Acoustic force model for the fluid flow under standing waves

2011 ◽  
Vol 72 (10) ◽  
pp. 754-759 ◽  
Author(s):  
Hong Lei ◽  
Daniel Henry ◽  
Hamda BenHadid
2008 ◽  
Vol 123 (5) ◽  
pp. 3406-3406
Author(s):  
Bart Lipkens ◽  
Jason Dionne ◽  
Michael Costolo ◽  
Edward Rietman

Author(s):  
Marwan Hassan

Fluidelastic instability is regarded as the most complex and destructive flow excitation mechanism in heat exchanger tube arrays subjected to cross fluid flow. Several attempts have been made for modelling fluidelastic instability in tube arrays in order to predict the stability threshold. However, fretting wear prediction requires a nonlinear computation of the tube dynamics in which proper modelling of the fluid forcing function is essential. In this paper, a time domain simulation of fluidelastic instability is presented for a single flexible tube in an otherwise rigid array subjected to cross fluid flow. The model is based on the unsteady flow theory proposed by Lever and Weaver [1] and Yetisir and Weaver [2]. The developed model has been implemented in INDAP (Incremental Nonlinear Dynamic Analysis Program), an in-house finite element code. Numerical investigations were performed for two linear tube-array geometries and compared with published experimental data. A reasonable agreement between the numerical simulation and the experimental results was obtained. The fluidelastic force model was also coupled with a tube/support interaction model. The developed numerical model was utilized to study a loosely-supported cantilever tube subjected to air flow. Tube-to-support clearance, random excitation level, and flow velocity were then varied. The results indicated that the loose support has a stabilizing effect on the tube response. Both rms impact force and normal work rate increased as a result of increasing the flow velocity or the support radial clearance. Contact ratio exhibited a sharp increase at a flow velocity higher than the instability threshold of the first unsupported mode. In addition, an interesting behaviour has been observed, namely the change of tube’s equilibrium position due to fluid forces. This causes a single-sided impact. At a higher turbulence level, double-sided impact conditions were dominant. The influence of these dynamic regimes on the tube/support parameters was also addressed.


2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Zijie Qu ◽  
Dominik Schildknecht ◽  
Shahriar Shadkhoo ◽  
Enrique Amaya ◽  
Jialong Jiang ◽  
...  

AbstractBiological systems control ambient fluids through the self-organization of active protein structures, including flagella, cilia, and cytoskeletal networks. Self-organization of protein components enables the control and modulation of fluid flow fields on micron scales, however, the physical principles underlying the organization and control of active-matter-driven fluid flows are poorly understood. Here, we use an optically-controlled active-matter system composed of microtubule filaments and light-switchable kinesin motor proteins to analyze the emergence of persistent flow fields. Using light, we form contractile microtubule networks of varying size and shape, and demonstrate that the geometry of microtubule flux at the corners of contracting microtubule networks predicts the architecture of fluid flow fields across network geometries through a simple point force model. Our work provides a foundation for programming microscopic fluid flows with controllable active matter and could enable the engineering of versatile and dynamic microfluidic devices.


2019 ◽  
Vol 97 (10) ◽  
pp. 1039-1048 ◽  
Author(s):  
S. Abdul Gaffar ◽  
Khalil Ur-Rehman ◽  
P. Ramesh Reddy ◽  
V. Ramachandra Prasad ◽  
B. Md. Hidayathulla Khan

Non-Newtonian viscoelastic fluid flow past an isothermal sphere embedded in non-Darcy porous medium is examined numerically in this work. To be specific, the non-Newtonian Powell–Eyring fluid in the presence of both the heat and mass characteristics is mathematically modelled in terms of differential system. A non-Darcy drag force model is employed to simulate the effects of linear porous media drag and second-order Forchheimer drag. The surface of the sphere is maintained at a constant temperature and concentration. The numerical solution of the resultant system is reported via the Keller box method. Both tabular and graphical forms are adopted to identify the variations in Powell–Eyring fluid velocity, Powell–Eyring fluid temperature, and Powell–Eyring fluid concentration. In addition, the surface physical quantities, namely, skin friction and heat and mass transfer rates, are explored. The obtained observations are validated with earlier Newtonian studies. We found an excellent match in this regard. It is found that the velocity is reduced with increasing fluid parameter (ε), Forchheimer parameter (Λ), and tangential coordinate (ξ). In contrast, the temperature and concentration are increasing with increasing value of ε. A very slight increase in velocity is seen with an increase in the local non-Newtonian parameter, δ. But the temperature and concentration decrease slightly with an increase in δ. An increase in Darcy parameter enhances velocity but reduces both temperature and concentration. The present study finds an extensive array of applications in modern nuclear engineering, mineral and chemical process engineering, nuclear waste in geomaterial repositories, petroleum product filtration, and insulation systems.


2017 ◽  
Author(s):  
Mike D. Menz ◽  
Patrick Ye ◽  
Kamyar Firouzi ◽  
Kim Butts Pauly ◽  
Butrus T. Khuri-Yakub ◽  
...  

AbstractFocused ultrasound has been shown to be effective at stimulating neurons in vivo, ex vivo and in vitro preparations. Ultrasonic neuromodulation is the only non-invasive method of stimulation that could reach deep in the brain with high spatial-temporal resolution, and thus has potential for use in clinical applications and basic studies of the nervous system. Understanding the physical mechanism by which energy in a high acoustic frequency wave is delivered to stimulate neurons will be important to optimize this technology. Two primary candidates for a physical mechanism are radiation force, the delivery of momentum by the acoustic wave, and cavitation, oscillating gas bubbles. We imaged the isolated salamander retina during ultrasonic stimuli that drive ganglion cell activity and observed micron scale displacements consistent with radiation force. We recorded ganglion cell spiking activity with a planar multielectrode array and changed the acoustic carrier frequency across a broad range (0.5 - 43 MHz), finding that increased stimulation occurs at higher acoustic frequencies, a result that is consistent with radiation force but not cavitation. A quantitative radiation force model can explain retinal responses, and could potentially explain previous in vivo results in the mouse, suggesting a new hypothesis to be tested in vivo. Finally, we found that neural activity was strongly modulated by the distance between the transducer and the electrode array showing the influence of standing waves on the response. We conclude that radiation force is the physical mechanism underlying ultrasonic neurostimulation in the ex vivo retina, and that the control of standing waves is a new potential method to modulate these effects.


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