• Ocean Systems Engineering
• /
• 제6권2호
• /
• pp.191-201
• /
• 2016

Stern bearing is a key component of marine propulsion plant. Its environment is diverse, working condition changeable, and condition severe, so that stern bearing load is of strong time variability, which directly affects the safety and reliability of the system and the normal navigation of ships. In this paper, three affecting factors of the stern bearing load such as hull deformation, propeller hydrodynamic vertical force and bearing wear are calculated and characterized by random theory. The uncertainty mathematical model of stern bearing load is established to research the relationships between factors and uncertainty load of stern bearing. The validity of calculation mathematical model and results is verified by examples and experiment yet. Therefore, the research on the uncertainty load of stern bearing has important theoretical significance and engineering practical value.

• Coupled systems mechanics
• /
• 제7권4호
• /
• pp.421-440
• /
• 2018

In this study, a computational method for wall shear stress combined with an implicit direct-forcing immersed boundary method is presented. Near the immersed boundaries, the sub-grid stress is determined by a wall model in which the wall shear stress is directly calculated from the Lagrangian force on the immersed boundary. A coupling mathematical model of the transition process for a model Francis turbine comprising turbulent flow and rotating rigid guide vanes is established. The spatiotemporal distributions of pressure, velocity, vorticity and turbulent quantity are gained with the transient process; the drag and lift coefficients as well as other forces (moments) are also obtained as functions of the attack angle. At the same time, analysis is conducted of the characteristics of pressure pulsation, velocity stripes and vortex structure at some key parts of flowing passage. The coupling relations among the turbulent flow, the dynamical force (moment) response of blade and the rotating of guide vane are also obtained.

• Macromolecular Research
• /
• 제15권2호
• /
• pp.109-113
• /
• 2007

The surface molecular motion of monodisperse polystyrene (PS) films was examined using scanning vis-coelasticity microscopy (SVM) in conjunction with lateral force microscopy (LFM). The dynamic storage modulus, E', and loss tangent, $tan\delta$, at a PS film surface with number-average molecular weights, $M_n$, smaller than 30 k were found to be smaller and larger than those for the bulk sample, even at room temperature, meaning that the PS surface is in a glass-rubber transition or fully rubbery sate at this temperature when the $M_n$ is small. In order to quantitatively elucidate the dynamics of the molecular motion at the PS surface, SVM and LFM measurements were performed at various temperatures. The glass transition temperature, $T_g$, at the surface was found to be markedly lower than the bulk $T_g$, and this discrepancy between the surface and bulk became larger with decreasing $M_n$. Such an intensive activation of the thermal molecular motion at the PS surfaces can be explained in terms of an excess free volume in the vicinity of the film surface induced by the preferential segregation of the chain end groups.

• Bulletin of the Korean Chemical Society
• /
• 제19권5호
• /
• pp.533-539
• /
• 1998

A magnetic film was deposited on a slide glass substrate from aqueous solutions of $FeCl_2$ and $NaNO_2$ at 363 K. XRD analysis showed that the film was polycrystalline magnetite $(Fe_{3(1-{\sigma})}O_4)$ without impurity phase. The lattice constant was 0.8390 nm. Mossbauer spectrum of the film could be deconvoluted by the following parameters: isomer shifts for tetrahedral $(T_d)$ and octahedral $(O_h)$ sites are 0.28 and 0.68 mm/s, respectively, and corresponding magnetic hyperfine fields are 490 and 458 kOe, respectively. The estimated chemical formula of the film by the peak intensity of Mossbauer spectrum was $Fe_{2.95}O_4$. Low temperature transition of the magnetite (Verwey transition) was not detected in resistivity measurement of the film. Properties of the film were discussed with those of pressed pellet and single crystal of synthetic magnetites. On the surface of the film, magnetite particles of about 0.2 μm in diameter were identified by noncontact atomic force microscopy (NAFM) and magnetic force microscopy (MFM).

• 소성∙가공
• /
• 제8권3호
• /
• pp.271-271
• /
• 1999

A concentration change during grade transition operation in thin slab casting is investigated through computer simulation and the results are compared with experimental measurements. Fluid flow and mixing patterns in various tundish levers and flow rates were analysed by a three-dimensional mathematical model. Based on the contained results, a simple, efficient and accurate computational model is suggested to predict the concentration profile at the outlet of the tundish. Based on the model, mixing in and below the mold was analyzed considering electromagnetic braking force. The predicted concentration profiles show good agreements with the measured values. It is found that the lower vortices in the mold are suppressed by the electromagnetic field and a plug-like flow region develops, which decreases the intermixing of two different grades of steel and shortens the length of transition region.

• 한국재료학회:학술대회논문집
• /
• 한국재료학회 1998년도 IUMRS-ICEM ABSTRACT BOOK
• /
• pp.82.4-82
• /
• 1998

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
• /
• pp.185.1-185.1
• /
• 2005

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2007년도 춘계 학술대회논문집
• /
• pp.3-7
• /
• 2007

The characteristics of asymmetric vortex and side force of tangent-ogive-cylinder flight vehicle at high angles of attack have been performed by using upwind Navier-Stokes method with the ${\kappa}-{\omega}$ turbulence model. And Asymmetric transition positions are considered for generation of asymmetric vortex.

• 정보와 통신
• /
• 제31권9호
• /
• pp.17-23
• /
• 2014

본 논문에서는 국제 표준화 기구인 IETF(Internet Engineer Task Force)내 V6OPS WG(IPv6 Operation Working Group)를 중심으로 IPv4/IPv6 공존 상황에서 IPv6 운용(Operation) 및 전환(Transition) 관련 표준 기술 동향을 파악하고 주요 기술에 대해서 소개를 하고자 한다. 첫 번째로, V6OPS WG의 전신인 NGTRANS WG을 소개하고 개발된 표준기술을 간단히 기술한다. 두 번째로, V6OPS WG에서 개발된 표준화 기술을 운용과 전환으로 구분하여 소개하고 주요 기술을 기술한다. 특히, 전환 기술에 대해서는 IPv6 도입의 필요성이 다시 높아진 최근에 개발된 내용을 중심으로 다룬다. 마지막으로, V6OPS WG에서 현재 논의 중인 표준 기술을 소개한다.

• Bulletin of the Korean Chemical Society
• /
• 제15권8호
• /
• pp.631-636
• /
• 1994

For the Schlogl model with the second order transition under the influence of the multiplicative noise singular at the unstable steady state, the detailed discussions are presented for various kinds of stochastic phenomena, suchas the effects of parameters on stationary probability distribution, noise-induced phase transitions and escape rate.