Effect of Gravity on a Free-Free Fluid-Structure System

2002 ◽  
Author(s):  
Jean-Se´bastien Schotte´ ◽  
Roger Ohayon
Keyword(s):  
Free Surface ◽  
Rigid Body ◽  
Gravity Field ◽  
Strong Coupling ◽  
Variational Formulation ◽  
Free Fluid ◽  
Inviscid Liquid ◽  
Liquid Free Surface ◽  
Rigid Body Modes ◽  
Elastic Tank

In this paper, we propose a symmetric variational formulation for the eigenmode computation of a free-free elastic tank partially filled with an incompressible inviscid liquid in presence of a gravity field. The originality of this model is to take into account the strong coupling between the sloshing of the liquid free surface and the hydroelastic deformations of the tank. We will show that this allows the rigid body modes of the system to be predicted correctly.

Transformation of Arbitrary Elastic Mode Shapes Into Pseudo-Free-Surface and Rigid Body Modes for Multibody Dynamic Systems

2012 ◽  
Vol 7 (2) ◽  
Author(s):  
Karim Sherif ◽  
Hans Irschik ◽  
Wolfgang Witteveen
Keyword(s):  
Free Surface ◽  
Rigid Body ◽  
Mode Shape ◽  
Frame Of Reference ◽  
Mode Shapes ◽  
Surface Mode ◽  
Elastic Mode ◽  
Surface Modes ◽  
Rigid Body Modes ◽  
Floating Frame

In multibody dynamics, the flexibility effects of each body are captured by using a linear combination of elastic mode shapes. If a co-rotational and co-translating frame of reference is used together with eigenvectors of the unconstraint body, which are free-surface modes, some spatial integrals in the floating frame of reference configuration do vanish. The corresponding coordinate system is the so-called Tisserand (or Buckens) reference frame. In the present contribution, a technique is developed for separating an arbitrary elastic mode shape into a pseudo-free-surface mode and rigid body modes. The generated pseudo-free-surface mode has most of the advantageous characteristics of a free-surface mode, and spans together with the rigid body modes the same solution space as it is spanned by the original mode shape. Due to the fact that, in the floating frame of reference configuration, the rigid body motions are already described by special generalized coordinates, only the resulting pseudo-free-surface modes are finally used to capture the flexibility effects of each body. A result of the generated pseudo-free-surface modes is that some of the spatial integrals do vanish and, thus, the equations of motion are significantly simplified. Two examples are presented in order to illustrate and to demonstrate the potential of the proposed method.

scholarly journals Combined motion of reservoir with liquid for angular motions of carrying body

2009 ◽  
Vol 31 (2) ◽  
pp. 103-121
Author(s):  
Oleg S. Limarchenko
Keyword(s):  
Free Surface ◽  
Variational Principle ◽  
Boundary Conditions ◽  
Variational Formulation ◽  
Discrete Model ◽  
Wave Motion ◽  
Ideal Liquid ◽  
Combined Motion ◽  
Liquid Free Surface ◽  
Pendulum Suspension

We consider peculiarities of the modeling of wave motion of ideal liquid in a reservoir, which performs inclined motions. For description of behavior of the system we use variational formulation of the problem on the basis of the Hamilton-Ostrogradskiy variational principle with preliminary satisfying all kinematic boundary conditions of the problem. It is shown that this approach makes it possible to reduce considerably the number of unknowns of the problem and reduce it description only to parameters of motion of a liquid free surface and parameters of motion of a carrying body. The constructed nonlinear discrete model of the system was applied for investigation of motion of a reservoir with liquid on pendulum suspension, on taking into account liquid outflow and other problems, which have theoretical and applied meaning.

Profilometry of a liquid-free surface with large slope variations

1997 ◽  
Vol 36 (13) ◽  
pp. 2905
Author(s):  
Luis P. Thomas ◽  
Roberto Gratton ◽  
Beatriz M. Marino
Keyword(s):  
Free Surface ◽  
Liquid Free Surface

Generalized Modes in Time-Domain Seakeeping Calculations

2012 ◽  
Vol 56 (04) ◽  
pp. 215-233
Author(s):  
Johan T. Tuitman ◽  
Šime Malenica ◽  
Riaan van't Veer
Keyword(s):  
Rigid Body ◽  
Transient Response ◽  
Time Domain ◽  
Large Amplitude ◽  
Degrees Of Freedom ◽  
Mode Shapes ◽  
Nonlinear Load ◽  
Large Amplitude Motions ◽  
Rigid Body Modes ◽  
The Time Domain

The concept of "generalized modes" is to describe all degrees of freedom by mode shapes and not using any predefined shape, like rigid body modes. Generalized modes in seakeeping computations allow one to calculate the response of a single ship, springing, whipping, multibody interaction, etc., using a uniform approach. The generalized modes have already been used for frequency-domain seakeeping calculations by various authors. This article extents the generalized modes methodology to be used for time-domain seakeeping computations, which accounts for large-amplitude motions of the rigid-body modes. The time domain can be desirable for seakeeping computations because it is easy to include nonlinear load components and to compute transient response, like slamming and whipping. Results of multibody interaction, two barges connected by a hinge, whipping response of a ferry resulting from slamming loads, and the response of a flexible barge are presented to illustrate the theory.

A Comparison of Strong and Weak Coupling Schemes for Computational Aeroelasticity in OpenFOAM

2018 ◽  
Author(s):  
Sabet Seraj ◽  
Amin Fereidooni ◽  
Anant Grewal
Keyword(s):  
Rigid Body ◽  
Strong Coupling ◽  
Weak Coupling ◽  
Body Motion ◽  
Coupling Scheme ◽  
Lower Sensitivity ◽  
Step Size ◽  
Time Step ◽  
Time Step Size ◽  
Structure Interaction

Two coupling schemes for fluid-structure interaction using the OpenFOAM structural solver sixDoF Rigid Body Motion are developed. The first scheme is developed by modifying the baseline leapfrog weak coupling scheme to minimize the lag between the fluid and structural solvers. The second is a strong coupling scheme based on the Crank-Nicolson method. The two newly implemented schemes and the baseline are compared through the aeroelastic simulation of a NACA 64A010 airfoil and the Benchmark Supercritical Wing. The aeroelastic solutions obtained using the newly implemented schemes exhibit significantly lower sensitivity to changes in time step size compared to the baseline weak coupling scheme. The modified weak coupling and strong coupling schemes perform comparably for the cases studied.

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