• 소음진동
• /
• 제8권2호
• /
• pp.353-360
• /
• 1998

In this paper, a modeling method for the bending vibration analysis of rotating Timoshenko beams with concentrated mass and mass moment of inertia is presented. The shear and rotary inertia effects become critical for the accurate estimation of the natural frequencies and mode shapes as the slenderness ratio decreases. The natural frequencies obtained by using the Timoshenko beam theory are lower than those by using the Euler beam theory. The critical angular speed, which does not exist only with the concentrated mass, exists with the concentrated mass moment of inertia.

• 한국기계가공학회지
• /
• 제9권5호
• /
• pp.90-95
• /
• 2010

The dynamic instability and natural frequency of elastically restrained pipe conveying fluid with the attached mass are investigated in this paper. Based on the Euler-Bernoulli beam theory, the equation of motion is derived by using extended Hamilton's Principle. The influence of attached mass and its position on the dynamic instability of a elastically restrained pipe system is presented. Also, the critical flow velocity for the flutter and divergence due to the variation in the position and stiffness of supported spring is studied. Finally, the critical flow velocities and stability maps of the pipe conveying fluid with the attached mass are obtained by changing the parameters.

• 한국강구조학회 논문집
• /
• 제17권6호통권79호
• /
• pp.699-705
• /
• 2005

이 논문은 자유단에 집중질량을 갖고 종동력이 작용하는 변단면 캔틸레버 기둥의 임계하중에 관한 연구이다. 기둥의 단면을 중실 직사각형 단면을 갖는 선형 변단면으로 채택하고, Bernoulli-Euler 보 이론에 의한 자유단 집중질량을 갖고 종동력을 받는 소위 Beck 기둥의 자유진동을 지배하는 미분방정식을 유도하였다. 이 미분방정식을 수치해석하여 하중-고유진동수 곡선을 얻고 이로부터 발산임계하중 및 동요임계하중을 산출하였다. 수치해석의 결과로부터 변단면 형태, 경사변수 및 질량비가 임계하중에 미치는 영향을 고찰하였다.

• 호남수학학술지
• /
• 제31권1호
• /
• pp.45-61
• /
• 2009

We consider finite time blowup solutions of the $L^2$-critical focusing Hartree equation on $\mathbb{R}^n$, $n{\geq}3$ below $H^1$.

• 한국안전학회지
• /
• 제11권4호
• /
• pp.3-9
• /
• 1996

In this study, comparison of theoretical solutions with experimental results is examined through fracture conditions for the case of float glasses subjected static loading. The range of fracture generation limits and critical penetration energies are solved according to the impactor mass under the high velocity, and analytical method of fracture strength and penetration strength are presented. Also, fracture patterns are investigated according to impact velocities. The results obtained from this study are as follows ; 1) Radial cracks are generated from the loading point regardless of plate thickness in the case of the plate subjected to the static loading. In the case of high-speed impact, dimensions of ring cracks become to smaller and length of radial cracks becomes shorter with the rapidity of impact velocity. 2) Kinetic change volume of collision after/before is constant regardless of velocities over the range of critical penetration velocity. 3) Although the same impact energy is working, the critical penetration energy is increased with the shorter of impactor mass. 4) Although the same impact energy is working, the penetration fracture of lighter Impactor mass is generated more than that of heavier impactor mass, and the impulse of lighter impacter mass appear more than that of heavier impactor mass. Therefore, the penetration fracture in the case of greater impulse is generated earlier regardless of the of the dimensions of Impact loading.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
• /
• pp.227-230
• /
• 2006

The method of mass flow rate measurement using a critical nozzle is well established in the flow satisfying ideal gas law. However, in the case of measuring high-pressure gas flow, the current method shows invalid discharge coefficient because the flow does not follow ideal gas law. Therefore an appropriate equation of state considering real gas effects should be applied into the method. The present computational study has been performed to give an understanding of the physics of a critical nozzle flow for high-pressure hydrogen gas and find a way for the exact mass flow prediction. The two-dimensional, axisymmetric, compressible Navier-Stokes equations are computed using a fully implicit finite volume method. The real gas effects are considered in the calculation of discharge coefficient as well as in the computation. The computational results are compared with the previous experimental data and predict well the measured mass flow rates. It has been found that the discharge coefficient for high-pressure hydrogen gas can be corrected properly adopting the real gas effects.

• Earthquakes and Structures
• /
• 제18권1호
• /
• pp.45-56
• /
• 2020

The application of critical excitation method with displacement-based objective function for multi degree of freedom (MDOF) systems is investigated. To this end, a new critical excitation method is developed to find the critical input motion of a MDOF system as a synthetic accelerogram. The upper bound of earthquake input energy per unit mass is considered as a new constraint for the problem, and its advantages are discussed. Considering this constraint, the critical excitation method is then used to generate synthetic accelerograms for MDOF models corresponding to three shear buildings of 10, 16, and 22 stories. In order to demonstrate the reliability of generated accelerograms to estimate dynamic response of the structures, three target ground motions with considerable level of energy contents are selected to represent "real critical excitation" of each model, and the method is used to re-generate these ground motions. Afterwards, linear dynamic analyses are conducted using these accelerograms along with the generated critical excitations, to investigate the key parameters of response including maximum displacement, maximum interstory drift, and maximum absolute acceleration of stories. The results show that the generated critical excitations can make an acceptable estimate of the structural behavior compared to the target ground motions. Therefore, the method can be reliably implemented to generate critical excitation of the structure when real one is not available.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.484-489
• /
• 2003

The mass flow rate of gas flow through critical nozzle depends on the nozzle supply conditions and the cross-sectional area at the nozzle throat. In order that the critical nozzle can be operated at a wide range of supply conditions, the nozzle throat diameter should be controlled to change the flow passage area. This can be achieved by means of a variable critical nozzle. In the present study, both experimental and computational works are performed to develop variable critical nozzle. A cone-cylinder with a diameter of d is inserted into conventional critical nozzle. It can move both upstream and downstream, thereby changing the cross-sectional area of the nozzle throat. Computational work using the axisymmetric, compressible Navier-Stokes equations is carried out to simulate the variable critical nozzle flow. An experiment is performed to measure the mass flow rate through variable critical nozzle. The present computational results are in close agreement with measured ones. The boundary layer displacement and momentum thickness are given as a function of Reynolds number. An empirical equation is obtained to predict the discharge coefficient of variable critical nozzle.

• Nuclear Engineering and Technology
• /
• 제54권3호
• /
• pp.834-841
• /
• 2022

System thermal-hydraulic (STH) code is adopted for nuclear safety analysis. The critical flow model (CFM) is significant for the accuracy of STH simulation. To overcome the defects of current CFMs (low precision or long calculation time), a CFM based on a genetic neural network (GNN) has been developed in this work. To build a powerful model, besides the critical mass flux, the critical pressure and critical quality were also considered in this model, which was seldom considered before. Comparing with the traditional homogeneous equilibrium model (HEM) and the Moody model, the GNN model can predict the critical mass flux with a higher accuracy (approximately 80% of results are within the ±20% error limit); comparing with the Leung model and the Shannak model for critical pressure prediction, the GNN model achieved the best results (more than 80% prediction results within the ±20% error limit). For the critical quality, similar precision is achieved. The GNN-based CFM in this work is meaningful for the STH code CFM development.

• 터널과지하공간
• /
• 제15권5호
• /
• pp.369-377
• /
• 2005

지하공동의 안정성은 생산성과 안전을 확보해야 하는 광산의 운영에 있어서 가장 중요한 관심사이다. 암반분류는 많은 경험적인 설계방법의 근간을 이룰 뿐만 아니라 수치해석을 위한 기초자료로 이용되고 있다. 공동의 안정성에 영향을 주는 많은 요소들 중 주어진 암반의 조건 중에서 공동폭은 하나의 중요한 설계요소가 된다. 이 논문에서는 Lug에 의해 제안된 한계 공동폭 기준, Mathews stability graph method 그리고 저자들에 의해 제안된 한계 공동폭 기준을 비교하였다. Methews stability graph method를 이용하여 저자들에 의해 수정된 한계 공동폭 기준을 제안하였고 이것을 여러 석회석 광산 지하공동의 안정성을 평가하는 데 사용하였다.