DETERMINATION OF LINEAR AND NONLINEAR ROLL DAMPING COEFFICIENTS OF A SHIP SECTION USING CFD

The most prevalently used method to obtain the nonlinear roll damping coefficient is the free roll decay test. However, this method can only be conducted at the resonance frequency and thus cannot consider the effect of the frequency. This is a certain limitation as the resonance frequency can be changed at any time by the ship’s loading conditions. Therefore, it is worth investigating the frequency dependency of the nonlinear roll damping coefficients. In this study, a numerical method was proposed to derive the linear and nonlinear roll damping coefficients of ships at different frequencies. Fully nonlinear CFD simulations of forced harmonic roll motion were conducted and the roll damping coefficients were calculated. Then, the damping coefficients were decomposed into the linear and nonlinear components using the linear regression analysis. The linear roll damping coefficients were compared with potential coefficients and showed a good agreement, while the nonlinear roll damping coefficients were compared with the coefficients calculated using a semi-empirical method. The nonlinear roll damping coefficients calculated from the proposed method showed a strong frequency dependency. Finally, possible rationales for the frequency dependence of the nonlinear roll damping coefficient were investigated

A NUMERICAL STUDY ON THE OPEN WATER PERFORMANCE OF A PROPELLER WITH SINUSOIDAL PITCH MOTION

When a ship operates in waves, the ship moves with 6 degrees-of-freedom, and a propeller at the stern of the ship cannot avoid moving due to the ship motion. Therefore, it is important to analyse the propulsion performance while considering the ship motion in waves for efficient ship operation. The pitch motion of the ship has a dominant effect on the variation of the propeller performance and results in sinusoidal pitch motion of the propeller. In this study, a numerical analysis was done using a KP458 model propeller with a diameter of 10 cm, which was designed for the KLVCC2 body plan. The propeller performance was calculated using computational fluid dynamics (CFD) at several constant tilt angles. Numerical simulations were then conducted with sinusoidal pitch motion in several conditions of varying pitch angle. The variations of the thrust and torque of the propeller in sinusoidal pitch motion were compared with the results obtained in constant tilt angles

A STUDY ON THE SENSITIVITY ANALYSIS OF THE HYDRODYNAMIC DERIVATIVES ON THE MANEUVERABILITY OF KVLCC2 IN SHALLOW WATER

To assess the manoeuvrability of ships in shallow water at the early design stage, reliable simulation models which present shallow water effect are required. However, studies on the manoeuvrability of ship at low speeds in shallow water have been performed less than manoeuvrability in deep water. Also, the limitation of model that the effects of the keel clearance on manoeuvrability are applied to has been validated through previous studies. In this study, the manoeuvrability characteristics of the ship sailing in shallow water at low speed are evaluated by applying the mathematical model considering the shallow water effect. And the sensitivity analysis on shallow water manoeuvring simulation is performed in order to determine hydrodynamic derivatives which are necessary to be derived exactly due to the limitation of the shallow water model used in previous studies. Through this study, it could be confirmed that great importance of estimation of manoeuvrability could be found through the sensitivity index factor of hydrodynamic derivatives changing in the situation operating the shallow water at low speed

Scale-up study for ex-vivo expansion of allogeneic natural killer cells in stirred-tank bioreactor

Natural killer (NK) cells are a type of lymphocyte in the blood that are responsible for innate and adaptive immune response, and they mature in the liver and bone marrow. Being a key role in host defense system with direct and indirect killing of virus-infected cells or cancer cells, NK cell has been considered an attractive candidate for cancer therapy. Peripheral blood shows the low frequency of NK cells, so ex vivo expansion method is important to obtain sufficient NK cells for therapeutic use. Currently, we successfully developed bioreactor process for NK cell expansion on lab-scale. Stirred-tank bioreactor could be considered as optimal alternative system for large-scale NK cell expansion compared with other ones because it is automated, less labor intensive, scalable, well-controlled and cost-effective. In bioreactor process, agitation is one of important parameters for NK cell expansion because it is necessary to provide homogenous culture conditions. So we defined effects of agitation in bioreactor and figured out an optimum condition. After that scale-up studies were carried out with manufacturing-scale bioreactor based on these results. The results in terms of growth rate, viability cytotoxicity and purity, were comparable with lab-scale

Treatment of a Recurrent Chest Wall Desmoid Tumor Using a CT-Guided Steroid Injection

We report on a 41-year-old woman with a chest wall desmoid tumour who was successfully treated with a computed tomography (CT)-guided steroid injection. She presented with a palpable mass in the right upper chest wall and was treated by surgical excision and postoperative radiation therapy due to recurrence of the mass at the surgical site. At 20 months after the second operation, a recurrent mass was again detected in the anterosuperior portion of the previous surgical site on CT. We performed a CT-guided steroid injection weekly for 4 weeks by applying a mixture of 3 mL of triamcinolone acetonide (40 mg/mL) and 3 mL of 1% Lidocaine, administering 4-6 mL of the mixture, to the lesion. Six months later, CT showed a marked decrease in the size of the mass

Successful Treatment of Malignant Superior Vena Cava Syndrome Using a Stent-Graft

We report successful outcomes after endovascular placement of a stent graft in a 74- and a 77-year-old men, both of whom had malignant superior vena cava syndrome caused by squamous cell carcinoma. In each patient, successful palliation of the malignant superior vena cava syndrome was achieved by placement of a stent graft. No procedure-related complications were observed. The patients were asymptomatic until their deaths, seven and 14 months after stent graft placement, respectively

Practical Application of Iterative Decomposition of Water and Fat with Echo Asymmetry and Least-Squares Estimation (IDEAL) Imaging in Minimizing Metallic Artifacts

Iterative decomposition of water and fat with echo asymmetry and the least-squares estimation (IDEAL) is a recently developed method for robust separation of fat and water with very high signal-to-noise-ratio (SNR) efficiency. In contrast to conventional fat-saturation methods, IDEAL is insensitive to magnetic field (B0 and B1) inhomogeneity. The aim of this study was to illustrate the practical application of the IDEAL technique in reducing metallic artifacts in postoperative patients with metallic hardware. The IDEAL technique can help musculoskeletal radiologists make an accurate diagnosis particularly in musculoskeletal imaging by reducing metallic artifacts, enabling the use of contrast enhancement, improving SNR performance, and providing various modes of MR images with one scan parameter

A remnant choledochal cyst after choledochal cyst excision treated with a lumen-apposing metal stent: a case report

A lumen-apposing metal stent (LAMS) is a saddle-shaped stent with large flanges at both ends, thereby preventing stent migration and helping with approximation of the adjacent structures. We report the case of a 25-year-old female with remnant choledochal cyst which was successfully treated with LAMS after initial treatment failure with a plastic stent. Although complete excision of the cyst is the definite treatment of choledochal cysts, endoscopic ultrasonography-guided cystoduodenostomy can be considered in cases wherein surgery is not feasible and dysplasia is not present. LAMS may be preferred to plastic stents for effective resolution of remnant choledochal cyst and prevention of ascending infection

Spotted Fever Group and Typhus Group Rickettsioses in Humans, South Korea

Multiplex-nested PCR and sequencing analysis indicated rickettsialike agents in serum specimens from febrile patients