Modeling Internal Flow Induced Motion with ANSYS …Modeling Internal Flow Induced Motion with ANSYS Multiphysics ... • Available for both Fluent and CFX – Fluent through System

1 © 2015 ANSYS, Inc. November 12, 2015 ANSYS Confidential

Modeling Internal Flow Induced Motion with ANSYS Multiphysics

Chris Wolfe, Michael Tooley

July 2015


• Flow Induced Motion

• Overview of Fluid-Structure Interaction Methods

• Examples

• Summary of ANSYS Multiphysics

Agenda




• Examples


Agenda


Important in many industries

• Construction

– Avoid resonance

• Energy

– Oil & Gas: Structures exposed to fluctuating flow

– Power Plants: Vibrating rods, damping

• Aerospace

– Aero-elasticity, flutter

• Automotive

– Reed valves, air filters

• Process Equipment

– Pipelines, meters

• Etc.

Flow Induced Motion

2-way FSI simulation of Tacoma Narrows Bridge


Safety and Reliability

• Failure due to resonance effects

• Wrong prediction of life length and maintenance needs

Impact of Not Managing Flow Induced Motion

Efficiency

• Optimal performance may be inhibited by vibration and flow induced motion

• Products must perform to consumer expectations

Tacoma Narrows Bridge, which collapsed 1940


Special Challenge

• Complex interaction of structures and the fluids inside them can lead to vibration and motion

• Desired and undesired effects

• Difficult to see what is happening inside pipelines and other enclosed spaces

• Performance and longevity of mass flow meters and other measurement tools are subject to fluid motion

• These measurement tools can also impact the generation of motion and vibration

Internal Flow Induced Motion




• Examples

• Validations

• Summary of ANSYS FSI Offering

Agenda


ANSYS Multiphysics ‘At A Glance’

FSI: Thermal Stress

FSI: Pressure/Force Electromagnetics – Thermal Fluid Cooling Coupling

Electromagnetics – Thermal Fluid Cooling – Thermal Stress Coupling

Electromagnetics – Thermal Stress Coupling

External Data

Structural Analysis

Fluid Flow Analysis

Low and High Frequency

Electromagnetics


FSI Workflows, Modeling Approaches Physical Coupling

Numerical Coupling

Stro

ng

W

eak

Ver

y St

ron

g

1-way (uncoupled)

2-way

Explicit Implicit

Iterative

Fully Coupled

CHT, small deformations (excluding turbulence induced), …

Vortex induced vibrations, …

Biomedical,

membranes, highly

deformable solids, …

Blade deformations, rigid bodies, …


• Deep understanding of flow-induced motion and complex interactions with other phenomena

– Develop better designs faster

– Address problems early

– Save money with fewer physical prototypes

• Fit multiphysics into your process

– Understand complex designs step-by-step

– Leverage simulation data already being generated

– Choose the method that provides the level of fidelity needed considering available resources and timelines

Multiphysics Simulations for Flow-Induced Motion


Drag-and-drop to pass thermal and force loads between Workbench systems. External data to pass loads from generic sources or between workbench projects.

FSI Workflows Static 1-way Load Transfers

Volumetric Temperature

Volumetric temperatures used for a thermal-stress analysis.

Wall HTC

Heat Transfer Coefficient from CFD used for a thermal analysis in Mechanical.


Transient 1-way Force can be passed from ANSYS CFD to Mechanical

– Time Domain: ACT extension available on customer portal

• A text format of transient CFD force can easily be mapped to the Mechanical model and used as transient load

– Frequency Domain

• A Fourier Transform of the transient CFD force can be used as load in a harmonic response analysis

Time or Frequency Domain

FSI Workflows Other 1-way Load Transfers

Transient Force

Turbulent structures around a cone flow meter Deformation of the flow meter due to fluid forces


2-way Force/Displacement

• Available for both Fluent and CFX – Fluent through System Coupling (SC)

– CFX through MFX or SC (beta in R16)

FSI Workflows 2-way Load Transfers

Earthquake structural and sloshing response for a liquid storage tank (displaying deformations and water level)

Fluid sloshing effects in a milk package (displaying deformations and water level)


FSI Workflows 2-way Load Transfers

• Coupling is achieved by transferring surface loads across physics interface

• An iterative coupling approach within each time step provides implicit coupling at each time step

• Fully conservative and profile-preserving options for mapping data between CFD and Mechanical solutions when using co-simulation


FSI Workflows Vibroacoustics and Modal Analysis

• Pressures and velocities from fluids can be used for additional analysis in Mechanical

• Vibroacoustics: Noise generated by turbulent pressure fluctuations create minute vibrations that transmit through materials and propagate as sound

• Modal and harmonic analysis: Check vibration frequencies, interactions and sinusoidal loading of structural parts

Pressures (FFT)

Modal Analysis – Free Vibration Harmonic Analysis – Sinusoidal Load, Response @ Frequency Domain




• Examples


Agenda


• Voith Hydro Water Turbine

• Engine Hydro-mount

• In Depth: Jumper Pipe

• Demo: Coriolis Mass Flow Rate Meter

Examples


Voith Hydro Water Turbines

Runner and shaft (red), guide vanes with servo motor (green)

Problem: Strong vibrations observed in the guide vanes of a Francis-type water turbine have the potential to cause fatigue cracking Impact: Harmful to machine performance, safety, and longevity Solution: Simulation used to uncover the unexpected source of vibration

Physical measurements of guide vane vibration All Images Courtesy of Voith Hydro


Voith Hydro Water Turbines: Structural Simulation

Guide vane natural frequencies

92 Hz 175 Hz 327 Hz 400 Hz

Images Courtesy of Voith Hydro

• Simulations: Calculated the first 4 mode shapes of a guide vane in water using undamped modal analysis

• Results: Natural frequencies are far

from measured frequencies • Ruled out self-excitation and

resonance


• Simulations: Unsteady CFD used to investigate vortex shedding from guide vanes and runner blades

• Results: Discovered vortex shedding from runner blades

• Does not effect guide vanes directly

Voith Hydro Water Turbines: Fluids Analysis


Vortex shedding from runner blades


Voith Hydro Water Turbines Understanding the Interaction is Key

What causes strong vibrations in the guide vanes of Voith Hydro’s water turbine?


• Simulations: Vibro-acoustic harmonic response analysis was performed for a domain including both structural and fluid elements. Rotating force patterns, in frequency domain, from the CFD simulation were applied on the runner blades.

• Results: Resonance peaks for both pressure and displacements were found in the domain close to the measured vibrations (295Hz & 306Hz)

• Modifying trailing edge design of the runner minimized and changed the vortex shedding which in turn reduced the guide vane vibrations substantially.

Pressure field and axial runner displacement of vibro-acoustic mode

shape at 325 Hz


• The purpose of this study is to investigate the influence of input excitations (discrete amplitudes with a frequency sweep) on the dynamic stiffness and phase angle of an engine hydro-mount and predict the associated clatter noise.

2-Way FSI of an Engine Hydro-mount

http://www.partinfo.co.uk/articles/169


-6

-5

-4

-3

-2

-1

0

0 2 4 6 8 10 12

Y [mm]

Time (Sec)

Pre-Stress Loading: 4.7 mm remote displacement applied over 8 sec, then hold for 2 sec, followed by 2 mm peak-to-peak vibration applied to the top of the aluminum insert.




Fluid Pressure

Cavitation

Dynamic stiffness Phase Angle






Examples


Jumper Pipe 2-way FSI Example Problem Description

Solve the FIV and VIV of a typical M-shape jumper pipe

– Multiphase flow, oil and gas

– Worst case flow scenario

• Slug flow injected into the system at frequency = 4.4 Hz

• Gas VOF = 0.45

– Seawater current of 0.4 m/s acting on the pipe

– Jumper clamped at both ends (fixed)

– Pipe material is structural steel

Internal Flow conditions • 2 phase flow: Oil and Gas • 55% VOF oil, 45% VOF gas • Oil and methane gas

• Velocity: 5 m/s


ANSYS Fluent ANSYS Mechanical

Jumper Pipe 2-way FSI Example Integrated Workflow

ANSYS Workbench provides geometry sharing between solvers and an easy FSI setup through System Coupling


One place to set all FSI controls

– Participating solvers,

– Contributing surfaces and variables to pass

– Solution sequence

– Total simulation time

– Time step

– Convergence criteria

– Monitor

– Solve, Pause and Restart solution

Jumper Pipe 2-way FSI Example System Coupling FSI Setup


Solve the FSI problem in WB

– Several ways to monitor the solution

• In participant solvers or in System Coupling (SC)

– Backup points and restarts managed by SC

– HPC support

Jumper Pipe 2-way FSI Example Solution Process


Time history of outlet oil flow shows strong correlation with slugging frequency

– Same was observed for internal force acting on pipe

1

2 3

4

Complex Multiphase flow passing through the jumper pipe

– Different multiphase flow regimes observed, e.g. slug, stratified, annular,…

Jumper Pipe 2-way FSI Example Results, Multiphase


Pipe Deformation at Selected Time Steps Time History and FFT of Deformation at

Selected Locations

Mode

Natural Frequency

[Hz]

1 0.857

2 1.749

3 2.063

4 2.069

5 3.180

6 3.599

7 5.212

8 6.177

Mode Shapes and Natural Frequencies of Jumper Pipe

Pipe Deformation strongly correlates to internal flow fluctuations Modal analysis shows a pipe mode shape at about 2.0 Hz • Care must be taken for any

resonance possibility

Jumper Pipe 2-way FSI Example Results, Deformation


Jumper Pipe 2-way FSI Example Results, Deformation

• Pipe Deformations • True scale showed in the

animation below


Stress plots:

• Max stress location changes in different transient time

• Max stress over time is observed at 1.8 s on the small elbow

t=0.2 s t=0.6 s t=1.8 s

t=16.21 s

First stress peak First stress drop

Secondary stress peaks

Jumper Pipe 2-way FSI Example Results, Stresses


• Life calculated based on max stress at 1.8 s using Stress-Life Approach

– ~400,000 cycle is the fatigue life if max stress happens once in the structure

– Since the structure will get excited at same location ~3 times

– Total fatigue life is ~400,000/3= 133,333 cycles (assuming stress level are same)

Jumper Pipe 2-way FSI Example Results, Fatigue


2-way FSI analysis performed for a typical subsea M-shape jumper pipe carrying multiphase flow

Worst case scenario of internal slugging flow considered

Results showed

– Maximum deformation of 0.08 m

– Pipe deformation correlates strongly with the flow slugging frequency

– Modal analysis is important to investigate any resonance possibility

– Fatigue risk after 133,000 load cycles

Jumper Pipe 2-way FSI Example Summary






Examples


Multiphysics Bundles

Multiphysics Bundle Included Solvers

ANSYS Mechanical CFD ANSYS CFD, Mechanical

ANSYS Mechanical Emag Maxwell ANSYS Mechanical Emag , Maxwell 3D

ANSYS Mechanical CFD Maxwell ANSYS Mechanical Emag, CFD, Maxwell 3D

• ANSYS CFD includes ANSYS Fluent and ANSYS CFX

• Share ANSYS HPC keys between ANSYS CFD and ANSYS Mechanical

• As of R16, the multiphysics bundles also include: SpaceClaim, Design Explorer, and AIM


Coriolis Flow Meter

• Excitation applied at the natural frequency of the tube

• Two tubes are used to minimize the effect of external vibrations

• Upsteam and downstream bends vibrate at the excitation frequency, but there’s a phase lag between the two bends

• Phase lag is a function of the fluid mass flow through the tubes


Coriolis Flow Meter Results

Small phase shift seen in tracked displacements

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 1 2 3 4 5

Mas

s fl

ow

rat

e (

kg/s

)

Phase shift (degrees)




• Examples


Agenda


SYSTEMS & MULTIPHYSICS

ELECTRO- MAGNETICS

STRUCTURAL MECHANICS

FLUID DYNAMICS

• Many Physics, One Vendor – Consolidated CAE partner

– Streamlined installation, licensing, and technical support

• Multiphysics Made Easy – Automated setup and workflows

– Analyze the whole system

• Flexible Solutions – 1-way data transfer

– 2-way co-simulation

– Single solver solutions

– Combine ANSYS with 3rd party tools

• Performance & Advanced Modeling – Best-in-class physics modeling

– Highly scalable HPC

– Design exploration and optimization

Multiphysics Simulations with ANSYS


Thank you!

Documents

Modeling Internal Flow Induced Motion with ANSYS …Modeling Internal Flow Induced Motion with ANSYS Multiphysics ... • Available for both Fluent and CFX – Fluent through System