No Bull Engineering, a high technology engineering/consulting firm, in Delmar, New York. He is re... more No Bull Engineering, a high technology engineering/consulting firm, in Delmar, New York. He is responsible for rotating equipment consulting services in the forms of engineering design and analysis, troubleshooting, and third-party design audits. Before beginning his consulting career at MTI in 1995, he spent 12 years in the aerospace industry designing pumps, valves, and controls for gas turbine engines. His expertise includes rotordynamics, fluid-film journal and thrust bearings, dynamic simulations, hydraulic and pneumatic flow analysis, CFD, FEA, and mechanical design.
No Bull Engineering, a high technology engineering/consulting firm, in Delmar, New York. He is re... more No Bull Engineering, a high technology engineering/consulting firm, in Delmar, New York. He is responsible for rotating equipment consulting services in the forms of engineering design and analysis, troubleshooting, and third-party design audits. Before beginning his consulting career at MTI in 1995, he spent 12 years in the aerospace industry designing pumps, valves, and controls for gas turbine engines. His expertise includes rotordynamics, fluid-film journal and thrust bearings, dynamic simulations, hydraulic and pneumatic flow analysis, CFD, FEA, and mechanical design. Mr. Corbo has B.S. and M.S. degrees (Mechanical Engineering) from Rensselaer Polytechnic Institute. He is a registered Professional Engineer in the State of New York, and is a member of ASME, STLE, and The Vibration Institute. He has authored more than a dozen technical publications, including one that won the "Best Case Study" award at Bently Nevada's ISCORMA conference in 2001. Clifford P. (Cliff) Cook is with ChevronTexaco, Inc., in Houston, Texas. He is Chairman of the API RP 687 Task Force on Repair of Special Purpose Rotors. He is a Texaco Fellow, registered Professional Engineer in the State of Texas, Chairman of the API Subcommittee on Mechanical Equipment, and a member of the Texas A&M Turbomachinery Symposium Advisory Committee. Mr. Cook is a member of API 617 (compressors), 613 (SP gears), 677 (GP gears), 616 (gas turbines), and past member of API 684 (rotordynamics tutorial), 610 (pumps), 618 (reciprocating compressors) task forces. Mr. Cook has a B.S. degree from the U.S. Merchant Marine Academy, Kings Point, and an M.S. degree (Mechanical Engineering) from Lehigh University.
No Bull Engineering, a high technology engineering/consulting firm located in Guilderland, New Yo... more No Bull Engineering, a high technology engineering/consulting firm located in Guilderland, New York. He is responsible for providing rotating equipment consulting services in the forms of engineering design and analysis, troubleshooting, and third-party design audits to various clients within the turbomachinery industry. Prior to beginning his consulting career at Mechanical Technology Incorporated in 1995, he spent 12 years in the aerospace industry designing pumps, valves, and controls for gas turbine engines. His fields of expertise include rotordynamics, fluid-film journal and thrust bearings, hydraulic and pneumatic flow analysis, computational fluid dynamics, finite element analysis, dynamic simulations, and mechanical design. Mr. Corbo has B.S. and M.S. degrees (Mechanical Engineering) from Rensselaer Polytechnic Institute. He is a registered Professional Engineer in the State of New York and a member of ASME, NSPE, STLE, and The Vibration Institute. He has authored thirteen technical publications.
Tutorialpg. 167One of the foremost concerns facing pump users today is that of rotordynamics. As ... more Tutorialpg. 167One of the foremost concerns facing pump users today is that of rotordynamics. As pump speeds have increased to provide improved efficiencies and lighter packages, rotordynamics has assumed a significantly greater role in determining pump reliability. Pump rotordynamic problems often manifest themselves as shaft fatigue failures and wear/failures of bearings, seals, and impellers. The aim of this paper is to provide users with a basic understanding of rotordynamics and a practical design procedure that can be used to ensure that their pumping systems will not encounter major difficulties in the field. Since pumps are inherently hydraulic devices, their rotordynamic behavior is considerable different from that of their pneumatic turbomachinery counterparts like compressors and turbines. Accordingly, the paper concentrates on these differences and how to handle them in the design process. The paper begins with a review of the fundamentals of rotordynamics and the types of analyses that should be employed in the design process. Guidelines are provided for modelling and for performing rotordynamic staples such as undamped critical speed, unbalance response, and damped natural frequency/stability analysis. The generation of a critical speed map and the tremendous amount of information that can be gleaned from it is also described in detail. Attention is then turned to the factors that render the rotordynamic analysis of pumps significantly different from that of pneumatic turbomachinery. First and foremost is the fact that the mass of fluid contained in hydraulic machines is significant compared with that of the rotor. The “wet” critical speeds of a pump are usually considerably different from their “dry” counterparts. A major factor in this difference is that locations of close-clearance annular fits, such as at seals, balance pistons, wear rings, and impellers, generate significant fluid-structure interaction forces that must be incorporated into the model as dynamic stiffness, damping, and mass coefficients. The presence of these additional supports can generate rotor instabilities and introduce errors into the calculation of journal bearing dynamic coefficients. Additionally, the liquid mass entrained within impellers can produce a “hydraulic unbalance” which is often larger than the mechanical unbalance and, thus, must be accounted for in response calculations. Finally, rotors immersed in liquid experience a fluid coupling with their casings that is not accounted for in conventional calculations. The unique problems often associated with vertical pumps are then explored in detail. Since the “casing” for many vertical pumps is a cantilevered flexible column, rotor-casing interactions must be accounted for by a means such as multilevel modelling. In addition, due to the absence of a gravity load, vertical pump bearing are usually lightly loaded, rendering them especially susceptible to instability problems. Finally, the use of process fluids to lubricate journal bearings often requires nonstandard means for determination of the dynamic coefficients. The paper concludes with a generic step-by-step procedure that users can utilize to analyze any pumping machine they might encounter
is a Project Design En gineer with Mechanical Te chnology Incorporated, a high technology enginee... more is a Project Design En gineer with Mechanical Te chnology Incorporated, a high technology engineering/ consulting firm. In this position, he is re sponsible for performing analytical studies, troubleshooting, and design audits in the areas of rotordynamics, fluid-film lubrica tion, and hydraulics for various customers within the turbomachinery industry. Prior to joining MTI in I 995, he spent 12 years in the aerospace industry designing and analyzing pumps, valves, controls, and electromechanical compo nents for gas turbine engines. His fields of expertise include rotordynamics, journal bearings, incompressible and compressible flow, computational fluid dynamic;s, stress analysis, finite element analysis, dynamic simulations, and mechanical design. He holds B.S. and M.S. degrees (Mechanical Engineering) from Rensselaer Polytechnic Institute. He is a member of ASME.
International Journal of Rotating Machinery, May 1, 2003
This 74-in-diameter blower had an overhung rotor design of titanium construction, operating at 50... more This 74-in-diameter blower had an overhung rotor design of titanium construction, operating at 50 pounds per square inch gauge in a critical chemical plant process. The shaft was supported by oil-film bearings and was directdriven by a 3000-hp electric motor through a metal disk type of coupling. The operating speed was 1780 rpm. The blower shaft and motor shaft motion was monitored by Bently Nevada proximity probes and a Model 3100 monitoring system. Although the blowers showed very satisfactory vibration levels during test runs at the manufacturer's plant, the vibration levels in situ had always been higher than was desirable. After several months of monitoring showed ever increasing vibration levels, one of the blowers was shut down in order to diagnose and resolve the problem. Several steps were taken to diagnose the problem: (1) The rotor was removed and the shop balance was checked and corrected. (2) The bearing support movement due to thermal expansion was measured. Then the shafts were misaligned in the cold condition in order to achieve near-perfect shaft alignment during normal operation. (3) The expected shaft vibration at the bearings was determined using lateral rotor dynamics analysis, including critical speed mapping. (4) A heavy sleeve was added to the blower shaft to increase the radial load on the drive-end bearing. (5) The metal disk type of coupling was replaced by a gear coupling. (6) The finite element and impact of the bearing support pedestal were tested to determine the stiffness of the bearing support. (7) The shaft movement was measured during a coast-down. (8) Tilting-pad bearings were evaluated as a possible replace-
A Comprehensive Torsional Vibration Analysis Procedure: Part I
<jats:title>Abstract</jats:title> <jats:p>One of the foremost concerns facing t... more <jats:title>Abstract</jats:title> <jats:p>One of the foremost concerns facing turbomachinery users today is that of torsional vibration. In contrast to lateral vibration problems, torsional failures are especially heinous since the first symptom of a problem is often a broken shaft, gear tooth, or coupling. The difficulty of detecting incipient failures in the field makes the performance of a thorough torsional vibration analysis an essential component of the turbomachinery design process.</jats:p> <jats:p>The aim of this paper1 is to provide users with a practical design procedure that can be used to ensure that their systems will not encounter major difficulties in the field. It has been the authors' experience that most turbomachinery users encounter little difficulty in determining their machine's natural frequencies due to the large number of resources available in that area. However, problems often arise when they must translate this information into an accurate prediction of whether or not their design will experience torsional vibration problems. Accordingly, this two-part paper concentrates on the steps that should be taken once the natural frequencies have been found.</jats:p>
One of the foremost concerns facing pump users today is that of pulsation problems in their pipin... more One of the foremost concerns facing pump users today is that of pulsation problems in their piping systems and manifolds. In cases where a fluid excitation is coincident with both an acoustic resonance and a mechanical resonance of the piping system, large piping vibrations, noise, and failures of pipes and attachments can occur. Other problems that uncontrolled pulsations can generate include cavitation in the suction lines, valve failures, and degradation of pump hydraulic performance. The potential for problems greatly increases in multiple pump installations due to the higher energy levels, interaction between pumps, and more complex piping systems involved. The aim of this tutorial is to provide users with a basic understanding of pulsations, which are simply pressure disturbances that travel through the fluid in a piping system at the speed of sound, their potential for generating problems, and acoustic analysis and, also, to provide tips for prevention of field problems. The ...
The use of long shaft vertical pumps is common practice in the nuclear waste processing industry.... more The use of long shaft vertical pumps is common practice in the nuclear waste processing industry. Unfortunately, when such pumps employ plain cylindrical journal bearings, they tend to suffer from rotordynamic instability problems due to the inherent lightly-loaded condition that the vertical orientation places on the bearings. This paper describes a case study in which the authors utilized rotordynamic analysis and experimental vibration analysis to diagnose such a problem and designed replacement tilting-pad bearings to solve the problem.
Tutorialpg. 167One of the foremost concerns facing pump users today is that of rotordynamics. As ... more Tutorialpg. 167One of the foremost concerns facing pump users today is that of rotordynamics. As pump speeds have increased to provide improved efficiencies and lighter packages, rotordynamics has assumed a significantly greater role in determining pump reliability. Pump rotordynamic problems often manifest themselves as shaft fatigue failures and wear/failures of bearings, seals, and impellers. The aim of this paper is to provide users with a basic understanding of rotordynamics and a practical design procedure that can be used to ensure that their pumping systems will not encounter major difficulties in the field. Since pumps are inherently hydraulic devices, their rotordynamic behavior is considerable different from that of their pneumatic turbomachinery counterparts like compressors and turbines. Accordingly, the paper concentrates on these differences and how to handle them in the design process. The paper begins with a review of the fundamentals of rotordynamics and the types of analyses that should be employed in the design process. Guidelines are provided for modelling and for performing rotordynamic staples such as undamped critical speed, unbalance response, and damped natural frequency/stability analysis. The generation of a critical speed map and the tremendous amount of information that can be gleaned from it is also described in detail. Attention is then turned to the factors that render the rotordynamic analysis of pumps significantly different from that of pneumatic turbomachinery. First and foremost is the fact that the mass of fluid contained in hydraulic machines is significant compared with that of the rotor. The “wet” critical speeds of a pump are usually considerably different from their “dry” counterparts. A major factor in this difference is that locations of close-clearance annular fits, such as at seals, balance pistons, wear rings, and impellers, generate significant fluid-structure interaction forces that must be incorporated into the model as dynamic stiffness, damping, and mass coefficients. The presence of these additional supports can generate rotor instabilities and introduce errors into the calculation of journal bearing dynamic coefficients. Additionally, the liquid mass entrained within impellers can produce a “hydraulic unbalance” which is often larger than the mechanical unbalance and, thus, must be accounted for in response calculations. Finally, rotors immersed in liquid experience a fluid coupling with their casings that is not accounted for in conventional calculations. The unique problems often associated with vertical pumps are then explored in detail. Since the “casing” for many vertical pumps is a cantilevered flexible column, rotor-casing interactions must be accounted for by a means such as multilevel modelling. In addition, due to the absence of a gravity load, vertical pump bearing are usually lightly loaded, rendering them especially susceptible to instability problems. Finally, the use of process fluids to lubricate journal bearings often requires nonstandard means for determination of the dynamic coefficients. The paper concludes with a generic step-by-step procedure that users can utilize to analyze any pumping machine they might encounter
One of the foremost concerns facing turbomachinery users today is that of torsional vibration. In... more One of the foremost concerns facing turbomachinery users today is that of torsional vibration. In contrast to lateral rotordynamics problems, torsional failures are especially heinous since the first symptom of a problem is often a broken shaft, gear tooth, or coupling. The difficulty of detecting incipient failures in the field makes the performance of a thorough torsional vibration analysis an essential component of the turbomachinery design process. The primary objective of this paper is to provide such a procedure for the special case where the turbomachine is driven by a synchronous motor. Synchronous motors are one of the most notorious sources of torsional vibration problems because of the large pulsating torques they generate during startups. The torsional shaft stresses generated by these large pulsations are usually greater than the shaft material endurance limits, thereby causing the lives of such machines to be limited. The determination of the number of startups that th...
One of the foremost concerns facing turbomachinery users today is that of torsional vibration. In... more One of the foremost concerns facing turbomachinery users today is that of torsional vibration. In contrast to lateral rotordynamics problems, torsional failures are especially heinous since the first 153 TORSIONAL VIBRATION ANALYSIS AND TESTING OF SYNCHRONOUS MOTOR-DRIVEN TURBOMACHINERY
One of the foremost concerns facing turbomachinery users today is that of torsional vibration. In... more One of the foremost concerns facing turbomachinery users today is that of torsional vibration. In contrast to lateral vibration problems, torsional failures are especially heinous since the first symptom of a problem is often a broken shaft, gear tooth, or coupling. The difficulty of detecting incipient failures in the field makes the performance of a thorough torsional vibration analysis an essential component of the turbomachinery design process. The authors' purpose is to provide users with a practical design procedure that can be used to ensure that their systems will not 189 encounter major difficulties in the field. It has been the authors' experience that most turbomachinery users encounter little difficulty in determining their machine's natural frequencies due to the large number of resources available in that area. However, problems often arise when they must translate this information into an accurate prediction of whether or not their design will experience t...
The two subject blowers operate in parallel to circulate wet chlorine gas. Both units had large s... more The two subject blowers operate in parallel to circulate wet chlorine gas. Both units had large synchronous vibrations that led to multiple bearing failures. After simple rotordynamics studies failed to identify the problem, a comprehensive model that accounted for both the motor and blower was successful at identifying the problem as high sensitivity to unbalance loads due to an extremely lightly-loaded (less than one pound) condition at the blower’s inboard bearing (refer to Gutzwiller and Corbo, 2001). Based on the results of the rotordynamic analysis, two changes were made to both units. The couplings were changed from disk to gear couplings, and the blower’s bearings were changed from plain cylindrical to tilting-pad designs. After implementing these changes, unit “A” ran smoothly for a period of six weeks, in accordance with the predictions of the rotordynamic analysis, and it appeared to all that the problem was completely solved. 17 PRACTICAL USE OF ROTORDYNAMIC ANALYSIS AND...
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Papers by Mark Corbo