Successful development, evaluation, and qualification of propulsion systems such as turbojet and turbofan engines and rocket motors require the measurement of the performance and reliability of these systems. Thrust stands or testers are instruments for solid and liquid motors test. These apparatuses extract the characteristics of motors such as temperature, pressure, force and torque. In this paper, the dynamic design principles of a typical thrust stand have been detailed and methods to improve dynamic response have been developed. A thrust stand should be affected by random vibrations of solid motors as slightly as possible during firing. At first some Power Spectral Density (PSD) of three kinds of solid motors has been calculated by MATLAB codes. Then a number of tester structures by Solidworks have been designed and their dynamic responses have been determined by ANSYS codes. An attempt has been made to improve dynamic responses through changing the structure. Results showed that just some models could be improved. Increase of natural frequencies protects the structure from motors random vibrations. Truss structure is a good choice for testers. Decrease of mass, using different types of tube sections and short members are effective methods for improving dynamic responses. تفاصيل المقالة

Successful development, evaluation, and qualification of propulsion systems such as turbojet and turbofan engines and rocket motors require the measurement of the performance and reliability of these systems. Thrust stands or testers are instruments for solid and liquid motors test. In this paper, a method for calculating of solid motors random vibrations effects on a thrust stand structure is developed. At first some Power Spectral Density (PSD) of three kinds of solid motors has been calculated by MATLAB codes. Then a typical thrust stand which has been designed based on special dynamics principles, has been modeled in Solidworks and transferred to ANSYS. In ANSYS, the structure has been analyzed modal and spectral. Then each motor's PSD has been applied on structure separately and maximum stress has been determined by ANSYS codes. Fallowed by structure fatigue life has been estimated by a formula derived from compound of Miner's cumulative fatigue damage ratio equation and Gaussian distribution curve. Results showed amount of PSD at first frequencies has more effect on structure fatigue life and just based on maximum motor thrust can not come to a definite conclusion about the vibrations effects. تفاصيل المقالة

One of the main factors in poor performance of machine tools is undesirable vibrations. Unbalancing in rotary elements of machine tools cause induced vibration in machine head that influences on precision of processing material. The work presented in this paper is intended to resolve this problem. In this paper, a 3- DOF system has been modeled with design parameters in a machine tool. Based on technical specification of material used in this milling machine real amount of parameters were calculated. The equations solved and the amplitude movement of machine head in a crucial condition of vibration obtained. The main aim of optimization in this work is to reduce this amplitude by considerable amount. For this purpose, two approaches have been suggested. The first approach is solving the dynamic equations of 3-DOF model and changing stiffness and damping property of machine body material so that reduce the head movement to the desired level. It was found that such an especial material is not easy available and in case of finding, is not economical. Therefore, the second approach was suggested, i.e. adding a dynamic absorber to the drilling machine in three different positions to improve the situation. In this approach, only one DOF is added to the model and solve four differential equations with unknowns of mass (MD) and stiffness constant of spring (KD) for dynamic absorber. The mechanical impedance was used for these equations and the results obtained in complex coordination. In MATLAB, a procedure for optimization of MD and KD of dynamic absorber has been developed. Finally, the range of available MD and KD in industrial market was defined. The results have shown that adding dynamic absorber both more effective and more economical than changing material. The final achievement is though, the place of installing dynamic absorber. If the dynamic absorber install on the machine head is much more effective than putting in the base of machine tools, as a regular practice. Finally, a design criteria has been suggested for mass and stiffness of the dynamic absorber. تفاصيل المقالة