In this research, Dynamic behavior of non-Linear finite element model of a drillstring is investigated. By considering total length of drillstring, a three-dimensional timoshenko beam element is employed. In addition the geometric stiffening effect, the added fluid mass and the contact between different parts of the drillstring and the borehole wall has been considered, with a more complete model than previous studies, the effects of these factors have been analyzed separately. The equations of motion are obtained and full order equations are used to drive the results. For the first time, a domain of drillstring points that the possibility of contact occurrence in them is more than other points, have been identified. The natural frequencies of the drillstring are evaluated and compared with the available commercial software results and recorded results for the actual drillstring. Coupling of vibrations of model is tested and the effect of Linear and nonLinear model in Analysis of Dynamic behavior and vibration of drillstring, especially in contact with the borehole wall and the effect of weight on bit change on the contact at stabilizers are analyzed and for the first time, the contact time in each of stabilizers have been evaluated.

The usual finite element methods reduce the infinite number of degree of freedom (D. O. F. ) of system to a model with a limited number of D. O. F. while capturing the significant physical behavior. Base relation methods reduce number of D. O. F. in new coordinate. One of the base relation methods is gained from Ritz-Wilson vectors which is much better than the conventional base relation methods and eigen value methods in a lot of cases because of simpler and dependence on Dynamic load. Also to be costly in large system calculations and to ignore loading parameter can be mentioned as the disadvantages of eigen vectors. Fewer number of required Ritz vectors in comparison with eigen values and considering place distribution of external loading and dominant frequency content of loading has pushed the researchers into applying Ritz vectors. Base alteration methods in nonLinear problems are not usually much applicable due to frequent matrix change of system. Generalized one dimensional subspace method presents an appropriate solution for geometric nonLinearity problems by means of Ritz-Wilson technique. In this article generalized one dimensional subspace method is combined with mode-acceleration technique in order to analyze nonLinear Dynamic problems. Based on inside error component and generalized one dimensional subspace method, a modified criterion using mode-acceleration technique in order to update required base vectors for stiffness changes in nonLinear Dynamic Analysis is proposed. The results indicate that the accuracy and speed of the modified method are appropriate.

In this paper, the most important existing studies were reviewed on the Dynamic Analysis of the saturated porous media. First, a brief evaluation of theoretical expressions, essential equations, and the most important solutions was illustrated for the mentioned problem. Then, by dividing the literature based on various Analysis approaches into two categories of analytical/semi-analytical and numerical methods, the available researches were classified in each category to report according to the publication year. In recent decades, by increasing the power of computers besides the development of numerical approaches, researchers were eager to use them for analyzing wave propagation problems as well as predicting the real response of topographic features more than ever. In this regard, modeling of the porous soil media was generally done for the quasi-static Analysis of the consolidation phenomenon. However, due to the complexity of the Dynamic formulation of porous media, it is very difficult to solve this kind of problem analytically with traditional approaches. Therefore, most of the studies to analyze the elastic porous media based on modern Dynamic formulations were done with the help of numerical approaches, in which it became possible to perform the Dynamic Analysis of wave propagation models in saturated porous media derived from poro-elastoDynamic theory. According to the formulation, the numerical methods can be usually divided into two general categories known as the domain and boundary methods. In the common domain methods, such as the finite element method (FEM) and finite difference method (FDM), it was required to discretize the whole body including internal parts of the model, the surrounding boundaries, and defining absorbing boundaries. Although the simplicity of domain methods makes them favorable for analyzing the seismic finite media, the models are complicated because of discretize the whole body and its boundaries at a considerable distance from the desired zone. This issue causes the number of elements as well as the required computational efforts to increase to reach accurate results, especially in a half-space soil medium. On the other side, in boundary methods which are mostly known today as the boundary element method (BEM), by concentrating the meshes only around the boundary of the desired features, the automatic satisfaction of wave radiation conditions at infinity, reducing the volume of input data, and Analysis time was remarkably achieved as well. Also, the high accuracy of the obtained results was guaranteed due to the large contribution of analytical processes in solving various problems by BEM. One main feature that made the BEM very interesting for analyzing the poro-elastoDynamic problems was its capability to obtain the half-space fundamental solutions by eliminating the meshes of far-field boundaries. This issue made it very comfortable to solve problems related to semi-infinite space. Therefore, the BEM presented a better manner for analyzing infinite/semi-infinite problems. By considering the high importance of boundary methods in analyzing the saturated porous media, the separation of studies was done in more detail in this field concerning its main elements. By reviewing the technical literature, it can be known that boundary methods can be divided into two main categories, direct and indirect approaches. In the direct method, all unknowns of the problem were calculated directly from the boundary integral equation (BIE). However, in the indirect method, it is required to define the estimator functions according to the unknowns of the problems, which results in a simplified BEM formulation. By looking at the recent studies, it is clarified that the BEM was always considered a suitable computational approach for analyzing the saturated porous domains, especially in investigating the seismic surface / subsurface topographies features.

Spar platforms are large structures which are used in deep waters. Because of their large dimension, Morrison’s Equation is not suitable to estimate hydroDynamic forces on this kind of platforms. Therefore in this study wave forces and hydroDynamic coefficients of a spar platform have been estimated in six degree of freedom using diffraction theory. The incident wave is assumed to be harmonic and Linear. Diffraction and radiation velocity potential were solved with finite difference method. The results showed that the developed model is able to estimate the wave forces and hydroDynamic coefficients on large structures considering diffraction theory with acceptable accuracy.

Aortic Valve simulation remains a controversial topic as a result of its complex anatomical structure and mechanical characteristics such as material properties and time-dependent loading conditions. This study aims to integrate physiologically important features into a realistic structural simulation of the aortic valve. A finite element model of the natural human aortic valve was developed considering Linear Elastic and Hyperelastic material properties for the leaflets and aortic tissues and starting from the unpressurized geometry. It has been observed that although similar stress-strain patterns were generated on Aortic Valve for both material properties, the hyperelastic nature of valve tissue can distribute stress smoothly and with lower strain during the cardiac cycle. The deformation of the aortic root can play a prominent role as its compliance changed significantly throughout cardiac cycle. Furthermore, Dynamics of the leaflets can reduce stresses by affecting geometries. The highest values of stress occurred along the leaflet attachment line and near the commissure during diastole. The effects of high +G acceleration on the performance of valve, valve opening and closing characteristics, and equivalent Von Mises stress and strain distribution are also investigated.

Hysteresis motors are self starting brushless synchronous motors which are being used widely due to their interesting features. Accurate modeling of the motors is crucial to successful investigating the Dynamic performance of them. The hysteresis loops of the material used in the rotor and their influences on the parameters of the equivalent circuit are necessary to be taken into consideration adequately. It is demonstrated that some of the equivalent circuit parameters vary significantly with input voltage variation and other operating conditions. In this paper, a comprehensive Analysis of a hysteresis motor in the start up and steady state regimes are carried out based on a developed d-q model of the motor with time-varying parameters being updated during the simulation time. The equivalent circuit of the motor is presented taking into account the major impact of the input voltage. Simulation results performed in Matlab-Simulink environment prove that the existing simple models with constant parameters can not predict the motor performance accurately in particular for variable speed applications. Swings of torque, hunting phenomenon, improvement of power factor by temporarily increasing the stator voltage and start up behavior of the hysteresis machine are some important issues which can accurately be analyzed by the proposed modeling approach.

In the present study the Dynamic behavior of a piezoelectric flow micro sensor based on vortex-induced vibrations (VIV) is investigated. This sensor is made by a cantilever beam, piezoelectric layer and a cylinder at free end which is used to measure the fluid velocity. The proposed VIV sensors have nonLinear Dynamic behavior for different flow velocities therefore in designing VIV micro sensors obtaining Linear operational working range is an important parameter. In this paper the Dynamic behavior of micro flow sensors based on the modified couple stress theory (MCST) is investigated and Linear operational working span is derived. The coupled governing equations of silicon based and piezoelectric layer cantilever beam, gauss electric and Van der pol equation are derived. Utilizing the derived equations the Dynamic behavior of the micro sensor on the basis of parameters such as damping coefficient, cantilever beam length, material length scale parameter and tip cylinder mass is analyzed. The operational work range of the micro sensor, the acceptable Linear behavior domain and error of Linear behavior assumption of the device is investigated. According to the results the maximum Linearization error is 3.5%. In addition to that reduction in cantilever beam length and tip cylinder mass increase the operational working range of the micro sensor. Analyzing the effect of damping coefficient on the Dynamic behavior of micro flow sensor show that increasing the damping coefficient decreases the beam deflection and output voltage, but has no effect on the operational working span of the system and in order to obtain precise output from this sensor the damping coefficient must be reduced. Findings indicate that parameters which make the device behave stiffer such as reduction in beam length or tip cylinder mass or considering non-classical stresses gives a wider acceptable voltage range at higher flow velocities for the micro sensor.