Effect Of Starvation On The Dynamic Properties Of Tilting Pad Journal Bearings

LectureA new 46 MW steam turbine became unstable as the load on the turbine was increased. The turbine had a relatively long slender shaft and the subsynchronous frequency was near the first critical speed of 1800 rpm. In an effort to allow the machine to reach full load a bearing redesign was undertaken. The bearing design was changed from the original 5 pad tilting pad journal (TPJ) bearings, orientated with the load on the bottom pad (LOP), to three pad TPJ’s also in the LOP configuration. Analysis indicated that the additional asymmetry in the dynamic coefficients would significantly increase the system logarithmic decrement (log dec) and allow the machine to run at full load without going unstable. With the three pad bearings installed the machine was brought up in speed and experienced subsynchronous vibration before reaching full speed. A design review of the bearings indicated that the top two pads of the three pad bearing were operating in the fully starved condition; that is they were not receiving sufficient oil to develop a hydrodynamic oil film. As such the horizontal stiffness went to near zero. This paper will present the results of the analysis work performed, including the starved bearing analysis, and the resulting redesign of the three pad bearing to run flooded. Operation as a flooded bearing allowed the machine to run fully loaded with no indications of unstable operation

Stabilizace, separace a rekonstrukce stavu nelinearnich systemu.

This thesis dealt with the problem of non-linear systems synthesis. The main aim of it is to integrate stabilization and state reconstruction methods of non-linear systems in order to analyze a separation principle problem for non-linear systems in order to analyze a separation principle problem for non-linear systems, and then to propose a possible solution for it. The stabilization and state reconstruction methods mentioned in the thesis are based on the same element. It is called the dissipation normal form. In case of the stabilization method the dissipation normal form is used in such a way that the structure of the representation of a closed loop system is only chosen in this form. An appropriate controller is determined so that our demands required of the behaviour of a closed loop system are realized. The method provides us more flexibility in the choice of closed loop system behaviour in comparison with pole placement or optimisation techniques. We can implement magnitude-dependent damping with the help of a non-linear damping function. Then, the controller containing the non-linear damping function has a greater damping ability than controllers designed in other ways. In case of the stet reconstruction method the dissipation normal form is used in such a way that the structure of the representation of an error system is only chosen in this form. It gives us similar advantages as on the possibilities of the stabilization method. We can implement magnitude-dependent damping with the help of a non-linear damping function again. Then, the error system containing the non-linear damping function has a greater damping ability than a linear one. By means of integrating the stabilization and state reconstruction methods we have managed to find the solution of the separation principle problem for a certain class of non-linear systems. It is embodied in the proposal of a compensation function that guarantees the asymptotical stability of a resulting closed loop system after performing separation if it is put to a designed controller as an addition.(Summary in EnglishAvailable from STL, Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi

Generalized Tellegen Principle and Physical Correctness of System Representations

The paper deals with a new problem of physical correctness detection in the area of strictly causal system representations. The proposed approach to the problem solution is based on generalization of Tellegen's theorem well known from electrical engineering. Consequently, mathematically as well as physically correct results are obtained. Some known and often used system representation structures are discussed from the developed point of view as an addition

Non-linear and signal energy optimal asymptotic filter design

The paper studies some connections between the main results of the well known Wiener-Kalman-Bucy stochastic approach to filtering problems based mainly on the linear stochastic estimation theory and emphasizing the optimality aspects of the achieved results and the classical deterministic frequency domain linear filters such as Chebyshev, Butterworth, Bessel, etc. A new non-stochastic but not necessarily deterministic (possibly non-linear) alternative approach called asymptotic filtering based mainly on the concepts of signal power, signal energy and a system equivalence relation plays an important role in the presentation. Filtering error invariance and convergence aspects are emphasized in the approach. It is shown that introducing the signal power as the quantitative measure of energy dissipation makes it possible to achieve reasonable results from the optimality point of view as well. The property of structural energy dissipativeness is one of the most important and fundamental features of resulting filters. Therefore, it is natural to call them asymptotic filters. The notion of the asymptotic filter is carried in the paper as a proper tool in order to unify stochastic and non-stochastic, linear and nonlinear approaches to signal filtering

Effect of Inclusions on Fatigue Strength of Heat Treated Components

Inclusions significantly affect fatigue properties of quenched and tempered parts. Data about inclusions importance in fatigue crack initiation process were acquired within the framework of a systematical fatigue test programme carried out to verify fatigue properties of CrNiMo(V) steels quenched and tempered to 800 1000 MPa strength. A valuable set of fatigue failures from the high lifetime area was acquired.Microfractographical analysis of these failures enabled to evaluate critically the influence of inclusions, their dimensions, character and morphology on the initiation and propagation of the fatigue cracks in the area of fatigue strength. Comparison of inclusions size "a" according to Murakami with size determined experimentally was made. Limiting influence of small single inclusions in the structure was shown. Initiation of secondary fatigue cracks on inclusions outside of the fracture initiation area was observed. Danger of the fracture initiation after very high lifetime was confirmed