advanced simulation: using finite element analysis and ... 2018... · applied technology services...

Appl ied Technology Services

Applied Technology Services

Commi t ted to de l i ve r ing p rac t i ca l so lu t i ons to cha l l eng ing p rob lems

Advanced Simulation: Using Finite Element Analysis and Computational Fluid Dynamics to Assess and Extend the Lifespan of In-Service Equipment

Dr. Brendan P. DooherDavid Wanner March 30, 2018


What is ANSYS?• ANSYS is the world’s most advance publically available numerical

Finite Element/Volume multiphysics solver• Developed to support NASA and the military aerospace

industries in the 60’s and 70’s• ANSYS Multiphysics software is an engineering analysis toolkit

that incorporates pre‐processing (geometry creation, meshing), numerical solver, and post‐processing modules in a graphical user interface.

• The system can numerically solve mechanical problems, including vibration, static/dynamic structural analysis (both linear and non‐linear), heat transfer, radiation, and fluid problems.

2


ANSYS Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD)

ANSYS structural finite element analysis (FEA) software enables the user to solve complex structural engineering problems and allows for complex retrofit and root cause analyses. Structural analysis software is used in the system in order to more fully understand problems and supplement and reduce the costs of physical testing.Computational Fluid Dynamics (CFD) allows for accurate quantitative predictions of fluid interactions and impacts on equipment, allowing us to assess equipment beyond design basis (such as with probable maximal flooding events).

3


Penstock CollapseFERC Required Analysis to Place Penstock Back in Operation


Penstock Collapse

5

Plant tripped and the upper portion of the penstock collapses• During collapse, penstock steel experienced plastic yield

• Analysis shows that collapse occurred at with only 1.6 psi of vacuum on penstock

• Unknown how penstock will structurally respond to re‐pressurization

o Required 5 psi to 8 psi

• FERC requested analysis prior to placing the penstock back in service. New penstock had already been ordered, but wouldn’t be ready for over a year

o Temporary penstock would be required if the old penstock was found to be unserviceable


Penstock Collapse

6

Stress Just After Collapse Stress: 1 psi reinflate

Stress: 8 psi re‐inflate Relaxed state, post‐inflate


Francis Turbine Pressure Relief ValvePredicting Destructive Cloud Cavitation Surges


Francis Turbine Pressure Relief Valve

8

Provide analysis to • Understand cavitation issues associated with the Rock Creek Pressure Relief Valve (PRV)

• Document Root Cause Analysis of Rock Creek PRV stilling well Destruction• Peer review consultant modelProvide suggestions to aid in design work conducted by consultant

Our model was built from crude scans of 2D Drawings• Work was done prior to acquisition of laser scanners• The physical geometry as modeled included spiral case effects and a conceptualized river


Francis TurbinePressure Relief Valve

9

Transient flow simulations show clear indications of cloud cavitation, an especially destructive cyclic phenomena, which had the destructive force of a shock wave. The cloud cavitation ripped apart the stilling chamber, sending concrete and steel into the river


Dam Probable Maximal Flooding Analysis FERC required analysis to assess dam stability and capability


The primary objectives of the numerical hydraulic model study were to:

Create a 3D CAD geometry and CFD model based on a stl model created from LIDAR data;Run the CFD model for several spillway flow distributions;Compare the results of the CFD model to a 1/40th physical scale model test results; and Analyze CFD model for potential wall overtopping and problematic pressure distributions on the training walls, as well as determine velocity profiles at various locations.


The ANSYS CFX numerical model also has the capability of performing sensitivity studies on such items as:

Sensitivity of spillway capacity to gate operation; and Scour potential along downstream river channel.These items are being explored in future efforts, but are not included here.


Dam Safety Analysis

Required to meet Federal Electric Regulatory Commission requirementsExamining potential for scour and undermining the dam through training wall overtoppingLooking at low pressure regions at the dam toe that could result in forces that would structurally undermine or damage the damExamine the potential for scouring downstream


Dam Probable Maximal Flooding Analysis

.

14

A 1:40 scale model was built initially, but the amount of data that could be interpreted from the scale model was minimal



.

15

Closed gate configuration was the standard for the last 40 years, based on an even earlier physical model. Note the extreme “rooster tails” and turbulence



.

16

Open gate configuration is the recommended operating state. The reason for the closed gate configuration was to reduce sediment erosion at the toe of the dam – a better solution is using large rock riprap to stabilize the soil and reduce erosion


Francis Turbine Wicket Gate ErosionFull analysis cycle:scanning reverse engineering CFD FEA(drawings/PI data)


Francis Turbine Wicket Gate Erosion (Scanning/RE/CAD/CFD/FEA)

ATS Uses Laser Scanning Techniques to gather data on damaged or worn equipment. Once scanned, the xyz point cloud is reverse engineered into a solid structure, that can then be assessed using numerical analysis.

18


Francis Turbine Wicket Gate Erosion (Scanning/RE/CAD/CFD/FEA)

19

Velocity patterns at the wicket gate surface match the areas where erosion is significant (with sediment being near base of the wicket gate)


Shaft SaglineCalculated sagline matches measured vibration from the field


Shaft Sagline (Results Match Field Data)

21

83”

83”

Side View

Top View


Girth Weld Fatigue Cracking


Girth Weld Fatigue Cracking

23

Scale Factor 45

Crack opening barely visible (SF 40)

Crack opening clearly visible (SF 39)


Draft Tube VibrationCalculated frequencies match results from field modal test


Draft Tube Vibration (Results Match Field Data)

25Old Foundation Ring New Foundation Ring

Frequency (Hz)1. 108.12. 108.673. 115.554. 116.465. 125.546. 129.78

Frequency (Hz)1. 111.412. 113.063. 116.894. 117.15. 124.746. 128.56

advanced simulation: using finite element analysis and ... 2018... · applied technology services...

Documents