• Nuclear Engineering and Technology
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• 제55권6호
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• pp.2011-2017
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• 2023

Gas submerged jet is an outstanding thermohydraulic phenomenon in pool scrubbing of fission products during a severe nuclear accident. Experiments were performed on the hydraulic characteristics in the ranges of air mass flux 0.1-1400 kg/m²s and nozzle diameter 10-80 mm. The results showed that the dependence of inlet pressure on the mass flux follows a power law in subsonic jets and a linear law in sonic jets. The effect of nozzle submerged depth was negligible. The isolated bubbling regime, continuous bubbling regime, transition regime, and jetting regime were observed in turn, as the mass flux increased. In the bubbling regime and jetting regime, the air volume fraction distribution was approximately symmetric in space. Themelis model could capture the jet trajectory well. In the transition regime, the air volume fraction distribution loses symmetry due to the bifurcated secondary plume. The Li correlation and Themelis model showed sufficient accuracy for the prediction of jet penetration length.

• 대한기계학회논문집B
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• 제29권8호
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• pp.911-920
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• 2005

The present study investigates heat/mass transfer and flow characteristics in a ribbed rotating passage with turning region. The duct has an aspect ratio (W/H) of 0.5 and a hydraulic diameter ($D_h$) of 26.67 mm. Rib turbulators are attached in the parallel arrangement on the leading and trailing surfaces of the passage. The ribs have a rectangular cross section of 2 m (e) $\times$ 3 m (w) and an attack angle of $70^{\circ}$. The pitch-to-rib height ratio (p/e) is 7.5, and the rib height-to-hydraulic diameter ratio (e/$D_h$) is 0.075. The rotation number ranges from 0.0 to 0.20 while the Reynolds number is constant at 10,000. To verify the heat/mass transfer augmentation, internal flow structures are calculated for the same conditions using a commercial code FLUENT 6.1. The results show that a pair of vortex cells are generated due to the symmetric geometry of the rib arrangement, and heat/mass transfer is augmented up to $Sh/Sh_0=2.9$ averagely, which is higher than that of the cross-ribbed case presented in the previous study for the stationary case. With the passage rotation, the main flow in the first-pass deflects toward the trailing surface and the heat transfer is enhanced on the trailing surface. In the second-pass, the flow enlarges the vortex cell close to the leading surface, and the small vortex cell on the trailing surface side contracts to disappear as the passage rotates faster. At the highest rotation number ($R_O=0.20$), the turn-induced single vortex cell becomes identical regardless of the rib configuration so that similar local heat/mass transfer distributions are observed in the fuming region for the cross- and parallel-ribbed case.

• 한국안전학회지
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• 제32권2호
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• pp.92-97
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• 2017

This study deals with new application method of the connecting tuned mass damper (CTMD) system for efficient vibration control of adjacent twin structures which have the same dynamic properties such as natural frequency and damping characteristics to each other. In the existing research, the vibration control of the twin structures has a limit to the application of the conventional damper-connection method of the twin structures. Due to the same frequency characteristics leading to the equally vibrating behaviors, it is impossible to apply the conventional connection method of the adjacent structures. In order to overcome these limitations induced by the symmetry of the dynamic characteristics, we propose a new CTMD-based control system that adopts the conventional connection configuration but unbalances the symmetric system by arranging the control device asymmetrically and then can finally achieve the efficient control performance. In order to demonstrate the applicability of the proposed system, numerical simulations of the optimally designed proposed system have been performed in comparison with the optimal design results of the existing independent single tuned mass damper (STMD) control system and the another optimal control system previously proposed by the same author, hereafter called CTMD-OsTMD. The comparative results of the control performances among STMD, CTMD-OsTMD and the proposed CTMD systems verified that the newly proposed control system can be a control-efficient and cost-effective system for vibration suppression of the two adjacent twin structures.

• International Journal of Safety
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• 제11권1호
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• pp.22-25
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• 2012

Scoliosis can be biomechanically described as a three dimensional deformity of the spine, with deviations from the physiologic curves in the sagittal and frontal planes, usually combined with intervertebral rotation. Various factors are suspected such as genetic defects, uneven growth of the vertebrae, hormonal effects, abnormal muscular activity, postural problems, or a mix of some of these elements, but its initial cause is known in only 15-20% cases. The screening test for diagnosing scoliosis is called the Adams Forward Bend Test. During the experiment, the subjects were asked to bend over, with arms dangling, until a curve could be observed. The Scoliometer was placed on the back of the subjects and used to measure the difference between the left and right apex of the curve in the thoracic, thoracolumbar and lumbar area. Then, the subjects were asked to perform Maximum Voluntary Contractions (MVCs) using the digital back muscle dynamometer in three different postures: (1) 0o (sagittally symmetric); (2) 30o from the mid-sagittal plane (clockwise); and (3) 30o from the mid-sagittal plane (counterclockwise). In addition to the experimental data, subject-dependent variables including Body Mass Index (BMI), percentage of body fat and muscle mass of left/right arms and legs were employed to reveal the cause of difference among three MVC conditions. All those variables were tested using statistical methods.

• 대한기계학회논문집B
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• 제23권5호
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• pp.670-677
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• 1999

An analysis of generation and growth of multicomponent particles has been carried out to predict the size and composition distributions of particles generated in the Modified Chemical Vapor Deposition(MCVD) process. In MCVD process. scale-up of sintering and micro-control of refractive index may need the Information about the size and composition distributions of $SiO_2-GeO_2$ particles that are generated and deposited. The present work solved coupled steady equations (axi-symmetric two dimensions) for mass conservation, momentum balance. energy and species(such as $SiCl_4$, $GeCl_4$, $O_2$, $Cl_2$) conservations describing fluid flow. heat and mass transfer in a tube. Sectional method has been applied to obtain multi-modal distributions of multicomponent aerosols which vary in both radial and axial directions. Chemical reactions of $SiCl_4$ and $GeCl_4$ were included and the effects of variable properties have also been considered.

• 대한기계학회논문집B
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• 제33권2호
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• pp.93-100
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• 2009

Characteristics of micro-sonic/supersonic axi-symmetric jet impinging on a flat plate with a pre-drilled hole were both experimentally and numerically studied, to observe the role of assist-gas jet to eject melted materials from the cut zone in the laser machining. For various Mach numbers of the nozzle and the total pressures of the assist gas, detailed impinging jet flow structures over the plate and the variations of mass flux through the pre-drilled hole were observed. It was found that the present experimental and numerical results show a good agreement, which proves the accountability of the present work. From the present study, it was also observed that the mass flow rate through the hole was closely related with the total pressure loss caused by the Mach disc on the work piece, and that supersonic nozzle could perform more efficient roles as blowing the assist-gas jet in the laser machining, as compared to sonic nozzles.

• Bulletin of the Korean Chemical Society
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• 제32권11호
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• pp.3899-3903
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• 2011

General, fast, and efficient fusion methods for the synthesis of dendrimers with 1,3-diynes at a core were developed. The synthetic strategy was employed the oxidative homo-coupling of terminal alkyne. The oxidative homo-coupling reaction of the alkyne-functionalized Frechet-type dendrons 1-Dm was allowed to provide first through fourth generation dendrimers 2-Gm with 1,3-diynes at core. The fusion of the propargylfunctionalized PAMAM dendrons 3-Dm by homo-coupling of terminal alkyne lead to the formation of symmetric PAMAM dendrimers 4-Gm. Their structure of dendrimers was confirmed by $^1H$ and $^{13}C$ NMR spectroscopy, IR spectroscopy, mass spectrometry, and GPC analysis.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1989년도 봄 학술발표회 논문집
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• pp.56-60
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• 1989

It is well known that the symmetric buildings have higher resistance than the unaymetric ones do under seismic load. However, it is sometimes inevitable to build an unsymmetric structure due to the site conditions or architectural needs. The unsymmetric building has structural disadvantages under seismic load. In such a case the structural seperation joints are often used to avoid those disadvantages. This paper presents a method to determine the width of the seperation joints for unsymmetric, reinforced concrete apartments structured by walls and slabs only. The variables of the study were the ratio of shear-wall stiffness to the building length in the same directron, the building height and the story mass.

• Nuclear Engineering and Technology
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• 제49권7호
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• pp.1396-1404
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• 2017

The mathematical aspects of Dufour and Soret phenomena on the peristalsis of magnetohydrodynamic (MHD) Jeffrey liquid in a symmetric channel are presented. Fluid viscosity is taken variably. Lubrication approach has been followed. Results for the velocity, temperature, and concentration are constructed and explored for the emerging parameters entering into the present problem. The plotted quantities lead to comparative study between the constant and variable viscosities fluids. Graphical results indicate that for non-Newtonian materials, pressure gradient is maximum, whereas pressure gradient is slowed down for variable viscosity. Also both velocity and temperature in the case of variable viscosity are at maximum when compared with results for constant viscosity.

• Steel and Composite Structures
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• 제21권5호
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• pp.999-1016
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• 2016

This study presents free vibration of beam made of porous material. The mechanical properties of the beam is variable in the thickness direction and the beam is investigated in three situations: poro/nonlinear nonsymmetric distribution, poro/nonlinear symmetric distribution, and poro/monotonous distribution. First, the governing equations of porous beam are derived using principle of virtual work based on Euler-Bernoulli theory. Then, the effect of pores compressibility on natural frequencies of the beam is studied by considering clamped-clamped, clamped-free and hinged-hinged boundary conditions. Moreover, the results are compared with homogeneous beam with the same boundary conditions. Finally, the effects of poroelastic parameters such as pores compressibility, coefficients of porosity and mass on natural frequencies has been considered separately and simultaneously.