Search

This paper proposes a feasible numerical approach to investigate motion responses of the intact and damaged DTMB 5415 model in still water and regular waves at zero speed. Overset mesh with Adaptive Mesh Refinement (AMR) technique is applied to deal with the ship's motions. Theoretical wave analysis and one benchmarking study are performed to verify the reliability of the applied numerical method. The results show that no matter whether the damaged ship is in still water or waves, asymmetric flooding always makes the ship maintain a larger heel angle. If the damaged ship further encounters beam waves towards the intact side, the possibility of capsizing will be greatly increased. Moreover, due to the wave excitation, the pitch and heave motions are more intense than motions in still water. However, the intense motions will not threaten the ship's safety. Finally, by comparing with motions of the intact ship in waves, influences of asymmetric flooding and beam waves are quantified. It is concluded that the rolling effect caused by asymmetric flooding should be firstly reduced. Generally, to facilitate the safe return of the damaged ship to port, it is necessary to reduce the asymmetric effect and set the appropriate course. [ABSTRACT FROM AUTHOR]

The solution of the nonlinear equation for a ship's rotational motion around its longitudinal axis, even with simplifying assumptions, is complicated. This oscillatory motion, which is known as the roll motion, is generated when the ship sails in the waves, and the irregular behavior of the waves causes time-varying dynamics. Calculating the ship's roll response is possible by determining roll equation coefficients. In the current study, the coefficients were determined from the dynamic response of the ship using a training feed-forward neural network. The training was carried out in two modes: as a free swing in calm water and forced oscillation in irregular waves. The DTMB 5415 vessel was selected as the case study ship. The results of the simulation by the neural network were validated by numerical analysis and model test results. [ABSTRACT FROM AUTHOR]

Hull roughness, attributed to factors such as corrosion, the degradation of marine coatings, and, notably, biofouling colonisation, leads to increased fuel consumption, thus entailing significant environmental and economic penalties. While this issue on commercial ships is well documented in recent studies, the specific impact on the speed of warships has received limited attention. To fill this gap, this research quantifies the resistance and power penalties, as well as the speed reduction under various fouling scenarios, and explores the resultant changes in flow characteristics around the hull. For this purpose, full-scale simulations of a naval ship, specifically the DTMB 5415, utilise the unsteady Reynolds Averaged Navier-Stokes (URANS) method. A modified wall function model was incorporated into the numerical model to accurately simulate the effects of surface roughness. • CFD simulations of the DTMB 5415 were carried out to investigate the impact of biofouling on the speed reduction. • Modified wall-function approach was used for roughness effect modelling. • With small calcareous fouling, the increase in frictional resistance at 30 knots was 85.7% compared to smooth condition. • Speed penalties were estimated to be 6.67% for small calcareous fouling, compared to typical antifouling coating condition. [ABSTRACT FROM AUTHOR]

Despite technological advances, rolling motion is the most critical motion for the stability and survivability of ships. This study examines the possibility of using Anti Roll Gyrostabilizer System (ARGS) as a control actuation system to mitigate the roll motion of the DTMB 5415. In the scope of conceptual study, state space model of the DTMB 5415 Combatant Warship has been obtained. Then, ARGS dynamics have been integrated into the roll motion dynamics. Parameters of the DTMB 5415 and actuator are identified from the literature. Comparing experimental and numerical studies in the literature have also expanded the damping term parameters in the equation of roll motion. However, a Monte Carlo analysis is carried out to define the preliminary parameters of ARGS. An actuator-saturated Linear Matrix Inequality (LMI) Full State-Feedback H ∞ Optimal Controller is tested for this design iteration. The results are also contrasted with the requirements that military ships must meet. Ship roll amplitudes have significantly decreased (over 95% for various sea conditions) and have complied with STANAG 4154 standards. The 1 radian Precession Angle limit has not been overshot. Continuous and discrete-time control rules are implemented, thus demonstrating the applicability of this actuation and control method are shown. • This paper shows the effectiveness of Anti Roll Gyro Stabilizer (ARGS). • Optimization of AGRS with Monte Carlo Simulations is performed. • ARGS is not applied on DTMB 5415 combined with H ∞ Optimal control in the literature. • Continuous and Discrete time H ∞ Optimal control is applied with actuator saturation. [ABSTRACT FROM AUTHOR]

The paper shows the results of assessing the possibilities of computational fluid dynamics for predicting the motions of a ship with a moonpool and vertical water motions in a moonpool in regular head waves with a zero ship speed. A moonpool is a well which is used in different types of ships such as cable laying, drill and FPSO, survey, research and so on. This well is used for launching and lifting of different devices, divers, rescue bells, cables and risers, which are protected from outboard wind and waves. The results of the numerical simulation in the OpenFOAM software of heave and pitch motions of the DTMB 5415 model in regular head waves with and without ship speed show good agreement with the experimental data. The experiment was organized with a series 60 model, which was equipped with different moonpool shapes modules in regular head waves with a zero ship speed for determining heave and pitch RAOs and vertical water motions in the moonpool. The results do not show any influence of the moonpool for heave and pitch ship motions. These data are necessary for numerical simulation verification. The results of the numerical simulation of experimental research show good agreement, which means the good efficiency of computational fluid dynamics in heave and pitch motions and vertical water motions in moonpool calculation of a ship with a moonpool. Numerical simulation should be advised for calculations during the ship design process.

The purpose of this study is to assess the quality of the manoeuvre prediction of a twin-shaft naval vessel by means of a time-domain simulator based on Computational Fluid Dynamics (CFD) hydrodynamic coefficients. The simulator uses a modular approach in which the hull, rudders, appendices and propellers are based on different mathematical models. The hydrodynamic coefficients of the hull in the bare and appended configurations are computed using virtual captive tests performed with an open-source CFD code: OpenFoam. This paper demonstrates that the application of the CFD hydrodynamic coefficients led to a good estimate of the macroscopic characteristics of the main IMO manoeuvres with respect to the experimental measures. The adopted test case is the DTMB 5415M frigate both with and without appendages. This test case has been investigated in several research studies and international benchmark workshops, such as SIMMAN 2008, SIMMAN 2014 and many CFD workgroups.

Abstract A novel and fast technique is proposed to predict the parameters of turning maneuvering performance of a surface combatant at mid and high Froude numbers. An empirical model with two parameters (ship advance speed and rudder angle) and three unknown coefficients is introduced. First, resistance of rudder appended hull has been computed by the time-dependent straight-ahead towing simulations. The code has been verified by implementing three different solution verification methods; Grid Convergence Index (GCI), Correction Factor (CF) and Factors of Safety (FS). After this, Direct Maneuvering Simulations (DMS) have been performed by implementing overset grid technique. Singular body forces located at the same position and direction with the propellers have been applied to the vessel for propulsion during DMS. The method has been validated by comparing the results of bare hull straight-ahead towing case and δ = 35° turning circle simulation ones with the available experimental data. The numerical results have then been used to calculate the unknown coefficients by linear regression analysis. It has been found that the proposed CFD-based empirical model is reliable and robust for both interpolated and extrapolated cases as well as the test matrix with reasonable accuracy and also applicable to similar surface ships. Highlights • A novel and quick method is presented to obtain the turning circle parameters of ships at medium and relatively high Froude numbers. • The turning manoeuvre has been simulated using overset grid technique with relatively coarse grid. • The numerical simulation results have been verified using the latest solution verification methods and have been validated. • A new empirical method, which is based on rudder angle and ship advance speed, has been developed. [ABSTRACT FROM AUTHOR]

Abstract The turning circle and zigzag maneuvering performance of surface combatant, DTMB 5415 have been investigated by using system-based method. Unsteady Reynolds averaged Navier Stokes (URANS) approach is utilized to estimate hydrodynamic derivatives and hull-propeller-rudder interactions. DTMB 5415 is a twin-propeller / twin-rudder ship and there are some studies on the derivation of maneuvering coefficients in the literature but none of them took into account the propeller and rudder forces. In this study, static drift, pure yaw, combined yaw and drift, self-propulsion and rudder tests of DTMB 5415 hull have been simulated in calm and deep water condition. Bare hull PMM simulations were carried out for a fixed Froude number of F r = 0.28 , while the simulations related to rudder and propeller were performed at F r = 0.25. Computational results were used by MMG (Maneuvering Modeling Group) model to estimate the maneuvering performance of the ship. Hydrodynamic derivatives from numerically generated forces and moment data were obtained by single-run and multiple-run methods. The results from both methods were tested in an in-house maneuvering simulation code (MANSIM) that solves for ship motions and they were compared with computed turning circle and zigzag maneuvering performances. Although it is known a priori that the multiple-run method would give better solution in overall, it was found that the single-run method can be a good alternative in some specific cases. For the zigzag and turning circle tests, the results from single-run method were found satisfactory when correct PMM test conditions were adopted. [ABSTRACT FROM AUTHOR]

The stability of a damaged ship is influenced especially by ship motions and floodwater behaviour with their interactions. The behaviour of floodwater is highly nonlinear so that a physical experiment is one of the best ways to obtain the assessment of damaged ship behaviour. The present study investigates experimentally on the performance of an intact and damaged combatant vessel DTMB-5415 in beam waves. Ship model is moored at the bow and stern during the tests in regular waves, and damaged opening is located at the starboard midships and two compartments are flooded. It is shown that ingress and egress of floodwater and the interaction between ship behaviour and water surface effect have a significant impact on ship motions and loads acting on the ship. [ABSTRACT FROM AUTHOR]

This paper aims to obtain mathematical model of the full-scope roll motion for DTMB 5415 Combatant Warship and provide an optimal control by using Active Roll Fin Stabilizer (ARFS) structures. The mathematical model of the warship and the actuator model have been obtained in according to literature. Furthermore, the damping term parameters in the equation of the roll motion have been extended by comparing experimental and numerical studies in the literature. In order to ensure the required control moment and roll damping ratio, ARFS section (NACA 0015) has been selected and the fin structure is designed. As a controller method, actuator saturated Linear Matrix Inequality (LMI) Based State-Feedback H ∞ Optimal Controller has been used to stabilize the roll motion of the DTMB 5415 Combatant Warship with ARFS Structure. Moreover, the results are compared with the criteria that military ships should comply. Significant decrement (above 90% for different sea states) of the ship roll amplitudes have been occurred and met the standard of STANAG 4154. Fin angle saturation limit of 24 degree has not been reached. Control rule are carried out for continuous and discrete time domains with similar performances. Hence applicability of this actuation and control method have been stated. • Active Roll Fin Stabilizer is designed for DTMB 5415 in different sea states. • H ∞ Optimal Control are applied to mitigate of the roll motion of the warship. • Control Method is applied both continuous time and discrete time. • Actuator saturation problem is taken account. • Actuator mathematical model is implemented to the roll motion mathematical model. • Suitability of the fin angles for different sea states is obtained. • Controllers damped roll motion amplitudes up to 90%. • Military standards mentioned by STANAG 4154 is met for DTMB 5415 Combatant warship. [ABSTRACT FROM AUTHOR]

Simulation-based design optimization methods integrate computer simulations, design modification tools, and optimization algorithms. In hydrodynamic applications, often objective functions are computationally expensive and noisy, their derivatives are not directly provided, and the existence of local minima cannot be excluded a priori, which motivates the use of deterministic derivative-free global optimization algorithms. The enhancement of two algorithms of this type, DIRECT (DIviding RECTangles) and DPSO (Deterministic Particle Swarm Optimization), is presented based on global/local hybridization with derivative-free line search methods. The hull-form optimization of the DTMB 5415 model is solved for the reduction of the calm-water resistance at Fr = 0.25, using potential flow and RANS solvers. Six and eleven design variables are used respectively, modifying both the hull and the sonar dome. Hybrid algorithms show a faster convergence towards the global minimum than the original global methods and are a viable option for ship hydrodynamic optimization. A significant resistance reduction is achieved both by potential flow and RANS-based optimizations, showing the effectiveness of the optimization procedure. [ABSTRACT FROM AUTHOR]

The presence and elimination of irregular frequencies in wave-body interaction are reviewed by referring to the fundamental properties of the integral equations and a predictive measure that can be beneficial for wave-induced response assessment is proposed through numerical applications. By adopting higher-order elements and considering the hydroelastic response of the floating body, this study explores three interrelated questions: (i) how widely adopted irregular frequency suppression techniques perform, (ii) how, if possible, can these techniques be effectively applied, and (iii) how can the estimations be accepted as accurate for a given discretization, that is, finding a quantitative measure to relate the employed discretization to the frequency range for which the specified error threshold is not exceeded. The investigation involves three hull forms, a barge model along with the DTMB 5415 and KCS ships, and two techniques that extend the solution domain for suppression, namely the extended boundary integral equation method (EBIEM) and combined boundary integral equation method (CBIEM). The barge model is used for preliminary analyses to identify the existing patterns. DTMB 5415 and KCS allow the transfer of findings to practical applications and assess their validity. Three assessment measures in terms of frequency are employed by considering the hydrodynamic coefficients. In the present setting, it is observed that EBIEM is far more effective, and CBIEM cannot provide adequate suppression. The frequency envelope obtained by taking two quadratic elements per wave length is found to be a proper measure for estimating the frequency range that can be confidently studied. • EBIEM with discontinuous free-surface elements elegantly suppresses irregularities. • CBIEM with higher-order elements fails to eliminate irregular frequencies. • The quadratic envelope offers a proper measure to assess accuracy of predictions. [ABSTRACT FROM AUTHOR]

The Fourier–Kochin theory—an indirect solution approach for the boundary integral representations of free-surface flows that rely on free-surface Green function—is investigated by considering effective computation and reliable prediction. The present study addresses wave–body interaction with zero forward speed by adopting a higher-order approximation. Three distinct hull forms, the DTMB 5415, a scaled model reproduced from it, and a barge are used for practical application. The scaled frigate and barge models are used for comparative analysis to assess the performance of different computation techniques, modeling elements, and solution methods and to find the best course; the purpose of studying DTMB 5415 is to provide a realistic application based on a full-scale hull form by using the findings of the earlier benchmark studies. The analyses that cover both the rigid-body and elastic responses indicate that an adaptive approach for the computation of Fourier components has the potential to eliminate the numerical drawbacks of the presented implementation the Fourier–Kochin theory, but also stringently needs parallelism, preferably using the Single Program Multiple Data model. Using discontinuous elements for free-surface discretization when applying the Extended Boundary Integral Equation Method, the featured technique for irregular frequency suppression, is also promoted. • Fourier–Kochin theory provides a reliable basis to investigate wave-body interaction. • Adaptive integration of the Fourier components is effective in low-frequency region. • Discontinuous free-surface elements effectively suppress irregular frequencies. • EBIEM is more efficient compared to CBIEM, within the Fourier–Kochin framework. • The SPMD parallelism model through coarrays provides significant acceleration. [ABSTRACT FROM AUTHOR]

• This paper demonstrates the application of CFD technique to investigate the effects of several factors caused by the internal opening combinations on the motion responses of the damaged ship, including the flooding form, the air compressibility, the overflow path of the compressed air, and the down-flooding. • The VOF method is used to capture the hydrodynamic behaviors in the flooding process, predicting the flooding propagation. • The URANS solver with the DFBI morphing technique is used to deal with the mesh adaptation of the free surface and solve the motion response of the damaged ship. • A benchmarking study about the roll decay of the damaged DTMB 5415 model is performed to validate the accuracy of the applied numerical approach in dealing with motions of the damaged ship. Both cruise and naval ships have complex subdivisions and compartment connectivity with various opening arrangements. To better understand the hydrodynamic performance of a damaged ship, it is necessary to perform an investigation into the effect of opening combinations on the floodwater propagation and motion responses. In this paper, the Volume of Fluid (VOF) method is used to visualize the hydrodynamic behaviors in the flooding process. The Unsteady Reynolds Average Navier Stokes (URANS) solver combined with the Dynamic Fluid Body Interaction (DFBI) morphing technique is used to solve the motion responses of the damaged ship and deal with the mesh adaption of the free surface. A benchmarking study about the roll decay of the damaged DTMB 5415 model is performed to validate the accuracy of the numerical approach in dealing with the motion of the damaged ship. Simulation results show that different opening arrangements result in different flooding forms, including symmetric and asymmetric flooding. The compressed air impedes the flooding flow in the potential compartments. Even if the flooding compartments are the same, different flooding paths and overflow paths of the compressed air affect motion responses of the damaged ship. Moreover, good visualization capability can predict the flooding development, which can provide necessary information for decision support. [ABSTRACT FROM AUTHOR]

The purpose of this study is to assess the quality of the manoeuvre prediction of a twin-shaft naval vessel by means of a time-domain simulator based on Computational Fluid Dynamics (CFD) hydrodynamic coefficients. The simulator uses a modular approach in which the hull, rudders, appendices and propellers are based on different mathematical models. The hydrodynamic coefficients of the hull in the bare and appended configurations are computed using virtual captive tests performed with an open-source CFD code: OpenFoam. This paper demonstrates that the application of the CFD hydrodynamic coefficients led to a good estimate of the macroscopic characteristics of the main IMO manoeuvres with respect to the experimental measures. The adopted test case is the DTMB 5415M frigate both with and without appendages. This test case has been investigated in several research studies and international benchmark workshops, such as SIMMAN 2008, SIMMAN 2014 and many CFD workgroups. [ABSTRACT FROM AUTHOR]