Thermally Induced Synchronous Instability of a Radial Inflow Overhung Turbine: Part I

1997 ◽

Author(s):

H. B. Faulkner ◽

W. F. Strong ◽

R. G. Kirk

Keyword(s):

Thermal Expansion ◽

Operating Speed ◽

Lateral Motion ◽

Turbine Wheel ◽

Thermally Induced ◽

Lateral Dynamics ◽

Morton Effect ◽

Speed Range ◽

Differential Thermal Expansion ◽

Rotor Dynamic

Abstract This paper is in two parts, and concerns the lateral dynamics of a large turbocharger rotor with overhung wheels. Initial rotor dynamic analysis indicated no excessive motion in the operating speed range. However, testing showed excessive motion, which was initially traced to the radial-inflow turbine wheel becoming loose on the shaft, due to transient differential thermal expansion in the wheel on startup. The attachment of the wheel was modified to eliminate this problem. The discussion up to this point is in Part I of the paper, and the remainder is in Part II. The wheel attachment modification extended the range of satisfactory operation upward considerably, but excessive lateral motion was again encountered near the upper end of the operating speed range. This behavior was traced to thermal bowing of the shaft at the turbine end, known as the Morton Effect. The turbine end bearing was modified to eliminate this problem, and satisfactory operation was then achieved throughout the operating speed range.

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The dynamic nature of rotor thermal bending due to unsteady lubricant shearing within a bearing

Proceedings of the Royal Society of London. Series A: Mathematical and Physical Sciences ◽

10.1098/rspa.1994.0061 ◽

1994 ◽

Vol 445 (1924) ◽

pp. 273-290 ◽

Cited By ~ 25

Keyword(s):

Journal Bearing ◽

System Stability ◽

Source Distribution ◽

Time Varying ◽

Dynamic Nature ◽

Thermally Induced ◽

Speed Range ◽

Thermal Bending ◽

Bearing Design ◽

Rotor Dynamic

The influence upon the temperature distribution within a hydrodynamically lubricated journal bearing of a time varying journal orbit is considered and the oscillatory source distribution arising as a result of unsteady shearing of the lubricant is examined with respect to axes which rotate with the journal. The time dependent thermal bend induced in a rotor by such a process has been evaluated and incorporated into a rotor dynamic model for the assessment of system stability. Techniques have been developed enabling calculations to be carried out on an idealized rotor-bearing configuration and the speed range over which instability occurred was established. The rate of growth of the unstable vibrations together with the rate and direction of ‘spiralling’ of the thermal bend vector were also determined. Features of rotor and bearing design having an influence on such thermally induced instability are assessed.

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Microprocessor controlled DC power supply for the generator control unit of a future aircraft generator with a wide operating speed range

Second IEE International Conference on Power Electronics, Machines and Drives ◽

10.1049/cp:20040331 ◽

2004 ◽

Cited By ~ 3

Author(s):

C. Cossar

Keyword(s):

Power Supply ◽

Control Unit ◽

Operating Speed ◽

Dc Power ◽

Speed Range ◽

Dc Power Supply ◽

Wide Operating

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Transformation behavior of yttria stabilized tetragonal zirconia polycrystal–TiB2 composites

Journal of Materials Research ◽

10.1557/jmr.2001.0294 ◽

2001 ◽

Vol 16 (7) ◽

pp. 2158-2169 ◽

Cited By ~ 21

Author(s):

B. Basu ◽

J. Vleugels ◽

O. Van Der Biest

Keyword(s):

Thermal Expansion ◽

Phase Transformation ◽

Low Temperature ◽

Tetragonal Zirconia ◽

Mechanical Analysis ◽

Transformation Behavior ◽

Thermal Expansion Data ◽

Thermally Induced ◽

First Time ◽

Tetragonal Zirconia Polycrystal

The objective of the present article is to study the influence of TiB2 addition on the transformation behavior of yttria stabilized tetragonal zirconia polycrystals (Y-TZP). A range of TZP(Y)–TiB2 composites with different zirconia starting powder grades and TiB2 phase contents (up to 50 vol%) were processed by the hot-pressing route. Thermal expansion data, as obtained by thermo-mechanical analysis were used to assess the ZrO2 phase transformation in the composites. The thermal expansion hysteresis of the transformable ceramics provides information concerning the transformation behavior in the temperature range of the martensitic transformation and the low-temperature degradation. Furthermore, the transformation behavior and susceptibility to low-temperature degradation during thermal cycling were characterized in terms of the overall amount and distribution of the yttria stabilizer, zirconia grain size, possible dissolution of TiB2 phase, and the amount of residual stress generated in the Y-TZP matrix due to the addition of titanium diboride particles. For the first time, it is demonstrated in the present work that the thermally induced phase transformation of tetragonal zirconia in the Y-TZP composites can be controlled by the intentional addition of the monoclinic zirconia particles into the 3Y-TZP matrix.

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Hybrid Active Vibration Control of Rotorbearing Systems Using Piezoelectric Actuators

Journal of Vibration and Acoustics ◽

10.1115/1.2930303 ◽

1993 ◽

Vol 115 (1) ◽

pp. 111-119 ◽

Cited By ~ 42

Author(s):

A. B. Palazzolo ◽

S. Jagannathan ◽

A. F. Kascak ◽

G. T. Montague ◽

L. J. Kiraly

Keyword(s):

Vibration Control ◽

Search Algorithm ◽

Active Vibration Control ◽

Piezoelectric Actuators ◽

Operating Speed ◽

Speed Range ◽

Active Vibration ◽

Linear Fit ◽

Hybrid Interface ◽

Grid Search Algorithm

The vibrations of a flexible rotor are controlled using piezoelectric actuators. The controller includes active analog components and a hybrid interface with a digital computer. The computer utilizes a grid search algorithm to select feedback gains that minimize a vibration norm at a specific operating speed. These gains are then downloaded as active stiffnesses and dampings with a linear fit throughout the operating speed range to obtain a very effective vibration control.

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Application of an Epoxy Cap in a Flip-Chip Package Design

Journal of Electronic Packaging ◽

10.1115/1.3226501 ◽

1989 ◽

Vol 111 (1) ◽

pp. 16-20 ◽

Cited By ~ 4

Author(s):

E. Suhir

Keyword(s):

Thermal Expansion ◽

Flip Chip ◽

Coefficient Of Thermal Expansion ◽

Preliminary Test ◽

Elastic Stability ◽

Thermally Induced ◽

Package Design ◽

Silicone Gels ◽

Low Modulus ◽

Supporting Frame

In order to combine the merits of epoxies, which provide good environmental and mechanical protection, and the merits of silicone gels, resulting in low stresses, one can use an encapsulation version, where a low modulus gel is utilized as a major encapsulant, while epoxy is applied as a protecting cap. Such an encapsulation version is currently under consideration, parallel with a metal cap version, for the Advanced VLSI package design which is being developed at AT&T Bell Laboratories. We recommend that the coefficient of thermal expansion for the epoxy be somewhat smaller than the coefficient of thermal expansion for the supporting frame. In this case the thermally induced displacements would result in a desirable tightness in the cap/frame interface. This paper is aimed at the assessment of stresses, which could arise in the supporting frame and in the epoxy cap at low temperatures. Also, the elastic stability of the cap, subjected to compression, is evaluated. The calculations were executed for the Advanced VLSI package design and for a Solder Test Vehicle (STV), which is currently used to obtain preliminary information regarding the performance of the candidate encapsulants. It is concluded that in order to avoid buckling of the cap, the latter should not be thinner than 15 mils (0.40 mm) in the case of VLSI package design and than 17.5 mils (0.45 mm) in the case of STV. At the same time, the thickness of the cap should not be greater than necessary, both for smaller stresses in the cap and for sufficient undercap space, required for wirebond encapsulation. The obtained formulas enable one to evaluate the actual and the buckling stresses. Preliminary test data, obtained by using STV samples, confirmed the feasibility of the application of an epoxy cap in a flip-chip package design.

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Measurement and interpretation of stress in copper films as a function of thermal history

Journal of Materials Research ◽

10.1557/jmr.1991.1498 ◽

1991 ◽

Vol 6 (7) ◽

pp. 1498-1501 ◽

Cited By ~ 113

Author(s):

Paul A. Flinn

Keyword(s):

Mechanical Properties ◽

Thermal Expansion ◽

Elastic Modulus ◽

Thermal History ◽

Copper Films ◽

Thermally Induced ◽

Aluminum Films ◽

Interconnection Material ◽

Interconnect Systems

Since copper has some advantages relative to aluminum as an interconnection material, it is appropriate to investigate its mechanical properties in order to be prepared in advance for possible problems, such as the cracks and voids that have plagued aluminum interconnect systems. A model previously used to interpret the behavior of aluminum films proves to be, with minor modification, also applicable to copper. Although the thermal expansion of copper is closer to that of silicon and, consequently, the thermally induced strains are smaller, the much larger elastic modulus of copper results in substantially higher stresses. This has implications for the interaction of copper lines with dielectrics.

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