Experimental Study on the Dynamics of Four Flexible Cylinders in Square Arrangement Subjected to Uniform Cross-Flow

2012 ◽  
Author(s):  
Bijan Sanaati ◽  
Naomi Kato
Keyword(s):  
Amplitude Ratio ◽  
Lift Coefficient ◽  
Cross Flow ◽  
Mass Ratio ◽  
Drag Forces ◽  
Low Mass ◽  
Drag And Lift ◽  
Low Mass Ratio ◽  
Lift And Drag ◽  
Four Cylinders

Groups of cylinders can be found in many engineering fields such as marine and civil applications. The behaviors of the group cylinders can be very complex because it undergoes the mutual effects of adjacent cylinders arranged in different positions. In this paper, we present the results of a study on the dynamics of a group of flexible cylinders in square arrangements along with a single (isolated) cylinder subjected to uniform cross-flow (CF). Four cylinders of the same size, properties, and pretensions were tested in two configurations with different centre-to-centre separations. Horizontal and vertical separations were 2.75D & 2.75D and 5.50D & 2.75D for the first and second configurations, respectively. The tandem (horizontal) separations between the downstream and upstream cylinders, i.e., 2.75D and 5.5D, correspond to the reattachment and co-shedding regimes, respectively. Vertical separation, i.e., 2.75 was chosen in a range where the side-by-side cylinders can have proximity interference. Reynolds number ranged from 1400 to 20000 (subcritical regime). The parameter of reduced velocity reached up to 19. The aspect ratio of all the cylinders was 162 (length/diameter). Mass ratio (cylinders mass/displaced water) is 1.17, a low mass ratio. The amplitude ratio of the CF vibration of the downstream cylinders, hydrodynamic force coefficients including mean and fluctuating components of the drag and lift forces, and frequency responses for both CF and inline (IL) directions were analyzed. All the cylinders excited up to the second and fourth mode of vibrations for CF and IL directions, respectively. Mean drag coefficient of the upstream cylinders are almost twice those of the downstream cylinders at high reduced velocities. The mean lift coefficient is much higher for the upstream cylinders than the downstream cylinders with a negative value. Obvious IL and CF lock-in regions exist for all four cylinders at low reduced velocities. Among the four cylinders, the upper downstream cylinder shows the least and the most fluctuating lift and drag forces, respectively. The IL and CF frequencies of the downstream cylinders are much lower than those of the upstream ones and the single cylinder.

Hydroelasticity of Four Flexible Cylinders in Square Arrangement Subjected to Uniform Cross-Flow

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
Bijan Sanaati ◽  
Naomi Kato
Keyword(s):  
Hydrodynamic Force ◽  
Amplitude Ratio ◽  
Lift Coefficient ◽  
Cross Flow ◽  
Mass Ratio ◽  
Subcritical Regime ◽  
Frequency Responses ◽  
The Mean ◽  
Drag And Lift ◽  
Fourth Mode

Groups of cylinders can be found in many engineering fields such as marine and civil applications. The behavior of the group cylinders can be very complex because it undergoes the mutual effects of adjacent cylinders arranged in different positions. In this paper, the results of a study on the dynamics of a group of flexible cylinders in square arrangements along with a single (isolated) cylinder subjected to uniform cross-flow (CF) are presented. Four flexible cylinders of the same size, properties, and pretensions were tested in two configurations with different center-to-center separations. Reynolds number ranged from 1400 to 20,000 (subcritical regime).The parameter of reduced velocity reached up to 19. The aspect ratio of all the cylinders was 162 (length/diameter). Mass ratio (cylinders mass/displaced water) was 1.17. The amplitude ratio of the CF vibration of the downstream cylinders, hydrodynamic force coefficients including mean and fluctuating components of the drag and lift forces, tension variation of the downstream cylinder, and frequency responses in both CF and inline (IL) directions were analyzed. All the cylinders excited up to the second and fourth mode of vibrations for CF and IL directions, respectively. Mean drag coefficient of the upstream cylinders are almost twice those of the downstream cylinders. The mean lift coefficient is much higher for the upstream cylinders than the downstream cylinders with different positive and negative signs. The IL and CF frequencies of the downstream cylinders are lower than those of the upstream ones and the single cylinder.

Vibration Excitation Forces in a Normal Triangular Tube Bundle Subjected to Two-Phase Cross Flow

2011 ◽  
Author(s):  
E. S. Perrot ◽  
N. W. Mureithi ◽  
M. J. Pettigrew ◽  
G. Ricciardi
Keyword(s):  
Tube Bundle ◽  
Cross Flow ◽  
Random Excitation ◽  
Two Phase ◽  
Constant Frequency ◽  
Fluid Forces ◽  
Drag Forces ◽  
Wide Range ◽  
Drag And Lift ◽  
Lift And Drag

This paper presents test results of vibration forces in a normal triangular tube bundle subjected to air-water cross-flow. The dynamic lift and drag forces were measured with strain gage instrumented cylinders. The array has a pitch-to-diameter ratio of 1.5, and the tube diameter is 38 mm. A wide range of void fraction and fluid velocities were tested. The experiments revealed significant forces in both the drag and lift directions. Constant frequency and quasi-periodic fluid forces were found in addition to random excitation. These forces were analyzed and characterized to understand their origins. The forces were found to be dependent on the position of the cylinder within the bundle. The results are compared with those obtained with flexible cylinders in the same tube bundle and to those for a rotated triangular tube bundle. These comparisons reveal the influence of quasi-periodic forces on tube motions.

Towing Tank Experiments on the Vortex-Induced Vibrations of a Long Flexible Cylinder in a Stepped Current

2013 ◽  
Author(s):  
Francisco J. Huera-Huarte ◽  
Zafar A. Bangash ◽  
Leo M. González
Keyword(s):  
Cross Flow ◽  
External Diameter ◽  
Flexible Cylinder ◽  
Towing Tank ◽  
Supporting Structure ◽  
Drag Forces ◽  
Vortex Induced Vibrations ◽  
Curvature Measurements ◽  
Low Mass ◽  
Low Mass Ratio

We describe recent results showing the dynamic response, excited by vortex shedding, of a long flexible cylinder subject to a stepped current. The experiments were conducted at the Naval Architecture Department towing tank of the Technical University of Madrid (UPM) during March 2012. The tank is 100 m long with a cross-section of 3.8 × 2.5 m, and it is able to deliver speeds over 4 m/s. A supporting structure was designed in order to provide support for a 3 m long cylinder with an external diameter of 19 mm. The cylinder was instrumented with strain gauges providing curvature measurements in the in-line and the cross-flow directions at 11 locations along its length. Tension and drag forces were also measured at both ends of the model. More than 50 runs were conducted with the cylinder being placed vertically having its lower 65% length under the water free surface, connected to the structure by means of universal joints. The supporting structure allowed to configure different top end conditions and to apply different top tensions. Tests were conducted for Reynolds numbers as high as 34000. The cylinder had a low flexural stiffness and very low mass ratio m* of 0.67. Fundamental natural frequencies were in the range from about 4 to 7.9 Hz, and the cylinder responded in modes up to the third cross-flow. In this article we will describe the experiments and the instrumentation used, the modal tests conducted and the results obtained during the experiments.

Characteristics of the Flow-Induced Vibration and Forces With 1- and 2-DOF Vibrations and Limiting Solid-to-Fluid Density Ratios

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Osama A. Marzouk
Keyword(s):  
Density Ratio ◽  
Fluid Motion ◽  
Cross Flow ◽  
Fluid Density ◽  
Flow Induced Vibration ◽  
Drag Forces ◽  
Wide Range ◽  
Low Mass ◽  
Lift And Drag ◽  
Density Ratios

We studied various characteristics of the flow-induced vibration (FIV) of a spring-mounted cylinder, and the fluctuating lift and drag forces exerted on the cylinder due to the periodic changes in the fluid motion and vortex structure. We compared two conditions, which represent the limiting cases for the solid-to-fluid density ratio: the cylinder density is negligible relative to the fluid density, and the fluid density is negligible relative to the cylinder density. For both conditions, we examined the changes in these characteristics over a wide range of nondimensional mass-damping for one degree of freedom (1-DOF, cross-flow) and 2-DOF (cross-flow and in-line) vibration. The four cases exhibit differences (especially at low mass-damping) but also have some similarities in the characteristics of the FIV, induced forces, and energy extraction from the flow. We examined these differences and similarities, the implied errors when the in-line DOF is neglected, and the feasibility of using a single mass-damping parameter to describe the FIV.

Towing Tank Experiments on the Vortex-Induced Vibrations of a Flexible Cylinder With Wake Interference

2014 ◽  
Author(s):  
Francisco J. Huera-Huarte ◽  
Zafar A. Bangash ◽  
Leo M. Gonzalez
Keyword(s):  
Cross Flow ◽  
External Diameter ◽  
Flexible Cylinder ◽  
Towing Tank ◽  
Supporting Structure ◽  
Drag Forces ◽  
Vortex Induced Vibrations ◽  
Curvature Measurements ◽  
Low Mass ◽  
Low Mass Ratio

We describe recent results showing the dynamic response, excited by vortex shedding, of a long flexible cylinder subject to a stepped current immersed in the wake of another cylinder, placed upstream in tandem configuration. Experiments were conducted at the E.T.S.I. Navales towing tank of the Technical University of Madrid during March 2012. The tank is 80 m long with a cross-section of 4 × 2.5 m. A supporting structure was designed in order to provide support for a 3 m long cylinder with an external diameter of 16 mm. The cylinder was instrumented with strain gauges providing curvature measurements in the in-line and the cross-flow directions at 11 locations along its length. Tension and drag forces were also measured at both ends of the model. For these experiments, the upstream rigid cylinder was made stationary by fixing it at both ends, and it was located at different centre to centre distances. More than 200 runs were conducted, with its lower 65% length under the water free surface, connected to the structure by means of universal joints. The supporting structure allowed to configure different top end conditions and to apply different top tensions. Tests were conducted with speeds up to 1.4 m/s. The cylinder had a low flexural stiffness of 6.04 Nm2 and low mass ratio of 2.7. Fundamental natural frequencies were in the range from about 2.3 to 6.2 Hz, and the cylinder responded in modes up to the third cross-flow.

scholarly journals Photometric Analysis of Wide and Narrow Hα Band Observations of R Canis Majoris

1992 ◽  
Vol 151 ◽  
pp. 303-306
Author(s):  
M. Taghi Edalati ◽  
Timothy Banks ◽  
Edwin Budding
Keyword(s):  
Hot Spot ◽  
Optimal Estimate ◽  
Mass Ratio ◽  
Transfer Effects ◽  
Photometric Analysis ◽  
Index Variation ◽  
Algol System ◽  
Low Mass ◽  
Low Mass Ratio ◽  
Optimisation Technique

Wide and narrow Hα lightcurves of R CMa were analysed using Wilson-Devinney (WD) and Information Limit Optimisation Technique (ILOT) approaches. A range of mass ratios, tested by both methods, led to an optimal estimate of around 0.45, at variance with the spectroscopic value. The distortion on the light curve affects the modelling, and so, in a second fitting, this was represented by a ‘hot spot’, associated with mass transfer effects. A semi-detached configuration was then derived. This is supported by the form of the Hα index variation, which has also been modelled. Although thus appearing as a ‘classical Algol’ system, R CMa retains its inherent peculiarity of low mass ratio with low period, which cannot be reconciled with conservative evolution scenarios.

scholarly journals Marginally low mass ratio close binary system V1191 Cyg

New Astronomy ◽  
2012 ◽  
Vol 17 (1) ◽  
pp. 46-49 ◽  
Author(s):  
B. Ulaş ◽  
B. Kalomeni ◽  
V. Keskin ◽  
O. Köse ◽  
K. Yakut
Keyword(s):  
Binary System ◽  
Close Binary System ◽  
Close Binary ◽  
Mass Ratio ◽  
Low Mass ◽  
Low Mass Ratio

scholarly journals Two Contact Binaries with Mass Ratios Close to the Minimum Mass Ratio

2021 ◽  
Vol 922 (2) ◽  
pp. 122
Author(s):  
Kai Li ◽  
Qi-Qi Xia ◽  
Chun-Hwey Kim ◽  
Shao-Ming Hu ◽  
Di-Fu Guo ◽  
...  
Keyword(s):  
Gyration Radius ◽  
Mass Ratio ◽  
Mass Ratios ◽  
Contact Binaries ◽  
Contact Binary ◽  
Low Mass ◽  
Ratio Limit ◽  
Low Mass Ratio ◽  
Diagram Analysis

Abstract The cutoff mass ratio is under debate for contact binaries. In this paper, we present the investigation of two contact binaries with mass ratios close to the low mass ratio limit. It is found that the mass ratios of VSX J082700.8+462850 (hereafter J082700) and 1SWASP J132829.37+555246.1 (hereafter J132829) are both less than 0.1 (q ∼ 0.055 for J082700 and q ∼ 0.089 for J132829). J082700 is a shallow contact binary with a contact degree of ∼19%, and J132829 is a deep contact system with a fill-out factor of ∼70%. The O − C diagram analysis indicated that the two systems manifested long-term period decreases. In addition, J082700 exhibits a cyclic modulation which is more likely resulting from the Applegate mechanism. In order to explore the properties of extremely low mass ratio contact binaries (ELMRCBs), we carried out a statistical analysis on contact binaries with mass ratios of q ≲ 0.1 and discovered that the values of J spin/J orb of three systems are greater than 1/3. Two possible explanations can interpret this phenomenon. One explanation is that some physical processes, unknown to date, are not considered when Hut presented the dynamic stability criterion. The other explanation is that the dimensionless gyration radius (k) should be smaller than the value we used (k 2 = 0.06). We also found that the formation of ELMRCBs possibly has two channels. The study of evolutionary states of ELMRCBs reveals that their evolutionary states are similar with those of normal W UMa contact binaries.

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