• 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 the Korean Society for Aeronautical & Space Sciences
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• v.32 no.6
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• pp.34-48
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• 2004

In this paper an optimization algorithm is suggested to reduce the huge computation time in the optimum design of large structures, especially in spacecraft structures. It combines the coupled load analysis model using a constrained mode of component mode synthesis and the modal transient analysis. The computer simulation code is developed and evaluated in optimizing spacecraft platforms. The developed algorithm can alleviate the computational load with adequate accuracy. From the optimization of a spacecraft structural member, the characteristics of each structural member can be understood.

• Structural Engineering and Mechanics
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• v.22 no.6
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• pp.647-664
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• 2006

The main purpose of this paper is to investigate the effect of transient stochastic analysis on nonlinear response of earth and rock-fill dams to spatially varying ground motion. The dam models are analyzed by a stochastic finite element method based on the equivalent linear method which considers the nonlinear variation of soil shear moduli and damping ratio as a function of shear strain. The spatial variability of ground motion is taken into account with the incoherence, wave-passage and site response effects. Stationary as well as transient stochastic response analyses are performed for the considered dam types. A time dependent frequency response function is used throughout the study for transient stochastic responses. It is observed that stationarity is a reasonable assumption for earth and rock-fill dams to typical durations of strong shaking.

• Computational Structural Engineering
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• v.10 no.3
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• pp.217-223
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• 1997

This paper deals with the basic concepts of sensitivity analysis in a time domain for the transient response of a lumped mass system. Sensitivity analysis methods in thme domain for determining the effects of parameter changes on the response of a dynamic system by external excitation are presented. The parametric sensitivity of a lumped mass system in time domain can be investigated using different types of sensitivity functions, including first order standard and percentage sensitivity functions. These sensitivity functions are determined as a function of partial derivatives of system variables taken with respect to system parameters. In addition, we compared the results of the analytical method by direct method and those of numerical methods.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.4
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• pp.150-159
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• 2018

The present research deals with a finite element analysis and fatigue evaluation of a steam separator of a high-pressure evaporator for the Heat Recovery Steam Generator (HRSG). The fatigue during the expected life of the HRSG was evaluated according to the ASME Boiler and Pressure Vessel Code Section VIII Division 2 (ASME Code). First, based on the eight transient operating conditions prescribed for the HRSG, temperature distribution of the steam separator was analyzed by a transient thermal analysis. Results of the thermal analysis were used as a thermal load for the structural analysis and used to determine the mean cycle temperature. Next, a structural analysis for the transient conditions was carried out with the thermal load, steam pressure, and nozzle load. The maximum stress location was found to be the riser nozzle bore, and hence fatigue was evaluated at that location, as per ASME Code. As a result, the cumulative usage factor was calculated as 0.00072 (much less than 1). In conclusion, the steam separator was found to be safe from fatigue failure during the expected life.

• 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 Aviation and Aeronautics
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• v.15 no.4
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• pp.24-32
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• 2007

In this study, computational structural vibration analyses of a smart unmanned aerial vehicle (SUAV) with tilt-rotors due to dynamic hub loads have been conducted considering detailed supporting structures of installed equipments. Three-dimensional dynamic finite element model has been constructed for different fuel conditions and tilting angles corresponding to helicopter, transition and airplane flight modes. Practical computational procedure for modal transient response analysis is successfully established. Also, dynamic loads generated by rotating blades and wakes in the transient and forward flight conditions are calculated by unsteady computational fluid dynamics technique with sliding mesh concept. As the results of present study, transient structural displacements and accelerations of the vibration sensitive equipments are presented in detail. In addition, vibration characteristics of structures and installed equipments of which safe operation is normally limited by the vibration environment specifications are physically investigated for different flight conditions.

• Structural Engineering and Mechanics
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• v.59 no.2
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• pp.243-259
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• 2016

This research develops a finite element code for the transient dynamic analysis of tapered fiber reinforced polymer (FRP) poles with hollow circular cross-section and flexible joints used in power transmission lines. The FRP poles are modeled by tapered beam elements and their flexible joints by a rotational spring. To solve the time equations of transient dynamic analysis, precise time integration method is utilized. In order to verify the utilized formulations, a typical jointed FRP pole under step, triangular and sine pulses is analyzed by the developed finite element code and also ANSYS commercial finite element software for comparison. Thereafter, the effect of joint flexibility on its dynamic behavior is investigated. It is observed that by increasing the joint stiffness, the amplitude of the pole tip deflection history decreases, and the time of occurrence of the maximum deflection is earlier.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.245-251
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• 1999

The structural analysis of a reactor coolant pump(RCP) of a nuclear power plant is very important for the safety assessment of the plant. Accurate boundary conditions for the heat transfer coefficient are required for reliable thermal stress analysis of the pump casing, especially in transient operations of the pump since the coolant properties are largely dependent on operational conditions. In the present study, a 3D mixed flow type coolant pump was modeled from the RCP drawings and analyzed in the steady state and number of transient flow conditions by using a commercial code STAR-CD. From the result of the computation, it is seem that the average heat transfer coefficients for the cases considered are found to be the suggested values of the manufacturer, Westinghouse Energy System. The unevenness in local heat transfer coefficients, however, is found to be considerable so that the use of average heat transfer coefficients in all boundaries might not give reliable thermal stresses.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.5
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• pp.451-456
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• 2011

To ensure structural integrity of membrane type LNG tank, the rational assessment of the sloshing impact responses of tank structures should be preceded. The sloshing impact pressures acting on the insulation system of LNG tank are typical irregular loads and the resulting structural responses show very complex behaviors accompanied with fluid structure interaction. So it is not easy to estimate them accurately and immense time consuming calculation process would be necessary. In this research, a simplified method to analyse the dynamic structural responses of LNG tank insulation system under pressure time histories obtained by sloshing model test or numerical analysis was studied. The proposed technique based on the concept of linear combination of the triangular response functions which are the transient responses of structures under the unit triangular impact pressure acting on structures. The validity of suggested method was verified through the example calculations and applied to the dynamic structural response analysis of a real Mark III membrane type insulation system using the sloshing impact pressure time histories obtained by model test.