Webinar: Simulation of Thermal-Structure Interaction – July 17th

Simulation of Thermal-Structure Interaction – July 17th

 

On Thursday, July 17th, Mechanical Engineering and COMSOL will give a free webinar on “Simulation of Thermal-Structure Interaction.”
Details and registration are available below.

 

Live Presentation – Thursday, July 17th, 2014, 2:00pm EDT
http://comsol.com/c/17br

 

Speakers:
Kyle C. Koppenhoefer from AltaSim Technologies
Shankar Krishnan, Applications Engineer, COMSOL

 

Multiphysics simulation can be used to model thermal-structure interaction and involves coupling structural analysis and heat
transfer. One application includes simulating thermal expansion in order to analyze thermally induced stresses in electronics, MEMS
devices, and machineries. In this webinar we will cover related topics, including thermal and mechanical contact. We will explore
features of COMSOL Multiphysics(R) that are needed for solving thermal-structure interaction problems. The webinar will include
a live demonstration showing how to set up such a problem, and will conclude with a Q&A session.

 

For more information and to register, visit:     http://comsol.com/c/17br

 

If you are unable to attend the live event, register and you’ll receive notification once the recorded version is available.

 

Tomorrow’s technologies lend themselves to a growing need for multiphysics simulation, and both COMSOL and AltaSim Technologies are committed to helping more and more people become skilled in the use of COMSOL Multiphysics(R). We have just updated our Training Calendar for the next six months and invite our readers to check out and register for upcoming classes as an investment in the future of simulation. Excellence is not an accident. We want to help you get there.

Solver Settings Class Wrap Up

Our COMSOL Training enables students to be leaders in solving problems with COMSOL Multiphysics

Solver Settings Class Wrap Up

 

We held another Solver Settings Class recently, the second time we have offered this class via the Web. Offering web-based classes is something we have started to do recently, and based on the feedback we received, something we will do more and more of moving forward. Josh Thomas was our lead instructor for this class, and as you can see from the feedback highlighted below, participants left well-equipped for Advanced COMSOL Analysis.

 

Here’s what a couple students had to say:

 

“This has been an excellent class, well designed and well delivered.  The most critical aspects have been Josh’s extensive description of the study-node structure, and how the solvers operate on different levels. The COMSOL classes really obscure this by distinguishing the iterative solver only from the direct solver.  I see now how iteration can occur on any of at least 3 different levels and only in this class have those levels become plain to me.  In addition, this class has helped me interpret information that the COMSOL gui presents in a confusing way, especially in cases where there are partial solutions at numerous substeps.  At my job, I will use what I’ve learned immediately.” (Thomas Dreeben, Staff Scientist at Osram Sylvania)

 

“Really want to thank you for offering this course.  It probably saved me more than 6 months to a year of time trying to figure out just the solver node.  I am thinking to take the 4 day training just to re-enforce my experience with COMSOL.  Hopefully I can get someone to sponsor me here.  Will let you know if I do.” (Chung M. Wong, Ph.D., Member of Technical Staff, Contamination Group, Space Materials Laboratory, The Aerospace Corporation)

 

“I really appreciate your kind help and information about this class. It is a very good and informative class. Josh did a really great job and that quite helps me using COMSOL in future.” YUECUN LOU (Terry), Graduate Assistant (Ph.D), University of Toledo, Chemical & Environmental Engineering

 

Doing any advanced COMSOL analysis can quickly push the limitations of hardware due to the amount of RAM it requires and the time it takes to process. Since we utilize COMSOL everyday, we completely understand these issues. This Solver Settings class is specifically geared towards these challenges – it helps you run COMSOL within the existing boundaries of your hardware. The web-based version, spread out over three days, actually gives participants more time to work through course material than our one-day, in-person class does. Driven by our desire to see more and more people master COMSOL, we will continue to explore ways we can offer practical classes. Now we know for sure web-based classes work well.

 

Our next Solver Setting for Effective Analysis in COMSOL Multiphysics (web-based) class takes place August 19-21.

Computational Analysis of Scattering of Electromagnetic Waves by Particles

Computational Analysis of Scattering of Electromagnetic Waves by Particles

 

A computational model of Mie scattering was developed using COMSOL Multiphysics® and its RF Module. It solves for the scattering off a dielectric, magnetic or metal spherical particle with radius a. The model geometry is shown in Figure 1.

 

MIE Scattering

Figure 1: Model geometry for Mie scattering by a spherical particle

 

The air domain is truncated by a perfectly matched layer (PML) inserted to limit the extent of the model to a manageable region of interest. The solution inside the domain is not affected by the presence of the PML, which lets the solution behave as if the domain was of infinite extent. This layer absorbs all outgoing wave energy without any impedance mismatch that could cause spurious reflections at the boundary. The PML is useful in maintaining the solution at the desired level of accuracy and optimizing usage of computational resources.  COMSOL also supports far-field calculations, which are done on the inner boundary of the PML domain where the near field is integrated. The surface S is used to calculate total scattered energy. An incident plane wave travels in the positive x-direction (see Figure 1), with the electric field polarized along the z-axis. Perfect magnetic conductor (PMC) and perfect electric conductor (PEC) boundary conditions are used on the x-z and x-y symmetry planes, respectively. The plane wave incident on the sphere is defined by its amplitude, wave vector in the air and circular frequency.

 

Results

COMSOL conveniently provides all the necessary functionality to calculate scattering integrals. Scattering characteristics for the three types of particles considered are shown in Figures 2, 3, and 4. The results of the computational analysis show good agreement with available experimental results (see references).

 

 Fig2Blog2Figure 2. Cross-section parameters and radiation force for a dielectric particle with refractive index n and relative permeability MuFig3Blog2

Figure 3. Cross-section parameters and radiation force for a magnetic particle with relative permittivity Epsilon and relative permeability MuToo

Fig4Blog2Figure 4. Cross-section parameters and radiation force for a silver particle with dielectric constants.

Simulation of Mie scattering problems enables visualization of the effects of small particles on an incident electromagnetic wave (see Figure 5) to allow better understanding of the interactions.

 

 

Fig5Blog2

Figure 5: Distribution of the z-component of the electric field due to scattering of the incident electromagnetic wave by a particle of 0.1µm of 950 radius. The arrows show the time-averaged power flow of the relative fields at a frequency THz.

 

 

References

Mätzler, C.: MATLAB Functions for Mie Scattering and Absorption, Version 2, IAP Research Report, No. 2002-11, InstitutfürangewandtePhysik, Universität Bern, 2002.

AltaSim Receives SBIR Award

sbir_logo

AltaSim Receives SBIR Award

 

AltaSim Technologies was recently awarded an SBIR Award from The United States Department of Energy. The award was given to help AltaSim further develop the technologies that drive additive manufacturing.  Jeff Crompton, Ph.D., a principal here at AltaSim is quoted in the article. He states:

 

“We plan to create a manufacturing application that will use advanced computational tools and high-performance computing to help U.S. manufacturers improve manufacturing methods by increasing the use of additive manufacturing. Current methods for developing additive manufacturing methods do not use computational analysis due to the complex physics associated with this manufacturing method.”

 

Below are two links to access for the full article:

https://www.osc.edu/press/altasim_technologies_wins_doe_grant_for_additive_manufacturing

http://www.hpcwire.com/off-the-wire/altasim-technologies-receives-doe-grant-additive-manufacturing/

 

The Small Business Innovation Research (SBIR) program is a highly competitive program that encourages domestic small businesses to engage in Federal Research/Research and Development (R/R&D) that has the potential for commercialization. Through a competitive awards-based program, SBIR enables small businesses to explore their technological potential and provides the incentive to profit from its commercialization. By including qualified small businesses in the nation’s R&D arena, high-tech innovation is stimulated and the United States gains entrepreneurial spirit as it meets its specific research and development needs.

 

In the articles (linked above) you will notice mention of AweSim. AltaSim is a founding partner of the AweSim program (https://awesim.org), which was launched in 2013 when the Ohio Third Frontier Commission voted to help fund the $6.4 million public/private partnership led by the Ohio Supercomputer Center (OSC). This collaborative program is geared towards helping the small to mid-sized manufacturer gain access to Simulation-Driven Design in an affordable manner. If you are a small to mid-sized manufacturer in Ohio looking to Accelerate, Innovate and Collaborate, we encourage you to get connected to AweSim. We humbly accept the SBIR Award, simply as another way to help more companies realize tomorrow’s technology today.

Scattering of Electromagnetic Waves by Particles

Scattering of Electromagnetic Waves by Particles

 

Interaction between electromagnetic waves and particles produce unique scattering patterns that are wavelength and particle size dependent.

 

As electromagnetic waves propagate through matter they interact with particles or inhomogeneities and locally perturb the local electron distribution. This variation produces periodic charge separation within the particle causing oscillation of the induced local dipole moment, this periodic acceleration acts as a source of electromagnetic radiation thus causing scattering. The majority of the scattered wave oscillates at the same frequency as the incident wave and is termed elastic scattering. Interaction with the incident beam may also lead to absorption in the form of thermal energy. The combination of scattering and absorption attenuate the incident beam leading to extinction.

 

Scattering of electromagnetic waves by particles can be treated by two theoretical frameworks: Rayleigh scattering that is applicable to small, dielectric, non-absorbing spherical particles, and Mie scattering that provides a general solution to scattering independent of particle size. Mie scattering theory provide a generalized approach, has no particle size limitations and converges to the limit of geometric optics at large particle sizes. Consequently Mie scattering theory can be used to describe most scattering by spherical particles, including Rayleigh scattering, but due to the complexity of implementation, Rayleigh scattering theory is often preferred.

 

Rayleigh scattering is strongly dependent upon the size of the particle and the wavelength of the illuminating radiation. The intensity of the Rayleigh scattered radiation increases rapidly as the ratio of particle size to wavelength increases and is identical in the forward and reverse directions. The Rayleigh scattering model breaks down when the particle size becomes larger than approximately 10% of the wavelength of the incident radiation at which point Mie theory must be applied. The Mie solution is obtained through an analytical solution of Maxwell’s equations for the scattering of electromagnetic radiation by spherical particles in terms of infinite series rather than a simple mathematical expression.

 

Mie scattering differs from Rayleigh scattering in several respects: it is roughly independent of wavelength and it is larger in the forward direction than in the reverse direction, figure 1. The greater the particle size, the more of the light is scattered in the forward direction. In addition to explaining many atmospheric effects of light scattering, applications of Mie scattering include environmental areas such as dust particles in the atmosphere and oil droplet in water as well as medical technology to measure cell nuclei in biological systems or measurement of collagen fibers in body tissue.

 

Electromagnetic Waves

Figure 1: Electric field due to Mie scattering of incident wave in x direction showing enhanced scattering in forward direction.

 

 

Analysis of Mie Scattering

 

Implementation of analytical solutions for Mie scattering by a particle or object is complex and requires solution of Maxwell’s equations to represent the incident, scattered and internal fields. These are not simple mathematical expressions and take the form of infinite series expansion of vector spherical harmonics that allows the cross sections, efficiency factors and distributions of intensity to be predicted. Further, the influence of particle geometry, incident of the incident wave and the particle’s material properties can be investigated.

 

In electromagnetic wave scattering problems, the total wave decomposes into the incident and scattered wave components:

Electromagnetic Waves   (1)

Electromagnetic Waves   (2)

Maxwell’s wave equation is solved with respect to scattered electric field:

Electromagnetic Waves   (3)

and the scattered magnetic field is calculated from Faraday’s law:

Electromagnetic Waves   (4)

The time-average Poynting vector for time-harmonic fields gives the energy flux:

Electromagnetic Waves   (5)

For an incident plane wave, the magnetic field is related to the electric field by:

Electromagnetic Waves   (6)

where k is direction of the incident wave propagation, η = (μ/ε)1/2 is the characteristic impedance, ε is permittivity and μ is permeability of ambient medium. Hence, incident energy flux is calculated as

Electromagnetic Waves   (7)

Important physical quantities can be obtained from the scattered fields. One of these is the cross section, which can be defined as the net rate at which electromagnetic energy (W) crosses the surface of an imaginary sphere centered at the particle divided by the incident irradiationPinc. To quantify the rate of the electromagnetic energy that is absorbed (Wabs) and scattered (Wsca) by the particle, the absorption (σabs), scattering (σsca) and extinction cross sections are defined as:

Electromagnetic Waves   (8)

 

The total absorbed energy is derived by integrating the energy loss over the volume of the particle:

Electromagnetic Waves   (9)

 

 

The scattered energy is derived by integrating the Poynting vector over an imaginary sphere around the particle:

Electromagnetic Waves   (10)

 

 

where n is unit vector normal to the imaginary surface S.

 

Due to the particulate nature of electromagnetic waves they also carry momentum P-c and exert a force on the particle, called radiation pressure which can be obtained by integrating the Maxwell stress tensor over the surface of the sphere:

Electromagnetic Waves   (11)

 

 

where  σpr is the pressure cross-section, and <cosθ>  is the asymmetry parameter.

The radiation pressure cross section can be used to calculate force which the particle experiences in the incident direction:

Electromagnetic Waves   (12)

 

 

The total time-averaged force F acting on a particle illuminated with light can also be calculated using surface integral of the time-averaged Maxwell’s stress tensor T:

Electromagnetic Waves   (13)

 

 

Where Sp is surface enclosing particle volume Vp and n is unit normal vector to surface Sp.

 

In a following Blog we will demonstrate the implementation of Mie scattering into COMSOL Multiphysics and correlate the results with available analytical solution to simplified cases.

 

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