tips and tricks for thermal analysis - ansys · pdf file1 © 2011 ansys, inc. june 26,...

© 2011 ANSYS, Inc. June 26, 2014 1

Tips and tricks for Thermal Analysis

Ankit Adhiya Lead Engineer

([email protected])

© 2011 ANSYS, Inc. June 26, 2014 2

• Introduction

• General tips: Model building

• General tips: Meshing

• General tips: Convergence and stability

• General tips: Post processing

• ANSYS R.15 Updates

Content

© 2011 ANSYS, Inc. January 27, 2012 3 ANSYS Icepak – Validation 1

• Aim: The goal of the model must be clearly defined. This often gives direction to the subsequent steps.

• Some examples: – Optimize thermal vias inside a

package to minimize die temperature

–Board layout design to get the target packages die temperature under a specified value

– Selection and positioning of fans to maintain the required flow in the telecom box

Steps in a CFD Project

Define Goal

Solve

Analyze results

Next step!

Model building

Discretization

Numeric model

Define Goal


Tips and Tricks are applied in CFD projects to improve modelling efficiency, reduce design cycle and increase productivity.

Overview: Tips and Tricks

In CFD Simulations Tips and Tricks are used for

– Rapid model creation – Achieve high quality mesh – Improve solution accuracy – Better analyse and

postprocess the results

5 © 2014 ANSYS, Inc. June 26, 2014 ANSYS Confidential

Workflow in ANSYS Icepak

Post Processing

Solve

Flexible Meshing

Model Building

MCAD Through DM

ECAD


Define Your Goals

– What results you are looking for?

• Flow structure, Heat transfer, Temperature limit

– Degree of detail required

• System level Vs Board level simulation

– Is Radiation, Gravity important

• Natural convection Vs Forced Convection

– Laminar Vs Turbulence flow

• Reynolds number

General Tips: Before You Start


• Identify the domain:

– Use smallest possible domain without compromising the results.

– Can you use symmetry or periodic boundary?

– Use hollow blocks to change the shape of the domain and reduce mesh count.

– Apply correct boundary conditions o Constant T, convective BC, constant q”, …

General Tips: Domain Identification


General Tips: Model creation using Primitive Object

• Goal: Reduce run time and increase accuracy. – Start with a simple model or few components and then populate

the model. – Can you simplify or reduce the components?

• Replace irregular (Polygonal) shapes with regular (prism and cylinder) shapes.

– Can you reduce number of components? • Use ‘individual sides’ specification instead of using plates or

annular blocks.


General Tips: Model building using Macros

• ANSYS Icepak includes many macros designed to automate common model-building tasks.

• Icepak Macros can be used to assist creating different types of packages, PCBs, heat sinks, heat pipes, thermoelectric coolers, JEDEC test configurations and DELPHI package characterization


General Tips: Importing ECAD Files

• Finalize your analysis type – System, Board or Package Level

• No need to Import any Ecad (Trace) files for system level

• Try using IDF import for Board level – Allegro from Cadence, Boardstation from

Mentor, Visula from Zuken-Redac – Pro/Engineer, SCRC/IDEAS, Unigraphics

• Try including traces for Package level – BRD file ,Gerber files, NJB file, .BOOL file,

.TCB file, .ANF file



Post Processing

Solve

Flexible Meshing

Model Building

MCAD Through DM

ECAD


Flexible Meshing

• Powerful automated grid generation

• Types of mesh

o Hexa Unstructured o Hexa Cartesian o Hexa Dominant (HD) o Mixed meshing allowed

• Flexible mesh refinement o Domain level controls – applicable to all

objects o Individual object level controls o Multilevel meshing capability


General Tips: Meshing

• Start with a coarse mesh and always look for the warnings in the Icepak message windows. Any problem will be caught quickly.

• Ensure that all objects are meshed, especially fans, openings, vents, and

resistance plates.

• If some objects/face are not in the mesh – check whether any other objects (with high meshing priority) are occupying the same location.

• Invest time in creating a good quality and efficient (less number of cells with required resolution) mesh.


General Tips: Non Conformal Mesh

• Use non-conformal mesh where ever possible to reduce cell counts and to get a good quality mesh.

• Make sure all the non-conformal

rules (discussed in following slides) are satisfied during defining slack values.



Conformal Mesh Mesh Count=1,424,828

Non-conformal Mesh Mesh Count=386,667 (73% reduction)

Regions with mesh bleeding

Mesh isolated in regions of interest

Mesh secluded from outside interference



Conformal mesh Non-conformal mesh

V = 2 m/s

Tmax = 94.9 C

V = 2 m/s

Tmax = 93.85 C

Similar result with much smaller mesh count


• Model with care – Eliminate unnecessary small gaps/ overlaps

– Use Model: Snap to Grid and other co-ordinate snap tools as needed

– Helps minimize mesh count

• Local refinement applications:

– Openings/ grilles/ fan annulus - 4 to 6 elements per side

– Flow channels/gaps (example - between heat sink fins) - apply 3 to 5 cells

– Lumped PCBs - 3 or 4 elements in thickness

– Power dissipating objects - apply 3 elements per side

– Heat sinks - 4 to 8 count in Fin height + 3 count in Heat sink base thickness

Mesh Guidelines


• Mesh Verification – Ensure that mesh captures Design Intent – Ensure correctness of Meshing Priorities to achieve Design Intent – Minimum gaps - Apply suitable values to ensure all necessary

geometries remain – Quality Measures - check for recommended values

Mesh Guidelines : 2



Post Processing

Solve

Flexible Meshing

Model Building

MCAD Through DM

ECAD


General Tips: Numerical Model (Solver)

• Equations to solve: select only the required equations. – Conduction only problem – check only temperature

– Forced convection – use ‘sequential solve of flow and energy’ (advanced solve) for better and quicker convergence, gravity and radiation may not be necessary

– Natural convection – flow and energy must be solved together, radiation and gravity need to be included.

• Under Relaxation Factor:

– Pressure 0.3 and Momentum 0.7 for forced convection

– Pressure 0.7 and Momentum 0.3 for natural convection, complex forced convection and models with ‘more nonlinearity’, e.g. many fans, large velocity or pressure gradients, closed domain ...

• Always use monitor points to monitor convergence of solution.


General Tips: Radiation

• When is Radiation Important ? – Radiation is important if thermal resistance due to convection

is of the same order of radiation – Important in natural convection problems mostly

• A general rule of thumb is given below – Estimate the ambient/bulk fluid temperature in the model – Estimate the maximum temperature from the

solution(roughly) – Stefan Boltzmann law states the radiation flux is proportional

to σ*(Tsur4 – Tref

4 )

• As value of σ is very less, radiation flux will not be dominant unless the (Tsur

4 – Tref 4 ) is significant.



Post Processing

Solve

Flexible Meshing

Model Building

MCAD Through DM

ECAD


CFD Post : Case Comparison

• Multiple cases can be post processed simultaneously by enabling “Keep Current cases loaded” option

• Feature useful for comparison studies


Existing Simulation Knowledge Resources


Existing Knowledge Resource


ANSYS Icepak R15.0 Updates


Content

• Icepak parameters published to the Workbench parameter manager – Allows design points, design of experiments, and design

optimization with DesignXplorer

• Q3D Extractor – Icepak one-way coupling

• Graphics enhancements

• Solver enhancements

• Post-processing enhancements

• Miscellaneous Enhancements


• Icepak parameters can be published to the Workbench parameter manager

• Allows design points, design of experiments, and optimization with ANSYS DesignXplorer

• Enables multiple simultaneous design point solutions with HPC parametric packs

Icepak Parameters Published to WB

Design point study of heat sink in wind tunnel, DesignModeler geometry.


Icepak Parameters Published to WB

Icepak and DesignModeler parameters are now available in the Workbench parameter manger for design point studies and/or optimization with DX. Design point solutions can also be “exported” to review contour results.


• Design of Experiments solution to obtain response surface and MOGA (Multiple Objective Generic Algorithm) used to find power values from measured temperatures for PBGA package model

Icepak-DesignXplorer PBGA Example


• Import volumetric and surface losses from Q3D into

Icepak – Import volumetric and/or surface losses from Q3D into

Icepak via the Workbench project schematic

One-way Coupling with Q3D


Q3D-Icepak Coupling

Temperature contours and velocity vectors from steady-state solution

Q3D geometry linked to DesignModeler and simplified for Icepak

Forced convection cooling of a coaxial cable

DC simulation with Q3D to compute losses


• “Show metal fractions” display the percentage of copper for each trace layer of a package substrate or printed circuit board.

• The Metal fraction display provides a preview of the resulting thermal conductivity based on the metal fractions, which is useful for model verification.

View Metal Fraction

Metal fraction on top layer

Metal fraction on bottom layer

Trace import on a block


Display Objects by Type

Select Model > Show Objects by Type

Resulting display shows object by type and sub type.


Problem Setup Wizard

Right-click on Problem Setup to launch Problem Setup Wizard

Wizard guides users through a series of choices with guidance to properly setup the models physics


• Heat sink example • Couple P-V formulation 2.6x

faster versus segregated solver

• 163 versus 500 iterations • More robust convergence

behavior versus segregated solver with similar results

Coupled Pressure-Velocity Formulation

SIMPLE Formulation (Icepak default)

Coupled P-V Formulation


• New parallel option to enable GPU computing for certain solver operations

• Select using Parallel settings panel

• Accelerates view factor computations using ray-tracing radiation

• Accelerates Algebraic Multigrid (AMG) method for coupled pressure based solver

• ANSYS HPC license required for GPU computing

GPU Computing


• New summary report options to report conduction, convection and/or radiation heat flow for objects

• Both Icepak objects and CAD objects supported

• Easier to determine heat balance for objects

Report Conduction, Convection and Radiation for Objects


Happy Computing

tips and tricks for thermal analysis - ansys · pdf file1 © 2011 ansys, inc. june 26,...

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