Stiffness

About: Stiffness is a research topic. Over the lifetime, 26241 publications have been published within this topic receiving 424405 citations. The topic is also known as: rigidity.

Determination of Journal Bearing Stiffness and Damping at Hydropower Generators Using Strain Gauges

Abstract: In hydropower generators, the measurement of bearing load, vibration and shaft displacement are wildly used methods for indication of maintenance demand and troubleshooting. When measurement of bearing load and shaft displacement is performed the collected data make it possible to determine the bearing properties, such as stiffness and damping. In this paper a method to determine the bearing stiffness and damping properties for generator journal bearing in hydropower units is presented. The majority of hydropower generators are, however, not equipped with facilities for measurements of bearing loads. To provide the bearings with load sensors it is necessary to reconstruct the bearings, which is associated with heavy expenditures. In this paper an alternative method to obtain the bearing load is utilize, in which strain gauges installed on the generator bearing brackets is used. The collected data in the experiment were obtained from measurements on a 238 MW hydropower generator connected to a Francis type runner. The bracket that holds the generator bearing consists of 18 spokes and each of these spokes has been provided with strain gauges for load measurements. The displacement of the shaft has been measured relative to the generator-bearing casing. The generator-bearing model has been described as a system with two degrees of freedom containing both bearing stiffness and damping matrix as well as displacement and displacement velocity vector. When the calculation of the bearing properties are based on measured data, the irregularity in the calculated stiffness and damping has to be eliminated. To eliminate the unrealistic values of the calculated damping and stiffness, the samples that cause high condition numbers of the displacement–velocity matrix are neglected. The results of the calculation of bearing stiffness and damping are presented in polar plots. This method determines the bearing properties for the generator bearing in a certain point, the point where the generator shaft has its stationary position. The stationary position for the generator shaft depends on the static magnetic pull force acting on the generator rotor and the influence from the turbine. The influence on the bearing characteristics of nonstationary loads as acting on the bearing can be investigated. The non-stationary loads can for instance be rotor unbalance force, influence of thermal expansion and dynamical magnetic pull force. It is thereby possible to evaluate different loads effect on the generator bearing and in which way the bearing properties are affected.Copyright © 2005 by ASME

Contact stiffness of initially stressed neo-Hookean solids

Abstract: This work, using the solution given by Dhaliwal and Singh, presents analytical expressions of the incremental stress and displacement fields for the axisymmetrical indentation of initially stressed, incompressible neo-Hookean solids. A simple relation for the contact stiffness, contact area, elastic constants, and finite stretch can be obtained for the indentation by any rigid axisymmetric indenter, which can be described as a smooth function. The contact stiffness increases with the initial finite stretching; the finite stretching makes materials harder to deform. The results provide a basis for evaluating the effects of residual stresses on the nanoindentation of materials from the viewpoint of finite deformation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2513–2521, 2004

Optimizing Structures with Semi-Rigid Connections Using the Principle of Virtual Work

Abstract: In this paper, the virtual work optimization method (VWOM) has been generalised to consider structures with semi-rigid connections. The VWOM is an automated method that minimizes the mass of a structure with a given geometry, multiple deflection criteria and load cases, while adhering to Design code requirements. In the optimization process, members are selected from a discrete database to meet all strength and stiffness criteria. Connections are modelled using rotational springs, allowing some moment transfer. The rotational stiffness of each connection can be varied form rigid to pinned. The example of a pitched roof frame is used to explain the method. Two case studies are considered: (i) a three-storey two-bay and (ii) a four-storey three-bay office building. The VWOM produced results up to 26.7% lighter than results in the literature. Furthermore, the structures were optimized for a range of rotational stiffness, where all connections in the structure were assumed to have the same rotational stiffness. Characteristic jumps in the optimized mass versus rotational stiffness were observed.