• Journal of Ocean Engineering and Technology
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• v.23 no.1
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• pp.54-59
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• 2009

In this paper, the effect of the position and size of a lumped mass on the structural stability of a high speed underwater vehicle is presented. For simplicity, a real vehicle was modeled as a follower force subjected beam that was resting on an elastic foundation, and the lumped mass effect was simplified as an elastic intermediate support. The stability of the simplified model was numerically analyzed based on the Finite element method (FEM). This numerical simulation revealed that flutter type instability or divergence type instability occurs, depending on the position and stiffness of the elastic intermediate support, which implies that the instability of the real model is affected by the position and size of the lumped mass.

• Advances in materials Research
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• v.12 no.3
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• pp.243-261
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• 2023

This study aims to analyze the mechanical buckling behavior of a single-walled carbon nanotube (SWCNT) integrated with a one-parameter elastic medium and modeled as a Kerr-type foundation under a longitudinal magnetic field. The structure is considered homogeneous and therefore modeled utilizing the nonlocal first shear deformation theory (NL-FSDT). This model targets thin and thick structures and considers the effect of the transverse shear deformation and small-scale effect. The Kerr model describes the elastic matrix, which takes into account the transverse shear strain and normal pressure. Using the nonlocal elastic theory and taking into account the Lorentz magnetic force acquired from Maxwell relations, the stability equation for buckling analysis of a simply supported SWCNT under a longitudinal magnetic field is obtained. Moreover, the mechanical buckling load behavior with respect to the impacts of the magnetic field and the elastic medium parameters considering the nonlocal parameter, the rotary inertia, and transverse shear deformation was examined and discussed. This study showed useful results that can be used for the design of nano-transistors that use the buckling properties of single-wall carbon nanotubes(CNTs) due to the creation of the magnetic field effect.

• Journal of Advanced Research in Ocean Engineering
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• v.4 no.4
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• pp.146-162
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• 2018

The unsteady problem of a rigid body impact onto a floating plate is studied. Both the plate and the water are at rest before impact. The plate motion is caused by the impact force transmitted to the plate through an elastic layer with viscous damping on the top of the plate. The hydrodynamic force is calculated by using the second-order model of plate impact by Iafrati and Korobkin (2011). The present study is concerned with the deceleration experienced by a rigid body during its collision with a floating object. The problem is studied also by a fully-nonlinear computational-fluid-dynamics method. The elastic layer is treated with a moving body-fitted grid, the impacting body with an immersed boundary method, and a discrete-element method is used for the contact-force model. The presence of the elastic layer between the impacting bod- ies may lead to multiple bouncing of them, if the bodies are relatively light, before their interaction is settled and they continue to penetrate together into the water. The present study is motivated by ship slamming in icy waters, and by the effect of ice conditions on conventional free-fall lifeboats.

• Advances in nano research
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• v.16 no.3
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• pp.313-324
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• 2024

The main aims of this study are to develop a new nonlocal quasi-3D theory for the free vibration behaviors of the functionally graded sandwich nanobeams. The sandwich beams consist of a ceramic core and two functionally graded material layers resting on elastic foundations. The two layers, linear spring stiffness and shear layer, are used to model the effects of the elastic foundations. The size-effect is considered using nonlocal elasticity theory. The governing equations of the motion of the functionally graded sandwich nanobeams are obtained via Hamilton's principle in combination with nonlocal elasticity theory. Then the Navier's solution technique is used to solve the governing equations of the motion to achieve the nonlocal free vibration behaviors of the nanobeams. A deep parametric study is also provided to demonstrate the effects of some parameters, such as length-to-height ratio, power-law index, nonlocal parameter, and two parameters of the elastic foundation, on the free vibration behaviors of the functionally graded sandwich nanobeams.

• Journal of Industrial Technology
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• v.22 no.A
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• pp.229-240
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• 2002

This paper is an experimental and numerical work of Investigating the bearing capacity of shallow foundation of rubble mound under eccentric loads. Parametric centrifuge model tests at the 50g level environments with the model footings in the form of strip footing were performed by changing the loading location of model footing, relative density and materials for ground foundation. For the model ground, crushed rock sampled from a rocky mountain was prepared with a grain size distribution of having an identical coefficient of uniformity to the field condition. Model ground was also prepared with relative densities of 50 % and 80 %. For loading condition, model tests with and without eccentric load were carned out to investigate the effect of eccentric loads and a numerical analysis with the commertially available software of FLAC was performed. For numerical estimation with FLAC, the hyperbolic model of a nonlinear elastic constitutive relationship was used to simulate the stress-stram constitutive relationship of model ground and a series of triaxial compression test were carried out to find the parameters for this model Test results were analyzed and compared with Meyerhof method (1963), effective area method based on the limit equilibrium method, and a numerical analysis with FLAC.

• Earthquakes and Structures
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• v.8 no.5
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• pp.1241-1254
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• 2015

Spatially variable ground motions can be significant on the seismic response of a structure due to the incoherency of the incident wave. Incoherence of the incident wave is resulted from wave passage and wave scattering. In this study, wave passage effect on the response spectrum of a building structure built on a soft soil layer was investigated utilizing a finite element program of P3DASS (Pseudo 3-dimensional Dynamic Analysis of a Structure-soil System). P3DASS was developed for the axisymmetric problem in the cylindrical coordinate, but it is modified to apply anti-symmetric input earthquake motions. Study results were compared with the experimental results to verify the reliability of P3DASS program for the shear wave velocity of 250 m/s and the apparent shear wave velocities of 2000-3500 m/s. Studied transfer functions of input motions between surface mat foundation and free ground surface were well-agreed to the experimental ones with a small difference in all frequency ranges, showing some reductions of the transfer function in the high frequency range. Also wave passage effect on the elastic response spectrum reduced the elastic seismic response of a SDOF system somewhat in the short period range.

• Earthquakes and Structures
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• v.10 no.6
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• pp.1369-1389
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• 2016

The soil-structure interaction effect significantly influences the design of multi-storey buildings subjected to lateral seismic loads. The shear walls are often provided in such buildings to increase the lateral stability to resist seismic loads. In the present work, the nonlinear soil-structure analysis of a G+5 storey RC shear wall building frame having isolated column footings and founded on deformable soil is presented. The nonlinear seismic FE analysis is carried out using ANSYS software for the building with and without shear walls to investigate the effect of inclusion of shear wall on the moments in the footings due to differential settlement of soil mass. The frame is considered to behave in linear elastic manner, whereas, soil mass to behave in nonlinear manner. It is found that the interaction effect causes significant variation in the moments in the footings. The comparison of non-interaction and interaction analyses suggests that the presence of shear wall causes significant decrease in bending moments in most of the footings but the interaction effect causes restoration of the bending moments to a great extent. A comparison is made between linear and nonlinear analyses to draw some important conclusions.

• Advances in Computational Design
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• v.5 no.1
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• pp.35-54
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• 2020

One of the prevailing structural systems in high-rise buildings is the core-wall system. On the other hand, the existence of one or more underground stories causes the perimeter below-grade walls with the diaphragm of grade level to constitute of a very stiff box. In this case or a similar situation, during the lateral response of a tall building, underground perimeter walls and diaphragms that provide an increased lateral resistance relative to the core wall may introduce a prying action in the core that is called backstay effect. In this case, a rather great force is generated at the diaphragm of the grade-level, acting in a reverse direction to the lateral force on the core-wall system, and thus typically causes a reverse internal shear. In this research, in addition to review of the results of the preceding studies, an improved relationship is proposed for prediction of backstay force. The new proposed relationship takes into account the effect of foundation flexibility and is presented in a non-dimensional form. Furthermore, a specific range of the backstay force to lateral load ratio has been determined. And finally, it is shown that although all suggested formulas are valid in the elastic domain, yet with some changes in the initial considerations, they can be applied to some certain non-linear problems as well.

• Advances in nano research
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• v.10 no.1
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• pp.25-42
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• 2021

In this article, the vibration behavior of embedded Functionally Graded Nanoplate (FGNP) employing nonlocal Kirchhoff's plate theory has been investigated under hygrothermal environment. The FGNP is considered to be supported by Winkler-Pasternak foundation. The Eringen's differential theory is used for size effect on the vibration of the FGNP. Rayleigh-Ritz method with orthogonal polynomials are employed for the governing equations and edge constraints. The advantage of this method is that it overcomes all the drawbacks of edge constraints and can easily handle any combinations of mixed edge constraints. The coefficients viz. moisture expansion, thermal expansion and elastic coefficients are considered to be transversely graded across the FGNP. The similarity of the calculated natural frequencies is examined with the previous research, and a good concurrency is seen. The objective of this article is to analyze the parameters' effect on the nondimensionalized frequency of embedded FGNP under hygrothermal environment subjected to all possible edge constraints. For this, uniform and linear rise of temperature and moisture concentration are considered. The study highlights that the nonlocal effect is pronounced for higher modes. Moreover, the effect of the Pasternak modulus is seen to be prominent compared to the Winkler modulus on non dimensionalized frequencies of FGNP.

• Coupled systems mechanics
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• v.3 no.3
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• pp.305-318
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• 2014

The study deals with the physical modeling of a typical building frame resting on pile foundation and embedded in cohesive soil mass using complete three-dimensional finite element analysis. Two different pile groups comprising four piles ($2{\times}2$) and nine piles ($3{\times}3$) are considered. Further, three different pile diameters along with the various pile spacings are considered. The elements of the superstructure frame and those of the pile foundation are descretized using twenty-node isoparametric continuum elements. The interface between the pile and pile and soil is idealized using sixteen-node isoparametric surface elements. The current study is an improved version of finite element modeling for the soil elements compared to the one reported in the literature (Chore and Ingle 2008). The soil elements are discretized using eight-, nine- and twelve-node continuum elements. Both the elements of superstructure and substructure (i.e., foundation) including soil are assumed to remain in the elastic state at all the time. The interaction analysis is carried out using sub-structure approach in the parametric study. The total stress analysis is carried out considering the immediate behaviour of the soil. The effect of various parameters of the pile foundation such as spacing in a group and number piles in a group, along with pile diameter, is evaluated on the response of superstructure. The response includes the displacement at the top of the frame and bending moment in columns. The soil-structure interaction effect is found to increase displacement in the range of 58 -152% and increase the absolute maximum positive and negative moments in the column in the range of 14-15% and 26-28%, respectively. The effect of the soil- structure interaction is observed to be significant for the configuration of the pile groups and the soil considered in the present study.