• Structural Engineering and Mechanics
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• v.70 no.2
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• pp.179-197
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• 2019

In this article, the effect of different geometrical, materials and load parameters on the transient response of axisymmetric viscoelastic functionally graded annular plates with different boundary conditions are studied. The behavior of the plate is assumed the elastic in bulk and viscoelastic in shear with the standard linear solid model. Also, the graded properties vary through the thickness according to a power law function. Three types of mostly applied transient loading, i.e., step, impulse, and harmonic with different load distribution respect to radius coordinate are examined. The motion equations and the corresponding boundary conditions are extracted by applying the first order shear deformation theory which are three coupled partial differential equations with variable coefficients. The resulting motion equations are solved analytically using the perturbation technique and the generalized Fourier series. The sensitivity of the response to the graded indexes, different transverse loads, aspect ratios, boundary conditions and the material properties are investigated too. The results are compared with the finite element analysis.

• Nuclear Engineering and Technology
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• v.47 no.6
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• pp.766-775
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• 2015

The integrity assessment of reactor vessel internals should be conducted in the design process to secure the safety of nuclear power plants. Various loads such as self-weight, seismic load, flow-induced load, and preload are applied to the internals. Therefore, the American Society of Mechanical Engineers (ASME) Code, Section III, defines the stress limit for reactor vessel internals. The present study focused on structural response analyses of the upper guide structure upper flange. The distributions of the stress intensity in the flange body were analyzed under various design load cases during normal operation. The allowable stress intensities along the expected sections of stress concentration were derived from the results of the finite element analysis for evaluating the structural integrity of the flange design. Furthermore, seismic analyses of the upper flange were performed to identify dynamic behavior with respect to the seismic and impact input. The mode superposition and full transient methods were used to perform time-history analyses, and the displacement at the lower end of the flange was obtained. The effect of the damping ratio on the response of the flange was also evaluated, and the acceleration was obtained. The results of elastic and seismic analyses in this study will be used as basic information to judge whether a flange design meets the acceptance criteria.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.1 s.94
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• pp.63-71
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• 2005

In this study, structural vibration analyses of a composite smart unmanned aerial vehicle (UAV) have been conducted considering dynamic hub-loads of tilt-rotor. Practical computational structural dynamics technique based on the finite element method is applied using MSC/NASTRAN. The present smart UAV(TR-S2) structural model is constructed as full 3D configurations with both the helicopter flight mode and the airplane flight mode. Modal based transient response and frequency response analyses are used to efficiently investigate vibration characteristics of structure and installed electronic equipments. It is typically shown that the helicopter flight mode with the 90-deg tilting angle is the most critical case for the induced vibration of installed electronic equipments in the front.

• Proceeding of EDISON Challenge
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• 2017.03a
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• pp.259-269
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• 2017

Gust load is a very important load factor in designing various structures of an aircraft and judging its stability. This is because the blast effect on the aircraft in operation increases the risk of damage to the structure of the aircraft and causes a negative impact such as shortening the fatigue life by generating vibration. Particularly in the case of wing, a change in angle of attack is caused by gust load, and an additional lift acts on the wing, thereby being exposed to various excitational environments. Severe structural damage to the aircraft may occur if the natural frequencies of the aircraft wing are close to or coincident with the frequencies of the gust load applied to the wing. Recent trends of research include flight dynamics analysis considering discontinuous gusts or structural optimization of the blades under gust load. A number of studies have been conducted to interpret gust load response in consideration of irregularities in gusts. In this paper, we tried to imagine the situation of the aircraft subjected to the gust load as realistic as possible, and proposed an algorithm to track back the critical gust profile according to given aircraft characteristics from the viewpoint of preliminary engineering prediction.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.3
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• pp.175-181
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• 2020

For the success of a structural integrity management, it is essential to acquire structural response data at some critical locations with limited number of sensors. In this study, the structural response of numerical model was estimated by data fusion approach based on the Kalman filter known as stochastic recursive filter. Firstly, transient direct analysis was conducted to calculate the acceleration and strain of the numerical standing beam model, then the noise signals were mixed to generate the numerical measurement signals. The acceleration measurement signal was provided to the Kalman filter as an information on the external load, and the displacement measurement, which was transformed from the strain measurement by using strain-displacement conversion relationship, was provided into the Kalman filter as an observation information. Finally, the Kalman filter estimated the displacement by combining both displacements calculated from each numerically measured signal, then the estimated results were compared with the results of the transient direct analysis.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.3 s.73
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• pp.295-302
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• 2006

In this study, computational structural dynamic analyses of a gyrocopter have been conducted considering unsteady dynamic hub-loads due to rotating blades. 3D CATIA models with detailed mechanical parts we constructed and virtually assembled into the complete aircraft configuration. The dynamic loading generated by rotating blades in the forward flight condition are calculated by a commercial computational fluid dynamics (CFD) code such as FLUENT. Modal based transient and frequency response analyses are used to efficiently investigate vibration characteristics of the gyrocopter. Free vibration analysis results for different fuel and pilot conditions, frequency responses and transient responses for critical flight conditions are also presented in detail.

• Journal of Ocean Engineering and Technology
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• v.31 no.5
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• pp.357-363
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• 2017

The sloshing pressure acting on a membrane-type LNG CCS is a typical irregular impact load, and the structural response of a tank system induced by sloshing also shows very complex behavior, including fluid structure interaction. Therefore, it is not easy to accurately estimate the sloshing impact pressures and resulting structural response. Moreover, a huge time consuming process to deal with the enormous pressure data obtained during a model tank test and the following structural analysis would be inevitable. To reduce the computation time for structural analysis, in this study, a rational structural modeling strategy was considered, and a simplified scheme to analyze the dynamic structural responses of an LNG CCS was introduced, which was based on the concept of the linear combination of the triangular response functions obtained by a transient response analysis of structures under unit triangular impact pressure. A structural analysis of a real Mark III membrane type insulation system under the sloshing impact pressure time histories obtained by model tests was performed using the various proposed structural models and simplified analysis scheme. The results were investigated in detail, including the elastic support effects of the hull structure.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.7
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• pp.33-39
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• 2005

A mathematical model, GUNBLAST, of blast waves emitted from a gun muzzle is established, and structural response analyses for the blast load are performed. The blast wave can be divided into two kinds of waves, free field and reflected blast waves. In this research, the free field blast wave model is established by the use of a scaling approach, and the reflected blast wave is calculated by using the oblique shock theory and computational fluid dynamic calculation. GUNBLAST is applied to two kinds of structural models. To investigate the effect of the muzzle distance from a structural surface, the blast waves on a plate for various muzzle distances are compared to uniform loads. Moreover, the transient response analysis of an aircraft wing model with a 12.7mm gun is carried out by using MSC/NASTRAN. From the results, it can be shown that the blast wave can cause broad random vibration and high frequency damage to equipments mounted in the aircraft.

• Structural Engineering and Mechanics
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• v.7 no.3
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• pp.331-344
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• 1999

This paper provides an analysis of the transient behaviour of a right-angled bent cantilever beam subjected to a suddenly applied force at its tip perpendicular to its plane. Based on a rigid, perfectly plastic material model, a double-hinge mechanism is required to complete the possible deformation under a rectangular force pulse (constant force applied for a finite duration) with a four-phase response mode. The kinematics of the various response phases are described and the partitioning of the input energy at the plastic hinges during the motion is evaluated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.8
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• pp.826-831
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• 2009

The piping systems in nuclear power plant are composed of various typed pipes such as straight, elbow pipe, branch and reducer etc. The elbow is connected from straight pipe to another pipes in order to establish the complicated piping system. Elbow is one of very important components considering management of wall thinning degradation. It is however applied by various loads such as system pressure, earthquake, postulated break loading and many transient loads, which provoke simply the internal pressure, bending and torsional stress. In this study, firstly pipes in the secondary system of the nuclear power plant are classified as pipe size and type for selecting the investigating range. Next, a large number of finite element analysis considering the all typed dimensions of commercial pipe has been performed to find out the behavior of TES(twice elastic slop) plastic load of elbows, which is based on evaluation of the structural safety factor. Finally performance based structural safety factor was investigated comparing with maximum allowable load by construction code.