Abstract
Stability of a high-speed craft is an essential matter, and porpoising is one of the most critical instabilities that could occur in some planing hulls due to inappropriate design. In this paper, the porpoising phenomenon and variation of step location yielding resistance reduction are studied through experimental and numerical methods. The investigated models include a single-step model and a nonstep model with the same general shape, but with different step location. The nonstep model is previously tested, but the single-step model is examined in the present study. The nonstep model experiences porpoising at 8 m/s speed, but the single-step model remains stable at the same speed. A three-dimensional CFD analysis is conducted using the finite volume method (FVM). On the contrary, the volume of fluid (VOF) scheme is used for free surface modeling, and the overset mesh technique is implemented within StarCCM+ software. The CFD results of total hydrodynamic resistance and dynamic trim angle are compared against the experimental data. The numerical results are in good agreement with the experimental data. Subsequently, ten different stepped models are simulated to examine their effects. The longitudinal distance between steps and aft of these models are in the range of 19 to 50 percent of the length of models. The obtained results show that as steps are located farther than aft, the models become more stable, and resistance increases due to trim reduction. Finally, the optimum location of the step is extracted with the aim of minimizing the resistance through the design of experiment (DOE) method. Based on the DOE method, it is observed that the sensitivity of the drag value to the step location is higher than the speed.
Highlights
Most of the weight in planing hulls is compensated by hydrodynamic lift [1]
Experiments are conducted on a nonstep and a single-step model with the same shape in the National Persian Gulf Towing Tank, and results are used to validate the numerical results. e nonstep model is previously tested by Ghadimi et al [42], while the single-step model is examined in the present study. e length and beam of the model are 2.64 m and 0.551 m, respectively, and the model has a constant deadrise angle of 24°
Resistance, and rise-up are obtained experimentally and numerically. e contours of the wetted surface area and pressure underneath the models are presented. e studied models have a length of 2.64 m and a beam of 0.55 m. ese models are 1 : 5 scales of a prototype recreational vessel called Cougar. e center of gravity of all models is located at 0.791 m from the transom. e experimental study consists of single-step models with steps located at 670 mm from the transom
Summary
Most of the weight in planing hulls is compensated by hydrodynamic lift [1]. On the other hand, through an increase in the speed, the drag to lift ratio increases. Najafi and Nowruzi [29] analyzed the effects of five different types of transverse steps on the lift to drag ratio, resistance, trim angle, and sinkage of high-speed planing crafts. Problem Definition e length of wetted keel and wetted chine in a high-speed craft usually vary according to unsteady flow behind the vessel In this situation, improvement of the vessel’s performance is a laborious task. Hydrodynamic resistance of a single-step planing craft was experimentally investigated under different geometrical and physical conditions. To accomplish this task, a Fridsma body model with varying angles of deadrise was considered. E effects of transverse steps on the resistance reduction and stability of the vessel are studied in the present paper
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
