介绍“Mechanics of Wave-Induced Forces on Cylinders”一书

最近十多年来近海工程取得了重要进展。但是,流体动力载荷方面的文献却散见于OTC(offshore Technology Conference), International Oceanology Conference, International Ocean Development Confereuce, BOSS (Behavier of Offshore Structures), 美国Coastal Engineering Conference, Joint Conference of the MTS and IEEE on Oceanic Engineering, 以及欧洲的各国一些有关会议的论文集中,此外还散于各种专业期刊,这给有关科技人员了解流体动力载荷问题的进展和发展方向,寻找理想的科研课题带来困难。      

Effects of Bubbles on the Hydraulic Conductivity of Porous Materials – Theoretical Results

In a porous material, both the pressure drop across a bubble and its speed are nonlinear functions of the fluid velocity. Nonlinear dynamics of bubbles in turn affect the macroscopic hydraulic conductivity, and thus the fluid velocity. We treat a porous medium as a network of tubes and combine critical path analysis with pore-scale results to predict the effects of bubble dynamics on the macroscopic hydraulic conductivity and bubble density. Critical path analysis uses percolation theory to find the dominant (approximately) one-dimensional flow paths. We find that in steady state, along percolating pathways, bubble density decreases with increasing fluid velocity, and bubble density is thus smallest in the smallest (critical) tubes. We find that the hydraulic conductivity increases monotonically with increasing capillary number up to Ca 10^–2, but may decrease for larger capillary numbers due to the relative decrease of bubble density in the critical pores. We also identify processes that can provide a positive feedback between bubble density and fluid flow along the critical paths. The feedback amplifies statistical fluctuations in the density of bubbles, producing fluctuations in the hydraulic conductivity.     

Special issue on conveying and handling of particulate solids–Challenges of discrete element simulation,application and calibration

<正>A series of international Conveying and Handling of Particulate Solids(CHoPS)conferences was initiated in Herzliya,Israel in 1995and has since proceeded with six successive conferences held in Jerusalem(1997),the Dead Sea(2000),Budapest(2003),Sorrento(2006),Brisbane(2009)and Friedrichshafen(2012).The conference series covers processes involving particulate solids,for example     

12-Volume Edition “Mechanics of Composites”: Considerable Mile-Stone in the Centenary History of the S. P. Timoshenko Institute of Mechanics

International Applied Mechanics - New extended information on the 12-volume edition Mechanics of Composites is offered in English. It includes the contents of each volume and is addressed to the...     

Remarks on the notion of “pressure”

In addition to understanding the various meanings attached to the word “pressure” one also has to comprehend the meanings of the phrases in which the term “pressure” appears. For instance one comes across the following combinations: “static-fluid pressure”, “thermodynamic pressure”, “mechanical pressure”, “contact pressure”, “stagnation pressure”, “vapor pressure”, “electro-osmotic pressure”, etc., One also often comes across the comment that “pressure is the Lagrange multiplier that enforces the constraint of incompressibility” and that “pressure is the mean normal stress”. In general the word “pressure” with different significations, is used with gay abandon without paying proper attention to its usage¹. The distinction in the meanings of the above terms assumes paramount significance when discussing properties of materials, which could possibly depend on “pressure”. In this short note we discuss the distinction between various significations of the word “pressure”, and their implications with regard to response relations for bodies.     

On the cover of this issue: “Solid Cylinder Torsion for Large Shear Deformation and Failure of Engineering Materials” by W-Y. Lu et al.

Experimental Mechanics -     

Some Results on Dynamics of Special Double-Loop ΣΔ-Modulators

The dynamic behaviour of a specific two-dimensional state space model with discontinuity is studied. This model arises from the study of double-loop -modulators with constant input. Using mathematical tools we explain certain simulation results, and some properties are derived. Simulations based on time-varying input are also provided.     

Resonant-Based Identification of the Poisson’s Ratio of Orthotropic Materials

The resonant-based identification of the in-plane elastic properties of orthotropic materials implies the estimation of four principal elastic parameters: E ₁ , E ₂ , G ₁₂ , and ν ₁₂ . The two elastic moduli and the shear modulus can easily be derived from the resonant frequencies of the flexural and torsional vibration modes, respectively. The identification of the Poisson’s ratio, however, is much more challenging, since most frequencies are not sufficiently sensitive to it. The present work addresses this problem by determining the test specimen specifications that create the optimal conditions for the identification of the Poisson’s ratio. Two methods are suggested for the determination of the Poisson’s ratio of orthotropic materials: the first employs the resonant frequencies of a plate-shaped specimen, while the second uses the resonant frequencies of a set of beam-shaped specimens. Both methods are experimentally validated using a stainless steel sheet.     

Micromechanics Characterization on the Lower Bound Young’s Moduli of Composite Materials Measured from Nanoindentation

Experimental Mechanics - The measurements of the through-thickness Young’s moduli of composite materials are important, but they were not systematically reported because of the complexity. In...