A van der Pol–Duffing Oscillator Model of Hydrodynamic Forces on Canonical Structures

2009 ◽  
Vol 4 (4) ◽  
Author(s):  
Imran Akhtar ◽  
Osama A. Marzouk ◽  
Ali H. Nayfeh
Keyword(s):  
Duffing Oscillator ◽  
Lift Coefficient ◽  
Elliptic Cylinder ◽  
Oscillator Model ◽  
Van Der Pol ◽  
Drag Forces ◽  
Model Match ◽  
Computational Fluid Dynamics Cfd ◽  
The Time Domain ◽  
Lift And Drag

Numerical simulations of the flow past elliptic cylinders with different eccentricities have been performed using a parallel incompressible computational fluid-dynamics (CFD) solver. The pressure is integrated over the surface to compute the lift and drag forces on the cylinders. The numerical results of different cases are then used to develop reduced-order models for the lift and drag coefficients. The lift coefficient is modeled with a generalized van der Pol–Duffing oscillator and the drag coefficient is expressed in terms of the lift coefficient. The parameters in the oscillator model are computed for each elliptic cylinder. The results of the model match the CFD results not only in the time domain but also in the spectral domain.

scholarly journals Aerodynamic Analysis of a Flapping Wing Aircraft for Short Landing

2020 ◽  
Vol 10 (10) ◽  
pp. 3404
Author(s):  
Bing Ji ◽  
Zenggang Zhu ◽  
Shijun Guo ◽  
Si Chen ◽  
Qiaolin Zhu ◽  
...  
Keyword(s):  
Aerodynamic Characteristics ◽  
Flapping Wing ◽  
Aerodynamic Analysis ◽  
Drag Forces ◽  
Wing Model ◽  
Aerodynamic Model ◽  
Computational Fluid Dynamics Cfd ◽  
The Difference ◽  
Cfd Method ◽  
Lift And Drag

An investigation into the aerodynamic characteristics has been presented for a bio-inspired flapping wing aircraft. Firstly, a mechanism has been developed to transform the usual rotation powered by a motor to a combined flapping and pitching motion of the flapping wing. Secondly, an experimental model of the flapping wing aircraft has been built and tested to measure the motion and aerodynamic forces produced by the flapping wing. Thirdly, aerodynamic analysis is carried out based on the measured motion of the flapping wing model using an unsteady aerodynamic model (UAM) and validated by a computational fluid dynamics (CFD) method. The difference of the average lift force between the UAM and CFD method is 1.3%, and the difference between the UAM and experimental results is 18%. In addition, a parametric study is carried out by employing the UAM method to analyze the effect of variations of the pitching angle on the aerodynamic lift and drag forces. According to the study, the pitching amplitude for maximum lift is in the range of 60°~70° as the flight velocity decreases from 5 m/s to 1 m/s during landing.

Numerical Analysis of Flow Over the NASA Common Research Model Using the Academic Computational Fluid Dynamics Code Galatea

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Georgios N. Lygidakis ◽  
Ioannis K. Nikolos
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Numerical Analysis ◽  
Computational Study ◽  
Research Model ◽  
Drag Forces ◽  
Efficient Prediction ◽  
Wind Tunnel Data ◽  
Computational Fluid Dynamics Cfd ◽  
Lift And Drag

A recently developed academic computational fluid dynamics (CFD) code, named Galatea, is used for the computational study of fully turbulent flow over the NASA common research model (CRM) in a wing-body configuration with and without horizontal tail. A brief description of code's methodology is included, while attention is mainly directed toward the accurate and efficient prediction of pressure distribution on wings' surfaces as well as of computation of lift and drag forces against different angles of attack, using an h-refinement approach and a parallel agglomeration multigrid scheme. The obtained numerical results compare close with both the experimental wind tunnel data and those of reference solvers.

scholarly journals Aerodynamic Performance of Biomimicry Snake-Shaped Airfoil

2019 ◽  
Vol 9 (2) ◽  
pp. 3319-3323
Keyword(s):  
Cross Section ◽  
Lift Coefficient ◽  
Design Parameters ◽  
Drag Forces ◽  
Cross Section Shape ◽  
Section Shape ◽  
Wide Range ◽  
Lift And Drag ◽  
Drag Ratio ◽  
Lift To Drag Ratio

The cross-section shape and proportionality between geometrical dimensions are the most important design parameters of any lifting surfaces. These parameters affect the amount of the aerodynamic forces that will be generated. In this study, the focus is placed on the snake-cross-section airfoil known as the S-airfoil. It is found that there is a lack of available researches on S-airfoil despite its important characteristics. A parametric study on empty model of the S-airfoil with a cross-section shape that is inspired by the Chrysopelea paradise snake is conducted through numerical simulation. Simulation using 2D-ANSYS FLUENT17 software is used to generate the lift and drag forces to determine the performance of airfoil aerodynamic. Based on the results, the S-airfoil can be improved in performance of aerodynamic by reducing the thickness at certain range, whereby changing the thickness-to-chord ratio from 0.037 to 0.011 results in the increment of lift-to-drag ratio from 2.629 to 3.257. On other hand, increasing the height-to-chord ratio of the S-airfoil will increase maximum lift coefficient but drawback is a wide range of angles of attack regarding maximum lift-to-drag ratio. Encouraging results obtained in this study draws attention to the importance of expanding the research on S-airfoil and its usage, especially in wind energy.

The Study on Flow Past a Static Hydrofoil Using Deep Neural Network

2020 ◽  
Author(s):  
Xia Wu ◽  
Xinliang Tian ◽  
Yufeng Kou ◽  
Xin Li ◽  
Wenyue Lu
Keyword(s):  
Prediction Error ◽  
Deep Neural Networks ◽  
Pressure Field ◽  
Flow Fields ◽  
Loss Functions ◽  
Data Driven ◽  
Training Time ◽  
Drag Forces ◽  
Computational Fluid Dynamics Cfd ◽  
Lift And Drag

Abstract The study on flow around a hydrofoil has been performed using various methods experimentally and numerically. Here we use a purely data-driven model using deep neural networks (DNNs) to reconstruct the flow fields. Its results are also compared with that obtained by traditional methods. The datasets of flow fields around a static hydrofoil obtained from computational fluid dynamics (CFD) are used for training the DNNs and then the trained data-driven model is utilized to make reconstructions and predictions. 9 different physics informed loss functions, which contain the prediction error and the error measuring the violation of the conservation law, are proposed to train the parameters of DNNs. Effects of the proposed loss functions on reconstruction of velocity field and pressure field are analyzed. Lift and drag forces predicted during the training time are also analyzed. However, the data-driven model based on DNNs with the optimum loss function works well in the interpolation but fails in the extrapolation. The reasons causing the errors are discussed.

scholarly journals Numerical Investigation of the Hydrodynamics of Changing Fin Positions within a 4-Fin Surfboard Configuration

2020 ◽  
Vol 10 (3) ◽  
pp. 816
Author(s):  
Sebastian Falk ◽  
Stefan Kniesburges ◽  
Rolf Janka ◽  
Tom O’Keefe ◽  
Roberto Grosso ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Lift Force ◽  
Longitudinal Axis ◽  
Parameter Study ◽  
Computational Investigation ◽  
Inflow Velocity ◽  
Drag Forces ◽  
Computational Fluid Dynamics Cfd ◽  
Simulation Results ◽  
Lift And Drag

Most sports like surfing are highly developed. It is necessary to tease the last percentages out of the competitors and equipment—in the case of surfing the surfboard-fin-system—to win competitions or championships. In this computational investigation, a parameter study of the positioning of the two rear fins within a 4-fin configuration with fixed front fins on a surfboard is executed to find appropriate fin positions for specific surf situations. Four different inflow velocities are investigated. The RANS and URANS models combined with the SST k − ω turbulence model, which is available within the computational fluid dynamics (CFD) package STAR-CCM+, are used to simulate the flow field around the fins for angles of attack (AoA) between 0° and 45°. The simulation results show that shifting the rear fins toward the longitudinal axis of the surfboard lowers the maximum lift. Surfboards with 4-fin configurations are slower in nearly the whole range of AoA due to a higher drag force but produce a higher lift force compared to the 3-fin configuration. The lift and drag forces increase significantly with increasing inflow velocity. This study shows a significant influence of the rear fin positioning and the inflow velocity on lift and drag performance characteristics.

Dragonfly flight. I. Gliding flight and steady-state aerodynamic forces.

1997 ◽  
Vol 200 (3) ◽  
pp. 543-556 ◽  
Author(s):  
JM Wakeling ◽  
CP Ellington
Keyword(s):  
Steady State ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
The Body ◽  
Flat Plates ◽  
Viscous Forces ◽  
Drag Forces ◽  
Aerodynamic Properties ◽  
Gliding Flight ◽  
Lift And Drag

The free gliding flight of the dragonfly Sympetrum sanguineum was filmed in a large flight enclosure. Reconstruction of the glide paths showed the flights to involve accelerations. Where the acceleration could be considered constant, the lift and drag forces acting on the dragonfly were calculated. The maximum lift coefficient (CL) recorded from these glides was 0.93; however, this is not necessarily the maximum possible from the wings. Lift and drag forces were additionally measured from isolated wings and bodies of S. sanguineum and the damselfly Calopteryx splendens in a steady air flow at Reynolds numbers of 700-2400 for the wings and 2500-15 000 for the bodies. The maximum lift coefficients (CL,max) were 1.07 for S. sanguineum and 1.15 for C. splendens, which are greater than those recorded for all other insects except the locust. The drag coefficient at zero angle of attack ranged between 0.07 and 0.14, being little more than the Blassius value predicted for flat plates. Dragonfly wings thus show exceptional steady-state aerodynamic properties in comparison with the wings of other insects. A resolved-flow model was tested on the body drag data. The parasite drag is significantly affected by viscous forces normal to the longitudinal body axis. The linear dependence of drag on velocity must thus be included in models to predict the parasite drag on dragonflies at non-zero body angles.

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.

scholarly journals Pausing after clap reduces power required to fling wings apart at low Reynolds number

2020 ◽  
Author(s):  
Vishwa T. Kasoju ◽  
Arvind Santhanakrishnan
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
High Speed ◽  
Lift Coefficient ◽  
Pause Duration ◽  
Physical Models ◽  
Power Coefficient ◽  
Average Force ◽  
Drag Forces ◽  
Lift And Drag

AbstractThe smallest flying insects such as thrips (body length < 2 mm) are challenged with needing to move in air at chord-based Reynolds number (Rec) on the order of 10. Pronounced viscous dissipation at such low Rec requires considerable energetic expenditure for tiny insects to stay aloft. Free-flying thrips flap their densely bristled wings at large stroke amplitudes, bringing both wings in close proximity of each other at the end of upstroke (‘clap’) and moving their wings apart at the start of downstroke (‘fling’). From high-speed videos of free-flying thrips, we observed that their forewings remain clapped for approximately 10% of the wingbeat cycle before start of fling. We sought to examine if there are aerodynamic advantages associated with pausing wing motion after clap and before fling at Rec=10. A dynamically scaled robotic clap-and-fling platform was used to measure lift and drag forces generated by physical models of non-bristled (solid) and bristled wing pairs for pause times ranging between 0% to 41% of the cycle. In both solid and bristled wings, varying pause time showed no effect on average force coefficients generated within each half-stroke. This was supported by nearly identical time-variation of circulation of the leading and trailing edge vortices for different pause times. At smaller pause times, bristled wings showed larger reduction of cycle-averaged drag coefficient as compared to that of solid wings. For a given wing design (solid or bristled), the ratio of cycle-averaged lift coefficient to cycle-averaged drag coefficient was unchanged across different pause times. We observed 13.5% drop in cycle-averaged power coefficient and 3% drop in cycle-averaged lift coefficient when moving from 0% pause to 9% pause duration. Our results suggest that pausing at the end of clap can be beneficial for reducing the power required to fling, with a small reduction in lift.

scholarly journals Preliminary Results on the Dynamics of a Pile-Moored Fish Cage with Elastic Net in Currents and Waves

2020 ◽  
Vol 9 (1) ◽  
pp. 14
Author(s):  
Gianluca Zitti ◽  
Nico Novelli ◽  
Maurizio Brocchini
Keyword(s):  
Numerical Model ◽  
Laboratory Experiments ◽  
Numerical Models ◽  
Offshore Structures ◽  
Fish Farm ◽  
Maximum Displacement ◽  
Drag Forces ◽  
Real Size ◽  
Lift And Drag ◽  
Mesh Grid

Over the last decades, the aquaculture sector increased significantly and constantly, moving fish-farm plants further from the coast, and exposing them to increasingly high forces due to currents and waves. The performances of cages in currents and waves have been widely studied in literature, by means of laboratory experiments and numerical models, but virtually all the research is focused on the global performances of the system, i.e., on the maximum displacement, the volume reduction or the mooring tension. In this work we propose a numerical model, derived from the net-truss model of Kristiansen and Faltinsen (2012), to study the dynamics of fish farm cages in current and waves. In this model the net is modeled with straight trusses connecting nodes, where the mass of the net is concentrated at the nodes. The deformation of the net is evaluated solving the equation of motion of the nodes, subjected to gravity, buoyancy, lift, and drag forces. With respect to the original model, the elasticity of the net is included. In this work the real size of the net is used for the computation mesh grid, this allowing the numerical model to reproduce the exact dynamics of the cage. The numerical model is used to simulate a cage with fixed rings, based on the concept of mooring the cage to the foundation of no longer functioning offshore structures. The deformations of the system subjected to currents and waves are studied.

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