This guest contribution on Innovation Intelligence is written by Engineering Software Research & Development, Inc. (ESRD). StresscheckTM software by ESRD is a comprehensive finite element analysis tool with a pre- and post-processor and a suite of analysis modules that support advanced solution methods.
Business drivers in the Aerospace & Defense Industry
The global aviation, aerospace, and defense industries face unrelenting pressure for ever-increasing levels of operational performance, life cycle reliability, and mission robustness in their products, systems, and platforms delivered to commercial and military customers. This is occurring at the same time as increasing demand for aviation products that are faster, quieter, smarter, lighter, greener, and more connected, all while being less expensive to procure and maintain.
These business drivers have unleashed a level of interconnected complexity across nearly every function, process, and product line of the modern A&D enterprise. A new norm of debilitating complexity permeates the aerospace business throughout program management, requirements planning, system design, engineering analysis, product configurations, manufacturing variances, workflow processes, supply chain collaboration, and in-service sustainment. While dozens of new technologies, enterprise solutions, and software tools have emerged in recent years to advance each of these organizational functions, they have often added new layers of complexity.
While many OEMs and their supply chain contractors have risen to meet this challenge, others have struggled as evidenced by the number of major programs which encounter substantial overruns in budget, schedule, or both. A few years ago, the U.S. GAO reported that 100 major defense programs experienced an average schedule delay approaching two years, with an average budget overrun of more than 25%.
Diminishing returns from investing in more of what already exists
Faced with an avalanche of complexity, legacy generation methodologies and technologies–along with the organizational competencies and tools built upon them–have become rather non-linear to further investment and improvement. That is, an incremental improvement in one function does not always translate into immediate improvements across the entire product development ecosystem. Some highly-touted advancements often introduce more complexity, time, cost, and risk than the interconnected web of new product development can quickly absorb. Aerospace managers have come to realize that valuable innovations in one domain may cascade into hurdles elsewhere that are not always fully understood at the onset of a new technology adoption maturity curve.
In responding to schedule-eating, budget-busting complexity, engineering groups are seeking new methods and tools that not just advance their capacity to meet higher product performance requirements, but at the same time are simple, reliable, and robust for use by specialists and non-experts alike without diminishing the quality of their outputs. Technologies used in the structures, stress, fatigue, materials, and manufacturing groups of A&D contractors for digital prototyping and numerical simulation are particularly ripe for simplification such that the promise of simulation to compress product development cycles can finally be achieved.
The state of simulation tools in aerospace engineering groups
Over a period of four decades, software products developed for performing numerical simulation based on the finite element method (FEM) have progressed to deliver an ever-expanding list of functionality and features across a widening computational spectrum of multiple physics. As finite element analysis (FEA) software products became more capable, they also became more complex to learn, time consuming to master, prickly to operate, and difficult to trust. FEA is justifiably referred to as a craft if not an art form due to all the sources of assumptions, idealizations, approximations, judgement calls, and errors an engineer must consider to arrive at a “good” solution which they can defend.
The evidence speaks for itself that when solving a problem in computational mechanics by different users with different software, or using different models and element formulations, it is not unusual to generate very different results. It is no secret that most of the effort and time of FEA is spent in the laborious pre-processing steps of creating bad models to finally arrive at good ones, instead of in the post-processing stage leveraging the results to optimize design performance. Simulation analysts dutifully take pride in their profession for understanding all the nuances and minutia which influence the quality of their work.
As a consequence, some aerospace engineering managers think of FEA as the best analysis tool for the highest quality results, but only after all other analysis methods have been exhausted! The use of engineering handbooks, design curves, empirical data, closed form solutions, elaborate spreadsheets to calculate and pencil-whip margins of safety is seen as preferable to spending time building, running, debugging, and tuning finite element models. This is not to discount the power and accuracy of finite element-based stress analysis, especially when compared to the alternative of more physical testing, but a honest assessment that there is a significant cost in obtaining the higher-fidelity solutions that FEA offers.
Challenges with legacy simulation technologies
Across the engineering community there is much discussion about the democratization of simulation; meaning the reliable use of numerical simulation by non-simulation experts who may be design engineers, new analysts, or occasional users. The hope is that much of the complexity, time, and risk of performing FEA can be wrung out of simulation in a way that finally allows simulation-driven design to be led by design engineers. Indeed democratization has great potential in the A&D industry to compress the product development lifecycle, but is it realistic? The answer few may want to hear is that this will not be easy to accomplish using legacy FEA technologies, methodologies, and software tools.
The underlying theory and methods “under the hood” of most FEA codes on the market today are in fact many decades old. There is a reason why element libraries often contain dozens of variants, and why when some of these finicky elements are used in delicate meshes a model may break with even small changes to design geometry or boundary conditions.
While user interfaces, pre/post processing, high performance computing, optimization techniques, and licensing schemes have advanced greatly–as demonstrated so well by the impressive Altair Partner Alliance library of applications–many simulation software providers have had to find creative ways to compensate for the underlying limitations and inherent complexity of the FEM. Experiments to embed solvers into CAD software to hide complexity, or create templates to automate error-prone processes, have yet to move most FEA off of the expert’s desktop and place it into the hands of the design engineer. To learn more about why this is so we invite you to attend ESRD’s presentation at the NAFEMS Aerospace Conference in Wichita, Kansas on Nov. 8, which Altair and ESRD are sponsoring.
As a result, the strength engineer on an A&D program owns the overwhelming burden to produce higher-fidelity analyses of more demanding structural designs earlier in the NPD cycle, while using more sophisticated tools that take longer to learn, and to create all-encompassing 3D digital models with few details left behind. On top of this demanding responsibility, they are expected to perform this work in shorter time with a greater level of confidence in the results and less room for uncertainty, errors, or fat factors of safety that were acceptable in yesteryear’s aerostructures. It is no wonder that analysis organizations like NAFEMS report that Simulation Governance along with Verification, Validation and Uncertainty Quantification have become “The Big Issues” for engineering managers who often see their simulation teams struggle to deliver with all of these incompatible requirements.
Numerical Simulation that is S.A.F.E.R than finite element modeling
While finite element modeling as practiced over recent decades is rightfully considered a highly-skilled craft best performed by the well-trained expert, the goal of numerical simulation is not to deliver more of the same faster. Instead, numerical simulation is a predictive computational science that can be used more reliably by both the expert and non-specialist. Thus, a prerequisite for any numerical simulation software product is that it provides quantitative assessment of the quality of the results. Lacking that capability, it still requires an expert to subjectively ascertain if the solution is valid or not, and fails the most basic requirement for solution verification.
S.A.F.E.R. numerical simulation is a strategy for implementing Simulation Governance that produces engineering analysis which is Simple, Accurate, Fast, Efficient, and Reliable for experts and non-experts alike. APA Partner, ESRD, offers the high-fidelity stress analysis tool StressCheckTM which was developed for the A&D industry as the first numerical simulation product to support verification and validation for S.A.F.E.R. structural analysis.
StressCheck uses a far smaller and simpler element library of only five elements, all which map to solid geometry without the need for recreation or defeaturing. Smart solid elements may be used across variant scale geometries without loss of resolution or the need for intermediate highly simplified “stick & frame” or “plate & beam” models. Elements and corresponding meshes are no longer sensitive to organic geometries, poor aspect ratios, thickness constraints, hour-glassing, locking, parameter changes or other chronic ailments of legacy finite element methods. As a result, high-fidelity solutions can be obtained from coarse low-density meshes with an explicit automatic measurement of solution quality.
StressCheck models don’t break, nor do they have to be recreated, when changes in design geometry, boundary conditions, or analysis types (e.g., linear, nonlinear, dynamics) occur. Solutions are continuous throughout the entire domain as degrees of freedom are no longer associated with or locked to nodes. Any engineering data of interest can dynamically be extracted at any location, at any time, without loss of precision due to interpolation or other post-processing tricks. Proof of solution convergence is also provided for any function at any location. Thus, simulation results are far less dependent on the user, model, or mesh, and stress analysis becomes an inherently more reliable and repeatable competency for the engineering organization.
As a result, hyper-fidelity, not just high-fidelity, solutions of complex 3D solid model geometries with numerous joints and fastener connections typical of aerostructures may be obtained in less time, with reduced complexity and greater confidence. The business drivers to produce higher performing damage tolerant structures used in aviation now mandate not just a high, but a hyper level of engineering precision and confidence in numerous analysis types. This includes detail stress analysis, global/local modeling, bonded and fastened joints, manufacturing-induced residual stresses, composite materials, and durability and damage tolerant analysis.
To learn more
To see example applications from the A&D industry of hyper-fidelity stress analysis performed with ESRD’s StressCheck, attend the APA sponsored webinar on Oct. 17 at http://web2.altairhyperworks.com/2017-esrd-use-case-webinar.
To read subsequent articles in this series on S.A.F.E.R. Simulation for the A&D Industry visit ESRD’s website at https://www.esrd.com/about/safer-simulation/.
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