21 June 2023


Collaborative Engineering

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RHEA’s experts have been using concurrent design for nearly two decades to accelerate the early phases of complex engineering projects such as space programmes, defence systems, factory design and luxury yachts.

In this blog series, they share their insights into how you can ensure concurrent design sessions are rigorous and the outcomes are high quality.

By Gwendolyn Kolfschoten, Concurrent Design Expert

Catch up with last month’s post: Create shared understanding without looking stupid

9. How to Manage the Interfaces Between Subsystems

When designing complex systems, one area that is good to explore as early as possible is the interfaces between subsystems – how each one works or fits in with others. Identifying the conditions for these to work and implementing a way to keep track of each one during development is a significant task. It is also a key task, because even when an interface has been discovered and classified as challenging, this does not mean it is fixed.

Identifying interfaces

RHEA Group governance iconThe first challenge is identifying the interfaces that are not straightforward. We often do this by making an ‘N2’ diagram, in which we can identify the interdependencies between subsystems. Other ways of identifying interfaces include asking experts to indicate what information is missing for them to design their part and getting subsystem experts to present an overview of their system, with the rest of the team encouraged to comment if they foresee any interfaces with that system.

However, even after doing this, some interfaces may remain hidden because of the assumptions people make. For instance, an artificial intelligence (AI) expert may think he is going to provide the CPU for his solution but the technical officer intends to have only one CPU for the entire platform, which then needs to meet the joint demands of several experts, and thus automatically becomes a critical interface.

Whenever an interface surfaces that is not standard and is shared between different experts in the design team, we need to add it to a monitoring list.

Dealing with interfaces

rhea group new project iconTo deal with an interface, we first need to understand in what ways the systems will link or interact. Will they need to fit physically and to exchange power and/or data? Does the interface need to endure any force or traction? Always verify the facts, because many mistakes originate from false assumptions about standard interfaces.

Next, we need to understand to what extent one system constrains the design of the other, and which system should be adapted to fit the other. Establishing what needs to be sorted out in order to make a decision is important. What do we need to know to make this design decision? And when can we make that decision?

Finally, designing an interface in detail is not enough. To ensure it fits, we need to check, monitor and test it throughout the engineering process. Among other things, we need to make sure:

  • The interface requirements are listed and correct.
  • The solution has incorporated these requirements.
  • The detailed design of both systems includes all aspects of the interface.
  • The prototype fits.

At every step of the way a detail may get missed. When that happens, the consequences can be enormous.

Remember the external interfaces

RHEA Group icon illustrating external vulnerabilityA set of interfaces that is often forgotten during the early design stages are the external interfaces. For instance, when we build a ship, it should not only work as a ‘system of systems’, it should also be able to fit in its harbour, use power from the land-side and manoeuvre in the canal that leads to open water. It is all too easy for a team to lose focus on these aspects when their attention is on the internal design of the ship.

Tips to manage interfaces in system design

These tips may help you to help the team manage interfaces:

  • Establish who will be responsible for overall interface management and for specific interfaces.
  • For each interface, identify its nature, how it constrains any related subsystems and/or the overall system, and the extent to which it is critical to the design.
  • Find out when the decision on how to design the interface will be made, and what information the design will be based on. Also make sure it is clear how that decision will affect the ability of experts to move on with their design.
  • Make a list of challenging interfaces, and go through the list regularly with the team to learn about updates and changes that may impact them.
  • Make a follow-up plan to ensure each interface will be monitored throughout the design process.

Find out more

In this series of blog posts on concurrent design, we present techniques to improve rigour and quality. These offer a toolbox for concurrent design team leads to support their teams effectively in improving and testing the design. We cover aspects such as how to handle validation when working with rough estimates, how to capture the wisdom of the whole team of experts, and how to keep the team on track and motivated.

Follow RHEA Group on LinkedIn to be alerted to new posts in this series.

Catch up with our previous blog series on 10 Success Factors for Collaborative Design.