• Journal of the Korean Society for Precision Engineering
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• v.15 no.10
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• pp.140-147
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• 1998

The dynamic behavior of elastically restrained beams under the action of distributed tangential forces is investigated in this paper. The beam, which is fixed at one end, is assumed to rest on an intermediate spring support. The governing equations of motion are derived from the energy expressions, and the finite element formulation is employed to calculate the critical distributed tangential force. Jump phenomena for the critical distributed tangential force and instability types are presented for various spring stiffnesses and support positions. Stability maps are generated by performing parametric studies to show how the distributed tangential forces affect the frequencies and the stability of the system considered. Through the numerical simulations, the following conclusioils are obtained: (i) Only flutter type instability exists for the dimensionless spring stiffness K $\leq$ 97, regardless of the position of the spring support. (ii) For the dimensionless spring stiffness K $\leq$ 98, the transition from flutter to divergence occurs at a certain position of the spring support, and the transition position moves from the free end to the free end of the beam as the spring stiffness increases. (iii) For K $\leq$ 10$^{6}$ the support condition can be regarded as a rigid support condition.

• Journal of Korean Association for Spatial Structures
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• v.3 no.1 s.7
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• pp.87-97
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• 2003

The structural system that discreterized from continuous shells is frequently used to make a large space structures. As well these structures show the unstable phenomena when a load level over the limit load, and snap-through and bifurcation are most well known of it. For the collapse mechanism, rise-span ratio, element stiffness and load mode are main factor, which it give an effect to unstable behavior. In our real situation, most structures have semi-rigid joint that has middle characteristic between pin and rigid joint. So the knowledge of semi-rigid joint is very important problem of stable large space structure. And the instability phenemena of framed space structures show a strong non-linearity and very sensitive behavior according to the joint rigidity For this reason In this study, we are investigating to unstable problem of framed structure with semi-rigidity and to grasp the nonlinear instability behavior that make the fundamental collapse mechanism of the large space frame structures with semi-rigid joint, by proposed the numerical analysis method. Using the incremental stiffness matrix in chapter 2, we study instability of space structures.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.896-904
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• 2017

Lean premixed combustion was successful in meeting current NOx emission regulations. However, these often leads to combustion instability. This phenomena results from the feedback relationship between heat release perturbations and acoustic pressure oscillations in the combustor. Researches on the combustion instability in an annular combustor have recently received great attention due to the enhanced NOx requirement in aero-engines. In this study, the thermoacoustic network model has been developed in order to calculate the acoustics for longitudinal as well as circumferential modes in the annular combustor. The combustion model in the network model is calculated by flame transfer function(FTF). Numerical and analytical results are compared to an measurement data.

• Nuclear Engineering and Technology
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• v.55 no.1
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• pp.109-118
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• 2023

In this paper, the evaluation method of fluidelastic instability (FEI) of newly designed steam generator tubing in pressurized water reactor (PWR) nuclear power plants is discussed. To obtain the parameters for prediction of the critical velocity of FEI for steam generator tubes, experimental research is carried out, and the design parameters are determined. Using CFD numerical simulation, the tube array scale of the model experiment is determined, and the experimental device is designed. In this paper, 7 groups of experiments with void fractions of 0% (water), 10%, 20%, 50%, 75%, 85% and 95% were carried out. The critical damping ration, fundamental frequency and critical velocity of FEI of tubes in flowing water were measured. Through calculation, the total mass and instability constant of the immersed tube are obtained. The critical damping ration measured in the experiment mainly included two-phase damping and viscous damping, which changed with the change in void fraction from 1.56% to 4.34%. This value can be used in the steam generator design described in this paper and is conservative. By introducing the multiplier of frequency and square root of total mass per unit length, it is found that the difference between the experimental results and the calculated results is less than 1%, which proves the rationality and feasibility of the calculation method of frequency and total mass per unit length in engineering design. Through calculation, the instability constant is greater than 4 when the void fraction is less than 75%, less than 4 when the void fraction exceeds 75% and only 3.04 when the void fraction is 95%.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.11B no.4
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• pp.121-128
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• 2001

Numerical schemes for the simulation of the cold gas flow in the SF6 puffer type circuit breaker is presented. The governing equation is axisymmetric compressible Euler Equation and FVM is used to analyze the behavior of flow. The upwind scheme is used to avoid numerical instability and MUSCL is used to obtain high order accuracy. For the efficient calculation, AF-ADI scheme is used. The simulation result shows good agreement with the experimental data.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.178-182
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• 2004

Numerical analysis of a gaseous jet submerged in a liquid environment was carried out using the volume of fluid(VOF) method to simulate the kinematics of the gas-liquid interface. Two nozzle geometries were tested, one for Fanno tube and the other for converging diverging nozzle. Commercial code was used for the present calculation. Transient behavior of a gaseous jet since its start showed periodic nature of the jet, which was also observed in previous measurements.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.17-18
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• 2003

Drop deformation in a cylindrical contraction geometry, characterized here by the formation of a thread of drop fluid in the contraction, is predicted using a Volume-of-Fluid numerical technique. The predicted drop shape is found to closely follow the observed deformation. A capillary instability in the developing drop thread in the contraction was predicted, in agreement with experimental observation.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.33-40
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• 2001

In this research, the cracking of tunnel concrete lining was investigated and analyzed through long-term measurement and nonlinear numerical analysis. For one year after the casting of lining, the stresses and strains were measured by the sensors installed in hard rock tunnel lining. The measurements showed that only small stresses which were less than cracking stress occurred in every survey sections regardless of sensor directions. It could be induced that the external load applied to the lining was small or ignorable. Also, it was carried out short-term numerical analysis based on such site condition as ambient temperature, the- degree of overbreak and mold staying period. Long-term numerical analysis based on creep & shrinkage and nonlinear cracking was carried out. The output showed that construction condition and ambient environments could make the lining concrete crack without external loads. The cracks formed in this process does not indicate the structural instability of the tunnel.

• 한국전산유체공학회:학술대회논문집
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• 2006.05a
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• pp.341-345
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• 2006

• The Journal of the Acoustical Society of Korea
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• v.40 no.3
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• pp.213-218
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• 2021

It is known that total least-squares method shows better estimation performance than least-squares method when noise is present at the input and output at the same time. When total least squares method is applied to data with time series characteristics, Recursive Total Least Squares (RTS) algorithm has been proposed to improve the real-time performance. However, RTLS has numerical instability in calculating the inverse matrix. In this paper, we propose an algorithm for reducing numerical instability as well as having similar convergence to RTLS. For this algorithm, we propose a new RTLS using Iterative Wiener Filter (IWF). Through the simulation, it is shown that the convergence of the proposed algorithm is similar to that of the RTLS, and the numerical robustness is superior to the RTLS.