Fluid Mechanical Systems Research Articles

A New Approach on Modeling for Product Development. The Basic Concept of Functional Model.

A new approach on modeling is put forward for fully computer integrated product development.A basic concept of functional model is proposed for embodying this approach.This model is used mainly for explaning and simulating the functions and the efficiencies of various machines composed of many mechnical, fluid-mechanical and electrical parts.All organizations and engineers of various specialties in charge of the product development can collaborate one another using this model.This model can be used in all stages of product development from the initial plan through the design to the prototype testing.Functional models of single degree of freedom mechanical, electrical and fluid-mechanical systems are illustrated, and its validity and usefulness of the proposed approach are demonstrated.

Microfluidic system modeling using VHDL-AMS and circuit simulation

It is demonstrated that the operation of electrofluidic microsystems such as micropumps can be efficiently modeled by standard electrical circuit simulators, using the analog hardware description language (VHDL-AMS) to describe the models. As a representative example, compact models were developed for all constituent parts of an electromechanical micropump fabricated by silicon-based microstructure technology, including electrostatically actuated membrane drives, membrane valves and tubes together with the power supply and control circuitry. With the resulting macromodel of the micropump, the static characteristics as well as the dynamic behavior is correctly reproduced. Thus, with this approach it is possible to include fluidmechanical system components straightforwardly in conventional microelectronic design environments, allowing for easy full system analysis and optimization of even complex microsystems.

Hamiltonian description of the ideal fluid

The Hamiltonian viewpoint of fluid mechanical systems with few and infinite number of degrees of freedom is described. Rudimentary concepts of finite-degree-of-freedom Hamiltonian dynamics are reviewed, in the context of the passive advection of a scalar or tracer field by a fluid. The notions of integrability, invariant-tori, chaos, overlap criteria, and invariant-tori breakup are described in this context. Preparatory to the introduction of field theories, systems with an infinite number of degrees of freedom, elements of functional calculus and action principles of mechanics are reviewed. The action principle for the ideal compressible fluid is described in terms of Lagrangian or material variables. Hamiltonian systems in terms of noncanonical variables are presented, including several examples of Eulerian or inviscid fluid dynamics. Lie group theory sufficient for the treatment of reduction is reviewed. The reduction from Lagrangian to Eulerian variables is treated along with Clebsch variable decompositions. Stability in the canonical and noncanonical Hamiltonian contexts is described. Sufficient conditions for stability, such as Rayleigh-like criteria, are seen to be only sufficient in the general case because of the existence of negative-energy modes, which are possessed by interesting fluid equilibria. Linearly stable equilibria with negative energy modes are argued to be unstable whenmore » nonlinearity or dissipation is added. The energy-Casimir method is discussed and a variant of it that depends upon the notion of dynamical accessibility is described. The energy content of a perturbation about a general fluid equilibrium is calculated using three methods. {copyright} {ital 1998} {ital The American Physical Society}« less

Mechanical construction of a human vocal system for singing voice production

Various ways of vocal sound production are being actively studied. We are constructing a phonetic machine with a vocal chord and a vocal tract based on mechatronics technology. Mechanical construction of a human vocal system is considered to generate natural voice so that it can be advantageously applied to singing voice production. In voice generation, analysis and mechanical realization of the behaviors of the vocal chords and vocal tract are required. Furthermore, the fluid mechanical system is less stable, thus making control more difficult. Several motors are employed to manipulate the mechanical vocal system. Mappings between motor positions and the produced vocal sounds are automatically established in the learning phase. In the singing performance, the system is able to sing while vocal pitches and phonemes are adaptively controlled by an auditory feedback process. This paper presents the latest mechanisms of our mechanical vocal system together with adaptive tuning algorithms of the physical mechanism with an auditory system.

A New Approach on Modeling for Product Development. The Basic Concept of Functional Model.

A new approach on modeling is put forward in order to compose the virtual prototype which is indispensable for fully computer integrated concurrent devolopment of products. A basic concept of functional model is proposed for embodying this approach. This model is used mainly for explaining and simulating the functions and the efficiencies of various machines which are composed of many mechanical, fluid-mechanical and electrical parts. All organizations and engineers of various specialties in charge of the development can collaborate with one another using this model. This model can be used in all stages of product development from the initial plan through the design to the trial testing. Models of parts compose an organic system in the total product model. Functional models of some simple mechanical, electrical and fluid-mechanical systems are illustrated, and its validity and usefulness of the proposed approach are demonstrated.

Segregation and mixing in degenerate diffusion in population dynamics

We study the qualitative properties of degenerate diffusion equations used to describe dispersal processes in population dynamics. For systems of interacting populations, the forms of the diffusion models used determine if the population will intermix or remain disjoint (segregated). The dynamics and stability of segregation boundaries between competing populations is analyzed. General population models with segregation and mixing interactions are derived and connections to behavior in fluid mechanical systems are addressed.

103 A simulation program for analysis of any type of fluid mechanical systems “FLOWSIM”

103 A simulation program for analysis of any type of fluid mechanical systems “FLOWSIM”

A Simulation Program for Analysis of Any Type of Fluid Mechanical Systems "Flowsim"

Transients in fluid mechanical systems with any nunber and type of components are analyzed. The systems may be hydraulic or pneumatic (adiabatic or diabatic), with propagation, heat flow and friction taken into account. A particular fonn of the energy equation for gases takes care of any thermodynamic transfonnations. A simulation program lets know the state of the system in any instant.

Disordered fluid motion in a small closed system

We present the results of an experimental study of the development of disordered motion in a small scale fluid mechanical system as the Reynolds number is increased. The experimental arrangement is a variant of the Taylor-Coutte problem with two inner rotating cylinders and thus the flow is triply-connected. Two different dynamical attractors are investigated and it is shown that while one exhibits features of low-dimensional chaos the other appears to lack any obvious structure. This finding appears to contradict the currently held view that small aspect ratio fluid mechanical systems will always exhibit low-dimensional routes to chaos.

パルス管冷凍機の位相制御

Discussed are methods of controlling phase difference between oscillations of pressure and displacement at the hot end of a pulse-tube. Electric analogs of fluid mechanical system are discussed in the beginning and fluid mechanical components corresponding to capacitance, inductance and resistance in electric circuits are clarified. In the next the phase difference is discussed in terms of equivalent circuit-network. The moving-plug type by Y. Matsubara and A. Miyake is shown to belong to the third generation of pulse-tube refrigerator. The double-inlet one by S. Zhu et al. belongs possibly to the third generation. A differential pulse-tube refrigerator with a free-piston is proposed.

Role of fluctuations in fluid mechanics and dendritic solidification

Many recent advances have occurred in our understanding of the role of fluctuations in fluid mechanics and dendritic solidification. Our purpose here is to present a review of some of these. We shall argue that if one understands completely the simple diffusion-limited aggregation (DLA) model or the closely related dielectric breakdown model (DBM), one understands the role of fluctuations in a range of fluid mechanical systems, as well as in dendritic solidification. The detailed descriptions of some such systems requires suitably chosen variants, such as DBM with anisotropy and noise reduction.

Multifronts and transputer networks for solving fluid mechanical finite element systems

AbstractThis paper is concerned with the implementation of a multifrontal solver on a network of transputers. We briefly discuss the transputer, outline the frontal and multifrontal schemes and consider the implementation of these schemes on the network. Results are presented for two test problems in fluid mechanics showing that the solver displays close to linear speed‐up.

On the weak discontinuity surfaces and tapes of equation systems in fluid mechanics

The weak discontinuity surfaces for a system of quasi-linear differential equations of higher order are developed. The classification of equation systems in fluid mechanics is based on the propagative weak discontinuity surfaces. Types of equations for different flow models are discussed. The conclusion is as follows:

Role of fluctuations in fluid mechanics and dendritic solidification

Our purpose is to review certain recent advances in understanding the role of fluctuations in fluid mechanics and dendritic solidification; many of these represent joint work of the author and J. Nittmann. If one understands completely the simple Ising model, then one understands virtually all systems near their critical points— although the detailed descriptions of many such systems require a suitably-chosen variant of the Ising model (such as the XY or Heisenberg model). By analogy, we shall argue here that if one understands completely the simple diffusion limited aggregation (DLA) model or the closely-related dielectric breakdown model (DBM), then one understands the role of fluctuations in a range of fluid mechanical systems, as well as in dendritic solidification. The detailed descriptions of some such systems require suitably-chosen variants, such as DBM with anisotropy and noise reduction.

On current aspects of finite element computational fluid mechanics for turbulent flows

Numerous configurations for fluid mechanics systems involve motion of the fluid predominantly in a single well-defined direction. Examples include the wide range of aerodynamics as well as most fluids handling systems. Furthermore, in most of these situations, the flow is nominally steady, in all probability turbulent, and usually three-dimensional. A class of problems fitting this description is amenable to numerical simulation under the ‘parabolic’ simplification, wherein an order-of-magnitude analysis is employed to approximate the subsonic, three-dimensional, steady time-averaged Navier-Stokes equations for directed flows. The numerical solution of the resultant pressure Poisson equation is cast into complementary and particular parts, yielding an iterative interaction algorithm formulation. A parabolic transverse momentum equation set is constructed to enforce first-order continuity effects as a penalty constraint. A Reynolds stress constitutive equation, with low turbulence Reynolds number wall functions, is employed for closure, and requires solving the parabolic form of the two-equation turbulent kinetic energy-dissipation equation system. The theoretical aspects regarding accuracy and convergence are summarized, including the efficiency of the penalty constraint concept. The formulational aspects of the algorithm are presented. Numerical results for definitive flow geometries are summarized to document the overall robustness of the developed algorithm.

Automized interactive mesh generators applicable as preprocessors of numerical models simulating flow systems and structural elements

Mathematical modelling of large and geometrically complex systems in fluid mechanics or structural analysis are solved with appropriate numerical methods which in turn require automized mesh generators. Three simple computer programs are described which work interactively as mesh generators/preprocessors for finite difference, finite element (triangularization only) and integrated finite volume schemes.

Aerodynamic effects in the erosion process

Experimental investigations of velocity effects on the erosion of a ductile material by aerodynamically entrained solid particles indicate that erosion varies with the fourth power of velocity in normal or 90° impacts. For smaller angles of attack the exponent is less than 4 but greater than 2. Previous quantitative erosion models do not predict these high exponent values. In this study the two-phase fluid mechanical system is analyzed and an analytical expression is presented that predicts particle impact speeds varying with the square of the fluid free stream speed in normal impacts. It is shown that the high values found experimentally are the result of aerodynamic effects alone.

Stability of a catalytic reaction to finite amplitude disturbances

Methods developed for determining the stability of fluid mechanical systems to disturbances of finite amplitude are applied to the equations for a catalytic reaction. A variational approach to Liapunov stability provides an estimate of the largest perturbation for which a state can be shown to remain stable, while Fourier methods provide an estimate of a perturbation which will cause instability. For a model problem the region of uncertainty between these estimates is small.