Two-dimensional numerical simulation of acoustic wave phase conjugation in magnetostrictive elastic media

The effect of parametric wave phase conjugation (WPC) in application to ultrasound or acoustic waves in magnetostrictive solids has been addressed numerically by Ben Khelil et al. [J. Acoust. Soc. Am. 109, 75-83 (2001)] using 1-D unsteady formulation. Here the numerical method presented by Voinovich et al. [Shock waves 13(3), 221-230 (2003)] extends the analysis to the 2-D effects. The employed model describes universally elastic solids and liquids. A source term similar to Ben Khelil et al.'s accounts for the coupling between deformation and magnetostriction due to external periodic magnetic field. The compatibility between the isotropic constitutive law of the medium and the model of magnetostriction has been considered. Supplementary to the 1-D simulations, the present model involves longitudinal/transversal mode conversion at the sample boundaries and separate magnetic field coupling with dilatation and shear stress. The influence of those factors in a 2-D geometry on the potential output of a magneto-elastic wave phase conjugator is analyzed in this paper. The process under study includes propagation of a wave burst of a given frequency from a point source in a liquid into the active solid, amplification of the waves due to parametric resonance, and formation of time-reversed waves, their radiation into liquid, and focusing. The considered subject is particularly important for ultrasonic applications in acoustic imaging, nondestructive testing, or medical diagnostics and therapy.     

Numerical study of wave processes in a pressure-wave refrigerator

The paper provides some results concerning the numerical study of the strongly transient gasdynamic processes in a pressure-wave refrigerator (PWR). A hierarchical set of numerical models from the simplest one-dimensional to a fully three-dimensional formulation is introduced. The computations show that one-dimensional solutions give a reasonable foundation for the understanding of PWR operational principles but cannot satisfactorily predict the refrigeration efficiency. Good agreement with experiment is achieved by considering two- and three-dimensional effects of gas mixing by overlap of rotating nozzles and expansion tubes. Received Received 14 February 1996 / Accepted 1 June 1996     

Cocrystal Formation through Mechanochemistry: from Neat and Liquid‐Assisted Grinding to Polymer‐Assisted Grinding

Mechanochemistry is an effective method for the preparation of multicomponent crystal systems. In the present work, we propose an alternative to the established liquid‐assisted grinding (LAG) approach. Polymer‐assisted grinding (POLAG) is demonstrated to provide a new class of catalysts for improving reaction rate and increasing product diversity during mechanochemical cocrystallization reactions. We demonstrate that POLAG provides advantages comparable to the conventional liquid‐assisted process, whilst eliminating the risk of unwanted solvate formation as well as enabling control of resulting particle size. It represents a new approach for the development of functional materials through mechanochemistry, and possibly opens new routes toward the understanding of the mechanisms and pathways of mechanochemical cocrystal formation.     

Attenuation of weak shock waves along pseudo-perforated walls

In order to attenuate weak shock waves in ducts, effects of pseudo-perforated walls were investigated. Pseudo-perforated walls are defined as wall perforations having a closed cavity behind it. Shock wave diffraction and reflection created by these perforations were visualized in a shock tube by using holographic interferometer, and also by numerical simulation. Along the pseudo-perforated wall, an incident shock wave attenuates and eventually turns into a sound wave. Due to complex interactions of the incident shock wave with the perforations, the overpressure behind it becomes non-uniform and its peak value can locally exceed that behind the undisturbed incident shock wave. However, its pressure gradient monotonically decreases with the shock wave propagation. Effects of these pseudo-perforated walls on the attenuation of weak shock waves generated in high speed train tunnels were studied in a 1/250-scaled train tunnel simulator. It is concluded that in order to achieve a practically effective suppression of the tunnel sonic boom the length of the pseudo-perforation section should be sufficiently long. Received 23 June 1997 / Accepted 16 September 1997     

High speed jet formation by impact acceleration method

This paper describes the generation of high-speed liquid jets by the impact acceleration method using a vertical two-stage light gas gun specially designed and constructed for this project at the Interdisciplinary Shock Wave Research Laboratory, Institute of Fluid Science, Tohoku University. Results of pressure measurements and double exposure holographic interferometric visualization and high speed video-recording of shadow graph images of waves propagating in a conically shaped container of liquid are included. In the experiments, an optical fiber pressure transducer of 0.1 mm in diameter and resonant frequency of 100 MHz was used for precise pressure measurements of waves in the container at 300 m/s projectile impacts. To verify the contribution of longitudinal and transversal waves created in metal containers, we used a 10.6 mm × 10.6 mm container of water with thick acrylic observation windows and quantitatively visualized waves by using double exposure holographic interferometry. We found that: (1) longitudinal and transversal waves did exist in the metal parts of the container and also in the acrylic observation windows; (2) before the nozzle flow started, these waves and their reflected waves coalesced with the main impact generated shock wave; (3) the primary jet was driven by pressures of 12.4 GPa caused by the 300 m/s projectile impingement; (4) successive shock reflections inside the container of liquid drove intermittent multiple liquid jets; (5) the contribution of released longitudinal and transversal waves to multiple jet formation is marginal; and (6) negative pressures detected with the optical fiber pressure transducer are attributable to impact flash and have no physical significance.      

Experimental and numerical study of pressure wave refrigerator performance

A new compact pressure wave refrigerator has been designed and manufactured at the Shock Wave Research Center, Institute of Fluid Science, Tohoku University. The performance of this device was investigated for combinations of major operational parameters, such as the rotational speed of gas distributor, the length of expansion tubes, the input gas pressure. The maximum temperature decrease of 20 K has been measured. Some theoretical consideration to the efficiency of the pressure wave refrigerator and two-dimensional numerical simulations were carried out in order to understand the wave interactions that take place inside the device.Received: 26 May 2003, Accepted: 12 August 2003, Published online: 14 October 2003 Correspondence to: T. Saito     

Two-dimensional unstructured elastic model for acoustic pulse scattering at solid-liquid interfaces

Abstract. A numerical model to simulate elastic waves and acoustic scattering in two spatial dimensions has been developed and thoroughly tested. The model universally includes elastic solids and liquids. The equations of motion are written in terms of stresses, displacements and displacement velocities for control volumes constructed about the nodes of a triangular unstructured grid. The latter conveniently supports various geometries with complex external and internal boundaries separating sub-domains of different elastic properties. Theoretical dispersion for zero mode symmetric () and antisymmetric () waves in a plate has been reproduced numerically with high accuracy, thus verifying the method and code. Comparison of simulated acoustic pulse scattering at water-immersed steel plate with the respective experiments reveals a very good agreement in such delicate features as excitation of the surface (A) wave. The numerical results explain the peculiar location of the surface wave relative to the other ones in experimental registrations. Examples of acoustic pulse interactions with curvilinear metallic shells in water demonstrate flexibility of the method with respect to complex geometries. Potential applications as well as some directions for further improvement to the technique are briefly discussed. Received 5 September 2002 / Accepted 25 November 2002 Published online 4 February 2003 RID="*" ID="*"Permanent address: Ioffe Physical-Technical Institute, 26 Polytekhnicheskaya, 194021 St. Petersburg, Russia Correspondence to: P. Voinovich (e-mail: vpeter@scc.ioffe.ru)     

Mechanochemical reactivity inhibited,prohibited and reversed by liquid additives: examples from crystal-form screens

We demonstrate that liquid additives can exert inhibitive or prohibitive effects on the mechanochemical formation of multi-component molecular crystals, and report that certain additives unexpectedly prompt the dismantling of such solids into physical mixtures of their constituents. Computational methods were employed in an attempt to identify possible reasons for these previously unrecognised effects of liquid additives on mechanochemical transformations.

Liquid additives can exert catalytic, inhibitive or prohibitive effects on the mechanochemical formation of multi-component molecular crystals.     

Characterization of a quaternary liquid system improving the bioavailability of poorly water soluble drugs

The aim of this work is the characterization of the quaternary system composed of water, triacetin (oil), ethanol (alcohol), and Tween 80 (surfactant), as its results enable the enhancement of the bioavailability of nimesulide, a poorly water soluble nonsteroidal antiinflammatory drug widely employed in the pharmaceutical field. Particular attention is devoted to the surfactant-free ternary system, as it proved able to solubilize nimesulide as well, and the absence of a surfactant is desirable in order to keep the preparation as tolerable as possible. Both bulk and interfacial properties of this system are investigated, and a mathematical model to calculate the interface composition of a three-component two-phase system is developed. This model is based on Gibbs' theory on interfaces, which considers an arbitrary mathematical dividing surface so that the two phases continue uniformly up to it, although interface regions have no sharply defined boundaries. We find that both the quaternary and the ternary systems investigated show a miscibility lacuna and that, in the surfactant-free ternary system, an increase of the ethanol weight fraction is reflected as an impoverishment of the ethanol interfacial molar fraction.     

On stability of strong and weak reflected shocks

A time-realistic adaptive unstructured Euler code is used to demonstrate the numerical existence and investigate the stability of both weak and strong reflected shocks in regular reflection. For supersonic parallel flow in a channel, impinging on two symmetrical opposing wedges, the weak reflected configuration is insensitive to downstream pressure disturbances and therefore stable. The strong reflected shock configuration is unstable to positive perturbations in back-pressure and neutrally stable to negative perturbations. A unique -shock structure provides the transition mechanism between weak and strong reflected shock configurations. Received 6 September 1999 / Accepted 10 August 2000