scholarly journals Numerical Study on Wave Induced Flow Field around a Vibrant Monopile Regarding Cross-Sectional Shape

2019 ◽  
Vol 3 (2) ◽  
pp. 1-9 ◽  
Author(s):  
Mohammad Mohammad Beigi Kasvaei ◽  
◽  
Mohammad Hossein Kazeminezhad ◽  
Abbas Yeganeh-Bakhtiary ◽  
◽  
...  
Keyword(s):  
Flow Field ◽  
Numerical Study ◽  
Cross Sectional ◽  
Induced Flow ◽  
Sectional Shape ◽  
Wave Induced

Study of Correctly Expanded Sonic Jet with Air Tabs

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Arun Prasad R ◽  
Thanigaiarasu S ◽  
Sembaruthi M ◽  
Rathakrishnan E
Keyword(s):  
Numerical Study ◽  
Cross Sectional ◽  
Potential Core ◽  
Convergent Nozzle ◽  
Jet Mixing ◽  
Pressure Profiles ◽  
Constant Diameter ◽  
Sonic Jet ◽  
Sectional Shape ◽  
Length Reduction

AbstractThe present numerical study is to understand the effect of air tabs located at the exit of a convergent nozzle on the spreading and mixing characteristics of correctly expanded sonic primary jet. Air tabs used in this study are two secondary jets issuing from constant diameter tubes located diametrically opposite at the periphery of the primary nozzle exit, normal to the primary jet. Two air tabs of Mach numbers 1.0 to 1.4, in steps of 0.1 are considered in this study. The mixing modification caused by air tabs are analysed by considering the mixing of uncontrolled (free) primary jet as a reference. Substantial enhancement in jet mixing is achieved with Mach 1.4 air tabs, which results in 80 % potential core length reduction. The total pressure profiles taken on the plane (YZ) normal to the primary jet axis, at various locations along the primary jet centreline revealed the modification of the jet cross sectional shape by air tabs. The stream-wise vortices and bifurcation of the primary jet caused by air tabs are found to be the mechanism behind the enhanced jet mixing.

scholarly journals Numerical Study of the Velocity Decay of Offset Jet in a Narrow and Deep Pool

Water ◽  
2018 ◽  
Vol 11 (1) ◽  
pp. 59 ◽  
Author(s):  
Xin Li ◽  
Maolin Zhou ◽  
Jianmin Zhang ◽  
Weilin Xu
Keyword(s):  
Flow Field ◽  
Numerical Study ◽  
Expansion Ratio ◽  
Sudden Expansion ◽  
Mean Velocity ◽  
Cross Sectional ◽  
Potential Core ◽  
Early Region ◽  
Flow Development ◽  
Offset Jet

The present study examines the configuration of an offset jet issuing into a narrow and deep pool. The standard k-ε model with volume-of-fluid (VOF) method was used to simulate the offset jet for three exit offset ratios (OR = 1, 2 and 3), three expansion ratios (ER = 3, 4 and 4.8), and different jet exits (circular and rectangular). The results clearly show significant effects of the circumference of jet exits (Lexit) in the early region of flow development, and a fitted formula is presented to estimate the length of the potential core zone (LPC). Analysis of the flow field for OR = 1 showed that the decay of cross-sectional streamwise maximum mean velocity (Um) in the transition zone could be fitted by power law with the decay rate n decreased from 1.768 to 1.197 as the ER increased, while the decay of Um for OR = 2 or 3 was observed accurately estimated by linear fit. Analysis of the flow field of circular offset jet showed that Um for OR = 2 decayed fastest due to the fact that the main flow could be spread evenly in floor-normal direction. For circular jets, the offset ratio and expansion ratio do not affect the spread of streamwise velocity in the early region of flow development. It was also observed that the absence of sudden expansion of offset jet is analogous to that of a plane offset jet, and the flow pattern is different.

scholarly journals Modeling and Fuzzy PDC Control and Its Application to an Oscillatory TLP Structure

2010 ◽  
Vol 2010 ◽  
pp. 1-13 ◽  
Author(s):  
Cheng-Wu Chen
Keyword(s):  
Fuzzy Logic ◽  
Flow Field ◽  
Fuzzy Logic Controller ◽  
Separation Of Variables ◽  
Design Procedure ◽  
System Structure ◽  
Mathematical Framework ◽  
Control Force ◽  
Induced Flow ◽  
Wave Induced

An analytical solution is derived to describe the wave-induced flow field and surge motion of a deformable platform structure controlled with fuzzy controllers in an oceanic environment. In the controller design procedure, a parallel distributed compensation (PDC) scheme is utilized to construct a global fuzzy logic controller by blending all local state feedback controllers. The Lyapunov method is used to carry out stability analysis of a real system structure. The corresponding boundary value problems are then incorporated into scattering and radiation problems. These are analytically solved, based on the separation of variables, to obtain a series of solutions showing the harmonic incident wave motion and surge motion. The dependence of the wave-induced flow field and its resonant frequency on wave characteristics and structural properties including platform width, thickness and mass can thus be drawn with a parametric approach. The wave-induced displacement of the surge motion is determined from these mathematical models. The vibration of the floating structure and mechanical motion caused by the wave force are also discussed analytically based on fuzzy logic theory and the mathematical framework to find the decay in amplitude of the surge motion in the tension leg platform (TLP) system. The expected effects of the damping in amplitude of the surge motion due to the control force on the structural response are obvious.

Effect of Deterministic Asperity Geometry on Hydrodynamic Lubrication

2004 ◽  
Vol 126 (3) ◽  
pp. 527-534 ◽  
Author(s):  
Ravinder B. Siripuram ◽  
Lyndon S. Stephens
Keyword(s):  
Friction Coefficient ◽  
Cross Sections ◽  
Numerical Study ◽  
Hydrodynamic Lubrication ◽  
Leakage Rate ◽  
Area Fraction ◽  
Cross Sectional ◽  
Constant Height ◽  
Sectional Shape ◽  
The Impact

This paper presents a numerical study of the effects of different shapes of deterministic microasperities in sliding surface lubrication when hydrodynamic films are found. Positive (protruding) and negative (recessed) asperities of constant height (depth) are considered with circular, square, diamond, hexagonal and triangular cross-sections. Of particular interest is the impact of asperity/cavity cross-sectional geometry on friction and leakage, which has importance in sealing applications. The results indicate that the friction coefficient is insensitive to asperity/cavity shape, but quite sensitive to the size of the cross-section. By contrast, leakage rates are found to be quite sensitive to both cross-sectional shape and size, with triangular asperities giving the smallest leakage rate and square asperities giving a largest leakage rate. The minimum coefficient of friction for all shapes is found to occur at an asperity area fraction of 0.2 for positive asperities and 0.7 for negative asperities. Finally, the results indicate the existence of a critical asperity area fraction where the performance curves for positive and negative asperities cross over. These cross-over points are identified for friction coefficient and leakage rate.

Numerical Simulation of Flow Field Around a Circular-Bladed Butterfly Wind Turbine

2015 ◽  
Author(s):  
Yutaka Hara ◽  
Takahiro Sumi ◽  
Yuhei Matsubara ◽  
Yoshiyuki Yasumoto
Keyword(s):  
Flow Field ◽  
Wind Turbine ◽  
Three Dimensional ◽  
Vertical Axis ◽  
Dynamic Stall ◽  
Speed Ratio ◽  
Half Cycle ◽  
Cross Sectional ◽  
Tip Vortices ◽  
Sectional Shape

Three-dimensional computational fluid dynamics (3D-CFD) was performed to simulate the flow field around an aluminum circular-blade butterfly wind turbine, which is a vertical-axis-type turbine with four circular blades and a diameter of 2.06 m. Under the assumption of a loss factor of 0.8 due to a generator and an AC–DC converter, the CFD results agreed with the experimental results. Although tip vortices were observed at the top and bottom portions of the blades, the vorticity intensity was weaker than that of the straight-blade rotor case. In addition, the cross-sectional shape of the tip vortices seemed to be elliptical for circular blades rather than circular as for straight blades. As the tip speed ratio was less than 2, vortices arising from dynamic stall at maximum-radius portions of blades were observed at the downwind half-cycle as well as the upwind half-cycle. A feature of the vortices shed from a circular blade at the downwind half-cycle was the looped shape.

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