This page contains a Flash digital edition of a book.

object-based features eliminates the need for engineers to understand the computational part of CFD and instead enables them to focus on the fluid dynamics of the product that they understand. Preble completed the first software

prototype in just one day. The results revealed areas in which the old design could be improved, and by repeating a series of simulations at various flow rates, he was able to locate and correct the problem areas in the valve. The entire redesign was completed without building a single hardware prototype, and it reduced the pressure drop from 6.09 to 0.71psi. Equally important, the project met the purchaser’s urgent schedule requirements. ‘In the past we would have had to make

an educated guess on what was raising the pressure drop in the valve,’ elaborates Preble. ‘For each guess we would build a prototype to see if we were right or not. Each one would cost about $3,000 and take about a month to machine, assemble and test. One weakness of the build-and-test approach is that physical tests determine the pressure drop in each new design iteration, but provide very little additional information to help us diagnose problems such as determining which areas of the valve are constricting fluid flow.’

Magnets on a reaction sphere When launching orbiting satellites, every gram of payload is extremely valuable. Researchers at CSEM, the Swiss Centre for Electronics and Microtechnology, are working on ways to minimise the weight




of satellite attitude control systems. They are developing a single multi-axis reaction sphere, which replaces four conventional single-axis reaction wheels. In conventional three-axis stabilised spacecrafts, three reaction wheels are arranged along the three axes with a fourth for optimisation and redundancy; they are normally employed to implement attitude control systems with the required accuracy and without using fuel to fire jets. This attitude control allows the satellite to be pointed towards an object in the sky, towards a particular location on earth or to stabilise the satellite by compensating for disturbances it might encounter. The operating principle is relatively simple: an electric motor is attached to a flywheel. When the wheel accelerates, it builds up angular momentum in a certain direction, and the spacecraft rotates in the opposite direction due to the law of conservation of momentum. CSEM’s single reaction sphere is an iron


number of electric coils. The sphere is accelerated about any axis of rotation with a 3D motor. A project funded by the European Space Agency is investigating the viability of a reaction sphere for use in space. CSEM’s patented design is based on a 3D permanent magnet motor implemented with a multi- pole rotor and a 20-pole stator. The 20cm rotor consists of 728 permanent cylindrical magnets affixed to an iron sphere. The reaction sphere’s rotor can be accelerated about any desired axis and moved in any direction continuously without any disruption using, a 20-pole stator that produces an eight-pole rotating field. The researchers have turned to Comsol

Multiphysics to evaluate multiple designs; in software they can vary the reaction sphere’s mass, torque and magnetic fields, and they can also investigate unusual geometries for the magnets (identifying their optimal size and placement), or create the magnetic field from the coils in different ways. They can take an intuitive idea and, within several hours, evaluate whether a given design should be further investigated. In fact, there are certain designs they are currently evaluating that they would have not been able to test at all using analytical approaches, but with Comsol it takes just a few hours.

Complex control systems For unmanned planetary exploration, autonomous robotic rovers are needed. Dr Amir Khajepour from the University of Waterloo is working with the Canadian Space Agency to develop a solution for the power management of such units. Using symbolic modelling technology through MapleSim from MapleSoft, he rapidly developed a high-fidelity multi-domain model of a rover’s subsystems. The software does in hours what engineers previously did – derive the equations of motion, but doing so over weeks and months. Further, these equations provide an extremely concise representation of the motion. The initial model for the six-wheeled

The original Shaw Aero Devices solenoid valve shown here exhibited a pressure drop of more than 6psi; the cut plot from FloEFD shows the results of two design revisions that reduced the drop to about 1psi, and subsequent revisions reduced the drop to 0.71psi


vehicle includes such aspects as the differentials, wheels, motors, motor controllers and the power system. Each wheel has an independent suspension through planetary gears, each driven by a motor. But what size motors are required? This is especially important in a planetary exploratory system where it’s critical to minimise energy consumption. Dr Khajepour notes that the base model was developed in a month, ‘and we now have the mathematical model of a six-wheeled rover without writing down a single equation.’
