Effect of the Compressibility of the Fluid on the Parameters of a Hydraulic Gun

The effect of the compressibility of the fluid on the parameters of a hydraulic gun is evaluated. The quasionedimensional motion of an ideal compressible fluid is described by equations of nonstationary gas dynamics, which are solved numerically according to the algorithm proposed. The numerical solution for a compressible fluid is compared with an analytical solution for an incompressible fluid and with an experiment, which are performed by other authors. From an analysis of the results conclusions are drawn that the compressibility of the fluid can be disregarded. It is proposed that the Mach number the used as a criterion for assessing account for the compressibility of the fluid.     

Dried Molasses as a Direct Compression Matrix for Oral Controlled Release Drug Delivery II: Release Mechanism and Characteristics of Theophylline from a Molasses-Hpmc Matrix

Abstract

Investigation was conducted to evaluate dried molasses as a direct compression matrix for oral controlled release drug delivery system based on its tendency to form a gel-like layer around an inner dry core tablet when it comes in contact with fluid. Dried molasses matrix was modified by incorporation of hydroxypropylmethylcellulose (HPMC) at four concentration levels (12.5, 15.0, 20.0 and 28.57%) to obtain a gel layer of suitable characteristics, and compressed directly on an instrumented rotary tablet press. Theophylline was used as a model drug. Drug release study was performed using USP dissolution apparatus 2, rotated at 20 rpm, in distilled water, simulated gastric fluid pH 1.2, and simulated intestinal fluid pH 7.5. Theopylline was determined by a High Pressure Liquid Chromatographic method, utilizing beta-hydroxyethyl theophylline (BHET) as an internal standard. Results showed an inverse relationship between the rate of release and the level of HPMC, with release period ranging from 3 to 36 hours. Releases rate was greatest in intestinal fluid, least in distilled water, and intermediate in gastric fluid.     

Liquid impact, kinetic energy loss and compressibility: Lagrangian, Eulerian and acoustic viewpoints

From Lagrange's equations of incompressible fluid motion a model is derived for the collision between a liquid mass and a solid surface. The classical idea of pressure impulse, P, is re-expressed as a quantity following the fluid-particle motion. It is shown that within this formulation P=0 is the exact free-surface boundary condition and the domain of definition of P is unambiguously time-independent. Some of the total kinetic energy of the fluid is lost during impact and this is associated with the usual choice of boundary condition for inelastic impact. With elastic impact, in which the fluid rebounds from the solid target, there is no kinetic energy loss. Some simple potentials are used to express P for incompressible fluid impacts, which have non-singular velocity fields: (i) in an acute wedge; (ii) in a cylindrical container; and (iii) in an idealised sea-wave impact. In the last the impact of a triangular fluid domain, T, illustrates kinetic energy loss from an impacting sea wave. Impact is also investigated for the collision of T with a movable solid block. The subsequent displacement of the block, with friction, is also calculated. Lastly a solution is obtained within T composed of a compressible fluid impacting a rigid wall. Standing compression-waves store within T some of the kinetic energy lost from the incident wave water.     

A local RBF collocation method for band structure computations of 2D solid/fluid and fluid/solid phononic crystals

In this paper, an efficient local radial basis function collocation method (LRBFCM) is presented for computing the band structures of the two‐dimensional (2D) solid/fluid and fluid/solid phononic crystals. Both systems of solid scatterers embedded in a fluid matrix (solid/fluid phononic crystals) and fluid scatterers embedded in a solid matrix (fluid/solid phononic crystals) are investigated. The solid–fluid interactions are taken into account by properly formulating and treating the continuity/equilibrium conditions on the solid–fluid interfaces, which require an accurate computation of the normal derivatives of the displacements and the pressure on the fluid–solid interfaces and the unit‐cell boundaries. The developed LRBFCM for the mixed wave propagation problems in 2D solid/fluid and fluid/solid phononic crystals is validated by the corresponding results obtained by the finite element method (FEM). To the best knowledge of the authors, the present LRBFCM has yet not been applied to the band structure computations of 2D solid/fluid and fluid/solid phononic crystals. For different lattice forms, scatterers' shapes, acoustic impedance ratios, and material combinations (solid scatterers in fluid matrix or fluid scatterers in solid matrix), numerical results are presented and discussed to reveal the efficiency and the accuracy of the developed LRBFCM for calculating the band structures of 2D solid/fluid and fluid/solid phononic crystals. A comparison of the present numerical results with that of the FEM shows that the present LRBFCM is much more efficient than the FEM for the band structure computations of the considered 2D solid/fluid and fluid/solid phononic crystals. Copyright © 2016 John Wiley & Sons, Ltd.     

晃动的流体对渡槽结构振动的抑制与放大效应

本文对渡槽结构横向流-固耦合动力特性及其幅频响应特性进行了较为详尽的分析,分析表明：1)结构体系存在二个横向振动固有振动频率 、 , 当系统以较小的频率 （同相位频率）振动时,结构振动的方向与流体的晃动方向一致;当系统以较大的频率 （异相位频率）振动时,结构振动的方向与流体的晃动方向相反。2) 当外动力荷载的频率（或卓越频率）与 （或 ）接近时,结构体系会发生共振反应,流体对结构振动会产生放大效应。3)渡槽结构体系还存在一个特殊的振动频率 ,当外动力荷载的频率（或卓越频率）与 接近时,晃动的流体对结构起到减振的作用。4)渡槽内的流体质量可以分为固定质量与晃动质量两部分,其中固定质量会加大结构顶端的动力惯性反应,可能会对结构安全构成不利影响。     

Full SPH fluid–shell interaction for leakage simulation in explicit dynamics

This paper is devoted to the modeling of fluid leakage through a shell in case of impact loading. The modeling of the fluid and the shell is based on SPH formulation. The proposed model is devoted to the prediction of failure of a shell filled with fluid. This paper is devoted to the numerical modeling of fluid–structure interaction. The pinballs technique is used for contact analysis. Numerical predictions are compared with analytical as well as with an original experiment. Copyright © 2009 John Wiley & Sons, Ltd.     

A symmetric weak form of Biot's equations based on redundant variables representing the fluid,using a Helmholtz decomposition of the fluid displacement vector field

A novel symmetric weak formulation of Biot's equations for linear acoustic wave propagation in layered poroelastic media is presented. The primary variables used are the frame displacement, the acoustic pore pressure, the scalar potential and the vector potential obtained from a Helmholtz decomposition of the fluid displacement. Also a symmetric weak form based on the frame displacement, the pore pressure and the fluid displacement is obtained as an intermediate result. hp finite element simulations of a double leaf partition based on this new weak formulation is verified against simulation results from the classical frame displacement, fluid displacement formulation and a frame displacement pore pressure formulation. All three formulations simulated, displays the same rate of convergence with respect to finite element bases polynomial degree. The novel formulation also extends a previously published frame displacement, pore pressure, scalar fluid displacement potential formulation with an implicit irrotational fluid displacement assumption to a full representation of Biot's equations. Copyright © 2010 John Wiley & Sons, Ltd.     

Topology optimization for stationary fluid–structure interaction problems using a new monolithic formulation

This paper outlines a new procedure for topology optimization in the steady‐state fluid–structure interaction (FSI) problem. A review of current topology optimization methods highlights the difficulties in alternating between the two distinct sets of governing equations for fluid and structure dynamics (hereafter, the fluid and structural equations, respectively) and in imposing coupling boundary conditions between the separated fluid and solid domains. To overcome these difficulties, we propose an alternative monolithic procedure employing a unified domain rather than separated domains, which is not computationally efficient. In the proposed analysis procedure, the spatial differential operator of the fluid and structural equations for a deformed configuration is transformed into that for an undeformed configuration with the help of the deformation gradient tensor. For the coupling boundary conditions, the divergence of the pressure and the Darcy damping force are inserted into the solid and fluid equations, respectively. The proposed method is validated in several benchmark analysis problems. Topology optimization in the FSI problem is then made possible by interpolating Young's modulus, the fluid pressure of the modified solid equation, and the inverse permeability from the damping force with respect to the design variables. Copyright © 2009 John Wiley & Sons, Ltd.     

Steady forced flow of a micropolar fluid against a rotating disc

The steady forced flow of an incompressible micropolar fluid against a rotating disc is considered. The flow due to a rotating disc in an infinite fluid which is at rest and the axisymmetric stagnation flow on a flat plate are particular cases of this present problem. The equations of motion are solved numerically using the Gauss-Seidel iterative procedure and the Simpson's rule. The results are given in tabular form and compared with the known results for a Newtonian fluid.     

The dispersion of a chemically reacting solute in a micropolar fluid

The paper presents solution for the dispersion of a solute in a micropolar fluid flow in a circular pipe in the presence of an irreversible first order chemical reaction. It is shown that the solute is dispersed relative to a plane moving with the mean speed of the flow with an effective Taylor dispersion coefficient, dependent on two parameters, κ/μ and λ characteristic of the micropolar fluid and also on the reaction rate parameter a for a homogeneous reaction in the bulk of the fluid in which the solute is dispersed. It is found that for a given the effective Taylor dispersion coefficient decreases with an increase in κ/μ for fixed λ while it increases with increase in λ for fixed κ/μ. It decreases with increase in a for assumed values of κ/μ and λ.     

An experimental and finite element poroelastic creep response analysis of an intervertebral hydrogel disc model in axial compression

A hydrogel intervertebral disc (IVD) model consisting of an inner nucleus core and an outer anulus ring was manufactured from 30 and 35% by weight Poly(vinyl alcohol) hydrogel (PVA-H) concentrations and subjected to axial compression in between saturated porous endplates at 200 N for 11 h, 30 min. Repeat experiments (n = 4) on different samples (N = 2) show good reproducibility of fluid loss and axial deformation. An axisymmetric nonlinear poroelastic finite element model with variable permeability was developed using commercial finite element software to compare axial deformation and predicted fluid loss with experimental data. The FE predictions indicate differential fluid loss similar to that of biological IVDs, with the nucleus losing more water than the anulus, and there is overall good agreement between experimental and finite element predicted fluid loss. The stress distribution pattern indicates important similarities with the biological IVD that includes stress transference from the nucleus to the anulus upon sustained loading and renders it suitable as a model that can be used in future studies to better understand the role of fluid and stress in biological IVDs.     

Vibration analysis of fluid–solid systems using a finite element displacement formulation

This report presents a finite element solution for the vibration interaction between an inviscid fluid and a solid. The equation of motion governing the inviscid fluid is expressed in terms of the displacements. This ensures that compatibility and equilibrium will be satisfied automatically along the interface of the coupled systems. To suppress circulation modes with non-zero energy, reduced integration is used when computing the element stiffness matrix contributed by the fluid. In addition, a projection is used on the element mass matrix in order to remove the spurious modes which result from the use of reduced integration. Numerical examples for both fluid and coupled fluid–solid systems are performed and the results are shown.     

Slip in Quantum Fluids

In this review we describe theoretical and experimental investigations of general slip phenomena in context with the flow of the quantum liquids³He,⁴He and their mixtures at low temperatures. The phenomenon of slip is related to a boundary effect. It occurs when sufficiently dilute gases flow along the wall of an experimental cell. A fluid is said to exhibit slip when the fluid velocity at the wall is not equal to the wall’s velocity. Such a situation occurs whenever the wall reflects the fluid particles in a specular-like manner, and/or if the fluid is describable in terms of a dilute ordinary gas (classical fluid) or a dilute gas of thermal excitations (quantum fluid). The slip effect in quantum fluids is discussed theoretically on the basis of generalized Landau-Boltzmann transport equations and generalized to apply to a regime of ballistic motion of the quasiparticles in the fluid. The central result is that the transport coefficient of bulk shear viscosity, which typically enters in the Poiseuille flow resistance and the transverse acoustic impedance, has to be replaced by geometry dependent effective viscosity, which depends on the details of the interaction of the fluid particles with the cell walls. The theoretical results are compared with various experimental data obtained in different geometries and for both Bose and Fermi quantum fluids. Good agreement between experiment and theory is found particularly in the case of pure normal and superfluid³He, with discrepancies probably arising because of deficiencies in characterization of the experimental surfaces.     

XPS study of the process of apatite formation on bioactive Ti—6Al—4V alloy in simulated body fluid

Bioactive Ti—6Al—4V alloy, which spontaneously forms a bonelike apatite layer on its surface in the body and bonds to living bone through this apatite layer, can be prepared by producing an amorphous sodium titanate on its surface by NaOH and heat treatments. In this study, the process of apatite formation on the bioactive Ti—6Al—4V alloy was investigated in vitro, by analyzing its surface with X-ray photoelectron spectroscopy as a function of soaking time in a simulated body fluid 4SBF). Thin-film X-ray diffractometry of the alloy surface and atomic emission spectroscopy of the fluid were also performed complementarily. It was found that immediately after immersion in the SBF,the alloy exchanged Na¹ ions from the surface sodium titanate with H₃O¹ ions in the fluid to form Ti-OH groups on its surface. The Ti-OH groups, immediately after their formation,incorporated the calcium ions in the fluid to form calcium titanate. The calcium titanate thereafter incorporated the phosphate ions in the fluid to form an amorphous calcium phosphate, which was later crystallized into bonelike apatite. This process of apatite formation on the alloy was the same as on the pure titanium metal, because the alloy formed the sodium titanate free of Al and V by the NaOH and heat treatments. The initial formation of the calcium titanate is proposed to be a consequence of the electrostatic interaction of negatively charged units of titania dissociated from the Ti-OH groups with the positively charged calcium ions in the fluid. The calcium titanate is postulated to gain a positive charge and interact with the negatively charged phosphate ions in the fluid to form amorphous calcium phosphate, which eventually stabilizes into crystalline apatite.     

The structure and modes of a compressible superfluid film

A formal apparatus is constructed for study of the structure and modes of a single-component film system. The essential ingredients of this apparatus are an equation of motion for the two-dimensional complex order parameter and an energy functional that is the driving force in this equation. The film profile, energy, chemical potential, third sound velocity, etc., are studied for four model films: model 1, a free-standing self-bound fluid; models 2:0 and 2:1, a self-bound fluid in a substrate potential; and model 3, a non-self-bound fluid in a substrate potential. Model 1 can be studied analytically; models 2:0, 2:1, and 3 are studied numerically. Liquid⁴He is a self-bound fluid; spin-polarized hydrogen is a non-self-bound fluid.     

Oscillating two-phase flow in a prestressed thick elastic tube

Summary The pulsating flow of a fluid with dusty particles in a prestressed thick walled elastic tube has been studied. The tube, subjected to a static inner pressure P_i and an axial stretch λ, is taken to be an incompressible, isotropic, elastic material. The fluid with particles is treated as incompressible Newtonian. Employing the theory of small deformation superimposed on large initial deformations, for an axially symmetric perturbed motion the governing equations are obtained in cylindrical polar coordinates. The analytical solutions of the equations of motion for the dust and the fluid have been obtained. Because of the variable character of the coefficients of the resulting equations for the solid body they are solved numerically. The dispersion relation is obtained as a function of the stretch, the thickness ratio and the parameters for dusty particles.     

Thermodynamic optimization of ejector actuated refrigerating cycles

A cold generation system featuring a Rankine cycle powered refrigeration cycle actuated by a supersonic ejector was theoretically investigated in view of the thermo-fluid-dynamic optimization of the working fluid characteristics.

The ejector model was validated against well established performance charts relating to water. A reference system was considered in which a Rankine cycle at moderate top temperature delivers its expansion power by means of an ideal turbine to an ideal compressor of a refrigeration cycle. Two main optimizing variables were ascertained: the fluid critical temperature and the complexity of the fluid molecule. The best performance of such reference cycle is around 80% of that of an ideal fully reversible, Carnot cycle based, system (COP of 2.0 for t_E,PC = 150 °C, t_E,RC = 5 °C, and t_C = 35 °C). As easily predictable the ejector compression introduces severe losses mainly due to the normal shock and the mixing of the motive and of the driven fluid. Overall COP for the above quoted temperatures decreases from 2.0 (reference cycle) to 0.4–0.7. The optimization of the working fluid showed that comparatively low critical temperatures are favoured and that a fluid complexity similar to that of CH₅N or CH₂Cl₂ gives the best performance. A detailed losses analysis explains this behaviour. In particular at low reduced temperatures the theoretical gain related to the better shape in the T–S plane of both the power and the refrigeration cycle is more than offset by the higher ejector losses due to the stronger normal shock needed to cope with an increased pressure ratio.

Notwithstanding an extensive fluid screening we did not succeed in finding a fluid that could be considered optimum from all points of view including ambient and safety issues. However, a number of traditional (non-zero ODP) chloro-fluoro-carbons and of new (zero ODP) refrigerants were found that yield, on the whole, a satisfactory performance.

Provided calculated COP will be confirmed by experimental testing, ejector powered refrigerators could compete with absorption systems in many applications.     

XPS study of the process of apatite formation on bioactive Ti–6Al–4V alloy in simulated body fluid

Bioactive Ti–6Al–4V alloy, which spontaneously forms a bonelike apatite layer on its surface in the body and bonds to living bone through this apatite layer, can be prepared by producing an amorphous sodium titanate on its surface by NaOH and heat treatments. In this study, the process of apatite formation on the bioactive Ti–6Al–4V alloy was investigated in vitro, by analyzing its surface with X-ray photoelectron spectroscopy as a function of soaking time in a simulated body fluid (SBF). Thin-film X-ray diffractometry of the alloy surface and atomic emission spectroscopy of the fluid were also performed complementarily. It was found that immediately after immersion in the SBF, the alloy exchanged Na⁺ ions from the surface sodium titanate with H₃O⁺ ions in the fluid to form Ti-OH groups on its surface. The Ti-OH groups, immediately after their formation, incorporated the calcium ions in the fluid to form calcium titanate. The calcium titanate thereafter incorporated the phosphate ions in the fluid to form an amorphous calcium phosphate, which was later crystallized into bonelike apatite. This process of apatite formation on the alloy was the same as on the pure titanium metal, because the alloy formed the sodium titanate free of Al and V by the NaOH and heat treatments. The initial formation of the calcium titanate is proposed to be a consequence of the electrostatic interaction of negatively charged units of titania dissociated from the Ti-OH groups with the positively charged calcium ions in the fluid. The calcium titanate is postulated to gain a positive charge and interact with the negatively charged phosphate ions in the fluid to form amorphous calcium phosphate, which eventually stabilizes into crystalline apatite.