Porous Tube Plant Nutrient Delivery System development: a device for nutrient delivery in microgravity.

The Porous Tube Plant Nutrient Delivery System or PTPNDS (U.S. Patent #4,926,585) has been under development for the past six years with the goal of providing a means for culturing plants in microgravity, specifically providing water and nutrients to the roots. Direct applications of the PTPNDS include plant space biology investigations on the Space Shuttle and plant research for life support in Space Station Freedom. In the past, we investigated various configurations, the suitability of different porous materials, and the effects of pressure and pore size on plant growth. Current work is focused on characterizing the physical operation of the system, examining the effects of solution aeration, and developing prototype configurations for the Plant Growth Unit (PGU), the flight system for the Shuttle mid-deck. Future developments will involve testing on KC-135 parabolic flights, the design of flight hardware and testing aboard the Space Shuttle.     

A Comparison of Techniques for Solving the Poisson Equation in CFD

CFD is a ubiquitous technique central to much of computational simulation such as that required by aircraft design. Solving of the Poisson equation occurs frequently in CFD and there are a number of possible approaches one may leverage. The dynamical core of the MONC atmospheric model is one example of CFD which requires the solving of the Poisson equation to determine pressure terms. Traditionally this aspect of the model has been very time consuming and so it is important to consider how we might reduce the runtime cost. In this paper we survey the different approaches implemented in MONC to perform the pressure solve. Designed to take advantage of large scale, modern, HPC machines, we are concerned with the computation and communication behaviour of the available techniques and in this text we focus on direct FFT and indirect iterative methods. In addition to describing the implementation of these techniques we illustrate on up to 32768 processor cores of a Cray XC30 both the performance and scalability of our approaches. Raw runtime is not the only measure so we also make some comments around the stability and accuracy of solution. The result of this work are a number of techniques, optimised for large scale HPC systems, and an understanding of which is most appropriate in different situations.