scholarly journals Computational and Experimental Assessment of Turbulence Stimulation on Flow Induced Motion of a Circular Cylinder

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Omer Kemal Kinaci ◽  
Sami Lakka ◽  
Hai Sun ◽  
Ethan Fassezke ◽  
Michael M. Bernitsas
Keyword(s):  
University Of Michigan ◽  
Amplitude Response ◽  
Turbulence Control ◽  
Marine Renewable Energy ◽  
Vortex Induced Vibrations ◽  
Highly Nonlinear ◽  
Invaluable Tool ◽  
Induced Motion ◽  
The University ◽  
Passive Turbulence Control

Vortex-induced vibrations (VIVs) are highly nonlinear and it is hard to approach the problem analytically or computationally. Experimental investigation is therefore essential to address the problem and reveal some physical aspects of VIV. Although computational fluid dynamics (CFDs) offers powerful methods to generate solutions, it cannot replace experiments as yet. When used as a supplement to experiments, however, CFD can be an invaluable tool to explore some underlying issues associated with such complicated flows that could otherwise be impossible or very expensive to visualize or measure experimentally. In this paper, VIVs and galloping of a cylinder with selectively distributed surface roughness—termed passive turbulence control (PTC)—are investigated experimentally and computationally. The computational approach is first validated with benchmark experiments on smooth cylinders available in the literature. Then, experiments conducted in the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan are replicated computationally to visualize the flow and understand the effects of thickness and width of roughness strips placed selectively on the cylinder. The major outcomes of this work are: (a) Thicker PTC initiates earlier galloping but wider PTC does not have a major impact on the response of the cylinder and (b) The amplitude response is restricted in VIV due to the dead fluid zone attached to the cylinder, which is not observed in galloping.

Selective Surface Roughness to Suppress Flow-Induced Motion of Two Circular Cylinders at 30,000 < Re < 120,000

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Hongrae Park ◽  
Michael M. Bernitsas ◽  
Eun Soo Kim
Keyword(s):  
Surface Roughness ◽  
Amplitude Ratio ◽  
Flow Direction ◽  
Circular Cylinders ◽  
University Of Michigan ◽  
Marine Renewable Energy ◽  
Vortex Induced Vibrations ◽  
Smooth Cylinder ◽  
Induced Motion ◽  
The University

In the Marine Renewable Energy Laboratory of the University of Michigan, selectively located surface roughness has been designed successfully to suppress vortex-induced vibrations (VIV) of a single cylinder by 60% compared to a smooth cylinder. In this paper, suppression of flow-induced motions of two cylinders in tandem using surface roughness is studied experimentally by varying flow velocity and cylinder center-to-center spacing. Two identical rigid cylinders suspended by springs with their axes perpendicular to the flow are allowed one degree of freedom motion transverse to the flow direction. Surface roughness is applied in the form of four roughness strips helically placed around the cylinder. Results are compared to smooth cylinders also tested in this work. Amplitude ratio A/D, frequency ratio fosc/fn,water, and range of synchronization are measured. Regardless of the center-to-center cylinder distance, the amplitude response of the upstream smooth cylinder is similar to that of an isolated smooth cylinder. The wake from the upstream cylinder with roughness is narrower and longer and has significant influence on the amplitude of the downstream cylinder. The latter is reduced in the initial and upper branches while its range of VIV-synchronization is extended. Galloping is suppressed in both cylinders. In addition, the amplitude of the upstream rough cylinder and its range of synchronization increase with respect to the isolated rough cylinder.

Selective Surface Roughness to Suppress Flow-Induced Motion of Two Circular Cylinders at 30,000

2013 ◽  
Author(s):  
Hongrae Park ◽  
Michael M. Bernitsas ◽  
Eun Soo Kim
Keyword(s):  
Surface Roughness ◽  
Amplitude Ratio ◽  
Flow Direction ◽  
Circular Cylinders ◽  
University Of Michigan ◽  
Marine Renewable Energy ◽  
Vortex Induced Vibrations ◽  
Smooth Cylinder ◽  
Induced Motion ◽  
The University

In the Marine Renewable Energy Laboratory of the University of Michigan, selectively located surface roughness has been designed successfully to suppress vortex-induced vibrations of a single cylinder by 60% compared to a smooth cylinder. In this paper, suppression of flow-induced motions of two cylinders in tandem using surface roughness is studied experimentally by varying flow velocity and cylinder center-to-center spacing. The two identical cylinders are rigid, suspended by springs, and allowed to move transversely to the flow direction and their own axis. Surface roughness is applied in the form of four roughness strips helically placed around the cylinder. Results are compared to smooth cylinders also tested in this work. Amplitude ratio A/D, frequency ratio fosc/fn,water, and range of synchronization are measured. Regardless of the center-to-center cylinder distance, the amplitude response of the upstream smooth-cylinder is similar to that of the isolated smooth-cylinder. The wake from the upstream cylinder with roughness is narrower and longer and has significant influence on the amplitude of the downstream cylinder. The latter is reduced in the initial and upper branches while its range of VIV-synchronization is extended. In addition the amplitude of the upstream rough cylinder and its range of synchronization increase with respect to the isolated rough cylinder.

Map of Passive Turbulence Control to Flow-Induced Motions for a Circular Cylinder at 30,000

2013 ◽  
Author(s):  
Hongrae Park ◽  
Michael M. Bernitsas ◽  
Che-Chun Chang
Keyword(s):  
Circular Cylinder ◽  
Amplitude Ratio ◽  
Damping Ratio ◽  
Water Channel ◽  
University Of Michigan ◽  
Strong Suppression ◽  
Variable Parameters ◽  
Turbulence Control ◽  
The University ◽  
Passive Turbulence Control

Passive turbulence control (PTC) in the form of two straight roughness strips with variable width, and thickness about equal to the boundary layer thickness, is used to modify the flow-induced motions (FIM) of a rigid circular cylinder. The cylinder is supported by two end-springs and the flow is in the TrSL3, high-lift, regime. The PTC-to-FIM Map, developed in previous work, revealed zones of weak suppression, strong suppression, hard galloping, and soft galloping. In this paper the sensitivity of the PTC-to-FIM Map to: (a) the width of PTC covering, (b) PTC covering a single or multiple zones, (c) PTC being straight or staggered is studied experimentally. Experiments are conducted in the Low Turbulence Free Surface Water Channel of the University of Michigan. Fixed parameters are: cylinder diameter D = 8.89cm, m* = 1.725, spring stiffness K = 763N/m, aspect ratio l/D = 10.29, and damping ratio ζ = 0.019. Variable parameters are: circumferential PTC location αPTC ∈ [0°−180°], Reynolds number Re ∈ [30,000–120,000], flow velocity U ∈ [0.36m/s–1.45m/s]. Measured quantities are: amplitude ratio A/D, frequency ratio fosc/fn,w, and synchronization range. As long as the roughness distribution is limited to remain within a zone, the width of the strips does not affect the FIM response. When multiple zones are covered, the strong suppression zone dominates the FIM.

scholarly journals Virtual Spring–Damping System for Flow-Induced Motion Experiments

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Hai Sun ◽  
Eun Soo Kim ◽  
Marinos P. Bernitsas ◽  
Michael M. Bernitsas
Keyword(s):  
First Generation ◽  
Closed Loop ◽  
Hydrodynamic Force ◽  
Circular Cross Section ◽  
Data Generation ◽  
University Of Michigan ◽  
Hydrokinetic Energy ◽  
Vortex Induced Vibrations ◽  
Induced Motion ◽  
The University

Flow-induced motion (FIM) experiments of a single circular cylinder or multiple cylinders in an array involve several configuration and hydrodynamic parameters, such as diameter, mass, damping, stiffness, spacing, Reynolds number, and flow regime, and deviation from circular cross section. Due to the importance of the FIM both in suppression for structural robustness and in enhancement for hydrokinetic energy conversion, systematic experiments are being conducted since the early 1960s and several more decades of experimentation are required. Change of springs and dampers is time consuming and requires frequent recalibration. Emulating springs and dampers with a controller makes parameter change efficient and accurate. There are two approaches to this problem: The first involves the hydrodynamic force in the closed-loop and is easier to implement. The second called virtual damping and spring (Vck) does not involve the hydrodynamic force in the closed-loop but requires an elaborate system identification (SI) process. Vck was developed in the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan for the first time in 2009 and resulted in extensive data generation. In this paper, the second generation of Vck is developed and validated by comparison of the FIM experiments between a Vck emulated oscillator and an oscillator with physical springs and dampers. The main findings are: (a) the Vck system developed keeps the hydrodynamic force out of the control-loop and, thus, does not bias the FIM, (b) The controller-induced lag is minimal and significantly reduced compared to the first generation of Vck built in the MRELab due to use of an Arduino embedded board to control a servomotor instead of Labview, (c) The SI process revealed a static, third-order, nonlinear viscous model but no need for dynamic terms with memory, and (d) The agreement between real and virtual springs and dampers is excellent in FIM including vortex-induced vibrations (VIVs) and galloping measurements over the entire range of spring constants and velocities tested (16,000 < Re < 140,000).

RANS Simulation vs. Experiments of Flow Induced Motion of Circular Cylinder With Passive Turbulence Control at 35,000

2011 ◽  
Author(s):  
Wei Wu ◽  
Michael M. Bernitsas ◽  
Kevin Maki
Keyword(s):  
Circular Cylinder ◽  
Amplitude Ratio ◽  
Cylinder Wall ◽  
Turbulence Control ◽  
Induced Motion ◽  
High Reynolds ◽  
Vortex Patterns ◽  
Cylinder Flow ◽  
The University ◽  
Passive Turbulence Control

Two-dimensional RANS equations with the Spalart-Allmaras turbulence model are used to simulate the flow and body kinematics of a rigid circular cylinder mounted on springs, transversely to a steady uniform flow in the high-lift, TrSL3 regime with 35,000<Re<130,000. Passive Turbulence Control (PTC) in the form of selectively distributed surface roughness is used to alter the cylinder Flow Induced Motion (FIM). Simulation is performed by using a solver based on the open source CFD tool OpenFOAM, which solves continuum mechanics problems with a finite volume discretization method. Roughness parameters of PTC are simulated modeling tests conducted in the Marine Renewable Energy Lab (MRELab) of the University of Michigan. The numerical tool is first tested on smooth cylinder in VIV and results are compared with available experimental measurements and RANS simulations. For the cylinder with PTC cases, the sandpaper grit (k) on the cylinder wall is modeled as a rough-wall boundary condition. Two sets of cases with different system parameters (spring constant, damping) are simulated and the results are compared with experimental data measured in the MRELab. The amplitude-ratio curve shows clearly three different branches, including the VIV initial and upper branches and a galloping branch, similar to those observed experimentally. Frequency ratio, vortex patterns, transitional behavior, and lift are also predicted well for PTC cylinders at such high Reynolds numbers.

Sensitivity to Zone Covering of the Map of Passive Turbulence Control to Flow-Induced Motions for a Circular Cylinder at 30,000 ≤ Re ≤ 120,000

2017 ◽  
Vol 139 (2) ◽  
Author(s):  
Hongrae Park ◽  
Eun Soo Kim ◽  
Michael M. Bernitsas
Keyword(s):  
Circular Cylinder ◽  
Amplitude Ratio ◽  
Damping Ratio ◽  
Water Channel ◽  
University Of Michigan ◽  
Strong Suppression ◽  
Turbulence Control ◽  
Ann Arbor ◽  
The University ◽  
Passive Turbulence Control

Passive turbulence control (PTC) in the form of two straight roughness strips with variable width, and thickness about equal to the boundary layer thickness, is used to modify the flow-induced motions (FIM) of a rigid circular cylinder. The cylinder is supported by two end springs and the flow is in the TrSL3, high-lift, regime. The PTC-to-FIM Map, developed in the previous work, revealed zones of weak suppression (WS), strong suppression (SS), hard galloping (HG), and soft galloping (SG). In this paper, the sensitivity of the PTC-to-FIM map to: (a) the width of PTC covering, (b) PTC covering a single or multiple zones, and (c) PTC being straight or staggered is studied experimentally. Experiments are conducted in the low turbulence free surface water channel of the University of Michigan, Ann Arbor, MI. Fixed parameters are: cylinder diameter D = 8.89 cm, m* = 1.725, spring stiffness K = 763 N/m, aspect ratio l/D = 10.29, and damping ratio ζ = 0.019. Variable parameters are circumferential PTC location αPTC∈ (0–180 deg), Reynolds number Re ∈ (30,000–120,000), flow velocity U∈ (0.36–1.45 m/s). Measured quantities are amplitude ratio A/D, frequency ratio fosc/fn,w, and synchronization range. As long as the roughness distribution is limited to remain within a zone, the width of the strips does not affect the FIM response. When multiple zones are covered, the strong suppression zone dominates the FIM.

Hydrokinetic Energy Harnessing Using the VIVACE Converter With Passive Turbulence Control

2011 ◽  
Author(s):  
Che-Chun Chang ◽  
Michael M. Bernitsas
Keyword(s):  
Turbulent Shear ◽  
Motion Mechanism ◽  
Turbulence Control ◽  
Hydrokinetic Energy ◽  
Turbulent Shear Layer ◽  
Induced Motion ◽  
Layer Flow ◽  
Set Up ◽  
Energy Harnessing ◽  
Passive Turbulence Control

Passive turbulence control (PTC) in the form of selectively applied surface roughness is used on a rigid circular cylinder supported by two end-springs in transverse steady flow. The flow-induced motions are enhanced dramatically reaching the limits of the experimental facility and motion mechanism at amplitude to diameter ratio A/D ≅ 3. In comparison to a smooth cylinder, in the fully turbulent shear layer flow regime at Reynolds number on the order of 100,000, PTC initiates VIV earlier at reduce velocity U* ≅ 4, reduces VIV amplitude depending on damping, and initiates galloping at U* ≅ 10 rather than 20. Thus, back-to-back VIV and galloping are achieved expanding the synchronization range of Flow Induced Motion (FIM) beyond U* ≅ 15 and the capabilities of the experimental set-up. The harnessed horizontal hydrokinetic power increased by a factor of four due to increased velocities in the synchronization range without any adjustment of the motion mechanism particulars.

Multicylinder Flow-Induced Motions: Enhancement by Passive Turbulence Control at 28,000

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
Eun Soo Kim ◽  
Michael M. Bernitsas ◽  
R. Ajith Kumar
Keyword(s):  
High Amplitude ◽  
Field Of View ◽  
Flow Structures ◽  
Complex Flow ◽  
Turbulence Control ◽  
Marine Renewable Energy ◽  
Amplitude Spectra ◽  
Parameter Ranges ◽  
Passive Turbulence Control ◽  
Center Distance

The VIVACE converter was introduced at OMAE2006 as a single, smooth, circular-cylinder module. The hydrodynamics of VIVACE is being improved continuously to achieve higher density in harnessed hydrokinetic power. Intercylinder spacing and passive turbulence control (PTC) through selectively located roughness are effective tools in enhancement of flow induced motions (FIMs) under high damping for power harnessing. Single cylinders harness energy at high density even in 1 knot currents. For downstream cylinders, questions were raised on energy availability and sustainability of high-amplitude FIM. Through PTC and intercylinder spacing, strongly synergetic FIMs of 2/3/4 cylinders are achieved. Two-cylinder smooth/PTC, and three/four-cylinder PTC systems are tested experimentally. Using the “PTC-to-FIM” map developed in previous work at the Marine Renewable Energy Laboratory (MRELab), PTC is applied and cylinder response is measured for inflow center-to-center distance 2D-5D (D = diameter), transverse center-to-center distance 0.5–1.5 D, Re ε [28,000–120,000], m* ε [1.677–1.690], U ε [0.36–1.45 m/s], aspect ratio l/D = 10.29, and m*ζ ε [0.0283–0.0346]. All experiments are conducted in the low turbulence free surface water (LTFSW) channel of MRELab. Amplitude spectra and broad field-of-view (FOV) visualization help reveal complex flow structures and cylinder interference undergoing VIV, interference/ proximity/wake/soft/hard galloping. FIM amplitudes of 2.2–2.8D are achieved for all cylinders in steady flow for all parameter ranges tested.

scholarly journals Prediction of Dynamic Responses of Flow-Induced Vibration Using Deep Learning

2021 ◽  
Vol 11 (15) ◽  
pp. 7163
Author(s):  
Gi-yong Kim ◽  
Chaeog Lim ◽  
Eun Soo Kim ◽  
Sung-chul Shin
Keyword(s):  
Experimental Data ◽  
Electrical Energy ◽  
Clean Energy ◽  
Flow Speed ◽  
Dynamic Responses ◽  
University Of Michigan ◽  
Flow Induced Vibration ◽  
Marine Renewable Energy ◽  
The University ◽  
Good Agreement

Flow-induced vibration (FIV) is a phenomenon in which the flow passing through a structure exerts periodic forces on the structure. Most studies on FIVs focus on suppressing this phenomenon. However, the Marine Renewable Energy Laboratory (MRELab) at the University of Michigan, USA, has developed a technology called the vortex-induced vibration for aquatic clean energy (VIVACE) converters that reinforces FIV and converts the energy in tidal currents to electrical energy. This study introduces the experimental data of the VIVACE converter and the associated method using deep neural networks (DNNs) to predict the dynamic responses of the converter. The DNN was trained and verified with experimental data from the MRELab, and the findings show that the amplitudes and frequencies of a single cylinder in the FIV predicted by the DNN under various test conditions were in good agreement with the experimental data. Finally, based on both the predicted and experimental data, the optimal power envelope of the VIVACE converter was generated as a function of the flow speed. The predictions using DNNs are expected to be more accurate as they can be trained with more experimental data in the future and will help to substantially reduce the number of experiments on FIVs.

Computational and Experimental Assessment of Turbulence Stimulation on Flow Induced Motion of Circular Cylinder

2015 ◽  
Author(s):  
Omer Kemal Kinaci ◽  
Sami Lakka ◽  
Hai Sun ◽  
Michael M. Bernitsas
Keyword(s):  
Parametric Design ◽  
Fluid Dynamic ◽  
Circular Cylinders ◽  
Design Parameters ◽  
Turbulence Control ◽  
Hydrokinetic Energy ◽  
Flow Features ◽  
Induced Motion ◽  
Marine Hydrokinetic ◽  
The University

In the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan, Flow Induced Motion (FIM) is studied as a means to convert marine hydrokinetic energy to electricity using the VIVACE energy harvester [1–4]. Turbulence stimulation in the form of sand-strips, referred to as Passive Turbulence Control (PTC), were added to oscillating cylinders in 2008 [5]. PTC enabled VIVACE to harness hydrokinetic energy from currents/tides over the entire range of FIM including VIV and galloping. In 2011, the MRELab produced experimentally the PTC-to-FIM Map defining the induced cylinder motion based on the location of PTC [6]. In 2013, the robustness of the map was tested and dominant zones were identified [7]. Even though the PTC-to-FIM Map has become a powerful tool in inducing specific motions of circular cylinders, several parameters remain unexplored. Experiments, though the ultimate verification tool, are time consuming and hard to provide all needed information. A computational tool that could predict the FIM of a cylinder correctly would be invaluable to study the full parametric design space. A major side-benefit of PTC was the fact that PTC enabled computational fluid dynamic (CFD) simulations to generate results in good agreement with experiments by forcing the location of the separation point [8]. This valuable tool, along with experiments, is used in this paper to investigate PTC design parameters such as width and thickness and their impact on flow features with the intent of maximizing FIM and, thus, hydrokinetic energy conversion.

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