The Dynamics of Marine Vehicles With Inflectional Righting Moment Curves

1987 ◽  
Vol 109 (4) ◽  
pp. 335-344 ◽  
Author(s):  
M. H. Patel ◽  
J. A. Witz
Keyword(s):  
Frequency Domain ◽  
Numerical Solutions ◽  
Multiple Equilibrium ◽  
Roll Motion ◽  
Moment Curve ◽  
Marine Vehicles ◽  
Jump Phenomena ◽  
Righting Moment ◽  
Marine Vehicle ◽  
Fold Catastrophe

This paper investigates modifications to the dynamics of a marine vehicle caused by a point of inflection in its hydrostatic righting moment curve. Such inflections are shown to yield multiple equilibrium angles due to static over turning moments and to the occurrence of a classical fold catastrophe. Both frequency domain analyses and numerical solutions of the equation of roll motion are used to evaluate the influence of such inflections on the vessel’s dynamics. The analyses demonstrate that inflectional righting moment curves can yield unexpected roll amplitude jump phenomena close to resonance. The paper concludes with a discussion of the effects of such behavior on vessel hull designs.

A new generalized stiffness reduction method for 2D/2.5D frequency-domain seismic wave modeling in viscoelastic anisotropic media

Geophysics ◽  
2020 ◽  
Vol 85 (6) ◽  
pp. T315-T329
Author(s):  
Qingjie Yang ◽  
Bing Zhou ◽  
Mohamed Kamel Riahi ◽  
Mohammad Al-khaleel
Keyword(s):  
Free Surface ◽  
Frequency Domain ◽  
Seismic Wave ◽  
Reduction Method ◽  
Numerical Solutions ◽  
Anisotropic Media ◽  
Spectral Element ◽  
Wave Modeling ◽  
Adaptation Capacity ◽  
Stiffness Reduction

In frequency-domain seismic wave modeling, absorbing artificial reflections is crucial to obtain accurate numerical solutions. We have determined that, in viscoelastic anisotropic media (VEAM), the most popular absorbing boundary techniques, such as the perfectly matched layer and the generalized stiffness reduction method (GSRM), fail. Then, we develop a new version of the GSRM and incorporate it into a 2D/2.5D spectral element method. We find with extensive nontrivial numerical experiments that the new GSRM exhibits excellent features of simple and efficient implementation, while handling free-surface and subsurface interface topography. Furthermore, we find that sampling the positive wavenumber range is an efficient strategy to compute the 3D wavefield in arbitrary 2D VEAM, and the new version takes full advantage of the symmetry/antisymmetry of the wavefield. The new GSRM removes artificial reflections by damping the real and imaginary viscoelastic moduli in different ways. The wavefields in two vertically transverse isotropic and one orthorhombic viscoelastic homogeneous models are compared with the corresponding analytical solutions to show the high accuracy performance of the new GSRM. Finally, a complex 2D geologic model with irregular free-surface and subinterface is considered to present the modeling technique and its adaptation capacity for complex 2D VEAM.

A Novel Autonomous Docking Method of Unmanned Marine Vehicle Based on Manipulator

2013 ◽  
Vol 364 ◽  
pp. 370-374
Author(s):  
Jin Lei Chen ◽  
Yuan Dai ◽  
Zhong Qiang Zheng ◽  
Zong Yu Chang ◽  
Wen Dai ◽  
...  
Keyword(s):  
Data Exchange ◽  
Autonomous Underwater Vehicles ◽  
Underwater Vehicles ◽  
Kinematics Analysis ◽  
Marine Vehicles ◽  
Docking Method ◽  
Stability And Accuracy ◽  
Marine Vehicle ◽  
Limited Duration ◽  
Autonomous Docking

To extend underwater duration is an important issue for autonomous underwater vehicles. Limited duration restricts the working ability of an unmanned marine vehicle (UMV) and needs frequent surface support. One of the solutions to this problem is docking that can implement functions as recharging, data exchange, maintaining and so on. A novel docking method based on manipulator assistance is carried out. In this method, a fixed handle near docking port is caught by the manipulator on the vehicle firstly. The manipulator can be controlled to obtain the vehicles body a suitable position and orientation for autonomous docking. The manipulator with floating based can be looked on as one serial manipulator with a fixed anchor. The kinematics analysis is given by using the MATLAB and ADAMS. The simulation results suggest that docking method has more stability and accuracy, and it can also reduce the collision between docking port and the vehicle. The method provides a conception of docking process between all kinds of unman marine vehicles and docking ports.

Robust Maneuvering Control for Marine Vehicles Under Uncertain Ocean Currents

2013 ◽  
Author(s):  
Qingmin Huang ◽  
Ye-Hwa Chen ◽  
Xin Nie
Keyword(s):  
Ocean Currents ◽  
Design Parameters ◽  
Fast Time ◽  
State Transformation ◽  
Marine Vehicles ◽  
Control Scheme ◽  
Uniform Ultimate Boundedness ◽  
Stability Ball ◽  
Marine Vehicle ◽  
Structure Properties

We consider the problem of tracking a desired trajectory with a desired velocity for a marine vehicle. There are possibly fast time-varying uncertainties which may exist in the model, the inputs, the ocean currents, as well as environment disturbances. Based on the possible bound of the uncertainties and some structure properties the marine vehicle are met, a state transformation is made to the dynamics of error of the marine vehicle. A robust control scheme is proposed which renders the transformed system practically stable. A proof shows that the original uncertain marine vehicle under this control will also be practically stable. Furthermore, the uniform ultimate boundedness ball and uniform stability ball of the marine vehicle can be made arbitrarily small by suitable choice of the design parameters.

scholarly journals Multiple equilibria in a simple elastocapillary system

2012 ◽  
Vol 712 ◽  
pp. 273-294 ◽  
Author(s):  
Michele Taroni ◽  
Dominic Vella
Keyword(s):  
Multiple Equilibria ◽  
Microelectromechanical Systems ◽  
Numerical Solutions ◽  
Multiple Equilibrium ◽  
Type Model ◽  
Initial State ◽  
Micro Channels ◽  
Simple Model System ◽  
Stable Equilibria ◽  
The Stability

AbstractWe consider the elastocapillary interaction of a liquid drop placed between two elastic beams, which are both clamped at one end to a rigid substrate. This is a simple model system relevant to the problem of surface-tension-induced collapse of flexible micro-channels that has been observed in the manufacture of microelectromechanical systems (MEMS). We determine the conditions under which the beams remain separated, touch at a point, or stick along a portion of their length. Surprisingly, we show that in many circumstances multiple equilibrium states are possible. We develop a lubrication-type model for the flow of liquid out of equilibrium and thereby investigate the stability of the multiple equilibria. We demonstrate that for given material properties two stable equilibria may exist, and show via numerical solutions of the dynamic model that it is the initial state of the system that determines which stable equilibrium is ultimately reached.

Numerical Solutions of Transient Radiative Transfer Using Time and Frequency-Domain Approaches

2005 ◽  
Author(s):  
Mathieu Francoeur ◽  
Daniel R. Rousse
Keyword(s):  
Radiative Transfer ◽  
Frequency Domain ◽  
Numerical Solutions ◽  
Radiation Transport ◽  
Transfer Problem ◽  
Scattering Media ◽  
Frequency Method ◽  
Transmitted Radiation ◽  
Radiative Transfer Problem ◽  
Space Frequency

The one-dimensional transient radiative transfer problem in the Cartesian coordinate system — an absorbing and scattering medium illuminated by a short laser pulse — is solved by the use of time and frequency-domain approaches. In both cases, a Discrete Ordinates–Finite Volume method is adopted. Results for transmittance show that even if high order spatial schemes coupled with flux limiters can minimize the non-physical results associated with the temporal approach (transmitted flux emerging earlier than the minimal time required by the radiation to leave the medium), early transmitted radiation are always present. Transmittances obtained from the space-frequency method are more accurate, without unrealistic behaviors at early time periods. However, the frequency-dependent approach is computationally expensive with respect to its temporal counterpart, and the implementation of a Fast Fourier Transform algorithm is therefore considered. Finally, promising applications regarding optical diagnosis of absorbing and scattering media, using the radiation transport equation in the space-frequency domain, are briefly discussed.

scholarly journals Induced capacitance in the squid giant axon. Lipophilic ion displacement currents.

1983 ◽  
Vol 82 (3) ◽  
pp. 331-346 ◽  
Author(s):  
J M Fernández ◽  
R E Taylor ◽  
F Bezanilla
Keyword(s):  
Action Potential ◽  
Frequency Domain ◽  
Time Domain ◽  
Numerical Solutions ◽  
Ionic Current ◽  
Induced Polarization ◽  
Resting Potential ◽  
Axonal Membrane ◽  
Cable Properties ◽  
The Time Domain

Voltage-clamped squid giant axons, perfused internally and externally with solutions containing 10(-5) M dipicrylamine (DpA-), show very large polarization currents (greater than or equal to 1 mA/cm2) in response to voltage steps. The induced polarization currents are shown in the frequency domain as a very large voltage-and frequency-dependent capacitance that can be fit by single Debye-type relaxations. In the time domain, the decay phase of the induced currents can be fit by single exponentials. The induced polarization currents can also be observed in the presence of large sodium and potassium currents. The presence of the DpA- molecules does not affect the resting potential of the axons, but the action potentials appear graded, with a much-reduced rate of rise. The data in the time domain as well as the frequency domain can be explained by a single-barrier model where the DpA- molecules translocate for an equivalent fraction of the electric field of 0.63, and the forward and backward rate constants are equal at -15 mV. When the induced polarization currents described here are added to the total ionic current expression given by Hodgkin and Huxley (1952), numerical solutions of the membrane action potential reproduce qualitatively our experimental data. Numerical solutions of the propagated action potential predict that large changes in the speed of conduction are possible when polarization currents are induced in the axonal membrane. We speculate that either naturally occurring substances or drugs could alter the cable properties of cells in a similar manner.

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