Experimental Determination of Rotor Foundation Parameters for Improved Critical Speed Predictions

1997 ◽  
Author(s):  
Jiankang Xu ◽  
John M. Vance
Keyword(s):  
Critical Speed ◽  
Dynamic Test ◽  
Element Model ◽  
Modal Damping ◽  
Matrix Codes ◽  
Foundation Parameters ◽  
Rotor Dynamic ◽  
Foundation Structure ◽  
Large Rotor

Measurements on a large rotor dynamic test rig in the Turbomachinery Laboratory with a concrete and steel foundation have shown some critical speeds which can only be predicted if the foundation is included in the model. Mobility transfer function measurements on the foundation were made to obtain the required parameters for including the foundation in the rotordynamic computer model. These measurements eliminate the necessity for building a large finite element model of the foundation structure and allow the use of fast transfer matrix codes for modeling rotor bearing systems which have strong foundation participation. A method first described by Nicholas was used to get a set of equivalent bearing coefficients from a combination of the foundation parameters with the true bearing coefficients. Measurements made by the present authors show that the modal damping of the foundation can be obtained easily from the mobility curves, and that the improved critical speed predictions can be obtained in some cases by using only one foundation mode to calculate the equivalent bearing coefficients.

Rotor System Modeling With Foundation Matrices From Experimental Modal Data

1991 ◽  
Author(s):  
Robert W. Stephenson ◽  
Keith E. Rouch
Keyword(s):  
System Analysis ◽  
General Procedure ◽  
System Modeling ◽  
Dynamic Test ◽  
Element Model ◽  
Rotor System ◽  
System Model ◽  
Stiffness Matrices ◽  
Flexible Foundation ◽  
Foundation Structure

Abstract In a rotor system, the bearing housing and foundation structure can have a significant effect on the dynamics of the rotor. A general procedure is presented to include the foundation effects in a rotor system analysis. The procedure uses modal analysis techniques and measured frequency response functions of the actual foundation structure. From this test data, mass, damping, and stiffness matrices are constructed. These matrices can then be assembled with a finite element model of the shaft and bearings to form the overall rotor system model. Unbalance response and system natural frequencies obtained from a laboratory rotor mounted on a flexible foundation are presented, and compared to results computed from a system model which includes foundation matrices constructed from a dynamic test on the actual foundation.

scholarly journals Stiffness Estimation and Equivalence of Boundary Conditions in FEM Models

2021 ◽  
Vol 11 (4) ◽  
pp. 1482
Author(s):  
Róbert Huňady ◽  
Pavol Lengvarský ◽  
Peter Pavelka ◽  
Adam Kaľavský ◽  
Jakub Mlotek
Keyword(s):  
Boundary Condition ◽  
Finite Element ◽  
Boundary Conditions ◽  
Model Updating ◽  
Element Model ◽  
Computational Time ◽  
Stiffness Coefficients ◽  
First Case ◽  
Numerical Approaches

The paper deals with methods of equivalence of boundary conditions in finite element models that are based on finite element model updating technique. The proposed methods are based on the determination of the stiffness parameters in the section plate or region, where the boundary condition or the removed part of the model is replaced by the bushing connector. Two methods for determining its elastic properties are described. In the first case, the stiffness coefficients are determined by a series of static finite element analyses that are used to obtain the response of the removed part to the six basic types of loads. The second method is a combination of experimental and numerical approaches. The natural frequencies obtained by the measurement are used in finite element (FE) optimization, in which the response of the model is tuned by changing the stiffness coefficients of the bushing. Both methods provide a good estimate of the stiffness at the region where the model is replaced by an equivalent boundary condition. This increases the accuracy of the numerical model and also saves computational time and capacity due to element reduction.

Periodic Solutions in Rotor Dynamic Systems With Nonlinear Supports: A General Approach

1989 ◽  
Vol 111 (2) ◽  
pp. 187-193 ◽  
Author(s):  
C. Nataraj ◽  
H. D. Nelson
Keyword(s):  
Dynamic Systems ◽  
Original Problem ◽  
Squeeze Film ◽  
Algebraic Equations ◽  
Trigonometric Collocation ◽  
Nonlinear Algebraic Equations ◽  
The Stability ◽  
Future Work ◽  
Rotor Dynamic ◽  
Large Rotor

A new quantitative method of estimating steady state periodic behavior in nonlinear systems, based on the trigonometric collocation method, is outlined. A procedure is developed to analyze large rotor dynamic systems with nonlinear supports by the use of the above method in conjunction with Component Mode Synthesis. The algorithm discussed is seen to reduce the original problem to solving nonlinear algebraic equations in terms of only the coordinates associated with the nonlinear supports and is a big improvement over commonly used integration methods. The feasibility and advantages of the procedure so developed are illustrated with the help of an example of a typical rotor dynamic system with an uncentered squeeze film damper. Future work on the investigation of the stability of the periodic response so obtained is outlined.

Updating Finite Element Model of Combined Structures on the Basis of Dynamic Test Results

1996 ◽  
Author(s):  
Chen Xin ◽  
Qin Ye ◽  
Yuan Xiguang ◽  
Zhang Ping ◽  
Sun Jian
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Test Data ◽  
Dynamic Test ◽  
Element Model ◽  
Physical Parameters ◽  
Structural Joint ◽  
Combined Structure ◽  
Joint Parameters ◽  
Two Stages

Abstract According to the real situation, a new method of updating the finite element model (FEM) of a combined structure step by step is proposed in this paper. It is assumed that there are two types of error when establishing the FEMs. One of them results from the simplifications, in fact, it is severe for complicated structures, which usually assume many simplifications; the other is from the process of identifying structural joint parameters. For this reason, it is recommended that the FEM should be established in two stages. At the first stage, the local physical parameters relating with the simplifications are corrected by using the dynamic test data of the corresponding substructures. Then, the structural joint parameters that link the substructures are corrected by the dynamic test data of the combined structure as a whole. The updating formula is presented and proved, and its algorithm is also described. And the experimental results show that the efficiency and accuracy of the proposed method are quite satisfactory.

Use of DNVGL-RP-C203 for Determining the Fatigue Capacity of Connectors

2021 ◽  
Author(s):  
Anthony Muff ◽  
Anders Wormsen ◽  
Torfinn Hørte ◽  
Arne Fjeldstad ◽  
Per Osen ◽  
...  
Keyword(s):  
Finite Element ◽  
Fatigue Testing ◽  
Experimental Testing ◽  
High Strength ◽  
Element Model ◽  
Fatigue Analysis ◽  
Full Scale ◽  
The Finite Element Model

Abstract Guidance for determining a S-N based fatigue capacity (safe life design) for preloaded connectors is included in Section 5.4 of the 2019 edition of DNVGL-RP-C203 (C203-2019). This section includes guidance on the finite element model representation, finite element based fatigue analysis and determination of the connector design fatigue capacity by use of one of the following methods: Method 1 by FEA based fatigue analysis, Method 2 by FEA based fatigue analysis and experimental testing and Method 3 by full-scale connector fatigue testing. The FEA based fatigue analysis makes use of Appendix D.2 in C203-2019 (“S-N curves for high strength steel applications for subsea”). Practical use of Section 5.4 is illustrated with a case study of a fatigue tested wellhead profile connector segment test. Further developments of Section 5.4 of C203-2019 are proposed. This included acceptance criteria for use of a segment test to validate the FEA based fatigue analysis of a full-scale preloaded connector.

Dynamic Analysis of a Turbocharger Centrifugal Compressor Impeller

1991 ◽  
Author(s):  
V. Ramamurti ◽  
D. A. Subramani ◽  
K. Sridhara
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Centrifugal Compressor ◽  
Element Model ◽  
Simplified Model ◽  
Cyclic Symmetry ◽  
Compressor Impeller ◽  
Cyclic Symmetric ◽  
The Finite Element Model

Abstract Stress analysis and determination of eigen pairs of a typical turbocharger compressor impeller have been carried out using the concept of cyclic symmetry. A simplified model treating the blade and the hub as isolated elements has also been attempted. The limitations of the simplified model have been brought out. The results of the finite element model using the cyclic symmetric approach have been discussed.

Study of Influence of Residual Stresses on Crack Propagation in Particulate Ceramic Composites

2016 ◽  
Vol 258 ◽  
pp. 178-181 ◽  
Author(s):  
Zdeněk Majer ◽  
Luboš Náhlík ◽  
Kateřina Štegnerová ◽  
Pavel Hutař ◽  
Raúl Bermejo
Keyword(s):  
Residual Stresses ◽  
Crack Propagation ◽  
Element Model ◽  
Ceramic Composites ◽  
Particulate Composites ◽  
Micro Cracks ◽  
Dimensional Finite Element ◽  
Density Factor ◽  
Energy Density Factor

The aim of the present work is to analyze the influence of residual stresses in the particulate ceramic composite on the crack propagation. The crack propagation direction was estimated using Sih’s criterion based on the strain energy density factor. A two-dimensional finite element model was developed for determination of crack path. The residual stresses resulting from the mismatch of coefficients of thermal expansion during the fabrication process of the composite were implemented to the computational model. The effect of the particles shape on the crack propagation was investigated. Conclusions of this paper can contribute to a better understanding of the propagation of micro-cracks in particulate composites in the field of residual stresses.

Shock Spectra of an Armored Vehicle With Cutouts Using ADINA

1993 ◽  
Author(s):  
Aaron D. Gupta ◽  
Henry L. Wisniewski
Keyword(s):  
Impact Load ◽  
Element Model ◽  
Global Response ◽  
Vehicle Performance ◽  
Performance Accuracy ◽  
Secondary Systems ◽  
Frequency Regime ◽  
Armored Vehicle ◽  
Nonlinear Components

Abstract Light combat vehicles are playing an important support role for both troops and other heavily armored combat vehicles. As such, they have a much greater risk than in previous roles of being subjected to transient loads such as impact and overpressure loads. Propagation of ballistic shock from an impacted region to the critical locations and attachment points for secondary systems can cause damage and misalignment to sensitive equipments contributing to malfunction and reduction of vehicle performance. Accuracy of determination of dynamic response of these vehicles is directly dependent on the degree of refinement of the generated model and how well the model incorporates the essential features of the vehicle and correlates to its important characteristics without being over-burdened by non-essential details. Additionally, response of nonlinear components of the vehicle in high frequency regime may influence the overall global response of the vehicle. As a result, hatch openings and access door cutouts with unsymmetric locations may have to be incorporated in the finite element model to allow fair comparison with first order experiments involving a stripped vehicle hull. The current study is an attempt to assess the influence of multiple rectangular cutouts on the overall transient response of a vehicle hull subjected to a side-on impact load.

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