In this paper, vibrations reduction of piston engine of ultralight aircrafts was studied with considering a combination of experimental, analytical and numerical methods. Analytical equations of dynamic absorber were obtained. Afterward, experimental test was used to determine the system torque. Due to the difficulty of obtaining experimental data, the amount of angular acceleration and then velocity and angular displacement were calculated numerically using MATLAB software and verified with experimental results with a difference of less than 2%. Different components of the system were designed with reverse engineering method using SolidWorks software. After data transmission to Adams software, vibrational analysis of the system was performed and validated with analytical results with a difference of less than 1.91%. A suitable dynamic absorber was selected. The results showed that engine vibrations is reduced up to 40%. Manuscript profile

Vertical vibrations in the ambulance patient compartment due to road disturbances can cause serious injury to patients. In the present study, after extracting the vibrations entering an ambulance with passive suspension system, the use of a new active vibration isolation system between the patient's Compartment and the ambulance body is proposed. This isolation system includes an air spring, a linear shaft motor and a suitable active controller, which is abbreviated as AVI system. In this paper, instead of using one AVI system to control the vibrations of the stretcher, four AVI systems are used to control the vibrations of the patient's Compartment. The accurate modelling for ambulance with passive suspension system in both types non-isolated and active isolated patient's Compartment has been done by SOLIDWORKS software. Then by extracting the mathematical model, differential equations and state space model, the comparison of both types was done using MATLAB-SIMULINK software and finally the results were optimized using the Model Reference Adaptive Control (MRAC). In this control method, the functional parameters automatically adapt themselves by changing the position of the centre of gravity. The results obtained according to the IS02631 standard, show that with the present method, vertical vibrations are reduced by more than 80%. Manuscript profile

Protection of sled systems from destructive vibrations is inevitably under attraction due to the importance of sled testing in the aerospace industry. A pair of SBR dampers were used between the slipper and the sled body to reduce vertical vibrations, so a design of the sled model was studied. Both equivalent stiffness and equivalent damping of the sled system were obtained to reduce the transmission of vibrations from slippers to the body. A combination of analytical, numerical and experimental test methods was utilized and the results were validated. The stiffness values of 370500 and 391000 N⁄m were obtained from numerical and experimental measurements, respectively. Finally, by designing the sled model, first and second natural frequencies of 12.49 and 19.56 Hz and mode shapes of the sled system were obtained. The results show that the dampers used in the sled have an important role in reducing the transmission of vibrations to the sled body by withstanding the tension and pressure on the slippers. Manuscript profile

In this paper, the pressure distribution on the slippers of a mono-rail sled with vibration damping is investigated. Due to the many applications of sled testing in the aerospace industry, the study of system vibrations is highly noticeable. In this research, first, by mathematical modelling of the sled, the governing Equations are extracted and natural frequencies and vibration modes are obtained from the analytical method using the mass and stiffness matrix of the system. Then, using numerical simulation and validation methods with experimental results performed in wind tunnels, the modal analysis of the designed sled sample is performed. A difference of less than eight percent in both numerical and analytical methods proves the accuracy of the results. The results show that the role of the slipper in the vibrations created in the sled is very important due to the large torsional and transverse oscillations in different positions, and the highest static pressure occurs in the inner layer of the slipper. Manuscript profile

In this article, the vibration and dynamic response of an orthotropic composite cylindrical shell under thermal shock loading and thermal field have been investigated. The problem is that the shell is initially located at a first temperature, and some tension caused by a mild heat field is created, then the surface temperature of the cylinder suddenly increases. The partial derivative equations of motion are in the form of couplings with the heat equations. First, the equations of motion are derived by the Hamilton principle, here first-order shear theory and considering strain-shift relations of Sanders are used. Then, the equation system including the equations of motion and energy equations by the Runge–Kutta fourth-order methodare solved. In this study, the effects of length, temperature, thickness and radius parameters on natural frequencies and intermediate layer displacement are investigated. The results show that the increase in external temperature decreases the natural frequency and increases the displacement of the system. Also, the results of radial transitions were evaluated with previous studies and it was found that it is in good agreement with the results of previous papers. Manuscript profile