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Hydrodynamic Damping of a Fluttering Hydrofoil in High-speed Flows
Carl W. Bergan,Bjørn W. Solemslie,Petter Østby,Ole G. Dahlhaug 한국유체기계학회 2018 International journal of fluid machinery and syste Vol.11 No.2
A hydrofoil resembling a high head Francis runner blade was submerged in a rectangular channel and attached to the walls in a fixed-beam configuration. The hydrofoil was excited by piezoelectric Macrofiber composite actuators (MFCs), and the vibration was measured at the trailing edge with Laser Doppler Vibrometry (LDV) and semiconductor strain gauges. The hydrofoil was exposed to water velocities ranging from 0 to 25 m/s. Lock-in occurred at approx. 11m/s. The damping increased linearly with the water velocity, with a slope of 0.02 %/(m/s) below lock-in, and 0.13 %/(m/s) above lock-in. The natural frequency of the foil increased slightly with increasing water velocity below lock-in, due to the added stiffness of the passing water. Additionally, the natural frequency increased significantly when passing through lock-in, due to the vortex shedding phase shift.
Lee, S.y.,Jo, C.,Bergan, P.,Pettersen, B.,Chang, D. Elsevier Scientific Pub. Co 2016 Structural safety Vol.59 No.-
This study proposed a design procedure for determining optimal design load and reliability for offshore installations. The life-cycle cost (LCC) was estimated for a range of characteristic environmental loads. An iterative design optimization procedure was employed to find the target reliability at which the LCC was minimized. The structural system was designed for a given set of environmental loads caused by waves, currents, and winds. Extreme environmental conditions were estimated by a probabilistic model. The relationship between the characteristic load and the structural reliability was considered on the basis of the selected probabilistic model to study the variation of the LCC for the given set of environmental loads. The set of LCCs, which were the sum of the capital expenditure (CAPEX), operating expenditure (OPEX), and risk expenditure (RISKEX), were estimated to determine the optimal reliability. A case study was conducted for a pile-guide system (PGS) as a novel offshore installation. The PGS was designed to keep the position of large-scale floating installations. The system consists of guide piles supporting the floating installation, a subsea truss structure cross-linking the piles, and a seabed base platform fixed to the seabed. Two target locations near Busan city were considered to study the change of optimal reliability with respect to the same structural system. Finally, the optimal reliabilities at the two target locations were determined with the minimum LCC. The optimal reliability could vary depending on the types of structures, the economic roles of the system, and the environmental conditions at various locations. Thus, in contrast to the prescriptive strategy, the proposed procedure for determining the optimal design load and reliability would be meaningful and applicable to design of offshore structures.
Numerical and experimental study of a plate-stiffened prismatic pressure vessel
Choi, Younseok,Ahn, Junkeon,You, Hwalong,Jo, Choonghee,Cho, Younghee,Noh, Yeelyong,Chang, Daejun,Chung, Hyun,Bergan, På,l G. Elsevier 2018 Ocean engineering Vol.164 No.-
<P><B>Abstract</B></P> <P>This study evaluates the structural feasibility of a prismatic pressure vessel using strength assessments. A prismatic pressure vessel, which differs from a cylindrical or spherical pressure vessel, is proposed. A prismatic pressure vessel can be used to ship liquefied gas. A prototype of the prismatic pressure vessel was designed, manufactured and tested in accordance with the ASME Boiler and Pressure Vessel Code. Its design uses the “design-by-analysis” method, including protection against plastic collapse. The prototype of the prismatic pressure vessel uses typical construction materials considering their linear elastic and nonlinear plastic behaviors. The vulnerable components of the structure were obtained through numerical analysis using the finite element method. A pressure test with strain gauges was conducted, and the results demonstrate the feasibility of the prismatic pressure vessel as a suitable vessel for high-pressure fluids with high volume efficiencies. The prismatic pressure vessel has potential for general applicability in the shipping of liquefied gas.</P> <P><B>Highlights</B></P> <P> <UL> <LI> This study evaluates the structural feasibility of a prismatic pressure vessel using strength assessments. </LI> <LI> The structural feasibility of a prismatic pressure vessel was demonstrated through numerical and experimental. </LI> <LI> The proposed prototype pressure vessel can be used for real pressure vessel without any failure occur during operation. </LI> </UL> </P>
Heidi M. Vieira,David P. Kasper,Runqiu Wang,Lynette M. Smith,Charles A. Enke,Raymond C. Bergan,Benjamin A. Teply,Michael J. Baine 대한방사선종양학회 2023 Radiation Oncology Journal Vol.41 No.3
Purpose: The treatment approach for non-metastatic bladder cancer is guided by an invasion of the muscular layer of the bladder wall. Radical cystectomy is the recommended treatment for muscle-invasive disease. However, it has considerable morbidity and mortality and is not suited for many patients. Trimodality therapy consisting of chemoradiation after transurethral resection of bladder tumor offers a definitive approach with bladder-sparing potential. However, there is a lack of research defining the optimal combination of chemotherapy and radiation in this setting. Materials and Methods: We extracted patient data from the National Cancer Database to compare survival outcomes and demographic factors in 2,227 non-metastatic bladder cancer patients who were treated with chemotherapy sequential to or concurrently with radiation. Sequential treatment was defined as chemotherapy beginning >14 days before radiation, and concurrent was defined as beginning within 14 days of the first radiation. Results: The sequential treatment group patients were younger (mean age, 74 vs. 78 years; p < 0.001) with more advanced disease. We found no difference in overall survival between patients who received chemotherapy sequential to radiation and those who received concurrent chemoradiation only (p = 0.533). Conclusion: Our data are concordant with a previous prospective study, and support that chemotherapy prior to radiation does not decrease survival outcomes relative to patients receiving only concurrent chemoradiation. Given that the sequential group had an overall higher stage but no difference in survival, downstaging chemotherapy prior to radiation may be helpful in these patients. Further studies including a larger, multi-institutional clinical trial are indicated to support clinical decision-making.