• 소성∙가공
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• 제11권1호
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• pp.54-60
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• 2002

The purpose of the present paper is to investigate the effect of Process parameters such as internal pressure, amount of axial feeding, and frictional condition between the die and the material on the tube hydro-formability. For carbon steel tubes(STKM 12A, STBH 410 and SPS 290), simple bulging, circular bulging and Tee-fitting tests are performed to evaluate the hydro-formability of these materials which is determined by deformation characteristics such as thickness distribution, forming height and branch dome shape. The formabilities obtained from these tests are analysed and compared with the results of the numerical simulation.

• Smart Structures and Systems
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• 제25권6호
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• pp.693-705
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• 2020

In the current investigation, large amplitude free vibration behavior of shallow curved pipes (tubes) made of functionally graded materials is investigated. Properties of the tube are distributed across the radius of the tube and are obtained by means of a power law function. It is also assumed that all thermo-mechanical properties are temperature dependent. The governing equations of the tube are obtained using a higher order shear deformation tube theory, where the traction free boundary conditions are satisfied on the top and bottom surfaces of the tube. The von Kármán type of geometrical non-linearity is included into the formulation to consider the large displacements and small strains. Uniform temperature elevation of the tube is also included into the formulation. For the case of tubes which are simply supported in flexure and axially immovable, the governing equations are solved using the two-step perturbation technique. Closed form expressions are provided to obtain the small and large amplitude fundamental natural frequencies of the FGM shallow curved tubes in thermal environment. Numerical results are given to explore the effects of thermal environment, radius ratio, and length to thickness ratio of the tube on the fundamental linear and non-linear frequencies.

• Structural Engineering and Mechanics
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• 제89권1호
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• pp.13-22
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• 2024

The nonlinear snap-through buckling of functionally graded (FG) carbon nanotube reinforced composite (CNTRC) curved tubes is analytically investigated in this research. It is assumed that the FG-CNTRC curved tube is supported on a three-parameter nonlinear elastic foundation and is subjected to the uniformly distributed pressure and thermal loads. Properties of the curved nanocomposite tube are distributed across the radius of the pipe and are given by means of a refined rule of mixtures approach. It is also assumed that all thermomechanical properties of the nanocomposite tube are temperature-dependent. The governing equations of the curved tube are obtained using a higher-order shear deformation theory, where the traction free boundary conditions are satisfied on the top and bottom surfaces of the tube. The von Kármán type of geometrical non-linearity is included into the formulation to consider the large deflection in the curved tube. Equations of motion are solved using the two-step perturbation technique for nanocomposite curved tubes which are simply-supported and clamped. Closed-form expressions are provided to estimate the snap-buckling resistance of FG-CNTRC curved pipes rested on nonlinear elastic foundation in thermal environment. Numerical results are given to explore the effects of the distribution pattern and volume fraction of CNTs, thermal field, foundation stiffnesses, and geometrical parameters on the instability of the curved nanocomposite tube.

• 설비공학논문집
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• 제18권1호
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• pp.55-65
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• 2006

The air and water flow distribution are experimentally studied for a round header - flat tube geometry simulating a parallel flow heat exchanger. The number of branch flat tube is thirty. The effects of tube outlet direction, tube protrusion depth as well as mass flux, and quality are investigated. The flow at the header inlet is identified as annular. For the downward flow configuration, the water flow distribution is significantly affected by the tube protrusion depth. For flush-mounted configuration, most of the water flows through frontal part of the header. As the protrusion depth increases, more water is forced to the rear part of the header. The effect of mass flux or quality is qualitatively the same as that of the protrusion depth. Increase of the mass flux or quality forces the water to rear part of the header. For the upward flow configuration, however, most of the water flows through rear part of the header. The protrusion depth, mass flux, or quality does not significantly alter the flow pattern. Possible explanations are provided based on the flow visualization results. Negligible difference on the water flow distribution was observed between the parallel and the reverse flow configuration.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.535-540
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• 2000

The objective of the present study is to visualize the pulsatile flow fields by using three-dimensional computer simulation and the PIV system. A closed flow loop system was built for the steady and unsteady experiments. The Harvard pulsatile pump was used to generate the pulsatile pressure and velocity waveforms. Conifer powder as the tracing particles was added to water to visualize the flow field. Two consecutive particle images were captured by a CCD camera for the image processing. The cross-correlation method in combination with the moving searching area algorithm was applied for the image processing of the flow visualization. The pulsatile flow fields were visualized effectively by the PIV system in conjunction with the applied algorithm. The range validation and the area interpolation methods were used to obtain the final velocity vectors with high accuracy. The finite volume predictions were used to analyze three-dimensional flow patterns in the bifurcation model. The results of the PIV experiment and the computer simulation are in good agreement and the results show the recirculation zones and formation of the paired secondary flow distal to the apex of the bifurcated model. The results also show that the branch flow is pushed strongly to the inner wall due to the inertial force effect and helical motions are generated as the flow proceeds toward the outer wall.

• Steel and Composite Structures
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• 제52권4호
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• pp.487-499
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• 2024

The primary objective of this study is to analyze the free vibration behavior of a sandwich cylindrical shell with a defective core and wavy carbon nanotube (CNT)-enhanced face sheets, utilizing the three-dimensional theory of elasticity. The intricate equations of motion for the structure are solved semi-analytically using the generalized differential quadrature method. The shell structure consists of a damaged isotropic core and two external face sheets. The distributions of CNTs are either functionally graded (FG) or uniform across the thickness, with their mechanical properties determined through an extended rule of mixture. In this research, the conventional theory regarding the mechanical effectiveness of a matrix embedding finite-length fibers has been enhanced by introducing tube-to-tube random contact. This enhancement explicitly addresses the progressive reduction in the tubes' effective aspect ratio as the filler content increases. The study investigates the influence of a damaged matrix, CNT distribution, volume fraction, aspect ratio, and waviness on the free vibration characteristics of the sandwich cylindrical shell with wavy CNT-reinforced face sheets. Unlike two-dimensional theories such as classical and the first shear deformation plate theories, this inquiry is grounded in the three-dimensional theory of elasticity, which comprehensively accounts for transverse normal deformations.

• 천문학회지
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• 제29권spc1호
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• pp.339-340
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• 1996

In the present study we examine physical characteristics of a thin and rigid magnetic flux tube with a steady flow inside, which is embedded vertically upward in the solar atmosphere. We found from this study that (1) The downward material flow gives rise to a dominant heating in the flux tube which works with the conductive heating in the same direction. However, the upflow flow creates a dominant cooling which works against the conductive heating, resulting in a steeper temperature gradient with a shallower transition region. (2) Since the thickness of the transition region determines the material content in the transition region, a broader transition region of the downflow tube produces a larger differential measure.

• 한국동물위생학회지
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• 제33권2호
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• pp.151-156
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• 2010

This survey was carried out to investigate the seroprevalence of antibodies to Neospora caninum in Korean indigenous cattle that was raised in central area province Gyeongnam, Korea. A total of 719 sera were tested for N. caninum antibodies using ELISA (Herdcheck anti-Neospora, IDEXX Laboratories Inc., Westbrook, Maine USA). Seroprevalence of individual and farm were 29.8%(214/719) and 53.2%(50/94). Regional seropositive rates of the samples were 61%(47/77), 23.3%(7/30), 13.8%(49/355), 37.6%(77/205), 65.4%(34/52) at Changwon, Jinhae, Gimhae, Miryang, Yangsan, respectively. It showed difference at the age and on the herd size of farms. A herd of cattle above the age of 5 was more infective than under 4 years. And in seroprevalence by herd size farms having under 30 heads was top(35.7%). Seropositive 214 herds of N. caninum antibidies were tested for brucellosis by test tube. Positive rate of double infection was 16.4%(35/214).

• 대한소화기학회지
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• 제72권6호
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• pp.308-312
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• 2018

Percutaneous endoscopic gastrostomy (PEG) is widely used to provide nutritional support for patients with dysphagia and/or disturbed consciousness preventing oral ingestion, and PEG tube placement is a relatively safe and convenient non-surgical procedure performed under local anesthesia. However, the prevention of PEG-insertion-related complications is important. A 64-year-old man with recurrent pneumonia underwent tracheostomy and nasogastric tube placement for nutritional support and opted for PEG tube insertion for long-term nutrition. However, during the insertion procedure, needle puncture had to be attempted twice before successful PEG tube placement was achieved, and a day after the procedure his hemoglobin had fallen and he developed hypotension. Abdominal computed tomography revealed injury to a pancreatic branch of the superior mesenteric artery (SMA) associated with bleeding, hemoperitoneum, and pancreatitis. Transarterial embolization was performed using a microcatheter to treat hemorrhage from the injured branch of the SMA, and the acute pancreatitis was treated using antibiotics and supportive care. The patient was discharged after an uneventful recovery. Clinicians should be mindful of possible pancreatic injury and bleeding after PEG tube insertion. Possible complications, such as visceral injuries or bleeding, should be considered in patients requiring multiple puncture attempts during a PEG procedure.

• 한국동물위생학회지
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• 제30권3호
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• pp.375-384
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• 2007

This study was conducted to investigate the characteristics of brucellosis in Korean native cattle in a farm where bovine brucellosis was confirmed 3 times from September 2006 to March 2007. Of 74 bulls serum samples examined, 21 (28.4%) were positive by Rose-Bengal test (RBT) and Standard tube agglutination test (STAT). In the isolation test from seropositive bulls, B abortus was isolated and identified from 2 specimens (testis, intestinal lymph node) among 6 kinds of specimens including blood, urine, feces and soil. Isolation rate of intestinal lymph node and testis was 25% (3/12 cases) and 16.7% (2/12), respectively. B abortus was also isolated from calves below 12 months old, i.e., 1 isolate (25.0%) was confirmed from testis, 4 (40.0%) from supra-mammary lymph nodes and 1 (25.0%) from intestinal lymph node. All isolates had Brucella specific 16s r-RNA with 905-bp band detected by PCR assay. For the more effective control of bovine brucellosis in korea, this paper would like to suggest that all of bulls and calves should be included in the screening tests.