Interactions between a central bubble and a surrounding bubble cluster

The interaction of multiple bubbles is a complex physical problem.A simplified case of multiple bubbles is studied theoretically with a bubble located at the center of a circular bubble cluster.All bubbles in the cluster are equally spaced and own the same initial conditions as the central bubble.The unified theory for bubble dynamics[35]is applied to model the interaction between the central bubble and the circular bubble cluster.To account for the effect of the propagation time of pressure waves,the emission source of the wave is obtained by interpolating the physical information on the time axis.An underwater explosion experiment with two bubbles of different scales is used to validate the theoretical model.The effect of the bubble cluster with a variation in scale on the pulsation characteristics of the central bubble is studied.

Effect of a rigid structure on the dynamics of a bubble beneath the free surface

The coupling effect between a pulsating bubble and a free surface near a rigid structure is a complicated physical process.In this study,the evolution of an underwater explosion bubble and the free surface near a rigid structure is modeled by the boundary integral method.An approach of“double-node method”is used to maintain the stability of fluid-structure junction in the simulations,and meshes on the free surface and the structure are transformed to an open domain to ensure the calculation accuracy and efficiency.Validations are conducted against an underwater explosion experiment near a rigid structure.As a result,the simulations trace the jetting behavior of the bubble and the rise of the free surface.Finally,the bubble migration and the height of the free surface for different structure draughts are analyzed.

Theoretical analysis of the surface temperature regulation of an infrared false target subjected to periodical ambient conditions

Infrared false target is an important mean to induce the infrared-guided weapons,and the key issue is how to keep the surface temperature of the infrared false target to be the same as that of the object to be protected.One-dimensional heat transfer models of a metal plate and imitative material were established to explore the influences of the thermophysical properties of imitative material on the surface temperature difference（STD） between the metal plate and imitative material which were subjected to periodical ambient conditions.It is elucidated that the STD is determined by the imitative material’s dimensionless thickness（dim*,） and the thermal inertia(Pim).When dim* is above 1.0,the STD is invariable as long as Pim is a constant.And if the dimensionless thickness of metal plate（d,m*） is also larger than 1.0,the STD approaches to zero as long as Pimis the same as the thermal inertia of metal plate（Pm）.When dim* is between 0.08 and 1,the STD varies irregularly with Pim and dim*.However,if dm* is also in the range of 0.08-1,the STD approaches to zero on condition that Pim=Pm and dim*= dm*.If dim*,is below 0.08,the STD is unchanged when Pimdim* is a constant.And if dm* is also less than 0.08,the STD approaches to zero as long as Pimdim* = Pmdm*.Furthermore,an applicationoriented discussion indicates that the imitative material can be both light and thin via the application of the phase change material with a preset STD because of its high specific heat capacity during the phase transition process.

Effect of Zr Content on Formation and Optical Properties of the Layered PbZrxTi1-xO3 Films

PbZrxTi1-xO3(PZT)fims are fabricated on F-doped tin oxide(FTO)substrates using chemical solutions containing PVP polymer and rapid thermal annealing processing.The dependence of the layered PZT multilayer formation and their optical properties on the Zr content x are examined.It is found that all the PZT films are crystallized and exhibit 110-preferred orientation.When x varies in the region of 0-0.8,the PZT films display lamellar structures,and a high reflection band occurs in each optical reflectance spectrum curve.Especially,those PZT fikms with Zr/Ti atomic ratio of 35/65-65/35 show clearly layered cross-sectional morphologies arranged alternatively by porous and dense PZT layers,and have a peak optical reflectivity of>70%and a band width of>45 nm.To obtain the optimal Bragg reflection performance of the PZT multilayers,the Zr content should be selected in the range of 0.35-0.65.

Theoretical study on bubble dynamics under hybrid-boundary and multi-bubble conditions using the unified equation

This paper aims to use the unified bubble dynamics equation to investigate bubble behavior in complex scenarios involving hybrid free surface/wall boundaries and interactions between multiple bubbles.The effect of singularity movement on the unified equation’s form is analyzed after deriving the bubble pulsation equation using a moving point source and a dipole,followed by discussions on the effect of migration compressibility-related terms on the bubble dynamics.In addition,the present study accounts for the impact of hybrid boundaries,including crossed and parallel boundaries,by introducing a finite number of mirror bubbles for the former and an infinite number of mirror bubbles for the latter.Spark bubble experiments and numerical simulation are conducted to validate the present theory.The application of the unified equation in multi-bubble interactions is exemplified by computing a spherical bubble array containing more than 100 uniformly distributed cavitation bubbles under different boundary conditions.The bubble cluster-induced pressure peak can reach nearly two times or even higher than that of an individual bubble,highlighting the damage potential caused by cavitation bubble clusters.