• Smart Structures and Systems
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• 제4권3호
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• pp.279-290
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• 2008

The modeling and parameter estimation of a damped one-degree-of-freedom mass-spring system is examined. This paper presents a method for estimating the system parameters (damping coefficients and natural frequency) from measured free-vibration motion of a system that is modeled to include both subcritical viscous damping and kinetic Coulomb friction. The method applies a commercially available least-squares curve-fitting software function to fit the known solution of the equations of motion to the measured response. The method was tested through numerical simulation, and it was applied to experimental data collected from a laboratory mass-spring apparatus. The mass of this apparatus translates on linear bearings, which are the primary source of light inherent damping. Results indicate that the curve-fitting method is effective and accurate for both perfect and noisy measurements from a lightly damped mass-spring system.

• 대한수학회지
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• 제57권6호
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• pp.1451-1470
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• 2020

We are concerned with the following elliptic equations: $$\{(-{\Delta})^s_pu={\lambda}f(x,u)\;{\text{in {\Omega}}},\\u=0\;{\text{on {\mathbb{R}}^N{\backslash}{\Omega}},$$ where λ are real parameters, (-∆)^s_p is the fractional p-Laplacian operator, 0 < s < 1 < p < + ∞, sp < N, and f : Ω × ℝ → ℝ satisfies a Carathéodory condition. By applying abstract critical point results, we establish an estimate of the positive interval of the parameters λ for which our problem admits at least one or two nontrivial weak solutions when the nonlinearity f has the subcritical growth condition. In addition, under adequate conditions, we establish an apriori estimate in L^∞(Ω) of any possible weak solution by applying the bootstrap argument.

• Wind and Structures
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• 제15권3호
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• pp.247-261
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• 2012

Some numerical investigations are presented concerning the response of a given plate under turbulence driven excitations. Three different input loads are simulated according to the wall pressure distributions derived from the models proposed by Corcos, Efimtsov and Chase, respectively. Modal solutions (finite element based) are used for building the modal stochastic responses in the sub-critical aerodynamic frequency range. The parametric investigations concern two different values of the structural damping and three values of the boundary layer thickness. A final comparison with available experimental data is also discussed. The results demonstrate that the selection of the adequate TBL input model is still the most critical step in order to get a good prediction.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2001년도 제22회 KOSCI SYMPOSIUM 논문집
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• pp.106-118
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• 2001

A rigorous study of single droplet vaporization under quiescent high pressure atmosphere is attempted adopting method of flash evaporation calculation for vapor-liquid equilibrium. Results due to flash method shows excellent agreement with measurement. Also shown is the present model fairly capable of depicting transients of droplet vaporization under high pressure environment, such as ambient gas solubility, property variation, and multicomponent transports. Systematic treatment of these effects with emphasis on vapor-liquid phase equilibrium revealed; conventional treatment for subcritical droplet vaporization, such as $d^2$-law, leads to erroneous prediction of droplet history, augmented gas solubility is significant under supercritical pressure, and vaporization rate proportionally increase with pressure.

• 한국분무공학회지
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• 제18권3호
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• pp.140-145
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• 2013

Sub/supercritical spray experiments were conducted, and cryogenic nitrogen and gaseous argon were selected for simulants. liquid nitrogen and gaseous argon were injected in subcritical case, and supercritical nitrogen and near-critical gaseous argon were injected in near-critical/supercritical cases. shadowgraph method was used to visualize spray, and analyzed about the breakup length. The breakup length was measured from numbers of Instantaneous shadowgraph Images from each case, and they were compared with momentum flux ratios and density ratios. It was observed that the relation between breakup length and momentum flux ratio was fitted into former experiment results. and the reasonable constant was suggested about the relation between breakup length and density ratio.

• 한국기계가공학회지
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• 제4권2호
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• pp.50-56
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• 2005

To demonstrate the feasibility of utilizing FCAD chart proposed in our previous work, series of crack growth/arrest behavior in the integrally stiffened panels were simulated by numerical method using upper mentioned FCAD charts and a new crack growth rate equation. It is concluded that proposed family of FCAD curves, in the form of non-dimensional arrest load ranges, are reliable indicators of fatigue crack growth/arrest behavior of integrally stiffened panels considered here.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.872-877
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• 2001

This study analyzed the design performance of the bottoming system of combined cycle power plants adopting a single-pressure once-through heat recovery steam generator with reheat. A computer program was constructed and parametric analyses were carried out to present the criteria for determining the reheat pressure and the location of the starring point of the reheater in the HRSG. The performance of the bottoming system was presented for the range from high subcritical to supercritical pressures. It was founded that the power of the bottoming system can be as high as that of the present triple-pressure bottoming system even with a higher exhaust gas temperature. A requirement for this high performance is a proper arrangement of the reheater.

• Wind and Structures
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• 제4권2호
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• pp.85-100
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• 2001

The mechanism of wind-induced ovalling vibrations of cylindrical shells is numerically investigated by using a vortex method. The subject of this paper is limited to a two-dimensional structure in the subcritical regime. The aerodynamic stability of the ovalling vibrations in the second to fourth circumferential modes is discussed, based on the results of a forced-vibration test. In the analysis, two modal configurations are considered; one is symmetric and the other is anti-symmetric with respect to a diameter parallel to the flow direction. The unsteady pressures acting on a vibrating cylinder are simulated and the work done by them for one cycle of a harmonic motion is computed. The effects of a splitter plate on the flow around the cylinder as well as on the aerodynamic stability of the ovalling vibrations are also discussed. The consideration on the mechanism of ovalling vibrations is verified by the results of a free-vibration test.

• 한국철도학회논문집
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• 제8권2호
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• pp.116-121
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• 2005

In this report, numerical investigations have demonstrated, that the displacement underneath a moving loading reach a maximum value, if the speed of the load is equal to propagation velocity of the maximum wave. The load speed for which the maximum displacement occurs is called critical speed. The critical speed divides the velocities in a subcritical and a super-critical region. By means of calculations the dynamic behaviour of the slab track-soil is investigated. For concrete slab track dynamic wheel load are given in dependence of relevant excitation mechanismen and speed of the train. These loads can be used for the dimensioning of the track as well as far the prognosis of the vibrations at the track and the surrounding soil.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1294-1299
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• 2009

Since the operating pressure of $CO_2$ gascooler is so high compared with that of previous subcritical condenser, the optimization of gascooler is needed for improve heat exchanger performance. In this study, the performance characteristics of five kinds of heat exchangers were analyzed and compared with operating conditions. As a result, the 4-20 HX-tube shows the maximum gascooler capacity because the heat transfer is effective and pressure drop is small. Beside, the high performance of 4-20 HX-tube could be keep for wide operating condition.