نشریه مهندسی مکانیک ایران
سال بیست و ششم شماره 1 (پیاپی 74، بهار 1403)

The trapezoidal shape of composite corrugated cores has made it possible to increase their resistance against destruction. In this article, the effect of changing the geometric parameters of trapezoidal core edge angle and fiber angle in the porcelain layer of sandwich panels under quasi-static compressive loading has been studied. In the construction of composite panels used a combination of glass and metal fibers. The angle of the edges of the core is 46, 52, and 58 degrees, and the angle of the fibers in the porcelain layer is 30, 60, and 90 degrees are chosen. The absorbed energy and maximum force in the form of destruction samples were discussed after the quasi-static compression test. The results have shown that increasing the fiber angle from 30 to 90 degrees can increase the maximum force by 123% and energy absorption by 260%. The mechanism of plastic deformation of metal fibers and breakage of glass fibers in the area of plastic hinge formation at the edges of the core are the main mechanisms of destruction, and no delamination was seen in the plates. Also, the separation of the core from the top of the composite was not observed in the panel due to the high adhesion of the core and the tops of the plates, which indicates the high quality of these panels.

In this paper, optimal guidance law design considering fixed final state and time for the final phase booster landing problem of a spacecraft or launch vehicle is investigated and studied. This guidance law, not only satisfied a specific optimality criterion, but it also has the least sensitivity to the initial state’s deviations; which is due to the inclusion of the nonlinear terms in the mathematical modeling using the high order expansions method. The main goal of this research, is to investigate the development and to augment the capability of the high order expansions method for guidance law design. Different implementations of this approach including the differential algebra high order, the generating function based high order and vectorized high order expansions methods have been investigated. After reviewing the implementation concepts of the high order expansions method, the effectiveness of this method has been studied. Then a 3-dimensional booster landing problem has been chosen as the case study and after extracting the mathematical model and nominal optimal solution, the sensitivity variables have been extracted up to the 3rd order. Afterwards, to investigate the performance of the designed guidance law, the Monte Carlo simulations have been performed and it has been shown that the designed guidance law on the basis of the Taylor series and high order expansions method has a good accuracy and is a valuable alterative to the nominal trajectory tracking guidance approach.

This paper aims to achieve real-time optimum push recovery and high-speed pattern generation for a 3D humanoid robot.  For this purpose, a divergent component of motion (DCM) based locomotion is planned using a three-mass inverted pendulum model. To improve push recovery robustness in the presence of strong disturbances during walking, a quadratic optimization strategy algorithm is introduced, including weighted step time adaption, step position adjustment, and ankle strategy. The minimum error push recovery cost function is obtained through quadratic programming. To validate our proposed model different scenarios for real-time navigation of robot considering strong disturbances in various speeds of walking from 0/8 to 1/6 meters per second are analyzed. The verification methods indicate that the proposed method recovered from 34.5 N.s disturbances at 1/6 meters per second speed, while conventional push recovery methods guaranteed lower speeds robust stable locomotion in the same disturbances. In this paper, a real humanoid robot and actual physical conditions were considered for validation of navigation and robust optimum push recovery.

In this paper, the elasto-plastic behavior of thick-walled cylindrical shell under uniform pressure is studied. Mirsky-Herman shear deformation theory, in which shear deformations are considered, has been used to obtain elastic equations using energy and virtual work methods. The studied cylindrical shell is axially symmetric and has clamp-clamp boundary condition at two ends. The material state of the shell is fully elastic-plastic, and the Prandtl-Reuss flow rule has been used to express the material behavior in plastic state, and the von Mises yield criterion has been used to determine the beginning of plasticization of the cylinder in the middle layer. The radial return mapping method has been investigated to obtain the stresses in the plastic state and to correct and restore the stress to the yield surface. To solve the obtained equations, the eigenvalue problem method and MAM perturbation technique are used. Also, the obtained results, including the yield stress and cylinder stresses in the middle layer, have been compared with the finite element method using Abaqus software. The obtained results show that the MAM perturbation technique and using Mirsky-Herman shear deformation theory has a good accuracy in the elasto-plastic solution of thick-walled cylinders.

In this paper, the low velocity impact response of sandwich panels with composites face sheets and aluminum based corrugated cores is modeled with numerical simulation, and the amount of energy absorption, contact force, deformation of the impact area and dimensions of the damage area are calculated and compared with experimental results. Sandwich panels with composite face sheets reinforced with carbon fibers and glass fibers and corrugated aluminum-based cores are in square, trapezoidal, arched, sinusoidal and triangular shapes. Through numerical simulations ten examples have been analyzed. Dimensions and weights of face sheets and cores of the samples are the same. The obtained results show that in the sandwich panel with trapezoidal and square corrugated cores, the contact force is applied to a larger area and the energy absorption and dimensions of the damage area are greater. Also, sandwich panels with arc and sinusoidal wave shape cores have the greatest displacement at the point location compared to other sandwich panels.

Due to the damage that air can cause to the intestines and diaphragm, it is essential to prevent air from entering peritoneal dialysis fluid. Bubble detection systems and air infiltration control systems are mandatory components of peritoneal dialysis machines. An infrared sensor is one of the most efficient ways to detect bubbles in the catheter tube. As the dialysis fluid passes through the infrared sensors, an output of approximately 1200 millivolts is produced. The voltage produced by infrared sensors is independent of the device's speed. Approximately 1200 millivolts can be obtained when the motor of the dialysis machine operates at speeds of 50, 40, and 30 RPM. Continuous measurement of this voltage is performed, and the processor checks the correctness of bubble detection by limiting the threshold level of output voltage. This threshold control to detect bubbles in the dialysis machine tubes is 1000 millivolts. If the output voltage drops below this value, the operation of the dialysis machine is prevented to prevent possible injuries to the patient.