Nonlinear Impact Loading in an Oblique Seaway

2003 ◽  
Vol 125 (3) ◽  
pp. 190-197 ◽  
Author(s):  
Patrick J. Finn ◽  
Robert F. Beck ◽  
Armin W. Troesch ◽  
Yung Sup Shin
Keyword(s):  
Time Domain ◽  
High Speed ◽  
Dynamic Instability ◽  
Vertical Plane ◽  
Direct Calculation ◽  
Wave Loads ◽  
Nonlinear Method ◽  
Strip Theory ◽  
The Impact ◽  
Flare Slamming

There is an increasing interest in developing direct calculation methods and procedures for determining extreme wave loads on ship girders (e.g. ISSC, 2000 [1]). Ships experiencing bottom and bow flare slamming have heightened the need for computational tools suitable to accurately predict motion and structural responses. The associated nonlinear impact problem is complicated by the complex free surface and body boundary conditions. This paper examines a “blended” linear–nonlinear method by which extreme loads due to bottom impact and flare slamming can be determined. Using a high-speed container ship as an example, comparisons of motions, shear and bending moments, and pressures are made in head and oblique bow-quartering waves. The time-domain computer program used in the comparison is based upon partially nonlinear models. The program, NSHIPMO, is an blended strip theory method using “impact” stations over the forward part of the ship and partially nonlinear stations over the rest. Body exact hydrostatics and Froude-Krylov excitation are used over the entire hull. The impact theory of Troesch and Kang [2] is employed to estimate the sectional nonlinear impact forces acting upon the specified nonlinear sections, while the linear theory of Salvesen et al. (STF) [3] is used to blend the remainder of the hydrodynamic forces, that is the radiation and diffraction components. Results from the simulation are presented with discussions of accuracy and time of computation. Several issues associated with the blended nonlinear time-domain simulation are presented, including modeling issues related to directional yaw-sway control and a vertical plane dynamic instability in long waves that has not previously been recognized.

Vertical-Plane Dynamics of Power-Augmented-Ram Vehicle

2013 ◽  
Author(s):  
Konstantin I. Matveev
Keyword(s):  
Control Systems ◽  
High Speed ◽  
Dynamic Models ◽  
Vertical Plane ◽  
Ground Effect ◽  
Forward Speed ◽  
Unsteady Forces ◽  
Wind Gusts ◽  
Strip Theory ◽  
Effect Theory

Power-augmented-ram vehicles represent novel air-assisted marine craft that can be used for high-speed amphibious transportation of heavy cargo. These vehicles rely on combined hydrodynamic and aerodynamic support that is also augmented by front air-based propulsors. Dynamic models for these craft in the presence of wind gusts and surface waves are needed for confident design of these vehicles, including motion control systems. This study addresses 3-DOF vertical-plane dynamics. The models for unsteady forces are based on the aerodynamic extreme-ground-effect theory and hydrodynamic added-mass strip theory. Modeling of the vehicle motions are carried out for cases of head and following wind gusts and waves of low and high amplitudes. Simulation results can be used for determining amplitudes of the vehicle responses, peak accelerations, and forward speed degradation.

Response Surface Models for Analyzing Planing Hull Motions in a Vertical Plane

2014 ◽  
Author(s):  
Tanvir Mehedi Sayeed ◽  
Leonard M. Lye ◽  
Heather Peng
Keyword(s):  
High Speed ◽  
Uniform Design ◽  
Vertical Plane ◽  
Statistical Design ◽  
Surrogate Models ◽  
Center Of Gravity ◽  
Design Parameters ◽  
Strip Theory ◽  
Calm Water ◽  
Sinkage And Trim

A non-linear mathematical model, Planing Hull Motion Program (PHMP) has been developed based on strip theory to predict the heave and pitch motions of planing hull at high speed in head seas. PHMP has been validated against published model test data. For various combinations of design parameters, PHMP can predict the heave and pitch motions and bow and center of gravity accelerations with reasonable accuracy at planing and semi-planing speeds. This paper illustrates an application of modern statistical design of experiment (DOE) methodology to develop simple surrogate models to assess planing hull motions in a vertical plane (surge, heave and pitch) in calm water and in head seas. Responses for running attitude (sinkage and trim) in calm water, and for heave and pitch motions and bow and center of gravity accelerations in head seas were obtained from PHMP based on a multifactor uniform design scheme. Regression surrogate models were developed for both calm water and in head seas for each of the relevant responses. Results showed that the simple one line regression models provided adequate fit to the generated responses and provided valuable insights into the behaviour of planing hull motions in a vertical plane. The simple surrogate models can be a quick and useful tool for the designers during the preliminary design stages.

Finite Element Analysis on the Structure Strength of Air Cushion Vehicle

2014 ◽  
Vol 918 ◽  
pp. 95-100 ◽  
Author(s):  
Ning Liu ◽  
Hui Long Ren ◽  
Jian Zhang Li ◽  
Lian Hui Jia
Keyword(s):  
High Speed ◽  
Normal Load ◽  
Structural Response ◽  
Fem Analysis ◽  
Direct Calculation ◽  
Wave Loads ◽  
Loading Test ◽  
Element Analysis ◽  
Air Cushion ◽  
Air Cushion Vehicle

Air Cushion Vehicle is widely used in the field of military and civil ship in recent years for its characteristic high speed and amphibian. Since the yield strength of aluminum sheet with stiffeners is relative low after welding, to ensure air cushion vehicle has significant strength under normal load and to avoid severe damage under adverse sea conditions, model loading test and theoretical prediction is used to determines the design values of wave loads, and FEM analysis with direct calculation method under the different load cases including the total longitudinal strength, cross-strength, torsional strength and shear strength, and then getting the structural response results. This essay gives several suggestions for the design according to the calculated results of stress and its deformation characteristics.

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.

A Linear Model Analysis of the Unsteady Force Response of a Planing Hull Through Forced Vertical Plane Motion Simulations

2020 ◽  
Author(s):  
Nicholas Husser ◽  
Stefano Brizzolara
Keyword(s):  
Linear Model ◽  
High Speed ◽  
Vertical Plane ◽  
Added Mass ◽  
Plane Motion ◽  
Force Response ◽  
Strip Theory ◽  
Planar Motion Mechanism ◽  
Unsteady Force ◽  
Traditional Approaches

The prediction of planing hull motions and accelerations in a seaway is of paramount importance to the design of high-speed craft to ensure comfort and, in extreme cases, the survivability of passengers and crew. The traditional approaches to predicting the motions and accelerations of a displacement vessel generally are not applicable, because the non-linear effects are more significant on planing hulls than displacement ships. No standard practice for predicting motions or accelerations of planing hulls currently exists, nor does a nonlinear model of the hydrodynamic forces that can be derived by simulation. In this study, captive and virtual planar motion mechanism (VPMM) simulations, using an Unsteady RANSE finite volume solver with volume of fluid approach, are performed on the Generic Prismatic Planing Hull (GPPH) to calculate the linearized added mass, damping, and restoring coefficients in heave and pitch. The linearized added mass and damping coefficients are compared to a simplified theory developed by Faltinsen [6], which combines the method of Savitsky [12] and 2D+t strip theory. The non-linearities in all coefficients will be investigated with respect to both motion amplitude and frequency. Nonlinear contributions to the force response are discussed through comparison of the force response predicted by the linear model and force response measured during simulation. Components of the planing hull dynamics that contribute to nonlinearities in the force response are isolated and discussed.

Nonlinear Prediction of Vertical Motions of a Fishing Vessel in Head Sea

1991 ◽  
Vol 35 (01) ◽  
pp. 32-39
Author(s):  
Forng-chen Chiu ◽  
Masataka Fujino
Keyword(s):  
High Speed ◽  
Practical Method ◽  
Wave Loads ◽  
Nonlinear Prediction ◽  
Fishing Vessel ◽  
Fishing Vessels ◽  
Impact Forces ◽  
Strip Theory ◽  
Development Center ◽  
Relative Motions

Several years ago the authors developed a practical method for calculating vertical motions and wave loads of a high-speed craft which travels in regular head sea, and verified its validity by comparing the computed motions and wave loads with the results of model tests. In order to clarify further its validity, the method is applied herein to compute the vertical motions of a fishing vessel, and the computed motions are compared with the results of experiments conducted by Bales and others at the David W. Taylor Naval Ship Research and Development Center (DTNSRDC). Also, the vertical motions and shipto-wave relative motions predicted by the method are compared with the numerical results of conventional linear strip theory computations performed at DTNSRDC. As a result, it is found that the present method, which in principle is based on the conventional Ordinary Strip Method synthesis but modified to be able to evaluate nonlinear hydrodynamic impact forces as well as dynamic lift in waves, can be applied to estimate vertical motions and ship-to-wave relative motions of fishing vessels traveling in head sea with enough accuracy for practical use.

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.

Coupled Aerodynamic and Hydroelastic Analysis of an Offshore Floating Wind Turbine System Under Wind and Wave Loads

2010 ◽  
Author(s):  
Kazuhiro Iijima ◽  
Junghyun Kim ◽  
Masahiko Fujikubo
Keyword(s):  
Wind Turbine ◽  
Time Domain ◽  
Response Analysis ◽  
Wave Loads ◽  
Structural System ◽  
Floating Structure ◽  
Floating Wind Turbine ◽  
Wind Turbine System ◽  
Offshore Floating Wind Turbine ◽  
The Impact

A numerical procedure for the fully coupled aerodynamic and hydroelastic time-domain analysis of an offshore floating wind turbine system including rotor blade dynamics, dynamic motions and flexible deflections of the structural system is illustrated. For the aerodynamic analysis of wind turbine system, a design code FAST developed by National Renewable Energy Laboratory (NREL) is employed. It is combined with a time-domain hydroelasticity response analysis code ‘Shell-Stress Oriented Dynamic Analysis Code (SSODAC)’ which has been developed by one of the authors. Then, the dynamic coupling between the rotating blades and the structural system under wind and wave loads is taken into account. By using this method, a series of analysis for the hydroelastic response of an offshore large floating structure with two rotors under combined wave and wind loads is performed. The results are compared with those under the waves and those under the winds, respectively, to investigate the coupled effects in terms of stress as well as motions. The coupling effects between the rotor-blades and the motions are observed in some cases. The impact on the structural design of the floating structure, tower and blade is addressed.

Determination of global design loads for large high-speed catamarans

2002 ◽  
Vol 216 (1) ◽  
pp. 79-94
Author(s):  
S E Heggelund ◽  
T Moan ◽  
S Oma
Keyword(s):  
High Speed ◽  
Bending Moment ◽  
Wave Loads ◽  
Strip Theory ◽  
Non Linear ◽  
Design Loads ◽  
Linear Effects ◽  
Operational Criteria ◽  
Vertical Bending Moment

Methods for calculation of design loads for high-speed vessels are investigated. The influence of operational restrictions on design loads is emphasized. Relevant operational criteria for high-speed displacement vessels are discussed. Procedures and criteria for numerical calculation of operational limits are incomplete and should be further investigated. Operational limits and design loads for a 60 m catamaran are calculated on the basis of linear strip theory. Non-linear effects on design loads are assessed from calculations in regular waves. Simplified formulae commonly used by classification societies for prediction of operational limits seem to over-predict the reduction of motions and wave loads at reduced speed. When operational limits typically given by the shipmaster or the operator are used, the design loads found by direct calculations are comparable with design loads given by classification societies. For vertical bending moment and torsion, the use of active foils is found to increase the linear loads. Owing to reduced motions, the foils reduce the non-linear loads and hence the total loads. The effect of non-linear horizontal loads is not investigated but can be important for transverse bending moment.

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.

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