Sensitivity Analysis in Parametric Rolling of a Modern Cruise Ship Using Numerical Simulations in 6-DOF

2020 ◽  
Author(s):  
Bülent Düz
Keyword(s):  
Sensitivity Analysis ◽  
Numerical Simulations ◽  
Time Domain ◽  
Nonlinear Phenomenon ◽  
Cruise Ship ◽  
Parametric Roll ◽  
Parametric Rolling ◽  
Maximum Angle ◽  
Strip Theory ◽  
The Time Domain

Abstract Parametric roll is a nonlinear phenomenon that can result in large roll angles coupled with significant pitch motions. These motions might induce large loads on the ship structure, and compromise the safety of the crew and the cargo. The severity of the motions might reach to such levels that capsizing might occur. In this study sensitivity analysis in parametric rolling of a modern cruise ship is investigated using numerical simulations. Several parameters were considered as sources of uncertainty such as the combined effect of GM and roll radius of gyration, roll damping, ship speed, and fin characteristics. In terms of fin characteristics, fin angle rate and maximum angle, fin area and aspect ratio, and fin gains were investigated. Additionally, the non-ergodicity of parametric roll was studied as well as the effect of simulation duration on the statistics of parametric roll. The simulations were carried out with a hybrid time-domain seakeeping and manoeuvring code. The time-domain code was used in combination with a strip-theory based frequency-domain program in order to calculate diffraction and radiation forces as well as added-mass. The time-domain code was able simulate the dynamic behavior of a steered ship in 6-DOF, where the motions can be large up to the moment of capsize.

Parametric Rolling Simulations of Container Ships

2013 ◽  
Author(s):  
Anton Turk ◽  
Jasna Prpić-Oršić ◽  
Carlos Guedes Soares
Keyword(s):  
Time Domain ◽  
Degrees Of Freedom ◽  
Equations Of Motion ◽  
Full Range ◽  
Ship Motions ◽  
Computationally Efficient ◽  
Parametric Roll ◽  
Parametric Rolling ◽  
Strip Theory ◽  
The Time Domain

A hybrid nonlinear time domain seakeeping analysis is applied to the study of a container ship advancing at different headings and encounter frequencies. A time-domain nonlinear strip theory in six degrees-of-freedom has been extended to predict ship motions by solving the unsteady hydrodynamic problem in the frequency domain and the equations of motion in the time domain which allows introducing nonlinearities in the linear model. The code is used to make parametric roll predictions for various speeds and headings and the results are summarized in a very intuitive 2D and 3D polar plots showing the full range of the parametric rolling realizations. The method developed is fairly accurate, robust, very computationally efficient, and can predict nonlinear ship motions. It is well suited to be used as a tool in ship design or as part of a path optimization model.

scholarly journals Lightning Channel-Base Current Identification as Solution of a Volterralike Integral Equation

2008 ◽  
Vol 2 (1) ◽  
pp. 160-165 ◽  
Author(s):  
Federico Delfino ◽  
Renato Procopio ◽  
Mansueto Rossi
Keyword(s):  
Integral Equation ◽  
Numerical Simulations ◽  
Time Domain ◽  
Measurement Noise ◽  
Induction Field ◽  
Base Current ◽  
Lightning Channel ◽  
Regularization Techniques ◽  
Ill Conditioning ◽  
The Time Domain

In this paper, a novel procedure to reconstruct the lightning channel-base current starting from the measurement of the induction field generated by it is presented. The procedure is based on a suitable mathematical manipulation of the equation expressing the induction field in the time domain, in order to transform it into a Volterra-like integral equation. Such kind of equations can be easily numerically solved without resorting to any sort of regularization techniques as they are not affected by the typical ill-conditioning of the inverse problems. The developed algorithm has been validated by means of several numerical simulations, which have shown its effectiveness also in presence of measurement noise on the induction field values.

A Comparative Assessment of Simplified Models for Simulating Parametric Roll

2017 ◽  
Vol 139 (2) ◽  
Author(s):  
Abhilash S. Somayajula ◽  
Jeffrey Falzarano
Keyword(s):  
Differential Equations ◽  
Analytical Solutions ◽  
Time Domain ◽  
Numerical Solutions ◽  
Nonlinear Differential Equations ◽  
Nonlinear Phenomenon ◽  
Concept Design ◽  
Parametric Roll ◽  
Statistical Confidence ◽  
Restoring Forces

The motion of a ship/offshore platform at sea is governed by a coupled set of nonlinear differential equations. In general, analytical solutions for such systems do not exist and recourse is taken to time-domain simulations to obtain numerical solutions. Each simulation is not only time consuming but also captures only a single realization of the many possible responses. In a design spiral when the concept design of a ship/platform is being iteratively changed, simulating multiple realizations for each interim design is impractical. An analytical approach is preferable as it provides the answer almost instantaneously and does not suffer from the drawback of requiring multiple realizations for statistical confidence. Analytical solutions only exist for simple systems, and hence, there is a need to simplify the nonlinear coupled differential equations into a simplified one degree-of-freedom (DOF) system. While simplified methods make the problem tenable, it is important to check that the system still reflects the dynamics of the complicated system. This paper systematically describes two of the popular simplified parametric roll models in the literature: Volterra GM and improved Grim effective wave (IGEW) roll models. A correction to the existing Volterra GM model described in current literature is proposed to more accurately capture the restoring forces. The simulated roll motion from each model is compared against a corresponding simulation from a nonlinear coupled time-domain simulation tool to check its veracity. Finally, the extent to which each of the models captures the nonlinear phenomenon accurately is discussed in detail.

Ship Motion Computations Using a High Froude Number Time Domain Strip Theory

2006 ◽  
Vol 50 (01) ◽  
pp. 15-30
Author(s):  
D. S. Holloway ◽  
M. R. Davis
Keyword(s):  
Froude Number ◽  
Time Domain ◽  
High Speed ◽  
Equations Of Motion ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Viscous Effects ◽  
Strip Theory ◽  
Large Amplitude Motions ◽  
The Time Domain

High-speed strip theories are discussed, and a time domain formulation making use of a fixed reference frame for the two-dimensional fluid motion is described in detail. This, and classical (low-speed) strip theory, are compared with the experimental results of Wellicome et al. (1995) up to a Froude number of 0.8, as well as with our own test data for a semi-SWATH, demonstrating the marked improvement of the predictions of the former at high speeds, while the need to account for modest viscous effects at these speeds is also argued. A significant contribution to time domain computations is a method of stabilizing the integration of the ship's equations of motion, which are inherently unstable due to feedback from implicit added mass components of the hydrodynamic force. The time domain high-speed theory is recommended as a practical alternative to three-dimensional methods. It also facilitates the investigation of large-amplitude motions with stern or bow emergence and forms a simulation base for the investigation of ride control systems and local or global loads.

NON LINEAR ANALYSIS OF SHIP MOTIONS AND LOADS IN LARGE AMPLITUDE WAVES

2021 ◽  
Vol 153 (A2) ◽  
Author(s):  
G Mortola ◽  
A Incecik ◽  
O Turan ◽  
S.E. Hirdaris
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Large Amplitude ◽  
Linear Time ◽  
Ship Motions ◽  
Wave Loads ◽  
Time Step ◽  
Strip Theory ◽  
Non Linear ◽  
The Time Domain

A non linear time domain formulation for ship motions and wave loads is presented and applied to the S175 containership. The paper describes the mathematical formulations and assumptions, with particular attention to the calculation of the hydrodynamic force in the time domain. In this formulation all the forces involved are non linear and time dependent. Hydrodynamic forces are calculated in the frequency domain and related to the time domain solution for each time step. Restoring and exciting forces are evaluated directly in time domain in a way of the hull wetted surface. The results are compared with linear strip theory and linear three dimensional Green function frequency domain seakeeping methodologies with the intent of validation. The comparison shows a satisfactory agreement in the range of small amplitude motions. A first approach to large amplitude motion analysis displays the importance of incorporating the non linear behaviour of motions and loads in the solution of the seakeeping problem.

Sensitivity Analysis of Cable Parameters on Tension of a Suspended Cable under Combination Resonances

2019 ◽  
Vol 19 (03) ◽  
pp. 1950025 ◽  
Author(s):  
Kyu Won Kim ◽  
No-Cheol Park ◽  
Weon Keun Song ◽  
Moon Kyum Kim ◽  
Manukid Parnichkun
Keyword(s):  
Sensitivity Analysis ◽  
Time Domain ◽  
Damping Coefficient ◽  
Sensitivity Analyses ◽  
Phase Portraits ◽  
Arc Length ◽  
Cable Tension ◽  
Suspended Cable ◽  
Direct Integration Method ◽  
The Time Domain

This paper studies the vibration of a suspended cable with small sag excited by a second excitation (normal) mode causing combination resonance in the three modes, i.e. tangent, normal and bi-normal modes. The displacement response spectra in the time domain and phase portraits are provided as evidence of the transition from the unstable steady-state motion to the stable one for nonlinear cable oscillation. A nondimensional equation for the cable tension is established with its variation evaluated for the unstable zone. The half-normalized sensitivity analysis of cable parameters, such as damping coefficient, excitation amplitude, arc length parameter and initial conditions, for their influence on cable tension is conducted in the time domain by a direct integration method. Also, the characteristics of the dynamic sensitivity of cable tension to the parameters are discussed. As a result, a sensitivity ranking chart is prepared based on the sensitivity analyses for the parameters considered. It is clearly revealed that cable tension is very sensitive to tangent and normal initial displacements in spite of their small values, whereas the same is not true for the arc length parameter and bi-normal damping coefficient. To verify the sensitivity analysis algorithm, a forced Rayleigh oscillator is introduced. A feasibility study using the oscillator shows that the numerical results obtained are in good qualitative agreement with the analytical predictions, implying that the associated algorithm works well.

Operation of T-Foils and Stern Tabs to Improve Passenger Comfort on High-Speed Ferries

2021 ◽  
pp. 1-20
Author(s):  
Michael R. Davis
Keyword(s):  
Time Domain ◽  
High Speed ◽  
Transfer Functions ◽  
Passenger Comfort ◽  
Strip Theory ◽  
Head Waves ◽  
Similar Range ◽  
Vertical Accelerations ◽  
The Time Domain ◽  
Passenger Discomfort

High-speed ferries of around 100 m length cruising at around 40 knots can cause significant passenger discomfort in head waves. This is due to the frequencies of encountering waves, of maximum hull response to encountered waves and of maximum passenger discomfort all falling within a similar range. In this paper, the benefit obtained by fitting active T-foils and stern tabs to control heave and pitch in head waves is considered. Ship motion responses are computed by numerical integration in the time domain including unsteady control actions using a time domain, high-speed strip theory. This obviates the need to identify transfer functions, the computed time responses including nonlinear hull immersion terms. The largest passenger vertical accelerations occur at forward locations and are best controlled by a forward located T-foil acting in combination with active stern tabs. Various feedback control algorithms have been considered and it is found that pitch damping control gives the greatest improvement in passenger comfort at forward positions. Operation in adaptive and nonlinear modes so that the control deflections are maximized under all conditions give the greatest benefit and can reduce passenger motion sickness incidence (MSI) by up to 25% in a 3-m head sea on the basis of International Organization for Standardization (ISO) recommendations for calculation of MSI for a 90-minute seaway passage.

Time-Domain Analysis of Large-Amplitude Vertical Ship Motions and Wave Loads

1998 ◽  
Vol 42 (02) ◽  
pp. 139-153 ◽  
Author(s):  
N. Fonseca ◽  
C. Guedes Soares
Keyword(s):  
Free Surface ◽  
Time Domain ◽  
Large Amplitude ◽  
Surface Condition ◽  
Memory Effects ◽  
Wave Loads ◽  
Strip Theory ◽  
Large Amplitude Motions ◽  
Free Surface Oscillations ◽  
The Time Domain

The vertical motions and wave induced loads on ships with forward speed are studied in the time domain, considering non-linear effects associated with large amplitude motions and hull flare shape. The method is based on a strip theory, using singularities distributed on the cross sections which satisfy the linear free surface condition. The solution is obtained in the time domain using convolution to account for the memory effects related to the free surface oscillations. In this way the linear radiation forces are represented in terms of impulse response functions, infinite frequency added masses and radiation restoring coefficients. The diffraction forces associated with incident wave scattering are linear. The hydrostatic and Froude-Krylov forces are evaluated over the instantaneous wetted surface of the hull to account for the large amplitude motions and hull flare. The radiation contribution for wave loads is also obtained in the time domain using convolution to account for the memory effects related to the free surface oscillations. Results of motions and wave loads for the S175 container ship are presented and analyzed. The results from the present method are compared with linear results.

Sign in / Sign up

Export Citation Format

Share Document