Chrysler Group has now added NX software, Siemens’ comprehensive digital product development solution, to provide efficiency gains in engineering and design and to help create a common product development platform.

Siemens PLM Software
www.siemens.com

::Design World::

Generally classified as sound between 0.05 and 20 Hz, infrasound cannot be heard by humans, but can be detected on specialized sub-audible microphones which operate on the principle of a vibrating pressure field generating recordable electronic impulses. Classical infrasound monitoring focuses on source-to-receiver distances greater than 250 km, where more recent infrasound monitoring research has focused on distances closer than 150 km, bridging the distance between long-range acoustics and true infrasound monitoring.

The Columbia Space Shuttle on takeoff.
(Photo courtesy of NASA)

Traditionally, parabolic equation (PE) methods have been developed for the numerical solution of long range (>500 km) infrasound propagation in a layered atmosphere. This technique can be powerful for long range propagation due to its simple numerical implementation and limited use of computational resources. PE techniques are analogous to frequency wave number investigations in observed data, predicting how trapped energy and spherical wave front phenomena interact not only in arrival times but also in the attenuation of the observed amplitude. The PE method approximates the wave equation by modeling energy propagation along a cone oriented in a preferred direction. This approximation provides reasonable accuracy over long propagation distances. However, for short-range propagation (<50 km), the mathematical formulations used in the PE method break down and do not provide sufficient accuracy needed for precise measurements and predictions.

Structure of the Atmosphere

An idealized atmospheric structure with a linear trend in the troposphere.

To produce high-fidelity propagation modeling coupled to complex source functions, the author worked with Dr. Kyle Koppenhoefer and Dr. Jeffrey Crompton of AltaSim Technologies to develop ?nite element method (FEM) based acoustic solutions, such as those implemented in COMSOL Multiphysics software, to accurately represent the propagation of acoustic waves without the approximations in the PE method. These solutions can be used to provide accurate solutions for short range propagation acoustic waves where the PE method is not well suited. However, FEM methods require large computational resources (such as memory and CPU time) to solve long range propagation problems making accurate solutions difficult. Thus, FEM and PE methods complement each other to solve the problem of infrasound propagation in layered atmospheres; FEM¬based solutions deliver accuracy in the short range and PE-based solutions accurately simulate behavior at large distances. To validate the use of COMSOL’s FEM acoustics code, we present two cases where the PE and FEM methods are evaluated.

Infrasound propagation
Infrasound propagation depends on the effective sound speed (C_eff) of the atmosphere through which it travels, so it is imperative to properly characterize the atmospheric conditions as close to the time and location of the propagation pathway as possible. The propagation pathways are governed by effective sound speed profiles, calculated by: C_eff= C_t+ n•v, where Ct ˜ 20.07(T)^½, T is absolute temperature in Kelvin, and n•v is the component of wind speed in the propagation direction. Temperature is the dominant factor in calculating the effective sound speed; wind speed and direction are only secondary factors. In order for up-going infrasonic energy to be observed at Earth’s surface, it must reach an area of higher sound velocity than at the point of origin. If this occurs, the energy turns and then returns to the surface of the earth.

How the atmosphere is quantified for data analysis and modeling depends on the particular areas of the atmosphere through which the infrasound propagates. For source-to-receiver paths of less than 200 km, local meteorological information is imperative to accurately characterize the propagation medium. Surface measurements are inadequate to properly characterize the whole height of the atmospheric profile through which the infrasound propagates. It is necessary to use radiosonde, weather balloon, or equivalent measurements for the temperature and wind profiles to create the C_eff used in modeling.

Energy propogation pathways through the lower
atmosphere for regional propogation at 2Hz

For distances greater than 200 km from the source to the receiver, the signal may travel through highly variable energy pathways that travel primarily through the upper atmosphere, the thermosphere, and propagate vast distances though a medium that changes little over the time span of months. Most of these sources are either large (such as energy from the Krakatoa volcano eruption in 1883, which reverberated around the world eight times before dying out), from substantial vertical seismic displacements from earthquakes, or occur in the upper atmosphere, such as meteorites.

The tropospheric structure is sometimes governed by fast moving weather systems and is considerably more variable than the atmosphere above the tropopause. Short-lived temperature inversions can create ephemeral ducts with higher sound speed velocities than are found at the ground. Being able to accurately quantify these ducts in time and space is imperative for remote monitoring using infrasound by developing computational methods to effectively manage discontinuities and rapid changes in temperature and wind with altitude.

Long-range infrasound propagation
Worldwide infrasound arrays observe a variety of sources at variable distances. Earthquakes, volcanoes, mining explosions, and man-made atmospheric explosions are some of the most common signals observed on infrasound arrays, but bolides (meteors) and shuttle reentries are also recorded at very long propagation distances, hundreds to thousands of kilometers.

Observations from supersonic atmospheric sources, such as space shuttle reentries, have been recorded on the infrasound arrays from initial installation and have been subject to intense study over the years. As early as1971, infrasound signals were observed from the Apollo space craft flights and recordings continue today.

Comparison of short duration local events to long duration, long propogation path events.

Variable signal character between near-regional and longrange (tele-infrasonic)propagation pathways

The events of the February 1, 2003 Columbia space shuttle reentry failure provide the first case where an explosion at altitude has a known location in four dimensional space and time, as well as a characterized atmospheric pro?le in addition to being recorded on an infrasound array approximately 600 km away in Lajitas, Tex. The three dimensional shuttle path was recorded by NASA and the timing of the events that led to the disintegration was known; the trajectory and timing can then be combined with a well characterized atmospheric pro?le to produce a graphical representation of the paths the acoustic energy takes through the atmosphere.

Originally adapted from underwater acoustic studies, PE modeling provides a ?eld solution for a complete vertical plane at one frequency. An infrasound monitoring community standard PE code was compared in this effort, and it steps forward from a source and calculates an attenuation field for predicting amplitudes along the vertical slice. In using the PE codes, it is imperative that the computational atmosphere be deep enough to include all viable energy pathways. This depth of ?eld required for PE modeling is where the high accuracy advantage of FEM breaks down.

One FEM solution for an atmospheric pro?le took ?ve days to run on a 16 GB quad core MacPro, for 0.25 Hz, and only propagated out to 200 km, rather than the full distance of 600 km. The results correlate well over the distances executed in the FEM model, bearing in mind the change in frequency content from 1 Hz to 0.25 Hz and associated change in wavelength. While accurate, the computational resources required to produce equivalent solutions to the PE codes at these distances indicate that the PE solutions would be more efficient.

Short-range infrasound propagation
At shorter ranges, the advantage of COMSOL’s FE method is apparent. Recently, infrasound propagation over short range, less than 100 km, has become of greater interest. At long distances, such as the Columbia propagation pathways, the ?ne-scale source structure found in the propagating energy is smeared in the observed signal. At the shorter distances of 30 – 100 km, retaining source character becomes more important, as there is less smearing in the observed signal.

COMSOL provides accurate solutions by solving the partial differential equation for acoustic wave propagation without the approximations used in the PE method. Thus, the full characteristics of the source will be included in the solution. Modeling sources as diverse as point explosions or structural emanations, the software supports integrating the source and propagation functions in the same model. This flexibility enables infrasound modeling of many conditions that were prev-iously difficult to solve. Thus, the software offers advantages beyond the additional accuracy found in the FEM solutions. It opens up the study of infrasound to a much broader range of sources while permitting the study of infrasound in the near field.

The technology also provides the capability to develop transient and time-harmonic solutions. The transient solution most accu-rately represents short duration sources, such as point source explosions. The propagation of a 2 Hz signal over 30 km was produced using COMSOL’s Acoustics Module. The variation of sound speed through the layers of the atmosphere strongly influ-ences the propagation of this signal. When the atmospheric conditions are favorable the acoustic energy refracts to the Earth’s surface. The duct at approximately 2 km traps the acou-stic energy necessary to produce favorable likelihood for observing infrasound energy from source to receiver.

While future research to optimize boundary conditions and mesh sizes to minimize run time and computational resources is ongoing, COMSOL’s Acoustic Module offers the long-range acoustics and near-regional infrasound monitoring community an effective tool to produce accurate, high-resolution propagation modeling for situations where integrating complex sources is important.

COMSOL
www.comsol.com

::Design World::

This image, created using the COMSOL Multiphysics Plasma Module, shows the electron temperature inside an Argon ICP reactor used for the fabrication of semiconductor devices.

“Simulation of plasmas is a daunting task that is now being addressed for the first time ever using true multiphysics technology,” comments Dan Smith, Lead Developer of the Plasma Module with COMSOL, Inc. “We leverage this technology in the Plasma Module to solve the complex interaction between the electromagnetic fields and charged particles which collectively constitutes plasma. Users will be able to turn to simulation for a wide range of plasma applications that will reduce the need for costly experiments and increase productivity. ”

Specialized Plasma Modeling Interfaces
Low temperature plasmas represent the amalgamation of fluid mechanics, reaction engineering, physical kinetics, heat transfer, mass transfer and electromagnetics. The net result is a true multiphysics problem involving advanced couplings between the different physics. The Plasma Module features application-specific physics interfaces that automatically implements the complicated coupling between each of the components which make up plasma.

There are specialized modeling interfaces for the most common types of plasma reactors including inductively coupled plasmas (ICP), DC discharges, wave heated discharges (microwave plasmas) and capacitively coupled plasmas (CCP). In the spirit of existing COMSOL products, each of the interfaces can be customized, modified and extended in arbitrary ways by the user.

The Plasma Module Model Wizard let users choose the type of plasma to model. This image shows the Inductively Coupled Plasma physics interface selected.

Modeling the interaction between the plasma and an external electrical circuit is an important part of understanding the electrical characteristics of a discharge. The Plasma Module provides tools to add circuit elements directly to a 1D, 2D or 3D model. Alternatively you can import an existing SPICE netlist into the model. The plasma chemistry is specified either by loading in sets of collision cross sections from a file, or by adding reactions and species directly in the user interface.

The module includes a set of fully documented models of:

• Capacitively coupled plasma (CCP)
• Microwave plasma
• DC discharge
• Dielectric barrier discharges(DBD)
• Reactive gas generator
• Thermal plasma
• The Gaseous Electronics Conference (GEC) reference cell
• Boltzmann analysis of swarm data

“The Plasma Module is truly a revolutionary product because it combines the universally acclaimed COMSOL Multiphysics user interface with industrial strength algorithms and numerical methods. The net result is a product with unprecedented ease of use which can handle arbitrarily complicated industrial and academic problems.” concludes Dan Smith.

Modeling an Inductively Coupled Plasma for the Gaseous Electronics Conference (GEC) reference cell using the COMSOL Multiphysics Plasma Module. The plot shows the electron density in the reactor for Argon plasma.

Plasma Module Highlights
• Application-specific interfaces for the most common types of plasmas.
• 2-term Boltzmann solver to compute source coefficients and transport properties from cross section data.
• Add and remove reactions, surface reactions and species to create arbitrarily complex plasma chemistries.
• Define reaction sources using cross section data, look-up tables, Arrhenius coefficients, rate constants or Townsend coefficients.
• Automatic computation of tensor transport properties for electrons and plasma conductivity when a static magnetic field is present.
• CHEMKIN file import for species thermodynamic and transport properties.

COMSOL
www.comsol.com

::Design World::

The CSA has a strong history of applying symbolic techniques in space robotics modeling. They have used these techniques in the design of various space robots deployed through the Space Shuttle program and the International Space Station. This new initiative at UW is using MapleSim to develop high fidelity, multi-domain models of the rover subsystems.

The general goal of the project is to design a rover system that can get the rover from point A to point B, taking into consideration all probable constraints. For example, what would the path be if the rover is to get to a specified location with minimum risk? Alternatively, if the rover is to get to a specified location using minimum energy, what would that path be?

Step one of this three-year project is to develop the initial rover model, including such aspects as battery, solar power-generation, terrain and soil conditions. The project, in its later stages, will also include a full range of hardware-in-the-loop (HIL) testing phases using real-time hardware and software from National Instruments, using system models that have been developed in, and automatically deployed from MapleSim. This is critical for optimizing system parameters that will maximize power conservation while still achieving mission goals.

“With the use of MapleSim, the base model of the rover was developed in a month,” says Dr. Khajepour. “The benefits of MapleSim compared to traditional tools are significant. We now have the mathematical model of the 6 wheeled rover without writing down a single equation. MapleSim was able to generate an optimum set of equations for the rover system automatically which is essential in the optimization phase.”

Dr. Khajepour was also impressed with MapleSim’s graphical interface. In MapleSim, “you can simply re-create the system diagram on your screen using components that represent the physical model. The resulting system diagram looks very similar to what an engineer might draw by hand. MapleSim can then easily transform the models into realistic animations. These animations make it easier to validate the system diagram and give greater insight into the system behavior.”

Maplesoft
www.maplesoft.com

“The Chemical Reaction Engineering Module is suitable for a diverse range of product and process development applications,” says Henrik von Schenk, Chemical Engineering Product Manager with COMSOL. “It’s particularly useful in the design of sensors for analytical instruments as well as for designing catalysts and filters in automotive exhaust systems. The Chemical Reaction Engineering Module will be especially valuable when developing products and processes in industries like consumer products, fine and specialty chemicals, pharmaceuticals, and bulk chemicals.

This image was created using the Chemical Reaction Engineering Module and shows the removal of CaCO₃ (lime) from heating elements in a boiler.

The Chemical Reaction Engineering Module, which combines functionality of two earlier modules, the Chemical Engineering Module and the Reaction Engineering Module, leverages the newly re-engineered COMSOL version 4 architecture to deliver major new functionality and superior usability. With the new module, engineers and scientists can investigate chemical reactions under the controlled conditions of perfectly mixed systems in laboratory studies. Since reactions are directly accessible in a single easy-to-use interface, users can study the influence of multiple concentration and temperature variations in real operating conditions.

“The fusion of our premier chemical engineering capabilities into a single dedicated solution offering an all-inclusive, easy-to-use environment is a great convenience for our customers,” says von Schenk. “Productivity jumps with the new workflow and the ease with which users can manage species, reactions, and material and energy transport in one simulation.

The Chemical Reaction Engineering Module’s easy-to-use customizable interfaces for defining chemical reactions, mass and energy transport, and porous media flow help users simulate reacting systems accurately. Fully integrated in the COMSOL Multiphysics model set up, the chemical reaction interface enables users to simply type in their chemical reaction formulas. The software then automatically computes the reaction kinetics as well as defines the mass and energy balances. When done, the resulting mass and energy balances are ready to be used to solve the reactor models for perfectly mixed systems of batch reactors, semi-batch reactors, CSTR, and plug-flow reactors.

Users can easily move up from these smaller, less computationally demanding simulations of perfectly mixed reactor models to larger-scale simulations of time- and space-dependent models. “The Chemical Reaction Engineering Module helps you make smart design decisions quickly using comparisons between ideal reactor models and detailed time and space simulations,” explains von Schenk. “It lets you handle simulations beginning at a simple level, which makes it easy to evaluate the chemistry of a system and find reaction time scales, temperatures, and ideal operating conditions. Then, you can use the identical model to run full 3D simulations for investigating and designing processes and reactors in real-world operating conditions.

The Chemical Reaction Engineering Module provides interfaces for mass transport that describe species transport by diffusion, convection, and migration in dilute and concentrated solutions. These interfaces can also describe transport in free and porous media. Based on principal physics effects that come as standard interfaces in COMSOL, laminar flow and heat transfer can be included in the simulation as well. Still, no matter what physics effect is involved, model set up is quick and follows the same intuitive operations. Users can also add and remove chemical reactions and species as well as change reaction mechanisms on the fly. Users can maintain several studies each with different chemistries and different operating conditions in the same model

Import Thermodynamic Property Data Into COMSOL

The Chemical Reaction Engineering Module is compliant with CAPE-OPEN standards for modeling, simulating, and designing the operations of chemical processes. Additionally, it has the ability to read CHEMKIN® files, which define complete reacting systems, including physical and thermodynamic properties, for combustion, atmospheric chemistry, and other gas-phase reacting systems.

With the Chemical Reaction Engineering Module’s built-in CAPE-OPEN Wizard, users can combine components from multiple third-party software vendors in their COMSOL simulations. An integrated CAPE-OPEN browser makes finding and selecting thermodynamic and physical property information in external property data packages easy. This flexible combination of openness and ease of use can lead to high-fidelity descriptions of such properties as viscosity, density, heat capacity, and other thermodynamic properties for gases and liquids.

The Chemical Reaction Engineering Module brings ease of use for the simulation of reacting system. With its built-in CAPE-OPEN support, users can combine thermodynamic property data from multiple third-party software vendors in their COMSOL simulations. The figure shows the results of the simulation of a hydroalkylation process carried out in a membrane reactor.

Chemical Reaction Engineering Module Highlights

• Automatic generation of reaction kinetics, mass, and energy balances from chemical reaction formulas
• Allows combinations of perfectly mixed reactor models to detailed time- and space-dependent descriptions in one model
• Extensive interfaces for simulating mass transport by diffusion, convection, and migration in dilute and concentrated solutions as well as in free and porous media
• Functionality for investigating different chemistries and operating conditions by adding and removing reactions, chemical species, and mass transport effects in different studies in a single model
• Predefined chemical reactor types such as batch and semi-batch reactors, CSTR, and plug flow reactors for continuous volume and variable volume simulations
• User-defined functions and expressions that extend usability for defining arbitrary reaction kinetics and for describing physical properties as a function of composition and temperature
• CAPE-OPEN interface for rapid thermodynamics and physical property calculations through connecting to third-party chemical engineering simulation software
• CHEMKIN file import for combustion, atmospheric chemistry, and other gas-phase reacting systems

The Chemical Reaction Engineering Module is available for the Windows, Linux, and the Macintosh operating systems directly from COMSOL and from COMSOL’s global network of distributors on June 28, 2010.

Users of the Chemical Engineering Module with a current software license subscription will receive a one-time upgrade to the Chemical Reaction Engineering Module plus the COMSOL CFD Module at no additional cost. Full details about the new Chemical Reaction Engineering Module, COMSOL Multiphysics version 4.0a, and related products are available at www.comsol.com.

COMSOL
www.comsol.com

::Design World::

The idea for the automotive crash-test dummy arose in the 1950s when U.S. Air Force flight surgeon Col. John Stapp realized that more of his fighter pilots were dying in car crashes than from accidents in their hi-tech jet aircraft. The Stapp Car Crash Conferences started that decade and continue today as a venue to share information on the latest research for improving vehicle crashworthiness and occupant safety. (Col. Stapp became an iconic figure to us engineers at White Sands and Holloman AFB for subjecting himself to high-speed sled experiments on the Holloman test track in that bygone era.)

A crash dummy (real at top, FEA virtual
model at bottom) has a complex internal
structure and multiple sensors that
record up to 35,000 data points in a
typical 150 millisecond crash.

A major challenge in the ongoing development of physical crash dummies is the need to reasonably represent how the human body responds in an automotive accident. But physical test dummies are only a part of the process. As computer-aided engineering software and computing resources rapidly advance, there is increasing emphasis being placed on developing ever-more-accurate virtual crash dummies.

Energy absorbing crumple zones and other structural innovations do help protect occupants during car crashes. The addition of air bags, combined with a properly worn lap/shoulder belt, reduces driver deaths by 61% in a frontal crash, according to the National Highway Traffic Safety Administration (NHTSA). But car manufacturers are now also legally obligated to certify the effects of crash events on the humans involved. As a result, crash dummies for front-impact (“Hybrid”), side-impact (SID) and rear-impact (RID) are now in use.

A single physical crash dummy can cost more than $200,000. Made from a variety of different materials, including custom-molded urethane and vinyl, they are based on true-to-life human dimensions. They have ribs, spines, necks, heads and limbs that respond to impact in realistic ways. And they are loaded with sensors (44 data channels on the current front-impact standard, the Hybrid III) that record up to 35,000 items in a typical 100-150-ms crash.

Neck and full-body tests of crash
dummy Abaqus FEA models. Simulia
uses SLM and Isight software to
qualify the results of these tests
across different versions
of FEA.

Simulating the crash simulator
Since a physical crash dummy is a manufactured product like any other, it is feasible to simulate performance with analysis (FEA) software. Given the power of FEA to cost-effectively reduce real-world testing, in the case of expensive crash dummies, and even more expensive vehicle prototypes, it definitely pays to simulate the simulator: You can crash a virtual car and dummy many times, much faster and at far less cost than a single physical test.

Since the goal of simulating a simulator of the complex human body is to closely represent reality, the resulting data must correlate well with physical crash test results. So standardization of FEA models is critical: Each virtual dummy must exhibit responses to crash impact loads and accelerations in a precise, repeatable manner that mirrors what happens to its corresponding physical crash dummy.

What’s more, the simulation must continue to run smoothly as each new and improved version of a physical crash dummy comes on the market and as each new version of crash simulation software is released. Simulation software companies go to great lengths to validate the consistency and accuracy of their software in a process called qualification. This software qualification process involves evaluating large quantities of FEA data, gathered from multiple simulations of various crash scenarios, run on different versions of simulation software and, in turn, correlated with new physical test data.

For example, a team of Simulia engineers qualifies and supports a range of virtual crash dummy models developed for their Abaqus FEA software by First Technology Safety Systems (FTSS), a leader in crash dummy innovation for over 40 years. This group also separately develops and qualifies its own virtual crash dummy models, which are versions of the BioRID (Biofidelic Rear Impact Dummy) and WorldSID (Worldwide Side Impact Dummy).

A typical FEA dummy model will have about 100,000 elements, 150,000 nodes and 500,000 degrees of freedom.

A component test is used to evaluate an individual FEA model of a dummy neck being bent, a lumbar spine being shoved sideways, or a head being dropped on a hard surface. A sub-assembly test assesses the stresses on a full rib cage model hit from the side by a pendulum, with the ribs being individually deformed and possibly intruding into the body cavity. And a full-body test incorporates an entire dummy model being hit from the side by a virtual “solid” barrier or subjected to a simulated sled test. Different testing standards (NHTSA, IIHS, etc.) require a variety of tests.

Manual qualification slows the work
Until recently, dummy qualification took the engineers about four weeks for each updated Abaqus virtual dummy model. (A completely new model, such as a WorldSID, would take far longer than that to create.) “These kinds of challenges meant a lot of man-hours for our team,” says Simulia crash engineering specialist George Scarlat.

Before they could even begin the analysis, Scarlat’s group had to create their databases by manually modifying each of the previous validation test responses to add proper filtering (which has to meet industry standards, such as J211 or ISO 6487) to the variables so that the results between different versions of Abaqus could be compared.

Next, the engineers had to manually launch and run the simulations for the 30-60 tests in the current and previous versions of Abaqus (usually four or five total). Once they completed the various manual analyses, the team then had to run a post-processing step to generate the curve plots describing the analysis results. The amount of data continues to multiply at this point because the results of a single FEA analysis of dummy rib-cage intrusions, for example, could produce up to 200 output variables (forces, displacements, etc.) per test.

Finally, a second post-processing step would take the analysis curves, two at a time, and generate statistical comparisons to quantify the agreement between the same variables in different versions of Abaqus. “So in terms of data you could have 60 tests multiplied by 200 variables multiplied by five different versions of Abaqus,” says Scarlat. “This was a lot of manual work. To meet our deadlines, we really needed to improve the efficiency of the entire process.”

SLM brings the power of PLM
So the group applied a combination of Simulia’s own Simulation Lifecycle Management (SLM) tool, and the company’s Isight software for simulation automation and design optimization, to automate and manage the tasks. The results were dramatic: “By using our own tools, we went from four weeks to four days for the qualification process,” says Scarlat.

The crash dummy qualification team used SLM as the underlying driver for running each of the three main dummy qualification tasks (preprocessing, analysis and postprocessing) sequentially. SLM automatically exported all the necessary files from its database for each task. It then automatically imported back into its database any specified result files after the activity was run.

SLM also leverages the capabilities of Isight, in this case for process automation. The crash group engineers first used Isight to create a workflow that enabled them to simultaneously launch all of the Abaqus analysis tasks on a compute cluster. A second Isight workflow was employed in the final postprocessing task to help determine the correlation between results from different versions of Abaqus software on identical dummy tests. A Python script was used to modify input files, compare results and generate comparison reports. The team ran each project on a Linux 64-bit compute cluster using an average of 1200 CPUs for a full run-through.

“Automating our tasks was a big help,” says Scarlat. “No user intervention was needed during the complicated workflow execution, which resulted in a significant reduction of our process time for the whole project.” His team qualified five FTSS dummies in the first year of using the new workflow—taking about the same number of man-hours needed to finish only one dummy qualification project before.

High school students from across the country are given the opportunity to work on a real world engineering challenge in a collaborative, team-based environment, applying lessons learned in the classroom to the technical challenges faced in today’s workplace. The theme of this year’s competition was “Green Aeronautical,” and the challenge was to improve the design of a business jet wing and tail to withstand specific physical conditions, while considering balance lift and weight—and thrust and drag—with zero pitching moments. A public and private partnership, the RWDC provides tools and resources to the schools to support Science, Technology, Engineering and Math (STEM) education. The Mechanical Analysis Division (MAD) of Mentor Graphics donated its leading FloEFD computational fluid dynamics software to all participating schools.

The Baldwin High School “Kansas Tornadoes” national champions, led by their teacher and coach Pam Davis, and mentor Sandy Barnes, is comprised of students Mason Johnson; Brandon Baltzell; Carson Barnes; Shelby Gregory; Carrie Deitz; MacHalpin and Austin Kraus. The second place team, from Iolani School in Hawaii, won last year’s RWDC event; the third place winners are from Hutchinson High School, Minnesota.

The aeronautical challenge requires the teams to apply the software, develop a paper on their findings, then make a presentation to a panel of expert judges. The judges then select the finalists and winning teams.

Mentor Graphics
www.mentor.com

::Design World::

About half of fossil fuels are used in heating, so there is a huge potential in replacing them with renewable sources such as solar power. But standard solar collectors use copper or aluminum as the energy-absorbing material, so if we were to supply just 1% of the world’s heating energy with conventional solar energy, collectors would require 22 million tons of copper – more than the worldwide output in 2006. And these metals are costly, so there is a clear impetus to examine polymers as an alternative.

However, polymers don’t have the same ability to withstand high temperatures as metals do, so we need completely new designs for solar collectors using them. Thus, it is necessary to analyze durability of future solar energy systems, using modeling with Multiphysics software to analyze complex relationships between stress, strain, heat, and flow.

Design optimization for collectors
Polymers in solar energy applications offer many advantages. First, of course, is its price compared to today’s collector materials. Next, polymers offer great freedom in terms of design – we can develop new collector layouts that would be impossible with conventional materials. For instance, with an extrusion process it might be possible to mass-produce complex geometries in lengths of kilometers and thus bring economies of scale. Further, polymers allow the manufacture of collectors that are lighter in weight.

One possible geometry for a solar absorber made of polymer materials.

Polymeric materials have a low intrinsic thermal conductivity. This, however, can be compensated by optimized collector geometries with the goal being a layout that assures homogenous flow and maximal contact area between the absorber and the heat-transfer fluid. With solar collectors, heat transfer is certainly dependent on a material’s thickness and heat conductivity. But an even more predominant effect can be the heat-transfer coefficient between the fluid and the wall, which is determined by the fluid dynamics in the vicinity of the surface, and they depend on the surface shape. Because polymeric materials can have almost any form, the goal is to optimize a polymeric absorber’s shape so that heat transfer by convection overcomes the lack of heat conductivity.

Advantages of design optimizations are best described by the results of adding an additional plate as absorber into the design, which could increase the internal conductance from 95 W/m2K to 540 W/m2K. The illustration above demonstrates a possible layout for a thermal absorber based on multi-wall sheets where the heat-transfer fluid passes through channels that are surrounded by channels filled with air to provide heat insulation from the environment.

The Von-Mises stress

The Von-Mises stresses within a polymer-based solar collector at a normal inlet temperature of 350 K can vary widely depending on the material; here a comparison of the stresses and deformation between polymethyl methacrylate(left) and polypropylene (right) is shown.

Stress level analysis
Because collectors deform when heated, stress distribution and deformation represent potential risks for their stability and durability, especially at mechanical connection points. We want to estimate a product’s useful lifetime due to mechanical stresses that arise not only during normal operation but also during stagnation, the worst-case situation when the energy storage is no longer able to take heat from the collector. We created a COMSOL model that accounts not only for the temperature distribution that varies with the position of the absorber layer but also other factors that affect the temperature level including the amount of irradiance, inlet temperature and the collector’s thermal losses. This temperature data, seen on the preceding page, enables the determination of the collector’s deformation and mechanical failures shortening the service lifetime.

Humidity transport in PV modules
Polymers can also improve cost efficiency of photovoltaic (PV) solar modules. These consist of a front cover of glass, encapsulated solar cells and a back sheet, which is usually made of polymers. These polymeric back-sheets and encapsulants provide a barrier to keep humidity, atmospheric gases and pollutants away from the silicon solar cells and protect them mechanically. The ingress of humidity is a serious reason for their degradation, which can hardly be measured without physically destroying the module. Therefore, we work on developing measurement technologies and the mathematical modeling of the humidity transport.

Through COMSOL modeling, we can compare different polymeric collector geometries and materials for various energy carriers to reach an optimal collector design in terms of efficiency and price. We have also confirmed that our design is as efficient as conventional collectors and that the mechanical stability is sufficient if the collector is constructed properly. The next step is to model longer time periods to guarantee sufficient durability.

Discuss this on the Engineering Exchange:

COMSOL Inc.
comsol.com/papers/5649/

::Design World::

Autodesk enhanced its specialized tools for product development professionals focused on conceptual design, design visualization, engineering, and manufacturing disciplines, The company embedded key functionality from these tools within its core Autodesk Inventor 3D mechanical design and engineering software. New direct manipulation capabilities in Inventor 2011 software improve the mechanical design process, helping accelerate design times as compared with Inventor 2010 software by approximately 40% on common tasks such as assembly modeling. Inventor 2011 software also incorporates Autodesk’s design visualization capabilities within the CAD application so you can better conceptualize and communicate designs with clients. New shading, lighting, and material properties provide a photo-realistic representation of designs, with Inventor software rendering designs as the user works.

Other highlights of Inventor 2011 include:

Simulation:  With added frame analysis, you can test responses of frame models to gravity and other loads and record animations of displacement and stress results. The software guides you through the steps required to define the best testing scenario, making simulation more accessible to CAD users.

Tooling: Inventor Tooling 2011 improves performance for a number of key operations by more than 50%, supports dynamic simulation of mold assemblies and helps you to automatically generate the mold core and cavity for a broader range of plastic parts, whether using native Inventor or imported files.

Design Automation: Inventor iLogic technology is integrated into Inventor 2011, simplifying rules-based design. The new iCopy feature enables customization of commonly used assemblies by automating the process of copying and positioning similar components.

Freeform Shape Modeling: Autodesk Alias Design for Inventor 2011 is a new product that integrates freeform shape-modeling capabilities in the Inventor parametric modeling environment.

Along with Inventor software, new applications within the Autodesk solution for Digital Prototyping offer powerful capabilities spanning conceptual design, engineering and manufacturing workflows.

AutoCAD Electrical 2011 software helps electrical controls designers to quickly create control system designs and more easily access extensive catalog information for large electrical controls projects.

AutoCAD Mechanical 2011 software’s streamlined design environment gives you improved access to power dimensioning functionality, which automatically aligns part dimensions with the rest of the drawing properties, without ever opening a dialog box.

Autodesk Algor Simulation 2011 mechanical simulation tools feature integration with Autodesk Moldflow 2011 software, allowing you to utilize Moldflow simulation results and the extensive Moldflow material database when performing structural simulations on plastic parts.

Autodesk Alias 2011 family – Alias Sketch, Alias Design, Alias Surface and Alias Automotive ? delivers surfacing capabilities supported by sketching, modeling, and visualization tools. New Autodesk Alias Sketch software’s unique hybrid paint and vector workflow helps you transform ideas into compelling design iterations more quickly.

Autodesk Inventor Publisher makes its commercial debut after its recent Technology Preview on Autodesk Labs. The software for creating product documentation helps enable manufacturers to provide their customers with clearer and more comprehensive technical instructions by leveraging the same digital model used in the design to manufacturing process.

Autodesk Moldflow 2011 software helps you validate and optimize plastic part and injection mold designs before manufacturing begins. You can export Moldflow simulation results to Autodesk Showcase 2011 visualization software to expose defects and see how the part will look in real life, helping to assess part quality and make better design decisions.

Autodesk Vault 2011 family, a workgroup solution for managing the complete digital prototype, features a new visual experience for graphically mapping Vault information directly to Inventor models to streamline workflows, fundamentally improve the reporting and decision-making process, and accelerate model selection and interaction.

Autodesk
www.autodesk.com

::Design World::

PTC also provides connections and access to mentors from its partner organizations across America who are participants in the competition and program management for the competition. The challenge is designed by professionals from industry, government, and academia and is one of the aerospace industry’s top priorities for workforce development in the student community.

The challenge provides high school students with the opportunity to work on real world engineering challenges in a collaborative, team-based environment, applying the lessons of the classroom to the technical problems of the workplace. The winning teams from each participating state, including Newburyport High School in Massachusetts, Warren Consolidated Schools – Career Prep Center in Michigan and Hutchinson High School in Minnesota, received an all expense paid trip to Washington D.C. to compete at the National Challenge Event March 26-29, 2010 and will receive their awards at an event at the National Air and Space Museum.

Every year the challenge is developed and implemented by a public-private partnership committed to providing resources to students and schools to support Science, Technology, Engineering and Mathematics (STEM) education. The partnership is dedicated to bringing professional tools and resources to students and providing real world engineering experiences in which they can apply science and mathematics principles. Student teams are asked to address a real challenge that confronts our nation’s industries. This year, teams were asked to design a plane looking at the forces of flight, lift, weight, thrust and drag, with the aim of enhancing fuel efficiency.

“The Real World Design Challenge is helping students develop 21^st century skills that are needed by the US to address workforce requirements for both national security and global economic competiveness,” said Dr. Richard R. Antcliff, Chief Technologist, Langley Research Center, National Aeronautics and Space Administration. “Working in tandem with our partners, we are helping to develop tomorrow’s pioneers, who are needed to fuel the future innovation of our economy.” 

In addition to PTC, other partner organizations contributed resources to make the Challenge free to all students including Cessna Aircraft Company, Federal Aviation Administration, and Mentor Graphics. Governors from 25 states also partnered in 2009/2010 and made the Challenge the “Governor’s Challenge” at the state level competition.

PTC
www.ptc.com

::Design World::