A Test Rig for the Experimental Investigation on the Nonlinear Dynamics in the Presence of Large Contact Interfaces and Numerical Models Validation

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Christian Maria Firrone ◽  
Giuseppe Battiato
Keyword(s):  
Permanent Magnets ◽  
Numerical Models ◽  
Harmonic Balance Method ◽  
Lap Joints ◽  
Forced Response ◽  
Fe Model ◽  
Friction Contact ◽  
Test Rig ◽  
Domain Integration ◽  
Riveted Lap Joints

Abstract The simulation of the coupling between components modeled by finite elements (FEs) plays an important role for the prediction of the forced response of the assembly in terms of resonant frequencies, vibration amplitudes, and damping. This is particularly critical when the time-varying stress distribution must be limited for vibrating components with thin thickness coupled with large contacts. Typical examples can be found in aeronautical structures (plates, panels, and bladed disk components) assembled with bolted flanges, riveted lap joints, or joints without hole discontinuities like rail-hook joints, lace wire sealings, and strip dampers. In this paper, a new test rig is introduced for the experimental validation of a reduced-order model (ROM) based on the Gram–Schmidt Interface (GSI) modes applied to a friction contact whose dimensions are not negligible with respect to the size of the substructures. In this case, classical approaches like Craig–Bampton technique might be not effective in reducing the size of the problem when many contact nodes subjected to nonlinear contact loads cannot be omitted. The technique is implemented in a solution scheme in the frequency domain using penalty contact elements and the harmonic balance method. The preload on the joint is produced by permanent magnets to enhance the friction contact without introducing uncertainties due to bolting. Measurements are compared with the ROM simulations and with standard time-domain integration of the full FE model. The advantage of using the GSI technique is shown in terms of time computation and accuracy of the simulation.

Finite-Element Modelling of an Experimental Mistuned Bladed Disk and Experimental Validation

2013 ◽  
Author(s):  
Jean de Cazenove ◽  
Scott Cogan ◽  
Moustapha Mbaye
Keyword(s):  
Finite Element ◽  
Model Building ◽  
Numerical Models ◽  
Dynamic Properties ◽  
Forced Response ◽  
Operating Conditions ◽  
Machining Process ◽  
Fe Model ◽  
Bladed Disk ◽  
Full Disk

Integrally bladed rotors dynamic properties are known to be particularly sensitive to small geometric discrepancies due to the machining process or in-service wear. In this context, it is straightforward that setting up accurate numerical models which take into account real mistuning patterns is a key issue in the prediction of forced response amplitudes under operating conditions. The present study focuses on an experimental bladed disk. Due to strong inter-blade coupling, the geometric mistuning is supposed to result in severe mode localization for the studied bladed disk, thus emphasizing the need of a realistic, predictive finite-element model. This paper describes the procedure which leads to the development and validation of a high-fidelity FE model for a realistic bladed disk, based on coordinate measurements by means of fringe projection. After giving an overview of the coordinate measurement and model building for the studied bladed disk, the comparison of cantilevered-blade and full disk calculated eigenfrequencies to individual blade and full disk in quasi-vacuum measurements are presented.

scholarly journals Influence of Rivet Diameter and Pitch on the Fatigue Performance of Riveted Lap Joints Based on Stress Distribution Analysis

Materials ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 3625 ◽  
Author(s):  
Jintong Liu ◽  
Anan Zhao ◽  
Zhenzheng Ke ◽  
Zhendong Zhu ◽  
Yunbo Bi
Keyword(s):  
Theoretical Model ◽  
Stress Distribution ◽  
Structural Parameters ◽  
Tensile Load ◽  
Lap Joints ◽  
Fatigue Performance ◽  
Fe Model ◽  
Distribution Analysis ◽  
Lap Joint ◽  
Riveted Lap Joints

Interference-fit riveting is one of the most widely used mechanical joining ways in aircraft assembly. The fatigue performance of riveted joints has a significant impact on the service life and reliability of aircraft. In this paper, the fatigue performance of the riveted lap joints with various rivet diameters and pitches are studied based on stress distribution analysis under tensile load. First, a theoretical model of the riveted lap joint under tensile load is developed by using the spring-mass model. The rivet-load stress, bypass stress, and interference stress around the riveted hole are analyzed. Then, the finite element (FE) model of riveted lap joints are established. The influence of rivet diameter and pitch on stress distribution around the riveted hole are discussed. Finally, the fatigue tests are conducted with riveted lap joint specimens to verify the theoretical model and FE results, and a good agreement is observed. Based on the simulation and experimental results, a good combination of structural parameters of the riveted lap joint is found which can optimize the stress distribution around the riveted hole and improve the fatigue life of the riveted lap joint.

scholarly journals Numerical and Experimental Investigations on a Friction Ring Damper for a Flywheel

2021 ◽  
Author(s):  
Xiaodong He ◽  
Zhiwei Zheng ◽  
Xiuchang Huang ◽  
Sen Wang ◽  
Xinsheng Wei ◽  
...  
Keyword(s):  
Vibration Amplitude ◽  
Damping Ratio ◽  
Nonlinear Dynamic Analysis ◽  
Harmonic Balance Method ◽  
Forced Response ◽  
Experimental Investigations ◽  
Response Analysis ◽  
Contact Interface ◽  
Friction Contact ◽  
Stick Slip

Abstract A damping strategy using a friction ring damper for an industrial flywheel was numerically and experimentally investigated. The friction ring damper, located on the arms of the flywheel, was experimentally found to effectively reduce the vibration amplitude of the flywheel. The vibration energy is dissipated when relative motions occur at the friction contact interfaces. Nonlinear dynamic analysis based on a lumped-parameter model of a flywheel equipped with a friction ring damper was conducted. A dimensionless parameter, κ, defined as the ratio of the critical friction force to the amplitude of harmonic force, was used to evaluate the damping performance. For several values of κ, steady-state responses under harmonic excitation and nonlinear modes were obtained using the harmonic balance method (HBM) combined with the alternating frequency–time domain method (AFT). The forced response analysis proved the existence of an optimal value of κ, which can minimize the vibration amplitude of the flywheel. The nonlinear modal analysis showed that all the damping ratio–frequency curves are completely coincident even for different κ, and the frequency corresponding to the maximum damping ratio is equal to the frequency at the intersection of the forced response curves under the fully slip and the fully stick states of the friction contact interface. By analyzing the behaviors of the friction contact interface, it is shown that the friction contact interface provides damping in the combined stick–slip state. The forced response under random excitation was calculated using the Runge–Kutta method and the friction interface behaviors were analyzed. Finally, spectral testing was conducted to verify the numerical results.

Nonlinear Vibration Analysis of Turbine Bladed Disks With Mid-Span Dampers

2020 ◽  
Author(s):  
Erhan Ferhatoglu ◽  
Stefano Zucca ◽  
Daniele Botto ◽  
Jury Auciello ◽  
Lorenzo Arcangeli
Keyword(s):  
Nonlinear Vibration ◽  
Vibration Analysis ◽  
Normal Load ◽  
Harmonic Balance Method ◽  
Response Prediction ◽  
Forced Response ◽  
Algebraic Equations ◽  
Friction Contact ◽  
Bladed Disks ◽  
Cyclic Symmetric

Abstract Friction dampers are one of the most common structures used to alleviate excessive vibration amplitudes in turbomachinery applications. There are very well-known types of contact elements exploited efficiently, such as underplatform dampers. However, different design approach is sometimes needed to maximize the effectiveness further. In this paper, computational forced response prediction of bladed disks with a configuration of the secondary structure commonly used by Baker Hughes design, the so-called mid-span dampers, is presented. Mid-span dampers are metal devices positioned at the middle section of the airfoil span and come into contact with the blade by the centrifugal force acting during rotation. Proposed damping mechanism is applied to a realistic steam turbine bladed disk under cyclic symmetric boundary conditions. Friction contact is modeled through a large number of contact nodes between the blade and the damper by using a 2D friction contact element with variable normal load. Harmonic Balance Method and Alternating Frequency/Time approach are utilized to obtain nonlinear algebraic equations in frequency domain and nonlinear forced response is computed by using Newton-Raphson method. The results obtained by numerical simulations show that mid-span dampers are an efficient configuration type of a damping mechanism to be used in the design of the bladed disks for nonlinear vibration analysis.

A Test Rig for Non-Contact Travelling Wave Excitation of a Bladed Disk With Underplatform Dampers

2010 ◽  
Author(s):  
Teresa Berruti ◽  
Christian M. Firrone ◽  
Muzio M. Gola
Keyword(s):  
Numerical Models ◽  
Experimental Tests ◽  
Calibration Procedure ◽  
Travelling Wave ◽  
Forced Response ◽  
Wave Excitation ◽  
Test Rig ◽  
Response Measurement ◽  
Static Test ◽  
Bladed Disk

The paper presents a static test rig called “Octopus” designed for the validation of numerical models aimed at calculating the nonlinear dynamic response of a bladed disk with underplatform dampers (UPDs). The test rig supports a bladed disk on a fixture and each UPD is pressed against the blade platforms by wires pulled by dead weights. Both excitation system and response measurement system are noncontacting. The paper features the design and the set-up of the noncontacting excitation generated by electromagnets placed under each blade. A travelling wave excitation is generated according to a desired engine order by shifting the phase of the harmonic force of one electromagnet with respect to the contiguous exciters. Since the friction phenomenon generated by UPDs introduces nonlinearities on the forced response, the amplitude of the exciting force must be kept constant at a known value on every blade during step-sine test to calculate Frequency Response Functions. The issue of the force control is therefore addressed since the performance of the electromagnet changes with frequency. The system calibration procedure and the estimated errors on the generated force are also presented. Examples of experimental tests that can be performed on a dummy integral bladed disk (blisk) mounted on the rig are described in the end.

A Simplified Finite Element Riveted Lap Joint Model in Structural Dynamic Analysis

2014 ◽  
Vol 1016 ◽  
pp. 185-191
Author(s):  
Marco Daniel Malheiro Dourado ◽  
José Filipe Bizarro de Meireles
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Dynamic Analysis ◽  
Numerical Models ◽  
Element Model ◽  
Lap Joints ◽  
Mode Shapes ◽  
Lap Joint ◽  
Structural Dynamic ◽  
Riveted Lap Joints

This paper proposes a simplified finite element model to represent a riveted lap joint in structural dynamic analysis field. The rivet is modeled byspring-damperelements. Several numerical models are studied with different quantities of rivets (1, 3 and 5) andspring-damperelements (4, 6, 8, 12, 16 and 20) per rivet. In parallel, samples of two aluminum material plates connected by different quantities of rivets (1, 3 and 5) are built and tested in order to be known its modal characteristics – natural frequencies and mode shapes. The purpose of the different settings is to get the best numerical riveted lap joint representation relatively to the experimental one. For this purpose a finite element model updating methodology is used. An evaluation of the best numerical riveted lap joint is carried out based on comparisons between the numerical model after updating and the experimental one. It is shown that the riveted lap joints composed by eight and twelvespring-damperelements per rivet have the best representation. A stiffness constant valuekis obtained for the riveted lap joints in study.

A Test Rig for Noncontact Traveling Wave Excitation of a Bladed Disk With Underplatform Dampers

2010 ◽  
Vol 133 (3) ◽  
Author(s):  
Teresa Berruti ◽  
Christian M. Firrone ◽  
Muzio M. Gola
Keyword(s):  
Traveling Wave ◽  
Numerical Models ◽  
Experimental Tests ◽  
Calibration Procedure ◽  
Forced Response ◽  
Wave Excitation ◽  
Test Rig ◽  
Response Measurement ◽  
Static Test ◽  
Bladed Disk

This paper presents a static test rig called “Octopus” designed for the validation of numerical models aimed at calculating the nonlinear dynamic response of a bladed disk with underplatform dampers (UPDs). The test rig supports a bladed disk on a fixture and each UPD is pressed against the blade platforms by wires pulled by dead weights. Both excitation system and response measurement system are noncontacting. This paper features the design and the setup of the noncontacting excitation generated by electromagnets placed under each blade. A traveling wave excitation is generated according to a desired engine order by shifting the phase of the harmonic force of one electromagnet with respect to the contiguous exciters. Since the friction phenomenon generated by UPDs introduces nonlinearities on the forced response, the amplitude of the exciting force must be kept constant at a known value on every blade during step-sine test to calculate frequency response functions. The issue of the force control is therefore addressed since the performance of the electromagnet changes with frequency. The system calibration procedure and the estimated errors on the generated force are also presented. Examples of experimental tests that can be performed on a dummy integral bladed disk (blisk) mounted on the rig are described in the end.

Leakage Flow Investigations on a Through-Wall Crack Related to Thermal Fatigue of Nuclear Power Plant Piping

2017 ◽  
Author(s):  
Stefan Schmid ◽  
Rudi Kulenovic ◽  
Eckart Laurien
Keyword(s):  
Experimental Data ◽  
Nuclear Power ◽  
Numerical Models ◽  
Measurement Techniques ◽  
Experimental Investigations ◽  
Leakage Flow ◽  
Test Rig ◽  
Reduced Pressure ◽  
Flow Rates ◽  
Set Up

For the validation of empirical models to calculate leakage flow rates in through-wall cracks of piping, reliable experimental data are essential. In this context, the Leakage Flow (LF) test rig was built up at the IKE for measurements of leakage flow rates with reduced pressure (maximum 1 MPA) and temperature (maximum 170 °C) compared to real plant conditions. The design of the test rig enables experimental investigations of through-wall cracks with different geometries and orientations by means of circular blank sheets with integrated cracks which are installed in the tubular test section of the test rig. In the paper, the experimental LF set-up and used measurement techniques are explained in detail. Furthermore, first leakage flow measurement results for one through-wall crack geometry and different imposed fluid pressures at ambient temperature conditions are presented and discussed. As an additional aspect the experimental data are used for the determination of the flow resistance of the investigated leak channel. Finally, the experimental results are compared with numerical results of WinLeck calculations to prove specifically in WinLeck implemented numerical models.

Forced Response Sensitivity Analysis Using an Adjoint Harmonic Balance Solver

2018 ◽  
Author(s):  
Anna Engels-Putzka ◽  
Jan Backhaus ◽  
Christian Frey
Keyword(s):  
Frequency Domain ◽  
Harmonic Balance ◽  
Unsteady Aerodynamics ◽  
Harmonic Balance Method ◽  
Forced Response ◽  
Algorithmic Differentiation ◽  
Design And Optimization ◽  
Initial Application ◽  
Reverse Mode ◽  
Geometric Changes

This paper describes the development and initial application of an adjoint harmonic balance solver. The harmonic balance method is a numerical method formulated in the frequency domain which is particularly suitable for the simulation of periodic unsteady flow phenomena in turbomachinery. Successful applications of this method include unsteady aerodynamics as well as aeroacoustics and aeroelasticity. Here we focus on forced response due to the interaction of neighboring blade rows. In the CFD-based design and optimization of turbomachinery components it is often helpful to be able to compute not only the objective values — e.g. performance data of a component — themselves, but also their sensitivities with respect to variations of the geometry. An efficient way to compute such sensitivities for a large number of geometric changes is the application of the adjoint method. While this is frequently used in the context of steady CFD, it becomes prohibitively expensive for unsteady simulations in the time domain. For unsteady methods in the frequency domain, the use of adjoint solvers is feasible, but still challenging. The present approach employs the reverse mode of algorithmic differentiation (AD) to construct a discrete adjoint of an existing harmonic balance solver in the framework of an industrially applied CFD code. The paper discusses implemen-tational issues as well as the performance of the adjoint solver, in particular regarding memory requirements. The presented method is applied to compute the sensitivities of aeroelastic objectives with respect to geometric changes in a turbine stage.

A Strain Energy-Based Equivalent Layer Method for the Prediction of Critical Collapse Pressure of Flexible Risers

2018 ◽  
Author(s):  
Xiao Li ◽  
Xiaoli Jiang ◽  
Hans Hopman
Keyword(s):  
Strain Energy ◽  
Critical Pressure ◽  
Numerical Models ◽  
Fe Model ◽  
Collapse Pressure ◽  
Layer Method ◽  
Flexible Risers ◽  
Collapse Behavior ◽  
Equivalent Properties ◽  
Equivalent Layer

Flexible risers are one kind of flexible pipes that transport fluid between subsea facilities and topside structures. This pipe-like structure consists of multiple layers and its innermost carcass layer is designed for external hydrostatic pressure resistance. For the flexible risers used in ultra-deep water fields, the critical collapse pressure of the carcass layers is one of the dominant factors in their safety design. However, the complexity of the interlocked carcass design introduces significant difficulties and constraints into the engineering analysis. To facilitate the anti-collapse analysis, equivalent layer methods are demanded to help construct an equivalent pipe that performs a similar collapse behavior of the carcass. This paper proposes a strain energy based equivalent layer method which trying to bridge the equivalence between those two structures by considering equivalent geometric and material properties for the equivalent layer. Those properties are determined through strain energy equivalence and membrane stiffness equivalence. The strain energy of the carcass is obtained through numerical models and is then used in a derived equation set to calculate the equivalent properties for the equivalent layer. After all the equivalent properties have been determined, an equivalent layer FE model is built and used to predict the critical pressure of the carcass. The prediction result is compared to that of the full 3D carcass model as well as the equivalent models that built based on other existing equivalent methods, which shows that the proposed equivalent layer method gives a better performance on predicting the critical pressure of the carcass.

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