 Publication Date:
 NSFPAR ID:
 10202720
 Journal Name:
 Journal of Fluid Mechanics
 Volume:
 907
 ISSN:
 00221120
 Sponsoring Org:
 National Science Foundation
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Underwater explosion poses a significant threat to the structural integrity of ocean vehicles and platforms. Accurate prediction of the dynamic loads from an explosion and the resulting structural response is crucial to ensuring safety without overconservative design. When the distance between the explosive charge and the structure is relatively small (i.e., nearfield explosion), the dynamics of the gaseous explosion product, i.e., the “bubble”, comes into play, rendering a multiphysics problem that features the interaction of the bubble, the surrounding liquid water, and the solid structure. The problem is highly nonlinear, as it involves shock waves, large deformation, yielding, contact, and possibly fracture. This paper investigates the twoway interaction between the cyclic expansion and collapse of an explosion bubble and the deformation of a thinwalled elastoplastic cylindrical shell in its vicinity. Intuitively, when a shock wave impinges on a thin cylindrical shell, the shell would collapse in the direction of shock propagation. However, some recent laboratory experiments have shown that under certain conditions the shell collapsed in a counterintuitive mode in which the direction of collapse is perpendicular to that of shock propagation. In other words, the nearest point on the structural surface moved towards the explosion charge, despite being impactedmore »

Abstract Shock waves from underwater and air explosions are significant threats to surface and underwater vehicles and structures. Recent studies on the mechanical and thermal properties of various phaseseparated elastomers indicate the possibility of applying these materials as a coating to mitigate shockinduced structural failures. To demonstrate this approach and investigate its efficacy, this paper presents a fluidstructure coupled computational model capable of predicting the dynamic response of airbacked bilayer (i.e. elastomer coating – metal substrate) structures submerged in water to hydrostatic and underwater explosion loads. The model couples a threedimensional multiphase finite volume computational fluid dynamics model with a nonlinear finite element computational solid dynamics model using the FIVER (FInite Volume method with Exact multimaterial Riemann solvers) method. The kinematic boundary condition at the fluidstructure interface is enforced using an embedded boundary method that is capable of handling large structural deformation and topological changes. The dynamic interface condition is enforced by formulating and solving local, onedimensional fluidsolid Riemann problems, which is wellsuited for transferring shock and impulsive loads. The capability of this computational model is demonstrated through a numerical investigation of hydrostatic and shockinduced collapse of aluminum tubes with polyurea coating on its inner surface. The thickness of themore »

Recent studies indicate that cavitation may play a vital role in laser lithotripsy. However, the underlying bubble dynamics and associated damage mechanisms are largely unknown. In this study, we use ultrahighspeed shadowgraph imaging, hydrophone measurements, threedimensional passive cavitation mapping (3DPCM), and phantom test to investigate the transient dynamics of vapor bubbles induced by a holmium:yttrium aluminum garnet laser and their correlation with solid damage. We vary the standoff distance ( SD) between the fiber tip and solid boundary under parallel fiber alignment and observe several distinctive features in bubble dynamics. First, long pulsed laser irradiation and solid boundary interaction create an elongated “pearshaped” bubble that collapses asymmetrically and forms multiple jets in sequence. Second, unlike nanosecond laserinduced cavitation bubbles, jet impact on solid boundary generates negligible pressure transients and causes no direct damage. A noncircular toroidal bubble forms, particularly following the primary and secondary bubble collapses at SD = 1.0 and 3.0 mm, respectively. We observe three intensified bubble collapses with strong shock wave emissions: the intensified bubble collapse by shock wave, the ensuing reflected shock wave from the solid boundary, and selfintensified collapse of an inverted “triangleshaped” or “horseshoeshaped” bubble. Third, highspeed shadowgraph imaging and 3DPCM confirm that the shock origins frommore »

Ultrasound directed selfassembly (DSA) allows organizing particles dispersed in a fluid medium into userspecified patterns, driven by the acoustic radiation force associated with a standing ultrasound wave. Accurate control of the spatial organization of the particles in the fluid medium requires accounting for medium viscosity and particle volume fraction. However, existing theories consider an inviscid medium or only determine the effect of viscosity on the magnitude of the acoustic radiation force rather than the locations where particles assemble, which is crucial information to use ultrasound DSA as a fabrication method. We experimentally measure the deviation between locations where spherical microparticles assemble during ultrasound DSA as a function of medium viscosity and particle volume fraction. Additionally, we simulate the experiments using coupledphase theory and the timeaveraged acoustic radiation potential, and we derive bestfit equations that predict the deviation between locations where particles assemble during ultrasound DSA when using viscous and inviscid theory. We show that the deviation between locations where particles assemble in viscous and inviscid media first increases and then decreases with increasing particle volume fraction and medium viscosity, which we explain by means of the sound propagation velocity of the mixture. This work has implications for using ultrasound DSAmore »

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