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NEiFusion Receives Award from Design News Magazine

Design News magazine awarded Noran Engineering its 2007 Golden Mousetrap Award for Best Product in the Category of Analysis & Calculation Software for NEiFusion v1.2. The award was presented at the National Design Engineering Show in Rosemont, IL in October. The award was particularly satisfying for NEi because Design News magazine is read by 170,000 subscribers involved in mechanical and electromechanical design and product development. Plus, NEiFusion was selected above many established brand names because of the many new features that make it an effective tool at the CAD design stage for virtual test and design validation.

To read more about the award please click here.

NEi Software Featured Success Story: Medical Applications (CenPRA, Brazil – Human Mandible Implant)

Renato Archer Research Center (CenPRA) is a Brazilian public federal research institute, under the Brazilian Science and Technology Ministry, dealing with many different research topics, ranging from micro-electronics to industrial applications of rapid prototyping technology. One of the most recent research lines of CenPRA is the application of high technology for medical demands in which a bioengineering analysis is used.

The use of mandibular implants for bar-clip fixation in order to provide infrastructure for a complete overdenture appliance is a common issue in Brazilian odontologic clinics. Due to this, the study of mechanical behavior and the influence of misfits related with the implant procedure are crucial.

The initiative of the Faculty of Odontology at Piracicaba, part of the State University of Campinas, to evaluate the influence of the misfit in a bar-clip fixation to one of the two mandibular implants applied to a central section of a mandibular bone was conducted with the support of CenPRA using a complex NEiNastran nonlinear welded contact model.

The high complexity of the model comes from the multiple body interaction, provided the mandibular bone is fully described, with cortical and trabecular structures defined, and the implant, screw and bar-clip attached to the mandible and one to each other using welded contact. Material properties were defined for each type of bone, metallic implant-screw system and barclip. For this study, besides the misfit of the bar-clip, the researchers wanted to know the influence of the variation of bar-clip material.

Thanks to NEiNastran welded contact model and the power of the nonlinear solvers, allied to the flexible pre- and post-processing of FEMAP, not only was a solution obtained but it could be easily visualized and comprehend by professionals of multidisciplinary areas, like dentists, physicians and engineers, typically working together in bioengineering applications. This kind of flexibility is a must for a successful partnership.

Farr Yacht Design's Use of NEi Nastran Featured at EntertainmentEngineering.com

EntertainmentEngineering.com an online publication that covers the technical side of the entertainment industry, featured Farr Yacht Design's application of NEi Nastran analysis software to the design of ocean racing yachts. See the story below or visit www.entertainmentengineering.com.

Farr Yacht Design (FYD) uses NEi Nastran to enhance its structural analysis and simulation for its line of yachts. FYD is a leader in the design and engineering of high performance racing yachts for major events including the America’s Cup and the Volvo Ocean Race, as well as custom and production yachts for builders around the globe.

“Structural analysis is an increasingly important component of successful racing yacht design”, comments Dave Fornaro, FYD design engineer. “We have been utilizing FEA for several years to validate and improve our designs and desired to enhance our suite of analysis tools with more advanced capabilities in several areas including laminated composites, nonlinear surface contact with friction, and bolted joints with pre-load. After an exhaustive review, NEi Nastran stood out as the best choice based on its advanced capabilities, cost-effectiveness, and quality technical support.”

FYD’s first application of Nastran is for its next-generation of designs for the Volvo Ocean Race, a grueling round-the-world race sailed in fully crewed, 70-foot carbon fiber yachts capable of speeds in excess of 40 knots. “These designs are forging new frontiers in ocean racing,” adds Dave Fornaro. “They operate in harsh and brutal conditions and require a rigorous level of structural design and analysis to ensure peak performance and safety.”

Two Phases of Analysis

A typical analysis for a racing yacht is split into two phases: global and detailed. In the global analysis phase, FYD models the entire hull, deck and internal structure as laminated composite shell elements. A typical model will contain approximately 125,000 elements. The composite materials are orthotropic in nature - that is they have different mechanical properties in different directions. This adds an extra layer of complexity as compared to isotropic materials such as metals.

According to Dave, “NEi Nastran has excellent capabilities for modeling laminated composite materials. We use spreadsheets to calculate the properties for individual plies and laminates (collections of plies) based on classical laminate theory. We have developed an automated method for transferring this data from the spreadsheets directly into NEi Nastran such that all ply and laminate definitions are read in with the correct naming and formatting of all mechanical properties. These properties are then applied to the appropriate areas of the model.”

Global models can contain as many as 150 different laminates, each with three plies representing two skins on either side of a core material. Several load cases are then run representing various typical sailing conditions as well as extreme load cases such as grounding or slamming into waves. These load cases are then post-processed in NEi Nastran and the results compared to criteria for global strains and deflections. This information can then be used to update the laminates as needed and re-run the analyses in an iterative fashion until all areas of the design meet the requirements.

“In the detailed analysis phase,” David said, “we look more closely at critical areas of the yacht that experience large strains.” Such areas are often at the junction of major structural elements such as canting keel pivot pins mounted into transverse bulkheads. For these detailed models, FYD’s design team will often remove a portion of the global model complete with enforced boundary conditions from a particular load case to use as the starting point. “We will then modify the models as required to study the areas of interest in more detail. Typically we will use a combination of solid and shell elements,” David said.

The solid elements are required in areas where transverse strains need to be calculated, or at contacting surfaces such as pin joints where through-thickness effects need to be captured. NEi Nastran has particularly good capabilities for modeling and analyzing contacting surfaces so as to accurately study pressure distributions and strains across the interface between the components. “This is very helpful for studying effects such as the distribution of loads among the fasteners in a bolted joint, including the effects of clamping and friction due to bolt pre-load,” David said.

Through the combination of global and detailed analyses, FYD is able to engineer their yachts to a much higher degree of fidelity than would be possible using traditional engineering methods alone. However, traditional engineering methods are still a very necessary part of the job, both for initial design work as well as for a check on the FEA results.         

NEi Software Product Release Information

The following lists include the top ten features that were recently released as well as the top ten features currently in Beta v9.2.  NEiNastran v9.2 is planned to be released in Summer 2008.

Recently released:

NEiNastran v9.2 scheduled for Summer, 2008 release:

Tech Tips

Using the Stress Error Quantification in NEi Nastran

A recently added feature of NEi Nastran is a value which quantifies the stress error for shell and solid elements, addressing the issue associated with mesh density.

When using shell and solid elements for stress contours, it is difficult to know when you have enough elements to capture the stress adequately. To provide a guideline for using both the Shell Element Stress Error and Solid Element Stress Error to determine when enough elements have been used, we created test cases where we incrementally increased the mesh size for various models to determine the Stress Error value corresponding to a 2% stress convergence. The max von Mises stress was used to quantify the Shell Element stress error, whereas the max Normal Stress was used to quantify the Solid Element Stress Error.

For a von Mises stress convergence within 2%, a Stress Error of approximately 0.015 or less is needed for shell elements. To achieve a Normal Stress convergence of 2%, a Stress Error of approximately 0.03 or less is needed from solid elements.

Shell Stress Error Contour for an L-shaped bracket with 32 Shell Elements.

Using the Extended Results Labels in NEi Nastran

There is now added support for extended results titles and labels in the FEMAP Binary results File (FNO). The new labels are now up to 80 characters long and provide a better description of the associated results measure.

The parameter RSLTFILEDBLERPRCS under Output Control Directives allows you to turn ON/OFF the double precision option for the FEMAP FNO. When set to OFF, it will use single precision data storage with extended length titles and labels. When set to ON, it will use double precision data storage with standard length titles and labels.  The OFF option is only compatible with FEMAP versions 9.3 and higher will provide better performance and more informative results labels.

In the two screenshots bellow you can see the difference in the results titles from when the RSLTFILEDBLERPRCS parameter is set to ON and when it is OFF. For example the shell element bottom side principle stress reads “SHELL MINOR-PRINCIPAL-1” when set to ON and “SHELL MINOR-PRINCIPAL-BOTTOM” when set to OFF.

Standard Length Titles and Labels, RSLTFILEDBLERPRCS = ON

Extended Length Titles and Labels, RSLTFILEDBLERPRCS = OFF

If you do not know what some of the result vectors are, you can look up descriptions in Appendix A of the NEi Nastran Reference Manual. Simply go to Start>All Programs> NEi Nastran > Documentation and open the NEi Nastran Reference Manual PDF file.  In Appendix A, results descriptions are separated into three types of results, Element, Grid Point, and Vector, and within each of these types they are separated by element type.

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