The fusion of faster hardware and smarter algorithms opens up entirely new opportunities. Multiphysics modeling has grown beyond FEA and CFD to simulate the real world.

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, mathematicians and physicists, 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 many manifestations of physics such as fluid motion, electromagnetic fields, and structural mechanics. In essence, the theoreticians realized that FEA was a way to translate these well-known mathematical objects into an approximate digital format.

Theoreticians then realized that FEA could address multiphysics – that is, coupled systems of physics. The need for multiphysics analysis tools was obvious: physics phenomena always interact in nature. For example, heat generation occurs wherever there is dynamics. Heat always affects 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 magnetohydrodynamics.

The algorithms underlying mathematical modeling have improved at a rate even greater than computer hardware over past decades.

But implementation of multiphysics simulation remained just a theory throughout the 1980s and 90s because computational resources were marginal for such analysis. 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 simulating 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 tools within reach for all engineers and scientists. The revitalization of FEA toward multiphysics opens up new opportunities 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 leverage PDEs for multiphysics analysis. Here are examples that give a more complete picture of the possibilities inherent in multiphysics.

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 using far-field analyses in the COMSOL Multiphysics Acoustics Module.

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, ultrasound equipment, inkjet droplet actuators, drug discovery, sonar transducers, bioimaging, and acousto-biotherapeutics.

A model of a piezoacoustic device would include three different physics: piezoelectric 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 environment 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.

Angiographic catheter: High-tech organizations see the improved engineering efficiency they get from multiphysics 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 researchers 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. 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 contrast material streaming from the nozzle and therefore minimizes the likelihood of the catheter contacting and damaging the blood vessel walls.

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

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 occurring 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 feasibility of new ideas without needing to develop too many prototypes.”

**Comsol Inc.**

www.comsol.com

::Design World::

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