A touchdown bearing with surface waviness: A dynamic model using a multibody approach

2017 ◽  
Vol 231 (4) ◽  
pp. 658-669 ◽  
Author(s):  
Oskari Halminen ◽  
Javier F Aceituno ◽  
José L Escalona ◽  
Jussi Sopanen ◽  
Aki Mikkola
Keyword(s):  
Frequency Domain ◽  
Dynamic Model ◽  
Domain Model ◽  
Velocity Analysis ◽  
Surface Waviness ◽  
Multibody Model ◽  
Inner Race

The amount of vibration induced by surface waviness in a touchdown bearing can be modelled with a multibody approach. This study develops a multibody model that accounts for surface waviness in races of touchdown bearings and employs the model to define the dissimilarities of the rotor and inner ring movements, and to perform inner ring velocity analysis in the frequency domain. Model results are compared with measured and simulated outcomes in the literature. Large movements are found in the orbits and velocities in the frequency domain due to surface waviness. Inner race eccentricity and ellipticity seem to be the cause of the most damaging surface waviness. In the frequency domain, all the significant peaks were noticed to be multiplications of rotor pendulum frequency, and the frequency of the inner ring was traceable in cases with waviness in the bearing. The model proposed in this study enables waviness to be taken into account in design of touchdown bearings.

A Simulation Study on the Effects of Race Surface Waviness on Cage Dynamics in High-Speed Ball Bearings

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Linkai Niu
Keyword(s):  
Wear Rate ◽  
Dynamic Model ◽  
High Speed ◽  
Wave Amplitude ◽  
Ball Bearing ◽  
Ball Bearings ◽  
Cage Effect ◽  
Surface Waviness ◽  
Slip Ratio ◽  
Wear Rates

The effects of the race surface waviness on the cage dynamics, including cage slip ratios, cage instabilities, and time-averaged cage wear rates, in high-speed ball bearings are investigated. A dynamic model of high-speed ball bearings considering the cage effect and the race surface waviness is proposed. Based on the proposed dynamic model, the effects of the maximum wave amplitude (MWA) and the wave order (WO) of race surface waviness on cage slip ratio, cage instability, and time-averaged cage wear rate are investigated. The results show that the race surface waviness has a great effect on the cage dynamics. The waviness would increase the random impacts between balls and cage pockets and thus cause more instable motion of the cage. Although the ball skidding and the cage slip ratio decrease with the increase of MWA, the cage instability and the cage wear rate become severe when MWA increases. In addition, the effect of WO on cage dynamics is nonlinear. The current investigation could provide a theoretical tool for an in-depth understanding of the dynamics in a high-speed ball bearing.

Simulating High Mode Vortex Induced Vibration of Riser in Linear Sheared Current Using an Empirical Time Domain Model

2020 ◽  
Author(s):  
Sang Woo Kim ◽  
Svein Sævik ◽  
Jie Wu
Keyword(s):  
Frequency Domain ◽  
Vortex Shedding ◽  
Time Domain ◽  
Structural Model ◽  
Cross Flow ◽  
Domain Model ◽  
Vortex Induced Vibrations ◽  
The One ◽  
The Time Domain ◽  
Empirical Coefficients

Abstract This paper addresses the performance evaluation of an empirical time domain Vortex Induced Vibrations (VIV) model which has been developed for several years at NTNU. Unlike the frequency domain which is the existing VIV analysis method, the time domain model introduces new vortex shedding force terms to the well known Morison equation. The extra load terms are based on the relative velocity, a synchronization model and additional empirical coefficients that describe the hydrodynamic forces due to cross-flow (CF) and In-line (IL) vortex shedding. These hydrodynamic coefficients have been tuned to fit experimental data and by considering the results from the one of existing frequency domain VIV programs, VIVANA, which is widely used for industrial design. The feature of the time domain model is that it enables to include the structural non-linearity, such as variable tension, and time-varying flow. The robustness of the new model’s features has been validated by comparing the test results in previous researches. However, the riser used in experiments has a relatively small length/diameter (L/D) ratio. It implies that there is a need for more validation to make it applicable to real riser design. In this study, the time domain VIV model is applied to perform correlation studies against the Hanøytangen experiment data for the case of linear sheared current at a large L/D ratio. The main comparison has been made with respect to the maximum fatigue damage and dominating frequency for each test condition. The results show the time domain model showed reasonable accuracy with respect to the experimental and VIVANA. The discrepancy with regard to experiment results needs to be further studied with a non-linear structural model.

scholarly journals Influence of a Taut Cable on the Performance of a Point-Absorber Wave Energy Converter

2018 ◽  
Author(s):  
R. Wang ◽  
Y. Wei ◽  
M. van Rooij ◽  
B. Jayawardhana ◽  
A. I. Vakis
Keyword(s):  
Frequency Domain ◽  
Wave Energy ◽  
Alternative Energy ◽  
Frequency Domain Analysis ◽  
Wave Energy Converter ◽  
Domain Model ◽  
Energy Harvest ◽  
Energy Converter ◽  
Point Absorber ◽  
Improved Model

In recent years, wave energy converters (WECs) have received considerable attention as an efficient way to harvest alternative energy sources. Within this class of systems, point-absorbers are popular and have become one of the most widely used renewable energy harvest designs all over the world, at least in the preliminary R&D stage, with many relevant research works having been published as well. However, unlike the single buoy and PTO systems which already have a comprehensive research basis, the connection cable has received little attention. The traditional taut cable analysis approach, initiated from the needs of the oil&gas industry, has been applied for WEC investigations. However, this approach utilizes an essential assumption that the oscillating term (PTO force) is much smaller than the static term of the cable force (pre-tension) and could be neglected, which may not be proper for WEC applications. In this work, a conventional frequency domain model is utilized to test and verify the validity of the previously mentioned assumption by presenting the ratio between two force terms. Then the ratio could be applied in combination with sea state contours to reveal the critical state of the cable. Then, a fully nonlinear time domain method of a numerical solution of the point-absorber wave energy converter is presented. According to the critical states obtained from the frequency domain analysis, an improved model of a slack cable is proposed. Its influence on the energy extraction performance is investigated using the open source code — WEC-Sim. This work provides insight into simulating a proper model of the cable and how the design of the cable influences the WEC performance.

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