The Sorby Environmental Fluid Dynamics Laboratory (SEFDL), based at the University of Leeds (www.see.leeds.ac.uk) was established in 1988 to study the sedimentary flow processes of the earth-surface, both naturally and through industrial or man-made interaction. A recently completed £1.2m expansion programme has allowed the facility to further build on its position as one of the best equipped and leading environmental fluid dynamics laboratories in the world.
The scope of research undertaken at SEFDL includes laboratory modelling, field study and computational fluid dynamics across a vast range of environmental studies that include river and coastal erosion, pollution analysis, dredging studies, pipe flow, and oil and gas exploration.
One of the largest projects involves the study of massive submarine channels, thousands of kilometres in length and hundreds of metres high that transport huge volumes of coarse sediments along the ocean floors and are increasingly important for hydrocarbon exploration and production.
The SEFDL facility has a wide range of flume tanks and measuring equipment to model these sedimentary processes. The most powerful is capable of moving 500 litres of water every second, enabling flows half a metre deep to move at a metre per second along the flume. Detailed two- and three-dimensional flow velocity measurement systems and powerful computing systems are on-hand to analyse the results. Some flume tanks are equipped to model flows containing multiple fluids or sediment types, and each of these phases can be separately monitored for velocity and concentration.
MiniTec, the Basingstoke based machine building and motion systems specialist has worked closely with SEFDL in supplying a number of automated belt driven X-Y actuators complete with micro-stepping drives and motion controls for the flume tanks. These are used to position flow velocity measurement probes and to synchronise readings to and from data logging equipment.
The scope of supply included the development of Visual Basic front-end software to allow users to input scanning speeds and measurement intervals, trigger data collection and provide an output of all the information to a data logging system. The program integrated all communications routines between the intelligent micro-stepping drives, a PC host, measurement probes and data logging equipment. Motion control covered simple selection of pre-calculated scanning routines and other positioning modes along with manual axis jogging, integrated diagnostics and status windows.
To simplify and standardise the SEFDL processes and improve data consistency, a key specification requirement called for the program to be used with all of the laboratory’s flume systems and to ensure that each shared identical user units and operational parameters. As the flume positioners had been supplied over a number of years, many had differing mechanics with correspondingly different positioning resolutions. To ensure identical input and output values, MiniTec included scaling functions that required only the variable resolution information to be entered at the initial set-up.
For each flume positioning system, a MiniTec LR series X-Y actuator is typically mounted above a working section of the flume tank and provides a positioning window of up to 5m along the length of the flume and 0.5m across its width. The depth of the probe is adjusted manually.
The LR series actuator and carriage assembly is based upon standard MiniTec aluminium machine frame profiles with the addition of double-row, angular contact bearings on hardened and ground precision shafts. With the possibility of creating extremely long travel lengths, the units are capable of carrying heavy loads with high acceleration. The positioners may be combined with other machine frame components to provide extremely robust and durable structures.
A typical MiniTec actuator used at SEFDL uses a fundamental resolution of 190mm linear travel for a single revolution of the input shaft. As the latter is driven by a 50,000 steps/revolution, micro-stepping motor through a 4:1 gearbox, the final theoretical resolution is in the order of just one micron.
Each motor is also fitted with a rotary encoder and scaled within the motion control system to effectively record real-time position and speed in increments of 0.1mm for the data logging system. Over-travel limits, datum switches and all interfacing cables with chain type cable management are included.
MiniTec provided the complete on-site installation for each flume tank with EN954-1 safety standard, wall mounted control enclosures complete with stepper drives, power supply, relays and EMC filtering equipment. The specification also included a separate mains isolation and supply system with E-stop.