저온분사 공정에서 알루미늄 분말의 산화가 임계 적층 속도에 미치는 영향

강기철,윤상훈,지율권,이창희,Kang, Ki-Cheol,Yoon, Sang-Hoon,Ji, Youl-Gwun,Lee, Chang-Hee 대한용접접합학회 2007 대한용접·접합학회지 Vol.25 No.4

In kinetic spraying process, the critical velocity is an important criterion which determines the deposition of a feedstock particle onto the substrate. In other studies, it was experimentally and numerically proven that the critical velocity is determined by the physical and mechanical properties and the state of materials such as initial temperature, size and the extent of oxidation. Compared to un-oxidized feedstock, oxidized feedstock required a greater kinetic energy of in-flight particle to break away oxide film during impact. The oxide film formed on the surface of particle and substrate is of a relatively higher brittleness and hardness than those of general metals. Because of its physical characteristics, the oxide significantly affected the deposition behavior and critical velocity. In this study, in order to investigate the effects of oxidation on the deposition behavior and critical velocity of feedstock, oxygen contents of Al feedstock were artificially controlled, individual particle impact tests were carried out and the velocities of in-flight Al feedstock was measured for a wide range of process gas conditions. As a result, as the oxygen contents of Al feedstock increased, the critical velocity increased.

Combined analytical and numerical solution for an elastically supported Timoshenko beam to a moving load

이영현,김성수 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.7

A combined analytical and numerical method is presented to get a response for an elastically supported Timoshenko beam to a movingload. The analytical steady-state solution as a particular solution is established and summed with the numerically calculated homogeneoussolution. A steady-state solution is sought analytically through the direct application of the Fourier transform to the moving step load. It is shown to be a compact formula composed of exponential and sinusoidal functions depending on the load velocity. The homogeneoussolution is established numerically to cancel out the discontinuities and the inconsistent boundary and initial conditions of the steady-statesolution. The discontinuities produced by the steady-state solution are removed using the physical characteristics related to the bar wave. Some response curves are shown to compare the beam motions at different load velocities.

Design of Ship Thruster and Seabed Scouring due to Effects of Water Velocity

Choi, Byoung-Yeol,Lee, Sang-Gil Korean Society of Ocean Engineers 2017 Journal of advanced research in ocean engineering Vol.3 No.3

This study considered the effects on the seabed of a harbor and quay wall from ship maneuvers in relation to the thruster jet flow and initial velocity. This study also included the engine capacity, RPM, and diameter and pitch of a ship's thruster for a required speed. The impact of a scour hole on the environment of a quay wall was investigated. Based on these results, a risk based analysis was conducted to evaluate different strategies and their consequences. There has been an increase in the loads on the bottom of a harbor during ship maneuvering. This increase is caused by the propeller loads of mooring and unmooring vessels. This indicates a greater number of arrivals and departures of vessels with larger drafts, larger thruster diameters, and larger available thruster power capacities. Another important cause could be an increase in the maneuverability of vessels from the use of bow thrusters. The increasing loads, which cause a higher jet flow above the bottom, can lead to undesirable scour holes.

Oxidation dependency of critical velocity for aluminum feedstock deposition in kinetic spraying process

Kang, K.,Yoon, S.,Ji, Y.,Lee, C. Elsevier Sequoia 2008 Materials science & engineering. properties, micro Vol.486 No.1

In kinetic spraying process, critical velocity is an important criterion which determines the deposition of feedstock onto the substrate. It has been proven experimentally and numerically that the critical velocity is determined by physical and mechanical properties and the state of materials such as initial temperature and size. In this study, the oxidation effect on critical velocity was investigated using experimental methods. As oxygen content of feedstock increased, critical velocity significantly decreased. In order to find out reasons for difference in critical velocity with oxygen content, individual impact behavior was analyzed and interface microstructure was observed. Due to high brittleness and hardness of oxide, oxide layer on particle influences the particle deformation behavior during impact. And oxide accumulated at interface obstructs the adhesion between activated particle and substrate surface during impact.

Investigation of hyperbolic dynamic response in concrete pipes with two-phase flow

Zheng, Chuanzhang,Yan, Gongxing,Khadimallah, Mohamed Amiine,Nouri, Alireza Zamani,Behshad, Amir Techno-Press 2022 Advances in concrete construction Vol.13 No.5

The objective of this study is to simulate the two-phase flow in pipes with various two-fluid models and determinate the shear stress. A hyperbolic shear deformation theory is used for modelling of the pipe. Two-fluid models are solved by using the conservative shock capturing method. Energy relations are used for deriving the motion equations. When the initial conditions of problem satisfied the Kelvin Helmholtz instability conditions, the free-pressure two-fluid model could accurately predict discontinuities in the solution field. A numerical solution is applied for computing the shear stress. The two-pressure two-fluid model produces more numerical diffusion compared to the free-pressure two-fluid and single-pressure two-fluid models. Results show that with increasing the two-phase percent, the shear stress is reduced.

서해안 지역의 세립토 지반 및 심층혼합처리 개량체의 침식성 평가

강경오(Gyeong-o Kang),김영상(Young-sang Kim),김종규(Jong-kyu Kim) 전남대학교 수산과학연구소 2022 수산과학연구소논문집 Vol.31 No.1

The purpose of this study is to evaluate the erosion characteristic on foundation part (clay and sand grounds and deep cement mixing (DCM) of coastal construction in the West Coast region. For erosion evaluation tests, clay and sand samples were prepared through consolidation and compaction, in the case of DCM sample was prepared by mixing the blast furnace cement considering real condition in the construction field. The erosion rate and shear stress were quantified using EFA (Erosion Function Apparatus). As result, the critical velocity and critical shear stress were calculated and its erodibility was evaluated by erodibility chart.

하수관거의 최저유속

유동훈,이정영 한국수자원학회 1999 한국수자원학회논문집 Vol.32 No.4

한수관내 침전물의 퇴적을 방지하기 위하여는 최저유속과 에너지경사, 관경을 산정하여 제시하여야 되는데 이들 수치를 바로 결정하는 양해법 산정식들을 개발하였다. 이를 위하여 토사의 임계전단력과 상용관 마찰계수 산정을 위하여 지수형 산정식들을 도입하였으며, 이들 지수형 산정식들은 기존 실험관측자료를 이용하여 개발되었다. 제시된 수치들의 적합성을 판별하기 위하여 여러 예들을 본 연구에서 개발된 산정식들을 적용하여 검토하였다. Explicit equations of minimum velocity, energy slope and pipe diameter are developed to ensure the cleaning of sewerage pipes. The equations of power form are employed for the estimation of critical shear stress of sediment particles and the friction fact

A Case Study of Sediment Transport on Trenched Backfill Granular and Cohesive Material due to Wave and Current

Choi, Byoung-Yeol,Lee, Sang-Gil,Kim, Jin-Kwang,Oh, Jin-Soo Korean Society of Ocean Engineers 2016 Journal of advanced research in ocean engineering Vol.2 No.2

In this study, after the installation of a subsea pipeline, backfilling was performed in the trenched area. During these operations, a stability problem in the subsea pipeline occurred. The pipeline was directly impacted by environmental loading such as waves and currents that were caused by backfill material when scouring or sediment transport and siltation was carried out. Therefore, this study reviewed whether trenching was necessary, and conducted research into an indigenous seabed property that contains granular soil. A study of cohesive soil was also conducted in order to cross-correlate after calculating the values of the critical Shields parameter relevant to elements of the external environment such as waves and current, and the shear Shields parameter that depends on the actual shearing stress. In case of 1), sedimentation or erosion does not occur. In the case of 2), partial sedimentation or erosion occurs. If the case is 3), full sedimentation or erosion occurs. Therefore, in the cases of 1) or 2), problems in structural subsea pipeline stability will not occur even if partial sedimentation or erosion occurs. This should be reflected particularly in cases with granular and cohesive soil when a reduction in shear strength occurs by cyclic currents and waves. In addition, since backfilling material does not affect the original seabed shear strength, a set-up factor should be considered to use a reduced of the shear strength in the original seabed.

사석의 수리적 안정성 실험식 개발

최흥식,박광호 한국수자원학회 2011 한국수자원학회논문집 Vol.44 No.6

사석 입자의 운동을 시작하는 한계평균유속은 사석의 평균입경, 수심에 대한 사석의 평균입경 비, Froude수 및 한계평균유속에 대한 난류전단속도 비에 따라 증가함을 실험을 통해 확인하였고, 이 값을 사석의 수리적 안정성을 지배하는 변수로 채택하여 회귀분석을 통한 사석의 안정성 실험식을 개발하였다. 개발된 사석 안정성 식은 기존 실험의 유속범위인 0.36~0.73 m/s에서 0~5.0 m/s까지 확장시켜 실제 하천에 적용 가능성을 검토하였다. 큰 값의 R By examining the experimental results, the critical mean velocity which initiates the movement of riprap is increased with the riprap size in mean diameter, the mean diameter over water depth (d/h), Froude number (Fr), and turbulent shear velocity over cr

수심적분 2차원 유사이동모형에 관계된 인자들의 민감도분석에 관한 연구

서상원,윤병만 한국수자원학회 1998 한국수자원학회논문집 Vol.31 No.1

본 논문에서는 수심적분 2차원 모형을 하나 소개하고, 이 모형이 가질 수 있는 오차의 한계를 민감도분석을 통해 제시하였다. 민감도 분석 결과, Manning 조도계수, 혼합계수, 침강속도, 한계전단력 등이 부유사농도에 대해 모형에 미치는 영향은 매우 크게 나타났으며, 조위와 확산계수의 영향은 거의 없는 것으로 나타났다. In this paper, a depth-averaged two-dimensional transport model is introduced, and its error bound is presented as the results of sensitivity analysis. The results show that the calculated SS concentration is highly dependant on Manning roughness coeffici