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Tensegrity is a kind of spatial structural system composed of cable (in tension) and strut (in compression). Stability is provided by the self-stress state between tensioned and compressed elements. When this structure is subjected to external dynamic loading, it may become unstable due to low structural damping. In this study, the proportional damping is considered and dynamical equations of the tensegrity structure are derived based on the equilibrium configuration. In addition the mass of cable element is taken into account. In general, linearized dynamic model provides a good approximation for analyzing the nonlinear behavior of tensegrity structures around an equilibrium configuration. So, state space method is implemented to obtain the dynamic response of the tensegrity system. Two different tensegrity structures are numerically evaluated using this approach in order to show its efficiency. Results reveal how the dynamic analysis of a tensegrity structure is essential. When resonance occurs, the compressive and in-tension members of a tensegrity system may dynamically buckle and slack respectively. In addition, the results show that the computational time to evaluate a tensegrity structure using the state space method is shorter than that of Newmark algorithm.

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Accurate measurement of unsteady pressure fluctuations along a surface requires experimental set up with high spacing resolution and high frequency domain. Therefore, in recent decades extensive studies have been conducted on remote microphone approach. In this method, instead of using flash mounted sensors, they installed remotely and connected to the model surface through one or several continuously connected tubes. Surface pressure fluctuations will travel within the tubing in the form of sound waves and they will be measured when passing over the remote pressure sensor, mounted perpendicular to the tubing. In the present study, an analytical solution of sound waves propagation inside the rigid tubes is used for modelling of the remote microphone system and to investigate the effects of its parameters on dynamic response. In order to verify the accuracy of proposed modeling, the dynamic response of a typical remote microphone has been obtained through experimental calibration. Comparing the analytical and experimental results indicates high accuracy of the analytical modeling. Results show that changes in tubing diameter leads to occurrence of resonance and creating harmonics in two frequency regions. The amplitude of low-frequency harmonics depends on the length of the damping duct and decreases with increasing of its length. Instead, the amplitude and frequency of high-frequency harmonics depend on the length of the first tube and they decrease with the increase of first tube length. Also, Increase of the first and second tube lengths lead to an increase in phase of dynamic response of the remote microphone system.

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Unbalance in rotating machines causes malfunction of the system operation and it may leads to its failure. Therefore, the sources for imbalance should be investigated, identified, and measured to solve the mentioned challenges. Rotating unbalance appears when the geometric and the inertia axes of the rotor do not coincide, and as a result this causes self- excited vibrations. One of the methods to control and reduce the unbalances is utilizing automatic ball balancer (ABB). In previous studies, the stability and the dynamic behavior of ABB have been mostly investigated by using numerical methods, and the perturbation methods are applied only for stability analysis. Because of the advantages of the analytical methods in studying the dynamics of the systems, in the present study, for the first time the dynamic behavior as well as the stability of a rotor equipped with an ABB is analyzed by the multiple scales method. To this end, nonlinear equations of the systems are derived using the Lagrange’s equations and firstly, the multiple scales method is applied to investigate the stability of system and then the response of the system is achieved considering one and two terms of approximation. The results demonstrate that the stability analysis using the multiple scales method and the first method of Lyapanov lead to the same results. Moreover, the responses obtained by the multiple scales method and the mostly used numerical method, Rung-Kotta technique, are in a good agreement.

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In structural dynamics, loads having varying positions has been broadly studied. Such loads are so called moving loads which appears in various applications in industry. High speed machining systems, overhead cranes, cable ways, pavements, computer disc memories and robot arms are a few examples of moving load dynamic problems. Vibration of bridge structures subject to moving vehicles is often referred to as an application of moving load problems. A great number of researchers proposed numerical and analytical methods to deal with the vibration of solids and structures under travelling loads. A famous classic approach in the simulation of moving loads is the moving force. In moving force model, a constant traveling force is assumed to act upon the base structure. However, this assumption yields to reasonable structural analysis if the mass of the moving object is negligible. Nowadays, with ongoing advances of transportation technology, the mass, speed and acceleration of moving vehicles are notably increased. In this regard, during the last few decades, many researchers showed that the moving force is no longer valid for large moving masses. Therefore, the moving mass simulation has been proved to be closer to the physical model of vehicle bridge interaction. As a common practice, bridges carrying moving vehicles has been assumed as vibrating beams excited by point moving masses. It has been very customary to consider the midspan or center point of the base beam as the reference point in order to assess the maximum dynamic response of the structure under moving mass; therefore, most of the existing computed design envelopes are related to the values occurring at the midpoint of the structure. However, the location of the maximum values occurrence is not necessarily at midspan. To shed light on this issue, in this research an analytical-numerical method is established to capture dynamic response of an Euler-Bernoulli beam traversed by a moving mass. Most of the available literature on moving load problem is concerned with the travelling loads having constant speeds. To remove this restrictive presumption, in this paper, the considered moving mass is assumed to move at non-zero constant acceleration. The beam is considered to be undamped and initially at rest. The moving mass is assumed to maintain full contact condition with the base beam while sliding on it. By exploiting a series of continuous shape functions having time varying amplitude factors, a norm space is provided by which the beam spatial domain is discretized. The problem is then transformed into time domain for which a time integration method is utilized. Absolute maximum dynamic response of the supporting beam under the passage of accelerated moving mass is extensively sought over the beam length. In this manner, whole beam length is being monitored for the maximum values at each time step of time integration procedure. The beam absolute maximum dynamic response is comprehensively computed considering different mass ratios and extensive range of linearly time varying velocities. Parametric studies are carried out on the absolute maximum values of dynamic flexural moments and deflections and compared to those captured at midspan. Finally, it highlighted that the midspan of the beam cannot be a valid reference to obtain the true maximum deflections and flexural moments of the base beam.

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This paper analyzes the effect of squeeze film and size effect on dynamic response of microplate. The microplate in this work is a clamped-clamped plate, which is excited using electrostatic force. The gap between microplate and substrate filled with air. First order shear deformation theory (FSDT) and couple stress theory (CST) and considering Von Karman’s strains are used to model the equation of motion of microplate. Non-linear Reynolds equation based on Micropolar theorem is deployed to apply the size effect on the fluid. Afterward, Equations are discretized by applying couple finite element method and finite difference method. The first-order differential equations are solved utilizing Newmark’s method. One of the contribution is presenting the influences of size effect and mid-plane stretching on the microplate dynamic behavior, also the influence of different parameters on the quality factor. According to the results, mid-plane stretching effect increases the microplate rigidity. Interestingly, this effect is more dominant for voltages with higher amplitude. This paper emphasizes that considering the plate size effect will increase the rigidity of the system. Moreover, the plate size effect increases the rigidity whereas, the fluid size effect decreases the rigidity of system. Increasing the fluid’s pressure results in decrease the amplitude of oscillations in step voltage excitation which postpones the dynamic pull-in. This paper concludes that increasing the coupling parameter of fluid increases the natural frequency of microplate, whereas increasing the fluid length scale parameter decreases the natural frequency and quality factor of the system.

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Designing explosion of gas pipelines, gun tubes, pulse detonation engine tubes and etc, all related to problem of cylindrical shell subjected to dynamic internal loads. In this paper, dynamic response of the thick cylindrical shell subjected to dynamic internal load with considering the high order shear deformation theory (HODT) is investigated and compared with the first order shear deformation theory of Mirsky- Hermann (FSDT). The effects of transverse shear deformation and rotatory inertia were included in the governing equations of the dynamic system. First, the equations of motion have been derived by using Hamilton’s principle then by changing variables the obtained partial differential equations have been converted to ordinary differential equations. With this method, the problem can be solved for various mechanical moving pressure loads without considering the effect of boundary conditions with long length assumption. The results of the present analytical method have been verified by comparing with finite element results, by using software. The comparison of the results with the finite element method shows that the high order theory and first order Mirsky-Hermann theory can predict the dynamic response of the thick cylindrical shell and the high order theory in areas away from the middle layer is more successful.

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Shape memory alloys are a category of smart materials which exhibit large deformations under temperature or magnetic stimuli due to micromechanical changes. These alloys offer a good potential in design of control systems, sensors and actuators due to two main effects called shape memory effect and superelastic effect. Main advantages of these systems are their small scale, low weight, low activation power, long life and high power to weight ratio. On the other hand, the main disadvantage of thermal ones is their low actuation frequency. In this work, inspired by human arm muscles, a new actuator is designed and its actuation time is minimized utilizing the thermoelectric effect. The process requires simultaneous analysis of heat transfer, constitutive equations, phase transformation and also the dynamic equations of the actuator. The dynamic response of the designed actuator is compared with the similar experimental data available in the literature and finally it is shown that, the actuation time of the proposed actuator can be reduced at least 50% thanks to the Peltier effect.

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Because of having amazing mechanical physical properties including noise pollution reduction, quiet, reliability, most cost-effective, sustainable and lasting life, asphalt pavement system has been utilized for parking lots, roadways, airstrips by the most state and federal governments highly prefer asphalt pavement by many civil engineers. Generally, asphalt pavement is made up of sand, stone (aggregate), liquid (petroleum) asphalt and additives. In the present study, the thermo-dynamic behavior of porous viscoelastic asphalt pavement system under a moving harmonic load based on the classical plate theory is analyzed. The asphalt pavement system is modeled as a rectangular sandwich plate structure. Three states of porosity distribution pattern, i.e., uniform porosity, non-uniform symmetric porosity, non-uniform asymmetric porosity distributions are considered for porous asphalt layer which are supposed to vary along the in-plane and thickness directions. The equations of motion are extracted in accordance with Hamilton’s variational principle and then solved using the expanded Fourier series. The accuracy and correctness of the extracted formulation are firmly demonstrated by comparing the data accessible in the literature and finite element simulation COMSOL Multiphysics®. In this study, the dynamic response of the asphalt pavement system was evaluated analytically and numerically by considering the porous asphalt layer under the harmonic load at various velocities in a thermal environment. The classical theory of plates was used for the analytical modeling of the system. The dynamic equations were derived in view of the relations for porosity and thermal strain in the stress-strain matrices in combination with Hamilton’s principle. With the aid of Fourier series expansions, and given the considered boundary conditions, the partial dynamic equations were transformed into differential dynamic equations. Furthermore, the dynamic response of the system was obtained using Laplace transform, which was then evaluated in terms of effective parameters. A finite element simulation software was also used to validate the results against the published articles. In this study, three case of uniform porosity, non-uniform symmetric porosity, non-uniform asymmetric porosity distributions are considered for modeling porous asphalt layer. Parameter studies reveal the impacts of the velocity and the excitation frequency of the harmonic moving load, porosity distributions, and temperature changes on the dynamic response of the pavement system. According to the conducted studies thus far, the dynamic behavior of asphalt pavement system is inevitably affected by such outcomes. Furthermore, the results demonstrated that non-uniform symmetric porosity case is more suitable than the other two types of porosity, The temperature changes lead to a softer asphalt pavement system, With increasing porosity, the dynamic response of the system rises in all the cases of porosity distributions and The amplitude of nondimensional dynamic deflection is directly proportional to the frequency of excitation up to the resonance.

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Sandwich panels which can be used as an explosion shield are important structures for absorbing explosion energy. Crushing and plastic deformation of the core with the plastic bending of the faces are the main factors in absorbing the explosion energy in this sandwich panel. Structural components undergo permanent deformation after explosion and energy absorption. In this paper, the energy absorption of the structure and the deformation of circular metal sandwich panels with tubular core under explosion load have been investigated analytically, numerically and experimentally. The tubes are arranged radially and symmetrically in the core constructions. The experiment have been performed by making sandwich panels under free blast load in order to evaluate and validate analytical and numerical results. The analytical solution is performed using the energy method by balancing the kinetic energy and the plastic work which is done by the different components of the sandwich panels. Numerical solution is performed in ABAQUS finite element software and the pressure function is generated by CONWEP method. The amount of energy absorbed by the structure and different parts of it is obtained. There is good agreement between the results in different ways.

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The health of structures, provision of safety, and the sense of security are among constant requirements and perpetual challenges of engineering and managers in the field of crisis management. Erosion and occurrence of minor local damage to structures and structural members in the early stages of construction or during operation, especially in critical structures such as power plants, tall buildings, stairs, dams, airports, and hospitals, among others, have always been among major problems. In case the damage sites are not identified timely and decisions are not made appropriately, substantial irreparable damage is expectable. Structures are always affected by various natural or unnatural factors such as earthquakes, explosions, and unprincipled excavations, which can aggravate the local damage in them and lead to their destruction, hence substantial human and financial losses. Therefore, it is highly crucial to monitor the health of structures and structural members. Therefore, health monitoring in structures and structural members is highly important. The column is one of the most significant members of engineering structures, especially in building structures and bridges, so that the instability of one of these members can lead to instability and destruction of the structure. Hence, design engineers expect columns to be the last members of structures to be damaged. In this paper, the health monitoring of the column as a structural member was performed by considering the effect of axial load on modal dynamic responses (i.e., natural frequencies and mode shapes). The results showed that the natural frequencies of all modes in both healthy and damaged states decreased with increasing axial load in proportions of the base critical load (the worst-case limit load). Also, at the same loads, the frequency of the healthy sample was always higher than that of the damaged sample so that the frequency difference between healthy and damaged states increased with greater severity of the damage. By introducing a Damage Detection Index (DDI) based on the wavelet coefficients obtained from the details of wavelet analyses of damaged and undamaged modes, the damage sites could be identified with a simple check and high accuracy by observing vibrations in DDI. Also, studies have shown that the DDIs of different damaged sites are independent of each other and are only affected by the severity of the damage and that the effects of axial load on DDI are very small and negligible. The independence of the DDIs of different damaged sites indicates the effectiveness of the proposed method in identifying damaged sites. Otherwise, failure to identify one damaged site may affect the identification of other damaged sites. The damage detection capability using the proposed DDI was investigated in columns with different support sections and conditions, and successful troubleshooting results were obtained. Moreover, investigations were performed with other wavelet functions, and the damage site was successfully identified. The proposed damage detection indicator is an efficient index in the column structures under the effect of axial load with axial buckling-prone support conditions and is proposed as a reliable method in identifying column damage sites in practical health monitoring of structures.