Minimization of Hydrodynamic Power Losses in Oscillating Submerged Structures by a Novel Shape-Morphing Strategy

2016 ◽  
Author(s):  
Syed N. Ahsan ◽  
Matteo Aureli
Keyword(s):  
Power Dissipation ◽  
Flexible Structures ◽  
Energy Losses ◽  
Moving Wall ◽  
Shape Morphing ◽  
Computational Fluid Dynamics Simulations ◽  
Expenditure Reduction ◽  
Newtonian Viscous Fluid ◽  
Dynamics Simulations ◽  
Interaction Problem

In this paper, we investigate the two dimensional fluid-structure interaction problem of the oscillation of a shape-morphing plate in a quiescent, Newtonian, viscous fluid. The plate is considered as a moving wall for the fluid undergoing two concurrent periodic motions: a rigid oscillation along its transverse direction coupled to a shape-morphing deformation to an arc of a circle with prescribed maximum curvature. Differently from studies concerned with passive flexible structures, here, we introduce the prescribed deformation to specifically manipulate vortex-shedding and modulate hydrodynamic forces and energy losses during underwater oscillations. Computational fluid dynamics simulations are performed to evaluate the effect of the prescribed deformation strategy on the added mass and damping effect along with the hydrodynamic power dissipation. We observe that a minimum in the hydrodynamic power dissipation exists for an optimum curvature of the plate. This finding may allow significant power expenditure reduction in underwater vibrating systems where minimization of energy losses or maximization of quality factor are desirable.

Three-Dimensional Analysis of Shape-Morphing Cantilever Oscillations in Viscous Fluids

2017 ◽  
Author(s):  
Syed N. Ahsan ◽  
Matteo Aureli
Keyword(s):  
Power Dissipation ◽  
Stokes Problem ◽  
Three Dimensional ◽  
Optimum Level ◽  
Power Losses ◽  
Linear Vibration ◽  
Shape Morphing ◽  
Propulsion Performance ◽  
Newtonian Viscous Fluid ◽  
Actuation Systems

In this paper, we study the linear flexural oscillations of a cantilever beam undergoing chord-wise shape-morphing deformation in a quiescent, Newtonian, viscous fluid. The shape-morphing deformation is prescribed for the beam cross section to an arc of a circle by specifying a periodic maximum curvature continuously along the axis of the structure. This particular strategy is investigated as a possible way to manipulate fluid-structure interaction mechanisms by modifying the hydrodynamic interactions in the vicinity of the submerged structure. Since we focus on the linear vibration of the beam, the fluid flow is described using three-dimensional unsteady Stokes hydrodynamics. By solving the linear unsteady Stokes problem in the frequency domain with a Stokeslet method, we identify the effect of the proposed shape-morphing strategy on the propulsion performance by estimating thrust, lift, and hydrodynamic power dissipation for a range of prescribed deformations. We verify the results obtained from our boundary element method against results from the existing literature. Our findings show a possible improvement in propulsion characteristics and minimization of hydrodynamic power dissipation, for an optimum level of shape-morphing deformation which is aspect ratio-dependent. Results from this study can aid in designing and operating cantilever-based underwater actuation systems for which the multi-objective goal of power losses reduction and propulsion performance improvement is sought.

Torsional Oscillations of a Shape-Morphing Plate in Viscous Fluids

2019 ◽  
Author(s):  
Syed N. Ahsan ◽  
Matteo Aureli
Keyword(s):  
Power Dissipation ◽  
Stokes Equations ◽  
Oscillation Amplitude ◽  
Finite Amplitude ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Torsional Oscillations ◽  
Shape Morphing ◽  
Moment Control ◽  
Interaction Problem

Abstract In this paper, we investigate finite amplitude torsional oscillations of a shape-morphing plate submerged in a quiescent, Newtonian, incompressible fluid. To address this problem, we focus on a two-dimensional cross section of the plate and para-metrically study hydrodynamic moments and power dissipation during the plate oscillation as a function of the shape-morphing deformation intensity and the oscillation amplitude. This fluid-structure interaction problem is tackled within the framework of a computational fluid dynamics model where the fluid flow is described via the Navier-Stokes equations and the deformations of the structure are prescribed. The results demonstrate a gradual reduction of hydrodynamic moment and nonmonotonic power dissipation behavior as the imposed shape-morphing becomes more aggressive. In addition, power dissipation can be minimized for an optimum value of the shape-morphing intensity. Results from this study are relevant in underwater systems subjected to torsional oscillations and demonstrate an avenue for hydrodynamic moment control and reduction of energy losses.

Modulation of Nonlinear Hydrodynamic Damping in Finite Amplitude Underwater Oscillations of Flanged Structures

2015 ◽  
Author(s):  
Syed N. Ahsan ◽  
Matteo Aureli
Keyword(s):  
Vortex Structure ◽  
Complex Dynamics ◽  
Added Mass ◽  
Finite Amplitude ◽  
Structure Interaction ◽  
Hydrodynamic Damping ◽  
Computational Fluid Dynamics Simulations ◽  
Newtonian Viscous Fluid ◽  
Dynamics Simulations ◽  
Hydrodynamic Fields

In this paper, we study the fluid-structure interaction problem of the harmonic oscillations of a flanged lamina in a quiescent, Newtonian, viscous fluid. Here, the flanges are introduced to elicit specific vortex-structure interactions, with the ultimate goal of modulating the nonlinear hydrodynamic damping experienced by the oscillating structure. The hydrodynamic forcing, incorporating added mass and hydrodynamic damping effects, is evaluated through boundary element method and computational fluid dynamics simulations. This allows to identify a model for the hydrodynamic forces in the form of a complex-valued function of three nondimensional parameters, describing oscillation frequency and amplitude and flange size. We find that the presence of the flanges results into larger fluid entrainment during the lamina oscillation, thus affecting the added mass. Further, we highlight the existence of a minimum in the hydrodynamic damping which is governed by complex dynamics of vortex-structure interaction. This peculiar phenomenon is discussed from physical grounds by analysis of the pertinent hydrodynamic fields. Finally, we propose a tractable form for the hydrodynamic function, to be used in the study of large amplitude underwater flexural vibrations of flanged structures.

scholarly journals Aerodynamic analysis of uphill drafting in cycling

2021 ◽  
Vol 24 (1) ◽  
Author(s):  
T. van Druenen ◽  
B. Blocken
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Speed ◽  
Scientific Literature ◽  
Sensitivity Analyses ◽  
Air Resistance ◽  
Wind Tunnel Measurements ◽  
Aerodynamic Effect ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

AbstractSome teams aiming for victory in a mountain stage in cycling take control in the uphill sections of the stage. While drafting, the team imposes a high speed at the front of the peloton defending their team leader from opponent’s attacks. Drafting is a well-known strategy on flat or descending sections and has been studied before in this context. However, there are no systematic and extensive studies in the scientific literature on the aerodynamic effect of uphill drafting. Some studies even suggested that for gradients above 7.2% the speeds drop to 17 km/h and the air resistance can be neglected. In this paper, uphill drafting is analyzed and quantified by means of drag reductions and power reductions obtained by computational fluid dynamics simulations validated with wind tunnel measurements. It is shown that even for gradients above 7.2%, drafting can yield substantial benefits. Drafting allows cyclists to save over 7% of power on a slope of 7.5% at a speed of 6 m/s. At a speed of 8 m/s, this reduction can exceed 16%. Sensitivity analyses indicate that significant power savings can be achieved, also with varying bicycle, cyclist, road and environmental characteristics.

scholarly journals Evaluation of Active Heat Sinks Design under Forced Convection—Effect of Geometric and Boundary Parameters

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2041
Author(s):  
Eva C. Silva ◽  
Álvaro M. Sampaio ◽  
António J. Pontes
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Additive Manufacturing ◽  
Pressure Drop ◽  
Forced Convection ◽  
Thermal Performance ◽  
Heat Sinks ◽  
Trapezoidal Shape ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

This study shows the performance of heat sinks (HS) with different designs under forced convection, varying geometric and boundary parameters, via computational fluid dynamics simulations. Initially, a complete and detailed analysis of the thermal performance of various conventional HS designs was taken. Afterwards, HS designs were modified following some additive manufacturing approaches. The HS performance was compared by measuring their temperatures and pressure drop after 15 s. Smaller diameters/thicknesses and larger fins/pins spacing provided better results. For fins HS, the use of radial fins, with an inverted trapezoidal shape and with larger holes was advantageous. Regarding pins HS, the best option contemplated circular pins in combination with frontal holes in their structure. Additionally, lattice HS, only possible to be produced by additive manufacturing, was also studied. Lower temperatures were obtained with a hexagon unit cell. Lastly, a comparison between the best HS in each category showed a lower thermal resistance for lattice HS. Despite the increase of at least 38% in pressure drop, a consequence of its frontal area, the temperature was 26% and 56% lower when compared to conventional pins and fins HS, respectively, and 9% and 28% lower when compared to the best pins and best fins of this study.

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