مجله مکانیک سازه ها و شاره ها
سال سیزدهم شماره 3 (امرداد و شهریور 1402)

Balancing accuracy and computational cost in modeling and analyzing engineering problems has always been a crucial concern in the field. The same principle applies to the modeling of wave propagation in structures and deriving dispersion curves, which are crucial in structural health monitoring and material property identification. The importance of maintaining this balance appears especially in cases where there is a need for repetition in modeling. In this study, we aimed to improve the accuracy and computational cost of the semi-analytical finite element method by incorporating hierarchical shape functions. The results indicate that using appropriate shape functions can enhance the performance of the semi-analytical finite element method for modeling wave propagation in structures. The study also investigated the impact of the number of degrees of freedom on the calculation of the cutoff frequency, the accuracy of the dispersion curves and the increase in modelling error as a result of this point.

In this paper, the flow field is investigated by solving the acoustics of the launch vehicle for a specific sample model . During the launch of a space vehicle, the intense sound pressure levels created around the vehicle. Therefor identification and analysis of acoustical loads of launch vehicle is an important issue of consideration. In this study, for calculation of acoustic pressure levels and prediction of noise at the discharge of the nozzle jet, presented formula of Eldred was used with the assistance of MATLAB software and the algorithm and code were obtained to handle acoustical loads. In this research, the geometry of one launch vehicle sample was used. The effective parameters including the slope of deflector and the ratio of nozzle outlet distance from launch pad to the jet outlet diameter, were identified and investigated. The curves of sound pressure levels and contours of SPL around the launch vehicle field are obtained versus to the interval of specified frequencies.

In this paper, two new algorithms are presented for calculating the workspace of parallel robot considering the limitation of active joints movement by combining interval analysis with two refinement methods. In proposed methods, the kinematic expressions of the chains are calculated based on the joint coordinates and geometrical constraints governing the kinematic chains of the parallel robot. In the following, two methods are presented for calculating the workspace of parallel robot by combining the concepts of interval analysis with two refinement algorithms, namely mean value form and slope form. The two presented algorithms and the interval analysis method without refinement operation are implemented on the 3-RRR planar parallel robot and the constant-orientation workspaces are obtained for different limitation of active joints movement. For the sake of comparison, the constant-orientation workspace of 3-RRR parallel robot is also obtained using the geometric method, and it is shown that if refinement is used in the interval analysis, the workspace of the parallel robot is entirely consistent with the results of the geometric method.

Selection of the proper material in manufacturing lightweight railway vehicles is a complex and essential challenge considering the available engineering materials. In this paper, the appropriate material has been selected for manufacturing railway wagons using a multi-criteria decision-making technique. Six engineering materials including DP600 steel, TRIP700 steel, TWIP steel, 6005-T6 aluminium, 60826-T6 aluminium and porous aluminium with closed cells were considered as engineering alternatives. Also, density, yield strength, ultimate tensile strength, the ratio of yield strength to maximum tensile strength, Young's modulus, cost and corrosion resistance were considered as selection criteria. To select the best material according to the mentioned criteria, the MOORA multi-criteria decision-making method was applied. By weighting the criteria and performing the analysis, it was found that the TWIP steel and 6082-T6 aluminium were chosen as the best candidates and aluminium foam and DP600 steel were selected as the worst candidates. Due to its maximum yield strength and ultimate tensile strength compared to other candidates, TWIP steel was chosen as the best material considering all criteria. Furthermore, the 6082-T6 material was chosen as the second-best material due to the high ratio of yield strength to ultimate tensile strength (0.88) and lower density and higher corrosion resistance than steel materials.

There are many engineering applications of pipes at different scales for conveying fluid. The dynamic characteristics of a spinning pipe conveying fluid in vertical configuration equipped with piezoelectric patches are analyzed in this study. Based on Euler–Bernoulli beam theory, the governing equations of the system are derived by applying Hamilton’s variational principle. In this equations, the gyroscopic coupling, electromechanical coupling and gravitational effects are considered. The Galerkin’s method is used to discretize the governing equations of motions. Numerical results are investigated to predict the influences of the piezoelectric layer spanning angle, spinning speed, pipe length and flow velocity, on the unbalance response of the system. The results indicate that, depending on excitation frequency, the vibration amplitude can be decreased or increased by increasing the piezoelectric layer spanning angle. The results of this research can be used to conduct piezoelectric pipe design and performance predictions for future pipe vibration control and energy harvesting applications.

In this research, the efficiency of error estimation based on two methods of recovering the equilibrium stress of patches and superconvergent points in guiding the adaptive solution of nonlinear problems by isogeometric method has been investigated. Also, by analyzing elasto-plastic problems based on material properties, and adaptive solution by temperature gradient method, the stress improvement process has been investigated. The method of the adaptive solution of this research is based on the movement of control points and it is used in stress recovery, taking into account the difference between the exact stress level and the stress level obtained from the isogeometric analysis for each element, as a criterion to determine the amount of error in it. The element is obtained. For this purpose, the modeling of two problems in the non-linear range, which has an exact solution, has been considered. The results have shown that the total norm difference of exact and approximate error in both stress recovery methods used is more than 33% and in the direction of improving the network of control points. Also, the method by equilibrium patches is more effective than the method based on superconvergent points, which can be used as a suitable solution to improve the stress field.

The orientation and shape of joints in cracked structures significantly impact the mechanical behavior of components and the optimization of the construction process. This study investigates the mechanical behavior of titanium grade 2 cracked components under quasi-static tensile loads, considering the crack length (central cracks of 1, 2, and 3 cm) and patch type (rectangular, oval, and hexagonal shapes) parameters. patch connections to the 50 × 40 × 0/5 mm titanium grade 2 base plate are examined according to ASTM E 8/E 8M – 08 and ASME SA-370 standards. A novel approach to patch connection is employed using the advanced diffusion method (SPS) at a temperature range of 820-850 degrees Celsius and a pressure of 47-50 megapascals, with potential applications in the aerospace industry. A scanning electron microscope (SEM) is used to investigate the quality of the joint area of the cracked pieces joined together. Results show that an increase in crack length leads to a decrease in component resistance under static tensile loading. The hexagonal patch demonstrates better resistance with averages of 0/534 and 0/691 compared to rectangular and oval patchs, respectively, due to its superior stress distribution along the entire length of the cracks.

The mechanical response of crystalline materials is affected by the flow and hardening of dislocations; that to describe them as a material model in finite element calculations, the flow and hardening parameters are implemented in the crystal plasticity code. In the present study, flow and hardening parameters for 1100 aluminium alloy were characterized by combining the experimental nanoindentation test and 3D crystal plasticity finite element simulations. Extracted parameters were validated by comparing the stress-strain curves of the experimental uniaxial tensile test and simulation of 3D crystal plasticity finite element on single crystal and polycrystal models. Also, the effect of the friction coefficient in determining the flow and hardening parameters was discussed. The results of this study showed that (i) parameters of initial yield stress, reference shear strain rate, and saturation stress, respectively had the highest positive correlation with the maximum load; (ii) the load-displacement curve obtained from the simulation of the nanoindentation test using the characterized parameters has a relative error of 0.50% compared to the experimental nanoindentation test at the maximum indentation depth; (iii) The characterized parameters significantly can estimate the yield stress and ultimate tensile strength with a relative error of 2.60% and 0.20% for the single crystal model and 10.18% and 12.44% for the polycrystal model, respectively. However, while accurately modeling the yield zone in the polycrystalline model, the accuracy of the characterized parameters is affected by the grain boundary orientation.

Parabolic solar collector, use highly reflective materials to collect and concentrate the heat energy from solar radiation. The thermal efficiency of the solar collectors increases by using nanofluid. It is necessary to consider some thermal properties of nanofluid and operating parameters to reach maximum efficiency. This article presents the heat transfer of a nanofluid in the absorber tube of a parabolic collector with non-uniform heat flux on the wall. Two types of nanofluids were utilised and prepared TiO2-Syltherm 800 and Al2O3-water with 1.0%, 2.0%, 3.0%, and 4.0% nanoparticle volume fractions are used as working fluids. Reynolds number is between 10,000 and 80,000. Comparing the Nusselt number of TiO2-Syltherm 800 and Al2O3-water nanofluid demonstrated that the nanofluid has better thermal performance than the base fluid. The highest percentage increase in Nusselt number of TiO2-Syltherm 800 and Al2O3-water compared to their base fluid is 66% and 57%, respectively. The highest increase in Nusselt number is related to TiO2-Siltherm 800 nanofluid. at Reynolds 10000 and concentration of 4%. In this case, the Performance evaluation criterion, PEC, is 2.93. For both nanofluids, PEC increases with increasing concentration. With increasing Reynolds number, PEC decreases for TiO2-Siltherm 800 and increases for Al2O3-water nanofluid.

In this article, the rate of freshwater production in the floating solar still using pumice stone is investigated. In this device, the use of a one-way valve has given this device the ability to direct lake or pool water into its basin in a controlled manner. By placing a type of photothermeral material (pumice stone) in the basin of the solar still, the efficiency of the device and the amount of fresh water production increase compared to the simple device. All experiments were performed in Semnan in Iran. The temperature, productivity, and exergy efficiency of this water softener without the use of limestone and modified with limestone were compared. Finally, a cost analysis wass performed to check the economic status of the device. The results showed that the daily production rate of the floating solar still modified with pumice stone in autumn and spring was 113 and 219 cm3, respectively, and for the conventional floating solar still was 82 and 189 cm3, respectively. The costs of producing each liter of fresh water for a floating solar still modified with pumice stone and the conventional floating solar still for the autumn were 0.0847 and 0.104 $/m2, respectively, and in the spring, this cost for the floating solar still modified with pumice stone is 0.043 $/m2.

The hydro-acoustic behavior and noise of marine propellers, especially in underwater vessels and submarines is of great importance. The main purpose of this article, is numerical modeling of the hydrodynamic noise of a high skew propeller sample from MAU marine standard series using computational fluid dynamics method with the help of Ansys-Fluent software under open water conditions. In the numerical simulation, the DES turbulence model was used, which is a good model for small vortices modeling near the wall. In order to validate the hydrodynamic and hydr-oacoustic results, the available data from the DTMB4119 benchmark propeller has been used. Comparison of the sound pressure level obtained for the DTMB4119 propeller in the present work and the available data from the reference shows a good compliance at frequencies higher than 20 Hz, but at frequencies lower than 20 Hz, about 20% error is observed. Based on the obtained results, with the increase in the number of propeller blades, the amount of vortex density around the blades decreases. The increase in the number of propeller blades has caused an increase in the average level of radiation noise in receivers at the axial direction. Increasing the number of propeller blades from 2 to a maximum of 7 blades has been able to reduce the radiated noise level in the axial direction by 15 decibels. In the radial direction, except the two-bladed propeller, the dipole radiated noises caused by the 3-7-bladed propellers have similar fluctuations.

The classical conduction heat transfer model which considers infinite thermal propagation speed, named Fourier model and its equations are in elliptic form and has numerous applications. This model is not appropriate for many industrial applications especially in medical applications and thus hyperbolic or non-Fourier model that considers finite heat propagation speed should be used. Temperature control in certain points of such systems obeying these types of equations is an important problem which has been studied in this paper. In this paper, firstly, the validity of the conjugate gradient method is approved using a known heat flux at a system boundary and then the method is used to estimate the boundary condition which leads to a desired temperature distribution in the geometry. Also, the modeling and inverse problem solution are studied for noise in input data and results showed appropriate accuracy and convergence even for considerable noise in input data. Also, the modeling and inverse problem solution are studied for noise in input data and results showed appropriate accuracy and convergence even for considerable noise in input data.