مجله مکانیک سازه ها و شاره ها
سال دوازدهم شماره 1 (فروردین و اردیبهشت 1401)

This paper is dedicated to a cooperative search and coverage problem in which we applied a distributed coverage control algorithm for automated victim search using a cooperative multi-UAVs system. Disaster management is a competition with time. So, fast response to disaster can significantly decrease damages and losses. It is obvious that a comprehensive map of the affected area immediately after disaster occurred, helps disaster control unit to quickly and initially evaluate the degree of damages, amount of economic losses and casualties. Therefore, they can plan for disaster management operations with more and detailed information. We considered a rectangular surveillance region in which four fixed-wing UAVs fly over the affected area to exactly localize the 18 stationary targets randomly distributed in the environment, as well as maximizing the coverage. For this purpose, UAVs cooperatively build the cognitive maps including Target Probability Map and Uncertainty Map. Then based on cognitive map and also their prediction from three steps ahead of their own and also neighboring agents moves, UAVs decide about their optimal collision-free paths. Comparison between cooperative and non-cooperative methods indicates that in cooperative distributed scheme, coverage percentage and global average uncertainty converges to their admissible maximum and minimum value in a considerably less time, respectively.

The knowledge of applied loads on the floating structure is necessary from the beginning of design procedure. One of the most important loads which is applied on the floating structure is the impact loads due to the rapid impact of the ship with the water surface. This type of load, known as slamming load which can increase the yield level and althought cuases high-amplitude vibrations in the struture, which are also known as whipping vibrations. The purpose of this paper is to investigate slamming loads and whipping vibrations in catamarans. In this paper, using computational fluid dynamic method (CFD), hydrodynamic loads and impacts on the vessel are investigated. Then, using the one-way fluid-structure interaction method, the effects of wave slaming impact on the catamaran is investigated and also the resulting vibrations is be investigated. Then, using the Miner-Palmgren cumulative life estimation method and the rainfall count cycle method, the effect of this type of vibration on the failure and destruction of the floating structure is investigated. The results illustrate that the whipping vibration have a significant effect on the life of catamaran.

Replacing steel pipes with composites is one way to combat corrosion in fluid transfer pipelines. Glass fiber polymer composites are corrosion resistant and in addition to having high strength, they are a cheaper option than steel pipes. In this paper, the mechanical behavior of composite and steel pipes used in oil transmission pipelines for fault angles at 45, 61, 75° under reverse fault is investigated using Abaqus software. The mechanical strength and maximum displacement size of composite pipes buried under reverse faulting are compared with steel pipes. The onset of damage in GREs and the yielding point of steel were predicted using Hashin’s initiation criteria considering four failure modes and the von Mises Stress, respectively. Quasi-static solution was used to analyze the soil’s behavior due to nature of loading. The yield point of soils was calculated according to Mohr-coulomb. The results showed that In reverse faulting, the compressive force will often be the yielding factor of buried pipes and In order to safely operate the buried pipe, steel pipes should be used at angles above 61° of reverse fault and unidirectional composite pipes at angles less than 61°. In addition, the maximum allowable displacement of the reverse fault at different angles of the fault is at least 70% higher for the unidirectional composite pipes of glass-epoxy fibers than the steel pipes. The results of this study can be used in the design studies of composite buried pipelines in areas with corrosive soils and active fault crossings.

Thermal Energy Storage (TES) is a high potential technology for different thermal energy applications. TES technology can be an appropriate approach to fill in the gap between electrical energy supply and demand. One efficient and modern method to store thermal energy is the use of phase-change materials (PCMs). The aim of this research is to study the feasibility of the use of PCM materials in the combination of free cooling and compression refrigeration systems. The combined system should be analyzed from energy and exergy viewpoints, in order to evaluate the amount of saved energy and the system performance upgrade. The medium temperature PCM coupled with the free cooling system, can be charged during the cool night time. During the hot day time, discharging this PCM would lower the temperature of the air entering the condenser and consequently; lower the HVAC system energy consumption. On the other hand, PCM discharge happens during the peak-hours in which the electrical energy price is high. Therefore, using PCM would reduce the building energy bills. Technical and economic results show that the proposed combined system would reduce the total electrical energy consumption up to 4.85%, energy consumption in peak-hours up to 14.76% and the electrical energy bill up to 6.71%.

Present paper has experimentally and numerically investigated the mechanical behaviour of composite sandwich panel with novel M-shaped lattice core subjected to three-point bending and compressive loads. For this purpose, a composite sandwich panel with M-shaped core made of carbon fiber has been fabricated in this experiment. In order to fabricate the sandwich panels, the vacuum assisted resin transfer molding (VARTM) has been used to achieve a laminate without any fault. Afterward, polyurethane foam with density of 80 Kg/m3 has been injected into the core of the sandwich panel. Then, a unique design was presented to sandwich panel cores. The study of force-displacement curves obtained from sandwich panel compression and three-point bending tests, showed that an optimum mechanical strength with a considerable lightweight. It should be noted that the experimental data was compared to numerical simulation in ABAQUS software and it turned out that numerical results are in good agreement with experimental ones and make it possible to use simulation instead of time-consuming experimental procedures for design and analysis.

While bare Aluminum does not have the desired properties for aerospace and naval industries, when converted to composite by reinforcing materials, the desired mechanical and other properties are achieved. In this study, Aluminum 7075-T6 was selected as the base phase and Silicon Carbide (SiC) particles were used as the reinforcing phase for the composite for the experiments on the yield strength, ultimate tensile strength, and fatigue life. According to the experiment design, the SiC was prepared with three different particle sizes, in nanometer, submicron and micron scales. SiC powder with different mass fractions with Aluminum was cast by vortex casting by a resistive furnace equipped with an electromagnetic coil and a vacuum pump, and the composite samples were cast according to the experimental design. The samples were then subjected to dissolution. Afterward, T6 heat treatment was performed on the samples. Ultimately, the prepared experimental samples were subjected to tensile and fatigue tests, followed by the relevant standards. According to the results, reinforcement of aluminum 7075-T6 with SiC particles improved properties such as yield strength, ultimate tensile strength, and fatigue life, but reduced the elongation and ductility of the samples. The results indicate that 1% sample with nanoparticle size has improved the final tensile strength by 21.33% and has the highest fatigue strength.

Nowadays analysis of mechanical seals is of great importance since it causes improvement in the performance of mechanical systems and it enables one to reduce the leakage in the seal. In this paper a MTM 30 mechanical seal has been analyzed. The analysis has been conducted in both thermal and isothermal modes using finite difference method. The pressure distribution as well as film thickness has been predicted and compared to the published results available in the literature. The results show that considering thermal effects results in an increase in pressure for 16.55% and a reduction in film thickness of 33.4% compared to the situations in which isothermal analysis is conducted. A parametric study has been conducted which evaluates the effect of speed, viscosity, and load on the performance of the mechanical seal. Film thickness, pressure distribution, and film thickness has been studied in this parametric study. The results in this method have been shown to be in good comparison with other results.

In this paper the research has been performed on the cross-axis flow Lucid spherical turbine. Three-dimensional steady numerical simulation is used to determine power output and performance of this kind of turbines for low velocities in a channel. The k-ω SST turbulence model is used to perform the turbulent steady flows around the turbine. Further, Bachant and Wosnik's experimental data reported for spherical Lucid turbine, is employed to confirm the simulations. The influence of three effective parameters of blades, including the chord length, the number of blades and the type of airfoil section on the turbine performance are investigated over a range of tip-speed-ratios. It was found that increasing the blade chord length in lower speed tip ratios cause to increase the power coefficient up to %15 compared to the original version. Also, for the turbine with three blades, the best results were obtained by which, the power coefficient increased by 12.5%. Finally, it is obtained that using asymmetric airfoil section for blades has a positive effect on the turbine performance.

In the present study, the dynamics associated with single bubble growth and its detachment has been studied using passive acoustic emission and high frame rate imaging methods. Synchronization of imaging with acoustic data acquisition demonstrated the functionality of the acoustic emission method in studying the dynamics of bubble growth and detachment. The investigations showed that the maximum amplitude of the oscillations in the time series of the acoustic emission signal occurs shortly before the bubble detaches. Instantly the rate of bubble volume rise is decelerating. in accordance with the dominant frequency of the acoustic emission wave that arises at the same time with the jump in acoustic time series, the bubble size based on the Minnaert equation with the corrected coefficients is estimated to be only 1.37% different from the results of image processing. According to the sequence of images recorded from the bubble growth frames, the ratio of the vertical and horizontal axis lengths of the bubble is continually changing during the bubble growth period and eventually, the bubble detaches from the orifice when the ratio approaches 1. Although by detachment, the bubble does not have a spherical shape due to the pressure forces.

Mathematical modeling plays an important role in designing and optimizing of heat transfer systems. Due to radiation heat transfer mode in a vacuum environment, the behavior of the system is very nonlinear. In this paper, a new nonlinear ODE model for a vacuum box heat chamber is developed which is suitable for online computation, and the validity of the model is investigated using an experimental set. A specific input is given to the both mathematical model and the experimental set. With some of this data, system parameters are extracted using the genetic algorithm. Then, the behavior of the mathematical model and the experimental system with the extracted parameters are compared using cycles that have not been used in optimization. The comparison shows the accuracy of the proposed mathematical model. Then, to examine the model more closely and to observe the effect of model parameters on system behavior, the Monte Carlo method was used to analyze the overall sensitivity of the model. For this purpose, Latin hypercube sampling and partial rank correlation coefficients have been used to rank the parameters. The results show that the thermal conductivity of insulators is the most important parameter affecting the behavior of the system.

A thermo-economic performance optimization has been carried out for a shell and tube condenser TEMA-E. In the considered model, the irreversibilities due to heat transfer between the hot and cold stream are taken into account. The objective function is defined as the actual heat transfer rate per unit total cost considering lost exergy and investment costs. The optimal performance and design parameters which maximize the objective function have been investigated. The effects of the technical and economical parameters on the general and optimal thermo-economical performances have been also discussed. The results show that the objective function increases with increasing heat capacity ratio and decreasing inlet temperature and ambient temperature ratio. The dominant term in entropy generation in this study is due to the heat exchange between the condensed fluid and the cold fluid. According to the operating conditions of the heat exchanger, a correlation has been obtained for the thermal efficiency that maximizes the objective function. Optimal value of the design variables obtained from Pattern search method and the Ant Lion Optimizer method are relatively different at about 0-0.13%; depending on the type of optimization method and its internal operators. But the optimal value of the objective function in both methods is approximately 16.08. The analysis and optimization presented herein may provide a basis for both determinations of the optimal performance parameters for real heat exchanger.

In this paper, the performance of a piezoelectric pump is numerically simulated by considering the main equations of fluid flow, elastic diaphragm and electric field. The simulation is conducted using the two-way fluid-structure interaction approach, as the fluid and structure affect each other in performance of piezoelectric pumps. The simulation results are compared with experimental results and the maximum error in steady analysis is obtained 9.66% and in un steady analysis is 8.95%. Due to the good time response and the possibility of flow control by piezoelectric pumps, the feasibility of using piezoelectric pumps as dosing pumps is investigated. The simulation results showed that the designed piezoelectric pump could be used as a dosing pump; so that if the pilot gas pressure reducing station operates at its maximum capacity (10,000 cubic meters per hour), the proposed pump will inject the required odorant at a voltage of 200 volts and a frequency of 0.167 Hz. The proposed odorizer system, in addition to the possibility of precise control of the amount of injected odor, has a lower initial cost and operation cost than the present bypass system at the station.