the standard and experimental Aklay and Rastrigin functions. In the hybrid DSM method, first, the efficiency value is calculated using data envelopment analysis for each set of meta-heuristic algorithm parameters, then the response procedure for performance is determined according to the meta-heuristic algorithm parameters using the response surface methodology. Finally, by optimizing the efficiency surface, the optimal values of the cuckoo algorithm parameters are obtained. In order to validate, the results of the proposed method have been compared with a similar method. The results show better performance of the hybrid algorithm in terms of solution time, number of iterations, and accuracy of the optimization function compared to other similar methods.

In this research, the effects of various parameters on system consisting of a heavy box sinking vertically into water have been studied. The classic configuration is due to Scott Russell who used the sinking box in 1844 to illustrate the formation of a solitary wave in a long rectangular tank. A FVM method has been used to solve the problem. The VOF method for wave profile and overset mesh for sinking the box into air and water, is used to clarify details of the wave and vortex formation. It was observed that as the box sinks the water is heaved up to form both the solitary wave and a vortex. This vortex follows the wave down the tank. The effects of box density, height of box and depth of water on the created wave height are effective. The simulation results are in satisfactory agreement with the experiments. The highest verification error was reported at 4 %. According to the results, with increasing density from 1800 to 3300 kg/m3 and box height from 0/4 to 0/55 m, wave height increased by 5/3 % and 10/2 %, respectively. In addition, with increasing water depth from 0/18 to 0/36 m, the wave height decreased by 2 % and the diameter of the resulting vortex decreased by 3/4 %. Therefore, the importance of impulsive waves in dam reservoirs with low depth and overlooking hills with high height is twofold, and these points should be considered by designers

To ensure the rigidity of the connection in the moment frame system, continuity plates are used at the level of the beam flanges. In box columns, due to the closed section, it is difficult to implement and is not very reliable. The present study introduces a new connection with external stiffeners. In the proposed connection, trapezoidal external stiffeners are used at the level of the beam flanges so that while transferring the force safely from the beam to the column, it can meet the seismic criteria of the connection well. The mentioned connection was investigated in two cases, first; hollow steel section and second column filled with concrete, and the sensitivity analysis of the thickness of the stiffeners were performed. ANSYS software was used to achieve the research objectives. SHELL element is used in modeling steel sections and SOLID element is used for modeling concrete. The parameters studied in the present study to express the adequacy of the connection are: strength, fixed percentage, connection cycle behavior, ductility, energy absorption and stress distribution across the connection. The results of studies show that the introduced connection provides the seismic criteria of the connection well and due to the increase in the width of the beam flange in the areas around the plastic hinge column, it leads to a safe and controlled area inside the beam.