Electrogas- and electrohydrodynamic control of gas and liquid jets and flows

The physical and mathematical principles of the method of electrogas-and electrohydrodynamic conversion of electrical signals to pneumatic (hydraulic) signals and vice versa for control of gas and liquid jets and flows in electropneumohydraulic systems are considered. St. Petersburg State Technical University, St. Petersburg 195251. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 2, pp. 25–31, March–April, 2000.     

Fatigue and static strength of notched and unnotched aluminum-alloy and steel specimens

This paper describes a method of presentation of fatigue data on three commonly used aircraft materials, 2024-T3 and 7075-T6 aluminum alloys and normalized SAE 4130 steel, such that variations in fatigue strength with stress-concentration factor can be shown. Comparisons of the fatigue strengths of 2024-T3 and 7075-T6 aluminum are made for the most useful range of stress-concentration factors. Static-strength results of notched and unnotched specimens of the three materials are presented to show how the strength varies with some parameters of the stress concentration. Comparison of the data with one theory for the strength of cracked specimens was made.     

STICTION AND ANTI—STICTION IN MEMS AND NEMS

Stiction in microelectromechanical systems (MEMS) has been a major failure mode ever since the advent of surface micromachining in the 80s of the last century due to large surfacearea-to-volume ratio. Even now when solutions to this problem are emerging, such as self-assembled monolayer (SAM) and other measures, stiction remains one of the most catastrophic failure modes in MEMS. A review is presented in this paper on stiction and anti-stiction in MEMS and nanoelectromechanical systems (NEMS). First, some new experimental observations of stiction in radio frequency (RF) MEMS switch and micromachined accelerometers are presented. Second, some criteria for stiction of microstructures in MEMS and NEMS due to surface forces (such as capillary, electrostatic, van der Waals, Casimir forces, etc.) are reviewed. The influence of surface roughness and environmental conditions (relative humidity and temperature) on stiction are also discussed. As hydrophobic films, the self-assembled monolayers (SAMs) turn out able to prevent release-related stiction effectively. The anti-stiction of SAMs in MEMS is reviewed in the last part. The project supported by the Distinguished Young Scholar Fund of NSFC (10225209), key project from the Chinese Academy of Sciences (KJCX2-SW-L2) and National “973” Project (G1999033103)     

水和水蒸汽热力学物性参数及导数的计算与应用

本文针对现代换热设备设计、两相流动与传热研究的需要,介绍了可供科研使用的水和水蒸汽物性计算方法,完善了计算程序。根据超临界锅炉设计中的超临界水的物性计算,两相流研究和换热设备动态特性研究中对物性导数计算的需要,提供了两个算例,并进行了定性分析。     

Fracture and stability of materials and structural members with cracks: approaches and results

A new alternative approach to fracture problems for materials and structural elements with cracks is set out. It is based on the mechanism of local instability near defects. The approach is used to study the fracture of materials compressed along interacting cracks and the fracture of thin structural members with cracks under tension with allowance for local buckling.__________Translated from Prikladnaya Mekhanika, Vol. 40, No. 12, pp. 18–64, December 2004.     

Fundamental properties of elasto-plastic matrix and existence and uniqueness of elasto-plastic stress and displacement

Based on the assumption that the yield criterionF(,)=0 is a differentiable surface in stress space and by starting from a specially defined real Euclidean space, the fundamental properties of the elasto-plastic matrix in the incremental theory of plasticity is discussed in detail. By using these results, a convex analysis is made to prove the existence and uniqueness of 1) the distribution of incremental elasto-plastic stress for work-hardening materrials; 2) the displacement distribution for work-hardening materials. Material isotropy is assumed in all discussions of relevant problems.     

Drawing and extruding: Theoretical and approximate formulas

Summary The problem of drawing of wires and of strips has been treated in several studies; among these the studies of Sachs seem essential. However, the results deduced according to similar theories are not always in accordance with the experimental results: reduction of area or of thickness are in fact usually smaller than those resulting from the theory. This is in dependance of the fact that Sachs has adopted the Limiting Condition of Yielding by v. Mises, according to which the limit values of stress in traction and compression are equal. More recently other AA. (Alberti, Noto La Diega, Bugini), admitting the Limiting Condition of Yielding by A. (or of the Paraboloid of Revolution) of which we have treated in one of our previous works, attain results tallying with the experience. In the present study the above said subjects are treated as to evidence their unitarian signifiance and clarify their several aspects. The approximate formulas proposed by A. result of easy and quick application. In the same manner are treated other problems, among which the problem of the extrusion (Bagarello, Ammendola).

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Sommario Il problema della trafilatura dei fili metallici e delle strisce di lamiera è stato trattato in diverse Memorie, fra le quali fondamentali sono quelle del Sachs. I risultati dedotti in base a tali studi non sempre però concordano con le risultanze sperimentali: i rapporti di riduzione delle aree o degli spessori sono infatti di norma inferiori a quelli che risultano da tali teorie. Ciò dipende dal fatto che il Sachs ha posto a base dei suoi studi la Condizione di Plastificazione del v. Mises secondo la quale i limiti di resistenza del materiale che si considera alla trazione e alla compressione semplice sono uguali. Più recentemente altri AA. (Alberti, Noto La Diega, Bugini), adottando la Condizione di Plastificazione dell' A. (o del Paraboloide di Rivoluzione), del quale abbiamo trattato in un precedente lavoro, pervengono a risultati più attinenti alla practica. Col presente studio gli argomenti vengono trattati mettendone in evidenza il significato unitario e chiarendone i vari aspetti. Le formule approssimate proposte dall' A. risultano di facile e immediata applicazione. In maniera analoga vengono trattati altri problemi, fra i quali quello dell'estrusione (Bagarello, Ammendola).

     

Fracture and contact problems for and elastic wedge

The paper deals with the plane elastostatic contact problem for an infinite elastic wedge of arbitrary angle. The medium is loaded through a frictionless rigid wedge of a given symmetric profile. Using the Mellin transform formulation the mixed boundary value problem is reduced to a singular integral equation with the contact stress as the unknown function. With the application of the results to the fracture of the medium in mind, the main emphasis in the study has been on the investigation of the singular nature of the stress state around the apex of the wedge and on the determination of the contact pressure.

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Résumé Dans cet essai le problème plan élastostatique de contact pour un coin élastique d'angle arbitraire est étudié. Le milieu est chargé à travers un coin rigide de profil symétrique sans friction. En utilisant la transformation de Mellin le problème de valeurs limites mixtes, est réduit à une équation intégrale singulière où l'effort de contact est la fonction inconnue. Avec l'application des résultats de la rupture du milieu, l'étude est concentrée principalement sur l'investigation de la nature singulière de l'état d'effort autour du sommet du coin et sur la détermination de la pression de contact.

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This work was supported by NSF under the Grant GK 42771X and by NASA under the Grant NGR 39-007-011.     

Data-driven modeling and learning in science and engineering

In the past, data in which science and engineering is based, was scarce and frequently obtained by experiments proposed to verify a given hypothesis. Each experiment was able to yield only very limited data. Today, data is abundant and abundantly collected in each single experiment at a very small cost. Data-driven modeling and scientific discovery is a change of paradigm on how many problems, both in science and engineering, are addressed. Some scientific fields have been using artificial intelligence for some time due to the inherent difficulty in obtaining laws and equations to describe some phenomena. However, today data-driven approaches are also flooding fields like mechanics and materials science, where the traditional approach seemed to be highly satisfactory. In this paper we review the application of data-driven modeling and model learning procedures to different fields in science and engineering.     

Microcanonical Entropy and Mesoscale Dislocation Mechanics and Plasticity

A methodology is devised to utilize the statistical mechanical entropy of an isolated, constrained atomistic system to define constitutive response functions for the dissipative driving-force and energetic fields in continuum thermomechanics. A thermodynamic model of dislocation mechanics is discussed as an example. Primary outcomes are constitutive relations for the back-stress tensor and the Cauchy stress tensor in terms of the elastic distortion, mass density, polar dislocation density, and the scalar statistical density.     

Sound and vorticity interactions: transmission and scattering

We review several aspects of the propagation of sound in vortical flows. We restrict ourselves to isothermal, humidity-free flows at low Mach number M. Since vorticity plays a major role in vortex-flow interactions we focus on vortical flows. We consider two main canonical situations. The first concerns the transmission of sound. We analyze the evolution of acoustic wavefronts as they propagate across a single vortex. The second situation addresses the scattering of sound waves by nonstationary vortices. We study the evolution of the acoustic pressure emitted in the far field, at an angle with the initial direction of propagation. In this geometry one performs direct spectroscopy of the flow vorticity field. In each case, we review theoretical results and compare with experimental measurements and numerical simulations when available. We also briefly report how the following new acoustic techniques have recently been used to study complex or turbulent flows: time-resolved acoustic spectroscopy, speckle interferometry and Lagrangian particle tracking. PACS 43.25, 43.28, 47.32, 67.40     

Flows around two airfoils performing fling and subsequent translation and translation and subsequent clap

The aerodynamic forces and flow structures of two airfoils performing “fling and subsequent translation“ and “translation and subsequent clap“ are studied by numerically solving the Navier-Stokes equations in moving overset grids. These motions are relevant to the flight of very small insects. The Reynolds number, based on the airfoil chord length c and the translation velocity U, is 17. It is shown that: (1) For two airfoils performing fling and subsequent translation, a large lift is generated both in the fling phase and in the early part of the translation phase. During the fling phase,a pair of leading edge vortices of large strength is generated; the generation of the vortex pair in a short period results in a large time rate of change of fluid impulse, which explains the large lift in this period. During the early part of the translation, the two leading edge vortices move with the airfoils;the relative movement of the vortices also results in a large time rate of change of fluid impulse, which explains the large lift in this part of motion. (In the later part of the translation, the vorticity in the vortices is diffused and convected into the wake.) The time averaged lift coefficient is approximately 2.4 times as large as that of a single airfoil performing a similar motion. (2) For two airfoils performing translation and subsequent clap, a large lift is generated in the clap phase. During the clap, a pair of trailing edge vortices of large strength are generated; again, the generation of the vortex pair in a short period (which results in a large time rate of change of fluid impulse) is responsible for the large lift in this period. The time averaged lift coefficient is approximately 1.6 times as large as that of a single airfoil performing a similar motion. (3) When the initial distance between the airfoils (in the case of clap, the final distance between the airfoils) varies from 0.1 to 0.2c, the lift on an airfoil decreases only slightly but the torque decreases greatly. When the distance is about lc， the interference effects between the two airfoils become very small.     

The fixed point and eigenelement of sum and product about concave and convex operators

In this paper, we obtain the sufficient conditions under which there exists the fixed point of sum and product about concave and – convex operators in the positive cone of linear semi-order space, and the iterative procedure and error estimate can be given. The relation between eigenvalue and eigenelement will also be studied in this paper.     

Legal and policy issues in genetics and insurance

Genetic screening and testing techniques provide a powerful diagnostic tool for the acquisition of predictive information. The potential value of such diagnostic techniques cannot be overstated. However, commercial organisations such as insurance companies and employers are also highly interested in the acquisition and use of genetic information. Concerns about the potential abuse of genetic information have stimulated a counter-current of public pressure for restrictions on the use which can be made of genetic diagnostic information. In a number of countries this pressure has generated enough concern to stimulate legislatures to enact laws which curtail the use and acquisition of genetic information. This pattern has clearly emerged in the United States of America and there are indications that similar trends are developing in Europe. This paper examines the law and policy issues arising from the interface between genetics and insurance.     

Calculation of friction and heat and mass exchange on rough permeable plane and axisymmetric bodies

The most effective methods of thermal shielding are characterized by the presence of a normal component of the velocity on the wall. They include porous cooling and the use of ablated coverings. If the heat-shielding materials have a granulated microstructure, their thermal expansion leads to roughness of the surface, as in the case of porosity of the wall. The present paper presents an integral method for calculating the drag and heat and mass transfer to a rough permeable surface in the case of a gradient flow of a compressible reacting gas.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 37–46, September–October, 1979.It is a pleasure to thank J. A. Schetz, who kindly sent tables of his experimental data, and also E. G. Zaulichny for discussing the work.