جستجوی مقالات مرتبط با کلیدواژه « مدلسازی » در نشریات گروه « مکانیک »

Due to the increasing environmental pollution and the reduction of fossil fuel resources, the choice of a suitable alternative for non-renewable fuels has been given much attention. Among several alternative fuels, biodiesel is also clean and is produced from renewable sources. In this work, the mathematical modelling and optimization of the catalytic transesterification process for producing soybean oil biodiesel by MATLAB software and differential evolution algorithm has been investigated. The potassium hydroxide was selected as a homogenous catalyst for transesterification reactions in a batch reactor. Based on the experimental data, a model has been proposed to predict the biodiesel production in the catalyst concentration range of (0.4-1wt%), methanol to oil molar ratio range of (5-12) and temperature range of (25-65 °C). In addition, the unknown kinetic parameters of this model have been calculated. There was a good consistency between the model and experimental data. The modeling results showed that there is a relationship between biodiesel yield and effective parameters (temperature, oil to alcohol molar ratio and catalyst concentration). By increasing the temperature and oil to alcohol molar ratio and decreasing the catalyst concentration, the yield of biodiesel increases. Finally, the model was assisted to find the optimal conditions of transesterification reaction to maximize biodiesel yield. In the optimal conditions (catalyst concentration of 0.4501 wt%, molar ratio of methanol to oil of 15 and temperature of 70°C) the biodiesel yield reached 96.87%.

This paper introduces a new and applicable dynamic vibration absorber to reduce the vibration of long-length of the boring bar. This dynamic vibration absorber reduces the transverse vibration of the tool in the machining process. For this purpose, firstly, the boring bar is modeled in the state equipped with the proposed dynamic vibration absorber. Then, the governing equations of the system are derived by calculating the kinetic energy and potential of the system and using the extended Hamilton's principle. Considering that the main vibration of the boring bar appears in the first mode, therefore, to design and determine the dimensions and technical specifications of the dynamic vibration absorber, the system of the boring bar and the absorber connected to it is approximated as a simple equivalent model of two degrees of freedom. Then, the stiffness equivalent and equivalent mass of the boring bar and the absorber are extracted. At the end, the effect of different system parameters on the amount of technical characteristics of the absorber is investigated and the results are presented in the form of graphs. The results show that according to the usable space for the dynamic vibration absorber, it is necessary to make a compromise to determine the dimensions and technical characteristics of the absorber. The results can help researchers and engineers in the industry to design a dynamic vibration absorber system to increase the quality of the machining process.

Sound reflection in different places intensifies the sound of sources. Acoustic reflection is useful in some cases and is often unavoidable. Accurate determination and control of disturbing reflections has always been one of the important positions of acoustic science. Most existing educational and office environments have a short reverberation time and cause the sound to be annoyingly loud.In this paper, the variables affecting the resonance time and its real values in the educational environments of a university site are measured and the existing computational models for estimating the resonance time are analyzed and compared. A developed experimental model is presented based on a logical method using data collected from real environments.The mean absorption coefficient of internal surfaces in Moore environments was 0.04 01 0.01 and the measured resonance time was 0.78 s 0.28 s. 9 common computational models for estimating the reflection time have unacceptable values and more than three times higher for the index. In this research, based on the development of Sabin model, a new experimental Regression model has been presented that the results of predicting its Reverberation time(RT) compared to the measured values are reliable and have a P.value = 0.001, RMSD=0.18 s and coefficient of determination equal to R2 = 0.58.

Wire electrical discharge machining (WEDM) is one of the methods of producing tungsten carbide parts, which due to its poor machinability; optimal cutting with traditional methods is not possible. Material removal rate and surface roughness are the most important output indicators of the wire cut process. In this research, the Wire cut electrical discharge cutting process on tungsten carbide alloy has modeled and optimized. Mathematical modeling has used to establish an accurate relationship between input parameters and process outputs. In this regard, first, the necessary data collected by conducting an experiment, designed by the Design of experiments (DOE) by Taguchi method. Then the types of regression functions including linear and second order fitted for this data. In the next step, the validity of these models has been assessed using statistical hypothesis tests and analysis of variance. With the help of the proposed model, the parameters that have the greatest impact on the two outputs of material removal rate and surface roughness can be determined. After determining the appropriate models, the process optimization is performed using the genetic algorithm based on non-dominated sorting (NSGA-II) and the optimal combination of input parameters table is presented. Finally, a validation experiment performed with one of the compositions of the optimal table and the results of this experiment compared with the results obtained through optimization. Obtained results show good confirmation.

Steam power plants are an advanced and complex design of the Rankin steam-liquid cycle. Therefore, understanding the concepts of effective parameters in increasing energy and exergy efficiency and also exergoeconomic are very important. The purpose of this study is to investigate the three basic scenarios of steam power plants, till the required changes in design and its effects on power plant efficiency to be determined. The third scenario has a preheater, a deaerator and two turbine extraction. The second scenario has a turbine extraction and preheater. In third scenario, energy and exergy efficiency are 20.74% and 26.91%, respectively. it’s increases of energy and exergy efficiency relative to second scenario are equal to 19.13% and 9.48%, respectively. Exergoeconomic analysis has shown that boiler and turbine have the highest total cost of investment, maintenance and exergy destruction, hence special attention should be paid to this equipment. The high relative cost factor of the boiler (r) indicates that the boiler efficiency can provide an overall improvement in the cost of this equipment. This can be done by reducing the exergy destruction by preheating and reducing losses and use of excess air. The Exergoeconomic coefficient of fk turbine is high. This means that to reduce the cost of the turbine, the possibility of reducing parameters such as inlet steam temperature, turbine pressure and it’s efficiency should be given more attention.

Fluid-structure intraction analysis of conveying fluid pipe is one of the important issues in the oil and gas industries. In this study, one of the process lines of Biston Petrochemical Company containing Paraffin fluid (about 90%) and Olefin (about 10%) with two different symmetric and asymmetric designs has been investigated. The investigations consist of two parts: expreiments and modeling. In the modeling section, the pipeline is first simulated in Ansys-Fluent software and the finite element results are entered into the software design section as a one-way coupling. The results of exprimental studies and finite element modelig showed that the root of vibration of this line is turbulence and oscillating pressure of the fluid on the wall of the pipe and with a combination of elastic and fixed constraints, the displacements of the pipeline can be controlled. A good agreement between the simulation and the practical results has been seen. The results also showed that the amplitude of vibration after including supports is reduced to 94% in the asymmetric branch pipeline and up to 86% in the symmetric design. Therefore, the support has a significant effect on the results.

In this paper, design, modeling and control of a grip-based planar climbing robot is performed which is consist of a triangular plate and three actuating legs. This robot is extremely applicable for many applications in which a human operator should climb through a truss infrastructure and implement some manipulations on the relevant installations. The proposed robot in this paper can be substituted and decrease the death danger and increase the safety of operation. In this paper however, a grip-based climbing robot is designed which is able to perform manipulating tasks. Overall kinematics and kinetics of the robot is modeled and its manipulation is controlled using Feedback Linearization for operational phase. All of the modeling are verified by conducting some analytic simulation scenarios in the MATLAB and the results are also compared with the results of the robot which is modeled and simulated in ADAMS software to investigate the correctness of modeling and simulations. It is shown that by the aid of the proposed and designed climbing robot, it is possible to climb and perform a complete operational task through trusses and infrastructures with the best status of safety and accuracy.

In this paper, using the concepts related to the information theory, the model of interaction between human and machine in a standard simulator of piloting tasks is created. For this purpose, baud rate generated in all subsystems of the simulator is calculated and by summing them, the total baud rate is obtained. Next, output baud rate produced by human during working with the simulator is computed and subsequently, a unique index facilitating human performance investigation is proposed. Finally, the capability of this index is examined in the simulator of piloting tasks via a practical test performed by some subjects for different levels of workload (low, medium, and high). Results demonstrate that when a substantial growth in the workload level occurs, subjects try to show extra effort through increasing their generated output baud rate. On the other hand, according to the statistics analysis it can be concluded that there is a significant difference between performance of subjects across low, medium, and high levels of workload, i.e. a severe growth in the workload level causes considerable drop in performance index.

One of the important issues to be considered in the design of space systems is the attention to the difference between the terrestrial and space environment. This issue changes the design and affects all subsystems of space systems. Radiation damage due to space radiation can cause disturbances in the functioning of space systems. In this paper, with a computational approach examines the most important radiation damage involving TID, DD and SEU in two satellites that have missions in LEO orbit. The calculations were performed using the OMERE software and finally, a comparison was made between different models for achieving different types of radiation damage.

Fuel cells have attracted considerable interest during the recent years. Among the different types, high temperature fuel cells are very promising because of their high efficiency, fuel flexibility and high temperature of the exhaust heat which can be used for cogeneration. Among the high temperature fuel cells, Molten Carbonate Fuel Cell (MCFC) has several advantages but is studied less than others. Co2 capturing and internal reforming are its benefits. Internal reforming eliminates the need for external reformers and increases the overall efficiency of the system. In order to better understand the performance of MCFC, in this study, the model of MCFC with indirect internal reforming is developed step by step. The model is developed in a way that has a proper response speed and accuracy. Given that MCFC is a developing technology particularly in our country, evaluating the performance of this technology under different condition could be useful in further progress of MCFC. In order to evaluate the parameters of molten carbonate fuel cell, the impact of parameters such as pressure, fuel cell inlet temperature, steam to carbon ratio, utilization factor of fuel and utilization factor of air and carbon dioxide on the efficiency of the fuel cell is examined. Given that MCFC is a developing technology, particularly in our country, evaluating the performance of this technology under different conditions could be useful in further progress of MCFC. According to the sensitivity analysis conducted, parameters such as pressure, steam to carbon ration, fuel cell inlet temperature and utilization factor of fuel have the most impact on the efficiency of MCFC. With increasing pressure, efficiency is reduced from 56% to 42%. Also, increasing steam to carbon ratio, fuel cell inlet temperature and utilization factor of fuel increases the efficiency by 6.2%, 7.5% and 14.3%, respectively. On the other hand, the utilization factor of air and carbon dioxide have the least impact on the efficiency of MCFC.

In this article, the creep behavior of the AlSiCuNiMg alloy, which has been widely utilized in the piston component of the vehicle engine, has been modelled at different temperatures and various stresse levels. For this objective, the creep test was done on casted standard specimens, under a constant temperature and a constant tensile loading condition. Temperatures in creep testing were considered as 250, 275 and 300°C and stress levels were 75, 100 and 125 MPa. Experimental data showed that at a constant stress level, by increasing the temperature, the minimum true strain rate increased and the final true strain decreased; however, at a constant temperature, by increasing the stress level, both mentioned values increased. Based on modeling results, the temperature-dependent power law was the superior strain rate-based model, with the lowest value for the relative error and the scatter-band. In addition, the Bailey-Norton model had better modeling results between strain-based models.

In today's world, the national security of most countries has depended on secure energy access, and therefore the optimum use of it has been the focus of attention of many statesmen and researchers. Expansion of consumption in the household sector and waste of energy in the urban community are among the obvious reasons for the rapid growth of energy consumption in the national economy. For this reason, energy consumption in the building sector needs to be considered. In this paper, after simulating an office building in Garmsar City with Design-Builder Software and validating it, the effect of the roof insulation and double wall parameters on the energy consumption has been investigated. The results show that the roof insulation and the use of a double wall can have a significant impact on building energy consumption.

The contribution of the building sector to the energy consumption of countries is significant, so in the last few decades, in most industrialized countries, basic measures have been taken to reform the consumption model , using various tools including regulations and criteria . In this study, the use of the type of material used in the walls of the city buildings in the Garmsar city building was analyzed. The comparison of the heat transfer coefficient of each material used on the external walls of the building is modeled and the building is evaluated with basic materials according to the climatic conditions of the city. Finally, using new materials in the outer wall and ceiling, building with double wall is a priority in reducing energy consumption.

In this paper, a capacitive 3-DOF vibratory rate micro gyroscope with 2-DOF oscillator in the sense mode and 1-DOF in the drive mode was studied. A complete model of the micro gyroscope, including mechanical and electrical parts was utilized. Based on the graphical and differential sensitivity analyses methods, variations of the system parameters were analyzed. In the first step, governing equations of the micro gyroscope were derived. In order to simulate the sensor operation, working frequency has been determined and then, output voltage of the sensor versus changes in mechanical and electrical elements is studied. According to the sensitivity analysis results, secondary mass (m2), permittivity, length and width of the electrostatic capacitors, also DC and AC components of the actuation voltage have been clustered as the most sensitive parameters. Initial gap of the electrostatic capacitors and stiffness are fairly sensitive. Primary mass (m1), mass of the decoupling frame (mf), and young module are considered as non-sensitive parameters. Variations of the output voltage based on secondary mass (m2), stiffness and initial gap are completely non-linear and in some areas have severe slopes. Wise choices in selecting appropriate values for these parameters will lead to the better performance and more output voltage of the sensor

Prediction of the behavior of T-shaped chambers due to its high complexity has always been of great interest researchers. In this article, based on experimental data and genetic programming, the optimal model was presented for mixing process response. To get system’s behavioral equations, first, by using the experimental results and by changing the input variables System, input – output data is extracted. In order to predict the behavior of the system, the equation of input – output data, is derived using genetic programming. To design the structure of genetic programming trees, multi-objective optimization with two objective functions are taken into consideration: model inaccuracy and complexity of structure. By minimizing the objective function at the same time, we are looking for simple equations (minimizing the complexity of the structure) and increasing the accuracy of modeling (minimizing the error). In order to achieve a less complex equation, depth of the generated trees in structure of genetic programming will be minimal. By using multi-objective optimization, optimum set of points have presented. Comparing the results obtained from the models and real data represents a very good match.

In this study evaporation of biodiesel droplet under different operating conditions is investigated. The model is a common droplet vaporization model for multicomponent fuels. In this model, gas phase quasi-steady equations are solved analytically and energy and species transport equation in liquid phase are solved numerically. The sub-models are modified to consider high pressure effects. Peng-Robinson equation of state is used for gas phase and phase equilibrium is determined using fugacity. Effects of pressure on the thermophysical and transport properties of gas phase are considered. Five biodiesel with different composition are studied. These biodiesel have different composition of methyl esters. Biodiesel composition has little effects on droplet lifetime and maximum difference is about 20%. It is observed that increasing ambient temperature leads to decrease in droplet lifetime and increases temperature gradient inside droplet. Ambient pressure has different effects on droplet vaporization behavior at different ambient temperature. At lower temperature environment, increasing of pressure increases the droplet lifetime while at higher temperatures droplet lifetime first increases and then decreases with pressure. Increasing initial velocity of droplet reduces the droplet lifetime. Results show that at high pressures, droplet temperature reach to values near to critical temperature and accuracy of quasi-steady approximation decreases. Radius of vapor influenced sphere increases with temperature and decreases with pressure.

Due to increasing the heat transfer surface area and high providing capillary pressure with high permeability, porous structures play a key role in improving the performance of two phase heat transfer devices such as heat pipes. New porous structures (bi-porous structures), have two distinct size distribution of pores of which the small pores provide the capillary pressure required for delivering liquid to the surface and large pores help vapor escape from the surface through increasing its permeability. The main goal is to gain a deeper understanding of the evaporator section of heat pipes and comparison between the performances of two sample biporous structures. Towards this goal first the Kovalev modeling technique is applied to determine the possibility of each phase’s existence in pores of different sizes throughout the computational domain. One dimensional heat transfer in a bi-porous wick is investigated. Inside the domain the conservation equations are solved for each phase and the results such as heat flux versus wall superheat are presented. Thermo-physical properties of the fluid and the matrix like the fluid properties, phase saturation and permeability and the conduction heat transfer coefficient are calculated from the geometry of the matrix and experimental relationships.

Ship maneuvering in calm water and waves are important topics to avoid collisions and broaching, therefore reliable ship maneuvering simulations are required for incident analysis and prevention. The maneuverability of planing crafts has been the subject of many research projects during the last few decades. To assess the maneuverability of planing crafts at the early design stage, reliable simulation models are required. Traditionally, these tools have used empiric descriptions of the forces and moments on the planing craft’s hull. However, nowadays new numerical modeling techniques are available enabling more reliable predictions of the maneuvering behaviour of planing crafts. Ship maneuvering performance evaluation is essential in primary design stages. Ship maneuvering calculations, horizontal plane motion control and development of maneuvering simulators need a mathematical description of ship maneuvering. In the recent years, different mathematical models are suggested for maneuvering of displacement vessels that are capable of estimation of vessel maneuvers with acceptable precision. But simulation of planing craft maneuverability through mathematical model is not common yet and is the subject of future research. In this paper different maneuvers are executed through the mathematical model. Then the mathematical model is solved and different maneuvers are simulated. Simulations are validated by model tests. Finally the influence of rudder angle on maneuverability of planing ship is studied. Different between simulation results and experimental are lower than ten percentages. At the end of this paper the effect of the rudder dimension on the tactical diameter of planing ship in turning maneuvering is evaluated.

The present study deals with the parametric analysis of a turbojet engine performance based on transient aero-thermodynamic governing equations. The required dynamic model developed in Simulink environment. From the complex factors affecting on transient performance, three factors including rotor dynamic, volume dynamic and heat soakage is presented in the model. To validate the model results, a deceleration operation from 100% to 70% of the design rotor speed is carried out and rotational speed, thrust, turbine inlet temperature and turbine exhaust gas temperature of the present model results were compared with commercial program GSP. The results show the ability of the model to simulate the transient performance so that the maximum percentage error is less than 4 percent in thrust prediction. Then in the transient response of the engine acceleration from 70% to 100% of the rotor speed, three different rate of fuel consumption is studied. The results indicate that with sudden acceleration, temperature overshoot at the inlet to the turbine and the occurrence of compressor surge can be harmful, such that the engine acceleration during 2.5 (s) can increase turbine inlet temperature to about 21 K with respect to reference value.