1,720,997 research outputs found
Acoustic-structural coupling in the frequency response of synthetic jet devices
No full textThis paper presents a general lumped element mathematical model of the operation of a synthetic jet actuator with a piezoelectric driver in order to investigate the frequency response of the device. The model shows that the system behaves as a two-coupled oscillators device. Analytical expressions are given in order to predict the two peak frequencies, corresponding to the modified Helmholtz and first-mode structural resonance frequencies. The model has been validated experimentally through systematic experimental tests carried out on three devices having different mechanical and geometrical properties. A very strict agreement between numerical and experimental findings is found
A Finite Volume approximation of the Navier-Stokes equations with nonlinear filtering stabilization
Full text linkWe consider a Leray model with a nonlinear differential low-pass filter for the simulation of incompressible fluid flow at moderately large Reynolds number (in the range of a few thousands) with under-refined meshes. For the implementation of the model, we adopt the three-step algorithm Evolve-Filter-Relax (EFR). The Leray model has been extensively applied within a Finite Element (FE) framework. Here, we propose to combine the EFR algorithm with a computationally efficient Finite Volume (FV) method. Our approach is validated against numerical data available in the literature for the 2D flow past a cylinder and against experimental measurements for the 3D fluid flow in an idealized medical device, as recommended by the U.S. Food and Drug Administration. We will show that for similar levels of mesh refinement FV and FE methods provide significantly different results. Through our numerical experiments, we are able to provide practical directions to tune the parameters involved in the model. Furthermore, we are able to investigate the impact of mesh features (element type, non-orthogonality, local refinement, and element aspect ratio) and the discretization method for the convective term on the agreement between numerical solutions and experimental data.33 pages, 18 figures, 6 table
Modeling and Experimental Validation of the Frequency Response of Synthetic Jets Actuators
No full textA lumped element mathematical model of the operation of a synthetic jet actuator driven by a thin piezoelectric disk is both analytically and numerically investigated in order to obtain information about the frequency response of the device. It is shown
that the system behaves as a two-coupled oscillators device and simple relationships are given in order to predict the two peak frequencies, corresponding to the modified Helmholtz and first-mode structural resonance frequencies. The model is validated
through systematic experimental tests carried out on three devices having different mechanical and geometrical characteristics. A very strict agreement between analytical and numerical findings is found, thus one can use the computer code as a practical tool for overall design purposes
Fluid-structure coupling effects in synthetic jet devices
No full textThis paper presents a general lumped element mathematical model of the operation of a synthetic jet actuator with a piezoelectric driver in order to investigate the frequency response of the device. The model shows that the system behaves as a two-coupled oscillators device. Analytical expressions are given in order to predict the two peak frequencies, corresponding to the modified Helmholtz and first-mode structural resonance frequencies. The model has been validated experimentally through systematic experimental tests carried out on three devices having different mechanical and geometrical properties. A very strict agreement between numerical and experimental findings is found
Thermomechanical Modelling for Industrial Applications
No full textIn this work we briefly present a thermomechanical model that could serve as starting point for industrial applications. We address the non-linearity due to temperature dependence of material properties and heterogeneity due to presence of different materials. Finally a numerical example related to the simplified geometry of blast furnace hearth walls is shown with the aim of assessing the feasibility of the modelling framework. Keywords: nonlinear thermomechanical model, finite element method, heterogeneous material, blast furnace
Scaling properties of resonant cavities driven by piezo-electric actuators
No full textAcoustic-structural properties of piezo-electric driven resonant cavities usually employed to generate the so-called synthetic jets are theoretically and numerically investigated in order to characterize the performances of such devices. It is shown that the actuator behaves as a two-coupled oscillators system and the dimensionless form of the governing equations allows one to identify various operating conditions, in particular those leading to their decoupling. The theoretical predictions are validated through analytical, numerical and experimental findings for devices having different mechanical and geometrical characteristics, designed to achieve an increasing coupling effect. Considerations about the strength of jet formation at the Helmholtz frequency are made as well
Modelling of efficiency of synthetic jet actuators
No full textA comprehensive and detailed modelling to evaluate the efficiency of energy conversion of
piezo-electric actuators driving synthetic jets is developed. The contribution is original because the
analysis is based on the energy equations of the two coupled oscillators, the membrane and the
acoustic one, which are directly derived from the corresponding motion equations. The modelling is
validated against numerical as well as experimental investigations carried out on a home-made
actuator having an aluminum shim on which the piezodisk is bonded. A major result is that for the
actuator under investigationthe global efficiency (representing the conversion of input Joule power to
kinetic power) decreases with increasing the applied voltage. Another finding is that the conversion
process of mechanical power transferred from the driving membrane to Helmholtz oscillator kinetic
power scales dramatically with
the coupling degree of the oscillators. The coupling degree infuences the efficiency of two cavities
actuators sharing the same piezo-diaphragm as
well. Considerations are reported to relate the theoretical orifice efficiency to the practical jetefficiency
issuing in the external field
Optimal transport-based displacement interpolation with data augmentation for reduced order modeling of nonlinear dynamical systems
Full text linkWe present a novel reduced-order Model (ROM) that leverages optimal transport (OT) theory and displacement interpolation to enhance the representation of nonlinear dynamics in complex systems. While traditional ROM techniques face challenges in this scenario, especially when data (i.e., observational snapshots) are limited, our method addresses these issues by introducing a data augmentation strategy based on OT principles. The proposed framework generates interpolated solutions tracing geodesic paths in the space of probability distributions, enriching the training dataset for the ROM. A key feature of our approach is its ability to provide a continuous representation of the solution's dynamics by exploiting a virtual-to-real time mapping. This enables the reconstruction of solutions at finer temporal scales than those provided by the original data. To further improve prediction accuracy, we employ Gaussian Process Regression to learn the residual and correct the representation between the interpolated snapshots and the physical solution.
We demonstrate the effectiveness of our methodology with atmospheric mesoscale benchmarks characterized by highly nonlinear, advection-dominated dynamics. Our results show improved accuracy and efficiency in predicting complex system behaviors, indicating the potential of this approach for a wide range of applications in computational physics and engineering
Global dynamics of gravitational liquid sheet flows
No full textUnsteady free-interface vertical liquid sheet flows are studied from the global viewpoint, where the dynamics is termed global because it refers to the whole fluid system. The development of a
proper mathematical model is presented initially, which accounts of pressure disturbances produced by the compliant interface in an air enclosure adjacent to the sheet. Our study has been
restricted to the sinuous (unsymmetric) solution of the linearized set of equations. It is found that, in absence of surface tension, the optimal disturbance energy exhibits a transient growth
characterized by high frequency and low frequency time-periodic oscillations; physical considerations are developed in order to estimate the relevant periods. In presence of surface tension,
the low frequency oscillations disappear and the optimal disturbance energy goes quickly to zero, after exhibiting an initial reduced peak. In order to give insight on the physical relevance
of such behaviours, an equation of energy budget is also derived which is used to estimate the contribution of the various physical effects evaluated via direct numerical simulation of the
linearized model
Global dynamics of transonic gravitational liquid sheet flows
No full textIt is known that the basic nature of the global dynamics of gravitational (and, therefore, spatially developing)
liquid sheet flows, in the presence of surface tension effects, depends crucially1,2 on the inlet Weber number,
2 /
We Uo ho , where is the liquid density, Uo is the inlet liquid velocity, ho is the initial half thickness of the
sheet, is the surface tension at the air-liquid interface. When We 1 , the local Weber number too is greater
than unity at each streamwise (i.e., vertical) location, so that the flow can be defined supersonic everywhere, in the
sense that the local flow velocity exceeds the capillary waves velocity / h , where h is the local sheet
thickness. On the other hand, when We 1 , there exists an initial region where the sheet flow is subsonic, up to
the transonic location, downstream of which the flow becomes supersonic. Since the experimental evidence is that
the sheet breaks-up in flow conditions of We 1 only, the analysis of the flow field initially subsonic, and hence
including the transonic line, is mandatory to predict the rupture conditions.
From the theoretical viewpoint the problem is not straightforward, because the equation governing the
evolution of global linear disturbances exhibits a singularity just at the transonic station, as documented also by
previous contributions of literature3,4, although the solution to the problem is not yet yielded. Thus, the present
work is aimed at developing a theoretical/numerical procedure to fill up this lack of information.
Within this framework, the flow is assumed inviscid and the problem is arranged in 1D formulation along the
streamwise direction by expressing all the physical quantities through a coordinate-type expansion in terms of
powers of the local lateral distance from the centerline position. The interaction with the external environment
refers to an air enclosure located on one side of the curtain. The linearized perturbation equations are
determined in a standard fashion by superimposing infinitesimal disturbances to the steady solution and the
modal global stability is studied by addressing the relevant singular eigenvalues problem.
The dimensionless governing equation of sinuous disturbances can be written as:
where U 1 2x is the classic free-fall Torricelli’s solution, f is the centerline deflection of the sheet, k is a
proper compressibility coefficient of the air enclosure and L is the curtain length.
It is shown that the transonic location can be classified as a regular singular point and a solution in terms of
Frobenius series5 is introduced in order to provide the local solution around the singularity. The non-linear
eigenvalues problem obtained accordingly is faced as a nonlinear two-point boundary problem (in which the
searched eigenvalue is considered as an unknown function) that is solved by means of a shooting technique6. The
boundary conditions are of null sheet displacement at inlet and boundedness at the singularity location3,4.
The numerical results show the spectra pattern obtained when the inlet We number is varied from subsonic to
transonic values, with particular attention to their evolution with respect to cases of entirely supersonic flow
analyzed with standard spectral methods. The physical relevance of the present findings is discussed as well.
a University of Naples Federico II, Dept. Industrial Eng., Aerospace Sector, Piazzale Tecchio 80, Naples, ITALY, [email protected]
1 de Luca, J. Fluid Mech. 399, 355 (1999).
2 Le Grand-Piteira et al., Phys. Rev. E 74, 026305 (2006)
3 Finnicum et al., J. Fluid Mech. 255, 647 (1993).
4 Weinstein et al., Phys. Fluids 9, 1815 (1997).
5 Bender and Orszag, Springer (1999).
6 Press et al., Cambridge University Press (1992).
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