PLANING HULL SEAKEEPING IN IRREGULAR HEAD SEAS
UDC 629.5.017/018.71 Summary The paper presents the results of planing hull seakeeping tests in irregular seas. The tested model belongs to a small systematic series developed at the University of Naples; it is a prismatic hull very similar to the well-known Fridsma’s models. The 16.7 degrees deadrise angle, length-to-breadth and load coefficient are representative of modern hull forms of pleasure boats. Tests in irregular waves have been performed at three speeds for one displacement in three sea states. The measured heave, pitch, acceleration at the centre of gravity and at bow have been analysed in the time domain and the results are presented in terms of significant values (the mean of 1/3 rd highest values). They are given in tabular and graphical form. Furthermore, the obtained results are commented with respect to the state of the art in planing hull seakeeping, and compared with the available experimental data from literature. The conclusions highlight the applicability of these data in design practice, commenting on trends and the range of significant parameters.
Experimental seakeeping assessment of a warped planing hull model series
Abstract One monohedral and three warped hard chine planing hull forms were designed at Department of Industrial Engineering, University of Naples. All models have the same transversal section at 0.25 L from the stern with 16.7° deadrise angle. Warped models have deadrise angle linearly varying along the hull length. In previous work the results of an extensive experimental program in calm water were presented. This paper is focused on the seakeeping assessment in regular waves. Aim of this research is the evaluation of the effect of deadrise angle variation along the hull length on seakeeping characteristics. Regular wave tests have been chosen to get better insight on motion and acceleration properties connected with warped hull forms and to provide a benchmark for CFD of planing hulls. Models with same load coefficient C Δ =0.428 were tested at three volumetric Froude numbers Fr V =1.92, 2.60 and 3.25. Reported results are nondimensional responses for heave, pitch, and accelerations at 0.5 L and bow. Particular emphasis was given to acceleration analysis by crest to trough method and spectral analysis of first and second harmonics. All results are commented with respect to hull form variation. Uncertainty analysis has been performed according to ITTC 2011 recommendations.
EVALUATION OF WHOLE-BODY VIBRATION IN VEHICLES
Abstract The vibration in 100 different vehicles has been measured, evaluated and assessed according to British Standard BS 6841 (1987) and International Standard ISO 2631 (1997). Vibration was measured in 14 categories of vehicle including cars, lift trucks, tractors, lorries, vans and buses. In each vehicle, the vibration was measured in five axes: vertical vibration beneath the seat, fore-and-aft, lateral and vertical vibration on the seat pan and fore-and-aft vibration at the backrest. The alternative methods of evaluating the vibration (use of different frequency weightings, different averaging methods, the inclusion of different axes, vibration dose values and equivalent r.m.s. acceleration) as defined in the standards have been compared. BS 6841 (1987) suggests that an equivalent acceleration magnitude is calculated using vibration measured at four locations around the seat (x -, y -, z -seat and x -backrest); ISO 2631 (1997) suggests that vibration is measured in the three translational axes only on the seat pan but only the axis with the most severe vibration is used to assess vibration severity. Assessments made using the procedure defined in ISO 2631 tend to underestimate any risks from exposure to whole-body vibration compared to an evaluation made using the guidelines specified in BS 6841; the measurements indicated that the 17 m/s1.75 “health guidance caution zone” in ISO 2631 was less likely to be exceeded than the 15 m/s1.75 “action level” in BS 6841. Consequently, ISO 2631 “allows” appreciably longer daily exposures to whole-body vibration than BS 6841.