• 대한기계학회논문집
• /
• 제12권1호
• /
• pp.81-94
• /
• 1988

본 연구에서는 표면상태가 다양한 고온면을 충돌온류에 의하여 냉각하는 방식이 광범위하게 응용되고 있는 점에 유의하여 표면조도, 노즐직경 및 분류속도를 변화시키고 노즐끝에 전열면의 직경과 동일한 원형판을 부착하여 비철액체를 막고 문극내에 온류액체를 강제유동시킴으로써 열전달에 미치는 모든 영향을 실험에 의해 고찰하고 고찰하고 포화수온류에 의한 열류속의 무차원관계식을 도출하는 것을 본 연구의 목적으로 하였다.

• Ocean Systems Engineering
• /
• 제13권2호
• /
• pp.123-146
• /
• 2023

In this paper, Moore-Gibson-Thompson theory of thermoelasticity is considered to investigate the fundamental solution and vibration of plane wave in an isotropic photothermoelastic solid. The governing equations are made dimensionless for further investigation. The dimensionless equations are expressed in terms of elementary functions by assuming time harmonic variation of the field variables (displacement, temperature distribution and carrier density distribution). Fundamental solutions are constructed for the system of equations for steady oscillation. Also some preliminary properties of the solution are explored. In the second part, the vibration of plane waves are examined by expressing the governing equation for two dimensional case. It is found that for the non-trivial solution of the equation yield that there exist three longitudinal waves which advance with the distinct speed, and one transverse wave which is free from thermal and carrier density response. The impact of various models (i)Moore-Gibson-Thomson thermoelastic (MGTE)(2019), (ii) Lord and Shulman's (LS)(1967) , (iii) Green and Naghdi type-II(GN-II)(1993) and (iv) Green and Naghdi type-III(GN-III)(1992) on the attributes of waves i.e., phase velocity, attenuation coefficient, specific loss and penetration depth are elaborated by plotting various figures of physical quantities. Various particular cases of interest are also deduced from the present investigations. The results obtained can be used to delineate various semiconductor elements during the coupled thermal, plasma and elastic wave and also find the application in the material and engineering sciences.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 추계학술대회논문집B
• /
• pp.397-403
• /
• 2000

In the present study, flow characteristics of turbulent pulsating flow in a square-sectional $180^{\circ}$ curved duct were experimentally investigated. Experimental studies for air flows were conducted to measure axial velocity and wall shear stress distributions and entrance length in a square-sectional $180^{\circ}$ curved duct by using the LDV with the data acquisition and the processing system. The experiment was conducted in seven sections from the inlet (${\phi}=0^{\circ}$) to the outlet (${\phi}=180^{\circ}$) at $30^{\circ}$ intervals of the duct. The results obtained from the experimentation were summarized as follows ; (1) When the ratio of velocity amplitude ($A_1$) was less than one, there was hardly any velocity change in the section except near the wall and any change in axial velocity distributions along the phase. When the ratio of velocity amplitude ($A_1$) was 0.6, the change rate of velocity was slow. (2) Wall shear stress distributions of turbulent pulsating flow were similar to those of turbulent steady flow. The value of the wall shear stress became minimum in the inner wall aid gradually increased toward the outer wall where it became maximum. (3) The entrance length of turbulent pulsating flow reached near the region of bend angle of $90^{\circ}$, like that of turbulent steady flow. The entrance length was changed by the dimensionless angular frequency (${\omega}^+$).

• 한국수소및신에너지학회논문집
• /
• 제25권1호
• /
• pp.47-58
• /
• 2014

The characteristics of flame shape, laminar burning velocity, emissions and heat flux of stagnation point in premixed impinging jet flame of syngas fuel with 10% hydrogen content were experimentally investigated. Also, the adiabatic temperature and burning velocity are calculated by Chemkin package with USC-II mechanism. The equivalence ratios(0.8~5.0) and dimensionless separation distance(2.0~5.0) with fixed Reynolds number(1800) are main parameters in this work. Different flame shapes and colors were observed for different impingement conditions. The experimental results of burning velocity by flame surface area have a consistent with previous works and numerical simulation of this work. The inner flame length could be predicted with the ratio of mixture velocity and burning velocity from a simple formulation by the laminar burning velocity definition. It has been observed that the heat fluxes at stagnation point are directly affected by the flame shape including the separation distance. The emission results in impinging flame of syngas fuel show that the characteristics of $NO_x$ emission traced well with adiabatic temperature trend and CO emission due to fuel rich condition increased continuously with respect to the equivalence ratio.

• Journal of Mechanical Science and Technology
• /
• 제20권4호
• /
• pp.533-544
• /
• 2006

The amplitude and phase lag of surface deformation were determined for a compliant coating under the action of turbulent pressure fluctuations. For this purpose, pressure fluctuations were measured experimentally. The amplitude and duration of coherent wave train of pressure fluctuations were investigated using digital filtration. The transient response was calculated for stabilization of forced oscillations of the coating in approximation of local deformation. The response of coating was analyzed with considerations of its inertial properties and limited duration of coherent harmonics action of pressure fluctuations. It is shown that a compliant coating interacts not with the whole spectrum of pressure fluctuations, but only with a frequency range near the first resonance. According to the analysis, with increasing elasticity modulus of the coating material E, deformation amplitude decreases as 1/E, and dimensionless velocity of the coating surface decreases as $1/\sqrt{E}$. For sufficiently hard coatings, deformation amplitude becomes smaller than the thickness of viscous sublayer, while surface velocity remains comparable to vertical velocity fluctuations of the flow.

• 대한기계학회논문집B
• /
• 제28권9호
• /
• pp.1058-1065
• /
• 2004

In the present study, characteristics of steady state laminar flows of a straight duct connected to a 180$^{\circ}$ curved duct were examined in the entrance region through experimental and numerical analyses. For the analysis, the governing equations of laminar flows in the Cartesian coordinate system were applied. Flow characteristics such as velocity profiles, and secondary flows were investigated numerically and experimentally in a square cross-sectional straight duct by the PIV system and a CFD code(STAR CD). For the PIV measurement, working fluid produced from mosquito coils smoke. The experimental data were obtained at 9 points dividing the test sections by 400 mm. Experimental and numerical results can be summarized as follows. Critical Reynolds number, Recr which indicates transition from laminar steady flow to transition steady flow was 2,150. As Reynolds number, Re, was increased, dimensionless velocity profiles at the outer wall were increased due to the effect of the centrifugal force and the secondary flows. The intensity of a secondary flow became stronger at the inner wall rather than the outer wall regardless of Reynolds number.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 2001년도 The 6th International Symposium of East Asian Resources Recycling Technology
• /
• pp.759-764
• /
• 2001

The separation performance of zigzag air classifier with angle of 90 degrees was studied using narrow size fractions of thin square samples and granular samples. The simulation results of air velocity inside the classifier indicated that the zigzag geometry induces a new pattern consisting of an upward flow and a circulation flow, Experimental results showed that overflow product recovery was described as an integral calculus of normal distribution as a function of dimensionless air velocity ( $V_{A}$ $V_{A50}$), where $V_{A}$ is superficial air velocity and $V_{A50}$ is the $V_{A}$ at the fifty percent recovery. The $V_{A}$ values were predicted using the equations derived from dynamics for a particle dropping in air. A monitoring system that utilizes changes in acoustic signals emitted during the process of air classification was developed to separate PET with desired recovery or grade. The technical feasibility of the on-line monitoring of the PET recovery and grade was demonstrated by measuring relative energy of the signals.signals.als.

• Journal of Advanced Marine Engineering and Technology
• /
• 제25권4호
• /
• pp.817-824
• /
• 2001

In the present study, flow characteristics of turbulent oscillatory flows in the exit region connected to the square-sectional $180^{\circ}$curved duct was investigated experimentally. The experimental study for air flows was conducted to measure velocity profiles, shear stress distributions by using the Laser Doppler Velocimetry(L.D.V) system with the data acquisition and processing system of Rotating Machinery Resolver(R.M.R) and PHASE software. The results obtained from the experimentation were summarized as follows : The critical Reynolds number for a change from transitional oscillatory flow to turbulent oscillatory flow was about 75,000 in the 90 region of dimensionless axial position (x/Dh) which was considered as a fully developed flow region. In the turbulent oscillatory flow, velocity profiles of the inflow period in the entrance region were gradually developed, but those of the outflow period were not changed nearly. Shear stress distributions of turbulent oscillatory flow was gradually increased as the flow proceeds to downstream.

• Structural Engineering and Mechanics
• /
• 제20권4호
• /
• pp.421-434
• /
• 2005

In this paper, the finite element method is applied to investigate the effect of the lateral boundary in homogenous soil on the seismic response of a superstructure. Some influencing factors are presented and discussed, and several parameters are identified to be important for conducting soil-structure interaction experiments on shaking tables. Numerical results show that the cross-section width L, thickness H, wave propagation velocity and lateral boundaries of soil layer have certain influences on the computational accuracy. The dimensionless parameter L/H is the most significant one among the influencing factors. In other words, a greater depth of soil layer near the foundation should be considered in shaking table tests as the thickness of the soil layer increases, which can be regarded as a linear relationship approximately. It is also found that the wave propagation velocity in soil layer affects the numerical accuracy and it is suggested to consider a greater depth of the soil layer as the wave propagation velocity increases. A numerical study on a soil-structure experimental model with a rubber ring surrounding the soil on a shaking table is also conducted. It is found the rubber ring has great effect on the soil-structure interaction experiments on shaking table. The experimental precision can be improved by reasonably choosing the elastic parameter and width of the rubber ring.

• 한국수자원학회논문집
• /
• 제44권1호
• /
• pp.65-72
• /
• 2011

자연하천은 사행을 보이며 만곡부 외측에 웅덩이 그리고 만곡과 만곡을 연결하는 직선 유로에 여울이 형성된다. 웅덩이는 수심이 깊으며 유속이 느리고, 여울은 수심이 비교적 얕고 유속이 빠른 특징이 있다. 사행유로를 따라 자연적으로 발달하는 웅덩이-여울 연속구조에 근래들어 관심이 집중되는 이유는 이러한 하천형태학적 구조가 생물학적인 다양성을 증가시키기 때문이다. 본 연구에서는 금강의 지류인 갑천 상류구간을 대상으로 웅덩이-여울 연속구조에서 하상토의 입도특성을 조사하였다. 대상구간인 갑천 상류부는 자갈하천으로 사행에 의한 웅덩이 1개소와 여울 3개소를 포함하고 있으며, 구간 상류측에 보로 인해 상하류에 형성된 웅덩이 2개소가 위치한다. 아울러 조사대상 구간의 습지 및 샛강에서 채취한 하상토의 입도특성도 살펴보았는데, 여울에서의 중앙입경이 웅덩이에서보다 약 4배 큰 것으로 나타났다. 또한, 평수량 및 홍수량에 대하여 부등류 계산을 실시하여, 유사이동에 중요한 웅덩이와 여울에서 평균유속, 전단응력, 무차원 전단응력(Shields 수), 그리고 무차원 전단속도를 검토하였다.