multiphysics simulation software - comsol

White Paper:

Multiphysics Simulation SoftwareThe fusion of faster hardware and smarter algorithms opens up entirely new opportunities for

multiphysics modeling and simulation of the real world.

David Kan, Ph.D.COMSOL, Inc.

COMSOL, Inc. 1 New England Executive ParkSuite 350Burlington, MA 01803USAwww.comsol.com

© 2008 COMSOL, Inc.COMSOL and COMSOL Multiphysics are registered trademarks of COMSOL AB. All Rights Reserved. Other products or brand names are trademarks or regis-tered trademarks of their respective holders.

Multiphysics Simulation Software

The fusion of faster hardware and smarter algorithms opens up entirely new opportunities for multiphysics modeling and simulation of the real world.

by David Kan, Ph.D., COMSOL Inc.

Soon after computers conquered the technology landscape, finite element analysis (FEA) emerged as an efficient method to solve real-world engineering problems. Through the work of engineers, applied mathematicians, and physicists over the years, theoreticians discovered an uncanny ability at the core of FEA: It could potentially solve for any system of physical phenomena because of its use of partial differential equations (PDEs), which can describe all sorts of physics such as fluid motion, elec-tromagnetic fields, and structural mechanics. In essence, the theoreticians realized that FEA was a way to translate these well-known mathematical objects in to an approxi-mate digital format.

Theoreticians then realized that FEA could address multiphysics – that is, coupled sys-tems of physics. The need for multiphysics analyses tools was obvious: physics phe-nomena always interact in nature. For example, heat generation occurs wherever there is dynamics. Heat always effects the properties of materials—electrical conductivity, chemical reaction rates, and the viscosity of fluids to name but a few. Other common multiphysics examples are fluid-structure interaction, piezoelectric effects, and magne-tohydrodynamics.

Figure 1: The algorithms underlying mathematical modeling have improved at a rate even greater than the hardware we have watched explode in capability the past decades. Source: Computation Science: Ensuring America’s Competitiveness, the President’s Information Technology Advisory Committee, 2005.

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But implementation of multiphysics simulation remained just a theory through-out the 1980s and 90s because the computational resources did not exist. So, as FEA modeling became a natural part of the research, design, and development cycle, engineering groups tended to limit its scope to single types of physics, most commonly mechanics and heat transfer, but also fluids and electromagnetics. It seemed that FEA was destined to widespread use as a single physics solver simu-lating mechanical parts.

Today, the landscape has changed. Decades of advances in computational science have brought us smarter algorithms and faster, more powerful hardware that puts multiphysics-capable FEA tools within reach for all engineers and scientists (see Figure 1). The revitalization of FEA toward multiphysics opens up new opportu-nities for modeling and simulating real-world applications as well as a world of technological investigation. The future of FEA lies in its innate capacity to lever-age PDEs for multiphysics analysis. Here is a series of examples to give you a more complete picture of the possibilities inherent in multiphysics FEA.

Piezoacoustics Three Physics in One

A piezoacoustic transducer can be used to transform an electric current to an acoustic pressure field or, conversely, to produce an electric current from an acoustic field. These devices are generally useful for applications that require the generation of sound in air and liquids, such as phased array microphones, ul-trasound equipment, inkjet droplet actuators, drug discovery, sonar transducers, bioimaging, and acousto-biotherapeutics.

A model of a piezoacoustic device would include three different physics: piezo-electric stress-strain, an electric field, and pressure acoustics in a fluid. A computer model could be built only by turning to a multiphysics-capable simulation envi-ronment that lets you define and couple the phenomena involved.

The piezoelectric domain is made of the crystal PZT5-H, which is a common material in piezoelectric transducers. At the interface between the air and crystal, the boundary condition for the acoustics is to set the pressure equal to the normal acceleration of the solid domain. This drives the pressure in the air domain. On the other hand, the crystal domain is subjected to the acoustic pressure changes in the air domain. A simulation is conducted to study the acoustic wave propagating from the crystal when applying an electric signal with an amplitude of 200 V and an excitation frequency of 300 kHz.


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Figure 2 shows the implementation of such a model using the COMSOL Multiphysics environment. The description of this model and its elegant result indicate that a signifi-cant amount of mathematics is behind the compact interface.

Reduced Time to Market

High-tech organizations see the improved engineering efficiency they get from multi-physics modeling as vital to ensuring their competitive edge. An important advantage of multiphysics is that you can run far more what-if analyses while building far fewer physical prototypes, enabling you to develop the optimal design of products more quickly and cost effectively. One such example comes from a group of researchers at MEDRAD Innovations Group in Indianola, PA. Led by Dr. John Kalafut, the research-ers use multiphysics modeling to investigate the injection of non-Newtonian fluids (blood cells) with high shear-rates through thin syringes.

A particularly novel device is MEDRAD’s Vanguard Dx Angiographic Catheter (see Figure 3). The diffusion tip’s nozzle design allows for a more uniform distribution of injected contrast materials (fluids that enhance the visibility of bodily objects during medical imaging) compared to a traditional end-hole catheter. Another problem with traditional end-hole catheters is that they tend to cause the contrast material to stream from the exit hole at high velocities, potentially endangering blood vessel walls. The Vanguard Dx Angiographic Catheter reduces the reaction forces associated with

Figure 2: Acoustic pressure wave (3D color plot) from a piezoacoustic transducer. The model includes the coupling of piezoelectric stress-strain, an electric field, and pressure acoustics. The simulation results were computed by us-ing far-field analyses in the COMSOL Multiphysics Acoustics Module.


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contrast material streaming from the nozzle and therefore minimizes the likelihood of the catheter contacting and damaging the blood vessel walls.

Here a crucial question arises: What is the ideal configuration of holes or slits around the catheter tip to optimize fluid delivery while preventing a structural deflection? Kalafut’s research team used COMSOL Multiphysics to couple forces from laminar flow with a stress-strain analysis and then model the fluid-structure interaction occur-ring in the catheters with various hole configurations, geometries, and flow patterns.

“One of our intern students, Ai Pi, an undergraduate bioengineer at Case Western Reserve University, generated many configurations of hole designs in different fluid regimes,” says Dr. Kalafut. “We used these results to limit the number of benchtop models the mechanical engineers needed to fabricate and to help determine the feasi-bility of new ideas without needing to develop too many prototypes.”

A Stirring Example of Applied Multiphysics

Patented in 1991, Friction Stir Welding (FSW) has since been used widely to create strong joints in aluminum alloys. The aircraft industry has started to adapt this tech-nology, and now the largest manufacturers–including Airbus–are studying how to cut manufacturing costs with it.

In the FSW process, a cylindrical tool made up of a shoulder and a threaded pin is spun and inserted into the joint between two pieces of metal. The rotating shoulder and the pin generate heat—but not enough heat to melt the metal. Instead, the softened, plasti-cized metal forms a solid phase made up of a fine-grained material with no entrapped oxides or gas porosity. The crushing, stirring, and forging action produces a joint with

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Figure 3. The Vanguard DX Angiographic Catheter allows for a very uniform distribution of contrast materials. Laser-drilled holes or slits force the contrast material to be transported radially from the catheter.

Figure 4: This COMSOL Multiphysics model of Friction Stir Welding couples a 3D thermal analysis to 2D axisym-metric swirl flow

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a finer microstructure than the parent material and with twice the strength. The process can even join dissimilar aluminum alloys.

Airbus funded several investigations to study FSW. Dr. Paul Colegrove of Cranfield University looked at modeling to help his group fully understand the process before manufacturers made massive investments in retooling their manufacturing lines.

”One of the first results was a research project that created a mathematical model of FSW that allowed Airbus engineers to look ‘inside’ a weld to examine temperature distributions and changes in microstructures,” says Dr. Colegrove. “To enable Airbus engineers to access the model easily, we created a GUI-driven simulation tool so they could look at a weld’s thermal properties and ultimate strength.”

The COMSOL Multiphysics model couples a 3D thermal analysis for calculating heat flow together with a 2D axisymmetric swirl flow simulation. This coupling, in turn, al-lows both the flow and heat generation to be calculated (see Figure 4). How it works is that the thermal analysis calculates the 3D temperature field from the heat flux imposed at the tool surface. It captures the effect of the tool movement, the thermal boundary conditions, and the thermal properties of the material being welded. The model then projects the temperature distribution near the tool surface from the 3D boundary to the domain in the 2D model.


Benchmarking Multiphysics

Simulations like the Airbus case demonstrate multiphysics simulation on an advanced level. As such simulation software continues to be developed, the need arises for objec-tive measurements of performance. For this benchmarks are crucial.

A suite of benchmarks problems has been published by Dr. Darrell W. Pepper of the University of Nevada, Las Vegas, and Dr. Xiuling Wang of Purdue University-Calu-met. Writing in their report Benchmarking COMSOL Multiphysics 3.�, Dr. Wang and Dr. Pepper say that the purpose of their benchmarking project, “was to solve four 3D standard benchmark problems using COMSOL Multiphysics 3.� as well as other well-known commercial packages in related areas and to compare performances in compu-tational cost, efficiency, and accuracy.”

The quartet of benchmark tests simulated fluid-structure interaction (FSI), fully cou-pled electronic current conduction with Joule heating and structural analysis, elec-tromagnetic wave propagation, and the magnetic fields around and inside a rotating electric generator.

The ��-page Benchmarking COMSOL Multiphysics 3.� provides complete descrip-tions of all benchmark problem definitions as well as the testing criteria, environment, and individual test methodologies. Scientific literature and experimental data are well annotated and compared with simulation results whenever possible. Simulation results include extensive comparison tables as well as a rich complement of full-color charts and screens shots for each benchmark test.

Benchmarks like these will become more important as the multiphysics technology becomes a standard tool in science and engineering. Still, comparing different codes in terms of performance raises an interesting observation: a multiphysics code can be as fast, or faster, than specialized codes. Whether you are doing structural, fluid flow, heat transfer, or electromagnetics analysis, solution speed hinges on solving a PDE system. All systems rely on similar solvers, and multiphysics codes share the same core algo-rithms for the computationally intensive tasks.

Enabling Technology for the Future

Thanks to advances in computational power, the predictions that FEA could become the basis for multiphysics simulation have proven to be true. Over the next few years, the wide accessibility of multiphysics modeling will have noticeable impact on science and engineering: Turnaround times for what-if simulations will shrink, increasing the number of design ideas via virtual prototypes, and innovation will be sparked by the understanding gained directly from performing simulations.


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For a many years, we knew that the future of FEA resided in multiphysics its inherent capacity to simulate more than just mechanical parts. The future is now. It is not too much to claim that multiphysics simulation is an enabling factor for the future progress of science and engineering.

AUTHOR BIOGRAPHY

David Kan received a Ph.D. in Applied Mathematics from UCLA in 1999. In 2001, he established the Los Angeles branch office of COMSOL, where he currently is the branch manager.

CONTACT INFORMATION & URLS

COMSOL, Inc. 1 New England Executive Park, Suite 350Burlington, MA 01803�81-2�3-3322�81-2�3-��03 (Fax)[email protected]://www.comsol.com

For more information on COMSOL or the stories referenced in this paper, visit the links below.

Modeling a Prescription for the Future: Faster, Safer Delivery of Therapeutic Substanceshttp://comsol.com/medradJohn Kalafut, Principal Research Scientist, MEDRAD

Airbus evaluates friction stir welding http://comsol.com/airbusDr. Paul Colegrove, Cranfield University, Cambridge, UK

Benchmarking COMSOL Multiphysics 3.�http://www.comsol.com/benchmarking Darrell Pepper, Professor of Mechanical EngineeringDirector of the Nevada Center for Advanced Computational Methods (NCACM)University of Nevada, Las VegasLas Vegas, NV

Xiuling WangPurdue University - CalumetHammond, IN


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multiphysics simulation software - comsol

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