Investigation into dynamics of a rolling body-bearing-support system in a cold rolling stand

University of Technology, Sydney. Faculty of Engineering and Information Technology.The objective of this thesis is to gain a good understanding of the chatter phenomenon incorporating the dynamic rolling model and mechanical system model of a rolling stand in cold rolling. Although such systems have received great attention in the academic literature, research to-date has not covered dynamic characteristics of the multiple rolling body-bearing-support system due to its complexity and nonlinearities. In this thesis, a steady-state rolling process model that includes the work hardening and work roll flattening effect was developed based on the homogeneous deformation theory with the relaxation of conventional assumptions. A dynamic model of the rolling process was then formulated by taking into account multiple nonlinearities such as the change in friction coefficient, rolling speed, roll gap (strip thickness) reduction and reduction rate with respect to time. In linearisation of rolling force variations as stiffness and damping coefficients, negative gradient of friction coefficient was introduced to identify the negative damping effect in the dynamic roll gap. Also, dynamic rolling force components were included in the analysis by the linearisation of variations of the strip thickness and rolJing speed at exit side and of variations of reduction rate with respect to time. ln addition, a mechanical system model was derived through the inclusion of the support bearings and surface contact between rolls. For the backup roll, a journal bearing model was introduced to examine oil-film thickness change and a tapered roller bearing model was adopted to model the work roll motion. In order to explain dynamics in the surface contact between the backup roll and work roll, Hertzian contact theory is incorporated into the mode-coupling theory. Finally, by coupling the dynamic rolling process 1nodel with a mechanical system model including support bearings and surface contact, a 6DOF mill vibration model for the analysis of vibrations symmetric to the ro11 gap was developed. In determination of stability in the derived cold rolling stand chatter model, stability analyses were performed through the change in the friction coefficient and rolling speed at a given friction gradient. Many different aspects of stability threshold curves (STC) have been obtained from the eigenvalues analysis of the system characteristic equation. Influences of 10 rolling parameters such as the friction gradient, strip width, roll radius, exit thickness, strain and strain-rate exponent, roll offset, bearing viscosity, length and clearance on mill stability were thoroughly investigated. With the linearised stiffness and damping coefficients at the given operating conditions, transient studies were executed to prove the validity of the presented model. Finally, in order to understand the effects of tension variations from the adjacent mill stand, three different tension models were applied into the dynamic roll gap. By so doing, the mill stability has been determined through the inclusion of transient characteristics in the dynamic roll gap. In light of observation from the practical mill configuration, simulation results suggest that chatter arises as the rolling speed increases and friction coefficient decreases under the steady-state rolling conditions. When tension variation applied, instability occurs as the inter-stand distance decreases and a strip feed-in speed variation frequency matches to one of the system natural frequencies

Optical Activities as Computing Resources for Space-time Symmetries

It is known that optical activities can perform rotations. It is shown that the rotation, if modulated by attenuations, can perform symmetry operations of Wigner's little group which dictates the internal space-time symmetries of elementary particles.Comment: 13 pages, to be published in J. Mod. Optic

Design and Fabrication of Electrolyte-Supported Tubular SOFC Combined with Supercritical Water Oxidation on Biomass Gas

Solid oxide fuel cells (SOFCs) are relatively simple and environmental friendly devices for the production of electricity from hydrocarbons. The use of a high pressure supercritical water (SCW) reactor containing a SOFC has the potential for using a multitude of logistical liquid fuels that would otherwise not be possible in a regular SOFC system. A SOFC-SCW system was designed to allow the anode to be exposed to the pressure and chemical milieu of the supercritical water oxidation reactor. The effects of the amount of water/fuel and oxygen fed into the reactor under SCW conditions at 400 degrees C were studied. The effects on electrochemical performance as well as preliminary results on a number of feed stocks, for example pectin, are also described.open1111Nsciescopu

Dynamic Web Content Filtering Based on User's Knowledge

This paper focuses on the development of a maintainable information filtering system. The simple and efficient solution to this problem is to block the Web sites by URL, including IP address. However, it is not efficient for unknown Web sites and it is difficult to obtain complete block list. Content based filtering is suggested to overcome this problem as an additional strategy of URL filtering. The manual rule based method is widely applied in current content filtering systems, but they overlook the knowledge acquisition bottleneck problems. To solve this problem, we employed the Multiple Classification Ripple-Down Rules (MCRDR) knowledge acquisition method, which allows the domain expert to maintain the knowledge base without the help of knowledge engineers. Throughout this study, we will prove the MCRDR based information filtering system can easily prevent unknown Web information from being delivered and easily maintain the knowledge base for the filtering system

An Illumination Identification System for the AIBO Robot

The Four Legged League is a division of the RoboCup initiative that uses Sony AIBOTM robots to further robotics research. Most participants implement vision systems that use the color of objects to perform identification. Calibration of the color classification system must be done and any changes to the lighting of the environment after calibration reduces the accuracy of the system, often to a point at which the robot is effectively blind. This study investigates the relationships in the color data of image pixels between lighting conditions in an effort to identify trends that can be used as the basis of a rule-based system. The aim of the system is to identify the current lighting level as one of a set of known conditions. The proposed systems uses the color data of image pixels and information about the AIBO’s location and orientation to identify lighting levels, allowing a vision system to switch to an appropriate pre-configured calibratio

Tuning Locality of Pair Coherence in Graphene-based Andreev Interferometers

We report on gate-tuned locality of superconductivity-induced phase-coherent magnetoconductance oscillations in a graphene-based Andreev interferometer, consisting of a T-shaped graphene bar in contact with a superconducting Al loop. The conductance oscillations arose from the flux change through the superconducting Al loop, with gate-dependent Fraunhofer-type modulation of the envelope. We confirm a transitional change in the character of the pair coherence, between local and nonlocal, in the same device as the effective length-to-width ratio of the device was modulated by tuning the pair-coherence length xi(T) in the graphene layer.open1133sciescopu