Real-time simulation and visualization techniques for combustion processes and general fluids

Real-time simulation and visualization techniques

for combustion processes and general fluids

Real-time simulation and visualization techniques

for combustion processes and general fluids

Marek Gayer (supervisor Pavel Slavík)

Computer Graphics GroupDepartment of Computer Science and Engineering

Faculty of Electrical Engineering Czech Technical University in Prague

The defense of the PhD thesis

April, 27, 2006 Prague, Czech Republic

www.cgg.cvut.cz/~xgayer/

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Outline of the presentationOutline of the presentation Introduction and motivation for visualization of

dynamic processes and objectives of the thesis Presentation of major thesis contributions

– Acceleration of simulation– Higher quality of images achieved by the use of

GPU – Interactive visualization of dynamic processes

with tree based data structuresFluid Simulator States (FSS)FSS TreeUnsteady Data Sets (UDS) Tree

Conclusion and future work Live demonstration of the dynamic visualization

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Thesis objectivesThesis objectives

Design and implement techniques that together could be used to form a solution allowing interactively visualize dynamic processes – namely for pulverized coal combustion processes in real time (2D, namely for education).

Contributions of the thesis should be reusable in general projects regarding fluids

No ambitions for reaching precision or compete professional combustion software

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www.cgg.cvut.cz/~xgayer/Objective: Interactive visualization of dynamic processes (e.g. fluid processes)

Objective: Interactive visualization of dynamic processes (e.g. fluid processes)

Understanding of a dynamic process is possible only with a dynamic (real-time) and interactive visualization

Dynamic processes are described by complex differential equations (slow to compute)

Combustion processes which our thesis deals with is a use case of solving this problem

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www.cgg.cvut.cz/~xgayer/Introduction and motivation to coal combustion modelling and visualization

Introduction and motivation to coal combustion modelling and visualization

Both for the ecological and economical reasons

Finding optimal boiler configurations– To reduce pollution– Combustion optimization– To find a way for optimal

fuel preparation How can visualization help

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www.cgg.cvut.cz/~xgayer/Modelling and visualization of combustion by existing CFD software

Modelling and visualization of combustion by existing CFD software

Most often: solving complex differential equations (e.g. Navier-Stokes)

Coal combustion as a CFD application Current solutions and systems:

Precise, robustSlow, complex, expensive, non real-time => unsuitable e.g. for education (ANSYS, Fluent => 1 frame = several minutes - hours)

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www.cgg.cvut.cz/~xgayer/Thesis contributions leading to dynamic, real-time visualization of dyn. processes

Thesis contributions leading to dynamic, real-time visualization of dyn. processes

1. Speeding up the computation of data for consecutive visualization

2. Use HW acceleration for quality yet fast visualization of the data

3. Pre-calculate parts of simulation, then run simulation accelerated so dynamic real-time visualization can be achieved

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www.cgg.cvut.cz/~xgayer/Problem 1: The classical simulation of combustion by existing solvers is slow

Problem 1: The classical simulation of combustion by existing solvers is slow

Solution / contribution of the thesis:

– Fast fluid simulator based on Euler and continuity equation allowing real-time interactivity

– Original virtual coal particle system using simplified combustion model, suitable for both the simulation and visualization

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The Fluid SimulatorThe Fluid Simulator

Dividing boiler area to structured grid cell arrays containing:– Velocities– Masses/Pressures

– O2 concentrations

– Temperatures State update Principle of local

simulation

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Virtual coal particle systemVirtual coal particle system Used for both simulation

and visualization of the combustion process

Virtual particle system approach

Simplified combustion and heat transfer computation

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Sample visualization - cell characteristicsSample visualization - cell characteristics

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Sample visualization – coal particlesSample visualization – coal particles

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www.cgg.cvut.cz/~xgayer/Problem 2: How to visualize simulated data fast and with good quality?

Problem 2: How to visualize simulated data fast and with good quality?

Solution / contribution of the thesis:

– High quality bicubic spline contours visualization

– Non-jagged isolines

– Computed parallel by pixel or vertex shaders on GPU’s of the current graphics accelerators

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www.cgg.cvut.cz/~xgayer/Real-time Visualization with Bicubic Spline Patches Interpolation

Real-time Visualization with Bicubic Spline Patches Interpolation

Better quality then linearComplex computations with 4x4 and 4x1 vector matrices (2x)Non real-time when not accelerated – (graphics hardware natively supports only linear interpolation)Our contribution utilizing Modern GPU’s paralell processing gains real-time performance

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Utilization of GPU shadersUtilization of GPU shaders

Vertex & fragment programs (shaders) Works on common current mainstream

graphics hardware Texture mapping interpolation core

running on GPU (high quality per-pixel / per-vertex)

Optional per-vertex subdivision - pixels between vertices are linear interpolated

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Side by side comparison with linear texture interpolationSide by side comparison with linear texture interpolation

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Non-Jagged Isolines (contour lines)Non-Jagged Isolines (contour lines)

Simple modification of mapping textures:

Simple, fast(no additionalcomputations at all!)

Smooth, non jagged

Blurry on certainplaces with lowgradients

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www.cgg.cvut.cz/~xgayer/Problem 3: How to gain real-time visualization even with slow simulation?

Problem 3: How to gain real-time visualization even with slow simulation?

Contribution / solution of the thesis:

– Fluid Simulator States

– Fluid Simulator States Tree

– Unsteady Data Sets Tree

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Storing results for real-time replayingStoring results for real-time replaying

Used when computation is too slow for real-time simulation and visualization

Results are stored on hard disk, then real-time replayed– Data sets for selected

characteristics– AVI and MPEG files– Limited interaction

Our contribution:HIERARCHICAL TREES OF PRE-COMPUTED DATA STRUCTURES (FSS, UDS Trees)

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Extending Fluid Simulator with Fluid Simulator States (FSS)Extending Fluid Simulator with Fluid Simulator States (FSS)

Simulation is divided into two phases:– Storing phase - fluid simulator states for

each time step are saved on HDD– Replaying phase - simulation runs

accelerated with pre-computed fluid simulator states; we can interactively set parameters of visualization

Except first frame, no other data are saved (e.g. particles, characteristics)

State files are stored in binary files

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Simulation system architectureSimulation system architecture

VisualizationVisualization

InteractionInteraction

Store FullData Sets

Store FullData Sets

Fluid simulatorFluid simulator

Combustion &heat transfer

engine

Combustion &heat transfer

engineParticlesystem

ParticlesystemGrid cellsGrid cells

Store FSSextension

Store FSSextension

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First frame (complete state)

Second Frame

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Collection of cascadingFSS states for

accelerateddatasets generation.

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.Frame N - 1

Last frame (complete state)

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Unsteady simulation datasets (UDS)Unsteady simulation datasets (UDS)

Stores one or more characteristics for selected time part

Can allow real-time replaying of results Full interactivity in visualization part After storing, no interactivity in

simulation part possible No additional changes to already

computed data and configuration

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Detailed comparison against data setsDetailed comparison against data sets

Store method /Grid size

FSS /20*40

FULL /20*40

FSS /50*100

FULL /50*100

Simulation time 1214s 1230s 5128s 5133s

Write [MB/s] 0.16 8.0 0.3 3.7

Replay time 627s 603s 816s 864s

Read [MB/s] 0.31 14.6 1.9 21.95

AVG Fps 19.1 19.9 16.3 15.4

Disk space GB 0.2 9.4 1.6 19.1

Total acceleration

x 1.9 x 2.0 x 6.2 x 5.9

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www.cgg.cvut.cz/~xgayer/Feature comparison of FSS against common unsteady data sets (UDS)

Feature comparison of FSS against common unsteady data sets (UDS)

Much less disk requirements (only fluid simulator states are being saved)

Lower disk bandwidthBetter scalability for large grids and/or tasks

with many particlesSame or even better acceleration resulting in

better interactivityNo seeking and skip frame ability

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Forming data to tree cluster structureForming data to tree cluster structure

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www.cgg.cvut.cz/~xgayer/Changing simulation parameters in each of the tree node

Changing simulation parameters in each of the tree node

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www.cgg.cvut.cz/~xgayer/Comparison of FSS and UDS tree advantages against direct simulation

Comparison of FSS and UDS tree advantages against direct simulation

Can run in orders fasterSeeking and skip frame ability (UDS)Creating hierarchy of replay-able resultsIncremental step-by-step solutionConstructing of paths of solutionInteractivity is allowed only in the nodes

of the treeUDS requires disk bandwidth and

capacity

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Reusability - possible applicationsReusability - possible applications

Originally used for our fluid application for combustion processes

Parts can be reused for other simulation and visualization applications– Fluid simulator– Contours visualization

E.g.: simulation and animation of liquids, water and gaseous phenomena

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Conclusion of major contributionsConclusion of major contributions

Fast data generator for dynamic visualization– Fast & simple real-time fluid simulator– Particle system with simplified combustion engine– Interactive changes to the model during run

Quality contours and contour lines visualization using pixel or vertex shaders on GPU

Real-time data based structures for interactive visualization and accelerated simulation– Fluid Simulator States– Fluid Simulator States Tree– Unsteady Data Sets Tree

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In general, create a more precise computational model or enhance and extend current equations

Enhancements to the combustion and thermodynamics engine and fluid simulator

Convert the whole project to 3D Create 3D FSS and UDS Trees Create more user-friendly user interface Dynamic visualization of other phenomena's

Possible future research and workPossible future research and work

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www.cgg.cvut.cz/~xgayer/The awards for the thesis contributions (fluid simulator, virtual particle system)

The awards for the thesis contributions (fluid simulator, virtual particle system)

2003, CTU FEE at PragueAward of Dean of the Faculty of Electrical Engineering of the Czech Technical University in Prague for work Simulation and Visualization of Combustion Powered by Fluid Simulator, presented at conference CTU Poster 2003

2003, Brno University of Technology, Faculty of Electrical Engineering and Communication (BUT FEEC) - Award of Dean for the best work in the International Competition of student creative projects Student EEICT 2003

2003, CTU in PraguePrice of the rector for placing between the best projects of PhD students, that were solved within scope of CTU internal grants and that were presented on conference CTU Workshop 2003

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Thank you for your attention.Thank you for your attention.

???Do you have any questions ?

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Question 1 (doc. Pavel Zemčík)Question 1 (doc. Pavel Zemčík)

The presented thesis does contain description of a novel “simplified” fluid and combustion modeling/simulation method (Chapter 5); it also contains comparison of the results of the method with other simulation system and from that comparison it seems that the simulation results of the proposed method are not very precise (some of the global values are over 20% different). Given these facts, is the proposed modeling/simulation method still usable for investigation of e.g. the airflow?

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Reply 1(Precision of the model)Reply 1(Precision of the model)

The level precision = weak part, because: Price for the interactive visualization; instead

of 1 picture / minutes => several pictures / seconds

Combustion experts from P.E. of faculty of M.E.CTU: for overview of dynamics is OK

Not for professional design By further improvement and adding some

equations could approach reality better. When using it for airflow only => less errors;

no dynamic combustion code

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Has the proposed combustion process visualization system been evaluated from the point of view of “accuracy” of perception of the process by humans? Do any visualization parameters (e.g. way of shading of the particles as shown in Figure 10-2 versus 10-3, color assignment, etc.) affect the “understandability” of the image by humans?

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Reply 2 (Particle visualization)Reply 2 (Particle visualization)

For the grid, we use visualization methods, that are standard for other combustion systems (our offers better quality and performance)

Particles - we have many possibilities to display– Using various palettes and colors (with scales)– Size of the particle, particle tracks– We can even use same methods as for the cells– Statistics

Moving particles and particle tracks display important visualization parameter – the dynamics

No tests of accuracy of perception of the users No user complaints regarding understandability Possitive feedback from student users

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The precision of the simulation process generally depends on the integration (simulation) time step. Does the proposed real-time simulation in general achieve optimum precision from this point of view? If not, does the system have any information about the precision of simulation (e.g. “now the simulation is too complex and to achieve real-time performance, the precision has been given up…”)?

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Reply 3 (Time steps and precision)Reply 3 (Time steps and precision)

To achieve fast performance, we are always choosing the lowest time steps as possible

The timestep is set manually Increased timestep, the results slightly more

precise in most characteristics, but still the difference between the Fluent not consid. better

The greater precision should be achieved by enhancing combustion and heat transfer equations, or replace fluid simulator with another one and use our proposed accelerating structures to keep it real-time.

Or use some precise simulator as data source

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www.cgg.cvut.cz/~xgayer/Q4 - How the 2d results can be composed into a 3d visualization system ? (doc. Andrej Ferko)

Q4 - How the 2d results can be composed into a 3d visualization system ? (doc. Andrej Ferko)

The 2D results represent the 3D boiler slice with selectable depth of the slice

By linear interpolation, we can divide the voxels & convert it to another grid

Alternatively, values of several slices of boiler could be computed and composed to display

We can use existing visualization systems and methods for visualization (e.g. volume rendering, flow visualization methods spot noise, LIC)

Last possibility – re-implement to 3D

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Real-time simulation and visualization techniques for combustion processes and general fluids