1,721,030 research outputs found
Unconventional interceptors in still water and in regular waves: Experimental study on resistance reduction and dynamic instability
No full textThe Naples Systematic Series – Second part: Irregular waves, seakeeping in head sea
No full textThe main aim of this study is to characterize the dynamic behavior of the Naples Systematic Series (NSS) in irregular head sea. A further aim of the study is to provide data to detect the influence of hull form on the sea-keeping performances in the planing and semi-planing speed range. The NSS derives from a parent hull that has shown to behave well in rough seas, characterized by high deadrise angles of the bottom at the bow, to reduce acceleration. All the models of NSS were tested in three different sea states and in Fr range from 0.515 to 1.197. The relatively high Froude numbers associated with the forms of the series make inappropriate the statistical analysis usually carried out to describe the behavior of the displacement ships. To overcome these unsuitableness, Cartwright Lounguet Higgins, extreme value and normal distribution fittings have been furnished for heave and pitch maxima and minima; gamma and extreme value have been furnished to represent acceleration in the centre of gravity and bow. Finally, a case study is presented to show a useful procedure for designer evaluation
Unconventional interceptors in still water and in regular waves: Experimental study on resistance reduction and dynamic instability
No full textThe study on Interceptors performed last years at the Università degli Studi di Napoli "Federico II" shown the high potentiality of the unconventional device Double Interceptors System (DIS). This paper supplies data on the new tests carried out on prismatic models fitted with DIS and towed in still water and in regular waves. The experimentation has been performed on three model whose deadrise angles β are 10, 20 and 30 deg. The still water tests highlighted the effect of deadrise on the DIS efficiency and explained the cause of dynamic instability observed at high value of Fn∇. The data on the behaviour of the DIS in regular waves concern the early stage of a study currently in progress. The paper shows the mean values of RT measured, at Fn∇ =2.15, on β 20 model crossing regular waves with different frequencies and heights. Furthermore resistance variations, pitch, heave and vertical accelerations measured in two points are shown in time domain. The study confirmed that both in the sailing conditions, still and regular waves, the DIS provides great resistance reductions: up to 35% (β 10 deg, Fn∇ =2.25 - in still water) and 48% (β 20, Fn∇ =2.15 and high frequency of encounter - in regular waves)
An experimental assessment of nonlinear effects of vertical motions of Naples systematic series planing hulls in regular waves
No full textA comprehensive experimental assessment of vertical motions and accelerations of two Naples warped hard chine hulls systematic series (NSS) hulls in regular waves is presented. The seakeeping performance in regular waves are investigated, in particular nonlinear motion responses in terms of transfer functions and higher harmonic response as a function of wave frequency, steepness, hull slenderness and speed. In order to highlight the effects of wave properties on motion responses, transfer functions of both motion harmonics and phases are presented via iso-frequency and iso-steepness plots. Slenderness ratio is found to have a notable effect on motion transfer functions only at higher speeds. The presence of a higher harmonics in motion and acceleration response is also observed and the proposed analysis shows that increasing wave steepness and speed lead to increased higher harmonics responses of both vertical motions and accelerations. The effect of slenderness ratio on the second harmonic response of heave and pitch is only noticeable at higher speed. Phase difference between wave and motions shows that higher second harmonic content is generally associated with a higher phase lead. The main novelty of the present work is represented by the extensive analysis of NSS planing hulls in regular waves. In particular the aspects concerning higher harmonics and their trends with respect to speed, wave and hull geometrical characteristics
Experimental study on the Efficiency of Trimaran Configuration for High Speed Very Large Ships
No full textExperimental study on the Efficiency of Trimaran Configuration for High Speed Very Large Ships
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