Nicklas Norrick

Convergence on unbalance identification process based on genetic algorithm applied to rotating machinery

This work focusses on the application of genetic algorithm to fault detection in rotating systems and an uncertainty analyses were applied to mass unbalance identification. A finite element model is used to represent the system. The journal bearing stiffness and damping coefficients have already been identified by a model updating process, and they have been included in the model of the system. In order to identify the unknown fault parameters, a genetic algorithm search process is applied. The convergence of the process was investigated with regard to the influence of the main genetic algorithm parameters, taking into account the mean and standard deviation related to the objective function convergence in several cases.

Low-frequency dynamics of an electrorheological fluid in squeeze and shear mode. Part I: experiments

Electrorheological fluids (ERFs) offer a rapid control of damping using very low power requirements. Different models have been proposed to simulate the hysteresis phenomenon observed experimentally in ERF. This paper describes the steps to be taken to extract measurements of an ERF in squeeze and shear mode. A novel modular test facility was designed to perform measurements of a specific ERF in squeeze and shear mode. This device allows the measurement of the dynamic response of the fluid under various excitation conditions. Dense measurement grids of fluid force and electrode displacement at harmonic excitation are collected in dependency of the excitation frequency, the displacement amplitude and the applied electric field. The main problems to be solved during the setup and execution of the measurements are discussed. The steps to be taken during signal processing to achieve high-quality measurements as inputs for material model fitting are described in detail. Example measurements for both squeeze and shear mode are presented. The fitting of the obtained results to a material model for ERF and discussion of the resulting extended Bouc–Wen model will be the topic of an accompanying paper.

Low-frequency dynamics of an electrorheological fluid in squeeze and shear modes. Part II: modeling and identification

Electrorheological fluids (ERFs) offer rapid control of damping using very low power requirements. Different models have been proposed to simulate the hysteresis phenomenon of ERFs. A modular test facility was designed to perform measurements of a specific electrorheological fluid in squeeze and shear modes in Part I. Based on these measurement cycles, material models for squeeze and shear modes are proposed and corresponding model parameters are identified within this parameter space. The fitted models are benchmarked against the measurement data and are capable of resembling the fluid’s dynamic properties at harmonic excitation, including transitions between Bingham-like and visco-elastic material behavior. Once model parameters are identified, the dynamics of an ERF are resembled excellently by phenomenological models. However, clear trends within the parameter space cannot be stated for all model parameters which prevents the derivation of analytical statements for the model parameters. Since the identification of model parameters is not transferable, a new adaptation is necessary for every application. Nevertheless, the presented procedure can be applied directly in these cases and is robust.

Statistical Consideration of Uncertainties in Bolted Joints of the Drive Train of Sheet-Fed Offset Printing Presses

This paper outlines a design process for the bolted joints of the drive train of sheet-fed offset printing presses incorporating statistical data and methods. Sheet-fed offset printing presses are driven by a continuous geared drive train along the length of the press. The bolted joints of the drive train connecting the gears to the cylinders of the press are subjected to high loads, especially during emergency stops. A nonlinear mechanical model of a printing press implemented in Matlab/Simulink is presented which is used to calculate the occurring loads. Measurements of linear and nonlinear system response are presented to support the quality of the mechanical model. The bolted joints between the main drive train gears and cylinders are designed according to current standards. Statistical information based on experimental data is considered during the application of the standardized method. Using the Monte Carlo technique, a more exact description of the joint’s strength is made possible. In this way, the maximum tolerable load for the screw connection is 16% higher than the same result from a standard worst-case calculation.