• 한국자동차공학회논문집
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• 제21권2호
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• pp.87-97
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• 2013

Recently the use of gas spring in the combat and commercial vehicle's suspension is increasing. Because of its nonlinear characteristics, the gas spring can support wide range of dynamic loads and gives good ride quality. In design of gas spring, isothermal and adiabatic processes are applied generally, but those processes could not produce heat transfer effect in the simulation. So in this study, heat transfer differential equation and BWR/Ideal state equation are used to calculate the pressure of gas spring which is changing with time. The numerical analysis showed that the pressure of gas spring forms a hysteresis loop in the both of the state equations. But the peak pressure value of BWR equation over 0.1Hz frequency are higher than that of adiabatic process. And the test results showed that the differences between test results and ideal gas equation are smaller than those of BWR equation, so the ideal equation is more accurate than BWR equation in this case.

• 대한수학회보
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• 제58권4호
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• pp.909-914
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• 2021

In this short note we prove new differential Harnack inequalities interpolating those for the static surface and for the Ricci flow. In particular, for 0 ≤ 𝜀 ≤ 1, α ≥ 0, 𝛽 ≥ 0, 𝛾 ≤ 1 and u being a positive solution to $${\frac{{\partial}u}{{\partial}t}}={\Delta}u-{\alpha}u\;{\log}\;u+{\varepsilon}Ru+{\beta}u^{\gamma}$$ on closed surfaces under the flow ${\frac{\partial}{{\partial}t}}g_{ij}=-{\varepsilon}Rg_{ij}$ with R > 0, we prove that $${\frac{\partial}{{\partial}t}}{\log}\;u-{\mid}{\nabla}\;{\log}\;u{\mid}^2+{\alpha}\;{\log}\;u-{\beta}u^{{\gamma}-1}+\frac{1}{t}={\Delta}\;{\log}\;u+{\varepsilon}R+{\frac{1}{t}{}\geq}0$$.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.103-108
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• 2003

In this paper, the current lead for superconducting device is studied by numerical method. The current lead is cooled by surrounded $N_{2}$ gas by natural convection. The heat conduction equation for current lead and boundary layer equation for $N_{2}$ gas must be solved simultaneously. The boundary layer equation for $N_{2}$ gas is highly nonlinear for varied temperature of current lead. So the linearization method is adopted for simplicity. Numerical results using natural convection cooling are compared with the conventional cooling methods such as conduction cooling and vapor cooling methods. The main difference of natural convection cooing is the non-zero temperature gradient at the top of current lead for the minimum heat dissipation into superconducting devices. For the optimized conduction-cooling and vapor-cooling current leads, the temperature gradient at the top of current lead is zero. Also, the heat flow at the cold end is much smaller than conduction cooling case.

• Structural Engineering and Mechanics
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• 제82권5호
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• pp.679-690
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• 2022

This research effort examines the flow behavior and heat transfer assessment of water carrying iron (iii) oxide magnetic fluid due to a rotating and moving plane lamina under the influence of magnetic dipole. The effect of rotational viscosity and magnetic body force is taken into consideration in the present study. The involvement of the moving disk makes a significant contribution to the velocity distribution and heat transfer in rotational flow. Vertical movement of the disk keeps the flow unsteady and the similarity transformation converts the governing equation of unsteady flow into nonlinear coupled differential equations. The non-dimensional equation in the present system is solved through the finite element procedure. Optimizing the use of physical parameters described in this flow, such results can be useful in the rotating machinery industries for heat transfer enhancement.

• 대한기계학회논문집B
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• 제30권10호
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• pp.942-949
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• 2006

A lumped model is proposed to predict liquid ejection characteristics of a thermally driven inkjet print head. The model is based on a two-dimensional heat conduction equation, an empirical pressure-temperature equation and a nonlinear hydraulic flow-pressure equation. It has been simulated through the construction of an equivalent R-C circuit, and subsequently analyzed using SIMULINK and a circuit simulation tool, PLECS. Using the model, heating and cooling characteristics of the head are predicted to be in agreement with the IR temperature measurements. The effects of the head geometry on the drop ejection are also analyzed using the nonlinear hydraulic model. The present model can be used as a design tool for a better design of thermal inkjet print heads.

• 대한기계학회논문집
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• 제17권10호
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• pp.2574-2581
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• 1993

A Shadow mask in C. R. T. (Cathod Ray Tube) undergoes a temperature increase due to impinging electron beams emitted from guns, and thermal deformation from such temperature rise may cause the electron beams to island on the panel, and thus give rise to depolarization. Hence the analysis of temperature distribution for a shadow mask is an important procedure for designing the shadow mask. In this paper, we are concerned with nonlinear finite element analysis of the temperature distribution on a shadow mask. First of all, we replace shadow mask, containing numerous apertures of a slit type, by an orthotropic shell without apertures, and calculate the apparent thermal conductivities. Because of thermal radiation, which is one of the major heat transfer mechanism for shadow masks, the resulting finite element equation is nonlinear and solved by the Newton method. Finally numerical examples are illustrated for a 21" FST(Full Square Tube) shadow mask, and followed by discussion.sion.

• 대한기계학회논문집
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• 제19권11호
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• pp.2995-3002
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• 1995

The cooling problem of the hot internal pipe flow has been investigated. Simultaneous conduction, convection, and radiation were considered with azimuthally varying convective heat loss at the pipe wall. A complex, nonlinear integro-differential radiative transfer equation was solved by the discrete ordinates method (or called S$_{N}$ method). The energy equation was solved by control volume based finite difference technique. A parametric study was performed by varying the conduction-to-radiation parameter, optical thickness, and scattering albedo. The results have shown that initially the radiatively active medium could be more efficiently cooled down compared with the cases otherwise. But even for the case with dominant radiation, as the medium temperature was lowered, the contribution of conduction became to exceed that of radiation.n.

• 한국가스학회:학술대회논문집
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• 한국가스학회 1997년도 추계학술발표회 논문집
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• pp.14-19
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• 1997

A numerical method for determining the temperature vartiation in a natural gas transmission line is presented. By considering an element of the gas pipeline and assuming radially lumped heat transfer at steady-state conditions, the energy equation is developed. The integration of the developed nonlinear differential equation is done numerically using the fourth order Runge-Kutta scheme. The results of the present study have been compared with the results of Coulter equations, and show a fairly good agreement.

• 설비공학논문집
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• 제1권2호
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• pp.173-181
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• 1989

Until recently there was a lack of reliable performance data for the design and operation of Ondol heating systems. This paper presents a calculation method on heat flux from Ondol floor surface. Total heat flux from floor consists of radiation and convection component. In order to analyse the characteristics of both radiation and convection heat flux, each surface temperature is measured and several temperatures near each wall are measured vertically and horizontally in a practical Ondol heating space. Radiation heat flux is calculated and analysed by Gebhart's Absorption Factor Method with the consideration of instantaneous radiant exchanges. Convection heat output is derived from the vertical temperature profiles near floor. The vertical temperature profiles could be expressed by nonlinear regression equation models and convection coefficients could be estimated by the equations. As a result, radiation, convection and total heat flux are suggested by the expression of difference between floor surface and room air temperature.

• 동력기계공학회지
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• 제18권2호
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• pp.77-82
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• 2014

The air spring is widely used in various fields such as a suspension system and an anti-vibration system because the natural frequency is kept constant regardless of the change in the load, spring constant is easy to change, and, vibration and shock isolation performance are excellent. The purpose of this study is to derive a nonlinear governing equation of an air spring, to analyze the effect of the various parameters on the dynamic stiffness of the air spring, and, to suggest a more efficient design method of an air spring system. In order to do so, this study investigates the impact of all the parameters that could affect the dynamic stiffness of the air spring while changing the excitation amplitude and the frequency with a developed governing equation.