تحلیل دینامیکی

As the living standards of building residents continue to improve, along with safety and economic considerations, engineers are placing greater emphasis on the comfort of inhabitants. One significant human-made crisis that threatens society is noise pollution. Over the past century, factors such as population growth and the proliferation of high-rise constructions have posed challenges to mental health. Unwanted noise can emanate from both inside and outside of buildings. One of the main sources of indoor noise is the impact sound caused by residents walking on building floors. Currently, this type of sound is managed only through non-structural measures, as outlined in Volume 18 of the Iranian National Building Code. Unfortunately, it lacks coverage in the structural analysis and design of building components. From a structural perspective, Volume 10 of the Iranian National Building Code inadequately addresses acoustic limitations. It presents only a table specifying a minimum frequency of 5 Hz for residential floors. This paper examines the effect of foot-induced vibrations in buildings with steel deck floors, utilizing ETABS software in conjunction with the AISC code. Despite the lack of comprehensive acoustic regulations, the results reveal that even when complying with the design criteria established in Volume 10 of the Iranian National Building Code, the vibrational comfort of residents in apartments with steel deck floors may not be adequately assured.

Wavelet transform, as an advanced tool for frequency analysis of waves, has various applications in different fields of engineering. The main characteristic of the wavelet transform, compared to more traditional frequency analysis tools such as the Fourier transform, is its ability to be time-frequency. In other words, by using the wavelet transform, it is possible to obtain the occurrence time of different frequencies in stable and unstable waves. In the last two decades, the use of this tool in structural and earthquake engineering has also extensively expanded. It can be said that this tool is used in structural and earthquake engineering in three main categories of frequency analysis of earthquake waves, damage detection and de-noising. In this article, wavelet theory is first explained in a way related to structural engineering and earthquakes. Then, in the next step, the important studies conducted in each of the mentioned fields are presented separately

In this paper, it is possible to change the alloy of the blades of the last row of steam turbine blades of Ahvaz Ramin power plant in order to increase the life with the vibration approach. After entering the geometric model into the ANSYS, dynamic analysis and stress analysis are performed on the model for steel alloy and titanium alloy, as well as crack growth in the single-blade model. In the dynamic analysis, the results showed that when we consider the material of the turbine blades as titanium alloy, we can create better vibration conditions in the turbine blades and prevent the possible occurrence of resonance phenomenon. Also in stress analysis, when titanium alloy is used in the blade, the Von Mises stress obtained is approximately equal to half the stress obtained from the steel alloy. When the blade cracks at the root, the amount of stress intensity calculated in the turbine blade is reduced by almost 50% when the blade is made of titanium alloy.

The sled system is used to test anti-penetration structures, ejection seat, and spacecraft equipment that its technology is owned by a few developed countries. In this research, the dynamic analysis of applied forces on the system has been investigated. The effective forces on the sled include propulsive force, drag force, lift force, and friction force, which are all variable. To obtain the propulsive force according to the functional and geometric specifications of the designed sled, the grain engine design has been carried out to reach 0.85 Mach in a second. After extracting the governing equations for extracting the propulsive force, the changes of the propulsive force during the combustion time were obtained and formulated. At the next step, numerical simulation is used to obtain the lift and drag forces and after validating the numerical solution with experimental research, the values of drag and lift forces at different speeds are extracted and formulated. Next, due to sled mass variations during the combustion step, the friction force between the rail and the slipper is obtained. Finally, the differential equation and dynamic behavior of the system are analyzed. The results show that amount of friction force is negligible in comparison with other forces. Also, the highest pressure is applied to the inner part of the slipper, which can lead to wear and damage of the rail surface at high speeds and lead to the sled deviating from the rail track.

In this paper, the dynamic behavior of a small-scale parallelogram (P) flexure is studied. First, using the beam constrain model and the modified strain gradient theory, the nonlinear strain energy of a small-scale beam is obtained in terms of its tip displacements. This energy expression is utilized to derive the strain energy of a P-flexure. Then the governing dynamic equations of motion are derived using Lagrange equations and are linearized around the operating equilibrium point. This linear model is employed to determine the allowable forces which do not lead to instability of the system. Moreover, the natural frequencies of the system are also extracted and the size effect as well as the static components of the applied loads on them are studied in detail. It is observed that by reducing the dimensions, the normalized transverse natural frequency of the system is increased. However, since there is no strain gradient in an axial mode, the axial normalized frequency is remained constant reducing the dimensions of the system. Moreover, it was observed that the tensile static forces lead to an increase, and transverse forces lead to a decrease in normalized natural frequency of the system. The procedure utilized for dynamic modeling of parallelogram flexures in this paper can be further extended for modeling more complex flexure systems.

Cylindrical shells are used tremendously in many engineering fields such as ships, submarines and fuel tank in airplanes. Stiffeners which are beam elements are used for increasing stiffenes of shells. In many cases shells are exposed to dynamic loads. One of dynamic loads in shells is internal moving pressure. Analysis of cylindrical stiffened shells under moving internal pressure are investigated in this research. Equations of motion are based on classic shell theory and derived from Hamilton’s method. Boundary conditions is assumed simply support. Displacement components are assumed Fourie double series based on boundary conditions. Equations of motions are solved by Galerkin weighted functions method for calculation of natural frequency and dynamic response of cylindrical shells under moving internal pressure. Codes in Fortran are used to derive natural frequency and dynamic response of cylindrical shells. Results are compared with other references and Abaqus software. The effect of geometrical parameters on natural frequency and dynamic response of cylindrical shells under moving internal pressure are investigated finally and results for stiffened shells and unstiffened shells with different stiffeners are compared.

Dynamic stability and liquefaction of tailings dams are great concerns for geotechnical engineers. In this study, the seismic response of the Esphordi mine tailing dam located in Bafgh seismic region of Yazd province is investigated. A finite-difference code (FLAC2D) is used to model the seismic liquefaction applying two constitutive criteria, namely Mohr-Coulomb and Finn-Byrne. For this purpose, a fish function is implemented into the code to simulate the non-linear elasto-plastic Finn-Byrne constitutive model. Horizontal and vertical displacements (subsidence) in the dam body, additional pore pressure, failure zones, and liquefaction due to seismic load were determined using the two selected criteria under the seismic load of the 6.4 magnitude earthquake occurred in 2005. Considering the type of behavioral model, Mohr-Coulomb and Finn-Byrne, the maximum horizontal displacement of 5 and 35 cm in the dam body and downstream, and subsidence of 4 and 23 cm at the dam crest and upstream are observed, respectively. Also, the calculated ratio of excess pore pressure (Ru), for both criteria, was less than the liquefaction limit (0.9), the maximum value of which was 0.7 for the Finn-Byrne criterion and 0.2 for the Mohr-Coulomb criterion. In general, the results show that considering the cumulative effect of the seismic load cycles in the Finn- Byrne model, this criterion provides a better understanding of the liquefaction phenomenon.

Expansion cycle rocket engines have unintelligible and sensitive dynamic behavior. Contrary to other types of rocket engine which have gas generator, Expansion cycle rocket engines utilizes mass flow of fuel propellant to provide power for rotating turbo pump. Which contributes to a complicated and difficult ignitions process in these engines. Priority and delay process in opening of control valves is important to prevent aforementioned phenomena. As opening and closing of control valves cause dynamic process in rocket engine, whose effects are expensive and difficult to predict by experimental tests. Therefore, dynamic modelling plays a key role in development of expansion cycle rocket engines and may decrees future expenses. In this article RL-10 rocket engine with sufficient data for validation has been chosen. The main goal of this article is dynamic modelling of expansion cycle rocket engine using mathematical non-linear models. Modelling results yield that the presented non-linear model is valid.

Biot equations that consider fluid and soil interaction at the same time are the most applicable relationships in the soil dynamic analysis. However, in dynamic analysis, due to the sudden increase in the excess pore pressure caused by seismic excitation and the occurrence of high hydraulic gradients, the assumption of the Darcy flow used in these equations is questionable. In the present study, in the u-p form of Biot equations, non-Darcy flow is considered. Also, the nonlinear behavior of soil is modeled by the Pastor-Zienkiewicz -Chan model. For validation, the VELACS No.1 experiment is modeled and the effect of the nonlinear fluid flow assumption on the results is examined. The results indicate that in the low permeability coefficients, the obtained results of the non-Darcy and Darcy flow are in agreement; however, in high permeability coefficients, these two methods differ by time and depth.

In this paper, applying the general form of the viscoelastic model, vibration characteristics of viscoelastic fluid conveying pipes are investigated. By considering various viscoelastic constitutive equations, the equation governing the motion of the fluid conveying pipes is obtained, and by introducing a new analytical method, the exact mode shapes of the system are derived. Then, the effect of various system parameters on the complex eigenvalues and the instability of kind divergence and flutter are studied. The results show that for a pipe with viscoelastic behavior, the natural frequencies decrease and at the higher modes, the divergence critical fluid velocity increases dramatically. As a new result, it is observed the viscoelastic fluid conveying pipes with certain values of viscoelastic parameters, can experience the flutter instability before the divergence one. In addition, because the viscoelastic behavior does not affect all the vibration mode shapes in the same manner, therefore, the coupled-mode flutter does not take place.

In this study, dynamic behavior of thick rectangular plates under a moving mass with constant velocity traversing the plate on a rectilinear path is investigated. A semi-analytical method with the aim of BCOPs (Boundary Characteristic Orthogonal Polynomials) is utilized to tackle with the solution of motion equations for different boundary conditions of the plate while accounting for shear deformations. The effects of thickness and boundary conditions of plate and weight and velocity of the moving mass on the dynamic response of plate are scrutinized. The obtained results revealed the accuracy of the proposed method in comparison with the other researchers’ results. The results also demonstrated the importance of the moving load inertia as well as the shear deformations of the host structures on its dynamic behavior. The importance of this study lies on the vibration of bridge-type structures with plate decks, where, the shear deformation of the base structure could be no more ignored, especially for heavy vehicles moving with high speeds.

The vibration analysis of curved composite structures under the moving vehicles, is rarely investigated in litreture. Therefore, this paper is studied the dynamic response of a simply supported laminated deep curved beam under a moving load based on Timoshenko beam theory.It is assumed that the curvature of the beam and the amplitude and the speed of the moving load areconstant.The governing equations of motion for the system is extracted by Hamilton principles. A numerical and analytical methods are applied to obtain the dynamic response of the system.Also, the critical speed of the moving load and the fundamental frequency of the beam are obtained. The effects of the moving load characteristics, geometrical and material parameters such as the moving load speed, the radius of curvature and the modulus of elasticity in principal direction on the dynamic responses, fundamental frequency and critical speed of the system are investigated. The results show that the minimum and maximum deflection of the beam are occurred for lay-up [90/0/90/0] and [45/-45/-45/45]respectively. Furethermore, the increasing of the speed movingload leads to the decreasing thedynamic deflection. It is also shown that the increasing of the radius of the curved beams leads to the decreasingof the frequency and critical speed moving load.

In recent years¡ knee diseases are spread especially in elderly people. Since performing daily activities such as walking and running¡ the knee supports the weight of the body¡ there is more likely to be injured. This issue is more important for elderly people who have weak muscles and almost all elderly people suffer from knee pain. One way to help this people in order to move normally is to use a wearable device to aid the knee. In this article¡ a passive wearable robot will be designed to improve the strength of the elderly who suffers from the knee pain. The robot uses the compliance elements to increase the power of the knee joint in parts of a cycle. This robot will be developed based on a Stephenson II six-bar mechanism. Using this mechanism has the advantage of producing the similar motion to a knee. In other words¡ this mechanism produces the linear and rotational motions simultaneously. Additionally¡ more compliance elements can be added to improve the performance of the wearable robot. The optimal dimensions of the robot will be Through the kinematics analysis and also the derivation of the dynamics equations and the numerical validations of these equations¡ the performance of the robot will be considered. The performance of the robot mounted on the leg is compared with the human. Obtained results show that the less power is required when a wearable robot is used. This proves the merits of the designed robot to be used for the elderly.

Dynamic behavior of an absorption chiller with silica-gel as absorbent and water as refrigerant is modeled. Effect of important parameter such as cycle time, switch time and Heat-Recovery on heat pump capacity and coefficient of performance are analyzed to find the optimum cooling capacity performance. The results are compared with experimental results which show excellent agreement. 450-second cycle time which is used by the manufacturer is the best value for maximum cooling capacity, which of course is only true for specified environmental conditions however coefficient of performance increases by increasing the cycle time. In case of using solar energy, more performance could be achieved if cycle time varies online regarding to solar power.

The purpose of this article is modal analysis of ionic polymer metal composite beams, then briefing the system to the unique parameters to help in up modeling of the actuator. In this paper at first using of Mathematical analysis and Closed form transfer function of cantilever beam dynamic response to the forces of different inputs (intensive and continuous) is calculated and for different types of systems resonance and anti-resonance points in frequency analysis are found, then with using modal analysis of system the entire response is briefed in the basic mode and parameters of un-damped natural frequency and damping coefficient in this mode is to introduced for the system, after the cantilever composite beam considered as an operator with the input voltage, displacement and produces a force on the free end, By observing the behavior of the system, analyzed responses to the inputs.

One of the major subsystems of each airplane is landing gear system which must be capable of tolerating extreme forces applied to the airplane during landing. Using conservative techniques to find landing loads result in overestimation and unnecessary extra structural weight. New commercial softwares can simulate real landing conditions with acceptable accuracy if detailed mechanical data about landing gear system subparts are provided. Although these softwares work well but due to lack of detailed information about the subparts at the conceptual design phase, complexity and time consuming of modeling, expensive license price, etc. they do not seem to be the best choice for design purpose. In this study, in order to calculate landing loads more precisely than the estimating conservative methods, flight dynamic differential equations of an airplane during landing phase are derived and through numeric and state space techniques are solved for different initial conditions including, three point landing, two point landing and one wheel landing. Each landing gear of the airplane is modeled as a two-degree of freedom mass-spring-damper set. Time history of the airplane center of gravity, pitch and roll angle, vertical landing loads of each landing gear and their spin-up loads for different landing types (different initial conditions) are obtained to show capabilities of this new, fast and accurate landing simulation code, generated.

In the high speed craft, the study of dynamic behavior is important issue. Always, stability and performance improvements are the main principles of design of the high speed craft in sea wave conditions. The complexity of the equations of motion will be increased by increasing boat velocity under wave force. In this paper, the boats behavior with planing form is investigated against irregular wave conditions. Due to nonlinearity and complexity of dynamic behavior under wave excitations, many limitations are imported in the analytical and numerical calculations. For this purpose, in this study, the behaviors of high speed craft are discussed by given the assumption to simplify the problem. Therefore, at first the equations of motion are modeled in regular waves, and then these equations will be developed for irregular waves so that nonlinear nature of motions has been maintained.

This paper aims at obtaining the dynamic models of twoconstraint-over parallel mechanisms (PM) with 3-DOF (degree of freedom) and 4-DOF, the Tripteron and the Quadrupteron. The reasoning used in this paper is based on a judicious concept in detaching the whole mechanism into several subsystems and consecutive synergies between kinematic analysis, Lagrangian and Newtonian approaches. In this regard, the mechanisms are made equivalent to some subsystems and the equations of kinematic constraints are derived for all subsystems. Afterwards upon resorting to Lagrangian approach and blending it with the latter kinematic relations, the dynamic model of each leg in task space is obtained. The dynamic model of the end- effector is written in virtue of Newton-Euler’s approach where yields to three differential equations. Finally, the problem leads to a system of 12 equations for the Tripteron and 16 equations for the Quadrupteron, which do not need usaul simplifications in such problems. For the sake of comparison, the results are put into contrast by the one obtained with a dynamic analyzer software. The results obtained by both approaches are coherent which affirms the correctness of the proposed algorithm.