scholarly journals How a ball free to orbit in a circular track mitigates the galloping of a square prism

2021 ◽  
Author(s):  
Michael Selwanis ◽  
Guilherme Rosa Franzini ◽  
Cédric Béguin ◽  
Frédérick P. Gosselin
Keyword(s):  
Nonlinear Energy Sink ◽  
Effective Range ◽  
Low Flow ◽  
Small Range ◽  
Force Coefficient ◽  
Engineering Structures ◽  
Square Prism ◽  
Flow Speeds ◽  
Circular Track ◽  
Response Modes

Abstract Transverse galloping is a type of flow-induced vibration (FIV) that leads to critical design considerations for engineering structures. A purely nonlinear energy sink (NES) composed of a ball free to rotate in a circular track experimentally mitigated the galloping of a square in a previous study. The current study introduces a model for simulating the dynamics of the square prism coupled with a ball-in-track (BIT) NES and predicting the system behaviour at high flow speeds beyond the limits of the previously presented experiments. Numerical simulations employ the fitting of experimental data as inputs to define parameters. Wind tunnel static experiments provide the galloping force coefficient [[EQUATION]] relative to the prism angle of attack. Additionally, free rotation tests allow evaluating the ball damping coefficient [[EQUATION]] as a function of its mass and the NES track radius. The result of the rotation tests provides a critical angular speed beyond which the ball damping increases non-linearly. We point out the damping variation as an advantage of the BIT-NES; less damping at low angular velocities helps the ball start its rotation, while relatively large damping at higher speeds dissipates more energy from the vibrating system. Numerical results exhibit four response modes for the NES; oscillatory at low flow speeds, intermittent within a small range of higher flow speeds, rotational at higher flow speeds, and ineffective regime at flow speeds out of the NES effective range. Modelling the primary mass as a parametric excitation source for the NES provides an analytical estimation of the boundary between the oscillatory and intermittent regimes. Furthermore, we advance an analytical analysis of the power flow across the integrated prism-NES system to explain the NES behaviour and predict the limit of its effective range.

scholarly journals Wind tunnel demonstration of galloping mitigation with a purely nonlinear energy sink

2020 ◽  
Author(s):  
Michael Makram Selwanis ◽  
Guilherme Rosa Franzini ◽  
Cédric Béguin ◽  
Frederick Gosselin
Keyword(s):  
Transmission Lines ◽  
Oil And Gas ◽  
Nonlinear Energy Sink ◽  
Oil And Gas Industry ◽  
Low Flow ◽  
Radial Clearance ◽  
Small Range ◽  
Flow Speeds ◽  
Energy Sink ◽  
Nonlinear Energy

Galloping is a critical type of flow-induced vibration (FIV) arising on power transmission lines, high rise buildings, pipe and cables bundles in the oil and gas industry. In this paper, we present a purely nonlinear energy sink (NES) that mitigates the galloping of a square prism. The NES is composed of a ball rotating freely in a circular track attached to the prism. The ball’s dynamics is coupled to that of the prism in a purely nonlinear way by inertia. We experimentally assess how this simple NES reduces the prism vibration by comparing the prism amplitude responses with and without the NES. A supplementary video presents these experiments, during which the NES ball exhibits different dynamics in three regimes; oscillatory, intermittent, and rotational. We characterize the ball behaviour and its effect on the prism response in each regime. The oscillatory regime appears at low flow speeds at which both the prism and the ball oscillate with small amplitude. The intermittent regime represents a transition mode within a small range of flow speeds and corresponds to a small jump in the vibration amplitude of the prism. The rotational regime appears at higher flow speeds, where the ball oscillates with relatively high angular speeds resulting in a strong modulated response of the prism. The design of the NES allows to easily vary its track dimensions to use a ball of different sizes and masses. Accordingly, we demonstrate the influence of the main NES parameters, which are the ball mass, NES track radius, ball friction, and radial clearance between NES track walls and the rotating ball, on both the prism response and the ball behaviour. The NES we present is directly amenable to mitigate other types of FIV.

Creation and Maintenance of Cavities Under Horizontal Surfaces in Steady and Gust Flows

2009 ◽  
Vol 131 (11) ◽  
Author(s):  
R. E. A. Arndt ◽  
W. T. Hambleton ◽  
E. Kawakami ◽  
E. L. Amromin
Keyword(s):  
Experimental Data ◽  
Scaling Laws ◽  
Substantial Effect ◽  
Low Flow ◽  
Water Tunnel ◽  
Sectional Area ◽  
Cross Sectional ◽  
Air Supply ◽  
Wide Range ◽  
Flow Speeds

An experimental study of air supply to bottom cavities stabilized within a recess under a horizontal surface has been carried out in a specially designed water tunnel. The air supply necessary for creating and maintaining an air cavity in steady and gust flows has been determined over a wide range of speed. Flux-free ventilated cavitation at low flow speeds has been observed. Stable multiwave cavity forms at subcritical values of Froude number were also observed. It was found that the cross-sectional area of the air supply ducting has a substantial effect on the air demand. Air supply scaling laws were deduced and verified with the experimental data obtained.

scholarly journals Avalanche Flow Dynamics with Material Locking

1985 ◽  
Vol 6 ◽  
pp. 5-8 ◽  
Author(s):  
Theodore E. Lang ◽  
Tsutomu Nakamura ◽  
Jimmle D. Dent ◽  
Mario Martinelli
Keyword(s):  
Flow Model ◽  
Parameter Variation ◽  
Uniform Flow ◽  
Flow Dynamics ◽  
Low Flow ◽  
Snow Avalanches ◽  
Total Drag ◽  
Flow Equations ◽  
Flow Speeds ◽  
Avalanche Flow

Reported are results of incorporating recent snow avalanche processes into hydrodynamic uniform flow equations, used to model motion of snow avalanches. Actual modifications include the relating of dissipative coefficients of the flow model to slab release depth, the representation of the material as a locking fluid, and the mini-segmentation of the avalanche path at low flow speeds in order to numerically accomodate viscous transition and avalanche cessation of motion. The purpose in looking at different formulations of the uniform flow hydrodynamic flow equations is to reduce the variation in the drag coefficients when the theory is applied to different avalanche paths, as compared to what has been previous experience. The model that reduced parameter variation the most was one in which the total drag force decreased in an intermediate velocity range, a mechanism that has had recent experimental verification.

scholarly journals Avalanche Flow Dynamics with Material Locking

1985 ◽  
Vol 6 ◽  
pp. 5-8 ◽  
Author(s):  
Theodore E. Lang ◽  
Tsutomu Nakamura ◽  
Jimmle D. Dent ◽  
Mario Martinelli
Keyword(s):  
Flow Model ◽  
Parameter Variation ◽  
Uniform Flow ◽  
Flow Dynamics ◽  
Low Flow ◽  
Snow Avalanches ◽  
Total Drag ◽  
Flow Equations ◽  
Flow Speeds ◽  
Avalanche Flow

Reported are results of incorporating recent snow avalanche processes into hydrodynamic uniform flow equations, used to model motion of snow avalanches. Actual modifications include the relating of dissipative coefficients of the flow model to slab release depth, the representation of the material as a locking fluid, and the mini-segmentation of the avalanche path at low flow speeds in order to numerically accomodate viscous transition and avalanche cessation of motion. The purpose in looking at different formulations of the uniform flow hydrodynamic flow equations is to reduce the variation in the drag coefficients when the theory is applied to different avalanche paths, as compared to what has been previous experience. The model that reduced parameter variation the most was one in which the total drag force decreased in an intermediate velocity range, a mechanism that has had recent experimental verification.

The DSMC-IP Simulation of Microchannel Cross Flow Over a Staggered Array of Square Cylinders

2008 ◽  
Author(s):  
U. Kursun ◽  
J. Kapat
Keyword(s):  
Cross Flow ◽  
Direct Simulation Monte Carlo ◽  
Low Flow ◽  
Information Preservation ◽  
Square Cylinders ◽  
Flow Speeds ◽  
Characteristic Theory ◽  
Simulation Monte Carlo ◽  
Pressure Boundary Conditions ◽  
Statistical Noise

A numerical simulation is performed to study two-dimensional cross flow over a staggered array of square cylinders in a microchannel using the non-isothermal Information Preservation (IP) method. The IP method works concurrently with the Direct Simulation Monte Carlo (DSMC) eliminating statistical noise from the DSMC results at low flow speeds. Pressure boundary conditions at the inlet and outlet based on the characteristic theory implemented. This study will form a base for our future particle-atomistic hybrid computations.

Gas Separation Using a Membrane

2013 ◽  
Author(s):  
Nawaf Alkhamis ◽  
Ali Anqi ◽  
Dennis E. Oztekin ◽  
Abdulmohsen Alsaiari ◽  
Alparslan Oztekin
Keyword(s):  
Fluid Flows ◽  
Mass Separation ◽  
Dynamics Simulation ◽  
Low Flow ◽  
Navier Stokes ◽  
Functional Surface ◽  
Navier Stokes Equation ◽  
Partial Pressures ◽  
Flow Speeds ◽  
Turbulent Modeling

Computational fluid dynamics simulation will be conducted for multicomponent fluid flows in a channel containing spacers. The Navier-Stokes equation and the species transport equations are solved for various values of Reynolds numbers. The membrane will be modeled as a functional surface, where the membrane fluxes of each component will be determined based on the local partial pressures of each species, the permeability and the selectivity of the membrane. Laminar flow modeling is employed for the flow inside the channel without the spacers; while k-ω turbulent modeling is used to simulate the flow inside the channel with the spacer, for Re = 100, 150 and 200. The spacers are placed in an inline arrangement. The presence of spacers in the channel improves the membrane performance at Re = 200. The effects of the spacer on the separation process at low flow speeds (Re = 100 and 150) are negligible. The performance of the system will be measured by the maximum mass separation with minimal friction losses.

Lateral Vibration of a Pipe Conveying a Fluid

1968 ◽  
Vol 10 (3) ◽  
pp. 228-238 ◽  
Author(s):  
S. Naguleswaran ◽  
C. J. H. Williams
Keyword(s):  
Exact Solution ◽  
Fourier Series ◽  
Flow Speed ◽  
Low Flow ◽  
Lateral Vibration ◽  
Series Solutions ◽  
Axial Distribution ◽  
Axial Tension ◽  
Flow Speeds ◽  
Speed Prediction

The lateral vibration of a pipe conveying a fluid is investigated theoretically and experimentally. An exact solution for the natural frequency, axial distribution of phase and modal envelope is computed for a pinned-pinned, fixed-fixed and pinned-fixed span. Approximate one and two term Galerkin, Rayleigh-Ritz and Fourier series solutions are obtained and compared with the exact solution. It is found that a two term Galerkin or Rayleigh-Ritz solution is simple to evaluate and provides a good estimate of frequency and phase. The influence of axial tension and internal pressure is included. The experimental results are in agreement with theory at low flow speeds but show the difficulty of accurate buckling flow speed prediction.

The dynamics of waves at the interface between a viscoelastic coating and a fluid flow

1985 ◽  
Vol 158 ◽  
pp. 177-197 ◽  
Author(s):  
J. H. Duncan ◽  
A. M. Waxman ◽  
M. P. Tulin
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Strain Relaxation ◽  
Finite Thickness ◽  
Single Layer ◽  
Flow Speed ◽  
Low Flow ◽  
Shear Wave Speed ◽  
Flow Speeds ◽  
Layer Flow

The dynamics of two-dimensional uniform wavetrains on the interface between a viscoelastic compliant coating and a boundary-layer flow are explored theoretically. The coating is treated as a single-layer isotropic Voigt material of finite thickness that is bonded to a rigid half-space. The flow is modelled first by potential theory and then modified to incorporate pressure phase shifts and magnitudes found in boundary-layer flow over wavy walls. The consideration of viscoelastic effects has led to an important dimensionless damping parameter γt = Ct τt/d (where τt is the strain relaxation time, Ct is the elastic shear-wave speed and d is the layer depth) that seems to have been overlooked by experimentalists. The flow and the damping are found to have dramatic effects on wave propagation. Using flow pressure and material-damping parameters typical of experiments, the results show that both upstream- and downstream-propagating waves exist at low flow speeds. At higher flow speeds, shorter waves can no longer propagate upstream. At still higher velocities, two instabilities, ‘static divergence’ and ‘flutter’, are found. Static divergence occurs for flow speeds above 2.86Ct and consists of slow waves moving with speeds of about 0.02Ct. These results compare fairly well with published experimental data. Static divergence is found to be a damping instability for these coating systems. When the flow speed is increased further, the flutter instability appears consisting of waves with phase speeds about equal to Ct.

Higher Order Modal Response of Riser Fairings

2008 ◽  
Author(s):  
Henning Braaten ◽  
Halvor Lie ◽  
Kjetil Skaugset
Keyword(s):  
Cross Flow ◽  
Higher Order ◽  
Low Flow ◽  
Rotational Degree ◽  
Current Profile ◽  
Scaled Model ◽  
Work Related ◽  
Research Activities ◽  
Modal Response ◽  
Flow Speeds

Riser fairings are designed to rotate freely about the riser axis and to passively align with the direction of incident flow so they will effectively streamline the flow and eliminate VIV (Vortex-Induced Vibrations). This rotational degree of freedom introduces the possibility of a complex dynamic phenomenon involving coupling between the hydrodynamic forces and the fairing / riser motions (e.g. cross-flow translation and rotation). Slocum et al. reported a scaled model test of a long flexible riser model with a freely-rotating riser fairing conducted at MARINTEK at OTC-2004. At low flow speeds, the test showed the fairings to be effective. However, at higher towing velocities they became unstable resulting in high displacements at its first bending mode. This paper presents the work related to a study of effectiveness of fairings and is one of several VIV research activities NDP (Norwegian Deepwater Programme) has conducted at MARINTEK in 2002–2007. The present work is partly a follow up activity to the work reported by Slocum et al. The purpose of the present work was to study possible higher order modal response of faired risers and in particular to find out if such response can occur in higher bending modes than the first. A vertically towed instrumented riser was tested with 2 different fairing designs in uniform current profile with different towing speeds. Fairing II was identical to the one used in Slocum et al (2004) while Fairing I represents an alternative design. The riser model was 9.32m long, had diameter of 20mm and was flexible. Both bare riser configuration and full coverage of the two fairing sets were tested. This study documented first-, second- and third-mode responses at high amplitudes (instability behavior) for Fairing II. Tests with Fairing I showed that the riser was stable, but the riser vibrations were found to be similar with respect to displacement amplitudes and frequencies to the bare riser VIV.

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