نشریه مهندسی مکانیک مدرس
سال بیستم شماره 5 (اردیبهشت 1399)

In this article, the effects of normalization heat treatment on girth weld with containing titanium oxide and titanium carbide microparticles (X-65 grade of the gas pipeline) were evaluated. The Charpy test results show that in the normalized sample containing titanium oxide microparticles and titanium carbide microparticles compared to the no heat treatment sample (containing titanium carbide microparticles and titanium carbide microparticles), has been respectively increased by 33% and 18%. Also, the ultimate strength of normalized samples containing titanium oxide microparticles and titanium carbide microparticles compared to the no heat treatment sample (containing titanium oxide microparticles and titanium carbide microparticles) has been increased by 9% and 11%, respectively. The results show that the fatigue life in both normalized micro-alloy samples has been increased. The fatigue life in the normalized sample of titanium carbide microparticles has increased more than the titanium oxide microparticles. The fatigue test results show that the fatigue life (150-N force) has been increased by 36% in the normalized sample containing titanium carbide microparticles compared to the normalized sample containing titanium oxide microparticles. In this loading, the fatigue life (normalized sample containing titanium carbide microparticles compared to the no heat treatment sample) has been increased by 27%. The hole-drilling strain-gage results show that in the normalized sample containing titanium oxide and titanium carbide microparticles, hoop residual stresses have been respectively decreased by 12% and 8%compared to the no heat treatment sample (containing titanium oxide microparticles and titanium carbide microparticles).

Titanium is one of the most important microalloy elements used in the gas transmission industry. In this paper, titanium nano-oxide and titanium nano-carbide were added to two separate samples. Then the shielded metal arc welding (SMAW) was performed on high-strength low alloy steel according to welding procedure specification of the national Iranian gas company. The effects of annealing heat treatment on girth weld with containing titanium oxide and titanium carbide nanoparticles (X-65 grade of gas transmission pipeline) were evaluated. The Charpy test results show that in the annealed sample containing titanium oxide nanoparticles and titanium carbide nanoparticles compared to the no heat treatment sample (Containing titanium carbide nanoparticles and titanium carbide nanoparticles), energy absorbed has been respectively increased by %13 and %9. Also, the ultimate strength of the annealed sample containing titanium oxide nanoparticles and titanium carbide nanoparticles compared to the non-heat treated sample has been respectively decreased by %8 and %3. The fatigue life in both annealed nano-alloy samples has been increased. Also, the fatigue life in the annealed sample of titanium carbide nanoparticles has increased more than fatigue life in the titanium oxide nanoparticles. The fatigue life (Annealed sample containing titanium carbide nanoparticles compared to the no heat treatment sample) has been increased by %16. The hole drilling strain gage results show that in the annealed sample containing titanium oxide nanoparticles and titanium carbide nanoparticles compared to the non-heat treated sample, hoop residual stresses has been respectively decreased by %31 and %19.

The intervertebral discs are of the most important body tissues that provides the required flexibility for the spine during daily activities. Due to the lamellar structure of the Annulus Fibrosus, that surrounds the central part of Nucleus Pulposus, it may show anisotropic behavior in carrying the applied loads. Therefore, this aspect was investigated using the experimental data that were obtained by confined compression relaxation tests on samples in three different directions: Axial, radial and circumferential. To obtain the experimental values of the permeability and aggregate modulus as material parameters, test data in three directions were fit to the constitutive equations that were based on the biphasic relaxation model. The results for the permeability and aggregate modulus in three directions show that the material parameters are almost independent of direction and therefore, it is concluded that AF can be treated as an isotropic material under the compressive loads.

Efforts to reduce the ballistic effects and achieve the good results have always been important. In this article, perforated targets were used in order to reduce the penetration depth of projectile. The use of these targets in the case of high-speed projectiles reduces the number of parameters, such as penetration depth, cost of target products, and target area density. The goal of this paper was to present a new and complete analytical model for projectile penetration in ceramic/metal semi-infinite perforated targets, based on the Fellows analytical model, one of the most important models for penetration. First, the Fellows model was modified for ceramic/metal semi-infinite none-perforated targets. This modified model, while perfectly improving the results of the penetration depth at low speeds and had a better fit with experimental results at high speeds. In the new analytical model, 7 different states were considered for the projectile to impact the perforated target. In each of these states, the angle of oblique and the speed of the projectile after reaching the metal varied with respect to the ceramic thickness and the speed of the projectile's impact. Regarding the oblique impact on the metal, corrected relations were rewritten for new conditions. Finally, the depth of penetration was achieved according to the target conditions. The numerical simulation in Abaqus software was used to compare the results. The results of the new analytical model has good agreement with numerical simulation.

One of the most important purposes of the drop weight tear test (DWTT) is to achieve the value of fracture energy for better evaluation of tested steel properties. In the present research, experimental and numerical measurement of fracture energy in drop weight tear test specimen with chevron notch on API X65 steel has been carried out. The purpose of the determination of this energy is to estimate the strength of material due to fracture. The test specimen was cut from an actual spiral seam welded steel pipe of API X65 grade with an outside diameter of 1219mm and wall thickness of 14.3mm and then it has been machined to standard size. Then chevron notch with a length of 5.1 was placed in the middle of the specimen and the specimen was fractured under dynamic loading with an initial impact velocity of 6.3m/s. The maximum force of 229kN and 225kN were achieved for experimental and numerical data, respectively by drawing force-displacement and energy-displacement curves. The fracture energy of the test sample for experimental and numerical data was obtained as 7085J and 6800J, respectively by evaluation of the area under the force-displacement curve. Based on the results of experimental curves, about %59 of fracture energy was used for crack propagation and the remaining was used for crack initiation and plastic deformation of test sample near anvils and striker regions. In the end, drawing a linear curve for fracture energy of specimen based on the hammer velocity showed that the slope of this curve could be a good criterion for estimating the energy loss and fracture behavior of the test specimen.

The aerodynamic of Vertical Axis Wind Turbine (VAWT) is more complex than a horizontal axis wind turbine. In the present research, the combination of the Wagner unsteady aerodynamic model, static stall and Double Multiple Stream Tube (DMST) aerodynamic model have been used to investigate the aeroelastic behavior of VAWT. For this purpose, the DMST aerodynamic model, which is related to the vertical axis wind turbine aerodynamics model, has been used to obtain two parameters of the angle of attack and relative velocity. Then these two parameters have been applied to the Wagner nonlinear aerodynamics, which considers the effect of the static stall. This flexible nonlinear presented model based on DMST is called NFDMST aerodynamic model. One-degree of freedom of typical section and two-degree of freedom model have been investigated for static aeroelasticity and dynamic aeroelastic behavior, respectively. The VAWT blade experiences a variety of attack angles and relative velocity in a spin, so the goal is to obtain the instability velocity in a different position and consider the effect of aerodynamic and structure nonlinearity. The results show that the nonlinear aerodynamic model has accurate results and the aeroelastic design condition associated with -90degree azimuth angle, in which the minimum instability velocity is 45.2m/s. In addition, the change of instability speed of rotating airfoil in a spin is about 6%.

Galloping is a large-amplitude, low frequency, wind-induced oscillation of overhead power transmission lines with one or multi loops of standing waves per span which occurs due to wind flow. Based on the field data, numerous galloping oscillations occurs in the form of one loop oscillation which whereby high dynamic loads are imported to the support structures. In this research, the results of wind tunnel tests have been performed on a two-span distorted scale model with an ice-accreted cross-section under uniform and non-uniform aerodynamic loadings. Dead-end and suspension insulators have been applied to the support points. Then, based on identifying the most critical state of the lines oscillation, a solution has been proposed based on increasing their bending strength through the application of hardening local covering. The results showed that the most critical state of the cables oscillation in the galloping is related to the one-loop oscillation, which occurs as a result of interactions between the cables of adjacent spans under uneven aerodynamic loading and the use of suspended insulators, and the dynamic forces applied to the supports are about 20% more than the case when the cables oscillate due to the dead-end connections attached to the support structure. Also, applying the local covering with a length of 20% of cable span leads to a 27% reduction in dynamic support reaction of one-loop galloping.

In this paper, a novel method for designing the flight paths of an aircraft is presented based on the concept of conformal mapping. Here, a low-altitude route-planning problem has been considered. In this problem, maintaining the control effort to reduce aircraft's altitude and increasing the speed with the limitations of Terrain Following (TF) and Terrain Avoidance (TA) issues, is the main strategy of this performance maneuver. In the proposed approach, attempts are made to convert the real space including terrains and obstacles, in which their data are provided using a digital elevation map, into a pseudo obstacle-free virtual space with no barriers and altitude constraints. In this regard, the concept of conformal mapping has been used as a facilitating mathematical tool for this problem-solving space transformation. The transformation of the problem-solving spaces under the mapping leads to solving the problem of dynamic reflection, the performance criterion, and the real altitude constraints in the virtual space. It is noteworthy that in designing a path in a newly converted space, the effect of barriers on the formation of flight routes is somehow included in the equations expressed in the virtual space. The results of multiple case studies and numerical optimizations performed for 2D geometrical terrains and obstacles show that the proposed approach is more consistent with the basic flight concepts as well as real-world applications.

In this research, airfoil turbine blade airfoil Darriues vertical axis selected from three airfoils NACA0015, NACA0018 and NACA0021. The maximum ratio of the lift coefficients to the drag coefficient was determined in the Q-Blade software, and finally the airfoil NACA 0015 at speeds of 5 and 10M/s has the maximum value of the lift coefficient to the drag coefficient at an attack angle of 13 degrees equal to 2.58 and an attack angle of 6.5 degrees equal to 15.3. Then airfoil NACA 0015 was selected for numerical analysis and the turbulence method K-ω SST was used for numerical analysis and the results were verified using laboratory results. The wind turbine was designed and developed in CATIA software. Four wind fans were used to create wind power. The instruments used in measuring, testing and fabricating were calibrated. The results showed that the Self-Starting power of the porous blade in the speeds of 3, 4, 5, 7, 8m/s was %35, %33, %31, %37 and %48 less than the direct blade wind turbine, respectively.

In this research, the effect of several unconventional obstructions with cubic, spherical, cylindrical, and cone geometries on the propulsion vector of a convergent-divergent micro nozzle as a new method in propulsion vector control is experimentally investigated. For this purpose, a convergent-divergent nozzle was designed and constructed in small dimensions. This nozzle is such that the Mach number is its nominal output in full expansion conditions 2. The wall of this nozzle is designed to measure pressure variations with pressure holes. Also, in the nozzle wall, a duct has been created to apply a bulge inside the nozzle. Pressure sensors and the shadograph system have been used to pressure measurement and check the outlet flow field respectively. The total pressure of the calming chamber is constant in all experiments and is equal to 5.5 times. The results of this study show that the maximum deviation is related to an obstruction with a cubic geometry which is 2.1 degrees. Also, the geometries that have sharp corners are more shock-shaped and hit the opposite wall. In this research, the shock formed by a cubic barrier has hit the opposite wall, but with a spherical shaped and cone-shaped barrier, the shock comes out from the nozzle. Also, these results indicate that the axial force of the nozzle has been reduced to a very small extent.

Critically refracted longitudinal (Lcr) wave is the refraction of the longitudinal waves emitted from the first medium parallel with the surface of the second medium. The relationship between stress and wave velocity is expressed by acoustoelastic law. The theoretical relations for calculation of the acoustoelastic coefficient are so complex because of the need for measurement of material second and third-order elastic constants. The purpose of this research is the introduction of an accurate experimental method for acoustoelastic coefficient calculation, the effect of thickness of emission environment on the Lcr waves and, finally, the investigation of the stress measurement in shells and thin plates. By transmitting waves at the surface of the substance and investigating the waves received by the receiver transducers, the breakdown and the formation of different groups in the propagation of Lcr waves were detected. While the transmitted wave is composed of only one group. The results of this study show that longitudinal wave propagation in low thickness causes the formation of components of symmetrical and antisymmetric Lamb waves. By applying tensile stress on the sheet in which an Lcr wave was sent, it was determined that all groups received in the middle of the receiver transducer having a critical longitudinal nature behave identically to stress variations, while the Lamb's components behave differently to stress changes. Also, the study of variations of waves with stress less than yield point (up to 30MPa) shows that in a sample with a thickness of 0.5mm, the variations the flight time of the Lamb's S0 and A0 waves are 3.75 and 1.91 times the changes in the Lcr waves.

Sheet metal clinching process is a forming-based method for joining sheet metal parts. To ensure sufficient joint strength, it is necessary to design the forming tool optimally. This paper deals with numerical and experimental study of the clinching process of steel sheets of dissimilar thicknesses using a fixed die in order to optimize the geometric parameters of the clinching tool. In this study, using the orthogonal experimental design (OED) method and finite element analysis in Abaqus software, the important input parameters of tool design including punch radius RP, die cavity depth Pm, die groove width Lm and punch face angle PBA were optimized in order to achieve the highest clinch strength F as the target variable. The upper and lower sheets used in this study are 1.5 and 2 mm in thickness, respectively, and made of DX51D galvanized steel, manufactured according to EN10346/00 by Mobarakeh Steel Company. After running the experiments designed based on the OED in the computer, the optimal values of RP= 2.6mm, Pm= 1.4mm, Lm= 1.2mm and PBA= 1° and F= 2319N were obtained. Next, a clinched joint tool was designed and fabricated based on the optimum geometric parameters. The evaluation and comparison of clinch geometry and tensile strength obtained from optimum design simulation and the experimental counterparts demonstrated very close correlations.

Investigating dense flows containing cohesive sediments (turbidity currents) in water environment has been a main interest for researchers in hydraulic and fluid mechanic science. This kind of flow streams at bed surface because of higher density than water and penetrate to overhead water, which causes turbidness.  In the following research, this kind of flow has been modeled using two-phase simulation with smoothed particle hydrodynamics Lagrangian method. A SPHysics2D code has been developed for modeling, in which pressure value is explicitly calculated using equation of state. Also, Herschel-Bulkley-Papanastasiou single relation non-Newtonian viscoplastic model has been used for modeling cohesive sediment phase. After that for investigating the amount of penetration of cohesive sediment mixture in limpid water, advection-diffusion equation was used for developing code. Finally, one and two phase results obtained from the present model were compared to experimental models. The study shows that the present developed model is able to model these flows desirably and could be utilized for studying concentration amount, dense flow penetration and their propagation in water environment.

In this research, the development of technical knowledge and the implementation of modern control strategies on the IoT platform has been investigated. In this regard, using multi-layer hierarchical control over the IoT platform enables the communication and transfer of information from lower layers to upper layers, and the ability to process data and provide of control solutions considering new conditions from upper layers to lower layers. One of the main applications of this approach is the control of high-inertia systems, by optimizing the local layer by the main layer. For this purpose, a two-layer controller has been considered, that controls the soil temperature and humidity time-delay systems in the bottom layer in the form of PID and IFTTT control, respectively. Meanwhile, the upper layer uses the obtained information and the differential evolution algorithm (DE) and ANFIS controller, adjust the PID controller coefficients applied to the subsystem and IFTTT workstations, respectively. This reduces the size and complexity of the hardware used in the lower layers and consequently reduces the costs involved. It allows the implementation of sophisticated controllers, especially on large-scale plants. On the other hand, it is also possible to control high-inertia systems. The simulation results and practical tests indicated that this control strategy was very effective in IoT platforms.

The asphalt pavements are exposed to daily solar radiation; hence the asphalt pavements provide the remarkable potential to heat a working fluid such as water. Simple structure and ease of fabrication of asphalt solar collectors (ASCs) promise applicability and low-cost operation of this class of thermal collectors. The current experimental and theoretical investigation evaluates the performance, efficiency and dynamic of ASCs in real operating condition at Bam County, Kerman. In this research, to investigate the performance of ASCs, a 1.2m2 prototype was fabricated and its dynamics was monitored under 6 hours a day in two different flow rates of water. The results illustrate that increasing the flow rate of water to collector by 2 times improves the collector efficiency by 25%, while the difference in the inlet and outlet water temperatures decreases. Furthermore, by utilizing the experimental data, a theoretical approach was utilized to predict the performance of ASC in the other flow rates of water. The developed analytic approach has good consistency with the obtained experimental test. The analytic approach provides an effective method to estimate the performance of ASCs with appropriate accuracy, when the experimental results are unavailable.

Due to the specific characteristics of composite wood plastic and increasing of this product due to its compatibility with the environment, the quality of the appropriate surface area during the various machining processes on this material has been considered more than before. In this study, after turning operation with self-rotary tool on samples by changing the parameters of spindle speed, the feed rate and cutting depth, to measure and compare the surface roughness of the turning surfaces, the surface quality assessment has been investigated by microscope as well as numerical analysis of the process. The results show that during turning with self-rotary tool, for the cutting depth of 1mm and the feed rate of 22.0mm/rev by increasing the spindle speed from 500 to 710rpm, the surface quality of about 17% improved that this amount compared with conventional turning is also Improved about 37%. Also, due to increasing machining forces, by increasing the feed rate from 22.0 to 44.0mm/rev, surface quality is reduced by about 21%. Comparing the obtained values for surface roughness showed that after the feed rate, the spindle speed had the highest impact on the quality and health of the turning surfaces. Also, comparing the roughness of the measured surfaces during the finite element method and the experimental method showed the proper accuracy and adaptability of these two methods.

Diseases such as heart and brain attacks, which sometimes lead to movement disorders in people, has raised with an increasing community age. Nowadays, medical scientists replaced rehabilitation robots instead of traditional therapeutic methods. Design and implementation of a low-cost and home-like usable device for a patient was the primary goal of this research. In this study, a robot which consisted of cable and springs for movement in the transverse plane of the human body was introduced. For this purpose, stiffness and free length of springs were achieved by an optimization process, firstly. Afterward, static and dynamic workspace calculated to identify robot mechanical characteristic. At the end, controllability of the system in different paths in two conditions of presence and absence of the patient's hand was investigated and verified by the results obtained by the built device. Dynamic and static workspace indicates that a patient can do exercises with the help of the designed robot. Also, the control results and the obtained results from the implemented device test shows the stability of the control system and its ability to eliminate possible error occurring in the path.

Two-stage centrifugal separators are the last generation of gravity separators for the separation and upgrading of minerals. Gravity upgrading techniques are methods by which a mixture of particles with different dimensions, shapes, and masses can be separated by gravity, centrifugal force, and other forces by the flow of fluid, especially water (or air). The fluid flow inside such separators is always turbulent. The selection of a suitable turbulence model is an important stage for the prediction of the fluid flow pattern in numerical simulation. The purpose of this research was to find the suitable turbulence model for the prediction of hydrodynamic parameters in a two-stage centrifugal separator using computational fluid dynamics (CFD) modeling. For this purpose, multiphase simulation of the separator has been performed using five turbulence model including k-e, renormalization group (RNG k-e) and Reynolds stress model (RSM). Air core pattern, velocity distribution and partition curve of discrete phase were used for evaluation of the effect of turbulence model on the flow field. The results of the CFD simulation were validated using experimental data. The difference between the results of RSM simulation with the experimental results for fluid recovery, air-core size in the first and second stage of separator were 4.73%, 4.3% and 5.2%, respectively. The results of turbulence models of k-e and RNG k-e were not in accordance with the experimental results.

The use of ultrasonic vibrations to reduce the temperature in bone drilling is one of the most important advanced processes that has attracted the attention of bone surgeons. Therefore, the study of temperature behavior in the ultrasonic-assisted drilling process and the prediction of temperature behavior have an important effect on improving the use of this method in orthopedic surgery. In this research, the influence of process parameters on change in the temperature was studied using response surface methodology and data analysis. Data analysis was carried out to find the effect of process factors such as rotational speed, feed speed, and ultrasonic vibrational amplitude and their interaction on the temperature. Moreover, using the statistical method of Sobol sensitivity, the effect, and sensitivity of each input factor on temperature were studied. The results show that the use of ultrasonic vibrations reduces the temperature, and rotational speed (%48), vibrational amplitude (%33) and feed speed (%19) had the greatest effect on temperature in ultrasonic-assisted bone drilling, respectively. As a result, the use of ultrasonic vibration can reduce the dependency of process temperature on the feed speed, and thus make it possible to perform surgery in a shorter time. The minimum temperature is 37°C at the rotational speed of 500rpm and the feed speed of 20mm/min and the vibration amplitude of 15μm.

In the present study, multilayer nanocomposites fabricated by accumulative roll bonding (ARB) process. Aluminum sheets, copper sheets (with 0.1 and 0.3mm thickness) and multiwall carbon nanotubes (MWCNTs) were used as experimental materials. The rolling process continued to five cycles. Then, microstructure, hardness, tensile strength and electrical conductivity of nanocomposites were investigated. Necking and fracturing recognized as mechanisms of copper layers distribution in the aluminum matrix. The bonding strength between layers increased with the number of cycles due to the improvement of MWCNTs distribution. The results show that the hardness of aluminum increased with increasing copper layer thickness and these increases were about 30 and 32% for composites without nano reinforcements and nanocomposites contain MWCNTs, respectively. The highest hardness (147HV), is related to the sample containing carbon nanotubes and 0.3mm copper sheet, after five rolling cycles (446% increase compared to aluminum sheets). The results confirm the positive effect of copper and the MWCNTs on the improvement of strength. The highest strength and elongation is observed in the aluminum-copper-MWCNTs nanocomposite after four cycles. The results also indicated that the addition of copper and MWCNTs can simultaneously increase the strength and electrical conductivity of the resulted composites.

The lubricant's ability to maintain the dynamic stability of rotor particularly in special conditions such as operating at critical speeds and instantaneous turbulences in loading or lubricant properties is always one of the most prominent characteristics of the journal bearings. Aspect or length to diameter ratio of bearing is an important factor that in different loading conditions will have an obvious effect on the performance of the trapped lubricant film between the rotor surface and bearings shell. So, the effects of aspect ratio on the damping of rotor disturbances with linear and nonlinear dynamic analysis approaches are studied in this research. Initially, the static equilibrium point of the rotor center in noncircular two, three and four lobe bearings space is obtained using the governing Reynolds equation of micropolar lubrication for different values of aspect ratio. Later, assuming the rotor perturbation as the limit cycle oscillations around the equilibrium point, critical mass and whirl frequency ratio are determined as the linear dynamic stability indexes for recognizing the converging disturbances. In nonlinear analysis model, the simultaneous solving of the lubrication and the rotor motion equations in successive time steps with Runge-Kutta method is done to differentiate the converging or diverging rotor perturbations. Results show that decreasing the aspect ratio improves the stability and the chance of controlling disturbances and returning the rotor center to static equilibrium position. Comparison of linear and nonlinear dynamic analysis results also indicates more cautious behavior and limited stability range of linear model in most of investigated cases.

The amount of entropy generation during the fatigue loading is treated as an indicator of the damage accumulation in the material. Using the thermography technique and recognizing the temperature field distribution at a specimen surface under cyclic loading and calculating the dissipated energy and also considering the possibility of the specimen heat transfer with the environment, the net entropy production rate of the system can be computed.  This research has been conducted to feasibility study and applicability of the methodology through numerical modeling and analysis. In this thesis, using the finite element numerical method and in the framework of Abaqus software, simulations of fully reversed bending are carried out on the standard specimens of aluminum (Al6061-T6) whose experimental test results are available in the literature. Based on results of the mechanical and thermal analysis, calculating the entropy production rate, fatigue fracture entropy, damage variable and remaining life assessment based on this variable are performed. The results obtained from the numerical simulation are compared and validated with the results of experimental tests. Also, a numerical analysis is carried out to estimate the temperature enhancement and fatigue self-heating phenomenon due to the cyclic loading based on the strain-life curve characteristics and dissipated energy on the axial specimen made of (AISI 4340). The results obtained from the research indicate that the infrared thermography technique as a non-destructive evaluation method in the low cycle fatigue range, is a suitable tool for the temperature field evaluation and subsequently, the accumulated damage estimation in material.

Rolling ring is one of the most important metal forming processes for fabricating rounded geometries with optimal mechanical properties in the environmental direction. The ability to fabrication of two-layer rings can be used in many industries. One of the properties of these rings is the lightweight with high strength or wear resistance along with high strength. In this research, we have tried to study the ring rolling process of the bonded two-layer ring and its effective parameters during the process using finite element analysis by ABAQUS software and experimental test. The rings are attached for process simulation and empirical testing. In the end, a ring of two-layer of pure Lead 99.99% and Tin 63% was formed. Based on the results obtained from this analysis and according to the dimensions and parameters considered for performing the process, the tension created in the bonded two-layer ring is between the values of 1.146×105-1.800×107Pa and it has a strain of 0-1.187. Its contours of strain and stress are represented to better understand the process. Considering the results obtained from the simulation of the process, an experimental study of the ring rolling process of the bonded two-layer ring was conducted. The method of this study was first designed by the modeling software to design the casting model and then by designing the test, the number of tests required for the experimental test was obtained and then the number of materials needed for the test was calculated. After testing, the mechanical and metallurgical properties of rolled double rolled rings were investigated.

Now a day most countries are interested in renewable energy due to the many problems with fossil fuel use. One of the best types of renewable energies is solar energy and can be produced in electrical, thermal and hybrid forms by photovoltaic cells equipped with thermal collectors. In this research a systemLinear parabolic focusers equipped with photovoltaic cells were designed and simulated in Optic Ray Tracing and Solidworks software and compared with experimental results. The thermal collector was simulated in a photovoltaic-thermal hybrid system with two longitudinal and transverse arrangements with internal diameters of 8 to 14 mm at three discharge levels.Simulation results of two longitudinal and transverse arrangements showed that the thermal efficiency in the longitudinal arrangement was better than the transverse ones. and by increasing diameter from 8 to 12 mm the thermal efficiency increased and the thermal efficiency from 12 to 14 mm alignment of the pipes did not change much. Also by increasing the fluid discharge from 1 to 3 l/min the thermal efficiency due to the decrease in thermal losses and the electrical efficiency due to the decrease in temperature Photovoltaic cell surface increased. Comparison of the simulation results and the experimental evaluation showed that the maximum thermal and electrical efficiency for the data Simulations were 61.18% and 12.58%, respectively, and for field data is calculated 58.14% and 12.03%, respectively.

Currently, composite structures have many applications in various industries including aerospace, automotive, marine, and petrochemicals. In most of these applications, the structure is under dynamic and static loads and it can cause buckling, vibration, and fatigue. Therefore, the static and dynamic analysis of these structures is essential in order to understand their characteristics, including buckling, natural frequency, and the shape of vibrating modes. One of the most important non-destructive methods for predicting the buckling load of the structure is the vibrational correlation technique (VCT), which is based on frequency variations with the axial load. In this study, an experimental study of the buckling load of composite sandwich plates with lozenge core has been investigated. The hand lay-up method has been used for fabrication of the composite sandwich plates. One of the specimens was used for the modal test. In order to verify the results of the VCT, the buckling load of four specimens was calculated by the experimental buckling test. The error of VCT was 2.1 %. Hence, the efficiency of the VCT for composite sandwich plates with lattice core was confirmed. Also, by investigating the effect of applied load percentage on the accuracy of the VCT, it was found that for the applied load of more than 63% of the buckling load, the accuracy of prediction of the vibrational correlation technique is acceptable.