FEM (MSC.Nastran SOL600) and Multibody(MSC.Adams flexible contact) solutions: an application example in helicopter rotor analysis

Daniele CatelaniMSC. Software - EMEA Aerospace Consultant

Francesca BianchiAgustaWestland – Structural Analyst Rotor Department

Stefano Orzi

Politecnico di Milano

FEM (MSC.Nastran SOL600) and Multibody(MSC.Adams flexible contact) solutions: an application example in helicopter rotor analysis

Daniele CatelaniMSC. Software - EMEA Aerospace Consultant

Francesca BianchiAgustaWestland – Structural Analyst Rotor Department

Stefano Orzi

Politecnico di Milano

• Contact analysis into model with flexible bodies

� Available technologies

� MSC.Nastran SOL600 (Marc embedded technology)

� MSC.Adams Flex2Flex contact feature

� Comparison between SOL600 and Adams

� Comparison and validation with Experimental Tests

• Example: Helicopter Tail Rotor control chain

• Workflow

� FEM model for experimental results correlation and validation

� Adams flex model

� correlation with SOL600

� DOE for parameters tuning and validation

� Model Improvements:

� full kinematic and flexible model

� Dynamic, transient analysis implementation

� DOE for design also

Introduction

Bushing

Pitch control Beam

Ring

Actuator shaft

2

• Helicopter Tail Rotor provides Thrust to compensate Main Rotor Torque

• Control chain allows the pilot to change the blade pitch and - consequently –to control the Thrust

• Control chain: assembly of moving parts mechanichally joined together, involving CONTACTS btw parts

• Control chain Stiffness has to be known for dynamic assessments

• Stiffness needs to be evaluated for different control configurations

• Evaluation is performed by test and by analysis on simplified models

It is evident the importance of a simulation tool

� well correlated wrt experimental results

� to be used for preliminary design

� because allows quick changes of control configuration (i.e. pilot control input)

Tail rotor: problem description

More than words….

Experimental tests

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• Scope

� Identify tail rotor control chain stiffness

� Evaluate coupling effect btw actuator shaft and bushing

� Identify CONTACT characteristics

• Equipment

� Actuators to apply the loads (statically and dynamically)

� Displacement transducers to measure the displacements at proper locations (i.e. Along the shaft and on the pitchcontrol beam)

� Strain gauges to study the load paths

� A proper rig allowing the control chain installation withoriginal parts

• Tests

� Collective and cyclic loads

• Results

� Test Data Post-processing allows the calculation of the control chain stiffness for subsequent dynamic assessments: bending moment/load curves shows the effect of contact btwbushing, ring and shaft

Bushing

Pitch control Beam

Actuator shaft

Ring

• Analysis

� SOL600 uses already existing Nastran bdf file (FEM data)

� All bodies modelled with solid elements (HEXA)

� Local Mesh Refinement for contact and stress evaluation

� Different materials are considered

� Rigid element for loads and constraints

� Applied loading conditions to reproduce physical tests

� Five contact bodies defined (“touched” and “glue” types)

� Deformable – deformable contact

� Parameters/Solution tuning

� Contact detection

� Tolerance parameters

� Bias distance

� Contact body/surface definition: Master/Slave

� The contacts mainly affecting the stiffness results are:

� actuator shaft – bushing installed in the power shaft

� actuator shaft – ring installed in the power shaft

SOL600 analysis

• Static analysis performed on the most complex sub-partof the assembly (pitch beam), properly clamped, forverifying correlation with experimental stiffness

• Static analysis to simulate the full control chain stiffnesstests: 2 configurations of the assembly are considered

� Max pitch

� Min pitch

� Note 1: No Analysis with time–dependent loads(performed in the lab test)

� Note 2: No Analysis with time-dependent changeof the assembly configuration and rotating shaft(performed with Adams)

� Note 3: CPU time to complete one SOl600 run on high performance multi-processors hardware : ~2 hours

SOL600 analysis

Sperimentale[UMR]

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• A few correlation OUTPUT chosen:

� Bending bridges reading the flexural moments along the actuator shaft

� Displacement transducers to compute the chain stiffness

• VERY GOOD final correlation wrt flexuralmoments and displacements after some tuning:

� Changing the “glue” contact with the pitch control beam on top of the actuator shaft: rigid bars have been used

� Resizing the gap between the actuator shaft and the bushing

• VERY SMALL final differences btw Test and SOL600:

� about 1% on the pitch control beam displacements

Correlation with Experimental tests

Numerical Physical

Before GAP changing

After GAP changing

Numerical Physical

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• FE beam model for shaft

• 3D flexible model for pitch control beams

• Introduction of Master nodes along the shaft fordefining contact points (discretized contact)

(Vector forces)

• Developed interpolation routine for smoothing the transition between discretized contact

Adams model – Adopted Solution older release

From 3D

to beams

For D(node,ring) = 0 F = FMAX

For D(node,ring) = D(node,node) F = 0

For D(node,ring) < D(node,node) F=f(D)

For D(node,ring) = 0 F = FMAX

For D(node,ring) = D(node,node) F = 0

For D(node,ring) < D(node,node) F=f(D)

• Adams model built from same flexible bodies usedfor SOL600

� shaft

� pitch control beam

� bushing

� Ring

• Introduction of Master nodes for constraints and concentrated loads and cards for SOL103 and MNF generation

• Kinematic model:

� Primitive joints

� Fixed joints

� Motion

• Two contacts regions defined:

� between the shaft and the bushing

� between the shaft and the ring

• Output:

� Displacement

� Loads on constraints

� Nodal loads (FEMDATA)

Adams model – Flex2Flex

Fixed

Primitive

Motion

• Workflow -1

� Submodels for tuning the contact parameters with SOL600:� A submodel shaft + bushing

� A submodel shaft + ring

� Tuning on the basis of the main OUTPUTs, i.e. displacements and forces

� Accurate tuning on Adams contact parameters (K, damp, exp) using DOE analysis and comparison with SOL600

Adams/SOL600 correlation

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� Submodels for tuning the contact parameters with SOL600:� A submodel shaft + bushing

� A submodel shaft + ring

Adams/SOL600 correlation

• Workflow -2

� Procedure applied to each contact to tune all parameters

� Evaluation of shaft deformation

� Evaluation of nodal loads and reactions

� Evaluation of displacements

Adams/SOL600 correlation

• Workflow -3

� Adams > SOL600:

� CPU time comparison: big advantage for Adams

� Adams allows easy parameterization and DOE analysis

� SOL600 > Adams:

� Adams needs contact parameters tuning and/or identification

� Adams needs solver parameters tuning

� DOE analysis has been useful

� Developed a procedure, using SOL101, for parameter contact identification when SOL600 results not available:

� Simple Nastran models

� Disp vs Applied Load

� Contact parameters estimation and Solver parameterstuning

� Parameters database linked to material

� Adams becomes a tool for prediction not validation only

Adams/SOL600 correlation

• Workflow -4

� Adams > SOL600:

� Adams allows high complexity of the model

� Adams allows transient analysis

Full Model:

� Once tuned ADAMS contact parameters on simplersubmodels, the full assembly has been simulated

� Same outputs used for correlation with experimentalresults: pitch beam displacement and bending moments

� Other outputs for correlation are : shaft deformationshape and reaction forces

� To achieve a good correlation, equivalent modelizationrules have been implemented into Adams and Sol600: rigid elements for the joint between the shaft and the pitch control beam (instead of a “glue” contact, to match experimental results as well)

� As before, two configurations of the control chain havebeen considered:

1. Max pitch

2. Min pitch

Adams/SOL600 correlation

Transient analysis:

Two additional cases studied in ADAMS only to assess the robustness of the described results:

1. Time-constant loads with rotating shaft

2. Time-variable loads (performed in lab tests)

Both cases with continuos change of configuration (frommaximum to minimum)

CPU time analogous to previous simpler analysis

Adams advanced analysis

• Scope of the work:

� Establish feasibility of SOL600 to evaluate/correlate experimental test in a analysis of contact btw flexible bodies

� Establish feasibility of Adams Flexible Contact feature to evaluate/correlate the sameSOL600 test case

• Main results:

� SOL600 vs. Experimental test: very good correlation on a number of significant measuredOUTPUTs

� SOL600 vs. Adams: very good correlation

• Achievements:

� Adams can be adopted as a predictive and design tool together with a database of good and reliable contact parameters

� Robustness of Adams solution has been confirmed by time-variable runs

• Time to complete an Adams run, without friction, is 1/10 of equivalent SOL600 one

Conclusion

• Repeat correlation with MDNastran SOL400

• Exploring friction effects in the contacts

• Extend to more materials the “SOL101” method adopted for the characterisation of Adams contact parameters

• Evaluation on more complex models: introduction of flexible blades, aerodynamic forces, …

Further development/investigation

Thank you