Enhanced Unified Theory with Forward-Speed Effect Taken into Account in the Inner Free-Surface Condition

Abstract

The enhanced unified theory (EUT) has been used as a core theory in the integrated system developed at the Research Initiative on Oceangoing Ships (RIOS) of Osaka University for predicting the propulsion and seakeeping performance of a ship in actual seas. In this study, the EUT is modified by adopting partially the solution method in the rational strip theory of Ogilvie and Tuck as a particular solution in the inner problem, thereby a forward-speed effect in the convection term of the free-surface condition is incorporated in the inner solution. This forward-speed effect is analytically shown to contribute only to the cross-coupling radiation forces. Some other forward-speed and 3D effects important in a low-frequency range are also included in the homogeneous component of the inner solution through matching with the outer solution in a similar manner to the unified theory of Newman. Numerical computations are implemented for a slender modified Wigley model and the RIOS bulk carrier model. Good agreement is confirmed in a comparison with experimental data for the cross-coupling added mass and damping coefficients between heave and pitch and also for the resulting ship motions, particularly in heave near the resonant frequency. The added resistance around the motion-resonant wavelength is found to be improved but sensitive to a slight change in heave and pitch motions. Thus, it is stressed that accurate prediction of the ship motions and resultant Kochin function is critical for more accurate prediction of the added resistance in waves.

Temperature interference in improved FBG pressure sensor for towing tank test

“…The superiority of ver. 7 was confirmed through this test, as will be described later, so the same investigation was conducted on the RIOS bulk carrier model, for which much data have been accumulated [4,6,26].…”

“…On the other hand, local physical quantities are integrands or components for the global physical quantities, such as the wave field around an oscillating ship and the pressure on the ship hull. To estimate these quantities more accurately, various theoretical calculation schemes have been developed as alternatives to the strip methods [1,2] (e.g., [3][4][5][6]). Recently, with the development of computer technologies, computed results of seakeeping performance have been produced with Computational Fluid Dynamics (CFD) (e.g., [7][8][9][10]).…”

Added resistance using Salvesen–Tuck–Faltinsen strip theory and the Kochin function

“…Note that the integrands in this equation are singular at k1 , k2 , k3 and k4 . These bounds are all integrable singularities and the line integrals can be calculated using the method proposed by Kashiwagi in [39] or in [40]. For the calculations in this paper instead, a numerical integration scheme is used which is open-ended at both the start and the end of the integration bounds.…”

“…The results are compared with the Enhanced Unified Theory (EUT) and New Strip Method (NSM) of Kashiwagi in [53]. The experimental measurements in the plot are denoted as Kashiwagi (2012), Kashiwagi (2016) and Kashiwagi (2017), see [53]. The most recent experimental data which is based on a novel approach and uses the unsteady pressure measurements technique, are due to Kashiwagi in [54].…”