• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.17 no.2
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• pp.109-113
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• 1981

Most existing theories on ship waves and wave resistance are based on the perturbation of the flow field by a small pararr.eter which specifies the slenderness of the ship hull. Since however, ship hulls in practice are neither so slender nor thin enough to secure the validity of the linearized theory, the agreen:ent between the theoretical prediction and the experimental result is not generally satisfactory. The author pointed out that the contribution by the non-linear term in the free surface condition can be represented by sorr.e source distribution over the still water plane. This paper leads to a forrr.ula for the wave resistance of not slender ships at low Froude nurr.bers. and deals with the asynptotic expression. As a nurr.erical example, the wave resistance of Wigley model is calculated, and the result is compared with experimental values. It is concluded that the wave resistance coefficient varies in the rate of Fn6 at low speed limit in general. A comparison with the result derived from the linearized free surface condition shows that the non-linearity of the free surface is irr portant at low speed.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.143-153
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• 2019

In this study, numerical simulations for the prediction of added resistance for KVLCC2 with varying wave steepness are performed using a Computational Fluid Dynamics (CFD) method and a 3-D linear potential method, and then the non-linearities of added resistance and ship motions are investigated in regular short and long waves. Firstly, grid convergence tests in short and long waves are carried out to establish an optimal mesh system for CFD simulations. Secondly, numerical simulations are performed to predict ship added resistance and vertical motion responses in short and long waves and the results are verified using the available experimental data. Finally, the non-linearities of added resistance and ship motions with unsteady wave patterns in the time domain are investigated with the increase in wave steepness in both short and long waves. The present systematic study demonstrates that the numerical results have a reasonable agreement with the experimental data and emphasizes the non-linearity in the prediction of the added resistance and the ship motions with the increasing wave steepness in short and long waves.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.118-123
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• 2001

The linear compressor have been widely used for pressure wave generation in the Stirling cryocooler and Stirling type pulse tube cryocooler for tactical purpose. The linear compressor has small and compact structure, and long life due to having non-contact sealing mechanism. and the pressure drop through regenerator was ver important role in the motion of displacer in the expander of the Stirling cryocooler. In this study, the characteristic of the linear compressor and the pressure drop through regenerator in the expander was experimentally investigated. The results show the resonance of the compressor is very important to get maximum performance. and the gas spring force in the compression space of the compressor has effect on the characteristic of reonance. and the results show the pressure drop through regenerator is very small than operating pressure change.

• Journal of Ocean Engineering and Technology
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• v.4 no.1
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• pp.43-48
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• 1990

The results of previous works on the wave energy conversion do not seem to be satisfactory due to irregularity, and the non-linear hydrodynamic effect which is inevitably featured due to the structural complexity of the ocean wave energy conversion device. These may cause the difficulty estimating the extracted wave power. In this paper a study on estimating the extracted wave power and its ratio. The present authors have developed another method estimating the extracted wave power using the three dimensional source distribution method, which was turned out to be an improved one. It has been observed that the present results may be used for the control of the wave energy conversion device and the optimal design has been derived from the several case studies.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.2
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• pp.126-131
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• 2010

The purpose of this study is to assess the condition of composites used in aircraft under varying temperature environment with ultrasound guided wave technique. Investigation of crucial influential factor on the composite health monitoring related to aircraft operational environments such as the number of thermal cycles and temperature deviation between ground level and flight altitude has been of a great concern for aircraft safety issue. In this study, ultrasonic guided wave health monitoring scheme is proposed to evaluate composite specimens damaged with the thermal fatigue simulating aircraft operational condition. Guided wave dispersion curves are used to select right modes which show a promising sensitivity to each different thermal fatigue damage level. The present approach can be also implemented as one of on-lines health monitoring tools for aircraft.

• Structural Engineering and Mechanics
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• v.14 no.4
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• pp.455-472
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• 2002

The paper involves the study on the elastic and elasto-plastic stress wave propagation in the 1-D and 2-D solid media. The Smooth Particle Hydrodynamics equations governing the elastic and elasto-plastic large deformation dynamic response of solid structures are presented. The proposed additional stress points are introduced in the formulation to mitigate the tensile instability inherent in the SPH approach. Both incremental rate approach and leap-frog algorithm for time integration are introduced and the new solution algorithm is developed and implemented. Two examples on stress wave propagation in aluminium bar and 2-D elasto-plastic steel plate are included. Results from the proposed SPH approach are compared with available analytical values and finite element solutions. The comparison illustrates that the stress wave propagation problems can be effectively solved by the proposed SPH method. The study shows that the SPH simulation is a reliable and robust tool and can be used with confidence to treat transient dynamics such as linear and non-linear transient stress wave propagation problems.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.11 no.4
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• pp.173-188
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• 1999

Kim et al.(I999) presented a non-linear finite element formulation of spatial ocean cables using multiple noded cable elements. The initial equilibrium state of ocean cables subjected to self-weights, support motions, and current forces was determined using the load incremental method and free vibration analysis were performed considering added mass, In this paper, the methods to generate regular and irregular waves and calculate wave forces due to these waves are discussed and challenging example problems are presented in order to investigate dynamic non-linear behaviors of ocean cables subjected to wave loadings.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.708-716
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• 1989

The purpose of this study is to investigate the breakup mechanism of a liquid jet in a coaxial air flow. By using the high speed camera, measured were the instantaneous change of the wave length, amuplitude of disturbance, propagation velocity of wave and breakup length, and the relationships between those data were examined. The shape of the surface of the liquid jet appeared to be rather complicated and irregular. The growth rate of disturbance was not constant, and was changed at the moment of 3ms prior to the disintegration of the liquid jet. Simultaneously at this moment, the propagation velocities of the sequential waves were reversed and the wave length was rapidly decreased.

• Geophysics and Geophysical Exploration
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• v.10 no.1
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• pp.1-18
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• 2007

Non-linear elastic wavefield inversion is a powerful method for estimating elastic parameters for physical constraints that determine subsurface rock and properties. Here, I introduce six elastic-wave velocity models by reconstructing elastic-wave velocity variations from real data and a 2D elastic-wave velocity model. Reflection seismic data information is often decoupled into short and long wavelength components. The local search method has difficulty in estimating the longer wavelength velocity if the starting model is far from the true model, and source frequencies are then changed from lower to higher bands (as in the 'frequency-cascade scheme') to estimate model elastic parameters. Elastic parameters are inverted at each inversion step ('simultaneous mode') with a starting model of linear P- and S-wave velocity trends with depth. Elastic parameters are also derived by inversion in three other modes - using a P- and S-wave velocity basis $('V_P\;V_S\;mode')$; P-impedance and Poisson's ratio basis $('I_P\;Poisson\;mode')$; and P- and S-impedance $('I_P\;I_S\;mode')$. Density values are updated at each elastic inversion step under three assumptions in each mode. By evaluating the accuracy of the inversion for each parameter set for elastic models, it can be concluded that there is no specific difference between the inversion results for the $V_P\;V_S$ mode and the $I_P$ Poisson mode. The same conclusion is expected for the $I_P\;I_S$ mode, too. This gives us a sound basis for full wavelength elastic wavefield inversion.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.5
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• pp.13-23
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• 2001

In the companion paper, F. E. formulation for the geometric and plastic non-linear analysis of steel jacket structures subjected to wave and earthquake loadings was presented and the main processor was developed. In this paper, the pre/post processor are developed in order to analyze the output results effectively as well as to prepare the input data efficiently. Furthermore, the numerical examples are presented and discussed for linear and non-linear analysis of steel jackets under environmental loadings.