• Structural Engineering and Mechanics
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• 제71권6호
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• pp.713-738
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• 2019

In the paper the dynamics of the oscillating moving load acting in the interior of the hollow cylinder surrounded with elastic medium is studied within the scope of the exact field equations of 3D elastodynamics. It is assumed that the oscillating load act on the certain arc of the internal circle of the cylinder's cross section and this load moves with constant velocity along the cylinder's axis. The corresponding 3D dynamic problem is solved by employing moving coordinate system, the exponential Fourier transform and the presentation these transforms with the Fourier series. The expressions of the transforms are determined analytically, however their originals are found numerically. Under the investigations carried out in the paper the main attention is focused on the so-called "gyroscopic effect", according to which, the influence of the vibration frequency on the values of the critical velocity and interface stresses are determined. Numerical results illustrated this effect are presented and discussed. In particular, it is established how the non-axisymmetricity of the problem acts on the influence of the load oscillation on its critical velocity and on the interface stresses.

• 대한기계학회논문집B
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• 제33권2호
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• pp.124-132
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• 2009

Experiments have been performed to investigate fluid-elastic instability of tube bundles, subjected to twophase cross flow. Fluid-elastic is the most important vibration excitation mechanism for heat exchanger tube bundles subjected to the cross flow. The test section consists of cantilevered flexible cylinder(s) and rigid cylinders of normal square array. From a practical design point of view, fluid-elastic instability may be expressed simply in terms of dimensionless flow velocity and dimensionless mass-damping parameter. For dynamic instability of cylinder rows, added mass, damping and the threshold flow velocity are evaluated. The Fluid-elastic instability coefficient is calculated and then compared to existing results given for tube bundles in normal square array.

• 대한기계학회논문집B
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• 제20권9호
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• pp.2909-2915
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• 1996

Precise and accurate pressure measurements are obtained using deadweight piston gauges. Pressure distribution and elastic distortion in the piston-cylinder unit are the leading factors in determination of effective area. The distortion depends upon the pressure distribution in the clearance between piston and cylinder and those are coupled each other. Considering the viscosity pressure relation of oil and governing flow equation in the clearance, a new numerical iterative algorithm is developed. The disagreement between the monotonous and sharp pressure profiles is an indication that the pressure profile will be different for each piston and cylinder unit due to material variances.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1999년도 학술발표대회 논문집 제18권 1호
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• pp.303-306
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• 1999

The paper describes a theoretical study on the speed of the torsional elastic waves propagating in a circular cylinder whose outer radius varies periodically as a harmonic function of the axial coordinate. The approximate solution for the phase speed has been obtained using the perturbation technique for sinusoidal modulation of small amplitude. It is shown that the wave speed in the cylinder with a corrugated outer surface is less than that in a smooth cylinder by the square of the amplitude of the surface perturbation. This theoretical prediction agrees reasonably with an experimental observation reported earlier. It is also shown that the wave speed reduction due to the surface corrugation becomes larger for a thinner cylinder and for a bigger density of corrugation.

• Smart Structures and Systems
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• 제13권1호
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• pp.1-24
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• 2014

The present study deals with two dimensional electro-elastic analysis of a functionally graded piezoelectric (FGP) cylinder under internal pressure. Energy method and first order shear deformation theory (FSDT) are employed for this purpose. All mechanical and electrical properties except Poisson ratio are considered as a power function along the radial direction. The cylinder is subjected to uniform internal pressure. By supposing two dimensional displacement and electric potential fields along the radial and axial direction, the governing differential equations can be derived in terms of unknown electrical and mechanical functions. Homogeneous solution can be obtained by imposing the appropriate mechanical and electrical boundary conditions. This proposed solution has capability to solve the cylinder structure with arbitrary boundary conditions. The previous solutions have been proposed for the problem with simple boundary conditions (simply supported cylinder) by using the routine functions such as trigonometric functions. The axial distribution of the axial displacement, radial displacement and electric potential of the cylinder can be presented as the important results of this paper for various non homogeneous indexes. This paper evaluates the effect of a local support on the distribution of mechanical and electrical components. This investigation indicates that a support has important influence on the distribution of mechanical and electrical components rather than a cylinder with ignoring the effect of the supports. Obtained results using present method at regions that are adequate far from two ends of the cylinder can be compared with previous results (plane elasticity and one dimensional first order shear deformation theories).

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.833-838
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• 2003

The problem of elastic wave resonance scattering from elastic targets is studied in this paper. A new resonance formalism to extract the elastic resonance information of the target from scattered elastic waves is introduced. The proposed resonance formalism is an extension of the works developed for acoustic wave scattering problems by the author. The classical resonance scattering theory computes reasonable magnitude information of the resonances in each partial wave, but the phase behaves in somewhat irregular way, therefore, is not clearly explainable. The proposed method is developed to obtain physically meaningful magnitude and phase of the resonances. As an example problem, elastic wave scattering from an infinitely-long elastic cylinder was analyzed by the proposed method and compared to the results by RST. In case of no mode conversion, both methods generate identical magnitude. However, the new method computes exact $\pi$ radian phase shills through resonances and anti-resonances while RST produces physically unexplainable phases. In case of mode conversion, in addition to the phase even magnitudes are different. The phase shifts through resonances and antiresonances obtained by the proposed method are not exactly $\pi$ radians due to energy leak by mode conversion. But, the phases by the proposed method show reasonable and intuitively correct behavior compared to those by RST.

• 비파괴검사학회지
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• 제33권2호
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• pp.138-146
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• 2013

본 논문에서는 두꺼운 배관에 존재하는 비 이상화된 원주방향 관통균열의 탄성 응력확대계수 해를 제시하였다. 이를 위해 3차원 탄성 유한요소해석을 수행하였으며, 배관의 형상 및 비 이상화된 원주방향 관통균열의 영향을 고려하기 위해 배관의 두께, 기준균열길이 및 관통균열길이 비를 체계적으로 변화시켰다. 하중 조건으로는 인장하중, 굽힘모멘트 및 내압을 고려하였다. 또한 본 논문에서는 이상화된 원주방향 관통 균열로부터 비 이상화된 원주방향 관통균열의 응력확대계수를 쉽게 계산하기 위해 관통균열 보정계수를 제시하였다. 본 논문의 결과는 실제 균열성장거동을 고려하여 원자력 배관의 배관파단확률을 보다 정확하게 계산하기 위해 적용될 수 있다.

• 한국압력기기공학회 논문집
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• 제8권3호
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• pp.13-22
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• 2012

According to recent research on leak-rate estimates to assess rupture probabilities of nuclear piping which contains a circumferential surface/through-wall cracks due to PWSCC, i.e., xLPR (Extremely Low Probability of Rupture) program, it has been revealed that the use of crack shape with an idealized circumferential through-wall crack during actual crack growth can lead to overestimate of the leak-rate. Thus, for accurate estimation of the leak-rate during crack growth, the more realistic crack shape that can simulate the crack shape transition from surface crack to through-wall crack should be used. In this context, in the present study, the elastic crack opening displacement of slanted circumferential through-wall crack in thick-walled cylinder was proposed based on 3-dimensional elastic finite element fracture mechanics analyses. To propose the elastic crack opening displacement of slanted circumferential through-wall crack in thick-walled cylinder, the geometric variables affecting crack opening displacement, i.e., thickness of cylinder, reference inner crack length and slant crack ratio were systematically varied. In terms of loading conditions, axial tension, global bending moment and internal pressure were considered. The present results can be applied to calculate the leak-rate considering more realistic crack shape transition from surface crack to idealized through-wall crack, and can be expected to enhance current leak-rate estimation scheme, for instance, in xLPR program etc.

• 대한기계학회논문집A
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• 제32권6호
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• pp.488-495
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• 2008

In order to achieve long fatigue lifetimes for cyclically pressurized thick cylinders, multi-layered compound cylinder has been proposed. Such compound cylinder involves a shrink-fit procedure incorporating a monobloc tube which has previously undergone autofrettage. The basic autofrettage theory assumes elastic-perfectly plastic behaviour. Because of the Bauschinger effect and strain-hardening, most materials do not display elastic-perfectly plastic properties and consequently various autofrettage mo dels are based on different simplified material strain-hardening models, which is assumed that combination of linear strain-hardenig and power strain-hardening model. This approach gives a more accurate prediction than the elastic-perfectly plastic model and is suitable for different strain-hardening materials. In this paper, a general autofrettage model that incorporates the material strain-hardening relationship and the Bauschinger effect, based upon the actual tensile-compressive stress-strain curve of a material was proposed. The model was obtained using the von Mises yield criterion and plane strain condition. The tensile-compressive stress-strain curve was obtained by experiment. The parameters needed in the model were determined by fitting the actual tensile-compressive curve of the material. Finally, strain- hardening model was compared with elastic-perfectly plastic model.

• Coupled systems mechanics
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• 제7권5호
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• pp.525-554
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• 2018

The paper deals with the study of the dynamics of the oscillating moving ring load acting in the interior of the hollow circular cylinder surrounded by an elastic medium. The axisymmetric loading case is considered and the study is made by employing the exact equations and relations of linear elastodynamics. The focus is on the influence of the oscillation of the moving load and the problem parameters such as the cylinder's thickness/radius ratio on the critical velocities. At the same time, the dependence between the interface stresses and load moving velocity under various frequencies of this load, as well as the frequency response of the mentioned stresses under various load velocity are investigated. In particular, it is established that oscillation of the moving load can cause the values of the critical velocity to decrease significantly and at the same time the oscillation of the moving load can lead to parametric resonance. It is also established that the critical velocity decreases with decreasing of the cylinder's thickness/radiusratio.