Vortex-Induced Vibration Characteristics for a Three Dimensional Flexible Tube

2016 ◽  
Author(s):  
Zhipeng Feng ◽  
Fenggang Zang ◽  
Yixiong Zhang
Keyword(s):  
Dynamic Behavior ◽  
Dynamic Equilibrium ◽  
Lateral Displacement ◽  
Lift Coefficient ◽  
Three Dimensional ◽  
High Mass ◽  
Lower Branch ◽  
Vortex Induced Vibration ◽  
Flexible Tube ◽  
Lock In

In order to study the vortex-induced vibration, the three-dimensional unsteady, viscous, incompressible Navier-Stokes equation and LES turbulence model are solved with the finite volume approach, and the dynamic equilibrium equations are discretized by the finite element theory. A three-dimensional numerical model for flexible tube vibration induced by cross flow is proposed. The model realized the fluid-structure interaction with solving the fluid flow and the structure vibration simultaneously. Based on this model, the dynamic behavior and response characteristic of the tube are investigated. Meanwhile, the limit cycle and bifurcation of lift coefficient and displacement are analyzed. Amplitude response, trajectory, phase difference, fluid force coefficient and vortex shedding frequency are obtained. The results reveal that, a quasi-upper branch is found in the present fluid-flexible tube coupling system with high mass-damping and low mass ratio. The three-dimensional flexible tube has a broader synchronization range and the amplitude is higher than elastically mounted two-dimensional rigid tube. In the quasi-upper branch and lower branch regime, the “lock-in” begins. In quasi-upper branch, the lateral amplitude increases with reduced velocity increasing. While in lower branch, the amplitude keeps almost constant. The drag force reaches its peak value before lift. The lift coefficient reaches its maximum value at the switch from initial branch to quasi-upper branch. The phase angle reaches zero under “lock-in” and the dynamic behavior is a periodic motion. There is no bifurcation of lift coefficient and lateral displacement occurred in three dimensional flexible tube submitted to uniform turbulent flow.

Research on Cross Flow Induced Vibration of Flexible Tube Bundle

2017 ◽  
Author(s):  
Zhipeng Feng ◽  
Wenzheng Zhang ◽  
Yixiong Zhang ◽  
Fenggang Zang ◽  
Huanhuan Qi ◽  
...  
Keyword(s):  
Critical Velocity ◽  
Dynamic Equilibrium ◽  
Tube Bundle ◽  
Lift Coefficient ◽  
Three Dimensional ◽  
Cross Flow ◽  
Nonlinear Phenomena ◽  
Flow Induced Vibration ◽  
Navier Stokes Equation ◽  
Flexible Tube

When the elastic deformation of the tube bundle is considered, the interaction between the flow field and the structure becomes more complicated. In order to investigate the flow induced vibration (FIV) problems in flexible tube bundle, a numerical model for fluid-structure interaction system was presented firstly. The unsteady three-dimensional Navier-Stokes equation and LES turbulence model were solved with the finite volume approach on structured grids combined with the technique of dynamic mesh. The dynamic equilibrium equation was discretized according to the finite element theory. The configurations considered are tubes in a cross flow. Firstly, the flow-induced vibration of a single flexible tube under uniform turbulent flow are calculated when Reynolds number is 1.35× 104. The variety trends of lift, drag, displacement, vertex shedding frequency, phase difference of tube are analyzed under different frequency ratios. The nonlinear phenomena of locked-in, phase-switch are captured successfully. Meanwhile, the limit cycle and bifurcation of lift coefficient and displacement are analyzed using trajectory, phase portrait and Poincare sections. Secondly, the mutual interaction of two in-line flexible tubes is investigated. Different behaviors, bounded by critical distances between the tubes, critical velocity, and wake vortex pattern are highlighted. Finally, four tube bundle models were established to study the effect of the number of flexible tube on the FIV characteristics. Thanks to several calculations, the critical velocity of instability vibration and the effect of tube bundle configurations on fluid forces and dynamics were obtained successfully. It is therefore expected that further calculations, with model refinements and other validation studies, will bring valuable informations about bundle stability. Further comparisons with experiment are necessary to validate the behavior of the method in this configuration.

scholarly journals A Stochastic Rockfall Model Related to Random Ground Roughness Based on Three-Dimensional Discontinuous Deformation Analysis

2021 ◽  
Vol 9 ◽  
Author(s):  
Lu Zheng ◽  
Zhiyuan Zhu ◽  
Qi Wei ◽  
Kaihui Ren ◽  
Yihan Wu ◽  
...  
Keyword(s):  
Dynamic Behavior ◽  
Lateral Displacement ◽  
Grid Point ◽  
Slope Angle ◽  
Three Dimensional ◽  
Discontinuous Deformation Analysis ◽  
Cumulative Distribution ◽  
Deformation Analysis ◽  
Discontinuous Deformation ◽  
The Impact

The use of feasible 3-D numerical methods has become essential for addressing problems related to rockfall hazard. Although several models with various degrees of complexity are available, certain trajectories and impact dynamics related to some model inputs could fall in the rockfall observations area but are rarely calibrated against reflecting its range, especially the lateral deviations. A major difficulty exists in the lack of simulating the apparent randomness during the impact-rebound process leading to both ground roughness and block irregularities. The model presented here is based on three-dimensional discontinuous deformation analysis (3-D DDA). Despite similarities to previous simulations using 3-D DDA, the model presented here incorporates several novel concepts: (1) ground roughness is represented as a random change of slope angle by height perturbation at a grid point in DEM terrain; (2) block irregularities are modelled directly using polyhedron data; (3) a scaled velocity restitution relationship is introduced to consider incident velocity and its angle. Lateral deviations of rebound velocity, both direction and value, at impact are similarly accounted for by perturbing the ground orientation laterally, thus inducing scatter of run-out directions. With these features, the model is capable to describe the stochastic rockfall dynamics. In this study, 3-D DDA was then conducted to investigate the dynamic behavior of the rockfall and examine the role of sphericity of the rock block travelling on bench slopes with different ground roughness levels. Parametric analyses were carried out in terms of cumulative distribution function (CDF) to investigate for spatial distribution (both runout distance and lateral displacement), velocity and jumping height. The effects of block shape and ground roughness revealed by these factors were discussed. It suggests that ground roughness amplifies the randomness and plays important roles on the dynamic behavior of the system; irregularity from block sphericity will further amplify the randomness especially when the size of the rock is relatively small compared to the roughness level. Both irregularities should be taken into consideration in simulating rockfall problems. Further calibration of the new model against a range of field datasets is essential.

scholarly journals Influence of Frequency Ratio on the Hydroelastic Response of a Cylinder with Degrees of Freedom under Vortex Induced Vibration

2019 ◽  
Vol 8 (9S3) ◽  
pp. 307-312
Keyword(s):  
Natural Frequency ◽  
Frequency Ratio ◽  
Degrees Of Freedom ◽  
Structural Parameters ◽  
Lift Coefficient ◽  
Cross Flow ◽  
Vortex Induced Vibration ◽  
Ocean Environment ◽  
Hydroelastic Response ◽  
Lock In

Vortex induced vibration of cylindrical structures is an extensively researched topic. Most of the studies have concentrated on the response of the cylinder in the cross flow (CF) direction. In a realistic ocean environment, structures such as drilling and marine risers are more or less free to vibrate both in CF and in line (IL) directions. It has also been observed that the IL vibrations have significant influence on the CF response. Interaction between the responses in inline and cross flow directions has still been not fully understood. This paper addresses the same through a simplified numerical method for understanding the interaction between these two responses using two dimensional computational fluid dynamics (CFD) simulations. Here analyzes two cases have been considered; where in the cylinder is modeled with two different values of ratio of natural frequency of the cylinder in the IL direction to that in the CF direction. The trends of variation of hydrodynamic and structural parameters have been analyzed to comprehend the effect of directional natural frequency ratio on the cylinder response and hydrodynamic force coefficients. The shedding pattern has also been studied in this paper. An increase by 18% in the value of the lift coefficient and 38 % of that in the drag coefficient has been observed when the frequency ratio is increased from 1 to 2. The results show that the cylinder with frequency ratio 2 is more prone to lock in vibration. This phenomenon may be related to the shifting of shedding pattern from 2S to P + S mode when the frequency ratio is 2.

Vortex-Induced Vibration of Horizontal Circular Cylinder in Uniform Flow

2004 ◽  
Author(s):  
Kentaroh Kokubun ◽  
Yasuhiro Wada
Keyword(s):  
Natural Frequency ◽  
Lift Coefficient ◽  
Vertical Displacement ◽  
Peak Frequency ◽  
Uniform Flow ◽  
Vortex Induced Vibration ◽  
Vortex Shedding Frequency ◽  
Nonlinear Form ◽  
Shedding Frequency ◽  
Lock In

This paper treats Vortex-Induced Vibration (VIV) of a cylinder in uniform flow. The cylinder is aluminum, rigid, circular, and 0.490 m in length, 0.025 m in diameter, and its weight is counterbalanced by buoyancy. The cylinder is horizontally mounted in a two-dimensional tank and allowed to move vertically by hanging through a spring during towing. The equation of motion of the structure is described in the nonlinear form and an approximate solution of the equation is obtained by using a vibrational theory. Lock-in phenomena appear when the vortex shedding frequency approaches to the natural frequency of the structure. Experimental results show that the oscillation of structure has remarkable two frequencies corresponding to the shedding frequency and the natural frequency of the structure. By using amplitude of vertical displacement at the top peak frequency, this paper proposes a way of estimating the transverse force, i.e., lift coefficient during VIV. The estimated lift coefficients are similar to the measured lift coefficients with the vertical displacement restricted to be zero. The estimated lift coefficients seem to be feasible.

Experimental Investigation of Vortex Induced Vibration of Cross Flow Response for a Flexible Cable Under Uniform Current

2020 ◽  
Author(s):  
Prethiv Kumar R ◽  
S. Nallayarasu
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Strouhal Number ◽  
Lateral Displacement ◽  
Lift Coefficient ◽  
Strain Gauges ◽  
Vortex Induced Vibration ◽  
Flexible Cable ◽  
Wide Range ◽  
Uniform Current

Abstract Vortex Induced Vibration (VIV) of slender cylindrical structures subjected to uniform flow is subject interest since the use of such elements is common in the offshore and naval industry. The numerical and experimental investigation of VIV for slender, flexible cable member in uniform current has been carried out in this study. The experiments were conducted in a towing tank of 85 m length and 2.8 m water depth mounted with the facility to control speed, The carriage has a range of velocity up to 5 m/s. A flexible cable of diameter 15 mm with an aspect ratio of approximately 100 has been used for the present study. The lateral displacement of cable has been measured using the strain gauges mounted along the length. The strain gauges measure the axial strain due to lateral bending of the cable and in turn, converted to lateral displacement. Experiments were carried out for a wide range of Reynolds number (Re) ranging from 3000 to 15000. From the measured responses, the Strouhal number (St) is back calculated. It is observed that the Strouhal number for flexible cable ranges from 0.13 to 0.17 for low Reynolds number from 3000 to 15000 and it falls within the expected range. The normalized RMS displacements (RMS A/D) have been obtained for specified range of Re. The lift coefficient (CL) attains a stable value of around 0.10 to 0.25 for reduced velocity (Vr) greater than 5.33 for different locations. The lift coefficient follows a similar trend along the span for different Vr. Numerical simulation has been carried out using Shear7 software with results matching reasonably well.

scholarly journals Direct coherent multi-ink printing of fabric supercapacitors

2021 ◽  
Vol 7 (3) ◽  
pp. eabd6978 ◽  
Author(s):  
Jingxin Zhao ◽  
Hongyu Lu ◽  
Yan Zhang ◽  
Shixiong Yu ◽  
Oleksandr I. Malyi ◽  
...  
Keyword(s):  
System Integration ◽  
High Performance ◽  
Mechanical Stability ◽  
Three Dimensional ◽  
High Mass ◽  
Wearable Electronics ◽  
Energy Storage Devices ◽  
Fabrication Procedure ◽  
Self Powered ◽  
Mechanical Devices

Coaxial fiber-shaped supercapacitors with short charge carrier diffusion paths are highly desirable as high-performance energy storage devices for wearable electronics. However, the traditional approaches based on the multistep fabrication processes for constructing the fiber-shaped energy device still encounter persistent restrictions in fabrication procedure, scalability, and mechanical durability. To overcome this critical challenge, an all-in-one coaxial fiber-shaped asymmetric supercapacitor (FASC) device is realized by a direct coherent multi-ink writing three-dimensional printing technology via designing the internal structure of the coaxial needles and regulating the rheological property and the feed rates of the multi-ink. Benefitting from the compact coaxial structure, the FASC device delivers a superior areal energy/power density at a high mass loading, and outstanding mechanical stability. As a conceptual exhibition for system integration, the FASC device is integrated with mechanical units and pressure sensor to realize high-performance self-powered mechanical devices and monitoring systems, respectively.

Dynamic Stall Simulation of Flow Over NACA0012 Airfoil at 1 Million Reynolds Number

2015 ◽  
Author(s):  
Venkata Ravishankar Kasibhotla ◽  
Danesh Tafti
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Lift Coefficient ◽  
Three Dimensional ◽  
Dynamic Stall ◽  
Sharp Drop ◽  
Airfoil Surface ◽  
Naca0012 Airfoil ◽  
Reduced Frequency ◽  
Edge Vortex

The paper is concerned with the prediction and analysis of dynamic stall of flow past a pitching NACA0012 airfoil at 1 million Reynolds number based on the chord length of the airfoil and at reduced frequency of 0.25 in a three dimensional flow field. The turbulence in the flow field is resolved using large eddy simulations with the dynamic Smagorinsky model at the sub grid scale. The development of dynamic stall vortex, shedding and reattachment as predicted by the present study are discussed in detail. This study has shown that the downstroke phase of the pitching motion is strongly three dimensional and is highly complex, whereas the flow is practically two dimensional during the upstroke. The lift coefficient agrees well with the measurements during the upstroke. However, there are differences during the downstroke. The computed lift coefficient undergoes a sharp drop during the start of the downstroke as the convected leading edge vortex moves away from the airfoil surface. This is followed by a recovery of the lift coefficient with the formation of a secondary trailing edge vortex. While these dynamics are clearly reflected in the predicted lift coefficient, the experimental evolution of lift during the downstroke maintains a fairly smooth and monotonic decrease in the lift coefficient with no lift recovery. The simulations also show that the reattachment process of the stalled airfoil is completed before the start of the upstroke in the subsequent cycle due to the high reduced frequency of the pitching cycle.

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