scholarly journals Investigation and Control of VIVs with Multi-Lock-in Regions on Wide Flat Box Girders

2017 ◽  
Vol 2017 ◽  
pp. 1-17 ◽  
Author(s):  
Bo Wu ◽  
Liangliang Zhang ◽  
Yang Yang ◽  
Lianjie Liu ◽  
Haohong Li
Keyword(s):  
Slenderness Ratio ◽  
Ventilation Rate ◽  
Control Mechanisms ◽  
Box Girders ◽  
Eddy Simulation ◽  
Vortex Induced Vibrations ◽  
Control Schemes ◽  
Large Eddy ◽  
Lock In ◽  
And Control

On the preliminary designing of a wide flat box girder with the slenderness ratio 12, vertical and torsional vortex-induced vibrations (VIV) are observed in wind tunnel tests. More than one lock-in region, which are defined as“multi-lock-in regions,”are recorded. Therefore, suspicions should be aroused regarding the viewpoint that wide box girders are aerodynamic friendly. As the three nascent vortexes originating at the pedestrian guardrails and inspection rails shed to near-wake through different pathways with different frequencies, the mechanisms of VIVs and multi-lock-in regions are analyzed to be determined by the inappropriate subsidiary structures. A hybrid method combiningLarge Eddy Simulation(LES) with experimental results is introduced to study the flow-structure interactions (FSI) when undergoing VIVs; the vortex mode of torsional VIV on wide flat box girders is defined as “4/2S,” which is different from any other known ones. Based on the mechanism of VIV, a new approach by increasing ventilation rate of the pedestrian guardrails is proved to be effective in suppressing vertical and torsional VIVs, and it is more feasible than other control schemes. Then, the control mechanisms are deeper investigated by analyzing the evolution of vortex mode and FSI using Hybrid-LES method.

Wind-Driven Natural Ventilation in an Areaway-Attached Basement with a Single-Sided Opening for Residential Purposes

2011 ◽  
Vol 383-390 ◽  
pp. 5344-5349
Author(s):  
Zhen Bu
Keyword(s):  
Natural Ventilation ◽  
Ventilation Rate ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Effective Ventilation ◽  
The Mean ◽  
Ventilation Rates ◽  
Les Model ◽  
Good Agreement

This paper discusses the sustainability of the areaway-attached basement concept with the attentions focused on wind-driven single-sided natural ventilation. First, numerical simulations were performed on an areaway-attached basement with a single-sided opening. Two CFD approaches: Reynolds averaged Navier-Stokes (RANS) and large-eddy simulation (LES) were used and compared with the previous experimental results of effective ventilation rate. A good agreement between the measurement and LES model was found and RANS model tends to underestimate the ventilation rates. Furthermore, Based on LES with the inflow turbulent fluctuations, the mean airflow patterns within and around the areaway-attached basement was investigated for different wind incidence angles to examine the influences of wind direction on ventilation performances.

Analysis of Unsteady Hydrodynamics Related to Vortex Induced Vibrations on Bluff-Bodied Offshore Structure

2017 ◽  
Author(s):  
Mandar Tabib ◽  
Adil Rasheed ◽  
Franz Georg Fuchs
Keyword(s):  
Drag Coefficient ◽  
Vortex Shedding ◽  
Pulsation Frequency ◽  
Offshore Structure ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Vortex Induced Vibrations ◽  
Shedding Frequency ◽  
Lock In ◽  
Inflow Conditions

Flows around a fixed cylinder with uniform and pulsating inflow conditions at different Reynolds numbers are simulated using Large Eddy Simulation (LES). For pulsating inflow, a sinusoidal profile, with an amplitude ΔU and a pulsation frequency fe, is superimposed onto the mean velocity U∞ at the inlet plane. The current study reveals that the pulsation can influence flow-physics in three possible ways as compared to uniform inflow conditions: (a) The vortex shedding pattern is seen to be more asymmetric for pulsating inflow than for uniform inflow. This needs to be validated with an experimental campaign devoted to the study of flow-asymmetricity due to pulsatile and uniform flow condition. (b) The dominant shedding frequency fd gets locked with respect to the frequency of the pulsating inflow fe, (for both the turbulent and transition regime) at a ratio of fe/fs0 equivalent to 0.65 – 0.75 (where fs0 is the vortex shedding frequency for uniform inflow) and ε = ΔU / (2πfeD) ≈ 0.2, where D is the diameter of the cylinder. This numerical observation is validated using the experimentally observed turbulent vortex regime work ( [1])in this range. For conditions with fe/fs0 > 0.75 the lock-in may happen at fe/2. (c) Compared to uniform inflow, the pulsating inflow leads to a larger drag coefficient. The drag coefficient is influenced by the ratios fe/fs0 and ΔU / U∞.

LES Analysis of Flows Around a Forced-Oscillating Circular Cylinder

2007 ◽  
Author(s):  
Norikazu Sato ◽  
Mitsuyoshi Kawakami ◽  
Masahide Inagaki
Keyword(s):  
Circular Cylinder ◽  
Arbitrary Lagrangian Eulerian ◽  
Frequency Range ◽  
Central Difference ◽  
Eddy Simulation ◽  
Quick Scheme ◽  
Large Eddy ◽  
Lock In ◽  
Lower Frequency Region ◽  
Good Agreement

Large eddy simulation (LES) of flows around a forcedoscillating circular cylinder is carried out using the Arbitrary Lagrangian-Eulerian (ALE) method and a central difference scheme for the convection terms, which is a newly proposed discretization scheme that improves the conservation properties of the mass, momentum, and especially kinetic energy. The results are compared with the measurements that are also carried out by authors, in terms of lock-in phenomenon. It is shown that the numerically predicted pressure and velocity distributions are in good agreement with the experimental data, both in the lower and the upper lock-in region, and the phase difference between the cylinder displacement and the vortex shedding is consistent with previous findings. In addition, it is clarified that the frequency range of the lock-in in LES is almost the same in width as that of the experiment, while it becomes wider in the comparative analysis, in which the QUICK scheme is employed for the convection terms. Such discrepancies between two calculations are prominent, especially in the stationary and the lower frequency region.

scholarly journals Unstructured Large Eddy Simulation Technology for Prediction and Control of Jet Noise

2010 ◽  
Author(s):  
Yaser Khalighi ◽  
Frank Ham ◽  
Parviz Moin ◽  
Sanjiva K. Lele ◽  
Tim Colonius ◽  
...  
Keyword(s):  
High Speed ◽  
Performance Metrics ◽  
Experimental Testing ◽  
Jet Noise ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Prediction And Control ◽  
Internal Mixer ◽  
And Control ◽  
Nozzle Thrust

Development of concepts for reduction of jet noise has relied heavily on expensive experimental testing of various nozzle designs. For example, the design of nozzle serrations (chevron) and internal mixer/ejector nozzles have relied largely on laboratory and full-scale testing. Without a deeper understanding of the sources of high-speed jet noise it is very difficult to effectively design configurations that reduce the noise and maintain other performance metrics such as nozzle thrust. In addition, the high complexity of the flow limits the success of a parametric black-box optimization.

scholarly journals Measurement of Vertical Kinetic Energy and Vertical Velocity Skewness in Oceanic Boundary Layers by Imperfectly Lagrangian Floats

2010 ◽  
Vol 27 (11) ◽  
pp. 1918-1935 ◽  
Author(s):  
Ramsey R. Harcourt ◽  
Eric A. D’Asaro
Keyword(s):  
Boundary Layer ◽  
Vertical Velocity ◽  
Fluid Velocity ◽  
Vertical Position ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy ◽  
And Control ◽  
Neutrally Buoyant ◽  
Mean Variance

Abstract The effects of upward buoyancy on the accuracy with which Lagrangian floats can measure the Eulerian mean variance 〈ww〉E and skewness SwE of vertical fluid velocity w in the wind-driven upper-ocean boundary layer is investigated using both simulated floats in large-eddy simulation (LES) models and two float datasets. Nearly neutrally buoyant floats are repeatedly advected by the turbulent velocities across the boundary layer. Their vertical position Z is determined from pressure measurements; their W variance 〈WW〉F and skewness SWE are determined from the time series of float W = dZ/dt. If the float buoyancy is small, then the simulated floats measure the Eulerian velocity accurately; that is, δW2 = 〈WW〉F − 〈ww〉E and δSW = SWF − SwE are small compared to 〈ww〉E and SwE respectively. If the floats are buoyant, and thus have an upward vertical velocity Wbias relative to the water, then δW2 and δSW can become significant. Buoyancy causes the floats to oversample both shallow depths and strong vertical velocities, leading to positive values of δW2 and negative values of δSW. The skewness SZ′F of depth measures the degree to which shallow depths are oversampled; it is shown to be a good predictor of Wbias/〈WW〉F1/2, δW2/〈WWF〉, and δSW/SWF over a wide range of float buoyancies and boundary layer forcings. Float data collected during two deployments confirm these results, but averaging times of several float days are typically required to obtain stable statistics. Significant differences in the magnitude of the effect may occur between datasets from different ocean forcing regimes and float designs. Other measures of float buoyancy are also useful predictors. These results can be used to correct existing float measurements of 〈ww〉E for the effects of buoyancy and also can be used as a means to operationally assess and control float buoyancy.

scholarly journals Large Eddy Simulation of Flow Pasta Twisted Cylinder

2020 ◽  
Vol 7 ◽  
Keyword(s):  
Passive Control ◽  
Careful Analysis ◽  
Spanwise Direction ◽  
Spiral Pattern ◽  
Eddy Simulation ◽  
Vortex Induced Vibrations ◽  
Large Eddy ◽  
Swirling Strength ◽  
The Mean ◽  
Effect Of Surface

The wavy cylinder has a sinusoidal variation incross sectional area along the spanwise direction and the twistedcylinder has been newly designed by rotating the elliptic crosssection along the spanwise direction, so that the cylinder surfacehas a twisted spiral pattern. A twisted cylinder is investigated toobserve the effect of twisted spiral pattern of the flow fields. Itguarantees the accuracy of the present numerical methods thatthe excellent comparisons with previous studies for the cases of asmooth circular cylinder. The effect of surface torsion which isnewly designed in here has been predicted and assessed in termsof the mean drag and root-mean-square (RMS) value offluctuating lift at the subcritical Reynolds number of 3000.Subsequently, the mechanisms of enhancing the aerodynamicperformance and passive control of vortex-induced vibrations arealso investigated by careful analysis with the flow structures. Theiso-surface of swirling strength has been imposed to identify thevortical structures in the turbulent wake

Vortex Induced Vibration Analysis of Twin Box Girders by Means of Computational Fluid Dynamics

2014 ◽  
Vol 638-640 ◽  
pp. 1012-1017
Author(s):  
Qing Liang Zhan ◽  
Zhi Yong Zhou ◽  
Ting Yang ◽  
Yao Jun Ge
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Time History ◽  
Box Girders ◽  
Vibration Displacement ◽  
Vortex Induced Vibration ◽  
Eddy Simulation ◽  
Cfd Models ◽  
History Of ◽  
Lock In

This paper analyzes the vortex induced vibration (VIV) phenomena of twin box bridge girders by means of 2D computational fluid dynamics (CFD) models. The modeling of turbulence follows a methodology known as large eddy simulation (LES) in which the large scales of turbulence are resolved, while the small ones are modeled by means of sub-grid-models. The dynamic response of structure in relation to the fluid is solved by embedding the code of Newmark-β method in user defined functions of Fluent. The time history of girder’s vibration displacement is obtained successfully, which agrees well with the experiment results of wind tunnel tests. “Lock-in”, “beat” phenomena and the displacement “detuning” phenomena in the locked field are also gained.

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