• Steel and Composite Structures
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• v.52 no.3
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• pp.273-291
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• 2024

This paper presents a three-dimensional displacement-based formulation to investigate the free vibration of functionally graded nanoplates resting on a Winkler-Pasternak foundation based on the nonlocal elasticity theory. The material properties of the FG nanoplate are considered to vary continuously through the thickness of the nanoplate according to the power-law distribution model. A general three-dimensional displacement field is considered for the plate, which takes into account the out-of-plane strains of the plate as well as the in-plane strains. Unlike the shear deformation theories, in the present formulation, no predetermined form for the distribution of displacements and transverse strains is considered. The equations of motion for functionally graded nanoplate are derived based on Hamilton's principle. The solution is obtained for simply-supported nanoplate, and the predicted results for natural frequencies are compared with the predictions of shear deformation theories which are available in the literature. The predictions of the present theory are discussed in detail to investigate the effects of power-law index, length-to-thickness ratio, mode numbers and the elastic foundation on the dynamic behavior of the functionally graded nanoplate. The present study presents a three-dimensional solution that is able to determine more accurate results in predicting of the natural frequencies of flexural and thickness modes of nanoplates. The effects of parameters that play a key role in the analysis and mechanical design of functionally graded nanoplates are investigated.

• Journal of Aerospace System Engineering
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• v.1 no.3
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• pp.26-31
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• 2007

This paper addresses a method for structural optimum design of composite rotor blade. The basic model of a composite helicopter main rotor blade is designed and its parameters determining the structural/dynamic properties are studied. Through the investigation of flap/lag/torsional stiffness, the structural properties of the model are analyzed. In this study, helicopter rotor blades are analyzed by using VABS. The computer program VABS (Variational Asymptotic Beam Section Analysis) uses the variational asymptotic method to split a three-dimensional nonlinear elasticity problem into a two dimensional cross-sectional analysis and a one-dimensional nonlinear beam problem. This is accomplished by taking advantage of certain small parameters inherent to beam-like structures. In addition, the rotational stability of the blade is estimated by the frequency diagram from FE analysis(MSC.Patran/Nastran) to understand its vibrational property. From the result, design parameters to determine and optimize the properties of the model are presented.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2005.04a
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• pp.505-509
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• 2005

Analysis program to estimate the dynamic characteristics of bridge is investigated by using three-dimensional analytical model considering vehicle-bridge interaction. A dynamic interaction models of the vehicle-bridge system are established, which is composed of a vehicle element model and a finite element bridge model. The vehicle models are established according to the structure and suspending properties of vehicle. The dynamic responses of the bridge are calculated. But the computer simulation program is being verified with field tests results, it must be corrected according to them.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.2805-2816
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• 1994

This paper describes dynamic finite element analyses performed to study the dynamic behaviors of a shipping container under the impact onto rigid target due to the accidental fall from the hight of 9 m. Using two and three dimensional techniques, the shipping container which gave the maximum damage, ten different drop orientations are considered ; at intervals of $5^{\circ}$ from $45^{\circ}$ to $90^{\circ}$ According to the present results, the orientation of the shipping container which gave the maximum damage is $85^{\circ}$ from horizontal for oblique drop in the primary impact. In the optimal design of the shipping container, the impact limiter material must be considered importantly because it's proper selection affects the weight and the manufacturing cost of the shipping container. The analysis of the shipping container in this paper demonstrated that the shipping container is structurally sound relative to the regulatory drop test requirements.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.1
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• pp.30-33
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• 2008

Understanding the characteristics of amputee gait is key in developing more advanced prostheses. The aim of this study was to quantitatively analyze a stair-climbing task for transfemoral amputees with a prosthesis and to predict the muscle forces and joint moments at musculoskeletal joints using a dynamic analysis. A three-dimensional musculoskeletal model of the lower extremities was constructed from a gait analysis using transformation software for two transfemoral amputees and ten healthy people. The measured ground reaction forces and kinematical data of each joint from the gait analysis were used as input data for an inverse dynamic analysis. Dynamic analyses of an transfemoral amputee climbing stairs were performed using musculoskeletal models. The results showed that the summed muscle forces of the hip extensor of an amputated leg were greater than those of a sound leg. The opposite was true at the hip abductor and knee flexor of an amputated leg. We also found that higher moments at the hip and knee joints of the sound leg were required to overcome the flexion moment caused by the body weight and amputated leg. Dynamic analyses using musculoskeletal models may be a useful means to predict muscle forces and joint moments for specific motion tasks related to rehabilitation therapy.

• Computational Structural Engineering
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• v.8 no.3
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• pp.91-102
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• 1995

For the wave propagation problems, the influence of time-dependent dynamic behavior must be accounted in the analysis. In this study, the dynamic analysis method which combines finite elements and boundary elements is developed for the wave propagation problem modelling the infinity of medium through 3-D boundary elements and underground structure through degenerated finite shell elements. Performing dynamic analysis of underground tunnels by the proposed coupling method of boundary and finite elements, it is found that the change of the stiffness of structures has a good effect on the response. It is also found that the consideration of the repeating effect due to moving traffic loads which is difficult with existing 2-D dynamic analysis can be possible with the 3-D analysis in time domain.

• Structural Engineering and Mechanics
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• v.41 no.1
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• pp.83-94
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• 2012

Assessment of a monumental concrete arch bridge with a total length of 210 meters having three major spans of 30 meters and a height of 65 meters, which is located in an earthquake-prone region in southern part of the country is presented in this study. Three-dimensional finite element model of the bridge was generated using a commercially available general finite element analysis software and based on the outcomes of a series of in-depth acceleration measurements that were conducted on-site, the model was refined. By using the structural parameters obtained from the dynamic and the static tests, calibrated model of the bridge structure was obtained and this model was used for necessary calculations regarding structural assessment and evaluation.

• Nuclear Engineering and Technology
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• v.51 no.5
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• pp.1231-1240
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• 2019

Unlike land-based nuclear power plants, a marine or floating reactor is affected by external forces due to ocean conditions. These external forces can cause additional accelerations and affect each system and equipment of the marine reactor. Therefore, in designing a marine reactor and evaluating its performance and stability, a thermal hydraulic safety analysis code is necessary to consider the thermal hydrodynamic effects of ship motion. MARS, which is a reactor system analysis code, includes a dynamic motion model that can simulate the thermal-hydraulic phenomena under three-dimensional motion by calculating the body force term included in the momentum equation. In this study, it was verified that the dynamic motion model can simulate fluid motion with reasonable accuracy using conceptual problems. In addition, two modifications were made to the dynamic motion model; first, a user-supplied table to simulate a realistic ship motion was implemented, and second, the flow regime map determination algorithm was improved by calculating the volume inclination information at every time step if the dynamic motion model was activated. With these modifications, MARS could simulate the thermal-hydraulic phenomena under ocean motion more realistically.

• Journal of Ocean Engineering and Technology
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• v.11 no.4
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• pp.76-89
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• 1997

The hydrodynamic interaction characteristics between multiple floating bodies of semisubmersible type are examined to present the basic data for the design of huge offshore structures supported by a large number of the floating bodies in multi-directional irregular waves. The numerical approach is based on a combination of a three-dimensional source distribution method, the wave interaction theory and the spectral analysis method. The effects of wave directionality on the wave exciting forces acting on multiple floating bodies in multi-directional irregular waves also have been pointed out.

• Structural Engineering and Mechanics
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• v.55 no.2
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• pp.245-261
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• 2015

A three-dimensional (3-D) method of analysis is presented for determining the free vibration frequencies of eccentric hemi-spherical shells of revolution with variable thickness. Unlike conventional shell theories, which are mathematically two-dimensional (2-D), the present method is based upon the 3-D dynamic equations of elasticity. Displacement components $u_r$, $u_{\Theta}$, and $u_z$ in the radial, circumferential, and axial directions, respectively, are taken to be periodic in ${\theta}$ and in time, and algebraic polynomials in the r and z directions. Potential and kinetic energies of eccentric hemi-spherical shells with variable thickness are formulated, and the Ritz method is used to solve the eigenvalue problem, thus yielding upper bound values of the frequencies by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Convergence to three or four-digit exactitude is demonstrated for the first five frequencies of the shells. Numerical results are presented for a variety of eccentric hemi-spherical shells with variable thickness.