Dynamic Trim Research Articles

Planing Hull Hydrodynamic Performance Prediction Using LincoSim Virtual Towing Tank

This work shows the performance of LincoSim, a web-based virtual towing tank enabling automated and standardized calm water computational fluid dynamics (CFD) data sampling, extending previous published applications to the case of a high-speed hull. The calculations are performed for a 1:10 scale model of a 43 ft powerboat hull form in the Froude number range from 0.3 to 2.0. The counterpart physical model is the experimental fluid dynamics (EFD) campaign performed at the University of Naples Federico II, where the resistance, sinkage and trim data have been measured. The EFD/CFD data comparison is performed and shown with a discussion of the spotted differences. The average percentage differences between the EFD and CFD data for the whole speed range are 1.84, 6.87 and 6.94 for the resistance, dynamic trim, and sinkage, respectively. These results confirm the maturity of the standardized and automated CFD modeling for calm water hydrodynamic analysis included in LincoSim, even at very high Froude numbers. The wetted length of the keel and chine and the wetted surface are calculated from numerical data using the advanced post-processing. Finally, as a work in progress, we test a first comparison for the same hull of the EFD and CFD data, considering two seakeeping conditions for head waves at a given wavelength for two velocity conditions. Also, this kind of analysis confirms the tight correlation between the measured and computed outcomes. This synergic interplay of EFD and CFD can link the advantages of both methods to support hull design but also requires experiment planning and final data analysis to obtain physical parameters not easily measurable in laboratory, such as the wetted surface, wetted lengths, proper viscous contribution, and pressure distribution both in calm water and in waves.

Numerical Investigation of Single and Double Steps in Planing Hulls

Incorporating steps into a hull reduces the wetted surface, promoting improved hydrodynamic lift and reduced resistance at high speeds, provided that the step is designed appropriately. Traditional hydrodynamics studies rely on scaled model testing in towing tanks, but numerical tools offer a more efficient alternative. This study focused on investigating the hydrodynamic performance of stepped hulls by modifying the parent hull of the Naples Systematic Series (C1). The Computational Fluid Dynamics (CFD) code SIEMENS PLM STAR CCM+ version 2302 was used for simulations, including four different beam Froude numbers (FrB = 1.13, 2.22, 2.56, and 2.96) and a total of 15 hull configurations with single and double steps. By employing a three-dimensional computational analysis of multiphase flow using Dynamic Fluid–Body Interaction (DFBI) and overset mesh, various performance parameters such as resistance coefficient, dimensionless wetted surface, sinkage, and dynamic trim were analyzed. The accuracy of the CFD results was confirmed through comparison with experimental data and grid uncertainty assessment. The study demonstrated that placing a single step near the transom decreased trim and increased resistance and wetted surface. Conversely, positioning a step in the forward section reduced the trim angle at lower step heights but increased trim at higher step heights in single-stepped hulls. The application of these findings contributes to the design optimization of stepped hulls for enhanced performance in high-speed maritime applications.

Prediction of the impact of biofouling roughness on a full-scale planing boat performance using CFD

This study investigates the crucial role of surface roughness caused by biofouling in contributing to increased drag in fast planing vessels. Through rigorous computational fluid dynamics (CFD) simulations using a full-scale reference hull, the impact of surface roughness on planing hull performance is examined. The results show that heavy slime roughness on the hull surface causes a significant increase in total resistance, ranging from 10% at low speeds to 80% at high speeds. Skin friction was identified as the most affected component of resistance, with additional changes in residual resistance. Although the change in residual resistance is relatively small, they give rise to dynamic phenomena such as variations in pressure distribution, wave elevation, and wave making formation. The study also explores the influence of surface roughness on dynamic lift forces, observing an increase in upward friction forces but ultimately concludes that overall hull performance was hampered due to the disproportionately higher increase in resistance caused by roughness (biofouling). Changes in dynamic trim, dynamic sinkage, and dynamic wetted surface area due to this roughness are also discussed.

Limit protection systems for safety operational envelope of submarine

To enhance the operational stability of submarines, this study conducts a comparative analysis of three pitch limit protection systems based on the reference model, potential function, and dynamic trim algorithm. The proposed depth limit protection system adjusts the depth command by comparing the desired depth, calculated by the outer-loop controller, against a predefined depth limit. Similarly, the pitch limit protection systems modify the command pitch calculated by the inner-loop controller to ensure it does not exceed the pitch limit. Submarine maneuvering simulations were conducted to verify the performance of the envelope protection system, which comprises depth and pitch limit protection systems. Simulation results confirmed the effectiveness of these methods, with the dynamic trim algorithm demonstrating superior control efficiency. This study advances submarine safety and stability by developing and validating advanced pitch limit protection systems.

A revisited verification and validation analysis for URANS simulation of planing hulls in calm water

Verification and Validation (V&V) is the foremost analysis which is carried out for evaluation of the accuracy level and dependability of computational fluid dynamic (CFD) simulations. The present study investigates the V&V of CFD models in predicting the dynamic trim and hull resistance of high-speed planing hulls with an aim to provide a deeper understanding of V&V analysis in this specific field of application. Two different planing hulls, namely the C05 stepped hull and the C1 interceptor hull, are analyzed with four different grids and time-steps using two mesh motion techniques, namely overset and morphing approach. The discretization (grid) and time-step uncertainties for each CFD simulation are estimated using the least squares method. The results indicate that the overset mesh approach performs better than the morphing grid method in terms of numerical uncertainty and validation achieved for both hulls. The error of both techniques in the prediction of resistance and trim angle of the boat shows an acceptable range of accuracy. The findings provide valuable insights for simulation-based designing and optimizing high-speed planing hulls, specifically by identifying the optimal mesh technique, cell number, and time-step for accurate prediction of wetted surface shape, ventilation formation, running attitude, and resistance.

Effect of Speed and Hull Length on the Hydrodynamic Performance of a Semi-Planing Hull of a Shallow-Draft Watercraft

Hydrodynamic performance is an essential factor in the design of a watercraft, and the navigation scenario determines the complexity of its operation. This study aims to identify the effect of speed and length on the hydrodynamic behavior of a semi-planing watercraft in shallow waters. A computational fluid dynamics tool was employed to predict the trim, heave, and resistance parameters of two different hulls: a base hull and a craft with an increased hull length. The two hulls had similar hydrodynamic characteristics. The effects of speed and hull length on these predicted parameters obtained for the two hulls were compared. The results showed a low resistance uncertainty and a reduction in dynamic trim for longer hull lengths. These findings highlight the importance of considering balance and dynamic trim in designing shallow-draft watercrafts to ensure an optimal performance in specific conditions, such as rivers with depth restrictions.

Simulation of turning maneuver using the 4+2DOF method in planing and semi-planing modes

Planing craft maneuver is dominated by attitude change which requires a 6DOF motion equations. Recently, 4+2DOF method as a kind of the 6DOF motion equations was introduced in which heave and pitch motion are replaced by rise-up and dynamic trim. The 4+2DOF method was employed for the turning maneuver that start and end in the planing mode. In this study, the application of 4+2DOF method is extended to examine a turning maneuver that starts in the planing mode and ends in the semi-planing mode. Simulations are conducted on a model which has already been tested in full-scale maneuver trials. Maneuver Hydrodynamic Coefficients (MHCs) are concluded from Plannar Motion Mechanism (PMM) tests in both the planing and semi-planing modes in a range of forward speeds. Having a verified computer code, effects of operation modes and forward speed are studied on the turning maneuver. This study quantitatively depicts that the Steady Turning Diameter (STD) in the planing mode is about four times larger than the semi-planing mode. It is also concluded that STD of a turning maneuver starts and ends in the planing mode, is about 2.5 times larger than that starts in the planing mode and ends in the semi-planing mode.

Analysis of the double steps position effect on planing hull performances

Along with developing high-speed craft technology, the planing hull is growing with modifications for better performance. One such technology is stepped hull, both single and double. Planing hull with steps allows the boat to run at a relatively low drag-lift ratio with lower frictional resistance due to reduced wetted area. In this study, the hull was modified with variations in the position of the double steps, which aimed to determine the effect of the first and second step positions on the total resistance, dynamic trim, and dynamic sinkage generated by computational fluid dynamics (CFD). Based on the analysis results, variations in the position of the stepped can change the hull performance. Shortening the distance between the two steps and moving both rearwards toward the transom can lower the total resistance. The dynamic trim and dynamic sinkage decreased as the position of the two steps was shifted further forward. An equation created in a non-dimensional form relates the positions of two steps to the desired results of total resistance, dynamic trim, and dynamic sinkage, namely: {(x1-x2)/L + (x1x2)/(LB)} × Fr∇, where x1 is distance the first step from transom, x2 is the distance of the second step, L is the length of the boat, B is the beam of the boat, and Fr∇ is the volume Froude number.

Numerical investigation on the effect of interceptor mechanism on maneuvering derivatives

ABSTRACT The effect of the interceptor mechanism on maneuvering motion is still unstudied while its positive effect on the total resistance and dynamic trim angle is well-known. Therefore, in the present study, the effect of the interceptor mechanism on the maneuvering derivatives is investigated numerically. Firstly, the calm water validation is performed for the bare hull and equipped with the interceptor. Then, the horizontal Planar Motion Mechanism simulations are conducted to calculate the maneuvering derivatives via computational fluid dynamics analyses. The results show that for the selected forward velocity the existence of the interceptor increases the amplitudes of the yaw moments and the sway forces. In addition to this, it has a remarkable effect on the sway force phases while the effect of yaw moment phases can be negligible. Since it changes phases and amplitudes, it causes a considerable increase in each linear horizontal maneuvering derivative for the selected case.

CONTROL OF DYNAMIC TRIM FOR PLANING VESSELS WITH INTERCEPTORS IN TERMS OF COMFORT AND MINIMUM DRAG

Nowadays, interceptors are often used to decrease total resistance and enhance comfort by reducing dynamic trim for high-speed planing vessels. They can be controlled manually as well as automatically by using a suitable closed-loop control system. Thus, in the present study, an automatically controllable system is presented to minimize the total resistance by reducing the dynamic trim in calm water. To reach this aim, a mathematical model which can represent the 2 degree of freedom vertical motion of a prismatic planing vessel is presented. The coefficients used in the model are calculated by using the Savitsky method. The standard dynamic trim angle and the optimum ones in terms of resistance are calculated by using the same method. For control action, a linear full state feedback control strategy (linear quadratic regulator) is applied, and instantaneous blade heights are found considering the change in forward speed. Therefore, the control-oriented model is able to change the blade height to reach the optimum trim angle in terms of the total resistance of the vessel for different forward speeds and speed profiles. The results show that the designed linear quadratic regulator control strategy is successful for reference trim tracking problems.

Simulation of Turning Manoeuvre of Planing Craft Taking Into Account the Running Attitude Change in a Simplified Manner

Abstract The modelling and simulation of planing craft manoeuvres requires coupled six degrees of freedom (6 DOF) motion equations. A coupled 6 DOF motion equation needs hundreds of manoeuvring hydrodynamic coefficients (MHCs) that are mostly determined using the planar motion mechanism (PMM) test. The number of test runs is too high, unless a kind of simplification is imposed to the motion equations. This study modifies 6 DOF motion equations to 4+2 DOF motion equations in which heave and pitch equations are replaced by dynamic draught and trim (so-called running attitude), respectively. The method is applicable for a manoeuvre that commences in the planing regime and ends in the same regime. On that basis, the PMM test is conducted and the model is restrained in the vertical plane at a certain running attitude, determined by a resistance test. The 4+2 DOF method, together with MHCs from the PMM test, are employed for the simulation of turning manoeuvres of a 25° prismatic planing hull. The results of the simulation indicate that the 4+2 DOF method reasonably predicts the path of the craft during the turning manoeuvre and cuts the number of PMM tests required at the same time. The PMM test results show that MHCs are highly related to forward speed and wetted surfaces. The turning manoeuvre simulation shows that the non-linear terms of MHCs cannot be ignored. The STD/L (Steady Turning Diameter divided by Length of the craft) for a planing craft is very large, compared to ships.

Numerical evaluation on the effects of interceptor layout and blade heights for a prismatic planing hull

Planing hulls are exposed to effects such as trim and resistance that have a negative impact on their hydrodynamic performances. Interceptors are one of the systems to find solutions to reduce these negative effects. In this study, the effects of the interceptor layout and blade height on the hydrodynamic characteristics of a planing hull were investigated numerically, at varying speeds. The hydrodynamic behaviors of the interceptor at a selected case were also investigated in regular head waves. To reach this aim, a scaled prismatic planing hull form equipped with an interceptor which is suitable for planing vessels 4–10 m in length was selected for all analyses. The numerical study was performed by using the CFD (Computational Fluid Dynamics) approach which uses a finite volume method to discretize the RANS (Reynolds Averaged Navier Stokes) equations. The uncertainty of the numerical study was also performed to show the credibility of numerical results. According to the results of the current study, it is found that the most proper location of the interceptors for lower resistance is between the chine and the centerline of the selected planing hull. It is also understood that the effects of the blade height are directly related to the forward speed. Besides, the resistance values can be decreased by using interceptors up to FnB =2.5, while the presence of the interceptor has a negative effect on resistance after this speed regardless of the layout and selected blade height. In addition to this, the best interceptor blade heights for lower resistance at different forward speeds of the planing hull form were found for the tested cases. For the selected case, it is shown that interceptors are also useful in regular waves in terms of reducing dynamic trim, sinkage and resistance.

A study on dynamic trim optimization of VLCC oil tanker in wind and waves

Ships have become the main means of transportation in the world trade. With paying more attention to global warming problems, the Greenhouse Gas (GHG) emission reduction of ships has been extensively studied. Trim optimization is taken as a GHG reduction technology. Considering trim optimization of calm water resistance is energy-saving, but it cannot always be the best state in practice affected by wind and waves. The difficulty on trim optimization in wind and waves is the calculation of added resistance. On account of the high-cost and long-period, the experimental method and Computational Fluid Dynamics (CFD) method are ill-suited for trim optimization. In this paper, high-efficiency and high-accuracy Taylor Expansion Boundary Element Method (TEBEM) and ITTC two-parameter spectrum are used for calculating added resistance in regular and irregular waves respectively. Wind load is estimated by empirical formula. Trim optimization of a 300K-ton VLCC oil tanker on a typical route is studied. Compared with calm water trim optimization, it is found that dynamic trim optimization in wind and waves can save about 949.3 kg fuel and the fuel saving potential is about 0.04%, based on the average sea states over the whole route. Therefore, dynamic trim optimization during navigation is more beneficial.

Kayıcı Teknelerde Minimum Direnç için Optimum Trim Açılarının Savitsky Yöntemi ile Belirlenmesi

In this paper, the minimization problem of the total resistance of a planing hull is studied for a wide range of Froude numbers. The Savitsky method is utilized to calculate optimum aspect ratios and dynamic trim angles of the hull. First, the aspect ratios, dynamic trim angles, and the total resistances of the hull are calculated with the Savitsky method. Then, the minimum drag forces are computed for each vessel speed by changing the aspect ratios systematically. Then, the required trim moments are calculated to find the optimum trim tab angles. The entire calculations are performed by using a Python program. The results showed that trim tabs can reduce the total drag up to 20% approximately. The obtained trim tab angles for minimum drag are demonstrated with figures and tables.

CFD analysis of a multiplatform catamaran by means of a web-based application: Experimental data comparison for a fully automated analysis process

The recently introduced LincoSim Web Based High Performance Computing (HPC) Cloud Platform for Automatic Virtual Towing Tank Analysis, which is based on open-source Reynolds Averaged Navier-Stokes (RANS) solvers (Salvadore & Ponzini, 2019), is herein applied to the hydrodynamic assessment of a catamaran vessel. An experimental data campaign was used to assess the effect of the demihull separation distance on the catamaran's resistance for a given demihull shape. The results of the comparison between the experimental and the automatically generated numerical ones are presented and discussed in the present work. The comparison is quite rich including data for a reference monohull, three demihull separations and two displacements conditions, each with the Froude number ranging from 0.145 to 0.904. The set of the experimental data acquired for the model scaled catamaran are the total resistance, the sinkage and the dynamic trim. Nevertheless, also the wave fields at three given locations are considered in the towing tank experiments in order to assess not only the effect on the hull, but also on the catamaran's wake field. The agreement between computational and experimental quantities is good for both the hull-related and flow-related ones, confirming the ability of the developed automated tool to discern between favorable and detrimental fluid dynamic conditions and to efficiently rank performances also for multihulls. Notably, thanks to the availability of numerical data for both model and full scale, also the effectiveness of the extrapolation process has been assessed.

Investigation of planing craft maneuverability using full-scale tests

Maneuverability of planing craft is a complicated hydrodynamic subject that needs more studies to comprehend its characteristics. Planing craft drivers follow a common practice for maneuver of the craft that is fundamentally different from ship’s standards. In situ full-scale tests are normally necessary to understand the maneuverability characteristics of planing craft. In this paper, a study has been conducted to illustrate maneuverability characteristics of planing craft by full-scale tests. Accelerating and turning maneuver tests are conducted on two cases at different forward speeds and rudder angles. In each test, dynamic trim, trajectory, speed, roll of the craft are recorded. The tests are performed in planing mode, semi-planing mode, and transition between planing mode to semi-planing mode to study the effects of the craft forward speed and consequently running attitude on the maneuverability. Analysis of the data reveals that the Steady Turning Diameter (STD) of the planing craft may be as large as 40 L, while it rarely goes beyond 5 L for ships. Results also show that a turning maneuver starting at planing mode might end in semi-planing mode. This transition can remarkably improve the performance characteristics of the planing craft’s maneuverability. Therefore, an alternative practice is proposed instead of the classic turning maneuver. In this practice, the craft traveling in the planing mode is transitioned to the semi-planing mode by forward speed reduction first, and then the turning maneuver is executed.

Performance Assessment of a Planing Hull Using the Smoothed Particle Hydrodynamics Method

Computational Fluid Dynamics simulations of planing hulls are generally considered less reliable than simulations of displacement hulls. This is due to the flow complexity around planing hulls, especially in the bow region, where the sprays are formed. The recent and constant increasing of computational capabilities allows simulating planing hull features, with more accurate turbulence models and advanced meshing procedures. However, mesh-based approaches based on the finite volume methods have shown to be limited in capturing all the phenomena around a planing hull. As such, the focus of this study is on evaluating the ability of the Smoothed Particle Hydrodynamics mesh-less method to numerically solve the 3-D flow around a planing hull and simulate more accurately the spray structures, which is a rather challenging task to be performed with mesh-based tools. A novel application of the DualSPHysics code for simulating a planing hull resistance test has been proposed and applied to the parent hull of the Naples warped planing hull Systematic Series. The drag and the running attitudes (heave and dynamic trim angle) are computed for a wide range of Froude’s numbers and discussed concerning experimental values.

Simulation study of surface sputtering and distribution of ions in silicon due to low-energy high-fluence cobalt irradiation

The study of the range and distribution of low-energy heavy ions implanted into lighter substrates is paramount important in terms of three-dimensional device fabrications. In this study, we report the re-distribution of implanted ions due to the sputtering of target atoms, simulated considering dynamic changes in the target due to the high-fluence irradiation of Co and Fe ions at low energy (55 keV) in Silicon substrate and nanowires. The simulations were compared by using various ion-solid interaction codes that are capable of incorporating the targets with both one-dimensional (1D) and three-dimensional (3D) structures. In the 1D simulation codes, the target is generally defined as a stack of sharp interfaced layers that have an infinite lateral extension. Both static code like "Stopping and Range of Ions in Matter (SRIM)" and dynamic code like "Static and Dynamic Trim for Sequential and Parallel computer (SDTrimSP)" were utilized to carry out the simulations in silicon substrates. However, to simulate the distribution of ions with target layers involving nanostructures with a curved surface such as nanowires “Ion range and damage in nanostructures (Iradina)” code was used. Silicon nanowires of different diameters were chosen as the target, and Co ions were implanted at single energy along the surface normal. The fluence of the Co ions was then varied to obtain the optimal distribution of implanted ions in the silicon nanowire. The Si nanowire shows a curved depth profile for the implanted ions with different ranges towards the edge and the center of the nanowire. The surface sputtering in the case of the nanowire was more as compared to the bulk Si substrate. However, in the case of the Si substrate, the atoms are found preferentially sputtered in the forward direction between 30° - 60° angle with a peak around 45° angle to the target surface normal with variation in the angle of incidence.

Numerical evaluation of hydrodynamic characteristics of planing hulls by using a hybrid method

The hydrodynamic characteristics of the planing hulls in particular at the planing regime are completely different from the conventional hull forms and the determination of these characteristics is more complicated. In the present study, calm water hydrodynamic characteristics of planing hulls are investigated using a hybrid method. The hybrid method combines the dynamic trim and sinkage from the Zarnick approach with the Savitsky method in order to calculate the total resistance of the planing hull. Since the obtained dynamic trim and sinkage values by using the original Zarnick approach are not in good agreement with experimental data, an improvement is applied to the hybrid method using a reduction function proposed by Garme. The numerical results obtained by the hybrid and improved hybrid method are compared with each other and available experimental data. The results indicate that the improved hybrid method gives better results compared to the hybrid method, especially for the dynamic trim and resistance. Although the results have some discrepancies with experimental data in terms of resistance, trim and sinkage, the improved hybrid method becomes appealing particularly for the preliminary design stage of the planing hulls.

Numerical Prediction of Hydrodynamic Performance of Planing Trimaran with a Wave-Piercing Bow

The central hull is the most important structure in the planing trimaran. In order to gain insight into the relationship between hydrodynamic performance and main hull shape, experimental tests and numerical simulations were carried out for volume Froude Number (FrΔ) ranging from 1.31 to 4.98. Dynamic sinkage and trim in the Dynamic Fluid Body Interaction (DFBI) six-degree-of-freedom model were considered. A validation study carried out by comparison of experimental test results with numerical results showed good consistency. To analyze the process of tunnel penetration and pressure change at the bottom of the boat, numerical simulation results for free surface, bottom streamline, and pressure distribution around the hull are given. A large triangular high-pressure area was observed in the front of the main hull for all volume Froude numbers. Consequently, the central drainage body, in reference to the profile of single planing craft with distinctive resistance performance, was redesigned into a wave-piercing shape. Total resistance, sinkage, and trim angle of the new model were then predicted by numerical method. The results show that the central drainage body has a significant impact on the hydrodynamic performance of the planing trimaran. Furthermore, the wave-piercing shaped main hull has a drag reduction effect.