Journal of Advanced Materials in Engineering (Esteghlal)

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The importance of the equipment and secondary systems in seismic design and performance evaluation is well recognized and has been the subject of many studies. In all of these studies, earthquake is considered as a single component, and in most of them the primary system is considered as shear building. Most attention has been concentrated on the response of secondary system and its response spectrum. In this paper, the transfer function for absolute acceleration of the secondary system is obtained. The squared modulus of transfer function relates the power spectral density function of the input (excitation) to the output (response), which is useful in the study of the various dynamic parameters of the system. In addition to transfer function, the autocorrelation and power spectral density function of absolute acceleration of the secondary system are obtained. Earthquake is considered as a multi-component system and the necessary formulation is developed for the calculation of these functions as well as the critical angle with and without interaction between the two systems. The damping of the system is considered as proportional in the decoupled analysis, and nonproportional in the coupled analysis. The formulation developed has been illustrated by considering a ten-story torsional builing. Various parameters such as eccentricity, correlation between components, tuning interaction and nonproportional damping are studied. Results show that eliminating the effect of multicomponentness of earthquake can cause large errors especially at large eccentricities. Keywords: transfer function, Random vibration, secondary systems, critical angle, interaction, nonproportional damping

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There is a worldwide interest in the proper design of embankment dams to resist earthquake loadings. For the first time in Iran, a complete ambient vibration survey due to low-level loads such as wind, machinery activities, low level tectonic activities, and water exit from bottom outlet was performed on Marun embankment dam. These kinds of ambient vibration tests are suitable for manifesting the lower vibration modes of the dam body. Using different signal processing methods such as Power Spectra Density, the results of in-situ tests have been used to evaluate the natural frequencies, mode shapes and modal damping of the dam body. Besides ambient vibration tests, the 3-D modal analysis of the dam body was performed using ANSYS software. The foundation and abutment flexibility effects on dynamic characteristics of the dam body was investigated and the dynamic soil properties were used from Engineer’s report and some empirical relations. Also initial shear modulus of the dam body and foundation materials were evaluated by refraction survey. In this paper, the test procedures, related signal processing results, numerical analysis results and its comparison with the dynamic characteristics of the dam body obtained from the full-scale dynamic tests will be presented. Finally, calibrating procedures of the numerical model (based on increasing the accuracy of dam body geometry, soil and rock material parameters and foundation and abutment flexibility) will be discussed. Keywords: Embankment Dam, Dynamic Characteristics, Ambient Vibration Test, Modal Analysis

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Based on classical plate theory, standard and spectral finite element methods are extended for vibration and dynamic stability of axially moving thin plates subjected to in-plane forces. The formulation of the standard method earned through Hamilton’s principle is independent of element type. But for solving numerical examples, an isoparametric quadrilateral element is developed using Lagrange interpolation functions. The spectral method is, in fact, the solution of motion equation for an axially moving plate. Although this method has some limitations concerning boundary condition of plate and in-plane forces, it leads to an exact solution of free vibration and stability of plates travelling on parallel rollers. The method can be used as a benchmark of accuracy of other numerical methods.

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An approximate numerical mthod is presented for analysis and determination of modal characteristics in straight, pretwisted non-unifom helicopter blades. The analysis considers the coupled flapwise bending (out of plane), chordwise bending (in plane), and torsion vibration of both rotating and non-rotating blades. The proposed method is based on the integral expansion of Green functions (structural influence functions) to develop the equations of motion for a clamped-free blade. Several examples are presented in various states such as flapwise bending, coupled bending-bending, coupled bending-torsion, and coupled bending-bending-torsion vibration analysis. The results obtained were compared with available numerical results in the literature. A modal testing and modal analysis were also carried out on a typical helicopter blade in static condition and the results were compared with the numerical ones. The results indicate that the proposed method is fast and robust and can be used for modeling of turbomachine blades, aircraft propellers and helicopter rotor blades.

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Investigation of vertical vibrations of a railway turnout is important in designing track components under moving loads of trains. In this paper, the turnout is simulated by a linear finite element model with modal damping. A section of the turnout has a length of 36 sleeper spans surrounding the crossing. Rails and sleepers are modeled with uniform Rayleigh- Timoshenko beam elements. The rails are connected via railpads (linear springs) to the sleepers, which rest on an elastic foundation. The rolling stocks are discrete systems of masses, springs, and dampers. By passing the trains at a constant speed, only vertical dynamics (including roll and pitch motions) is studied. The wheel-rail contact is modeled using a non-linear Hertzian spring. The train-track interaction problem is solved numerically by using an extended state space vector approach in conjunction with modal superposition for the turnout. The results show that the rail discontinuity at the frog leads to an increase in the wheel-rail contact force. Both smooth and irregular transitions of the wheels from the wing rail to the crossing nose have been examined for varying speeds of the vehicle. Under perfect conditions, the wheels will change quite smoothly from rolling on the wing rail to rolling on the nose. The impact at the crossing will then be small, giving a maximum wheel-rail contact force which is only 30--50 per cent larger than the static contact force. For uneven transitions, the severity of the impact loading at the crossing depends strongly on the train speed. The increase in the contact force, as compared with the static force, is in the order of 100 per cent at 70 km/h and 200 per cent at 150 km/h.