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In 2013, Boeing rolled out the first 787-9 Dreamliner, the newest member of the super-efficient 787 family. In order to power this massive aircraft, Rolls-Royce designed the state of the art Trent 1000 turbine engine with an impressive 50,000 horse power – the equivalent of 68 Formula 1 racing car engines. With approximately 18,000 complex individual components in each engine, it is no surprise that people wonder how these marvels of engineering are brought to life.
A Shining Light
A plethora of tools and technologies are employed in this endeavour but one of them shines brighter than the rest for its versatility and capability to optimise designs even before the first prototype is constructed: Finite Element Analysis (FEA), otherwise known as Finite Element Method (FEM).
This method of engineering is one of the most important tools used by Rolls-Royce in order to study several of the key aspects of any design process: stress, structural, life, vibration, dynamics, thermal aspects, thermo-mechanics, aeromechanics, optimisation and robustness analysis.
In fact, it is one of the most important technical capabilities employed by Rolls-Royce, second only to Computer Aided Design (CAD). FEA is an extremely prevalent Computer Aided Engineering (CAE) technique used in several industries, such as the oil, automotive, aerospace, construction industries, and even used by biomedical and textile businesses.
The Methodology of Finite Element Analysis
This analytical methodology has been used since the 1960s. In the years since its first use, Finite Element Analysis has grown and developed into a standard of design engineering worldwide. It has spawned several commercial software packages which are used around the world, such as: ABAQUS, ANSYS, NX Nastran and Autodesk Inventor. Whilst the applications and technological capabilities may vary between different pieces of software, the cornerstone principle of the methodology is a constant.
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In first step of the FEA process, the user generates a computer model of the geometry of the real object which is to be analysed. Next, the component is segmented into a huge number of individual elements (usually hundreds of thousands) with a basic shape, such as cubes or prisms. Material properties are assigned to each element and this model is subjected to various conditions, such as external forces or loads.
Simple mathematical equations then predict the behaviour for each of the elements. Using computational methods, all of these behaviours are combined and the overall behaviour of the actual object is predicted, from the stresses acting on a component to the vibration of each part.
The Keystone of Engineering Design
Currently, finite element methods are so embedded within the world of engineering that even an undergraduate mechanical engineering student would have already worked with a FEA package, such as ANSYS or ABAQUS, during his or her academic studies. Efforts are currently being made on an international scale by universities in conjunction with leading companies in order to train the next generation of design engineers.
One example is the program PACE (Partners for the Advancement of Collaborative Engineering), which is an impressive international effort involving universities from 10 different countries around the world. This program is ran in collaboration with the automotive giant General Motors (GM), as well as several other huge engineering companies such as Siemens, Autodesk, Ansys, Mathworks and DS Simulia.
This program allows students to work in multinational teams in order to design the next generation of automobiles. Students commonly use finite element techniques in order to evaluate their designs, such as gauging the strength of the chassis design in the event of a crash.
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This effort, spearheaded by GM, to train future automotive engineers in the finite element method should not come as a surprise considering that automotive companies across the globe rely mainly on finite element models to evaluate everything from a full vehicle in motion or the durability of car engine in its operational environment, to the welding and bolts that keep the chassis and the car seats together.
Garbage In-Garbage Out
However, the FEA method is not without fault and a bad assessment due to an inferior element selection or an inaccurate load selection can result in all kinds of failures. These can vary from extreme engine noise due to the excessive vibration of one component, to a critical failure of the chassis during an impact or collision, potentially resulting in the loss of human life.
This directs us to the most paramount and significant principle of finite element methods: ‘Garbage In-Garbage Out’. Essentially, this principle states that the finite element method can generate any results that the design engineer desires.
As a result, it is the responsibility of the user to completely comprehend the real properties of the component to be analysed and how they would interact with the environment in real life conditions, i.e. whether forces would be applied to it or its movement once it is assembled.
Further to this, different brands of finite element software present a wide variety of elements and computational algorithms that would yield more precise results depending on the conditions in which they are used, giving the user a responsibility to choose the right tool.
Finite element models are only an approximation of reality because the models cannot account for certain imperfections or variations that occur in real life such as manufacturing errors. As a result, simple finite element models of the components are experimentally validated before progressing with more complex simulations.
Multitude of Applications
Despite these limitations, the versatility of the method has made finite element models an important tool for the design of biomedical parts such as prosthetics limbs or implants for spinal fusion. The capabilities of the method of analysis are currently being used to study the human heart for the design of new pacemakers and even arterial stents, which clear blocked arteries. This has the potential to ensure more people can avoid invasive open-heart surgery.
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Finite element simulations are also used in more unexpected industries, such as within the textile trade, where the method has been used to analyse the behaviour of fabrics employed in the manufacturing of women’s underwear, in order to develop a more supportive and comfortable brassiere.
In addition to this, the FEA method is not limited to the design of new components but can also assist engineers in gaining an insight into the causes of certain tragedies. The most resounding example of this was the use of the FE method by the National Institute of Standards and Technology (NIST) during the research and studies into the collapse of the World Trade Centre during the 9/11 terrorist attacks.
Designing the Future
Finite element methods have proved their versatility and reliability over the past 50 years. Currently, with the development of High Processing Computing Centres (HPC) and the progress of computing capabilities, the chances are that this design and analysis tool will continue to progress into the future in conjunction with new manufacturing techniques (such as Rapid Prototyping).
In the future finite element methods will establish themselves as an important tool in the design and production of innovative, highly-efficient and more reliable products. The applications of FEA are so varied that they range from a heart stent to the next generation of aircraft, such as the Boeing 787.
Sources and Further Reading