Hydrodynamically coupled oscillators

2011 ◽  
Vol 677 ◽  
pp. 589-606 ◽  
Author(s):  
R. TIRON ◽  
E. KANSO ◽  
P. K. NEWTON
Keyword(s):  
Angular Momentum ◽  
Simple Model ◽  
Coupled Oscillators ◽  
Normal Modes ◽  
Mass Effect ◽  
Added Mass ◽  
Momentum Exchange ◽  
Ring Configuration ◽  
Curved Paths ◽  
Surrounding Fluid

A submerged spring–mass ring is analysed as a simple model for the way in which an underwater swimmer couples its body deformations to the surrounding fluid in order to accomplish locomotion. We adopt an inviscid, incompressible, irrotational assumption for the surrounding fluid and analyse the coupling response to various modes of excitation of the ring configuration. Due to the added mass effect, the surrounding fluid provides an environment which effectively couples the ‘normal modes’ of oscillation of the ring, leading to nonlinear trajectories if the ring is free to accelerate based on the effective forces the oscillations induce. Through a series of examples, we demonstrate various features that the model supports, including the locomotion on curved paths as a result of energy and angular momentum exchange with the surrounding fluid.

Fluid Added Mass Effect in the Modal Response of a Pump-Turbine Impeller

2009 ◽  
Author(s):  
Eduard Egusquiza ◽  
Carme Valero ◽  
Quanwei Liang ◽  
Miguel Coussirat ◽  
Ulrich Seidel
Keyword(s):  
Natural Frequencies ◽  
Experimental Tests ◽  
Mass Effect ◽  
Added Mass ◽  
Mode Shapes ◽  
Pump Turbine ◽  
Modal Response ◽  
Surrounding Fluid ◽  
Turbine Impeller ◽  
Good Agreement

In this paper, the reduction in the natural frequencies of a pump-turbine impeller prototype when submerged in water has been investigated. The impeller, with a diameter of 2.870m belongs to a pump-turbine unit with a power of around 100MW. To analyze the influence of the added mass, both experimental tests and numerical simulations have been carried out. The experiment has been performed in air and in water. From the frequency response functions the modal characteristics such as natural frequencies and mode shapes have been obtained. A numerical simulation using FEM (Finite Elements Model) was done using the same boundary conditions as in the experiment (impeller in air and surrounded by a mass of water). The modal behaviour has also been calculated. The numerical results were compared with the available experimental results. The comparison shows a good agreement in the natural frequency values both in air and in water. The reduction in frequency due to the added mass effect of surrounding fluid has been calculated. The physics of this phenomenon due to the fluid structure interaction has been investigated from the analysis of the mode-shapes.

scholarly journals Ships Added Mass Effect on a Flexible Mooring Dolphin in Berthing Manoeuvre

2021 ◽  
Vol 9 (2) ◽  
pp. 108
Author(s):  
Aleksander Grm
Keyword(s):  
Mass Effect ◽  
Added Mass ◽  
Hydrodynamic Effect ◽  
Theory Approach ◽  
Additional Mass ◽  
Strip Theory ◽  
Rocking Motion ◽  
The Mathematical Model ◽  
Surrounding Fluid ◽  
Zero Frequency

This paper deals with the hydrodynamic effect of the ship on a flexible dolphin during a mooring manoeuvre. The hydrodynamic effect refers to the change in momentum of the surrounding fluid, which is defined by the concept of added mass. The main reason for the present study is to answer the question, “What is the effect of the added mass compared to the mass of the ship during the mooring procedure for a particular type of ship?” Measured angular frequencies of dolphin oscillations showed that the mathematical model can be approximated by the zero frequency limit. This simplifies the problem to some extent. The mooring is a pure rocking motion, and the 3D study is approximated by the strip theory approach. Moreover, the calculations were performed with conformal mapping using conformal Lewis mapping for the hull geometry. The fluid flow is assumed to be non-viscous, non-rotating and incompressible. The results showed that the additional mass effect must be taken into account when calculating the flexible dolphin loads.

FEM/BEM Simulation of Vibroacoustics of a Fluid-Loaded, Stiffened Plate Under Combined Force-Moment Excitation

2000 ◽  
Author(s):  
H. Zheng ◽  
C. Cai ◽  
G. R. Liu ◽  
K. Y. Lam
Keyword(s):  
Numerical Simulation ◽  
Acoustic Radiation ◽  
Normal Modes ◽  
Vibration Response ◽  
Structural Vibration ◽  
Stiffened Plate ◽  
Coupled Modes ◽  
Force Moment ◽  
Surrounding Fluid ◽  
Element Method

Abstract A numerical simulation of structural vibration and acoustic radiation is presented for a finite, fluid-loaded plate reinforced with two sets of orthotropic stiffeners. The attempt is to achieve a physical understanding of the dynamic behaviour and especially the acoustic radiation of the stiffened plate under combined force and moment excitations. Finite element method (FEM) is employed for calculation of the in-vacuo normal modes of the stiffened plate. The coupled modes with a heavy fluid (water), vibration response and acoustic radiation of the plate under given force and/or moment excitation are calculated using boundary element method (BEM). Numerical simulation results are detailed to address the significance of moment in combined force-moment excitations and, more importantly, the cancelling of the combined excitation in both structural vibration response and the associated acoustic radiation into the surrounding fluid.

An Investigation to Added Mass Force on the Wing of Insect Inspired from a Rigid Sphere Model

2012 ◽  
Vol 476-478 ◽  
pp. 2485-2488
Author(s):  
Mei Jun Hu ◽  
Xing Yao Yan ◽  
Jin Yao Yan
Keyword(s):  
Insect Flight ◽  
Aerodynamic Force ◽  
Mass Effect ◽  
Added Mass ◽  
Rigid Sphere ◽  
Force Model ◽  
Mass Force ◽  
Real Time Control ◽  
Wing Model ◽  
Force Peak

There is a force peak at the beginning of each stroke during the insect flight, this force peak contributes a lot to the total aerodynamic force. To build a man made insect inspired man-made micro aero vehicle, this force need to be considered in the aero force model, and this model should as simple as possible in order to be used in feedback real-time control. Here we presented a simplified model to take the medium added mass effect of the wing into account. Simulated results show a high force peak at the beginning of each stroke and are quite similar to the measured forces on the physical wing model which were carried out by Dickinson et.al.

scholarly journals Structural seismic characteristics assessment of LMFR fuel assembly hexagonal wrapper over operational temperature range

2019 ◽  
Vol 34 (4) ◽  
pp. 313-324
Author(s):  
M. Khizer ◽  
Zhang Yong ◽  
Yang Guowei ◽  
Wu Qingsheng ◽  
Wu Yican
Keyword(s):  
Fuel Assembly ◽  
Fast Reactor ◽  
Natural Frequencies ◽  
Mass Effect ◽  
Added Mass ◽  
Reactor Fuel ◽  
Temperature Range ◽  
Fast Reactor Fuel ◽  
Lead Bismuth Eutectic ◽  
Reactor Fuel Assembly

In this study, the structural integrity of liquid metal fast reactor fuel assembly has been established for different parameters considering the optimum fuel design. Analytical calculation of added mass effect due to lead bismuth eutectic and verification through previously presented theories, has been established. The integrity of the hexagonal wrapper of fuel assembly has been guaranteed over the entire operating temperature range. Effect of temperature on the density of lead bismuth eutectic, the subsequent change in added mass of lead bismuth eutectic, the effect on natural frequencies and effect on stresses on wrapper, has been studied in detail. A simple empirical relationship is presented for estimation of added mass effect for lead bismuth eutectic type fast reactors for any desired temperature. An approach for assessment of fast reactor fuel assembly performance has been outlined and calculated results are presented. Nuclear seismic rules require that systems and components which are important to safety, shall be capable of bearing earthquake effects and their integrity and functionality should be guaranteed. Mode shapes, natural frequencies, stresses on wrapper and seismic aspect has also been considered using ANSYS. Modal analysis has been compared in vacuum and lead bismuth eutectic using the calculated added mass.

scholarly journals INFLUENCE OF A LIQUID ON THE NATURAL FREQUENCIES OF ALMOST CIRCULAR PLATES

2014 ◽  
Vol 06 (05) ◽  
pp. 1450052 ◽  
Author(s):  
MANUEL GASCÓN-PÉREZ ◽  
PABLO GARCÍA-FOGEDA
Keyword(s):  
Dynamic Characteristics ◽  
Natural Frequencies ◽  
Vibration Mode ◽  
Normal Modes ◽  
Virtual Mass ◽  
Circular Plates ◽  
Hankel Transformation ◽  
Fluid System ◽  
Surrounding Fluid ◽  
Good Agreement

In this work, the influence of the surrounding fluid on the dynamic characteristics of almost circular plates is investigated. First the natural frequencies and normal modes for the plates in vacuum are calculated by a perturbation procedure. The method is applied for the case of elliptical plates with a low value of eccentricity. The results are compared with other available methods for this type of plates with good agreement. Next, the effect of the fluid is considered. The normal modes of the plate in vacuum are used as a base to express the vibration mode of the coupled plate-fluid system. By applying the Hankel transformation the nondimensional added virtual mass 2 increment (NAVMI) are calculated for elliptical plates. Results of the NAVMI factors and the effect of the fluid on the natural frequencies are given and it is shown that when the eccentricity of the plate is reduced to zero (circular plate) the known results of the natural frequencies for circular plates surrounded by liquid are recovered.

Bifurcation of Nonlinear Normal Modes by Means of Synge’s Stability

2011 ◽  
Author(s):  
Young S. Lee ◽  
Heng Chen
Keyword(s):  
Harmonic Balance ◽  
Coupled Oscillators ◽  
Normal Modes ◽  
Harmonic Balance Method ◽  
Orbital Stability ◽  
Nonlinear Normal Modes ◽  
Energy Transfers ◽  
Wide Range ◽  
Energy Domain ◽  
Nonlinear Normal

We study bifurcation of fundamental nonlinear normal modes (FNNMs) in 2-degree-of-freedom coupled oscillators by utilizing geometric mechanics approach based on Synges concept, which dictates orbital stability rather than Lyapunovs classical asymptotic stability. Use of harmonic balance method provides reasonably accurate approximation for NNMs over wide range of energy; and Floquet theory incorporated into Synges stability analysis predicts the respective bifurcation points as well as their types. Constructing NNMs in the frequency-energy domain, we seek applications to study of efficient targeted energy transfers.

Orbital angular momentum exchange in parametric down conversion

2006 ◽  
Vol 53 (5-6) ◽  
pp. 647-658 ◽  
Author(s):  
J. A. O. Huguenin ◽  
M. Martinelli ◽  
D. P. Caetano ◽  
B. Coutinho dos santos ◽  
M. P. Almeida ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Momentum Exchange ◽  
Parametric Down Conversion ◽  
Down Conversion
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