• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2013년도 제46회 KOSCO SYMPOSIUM 초록집
• /
• pp.11-12
• /
• 2013

To investigate the effect of an inner diameter of the extension tube on the self-ignition when high pressurized hydrogen abruptly released through a tube, both experimental and numerical approach are used. The result show that there is a possibility to have successful ignition when the tube diameter is decreased even at the pressure that could not give sustainable flame with a larger diameter tube. Numerical simulation show the flame development inside the tube and weak and stretch flame spout the tube for 10.9 mm tube, whereas strong complete flame has been generated for 3 mm tube.

• 한국연소학회지
• /
• 제23권1호
• /
• pp.36-43
• /
• 2018

Numerical simulations and experiments are performed to investigate the flame development inside tubes with different diameters at the same burst pressure. It is shown that generation of a stable flame play a role in self-ignition. In the smaller tube, multi-dimensional shock interaction is occurred near the diaphragm. After flame of a cross-section is developed, stable flame remains for a moment then it grows having enough energy to overcome the sudden release at the exit. Whereas shock interaction generate complex flow further downstream for a larger tube, it results in stretched flame. This dispersed flame has lower average temperature which makes it easily extinguished.

• Korea-Australia Rheology Journal
• /
• 제11권4호
• /
• pp.293-304
• /
• 1999

Refinements of classical theories for entangled or crosslinked polymeric systems have led to incommensurable models for rubber networks and polymer melts, contrary to experimental evidence, which suggests a great deal of similarity. Uniaxial elongation and compression data of linear and branched polymer melts as well as of crosslinked rubbers were analyzed with respect to their nonlinear strain measure. This was found to be the result of two contributions: (1) affine orientation of network strands, and (2) isotropic strand extension. Network strand extension is caused by an increasing restriction of lateral movement of polymer chains due to deformation, and is modelled by a molecular stress function which in the tube concept of Doi and Edwards is the inverse of the relative tube diameter. Up to moderate strains, $f^2$ is found to be linear in the average stretch for melts as well as for rubbers, which corresponds to a constant tube volume. At large strains, rubbers show maximum extensibility, while melts show maximum molecular tension. This maximum value of the molecular stress function governs the ultimate magnitude of the strain-hardening effect of linear and long-chain branched polymer melts in extensional flows.

• Korea-Australia Rheology Journal
• /
• 제21권4호
• /
• pp.203-211
• /
• 2009

In flows with deformation rates larger than the inverse Rouse time of the polymer chain, chains are stretched and their confining tubes become increasingly anisotropic. The pressures exerted by a polymer chain on the walls of an anisotropic confinement are anisotropic and limit chain stretch. In the Molecular Stress Function (MSF) model, chain stretch is balanced by an interchain pressure term, which is inverse proportional to the $3^{rd}$ power of the tube diameter and is characterized by a tube diameter relaxation time. We show that the tube diameter relaxation time is equal to 3 times the Rouse time in the limit of small chain stretch. At larger deformations, we argue that chain stretch is balanced by two restoring tensions with weights of 1/3 in the longitudinal direction of the tube (due to a linear spring force) and 2/3 in the lateral direction (due to the nonlinear interchain pressure), both of which are characterized by the Rouse time. This approach is shown to be in quantitative agreement with transient and steady-state elongational viscosity data of two monodisperse polystyrene melts without using any nonlinear parameter, i.e. solely based on the linear-viscoelastic characterization of the melts. The same approach is extended to model experimental data of four styrene-butadiene random copolymer melts in shear flow. Thus for monodisperse linear polymer melts, for the first time a constitutive equation is presented which allows quantitative modeling of nonlinear extension and shear rheology on the basis of linear-viscoelastic data alone.

• Steel and Composite Structures
• /
• 제20권5호
• /
• pp.1067-1085
• /
• 2016

Recent research on steel moment-resisting connection between steel beams and concrete filled steel tubes has shown that there are considerable advantages to be obtained by anchoring the connection to the concrete infill within the tube using anchors in blind bolts. In the research reported here, extensive experimental tests and numerical analyses have been performed to study the anchorage behaviour of cogged deformed reinforcing bars within concrete filled circular steel tubes. This data in essential knowledge for the design of the steel connections that use anchored blind bolts, both for strength and stiffness. A series of pull-out tests were conducted using steel tubes with different diameter to thickness ratios under monotonic and cyclic loading. Both hoop strains and longitudinal strains in the tubes were measured together with applied load and slip. Various lead-in lengths before the bend and length of tailed extension after the bend were examined. These dimensions were limited by the dimensions of the steel tube and did not meet the requirements for "standard" cogs as specified in concrete standards such as AS 3600 and ACI 318. Nevertheless, all of the tested specimens failed by bar fracture outside the steel tubes. A comprehensive 3D Finite Element model was developed to simulate the pull-out tests. The FE model took into account material nonlinearities, deformations in reinforcing bars and interactions between different surfaces. The FE results were found to be in good agreement with experimental results. This model was then used to conduct parametric studies to investigate the influence of the confinement provided by the steel tube on the infilled concrete.

• 대한기계학회논문집A
• /
• 제30권4호
• /
• pp.420-427
• /
• 2006

The structural and leakage integrity of steam generator tubes should be sustained against all postulated loads even if a crack is present. During the past three decades, most of the efforts with respect to integrity evaluation of steam generator tubes have been focused on limit load solutions but, recently, the applicability of elastic-plastic fracture mechanics was examined cautiously due to its effectiveness. The purpose of this paper is to introduce a testing method to estimate fracture resistance characteristics of steam generator tubes with a through-wall crack. Due to limited thickness and diameter, inevitably, the steam generator tubes themselves were tested instead of standard specimen or alternative ones. Also, a series of three dimensional elastic-plastic finite element analyses were carried out to derive closed-form estimation equations with respect to J-integral and crack extension for direct current potential drop method. Since the effectiveness of $J_{IC}$ as well as J-R curves was proven through comparison with those of standard specimens taken from pipes, it is believed that the proposed scheme can be utilized as an efficient tool for integrity evaluation of cracked steam generator tubes.

• 한국산학기술학회논문지
• /
• 제13권8호
• /
• pp.3792-3799
• /
• 2012

본 연구에서는 전산유체역학(CFD)을 이용하여 산업체에 널리 적용되고 있는 충격기류형 탈진시스템의 탈진 특성을 규명하고, 그 성능을 향상시키기 위해 탈진부 유니트(unit) 형상을 개조한 경우의 탈진 성능을 비교하였다. 탈진부 각 형상별로 탈진 공기량과 기류 분포, 유입속도 분포 등을 검토한 결과, 블로우 튜브에 노즐을 설치한 경우(Case 3)와 벤츄리에 이중 유입관을 설치한 경우(Case4, 5)가 현재 현장에서 널리 적용되고 있는 구조(Case 1)에 비해 탈진 공기량의 증폭 효과 및 기류 폭의 확장 현상이 우수한 것으로 예측되었다. 선정된 Case-5를 상용 백필터의 사양(직경 150 mm)에 적용하기 위해 벤츄리 제원을 결정한 결과, 내측 유입관의 직경 50 mm, 외측 유입관의 직경 90 mm의 제원을 적용하면 탈진 공기량을 최대로 유지할 수 있을 것으로 판단된다.

• 생명과학회지
• /
• 제19권5호
• /
• pp.581-586
• /
• 2009

고랭지 파프리카 재배 초기에 기형과 및 단위결과 과실이 많이 발생하는데 야간 저온이 화분 활력 및 생식기관 발달에 미치는 영향을 알아보고자 본 연구를 수행하였다. 주간 $28^{\circ}C$ 동일 조건에서 야간온도를 $13^{\circ}C$ (LNT)와 $20^{\circ}C$ (ONT)로 달리 처리하여 생장상에서 파프리카(Capsicum annuum cv. Plenty)를 재배하였다. ONT와 LNT에서 화분을 채취하여 10, 15, 20, 25, $30^{\circ}C$에서 발아시켰다. 24시간 후 화분의 활력을 살펴 본 결과, 처리에 관계 없이$25^{\circ}C$ 에서 화분 활력이 가장 좋았고 다음이 $30^{\circ}C$였다. $25^{\circ}C$에서 발아율은 ONT화분이 42%, LNT 화분이 21%였다. 화분관 신장길이는 화분발아 온도에 관계 없이 ONT화분이 가장 길었다. 화분관 신장 속도는 $25^{\circ}C$ 에서 발아시킨ONT화분이 가장 빨랐다. 파프리카가 재배된 ONT와 LNT 조건에서 화분 활력의 차이를 알아보기 위해 배지에 화분을 치상 후 ONT와 LNT에서 화분발아 시험을 실시하였다. LNT에서는 야간($13^{\circ}C$) 동안 화분이 발아되지 않았지만 주간($13^{\circ}C$)조건으로 전환되자 화분이 발아되기 시작하였다. 하지만 ONT에서는 야간($20^{\circ}C$) 초기부터 화분이 발아되기 시작하여 주간($28^{\circ}C$)까지 계속 발아가 진행되었다. LNT에서는 과병길이, 자방지름, 수술길이, 화중 및 과중이 증가하였다. 종자수는 처리간 차이가 없었다. LNT처리구에서도 종자가 잘 형성되었던 것은 주간에 수분수정이 이루어졌기 때문인 것으로 보여지지만 기형과나 단위결과 발생 방지를 위해서는 화분발아를 저해하는 저온범위에 대한 정밀한 연구가 수행되어야 할 것으로 보여진다.