3D Panel Method Research Articles

Evaluation of the Effect of Container Ship Characteristics on Added Resistance in Waves

Added resistance in waves is one of the main causes of an increase in required power when a ship operates in actual service conditions. The assessment of added resistance in waves is important from both an economic and environmental point of view, owing to increasingly stringent rules set by the International Maritime Organization (IMO) with the aim to reduce CO2 emission by ships. For that reason, it is desirable to evaluate the added resistance in waves already in the preliminary ship design stage both in regular and irregular waves. Ships are traditionally designed and optimized with respect to calm water conditions. Within this research, the effect of prismatic coefficient, longitudinal position of the centre of buoyancy, trim, pitch radius of gyration, and ship speed on added resistance is investigated for the KCS (Kriso Container Ship) container ship in regular head waves and for different sea states. The calculations are performed using the 3D panel method based on Kelvin type Green function. The results for short waves are corrected to adequately take into account the diffraction component. The obtained results provide an insight into the effect of variation of ship characteristics on added resistance in waves.

Safety Analysis of Mooring Hawser of FSO and SPM Buoy in Irregular Waves

This paper provides a method to analyze the safety factor of the hawser line between Floating Storage Offloading (FSO) and Single Point Mooring (SPM) by using motions simulation. The simulation was conducted based on irregular wave arrival for 1 year and 100 years. A case study for a mooring system of a 55,081 tons displacement of FSO tanker to a 360 tons displacement of SPM buoy was simulated with the existing hawser line length of 45 m and the new hawser line length of 70 m. The wave forces and moments are computed using Ansys Aqwa based on the 3D Panel Method both in the frequency domain and time domain. The wave periods are 6 s and 8 s for the 1-year and 100-year data, respectively. The safety factor of the hawser line significantly improves by using the new hawser line.

Vertical Motions Prediction in Irregular Waves Using a Time Domain Approach for Hard Chine Displacement Hull

In this paper, the validation of the hybrid frequency–time domain method for the assessment of hard chine displacement hull from vertical motions is presented. Excitation and hydrodynamic coefficients in regular waves are obtained from the 3D panel method by Hydrostar® software, while coupled heave and pitch motions are calculated in the time domain by applying the Cummins equations. Experiments using a 1:15 scale model of a “low-drag” small craft are performed in irregular head and following waves at Froude numbers Fr: 0.2, 0.4, and 0.6 at University of Naples Federico II, Italy. Results obtained by hybrid frequency–time domain simulations for heave, pitch, and vertical accelerations at center of gravity and bow are compared with experimental data and showed high accuracy.

Numerical Analysis of a Surface Ship in Waves

Abstract Ship's resistance and engine power to sustain ship's speed in seaways are augmented due to complex non-linear interactions between the ship and the ambient sea (waves). Ship designers, in early design stage, use an ad hoc "sea margin" to account for the effects of seaways in selecting propeller and engine. A numerical tool capable of accurately predicting added resistance and power of a ship cruising in waves would greatly help select its powering (margin) requirement and determine the optimal operating point that can maximize the energy efficiency. For seakeeping analysis, strip theory-based methods have long been used. More recently, nonlinear time-domain three-dimensional (3D) panel methods have started being used widely. A more physics-based avenue to seakeeping analysis is offered by coupled solutions of two-phase unsteady Reynolds-Averaged Navier-Stokes equations and six degrees-of-freedom rigid-body motion (RBM) equations. The URANS approach also avails itself of including the effects of propulsors, either explicitly or approximately. By accounting for all the nonlinear effects in hydrodynamic forces and moments and the resulting ship motions, and the effects of fluid viscosity and turbulence, the coupled URANS-RBM method is believed not only able to predict added resistance and speed loss more accurately, but also to provide valuable insights into the physical mechanisms underlying added resistance and power. The objectives of this study are: (1) to validate a coupled URANS-RBM solver developed for high-fidelity prediction of added resistance, speed loss and added power on ships cruising in regular head sea and irregular waves, and (2) to conduct a detailed analysis of the interactions among ship hull, propeller and waves for a 1/49 scaled model of the ONR Tumblehome (ONRT) (Model 5613) in order to shed light on the physical mechanisms leading to added resistance, speed loss and added power. Figure 1 depicts the ONRT self-propellers with two 4-bladed propellers in regular waves. The main flow features such as the free surface, the hub vortices and blade-tip vortices from the propeller, as well as vortices generated by the sonar dome, shafts, shaft brackets and bilge keels are captured.

WAVE-INDUCED LOADS ON CROSS-DECK OF A WAVE-PIERCING TRIMARAN WITH DIFFERENT HULL FORMS OF OUTRIGGERS

Trimaran has unique hull form with a rapidly growth in recent years due to its application as a mode of transports and naval vessels. Designing trimaran faces many technical challenges because of its complex structural outlines and high-speeds operation. This article investigates the influence of side hulls configuration (symmetric, inboard and outboard types) for wave loads on cross-deck of a trimaran ship when advancing at sea in regular waves. The computation of these hydrodynamic forces is carried out using MAESTRO-Wave 3D panel method code. This code is based on potential flow theory that uses Green’s function with the forward speed correction in the frequency domain. The results demonstrate that the outboard side hull form has the best performance on wave-induced load among three kinds of side hull forms. Furthermore, the results of this study offer more information for selecting the side hull form of the trimaran.

An efficient computational model for fluid-structure interaction in application to large overall motion of wind turbine with flexible blades

Abstract This paper proposes a very efficient computational model for fluid–structure interaction problems corresponding to steady-state flow representing a large overall motion of wind turbines with flexible blades. The model of turbine blades is based upon the 3D solids finite elements with drilling rotations. The proposed 3D solids model is fully able to describe the flexibility blades large overall motion and easily capture both bending and torsional motion thanks to using an enhanced strain field. The model efficiency is further reinforced by using the 3D panel method that fits naturally with proposed 3D solid finite elements for blades. The proposed panel method is the corresponding modification of the potential fluid flow by introducing a vorticity layer at the fluid–structure interface and Bernoulli’s conservation momentum equation in order to provide quantification for the blade thrust. The fluid–structure interaction is enforced through an efficient iterative procedure providing on one hand a very fast computation of aerodynamic loads, which is sufficiently accurate for computing the overall thrust on the blade, and on the other hand a sufficiently accurate representation of the stress states suitable for fatigue studies. The proposed computational model performance is illustrated with several numerical simulations, including the practical case of a full-scale NREL 5MW wind turbine.

Simulation study of approach manoeuvre in lightering and reverse lightering operations

Generally, there exists a case wherein a laden service ship approaches a partially loaded very large crude carrier (VLCC) for cargo transfer. This process is called ‘reverse lightering operation’. The manoeuvrability of these nearly fully loaded ships under interaction loads should be understood for the operation safety. In this study, we presented at first a practical method to simulate the approach manoeuvre, taking the interaction loads estimated by a 3D panel method and other hydrodynamic loads based on experiments into consideration. A standard approach manoeuvre of an Aframax tanker to a VLCC was simulated, and the difference in the behaviour of conventional lightering operation and reverse lightering operation was discussed. One result indicated that the service ship might experience difficulty in keeping the heading angle in parallel with the VLCC at the final phase of the approach manoeuvre in the reverse lightering operation. This would be caused by the increase of interaction loads. • A standard approach manoeuvre of an Aframax tanker to a VLCC was studied. • Both lightering and reverse lightering operations were simulated. • Interaction loads between hulls were estimated by a 3D panel method. • The difference in the behaviour between different operations was discussed.

Experimental and numerical studies on added resistance of ship in oblique sea conditions

In this paper, the added resistance of a large tanker is estimated experimentally and numerically in oblique sea. Experiments on ship motion response and added resistance in oblique sea are performed in the SSPA seakeeping basin. The experiments are conducted using the self-propulsion test for seven wave directions between 180° and 0°. In the self-propulsion test, the added resistance is estimated from the difference between the thrust of the propeller in calm water and waves. In the case of the head sea, the results are compared with those obtained from the captive test at the towing test of Seoul National University. As numerical method, two methods are selected: the strip method and the 3D Rankine panel method. The maximum value of the added resistance is observed between the incident wave directions of 180° and 150°. From 120°, the added resistance tends to decrease and the peak of the added resistance shifted to the short waves. Through the two numerical analysis methods, the tendency of added resistance and the cause of the change of the added resistance in the oblique sea are investigated.

An Analysis of Rolling Damage Ship Motion Caused by the Wave Load on Bulk Carrier Vessels

Stabilitas menjadi syarat utama kapal yang laik layar. Artikel ini memuat analisa gerakan rolling pada kapal bulk carrier yang mengalami kebocoran ketika dikenai beban gelombang dengan sudut heading 90⁰ dan 270⁰ dan tinggi gelombang maksimum. Kapal berada pada kondisi muatan full load saat simulasi dan analisa dilakukan dengan skenario terjadi kebocoran pada ruang muatnya. Karena kapal dengan kebocoran kompartemen mengalami kondisi trim dan oleng maka hasil gerakan rolling menunjukkan perbedaan pada setiap arah datang gelombang. 3D diffraction panel method digunakan untuk mendapatkan gerakan rolling kapal sebagai fungsi waktu. Hasil penelitian tanpa efek sloshing menunjukkan bahwa kapal bulk carrier memiliki resiko tenggelam jika terdapat kebocoran pada dua ruang muatnya.

Modelling a spade rudder as a hollow two-way tapered Kirchhoff’s plate : free dry and wet vibration study with numerical verification

A semi-analytical approach to free dry and wet vibration of a trapezoidal, 2-way tapered, pivoted hollow spade rudder is presented. The rudder is modeled as a hollow Kirchhoff’s plate, with a NACA0018 profile chord section. The rudder pivot is modeled as a combination of a translational spring and a rotational spring. The span-wise and chord-wise non-uniform beam vibration is first analyzed by the Rayleigh-Ritz method, to establish the non-uniform beam modeshapes, which act as admissible functions to the Galerkin’s method for plate vibration. Eigenvalue analysis generates the plate natural frequencies and the plate modeshapes. Alternately, uniform beam modeshapes themselves are used as admissible functions into the Galerkin’s method. Frequencies are analyzed for various pivot positions, taper ratios, and NACA sections. For the wet vibration, constant strength source distribution technique is used to generate the added mass of a 2D aerofoil. Also, 3D panel method is used to generate the modal added masses, and hence the wet natural frequencies. The added mass coefficient is generated for various aerofoil fineness ratios, pivot fixities, taper ratios, aspect ratios.

Application of surf-riding and broaching criteria for the systematic series D models

The Second Generation Intact Stability Criteria (SGISC) have been introduced after the occurrence of stability-related accidents, which clearly demonstrated that “actual” intact stability criteria were not adequate. New generation criteria are based on the physical and failure mode analysis of parametric roll, pure loss of stability, surf-riding/broaching, dead ship condition and excessive accelerations.This paper is focused on the verification of surf-riding/broaching vulnerability criterion of semi-displacement hull form of the Systematic Series D by Kracht and Jacobsen (1992) representative of several naval ships built during 90ties. Levels 1 and 2, as amended in IMO relevant documents, have been calculated for all seven D Systematic Series ships from resistance and propulsion performances measured in calm water. After several and counteracting changes in the wave celerity definition by IMO, the calculations have been performed for all models with both linear and non-linear formulation.The influence of the diffraction component on the wave surging force has been analyzed according to the works of Feng et al. (2015, 2017). The total surge force, calculated by 3D panel method, has been compared against actual IMO formulation and calculation of vulnerability has been performed for three hulls.The limit Froude number for the considered 90 m ships is increased by improving the accuracy of 2nd level calculation, taking into account only nonlinear wave celerity or diffraction component and linear wave celerity.

A numerical simulation method for predicting global and local hydroelastic response of a ship based on CFD and FEA coupling

In this paper, a simulation method for predicting global and local hydroelastic response of a ship which couples CFD and FEA is developed and validated. By comparing the prediction with linear/nonlinear strip method, 3D panel method and towing tank test results under various wave conditions in terms of rigid body motions and slamming impact pressure, the effectiveness of the CFD-FEA coupling method is confirmed. The hydroelastic behavior, so-called the whipping moment, evaluated from the CFD-FEA coupling method is further validated by comparing with nonlinear strip method, 3D panel method and tank test results. Finally, the proposed method is applied to a realistic large container ship structure in severe waves. The structural response of the double bottom structure subjected to global and local bending moments is investigated.

Forced wet flexural dynamics of spade rudder in propeller slipstream: semi-analytical approach of pivoted FFFF plate

A semi-analytical approach of forced vibration of a trapezoidal, two-way tapered, hollow model spade rudder, is presented. The pivoted rudder is in the propeller slipstream; which causes harmonic hydrodynamic load. The excitation frequency of propeller-induced vibration (PIV) equals the propeller blade passing frequency. The rudder operates at a Reynolds’s number of the order of 108. It has a span of 1 m, root chord of 0.6 m, and tip chord of 0.5 m. It is considered as a hollow Free–Free–Free–Free Kirchhoff’s plate, with the chord section as an NACA0018 profile. The dry vibration is analyzed by the energy-based Galerkin’s method, using closed-form admissible functions in the two perpendicular directions. 3D constant-strength panel method is used to generate the modal added masses, and hence the wet natural frequencies. The drag and the lift coefficient of the rudder, at various angles of attack, are estimated to find the spatial distribution of the total PIV-causing normal force. The mean flow velocity about the rudder is the velocity of advance behind the propeller. The fluid velocity past the aerofoil section depends on the profile thickness and the angle of attack, thereby influencing the local lift. The hydrodynamic pressure varies parabolically along the span. The effect of the wake developed by the propeller, the stern shape, and the rudder angle on the hydrodynamic loading on rudder is included to express the transverse time-varying loading. The wet, forced vibration of the Kirchhoff’s plate is analyzed in MATLAB. The maximum bending stress and twisting sheer at the rudder stock is calculated for various angles of attack.

Hydrodynamic analysis of floating structures with baffled ARTs

In ocean industry, free surface type ART (Anti Roll tank) system has been widely used to suppress the roll motion of floating structures. In those, various obstacles have been devised to obtain the sufficient damping and to enhance the controllability of freely rushing water inside the tank. Most of previous researches have paid on the development of simple mathematical formula for coupled ship-ARTs analysis although other numerical and experimental approaches exist. Little attention has been focused on the use of 3D panel method for preliminary design of free surface type ART despite its advantages in computational time and general capacity for hydrodynamic damping estimation. This study aims at developing a potential theory based hydrodynamic code for the analysis of floating structure with baffled ARTs. The sloshing in baffled tanks is modeled through the linear potential theory with FE discretization and it coupled with hydrodynamic equations of floating structures discretized by BEM and FEM, resulting in direct coupled FE-BE formulation. The general capacity of proposed formulation is emphasized through the coupled hydrodynamic analysis of floating structure and sloshing inside baffled ARTs. In addition, the numerical methods for natural sloshing frequency tuning and estimation of hydrodynamic damping ratio of liquid sloshing in baffled tanks undergoing wave exiting loads are developed through the proposed formulation. In numerical examples, effects of natural frequency tuning and baffle ratios on the maximum and significant roll motions are investigated.

A New Methodology for Aerodynamic Design and Analysis of a Small Scale Blended Wing Body

The blended wing body (BWB) concept is a relatively new concept of an aircraft. The wings and the fuselage blend into one integral structure greatly reduce drag and increases lift thus making it a highly efficient design. The aim of the research was to design a radio controlled small scale BWB aircraft for use over long ranges at low altitudes in order to deliver payloads. The BWB was divided into the center body and the outer wing. Four airfoils, HS522, LA2573A, NACA 25111 and MH78 were analyzed in XFLR5. In consideration of their lift and moment characteristics, NACA 25111 and MH78 were selected for the center body and the wing respectively. The stall speed and wing loading were the primary factors used in determining the area and size of the aircraft which converged to a design having a five feet wingspan. Center of gravity was placed ahead of aerodynamic center to provide static and dynamic stability in pitch. Twist, dihedral and sweep were given to increase stability and controllability. The final design was tested in XFLR5 for stability and in commercial computational fluid dynamic code ANSYS-Fluent for comparison. These simulation results were compared to wind tunnel tests of a 20% scaled down prototype. 3D Panel Method results in XFLR5 were found to be very close to wind tunnel results but CFD results were seen to be not conforming to the wind tunnel results after 10° angle of attack. Thus, CFD was deemed to be unnecessary for designing a plane of this size. Ultimately, a larger test prototype was made out of polystyrene foam and a successful flight was achieved.

Numerical computation of motions and structural loads for large containership using 3D Rankine panel method

In this paper, we present the results of our numerical seakeeping analyses of a 6750-TEU containership, which were subjected to the benchmark test of the 2nd ITTC–ISSC Joint Workshop held in 2014. We performed the seakeeping analyses using three different methods based on a 3D Rankine panel method, including 1) a rigid-body solver, 2) a flexible-body solver using a beam model, and 3) a flexible-body solver using the eigenvectors of a 3D Finite Element Model (FEM). The flexible-body solvers adopt a fully coupled approach between the fluid and structure. We consider the nonlinear Froude–Krylov and restoring forces using a weakly nonlinear approach. In addition, we calculate the slamming loads on the bow flare and stern using a 2D generalized Wagner model. We compare the numerical and experimental results in terms of the linear response, the time series of the nonlinear response, and the longitudinal distribution of the sagging and hogging moments. The flexible-body solvers show good agreement with the experimental model with respect to both the linear and nonlinear results, including the high-frequency oscillations due to springing and whipping vibrations. The rigid-body solver gives similar results except for the springing and whipping.

Side wall effects on ship model testing in a towing tank

Due to the existence of the side walls in a towing tank, the measured hydrodynamic forces would present some discrepancies compared to the open sea results. This phenomenon is referred to as the side wall effect. The objective of the present study is to investigate the side wall effects on ship model testing in a towing tank. The method used in the present study involves a 3D panel method based on the Rankine type Green function. Both the steady and unsteady problems were investigated numerically. The numerical results were validated against ship model test results. After the validations, a large scale computations were performed to investigate the parameters which could determine the side wall effects. Two diagrams of side wall effects (one in calm water and the other one in waves), were obtained which showed whether the side wall effect was less than the permissible error to be included in the measured values.

CONTRA-ROTATING PROPELLER AERODYNAMICS SOLVED BY A 3D PANEL METHOD WITH COUPLED BOUNDARY LAYER

The aerodynamics of contra-rotating propellers is a complex three-dimensional problem of an unsteady flow, which is often approached by assuming numerous simplifications. Presented computational model combines a 3D panel method with a force-free vortex wake and a two-dimensional two-equation boundary layer model in an attempt to capture all the main contributing elements of the flow physics. An emphasis is placed on the interaction of the viscous boundary layer region with the inviscid region and the development of a portable method of their coupling. The kinematics of a force-free vortex wake is supplemented with a vortex aging due to a diffusion. Extra attention is paid to the process of the blade passing through the wake of another blade. To demonstrate the ability of the numerical model, several test cases are presented, illustrating the reaction of the system to various operational conditions.

Correction of wave surge forces to improve surf-riding/broaching vulnerability criterion check accuracy

Surf-riding/broaching is one of the five stability failure modes to be included into the International Maritime Organization (IMO) second generation intact stability criteria (which are risk-based stability criteria) that can ensure the safety of ships in actual seaways more effectively. This study focuses on the influence of wave surge force prediction accuracy on surf-riding/broaching vulnerability criterion check result. Firstly, it is demonstrated that the wave surge force prediction method adopted in the current vulnerability criterion check procedure is not accurate and may lead to wrong conclusions. The experimental data from captive model test and the numerical result based on 3D panel method both indicate that the diffraction effect must be considered to correctly predict the wave surge forces. Besides, sophisticated methods are not suitable for Level 2 vulnerability criterion check due to their complexity. Therefore, an empirical formula for wave surge force correction based on sample ship calculation results is proposed. The proposed empirical correction formula can effectively improve the vulnerability criterion check accuracy and thus contribute to the design and safety of the ships which are vulnerable to this stability failure mode.

AERODYNAMIC LOAD OF AN AIRCRAFT WITH A HIGHLY ELASTIC WING

In this article, a method for calculation of air loads of an aircraft with an elastic wing is presented. The method can predict a redistribution of air loads when the elastic wing deforms. Unlike the traditional Euler or Navier-Stokes CFD to FEM coupling, the method uses 3D panel method as a source of aerodynamic data. This makes the calculation feasible on a typical recent workstation. Due to a short computational time and low hardware demands this method is suitable for both the preliminary design stage and the load evaluation stage. A case study is presented. The study compares a glider wing performing a pull maneuver at both rigid and and elastic state. The study indicates a significant redistribution of air load at the elastic case.