Modelling / 3.4 / 
Computer-Aided Design

Modelling of design using CAD software falls into one of two categories: 

1. Direct modelling: Geometry is modelled without spending time explicitly defining interdependent features of parts or constraints on material or mechanical properties. Direct modelling is often compared to modelling in clay. 

2. Parametric modelling: Geometry is modelled using explicitly defined features and constraints. This allows users to automate repetitive features and changes to one part might automatically lead to changes to another part of a model. E.g. changing the diameter of a bolt might automatically change the diameter of a corresponding nut and the software might give a warning if the geometry of that nut does no longer fit in the product assembly.

Direct modelling usually is quicker and allows more freedom. Parametric modelling usually is more exact and more adjustable over multiple iterations or variations. 

When designing using a “bottom-up” approach, a designer starts with only a rough concept of the finished product and its parts or features without strict constraints or design criteria. The designer then starts modelling individual parts (starting with the most crucial ones) and worries about assembly later. In this approach, the design of individual parts may heavily influence the form and/or function of the end product. A well-known example of the bottom-up approach is the development of the Mars rover Curiosity in which different teams from different countries developed different components more or less independently and combined these later.

When designing using a "Top-down” approach, development starts with establishing a clear set of design criteria and technical specifications for the end product. Form and function are largely defined in this. The designer then works out individual parts that explicitly fit the defined end product. Top-down approaches are common in design projects where exploration while designing is expensive. 

Bottom-up and top-down approaches can apply to simple products as well as complex systems. Usually, a mix of both approaches is applied. If a more open-ended exploration of options is required a more bottom-up approach would be used. If a more result-driven process is required a more top-down approach would be used.

Digital humans are computer simulations of a variety of mechanical and biological aspects of the human body such as strength, field of vision and range of motion. They can be used to interact with a virtual prototype. Human simulation in product design enables a product to be developed more quickly, as there can be more design iterations in less time. 

Digital humans enable manufacturing plants to be developed more quickly and manual workflow to be optimized. They improve worker safety and reduce compensation costs resulting from accidents. Machines and other equipment can be positioned to optimize cycle time and avoid hazards. 

Digital humans are also used to train real people in completing tasks without the need for physical prototypes or actual equipment and so reduce the cost of training manufacturing and maintenance personnel.

There are many ways that digital humans can be developed and used to interact with products.

Motion capture is the recording of human and animal movement by any means, for example, by video, magnetic or electromechanical devices. A person wears a set of acoustic, inertial, LED, magnetic or reflective markers at each joint. Sensors track the position of the markers as the person moves to develop a digital representation of the motion.

A motion capture session records the movements of the actor, not their visual appearance. The captured movements are mapped to a 3D model (for example, human or robot) to move the model in the same way. Capturing a number of users’ movements will allow designers to design better ergonomic products. Motion capture allows the designer to understand the users’ physiological requirements.

Haptic technology is a technology that interfaces with the user via a sense of touch. Also known as force feedback technology, haptic technology works by using mechanical actuators to apply forces to the user. Haptic technology allows the user to become part of a computer simulation and interact with it, enabling the designer to observe the user’s performance and design a better outcome. It can also be used in situations where it is difficult to train in a real environment. Haptic technology is also used in feedback devices used in home entertainment consoles.

State-of-the-art or forced-feedback haptic devices allow the user to feel and touch virtual objects with a high degree of realism. This technology is also being used in pioneering remote surgery procedures. The surgeon can be in a completely different part of the world, and yet still complete complex surgery on a patient. 

Some commercial computer game consoles already benefit from early-developed haptic devices, like the steering wheels that torque and vibrate on driving games. 

Virtual reality is the ability to simulate a real situation on the screen and interact with it in a near-natural way. VR is computer generated and allows the user to interact with the data that gives the appearance of a three-dimensional environment using a headset and other wearable technology.

Animation is the ability to link graphic models and images together in such a way as to simulate motion or a process. Animation can be used to simulate various design concepts and contexts. They can also use digital humans to allow different scenarios to be tested.

Manufacturing companies can see how safe a product or production system will be when they are being produced through an animation of that system. Animations can also be used to test and evaluate products for potential design issues.

Finite Element Analysis (FEA) is a powerful computational method used to predict how a physical object will behave under certain conditions. It's like a virtual laboratory where engineers can test designs without building physical prototypes, saving time and resources. FEA uses the mathematics of the finite element method, a popular method for numerically solving differential equations arising in engineering and mathematical modeling.

Some benefits of Finite Element Analysis are:

• Cost-effective: FEA can significantly reduce the need for physical prototypes, saving time and money.

• Time-saving: Simulations can be run quickly, allowing for rapid design iterations and optimization.

• Improved design: FEA helps identify potential problems early in the design process, leading to better and more reliable products.

• Safety: FEA can assess the safety of products under various conditions, such as impact or extreme temperatures.

FEA is used in a wide range of industries, including:

• Aerospace: Designing aircraft structures, engines, and other components.

• Automotive: Developing cars, trucks, and other vehicles.

• Civil engineering: Analyzing bridges, buildings, and other infrastructure.

• Mechanical engineering: Designing machines and mechanical systems.

• Biomedical engineering: Simulating the behaviour of medical devices and implants.