Numerical analysis of shipping water impacting a step structure

Shipping water, the flow washing over and impacting the upper decks of ships and offshore structures, occurs frequently during their service life and often causes structural problems. For engineers to design safe floating structures subjected to shipping water it is essential to gain an in-depth understanding of its depth and flow field, and the resulting impact forces. In this work, Computational Fluid Dynamics (CFD) is applied to understand the physics of shipping water washing over a stepped platform. We find that the most accurate solutions are obtained with the turbulence closure. The hydrodynamic load generated by the shipping water is found to strongly depends on the kinematic energy of the water hitting the step. It is shown that with smaller values of the freeboard a more dynamic flow ensues, with a stronger vortex and larger velocity gradient resulting in deeper shipping water and a larger impact force

A comprehensive stepped planing hull systematic series: Part 1 - Resistance test

This work addresses the experimental study of a new systematic series of stepped planing hulls. Indeed, the interest in the stepped planing hulls is constantly growing, both in the industrial/commercial and academic fields. Designers and boat builders have been orienting toward the multi-stepped hulls solution to ensure good dynamic stability, reliable seakeeping and operability at high speeds. However, there is a lack of a compre hensive stepped hull systematic series with various step configurations including a forward V-shaped step, as typically used on modern boats. For the abovementioned reasons, a systematic series of eight different models of stepped hulls have been developed and tested. The towing tank tests have been carried out at the naval basin of the Universita ` degli Studi di Napoli “Federico II” Dipartimento di Ingegneria Industriale (DII) in calm water at different speeds (Fr∇ = 1.077–6.774) and for three different static trim conditions. All models are built with a transparent bottom to visualize the wetted surface and the eventual development of vortices generated behind the step. The eight models are defined by modifying three significant design parameters for stepped hulls (i.e. the number of steps, longitudinal step position, and step height)

Performance Prediction of Two-Stepped Planing Hulls Using Morphing Mesh Approach

Change in body shape characteristics is one of the ways to reduce the resistance and thereby increasing the speed of planing hulls. Creating the transverse steps is one of these variations. The main reason to use the steps in high-speed planing craft is that the wetted surface of the vessel is divided into small parts with higher width‐length ratio in high velocities and in this situation, the generated lift force is more efficient. In this article, by performing a three-dimensional numerical solution, motion characteristics of a two-stepped planing hull with transverse steps in calm water have been examined. For this purpose, the vessel is free to trim and sinkage, and by using the morphing mesh approach, the numerical simulation continued until the equilibrium condition of the two-stepped planing hull is satisfied. Resistance, lift, trim angle, and wetted surface in various velocities have been computed and compared against existing experimental data. Analysis of considered two-stepped hull in calm water shows that the numerical solution for resistance, trim, and lift are relatively precise in comparison to model test data. Furthermore, various hull characteristics such as wetted length of keel, chine wetted length, spray angle and, ventilation length have been investigated

A Theoretical Method to Explore the Influence of Free Roll Motion on the Behavior of a High-Speed Planing Vessel through a Steady Yawed Motion

This paper introduces a theoretically-based method to compute the behaviour of a planing hull in a steady yawed motion when it is free to roll. This method was developed by using 2D+T theory and the oblique-water entry of an asymmetric wedge. Sectional forces were determined using added mass theory. The forces and moments acting on the boat were computed by extending the sectional forces in the longitudinal direction. Trim angle and centre of gravity (CG) rise were found by solving the motion equations for the rigid body of the vessel. The results were compared against experimental data, and suggests that the current method has reasonable prediction accuracy for these parameters. Moreover, cases of free-to-roll and fixed-in-roll were determined and compared against each other, indicating that the trim angle of a boat is reduced, while CG rise increased in free roll

Dynamic of Tunneled Planing Hulls in Waves

A tunneled planing craft is a high-speed boat with two tunnels over the hull bottom that are designed to improve the vessel’s performance. Hydrodynamic performance of tunneled planing hulls in calm-water is well-known, however, current information on wave conditions is limited. In this study, two different tunneled planing hulls with two degrees of freedom in heave and pitch motions are studied in regular waves by using the computational fluid dynamics (CFD) method based on the Unsteady Reynolds Averaged Navier-Stokes Equations (URANSE) in conjunction with k−ϵ turbulence model. The results demonstrate that tunneled planing hull motions in waves are nonlinear. In addition, it is found that the dynamic responses of heave and pitch motions as well as occurrence portability of the fly-over phenomenon significantly increases as the Froude number grows. Fly-over motions resulted in vertical motions and acceleration up to 5g, high impact pressure, and large induced drag. At a very high planing speed, after flying over the water surface, when the vessel re-enters the water, the resulting hydrodynamic load leads to a second fly-over motion. Since the fly-over is an unwanted movement with adverse effects, these results can provide a better understanding of the fly-over motion that one may consider in future design for improving the planing hull performance

Effects of Vertical Motions on Roll of Planing Hulls

Roll motion of a planing hull can be easily triggered at high speeds, causing a significant change in hydrodynamic pressure pattern, which can threaten the stability of the vessel. Modeling and investigating roll motion of a planing vessel may require a strong coupling between motions in vertical and transverse planes. In the present paper, we have used a mathematical model to analyze the roll of a planing hull by coupling surge, heave, pitch, and roll motions using 2D + T theory to study the effects of roll-induced vertical motions on roll coefficients and response. Mathematically computed forces and moments as well as roll dynamic response of the vessel are seen to be in fair quantitative agreement with experimentally measured values of previously published data. Using the 2D + T method, it has been shown that to model the roll of a planing hull at high speeds, we need to consider the effects of heave, pitch, and surge motions. Through our mathematical modeling, it is found that freedom in vertical motions increases time-dependent roll damping and added mass coefficients, especially at early planing speeds. The results of dynamic response simulations suggest that freedom in the vertical plane can decrease the roll response

Performance prediction of a hard-chine planing hull by employing different cfd models

This paper presents CFD (Computational Fluid Dynamics) simulations of the performance of a planing hull in a calm-water condition, aiming to evaluate similarities and differences between results of different CFDmodels. The key differences between thesemodels are the ways they use to compute the turbulent flow and simulate themotion of the vessel. The planingmotion of a vessel on water leads to a strong turbulent fluid flowmotion, and themovement of the vessel fromits initial position can be relatively significant, which makes the simulation of the problem challenging. Two different frameworks including k-" and DES (Detached Eddy Simulation) methods are employed to model the turbulence behavior of the fluid motion of the air–water flow around the boat. Vertical motions of the rigid solid body in the fluid domain, which eventually converge to steady linear and angular displacements, are numerically modeled by using two approaches, including morphing and overset techniques. All simulations are performed with a similar mesh structure which allows us to evaluate the differences between results of the applied mesh motions in terms of computation of turbulent air–water flow around the vessel. Through quantitative comparisons, themorphing technique has been seen to result in smaller errors in the prediction of the running trim angle at high speeds. Numerical observations suggest that a DES model can modify the accuracy of the morphing mesh simulations in the prediction of the trim angle, especially at high-speeds. The DES model has been seen to increase the accuracy of the model in the computation of the resistance of the vessel in a high-speed operation, as well. This better level of accuracy in the prediction of resistance is a result of the calculation of the turbulent eddies emerging in the water flow in the downstream zone, which are not captured when a k-" framework is employed. The morphing approach itself can also increase the accuracy of the resistance prediction. The oversetmethod, however, overpredicts the resistance force. This overprediction is caused by the larger vorticity, computed in the direction of the waves, generated under the bow of the vessel. Furthermore, the overset technique is observed to result in larger hydrodynamic pressure on the stagnation line, which is linked to the greater trimangle, predicted by this approach. The DESmodel is seen to result in extra-damping of the second and third crests of transomwaves as it calculates the stronger eddies in the wake of the boat. Overall, a combination of themorphing and DESmodels is recommended to be used for CFDmodeling of a planing hull at high-speeds. This combined CFD model might be relatively slower in terms of computational time, but it provides a greater level of accuracy in the performance prediction, and can predict the energy damping, developed in the surrounding water. Finally, the results of the present paper demonstrate that a better level of accuracy in the performance prediction of the vessel might also be achieved when an oversetmeshmotion is used. This can be attained in future bymodifying themesh structure in such away that vorticity is not overpredicted and the generated eddies, emerging when a DESmodel is employed, are captured properly.QC 20220314</p

A numerical and Analytical Way for Double-Stepped Planing Hull in Regular Wave

The paper presents a comparison analysis between numerical method and nonlinear mathematical model for the prediction of the vertical motions of a double stepped planing hull in regular wave. The numerical method is to Unsteady Reynolds Averaged Navier-Stokes (URANS) equations solution via moving mesh techniques (overset/chimera), performed at different model speeds, wavelengths, and wave heights using the commercial software Siemens PLM Star-CCM+. Instead, the analytical solution is obtained using nonlinear mathematical model. The presented non-linear mathematical model is developed using a combined approach based on 2D+T theory, momentum theory, and linear wake profile. Under such assumption, the double stepped planing hull is divided into three planing surfaces, and hydrodynamic forces acting on each planing surface is found by extension of simulation of symmetric water entry of two-dimensional wedge section bodies. Then, each sub-problem is solved by extending the mathematical simulation of wedge penetrating water. Final vertical force and pitching moment are found and substituted in motion equation. The mathematical model is able to compute heave and pitch motion in calm water and regular waves. Results of numerical method and novel 2D+T analytical method are compared against each other

Dynamic of a planing hull in regular waves: Comparison of experimental, numerical and mathematical methods

The unsteady planing motion in waves is a complicated problem, that can lead to uncomfortable riding situation and structural damages due to large wave-induced dynamic responses and vertical accelerations. In the current research, this problem is investigated using different approaches, including towing tank tests, Computational Fluid Dynamics (CFD), and the 2D + t model. Results obtained from all three approaches are compared against each other in details. The spectral analysis shows that all motions can be nonlinear, but CFD and 2D + t model may predict weaker nonlinear behaviour at higher speed, especially for the case of vertical accelerations corresponding to longer waves. Interestingly, the vertical acceleration found by 2D + t model is seen to be under-predicted at moderate and long wavelengths and to be over-predicted at short waves. The values of sectional forces found by 2D + t model were compared against CFD results, showing that, while the 2D + t model computes smaller sectional forces, it can also compute negative sectional forces near the bow of the vessel at short waves when the boat exits the water. The emergence of negative sectional forces is likely to be the reason why the 2D + t model over-predicts the vertical acceleration in short waves