Introduction
Computer Aided Design is undoubtedly one of the most powerful tools at a designer’s disposal improving efficiencies in the design process by allowing complex shapes, structures and assemblies to be created, checked, analysed and drawn.
In this article I briefly summarise some of the types of digital tool used in design and the applications they can be used for as well as addressing some of the common pitfalls I have seen with new engineers entering the industry.
Finally, a simple step by step process is provided along with tips and suggestions to work around and mitigate some of the common pitfalls.

Digital Tools
The purpose of the article isn’t to go into detail on the pro’s and con’s of the numerous tools and software suites that are on the market but a quick summary of just some of the tools available to engineers include:

• 3D Modelling which provides the designer with a way of creating digital models of a range of components, structures and assemblies in order to provide a visual representation of the design which can then be used with other software functions or to allow non-technical parties to view and understand the design.

• 2D Draughting which allows a design to be created in a simpler two-dimensional environment or allows conversion of a 3D model into orthogonal and sectional views to allow dimensioning and detailing for manufacturing purposes.

• Finite Element Analysis which allows 3D models to be used within a computer simulation to understand how they behave when subjected to different forces or loads with outputs such as stresses or deflections then compared to allowable limits.

• Computation Fluid Dynamics which again allows a 3D model to be run within a simulation to understand the behaviour of the object in a hydrodynamic or aerodynamic environment.

• Catenary Analysis software which allows a pipeline or cable installation to be simulated with waves, currents, vessel motions and seabed conditions applied to understand its behaviour, tensions, bending and movements.

• Virtual Reality tools which allow users to access a virtual environment where operations can be practiced and simulated with weather responses, emergency scenarios and similar applied to the experience.

• Animations which can take 3D models and apply movement to constraints and components to represent their use in the real world, again allowing users to understand how they function and the range of motions to be checked for clashes.

Jumping in Too Early
Undoubtedly the most frequent error and the one with potentially the biggest impact is designers jumping into the use of a 3D tool too early on in the process, developing complex models before any real understanding of the problem has been gained and a solution fully thought out.
The more detail and components that are added to a model the greater the difficulty and the longer the time spent modifying the design to incorporate additional features or change the geometric layout.
Increasing a square hollow section in length in a 3D model might be reasonably easy but swapping it out for a bespoke fabrication and loosing constraints and relationships with other components can be frustrating at best and an inefficient use of time especially in fast paced projects where drawings need to be issued for manufacture as quickly as possible.
A clear understanding of an appropriate solution is therefore needed before a 3D CAD tool is deployed with interfaces to surrounding equipment or components clear, a firm understanding of the manufacturing, assembly and installation process known and a grasp of the required structural size appreciated.
Once these aspects have been developed and ideally reviewed by peers via a design review or similar at that point should the efficiencies of 3D CAD tools be embraced and the solution developed in detail on a “first time right” basis ahead of small changes and developments as calculations or analysis advise.

Creating The Impossible
A second pitfall, often pertinent with the use of 3D CAD before a solution has been fully developed, is the creation of a design which simply can’t be made to work.
Examples include where the manufacturing process hasn’t been fully considered with parts which are impossible to access for welding, components which can’t be machined or sub-assemblies which can’t be put together.
Other examples where aspects of the design haven’t been fully considered include not splitting large assemblies or fabrications into smaller modular pieces which as a worse case can result in something being made which can’t be moved without excessive police notice or limiting the range of suppliers who can machine, paint or manoeuvre the item leading to budget and schedule impacts.
In the design stage the proposed solution should be built up step by step as it would be in real life using sketches or CAD tools or considered in your mind. Sufficient clearance for welds, access for machining, transportation of parts and the full assembly process should all be thought through and the design adjusted as required.

Rubbish In Rubbish Out
This pitfall refers to an over reliance on data for example not questioning what the results of a computer simulation may mean and whether they make sense or not.
Analysis tools are extremely powerful, but some simple hand calculations with sensible assumptions should hopefully be able to demonstrate that the results are valid and in a similar order of magnitude. I’ve been presented analysis runs showing stresses of enormous magnitudes which experience suggests couldn’t possibly be true. A simple hand calculation can inform the software user that the analysis is flawed and there are either issues with how the model has been set up or some obvious error in the scale of the inputs i.e. tonnes rather than Kg have been used. As such any use of analysis tools should be accompanied by some form of high-level hand calculation to validate the information.
Another example of relying on the information in front of you is with drawings of sites or installations such as equipment on a ship. Invariably things will have changed over time with stairs and ladders moving, new features added, and older structures removed. Not undertaking as a minimum, a visual survey and relying on old, third party information is a recipe for disaster. If designing something which won’t be a standalone item, always try and see the equipment it will interface with or the site it will be installed at in person, photograph everything for future reference and compare the drawings with measurements taken on site.

Proven Process
The following simple process is how I have successfully approached numerous design problems and developed solutions in a quick and efficient manner. Clients like the approach as it simplifies the problem and allows the proposed solution to be easily visualised within an assembly or installation such as within the deck layout of the vessel allowing them to comment on it and feedback to be gained before any commitment to using 3D tools and going down a route which is time consuming and expensive to get back from.

1. The first step is to gain an understanding of the main aspects of the problem, what functions are required, what do we have to interface with at a high level and what does that look like i.e. do we need to connect to an existing pinned clevis arrangement or to a flanged connection. Then consider what sort of movement do we need to create with any mechanism i.e. moving a load up and down, in or out or around a point or feature.
2. Once this is known and the problem can start to be visualised it’s a case of sketching simple ideas out. This could be in something like PowerPoint with simple shapes and lines, on a whiteboard in the office or as is my preference on sheets of scrap paper with a set of coloured pens or pencils to allow different components to be sketched relative to each other.

At this stage the relative scale of different components isn’t important its about sketching various ideas out and quickly seeing which ideas work and which won’t. I generally start off with side views and if I get something which looks like it might work then recreating plan and front views to check it still works and then sketching rough section views to picture what it will look like.

3. I can’t emphasise enough how crude and simplistic these sketches need to be, really quick and easy to allow lots of ideas to be drawn out in a short time frame, evaluated to see if they work and then dismissed or developed further with more detail if they start to look plausible.
4. With sketches starting to show the basis of an idea now is the time to start using software – but hold back from 3D just yet, what size of components do you need, what details need to be further developed. I often start by sketching out the constraints in AutoCAD such as a space envelop in plan, side and front views and if I’m interesting with other equipment bringing in a simple block or representation of that. (If you have a 3D model of what you are going to be interfacing it’s a few minutes work to generate plan, side and front views in your 3D tool of choice and import into 2D).
5. As I’m going through this stage I will start to do some very basic sizing calculations, simple moments and shear forces to get approximate sizes for sections and components. I will then start creating simple blocks for each of the main components or systems in plan, side and front views and copy and paste them to start building up assembly views of the system in its various positions. As with step two using different colours for different parts can make this really easy to visualise and if being passed to clients for review will help them quickly understand it.
6. Now it’s time for 3D! Depending on the complexity of the design and confidence in the solution I will either jump in and start modelling parts up with a full numbering system, including all sub components such as individual components for fabrications and bring in models for 3rd party items or if the purpose of the 3D model is for purely for visualisation then I will create simple blocks for each moving assembly or feature knowing this should be sufficient.
7. Finals steps will depend on the end goal. If the models are for visualisations, use in animations or manuals then they can be rendered and used as required. If the models will used for fabrication, machining or assembly work then detail drawings with all necessary views, sections, dimensions and tolerances can be produced.
   

Conclusions and Actions
Computer aided design packages are an extremely power and helpful set of tools available to the designer, however their use should be approached with care as they can end up being time sinks if solutions aren’t understood, and the build process hasn’t been considered before they start being used and models have to be continually adapted as new information on the solution becomes available.
Used correctly and at the appropriate stage of the design process they will maximise efficiency and allow smaller developments and changes to be easily incorporated.
Over reliance on data should be avoided and common sense and sanity checks used within the design process.

About the Author
Andy Stevenson is a Chartered Engineer, Entrepreneur and Fellow of the Institution of the Mechanical Engineers. He currently works as the Founder and CEO of Laytrix, a business providing engineering services and developing innovative products for the global offshore sector as well as the Founder / Director of training and consultancy business Samson Forth Associates.
Based in the Northeast of England he has set up and successfully exited a number of previous businesses in similar sectors.
An alumnus of the University of Edinburgh, NED of a STEM Charity and a Royal Academy of Engineering Visiting Professor at Teesside University he has spent the majority of his career leading design teams developing bespoke equipment for offshore activities such as pipelay, cable burial and renewable energy generation and uses these experiences within his training and academic work.