Author
Dara W. Childs
Other affiliations: Colorado State University, University of Louisville, Texas A&M University System
Bio: Dara W. Childs is an academic researcher from Texas A&M University. The author has contributed to research in topics: Bearing (mechanical) & Labyrinth seal. The author has an hindex of 36, co-authored 241 publications receiving 4712 citations. Previous affiliations of Dara W. Childs include Colorado State University & University of Louisville.
Papers published on a yearly basis
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22 Mar 1993
TL;DR: In this paper, structural-Dynamic Models and Eigenanalysis for Undamped Flexible Rotors are presented. But they do not consider the non-uniformity of Rotordynamic Models for Liquid Annular Seals.
Abstract: Structural-Dynamic Models and Eigenanalysis for Undamped Flexible Rotors. Rotordynamic Introduction to Hydrodynamic Bearings and Squeeze-Film Dampers. Rotordynamic Models for Liquid Annular Seals. Rotordynamic Models for Annular Gas Seals. Rotordynamic Models for Turbines and Pump Impellers. Developing and Analyzing a System Rotordynamics Model. Example Rotor Analysis. Appendices. Index.
525 citations
TL;DR: In this article, a facility and apparatus are described which determine stiffness, damping, and added-mass rotordynamic coefficients plus steady-state operating characteristics of high speed hydrostatic journal bearings.
Abstract: A facility and apparatus are described which determine stiffness, damping, and added-mass rotordynamic coefficients plus steady-state operating characteristics of high speed hydrostatic journal bearings. The apparatus has a current top speed of 29,800 rpm with a bearing diameter of 7.62 cm (3 in.). Purified warm water, 55 C (130 F), is used as a test fluid to achieve elevated Reynolds numbers during operation. The test-fluid pump yields a bearing maximum inlet pressure of 6.9 Mpa (1000 psi). Static load on the bearing is independently controlled and measured. Orthogonally mounted external shakers are used to excite the test stator in the direction of, and perpendicular to, the static load. The apparatus can independently calculate all rotordynamic coefficients at a given operating condition.
152 citations
TL;DR: In this article, the authors derived dynamic coefficients for high pressure annular seals typical of neck-ring and interstage seals employed in multistage centrifugal pumps, and compared the stiffness, damping, and inertia coefficients derived herein based on Hirs' model and previously published results based on other models.
Abstract: Expressions are derived which define dynamic coefficients for high-pressure annular seals typical of neck-ring and interstage seals employed in multistage centrifugal pumps. Completely developed turbulent flow is assumed in both the circumferential and axial directions, and is modeled in this analysis by Hirs' turbulent lubrication equations. Linear zeroth and first-order 'short-bearing' perturbation solutions are developed by an expansion in the eccentricity ratio. The influence of inlet swirl is accounted for in the development of the circumferential flow field. Comparisons are made between the stiffness, damping, and inertia coefficients derived herein based on Hirs' model and previously published results based on other models. Finally, numerical results are presented for interstage seals in the Space Shuttle Main Engine High Pressure Fuel Turbopump and a water pump.
145 citations
TL;DR: In this paper, a finite-length solution procedure is developed for perturbation equations which are based on Hirs' (1973) turbulent lubrication model and apply to small motions about a centered position.
Abstract: A finite-length solution procedure is developed for perturbation equations which are based on Hirs' (1973) turbulent lubrication model. The equations apply to small motions about a centered position and include the influence of swirl and changes in Reynolds number due to perturbations in clearances. Numerical results are presented for a range of L/D ratios, with and without swirl. For zero swirl, changes in the L/D ratios show results which are similar to those obtained by Black and Jenssen (1970), but when L/D = 1, differences of about 15 percent appear. The results including swirl give physically insupportable results at small L/D ratios, such as a negative cross-coupled stiffness coefficient at L/D = 0.2. This result demonstrates that the complete Hirs turbulence model is not suitable for short seals with significant swirling flow.
131 citations
TL;DR: In this paper, an analysis based on the Jeffcott model is presented to explain 1/2 speed and 1/3 speed whirling motion occurring in rotors which are subject to periodic normal-loose or normal-tight radial stiffness variations.
Abstract: Analysis based on the Jeffcott model is presented to explain 1/2 speed and 1/3 speed whirling motion occurring in rotors which are subject to periodic normal-loose or normal-tight radial stiffness variations. The normal-loose stiffness variation results due to bearing-clearance effects, while normal-tight stiffness variations result from rubbing over a portion of a rotor's orbit. The results demonstrate that 1/2 speed subharmonic motion can be explained as either a linear parametric-excitation phenomenon or as a stable nonlinear subharmonic motion. The 1/3 speed motion is shown to be possible due to the radial stiffness nonlinearity. A linear parametric-excitation analysis demonstrates that during a normal-tight rubbing condition, Coulomb damping significantly widens the potential range of unstable speeds.
130 citations
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01 Feb 2011
TL;DR: In this article, the authors focus on the design issues associated with the flow of liquid through a rotating machine and the potential for cavitation and the high density of liquids that enhances the possibility of damaging unsteady flows and forces.
Abstract: The subject of this monograph is the fluid dynamics of liquid turbomachines, particularly pumps. Rather than attempt a general treatise on turbomachines, we shall focus attention on those special problems and design issues associated with the flow of liquid through a rotating machine. There are two characteristics of a liquid that lead to these special problems, and cause a significantly different set of concerns than would occur in, say, a gas turbine. These are the potential for cavitation and the high density of liquids that enhances the possibility of damaging unsteady flows and forces.
527 citations
TL;DR: A review of the interdisciplinary efforts to better understand the design principles for products with honeycomb structures, including their fabrication, performance (e.g., mechanical, thermal and acoustic properties) as well as optimization design is presented in this article.
451 citations
01 Mar 2010
TL;DR: In this article, the reader can understand the dynamics of rotating machines by using extremely simple models for each phenomenon, in which (at most) four equations capture the behavior of rotor vibration.
Abstract: This book equips the reader to understand every important aspect of the dynamics of rotating machines. Will the vibration be large? What influences machine stability? How can the vibration be reduced? Which sorts of rotor vibration are the worst? The book develops this understanding initially using extremely simple models for each phenomenon, in which (at most) four equations capture the behavior. More detailed models are then developed based on finite element analysis, to enable the accurate simulation of the relevant phenomena for real machines. Analysis software (in MATLAB) is associated with this book, and novices to rotordynamics can expect to make good predictions of critical speeds and rotating mode shapes within days. The book is structured more as a learning guide than as a reference tome and provides readers with more than 100 worked examples and more than 100 problems and solutions.
395 citations
01 Jan 2016
TL;DR: Formulas for natural frequency and mode shape is available in the authors' book collection an online access to it is set as public so you can get it instantly.
Abstract: formulas for natural frequency and mode shape is available in our book collection an online access to it is set as public so you can get it instantly. Our book servers hosts in multiple countries, allowing you to get the most less latency time to download any of our books like this one. Kindly say, the formulas for natural frequency and mode shape is universally compatible with any devices to read.
333 citations