Advanced Global Nonlinear Dynamic Simulations of Flexible Riser Systems

2014 ◽  
Author(s):  
Arya Majed ◽  
Phil Cooper
Keyword(s):  
Nonlinear Dynamic ◽  
Flexible Riser ◽  
Dynamic Simulations

A Nonlinear Dynamic Substructuring Approach to Global Dynamics of Flexible Riser Systems

2014 ◽  
Author(s):  
Arya Majed ◽  
Phil Cooper
Keyword(s):  
Dynamic Analysis ◽  
Nonlinear Dynamic ◽  
Nonlinear Dynamic Analysis ◽  
Nonlinear Effects ◽  
Global Dynamics ◽  
Computationally Efficient ◽  
Flexible Riser ◽  
Dynamic Simulations ◽  
Stick Slip ◽  
Global Dynamic

Standard riser global dynamic analysis software packages utilize line element models that cannot capture the complex behavior of flexible risers. This paper presents a computationally efficient nonlinear dynamic analysis methodology capable of incorporating detailed finite element models and scalable to global dynamic simulations of entire flexible riser systems. Subject methodology captures the global geometric nonlinear effects and its coupling to stick-slip friction — a clear requirement for accurate armour stress predictions. In addition, the method enables the formulation of stress transformation matrices which allow the direct recovery of armour stresses from the global simulations. A demonstration problem involving the nonlinear dynamic simulation of a 500m flexible riser system is presented.

Dynamic Simulation of a Woodpecker Robot Based on Self-Excited Vibration

2013 ◽  
Vol 753-755 ◽  
pp. 2020-2024
Author(s):  
Yong Xu ◽  
Wei Hu ◽  
Shan Ping Zhang
Keyword(s):  
Dynamic Simulation ◽  
Nonlinear Dynamic ◽  
Passive Movement ◽  
Robot System ◽  
Dynamic Simulations ◽  
Dynamic Behaviors ◽  
Excited Vibration ◽  
Time Histories ◽  
Stable Passive

This paper studies complex nonlinear dynamic behaviors of a woodpecker robot system which can only operate in the presence of friction as it relies on combined impacts and jamming. The woodpecker robot can periodically move without any drives and controls based on self-excited vibration phenomena. The whole time histories of the dynamic simulations in successive periods indicate its cyclical, stable passive movement. Keywords: Passive movement; Self-excited vibration; Dynamic simulation; impact and friction

Potentials and Limitations of an Extended Approximation Method for Nonlinear Dynamic Journal and Thrust Bearing Forces

2018 ◽  
Author(s):  
Daniel Vetter ◽  
Thomas Hagemann ◽  
Hubert Schwarze
Keyword(s):  
Differential Equation ◽  
Nonlinear Dynamic ◽  
Thrust Bearing ◽  
Journal Bearing ◽  
Variable Viscosity ◽  
A Priori ◽  
Cross Coupling ◽  
General Idea ◽  
Dynamic Simulations ◽  
Simulation Quality

Nonlinear dynamic journal bearing modeling within rotordynamic analyses requires the calculation of the nonlinear bearing forces particularly depending on shaft eccentricity and velocity. The bearing forces can be calculated properly using Reynolds differential equation and mass conserving cavitation algorithms, based for example on Elrod’s cavitation algorithm. This approach achieves high model accuracy and allows the consideration of additional effects like misalignment, variable viscosity and transient local oil distribution in the lubricant film. However, despite rising calculating capacity dynamic bearing analyses are still very CPU-time consuming and, consequently, approximation methods are commonly applied in multibody or rotordynamic analyses, especially in day-to-day business. While many approximation procedures are limited to special bearing geometries Glienicke et al. describe a method which is flexible to model different journal bearing geometries, as well as to consider many additional effects like oil supply pressure or starved lubrication conditions in a time averaged manner. It can be applied for both fixed-pad and tilting-pad journal bearings and its characteristic data is included in an a priori calculated map enabling a time-efficient call up of characteristic parameters of the bearing forces from a look-up table in dynamic simulations. Further, the data can be transferred to any other bearing if the requirements of the theory of similarity are supposed to be valid. In this investigation, the method is first successfully extended by the authors to consider misalignment. Secondly, the general idea of the procedure is transferred and applied to thrust bearings in order to enable a six degree of freedom rotordynamic modeling. In case of a simply lateral movement and rotation-symmetric bearing design the procedure is simple, though, in case of tilting movements it becomes more complicated. A misaligned thrust bearing provides tilting and cross-coupling moments. Cross coupling moments are smaller than the main moments, but have similar orders of magnitude and should therefore be considered. Strategies are investigated for a proper approximation of the nonlinear thrust bearing main and cross-coupling forces and moments. All steps are verified using a direct solution of Reynolds differential equation based on an extended mass conserving algorithm adapted from Elrod’s numerical implementation for the stationary case. Finally, the whole procedure and its application to rotordynamic analysis is verified by comparisons with results gained using direct online solution of Reynolds equation in rotordynamic simulation. While good simulation quality of this approximation approach is documented for selected rotor-bearing-systems in literature the range of validity is not clearly defined. Here, the influences of different parameters on the simulation error are investigated conducting different variation calculations for an overhung rotor with documented vibrational behavior from literature. It is shown that the simulation quality depends on the cavitation zone and decreases with rising vibrational velocity. The root cause for this upcoming error and a possible modification for the elimination of this limitation are presented.

Nonlinear Dynamic Analyses of a Gas Turbine Blade for Attainment of Reliable Shroud Coupling

2005 ◽  
Author(s):  
J. Szwedowicz ◽  
S. Slowik ◽  
A. Mahler ◽  
C. J. Hulme
Keyword(s):  
Gas Turbine ◽  
Nonlinear Dynamic ◽  
Contact Stiffness ◽  
Nonlinear Resonance ◽  
Contact Problems ◽  
Complex Problem ◽  
Dynamic Simulations ◽  
Friction Forces ◽  
The One ◽  
Nonlinear Dynamic Analyses

The major objective of this paper is to evaluate a stand-point for integral shroud coupling, regarding the complex problem of nonlinear resonance vibrations of a shrouded blade with friction and impact effects. Following the load sequence in the start-up and further uploading to base load, a nonlinear cyclic FE static computation with friction forces at the shroud interface delivers contact stress results essential for assessment of a reliable shroud coupling. The FE refinement study at the shroud interface proves the reliability of the computed eigenfrequencies with respect to the harmonic engine excitation. Using nonlinear dynamic simulations of the shroud connection with friction forces, contact stiffness, surface roughness and impacts, the decoupling between the static and dynamic motions at the shroud interface is demonstrated. Based on the one-dimensional description of vibration characteristics for the shrouded blade, the resulting normal and tangential contact stiffness are evaluated from the computed 3D FE nodal diameter diagrams. The excitation forces acting on the blade are determined with the stimulus concept, in which an empirical factor is estimated from pulsation measured in the combustor chamber over the frequency range of the blade vibrations. The entire process is illustrated for the redesigned Z-lock interface on the shroud of a gas turbine stage whose contact surfaces had shown fretting problems. The numerical results confirm possible contact failures for the old shroud configuration. The blade calculated with the modified shroud connection shows numerically, stable dynamic behavior and will therefore prevent further fretting contact problems.

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