Dynamics of Rotors—Stability and System Identification

Abstract

Concrete structures are normally full of cracks, more so than structures of any other material, and the typical mode of failure of concrete is fracture rather than plasticity. Yet, fracture mechanics so far has not been introduced in standard specifications for concrete design. Its applicability has been doubted by concrete engineers, due to the fact that the linear elastic fracture mechanics was shown long ago to disagree with tests of brittle failures almost as much as the plastic limit analysis. Recent research, however, has shown that fracture mechanics formulations which take into account the nonlinear behavior in the fracture process zone and the distributed nature of cracking can be brought in good agreement with the test results. This has led in recent years to a tremendous surge of interest and intensification of research in the fracture mechanics of concrete. The present volume, which summarizes the recent research results, is thus a very welcome addition to the literature. The book consists of six chapters. Chapter 1, written by G. C. Sih, deals with the mechanics of material damage in concrete, which is characterized chiefly by the material strain energy density function. Chapter 2, prepared by A. DiTommaso, discusses the evaluation of concrete fracture, its microscopic aspects as well as the consequences of cracking for stress-strain relations. Chapter 3, authored by S. Mindess, is the largest chapter which treats fracture testing of cement and concrete and discusses the physical phenomena involved in fracture, the rate of loading effects, notch sensitivity, the fracture toughness parameters and their measurement techniques, and the effect of specimen size. A valuable aspect of this chapter is an extensive and detailed summary of the concrete fracture test data available in the literature. An excellent historical review, documented by a set of 175 references, is also given in this chapter. Chapter 4, written by S. P. Shah, analyzes the dependence of concrete fracture toughness on specimen geometry and composition. This chapter presents a lucid and thorough discussion of the resistance curves and their measurement techniques, proposes a theoretical model for the nonlinear fracture process zone, and gives many comparisons with test data. Fracture of fiber reinforced concrete is also discussed and a new model is presented. Chapter 5, by F. O. Slate and K. C. Hover, deals with microcracking in concrete, discussing the microscopic observations of microcracks as well as their effect on the properties of concrete, with particular attention to the differences between high strength and low strength concretes. Finally, Chapter 6, prepared by P. Jacquot, addresses the specialized field of interferometry

Application of an Open Environment for Simulation of Power Plant Unit Operation under Steady and Transient Conditions

“…A lateral vibration model considers the elastic shaft of the high slenderness ratio consists of several rigid discs, mounted horizontally embedded in hydrodynamic bearings arranged upon the supports [42,43]. All system mass is concentrated in the nodes.…”

Experimental Study on Vibration of a Rotating Blade

“…In the past two decades, both analytical methods and experimental measurement techniques have been developed to analyze the vibration behavior of a rotating blade (Leissa 1981). The stability of the blade vibration is affected by the centrifugal force due to the rotation, the stagger angle of the blade, pre-twist and taper of the blades (Mahrenholtz 1984). In this work the effects of the rotating speed and blade stagger angle on the blade natural frequencies are studied.…”