http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Seok, Woochan,Park, Sae Yong,Rhee, Shin Hyung The Society of Naval Architects of Korea 2020 International Journal of Naval Architecture and Oc Vol.12 No.-
In this study, the effects of hydrodynamic interceptors on a high-speed vessel were investigated to identify the operating principle based on experiments. Model tests were performed using a high-speed towing carriage. The resistance, trim and rise of Center of Gravity (CG) of the high-speed vessel were measured for various ship speeds and interceptor heights. As the interceptor height increased, the trim and rise of CG were reduced. In order to quantitatively analyze these phenomena, the pressure at the stern bottom was measured using tactile sensors. The reliability of the measured results from the tactile sensors was verified through repeat tests. The pressure on the stern bottom increased in proportion to the interceptor height, as the interceptor partially blocked the flow there. Then, the trim was reduced. However, as the ship speed increases, the pressure at the location close to the interceptor decreases when the interceptor height is small, leading to increased trim. Therefore, the interceptor height for running attitude control should be carefully determined considering multiple factors in the operating condition of the high-speed planing hull.
Seok, Woochan,Park, Sae Yong,Rhee, Shin Hyung The Society of Naval Architects of Korea 2020 International Journal of Naval Architecture and Oc Vol.12 No.1
In this study, the effects of hydrodynamic interceptors on a high-speed vessel were investigated to identify the operating principle based on experiments. Model tests were performed using a high-speed towing carriage. The resistance, trim and rise of Center of Gravity (CG) of the high-speed vessel were measured for various ship speeds and interceptor heights. As the interceptor height increased, the trim and rise of CG were reduced. In order to quantitatively analyze these phenomena, the pressure at the stern bottom was measured using tactile sensors. The reliability of the measured results from the tactile sensors was verified through repeat tests. The pressure on the stern bottom increased in proportion to the interceptor height, as the interceptor partially blocked the flow there. Then, the trim was reduced. However, as the ship speed increases, the pressure at the location close to the interceptor decreases when the interceptor height is small, leading to increased trim. Therefore, the interceptor height for running attitude control should be carefully determined considering multiple factors in the operating condition of the high-speed planing hull.
Death Spiral Issues in Emerging Market : A Control Related Perspective
Woochan Kim,Woojin Kim,Hyung-Seok Kim 한국재무학회 2009 한국재무학회 학술대회 Vol.2009 No.11
This paper studies the motive of issuing floating-priced convertibles or warrants, known as death spirals, in a country where the private benefit of control is high. Using a total of 199 death spiral issuances by public firms listed in the Korea Stock Exchange during 1998-2006, we find a number of pieces of empirical evidence that are less consistent with the last-resort financing hypothesis, but rather consistent with the control enhancing or control transferring hypothesis. First, operating performance of death spiral issuers are not necessarily poor at the time of the issue, nor do they deteriorate over time following the issue. Second, we do not observe subsequent changes in the controlling shareholder in more than 60% of the issuers and these firms exhibit superior operating performance at the time of the issue compared to other death spiral or non-death spiral issuers. Third, this same set of firms do not experience a decrease in proportional ownership by the controlling party, while family members other than the controlling shareholder experience the most pronounced increases in the number of shares held. Finally, in approximately half of these firms, at least one member of the controlling party holds hybrid securities that can be later converted into the firm’s voting shares.
What makes firms issue death spirals? A control enhancing story
Woochan Kim,Woojin Kim,Hyung-Seok Kim 한국재무학회 2008 한국재무학회 학술대회 Vol.2008 No.11
In this paper, we study the motive of issuing floating-priced convertibles or warrants, known as death spirals, in a country setting where the private benefit of control is high. Using a total of 199 death spiral issuances by public firms listed in the Korea Stock Exchange during 1998-2006, we find a number of empirical evidences that are not consistent with the last-resort financing hypothesis, but rather consistent with the control enhancing or control transferring hypothesis. First, death spirals are not necessarily issued by firms with poor operating performances. Second, death spiral issuers, where control is preserved within the family, experience an increase of ownership by affiliated firms. Third, this group of death spiral issuers tends to perform better than those in which family loses control.
What makes firms issue death spirals? A control enhancing story
Woochan Kim,Woojin Kim,Hyung-Seok Kim 한국재무학회 2009 한국재무학회 학술대회 Vol.2009 No.08
This paper studies the motive of issuing floating-priced convertibles or warrants, known as death spirals, in a country where the private benefit of control is high. Using a total of 199 death spiral issuances by public firms listed in the Korea Stock Exchange during 1998-2006, we find a number of pieces of empirical evidence that are not consistent with the last-resort financing hypothesis, but rather consistent with the control enhancing or control transferring hypothesis. First, operating performance of death spiral issuers are not necessarily poor at the time of the issue nor do they deteriorate over time following the issue. Second, death spiral issuers that are more likely to be motivated by control enhancing or transferring purposes - firms with no subsequent changes in control - exhibit superior operating performance at the time the issue compared to other death spiral or non-death spiral issuers. Third, these firms do not experience a decrease in proportional ownership by the controlling party, while family members other than the controlling shareholder experience the most pronounced increases in the number of shares held. Fourth, in approximately half of these firms, at least one member of the controlling party holds hybrid securities that can be later converted into the firm’s voting shares.
Computational analysis of strut effects on a BB2 submarine at drift angle 0, 6, and 12°
Junyoung Park,Woochan Seok The Society of Naval Architects of Korea 2023 International Journal of Naval Architecture and Oc Vol.15 No.-
Struts are attached to a submarine to maintain its submerged depth when conducting the model tests. While previous studies have mentioned that the attachment of the struts has a negligible effect on the performance of a submarine, it is difficult to find studies that clearly explain the effects of the struts. The present study examines the effect of struts with a circular cross-section on the resistance and propulsion performances of a submarine under both straight-ahead (β = 0°) and static-drift (β = 6° and 12°) conditions. For this analysis, the open-source computational fluid dynamics (CFD) toolkit OpenFOAM was utilized. A generic submarine Joubert BB2 was selected as a test model, which was modified by the Maritime Research Institute Netherlands (MARIN). Analyses of resistance were conducted in straight-ahead and static-drift conditions, and the flow characteristics such as pressure, velocity, vorticity, and turbulent kinetic energy were compared to identify differences caused by the struts on the BB2 submarine. The results showed that as the drift angle increased, the struts had a smaller effect on the submarine along the hull to the propeller plane. From the results, it was predicted that the effect of the struts should be considered during the design process for the submarine.
Maneuvering simulation of an X-plane submarine using computational fluid dynamics
Cho, Yong Jae,Seok, Woochan,Cheon, Ki-Hyeon,Rhee, Shin Hyung The Society of Naval Architects of Korea 2020 International Journal of Naval Architecture and Oc Vol.12 No.1
X-plane submarines show better maneuverability as they have much longer span of control plane than that of cross plane submarines. In this study, captive model tests were conducted to evaluate the maneuverability of an X-plane submarine using Computational Fluid Dynamics (CFD) and a mathematical maneuvering model. For CFD analysis, SNUFOAM, CFD software specialized in naval hydrodynamics based on the open-source toolkit, OpenFOAM, was applied. A generic submarine Joubert BB2 was selected as a test model, which was modified by Maritime Research Institute Netherlands (MARIN). Captive model tests including propeller open water, resistance, self-propulsion, static drift, horizontal planar motion mechanism and vertical planar motion mechanism tests were carried out to obtain maneuvering coefficients of the submarine. Maneuvering simulations for turning circle tests were performed using the maneuvering coefficients obtained from the captive model tests. The simulated trajectory showed good agreement with that of free running model tests. From the results, it was proved that CFD simulations can be applicable to obtain reliable maneuvering coefficients for X-plane submarines.
Multi-fidelity optimization of blade thickness parameters for a horizontal axis tidal stream turbine
Kumar, P. Madhan,Seo, Jeonghwa,Seok, Woochan,Rhee, Shin Hyung,Samad, Abdus Elsevier 2019 RENEWABLE ENERGY Vol.135 No.-
<P><B>Abstract</B></P> <P>Cross-sectional geometry of a horizontal axis tidal stream turbine (HATST) blade was optimized using surrogate models and computational fluid dynamics (CFD) analysis. The blade thickness parameters of a 100 kW class HATST model, i.e., relative thickness and maximum relative thickness location, were varied to examine change of turbine performance in terms of power coefficient. Multiple surrogates such as response surface approximation, radial basis function, Kriging and weighted average surrogates were implemented to the CFD analysis results with design parameter variation to search the optimal design. It was found that the Kriging model was suitable for this HATST optimization problem as it produced the smallest cross-validation error and high accuracy. The optimized design enhanced the power coefficient by 17.9%, which shows a way to implement the present approach to tidal stream turbine design and optimization.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Blade profile of a HATST was optimized using surrogate models and computational fluid dynamics analysis. </LI> <LI> The numerical method for the turbine performance analysis was validated by comparisons with experiments. </LI> <LI> Kriging surrogate model showed the best performance in optimizing the turbine blade profile. </LI> <LI> The blade thickness was increased to reduce adverse pressure gradient on the suction side. </LI> </UL> </P>