In this study, the feasibility of Fiber Bragg Gratings (FBG) pressure sensors is verified for hull structural strength evaluation. To investigate the effectiveness of FBG pressure sensors for the strength evaluation, the towing tank test is carried out with a pure hydro-structural (PHS) ship model, which is capable of elastic deformation. FBG pressure sensors are installed on the outer hull surface and FBG strain sensors are installed inside the hull to calculate a vertical bending moment (VBM). Measured water pressure is interpolated on the whole hull surface by using the weighted average approach based on relative distance. Finite Element Analysis (FEA) is carried out based on interpolated water pressure. In FEA, inertia force is considered according to the inertia relief method, and VBM is calculated by FEA results. The strain measured by FBG strain sensors is transformed to VBM based on the calibration coefficient obtained by the vertical bending test. Finally, VBM obtained by the measured water pressure and strain are compared. As a result, VBM obtained by the measured water pressure is consistent with ones obtained by the measured strain. Therefore, the availability of water pressure measured by the FBG pressure sensors is validated for the hull structural strength evaluation in terms of VBM.

In order to preliminary investigate structural response of stiffened panel due to slamming impact, two series of fluid structure coupling analysis is carried out using a new fluid structure interaction (FSI) methodology of Incompressible Fluid Dynamics (ICFD) [1]. ICFD is the method where structure and fluid are modeled as both Lagrange methods. Firstly, slamming impact of a sphere is analyzed with ICFD and SPH methods respectively and compared with experimental and analytical results. Acceleration, slamming force and pressure are compared and discussed in detail. Secondary a fixed stiffened flat panel of offshore structure subjected to slamming impact is investigated as a part of the ISSC II.1 benchmark study. Effect of mesh size is investigated. Analysis results are compared with existing ALE method [1] as well as other results within the framework of ISSC II.1 benchmark study. In both studies, structure is modeled by elastic-plastic and by rigid respectively. By comparing these two results, effect of structural rigidity on the slamming pressure as well as slamming force is investigated.

The development of FOWTs (Floating Offshore Wind Turbines) is going into the commercial stage from the demonstration one. One of the subjects for success in the commercial stage is how to reduce the construction cost. For example, watertight bulkheads in narrow space of FOWTs are obstacles for the cost reduction from the perspective of structural complexity and manufacturing. On the other hand, new IEC 61400-3-2 standard describes the unnecessity of the damage stability requirement under certain conditions. To satisfy enough safety without the damage stability requirement according to the IEC 61400-3-2, an examination method with a probability theory and the FEM analysis is proposed in this paper. The collision probability with cruising ships, P1, around a FOWT is decided to use by the AIS data, and the probability of structural total loss, P2, due to the ship collision is indicated according to the total loss curve which is delivered from the FEM collision analysis. The joint probability which is represented by the product of P1 and P2 is compared to the target damage probability, 10 −4 per year. The detailed information about this method and the results of trial analyses for a FOWT off the coast of Nagasaki Prefecture are also introduced in this paper.

We experimentally investigated the influence of the geometries of a modulated wave train on the vertical-bending and torsional moments acting on a container ship in bow-quartering sea conditions. We conducted a towing experiment with a hydro-structural container ship model in the Actual Sea Model Basin (ASMB) (80 m deep, 40 m wide, and 4.5 m deep) at the National Maritime Research Institute. The ship model is made of urethane foam and was designed to have similar vertical bending and torsional vibration mode shapes to an actual ship. A modulated wave train was generated in the ASMB by the higher-order spectral-method wave generation (HOSM-WG) method such that the maxim crest appeared at the center of the basin. The ship model was towed in the modulated wave train with a relative heading angle of 120 degrees. A series of tests was performed by varying the encounter timing of the ship model and the maximum crest of the modulated wave train. In the experiment, fiber-Bragg-grating strain gauges successfully measured whipping vibrations of the ship model due to a slamming impact. The experimental results revealed that the rear wave height H r and the ratio of the rear and front wave heights H r /H f were the dominant parameters governing the maximum sagging and torsional moments of a ship in bow-quartering modulated wave trains.

This paper describes a series of towing tank tests using a scaled model of a recent container ship for validating the First Order Reliability Method (FORM) based approach to predict the maximum response. The FORM based approach is adopted in conjunction with the nonlinear strip method as an estimation method for the most probable wave episodes (MPWEs) leading to the given extreme wave-induced vertical bending moments (VBMs). Tank tests under the pre-determined MPWEs are conducted to evaluate the extreme wave-induced VBMs. Numerical simulations based on the coupled Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) are also conducted and are compared with the test results under the MPWEs. Furthermore, to estimate the extreme VBM statistics, tank tests under random irregular waves are conducted. A series of validations of the probability of exceedances (PoEs) of the VBM evaluated from the FORM based approach is carried out. The effect of hydroelastic (whipping) vibrations on the extreme VBM statistics are finally discussed.

Most of stiffened panels subjected to bi-axial compression mainly in transverse direction collapse with the buckling deformation of one times one half-wave in a local panel between longitudinal stiffeners and transverse frames. The authors defined this collapse mode as “local panel buckling mode”. In this study, the collapse behavior of the stiffened panel with local panel buckling mode is investigated in detail. Then, a simple design formula to estimate ultimate strength of a stiffened panel with local panel buckling mode is derived based on the collapse behavior. This formula is composed of a formula to predict the ultimate strength of a rectangular unstiffened panel subjected to uniaxial transverse compression, and the effects of stiffeners, bi-axial compression and von Mises yield condition are added to the formula. The ultimate strength calculated by the proposed formula is in good agreement with FEA results. Finally, the proposed formula is compared with an existing method and formulae used in the CSR-OT, CSR-BC and H-CSR. As a result, it is confirmed that the proposed formula has sufficient accuracy and high availability.

In this study, for the stiffened panels subjected to the in-plane cyclic compression loads, the two followings are clarified. One is a generating process of the cumulative buckling deformation at panel parts of stiffened panels. The other is the effect of the cumulative buckling deformation on the ultimate strength of stiffened panels. To clarify them, the cyclic compression loading experiments were carried out with two stiffened panel specimens by using Multi Axis Loading System in National Maritime Research Institute (NMRI) in Japan. For one stiffened panel specimen, the thirty-one sets of compression test cases were conducted with different strokes and for each case. The number of cycles in each set was 100. While, for the other, it was subjected to the cyclic compression loads until it collapsed. In addition, Finite Element Method (FEM) analyses for stiffened panels subjected cyclic compression loads are carried out with the same condition as the experiments by using commercial FEM software, LS-DYNA.