• Structural Engineering and Mechanics
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• 제61권4호
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• pp.539-549
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• 2017

In this paper, the wave propagation in an infinite poroelastic cylindrical bone with cavity is studied. An exact closed form solution is presented by employing an analytical procedure. The frequency equation for poroelastic bone is obtained when the boundaries are stress free and is examined numerically. The magnitude of the frequency equation, wave velocity and attenuation coefficient are calculated for poroelastic bone for different values of magnetic field, density and frequency. In wet bone little frequency dispersion was observed, in contrast to the results of earlier studies. Such a model would in particular be useful in large-scale parametric studies of bone mechanical response. Comparison was made with the results obtained in the presence and absence of magnetic field. The results indicate that the effect of magnetic field, density and frequency on wave propagation in poroelastic bone are very pronounced.

• 한국해양공학회지
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• 제1권2호
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• pp.83-92
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• 1987

Inorder ot estimate the running life of turbine rotors, fatigue crack propagation low, da/dN = C(${\DELTA}K)^m$, proposed by paris et al. has been widely applied. In this study, fatigue crack propagation rates for 16 samples of 1% Cr-Mo-V rotor steel were measured and statistical characteristics of m and C values in above equation were reviewed. The results are summarized as follows. 1. C and m follow a log-normal distribution and normal distribution, respectively. And the relation of C and shows a strong negative correlation. 2. Fatigue crack propagation equation can be expressed as da/dN=$4.11{\times}10^{-4}({\Delta}K/153.8)^m$, introducing the ralationship C=$C_oK_o^{-m}$. In this case, contribution of $C_o$ distribution to the distribution of log C shows very small compared to degrees of contribution by m.

• 한국음향학회지
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• 제19권5호
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• pp.46-52
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• 2000

본 논문에서는 수중 음 전달에 대한 내부파의 영향을 파악하기 위하여 내부파에 의한 음속의 변화량을 수치적으로 구현하고 이를 바탕으로 내부파가 존재할 경우의 음 전달 실험을 수치적으로 수행하였다. 음 전달 수치 실험의 결과를 한국 동해에서 수행된 음향 실험 자료와 비교하였다. 수중 음 전달 수치 실험을 위해서는 Galerkin방법을 이용한 고차포물선 방정식법(SNUPE)를 사용하였다. 음 전달에 대한 내부파의 영향을 파악하기 위하여 불규칙 계수(Scintillation index)를 사용하였고 이를 실제 음향 실험 자료와 비교하였다.

• 한국광학회지
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• 제14권4호
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• pp.429-433
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• 2003

전파정수가 랜덤하게 분포하는 선로 상에서 파동함수의 해의 성질을 고찰함으로써 랜덤한 매질 내의 파동의 국재현상에 대한 이론적 해석을 시도하였다 파동의 국재는 함수의 해가 증대에서 감쇠로 전환하는 과정에서 발생하므로, 먼저 파동의 증대가 감쇠로 전환되는 과정을 이론적으로 규명하기 위하여 2차 파동방정식을 Bragg조건 등을 이용하여 근사적으로 1차 슐뢰딩거의 방정식의 형태로 유도하였다. 그리고 이 방정식이 취할 수 있는 여러 가지 해의 성질과 그 해가 성립하기 위한 조건에 대하여 고찰하였으며, 파동방정식의 해의 국재성과 전파정수의 변동에 대한 관계에 대하여 몇 가지 조건을 조사하였다. 지수형의 해에서 유전율이 $\varepsilon$=(0,0,$\varepsilon$$_{0}$)인 경우 $\varepsilon$$_{0}$는 파동의 위상에 관여하여 국재현상을 일으키는 요소가 된다는 것을 확인하였다.

• 한국안전학회지
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• 제9권3호
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• pp.13-21
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• 1994

Effects of tensile and compression residual stresses in the welded SS41 and A17075-76 on fatigue crack propagation behavior are investigated when a crack propagates from residual stresses region. We propose the fatigue crack growth equation on tensile and compression residual stresses in welded metal. The results obtained in this experimental study are summarized as follows . 1 ) A fatigue crack growth equation which applied fatigue fracture behavior of the welded metal is proposed. (equation omitted) where, $\alpha$, $\beta$, ${\gamma}$ and $\delta$ are constants, and R$_{eff}$ is effective stress ratio [R$_{eff}$=(Kmin+Kres)/(Kmax+Kres)], Kcf is critical fatigue stress intensity factor. The constants are obtained from nonlinear least square method. The relation between crack length and number of cycles obtained by integrating the fatigue crack growth rate equation is in agreement with the experimental data. 2) The experimental results confirmed that the cause of crack extension and retardation by residual stresses has relation to the phenomenon of crack closure. 3) The relaxing trend of residual stresses by the crack propagation was greater In case of compressive residual stress than that of tensile residual stress in the welded metal.tal.

• Earthquakes and Structures
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• 제12권6호
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• pp.619-628
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• 2017

The intent of this paper is to investigate the propagation of Love waves in a dry sandy medium sandwiched between fiber-reinforced layer and prestressed porous half-space. Separate displacement components have been deduced in order to characterize the dynamics of individual materials. Using suitable boundary conditions, the frequency equation has been derived by means of separation of variables which reveals the significant role of reinforcement parameters, sandiness, thickness of layers, porosity and prestress on the wave propagation. The phase velocity of the Love wave has been discussed in accordance with its typical cases. In both cases when fiber-reinforced and dry sandy media are absent, the derived equation of Love type wave coincides with the classical Love wave equation. Numerical computations have been performed in order to graphically illustrate the dependencies of different parameters on phase velocity of Love waves. It is observed that the phase velocity decreases with the increase of parameters pertaining to reinforcement and prestress. The results have certain potential applications in earthquake seismology and civil engineering.

• Journal of Advanced Marine Engineering and Technology
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• 제29권4호
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• pp.391-398
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• 2005

In this investigation, turbulent premixed combustion and flame front propagation in a gas turbine combustion chamber is studied. Direct numerical simulation of turbulent reacting flows demands extremely high computational resources, especially in more complicated geometry. The alternative choice may be left for Large Eddy Simulation (LES) by which only large scales are solved directly. In combustion problems, capturing the large scales' behavior without solving the details of small scales is a difficult task. Using a transport equation for description of the flame front propagation and therefore avoiding the calculation of inner flame structure is the basic idea of this study. For this purpose. the so-called G-equation has been used by which any iso-level of the G variable provides the flame location. A comparison with the experiment indicates that the present method can predict a turbulent velocity field and also capture a instantaneous 3-dimensional flame structure.

• Journal of Mechanical Science and Technology
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• 제20권8호
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• pp.1240-1247
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• 2006

Large eddy simulation of turbulent premixed flame in turbulent channel flow is studied by using G-equation. A flamelet model for the premixed flame is combined with a dynamic subgrid combustion model for the filtered propagation flame speed. The objective of this work is to investigate the validity of the dynamic subgrid G-equation model to a complex turbulent premixed flame. The effect of model parameters of the dynamic sub grid G-equation on the turbulent flame speed is investigated. In order to consider quenching of laminar flames on the wall, wall-quenching damping function is employed in this calculation. In the present study, a constant density turbulent channel flow is used. The calculation results are evaluated by comparing with the DNS results of Bruneaux et al.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2015년도 제51회 KOSCO SYMPOSIUM 초록집
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• pp.75-76
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• 2015

Lifted flame stabilization mechanism can be explained with constant Schmidt number from the equation of $H^{\ast}_L/d^2_o=const{\times}v_e^{(2Sc-1)/(Sc-1)}$. In this research, a method of local Schmidt number was applied in order to measure edge flame propagation velocities, and edge flame propagation velocity was calculated from the trend between lift-off height and nozzle flow rate.

• 대한기계학회논문집
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• 제16권9호
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• pp.1691-1699
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• 1992

The experimental results of fatigue crack propagation under constant amplitude loading show that intra-and inter-specimen variability exist. In this paper, a stochastic model for the estimation of mean and variance of crack propagation life is presented To take into account the intra-specimen variability, the material resistance against crack propagation is treated as an 1-dimensional spatial stochastic process, i. e. random field, varying along the propagation path. For the inter-specimen variability, C in paris equation is assumed to be a random variable. Compared with experimental results reported, the present method well estimate the variation in fatigue crack propagation life. And it is confirmed that the thicker the specimen thickness is, the less the variation of propagation life is.