JOURNAL OF MECHANICAL ENGINEERING AMIRKABIR (AMIRKABIR)
Year:2025 | Volume:57 | Issue:6|Papers Count:6

Due to global problems such as increasing energy costs, environmental pollution and global warming, the use of renewable energies such as solar energy has gained special importance. Photovoltaic/thermal (PV/T) systems with the ability to simultaneously produce electricity and heat are an efficient way to use solar energy. This paper investigated the performance of a standalone photovoltaic/thermal system and a combination with thermoelectric generator (TEG) module’s, heat well and fan at different mass flow rates of 100, 200 and 300 cm3/min under the climatic conditions of Semnan, Iran. The results showed that the maximum power output for the photovoltaic/thermal system at three different mass flow rates was about 78.2 W, 78.7 W and 9.7 W, respectively, and with thermoelectric module’s was 79.1 W, 78.81 W and 4.84 W, respectively. The maximum thermal efficiency for the photovoltaic/thermal system at a flow rate of 100 cm3/min was 31.9 % and the electrical efficiency at a flow rate of 300 cm3/min was 14.1 %, and with thermoelectric module’s it was 27.3 % and 14.9 %, respectively. The Nusselt number also improved by an average of 28.6 % at three different flow rates compared to the standalone system. This improvement in efficiency and heat transfer provides a bright prospect for the application of these systems in buildings and commercial spaces to provide simultaneous power and heating.

Maintaining upright stability is a fundamental challenge due to the dynamic instability of the human body, particularly in older adults, where age-related decline in the nervous system increases the risk of falls and related injuries. This study evaluated neural response quality in balance control by analyzing the balanceable regions and reaction times. Using a single inverted pendulum model in the sagittal plane, the mechanical, experimental, and real balanceable regions were determined for seven healthy young adults (mean age: 24 years; 4 females, 3 males). Reaction time tests (visual, auditory, and tactile) were conducted using an LED, buzzer, and piezoelectric sensor, while an out-of-balance experiment was performed using a sudden perturbation near the center of mass. Data were recorded with a force plate (600 Hz) and motion capture cameras (125 Hz). Results indicated that auditory reaction time (144–186 ms) was shorter than visual (188–260 ms) and tactile (153–238 ms) reaction times. The ratios of experimental to mechanical and real to mechanical balanceable regions ranged from 41% to 74% and 42% to 91%, respectively. The dynamic model was validated against experimental data and demonstrated that reaction time significantly reduces the balanceable region, with males responding approximately 10 ms faster than females. These findings have potential applications in designing rehabilitation programs, enhancing athletic performance, and enabling early diagnosis of neurological disorders.

The suspension system plays a critical role in off-road vehicles, exerting a considerable influence on control, stability, handling, and the ability to adjust the spring response with variations of the vehicle weight. This study investigates the effect of adding an air spring into a double wishbone suspension system, which is further augmented by a shock absorber and a torsion bar. Initially, the differential equations governing the air suspension system—characterized by nonlinear parameters—are simplified to calculate the air spring's coefficient. Subsequently, a model of the double wishbone suspension system, including two hydraulic shock absorbers, a torsion bar, and an air spring, is modeled in Adams Car and TruckSim software. The model analyzes the force-displacement relationship of the air spring based on the main input data such as the stiffness coefficient of the torsion bar, the force-velocity characteristics of the shock absorbers, the suspended and unsuspended masses, and the tire stiffness coefficient. The performance of the vehicle is studied for the suspension system with and without an air spring. The kinematic and Compliance tests are conducted utilizing Adams Car while handling, stability, and comfortability evaluations are performed employing TrackSim software. The results show that the suspension system's performance is enhanced regarding stability and handling when utilizing air springs, resulting in reduced vertical acceleration of the vehicle and a more seamless driving experience on curved and sine-wave roads.

This research investigates the low-velocity impact on sandwich beams with 2D curved reentrant auxetic cores. Using a 3D printer, tensile test specimens are fabricated and their mechanical properties are extracted. In addition, using a 3D printer, sandwich beam specimens with 2D curved reentrant auxetic cores are fabricated, consisting of curved unit cells at angles of 30, 45, and 60 degrees. Three-point bending and drop-weight impact tests are performed on the specimens. Polylactic acid is used as the material for the beams. The findings from the three-point bending test show that increasing the internal angle of the curved unit cell corresponds to decreasing the slope of the linear portion of the graph and the amplitude of the applied bending force. The impact response history includes factors such as contact force, absorbed energy, impactor velocity, impactor displacement, and displacement of sandwich beams with 2D curved reentrant auxetic cores when subjected to a 3 J drop-weight impact test. Also, Poisson's ratio and relative density of 2D curved reentrant auxetic unit cells with angles of 30, 45, and 60 degrees are obtained. One of the important findings of the impact test is that in order to maximize energy absorption, sandwich beams with 2D curved reentrant auxetic cores with unit cells of 30 degrees angle perform best compared to other angles.

This work aims to evaluate the thermomechanical and isothermal fatigue behavior of an Inconel 718 specimen under various loading conditions, including low-cycle fatigue (LCF) at 350°C and 650°C, as well as in-phase (IP) and out-of-phase (OP) thermal loading cycles. An entropy-based approach combined with finite element analysis and continuum damage mechanics was used to examine the fatigue response under three different mechanical loading conditions. The ABAQUS program facilitated the development of the finite element model, while the model for predicting fatigue life was evaluated using the USDFLD subroutine code. The entropy-based approach, rooted in Boltzmann theory and continuum damage mechanics, enabled the calculation of entropy growth rates and damage accumulation parameters. The results show that the entropy-based method accurately captures the trends in fatigue life and damage formation under thermomechanical and isothermal fatigue conditions. These findings support previous experimental results, confirming the reliability and accuracy of the entropy-based model in predicting material degradation. This study highlights the value of using entropy as a precise parameter for assessing fatigue behavior, which is vital to developing more durable materials for high-performance applications.

The viscoelastic material was presented using Boltzman viscoelastic model and Shapery constitutive equation for orthotropic material with a multidimensional integral. Employing Prony series, solution of the time integral was obtained in the form of a recursive-iterative approach that estimate the current time parameters based on parameters of the preceding time. After finding the lamina properties, overall properties of laminate are obtained with 3D lamination theory of Pagano. These properties are assigned to every integration point of the finite elements. Since this material is not available in standard finite element codes, viscoelastic laminated composite system was developed for commercial codes. The formulation was implemented into ANSYS USERMAT subroutine which is applicable for 3D structures with only one element through the thickness. For instance, buckling problem of a plate with a circular cutout was considered. Force-deflection curves of elastic material were obtained with ANSYS and subroutine material and compared well. For viscoelastic response, creep buckling of viscoelastic plate was obtained for various applied loads and imperfection. Long-term deflections and end-shortenings versus time were illustrated for two different fiber orientations. The results show that for creep bulking, imperfections do not have significant effect on end-shortening.