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排序方式: 共有3516条查询结果,搜索用时 484 毫秒
921.
922.
Seok-Hwan Ahn Ki-Woo Nam Koji Takahashi Kotoji Ando 《Nuclear Engineering and Design》2006,236(2):140-155
Fracture behaviors of pipes with local wall thinning are very important for the integrity of power plant piping system. In this study, monotonic bending tests without internal pressure are conducted on 48.6 mm diameter Schedule 80 (thickness, 5.1 mm) STS370 full-scale carbon steel pipe specimens. Fracture strengths of locally wall-thinned pipes were calculated by elasto-plastic analysis using finite element method. The elasto-plastic analysis was performed by FE code ANSYS. We simulated various types of local wall thinning that can be occurred at pipe surface due to coolant flow. Locally wall thinned shapes were machined to be different in size along the circumferential or axial direction of straight pipes. We investigated fracture strengths and failure modes of locally wall thinned pipes by four point bending test. And, the allowable limit of pipes with local wall thinning was investigated. In addition, we compared the simulated results by finite element analysis with experimental data. The failure mode, fracture strength and fracture behavior obtained from FE analyses showed well agreement with experimental results. From the test results, we identified three types of failure modes into ovalization, local buckling and crack initiation. These failure modes could be classified according to thinned depth, thinned length and thinned angle of a pipe. For locally wall-thinned specimens, maximum moments (Mmax) were estimated by using the net-section stress criterion. Pipes with local wall thinning can be estimated using σu instead of σf because of 1.19σf σu. Also, the axial strain affects failure modes occurred on local wall thinning. the allowable limit of local wall thinning for carbon steel pipe used can be given as follows; in the case of Mmax ≥ My, if 10 ≤ l < 25 mm, d/t can be allowed to about 55%, and if 25 ≤ l < 100 mm, d/t can be allowed to about 50%. Also, if 100 ≤ l ≤ 120 mm, d/t can be allowed to about 29%. 相似文献
923.
Dong Hyup Jeon Kwang Nam KimSeung Man Baek Jin Hyun Nam 《International Journal of Hydrogen Energy》2011,36(19):12499-12511
The effect of relative humidity of the cathode (RHC) on proton exchange membrane (PEM) fuel cells has been studied focusing on automotive operation. Computational fluid dynamics (CFD) simulations were performed on a 300-cm2 serpentine flow-field configuration at various RHC levels. The dependency of current density, membrane water contents, net water flux on the performance and the uniformity was investigated. The uniformity of current density and temperature was evaluated by employing standard deviation. The water balance inside a fuel cell was examined by describing electro-osmotic drag and back diffusion. It was concluded that the RHC has strong effect on the cell performance and uniformity. The dry RHC showed low cell voltage and non-uniform distributions of current density and temperature, whereas high RHC presented increased cell performance and uniform distributions of current density and temperature with well-hydrated membrane electrode assembly (MEA). Also the local current density distribution was strongly dependent on the local membrane water contents distribution that has complex phenomena of water transport. The elimination of external humidifier is desirable for the automotive operation, but it could degrade cell performance and durability due to dehydration of the MEA. Therefore a proper humidification of the reactant is necessary. 相似文献
924.
W. Chung K. Nam C.H. Noh D.K. Kang S.M. Kang Y.G. Oh S.W. Choi S.H. Kang Y. Utin K. Ioki N. Her J. Yu 《Fusion Engineering and Design》2011,86(9-11):1928-1932
A full-scale mock-up of VVTS inboard section was made in order to validate its manufacturing processes before manufacturing the vacuum vessel thermal shield (VVTS) for ITER tokamak. VVTS inboard 10° section consists of 20 mm shells on which cooling tubes are welded and flange joints that connect adjacent thermal shield sectors. The whole VVTS inboard is divided into two by bisectional flange joint located at the center. All the manufacturing processes except silver coating were tested and verified in the fabrication of mock-up. For the forming and the welding, pre-qualification tests were conducted to find proper process conditions. Shell thickness change was measured after bending, forming and buffing processes. Shell distortion was adjusted after the welding. Welding was validated by non-destructive examination. Bisectional flange joint was successfully assembled by inserting pins and tightening with bolt/nut. Bolt hole margin of 2 mm for sector flange was revealed to be sufficient by successful sector assembly of upper and lower parts of mock-up. Handling jig was found to be essential because the inboard section was flexible. Dimensional inspection of the fabricated mock-up was performed with a 3D laser scanner. 相似文献
925.
The corrosion resistance and conduction properties of polyaniline (PANi)-coated 316L stainless steel were improved by the thermal treatment. Electrochemical analyses of the PANi specimens demonstrated excellent corrosion resistance with high protection efficiency (?96.21%) and charge transfer resistance, as well as a very low corrosion current density (<1 μA/cm2). In addition, it also performed better conductive properties due to lower contact and surface resistance (<5 Ω cm2), comparing with untreated specimens. These were attributed to the presence of the interaction of the carbonyl group with the NH group in PANi as a physical barrier layer, which provides passivity protection in polymer coatings. 相似文献
926.
Young-Taek Lee Jaechun Lee Sangwook Nam 《Microwave and Wireless Components Letters, IEEE》2005,15(1):39-41
This letter presents a new method to reduce the phase noise in oscillator based on the loaded Q improvement approach. A hairpin resonator is weakly coupled to the two microstrip lines to improve the loaded Q of it and the dual feedback topology is used to enable the start-up oscillation condition to be satisfied. The high loaded Q property of the resonator in the proposed oscillator circuit is analyzed using the CAD simulation. For comparison the phase noise performances of the conventional hairpin resonator oscillator and the oscillator using the dual feedback are measured. Measurements show that the oscillator using the dual feedback exhibits a low phase noise performance of -109.1 dBc/Hz at 100-kHz offset at 10 GHz, which is reduced by about 10 dB compared to that of the conventional one. 相似文献
927.
Mark Howells Kiho Jeong Lucille Langlois Man Ki Lee Kee-Yung Nam Hans Holger Rogner 《Energy Policy》2010
This paper approximates the emissions rebound effects1 associated with substituting expensive and GHG emitting natural gas (LNG) power plants, with apparently cheaper and lower emitting nuclear plant. It then evaluates the effect this has on economy wide electricity use as well as net GHG emissions changes. 相似文献
928.
Jin Ha Lee Seong Hee Nam Hyen Joung Park Young-Min Kim Nahyun Kim Ghahyun Kim Eun-Seong Seo Seong-Soo Kang Doman Kim 《Food science and biotechnology》2010,19(3):757-762
Appreciably elevated levels of dextranase from Arthrobacter oxydans (AODex) isolated from sugar-cane farm soil was resulted from the culture on the Luria-Bertani (LB) medium containing 1%(w/v)
soluble starch, glycerol, or dextran. The responsible gene (aodex) was cloned, its nucleotide sequence was determined, and expression of the encoded protein was achieved in Escherichia coli. An open reading frame was composed of 1,863 bp putatively encoding a 68.3 kDa protein. Recombinant A. oxydans dextranase (rAODex) was purified about 16 fold by nickel-nitrilotriacetic acid affinity column chromatography; K
m value for dextran T2000 was 0.85 mg/mL (w/v). AODex treatment of stale sugar cane juice resulted in a yield of square and
light-colored sugar crystals. 相似文献
929.
Nam T.P. Le Craig White Jason M. Reese Rho S. Myong 《International Journal of Heat and Mass Transfer》2012,55(19-20):5032-5043
The simulation of nonequilibrium thermal gas flow is important for the aerothermodynamic design of re-entry and other high-altitude vehicles. In computational fluid dynamics, the accuracy of the solution to the Navier–Stokes–Fourier (N–S–F) equations depends on the accuracy of the surface boundary conditions. We propose new boundary conditions (called the Langmuir–Maxwell and the Langmuir–Smoluchowski conditions), for use with the N–S–F equations, which combine the Langmuir surface adsorption isotherm with the Maxwell/Smoluchowski slip/jump conditions in order to capture some of the physical processes involved in gas flow over a surface. These new conditions are validated for flat plate flow, circular cylinder in cross-flow, and the flow over a sharp wedge for Mach numbers ranging from 6 to 24, and for argon and nitrogen as the working gases. Our simulation results show that the new boundary conditions give better predictions for the surface pressures, compared with published experimental and DSMC data. 相似文献
930.
The effect of iron(III) p-toluenesulfonate hexahydrate (Fe(PTS)3) concentration on the formation and patternability of poly(3,4ethylenedioxythiophene) (PEDOT) films on (3-aminopropyl)trimethoxysilane (APS) monolayer was investigated. Low deposition rate yielded highly conductive and very smooth PEDOT films. However, the spin-coated oxidants in low Fe(PTS)3 concentrations were susceptible to moistures, leading to the poorly patterned PEDOT films. Increasing Fe(PTS)3 concentration enabled the fine patterning of the films. The fabricated thin film transistors with PEDOT electrodes formed on 30 wt.% Fe(PTS)3 revealed the saturation mobility of 0.16 cm2/V s and subthreshold slope of 0.5 V/decade. The obtained low contact resistance was 12 kΩ cm, possibly due to the negligible interface morphological discontinuity at the pentacene-PEDOT interface. 相似文献