The Challenge
We were first approached by the University of Exeter in 2015 for a customised submersible load cell for their (DMaC) test rig. Our load cell has been successfully monitoring dynamic tensile forces up to 20 tonnes in their Dynamic Marine Component (DMaC) test facility, with regular underwater tests.
Now, they wanted an additional sensor to monitor the elongation of the mooring rope under test. This new sensor would need to withstand long-term submersion in potable water measuring displacement of up to 1m.
The Dynamic Marine Component (DMaC) test facility, owned and operated by the University of Exeter, is a purpose-built test rig that aims to replicate the forces and motions that components are subjected to in offshore applications.
The test rig comprises of a linear hydraulic cylinder at the tailstock that can apply tension and compression forces or displacements to replicate heave motion. At the other end of the rig, the headstock, with three degrees of freedom, can apply bending moments (torque) and angular displacements to replicate the pitch, roll and yaw motions. The combination of headstock and tailstock simulates the motion of a floating body.
Monitoring the pitch, yaw and roll in the rig helps to understand the impact of heave motion on offshore mooring ropes, aiding in the development of reliable, low-cost offshore renewable energy.
DSCC Pancake Load Cell
Ideal for Dynamic Force Testing
The University of Exeter wanted a customised replacement for an existing competitor’s load cell to measure dynamic tensile forces up to 20 tonnes, in potable water. So, we recommended our stainless steel DSCC pancake load cell which we customised with bespoke dimensions, submersible IP68 environmental protection rating, threads and counterbores.
Thanks to its low profile body and custom dimensions, our DSCC pancake load cell was easily installed as a direct replacement for their existing load cell between the hydraulic ram and the rope end in their DMaC rig.
For this application, the pancake load cell design was modified to make it capable of withstanding permanent submersion in potable water to a depth of 1m.
Its high-frequency response and high accuracy of better than ±0.05 of the rated capacity made it ideal for this dynamic force measuring application.
IP69K Submersible Draw Wire Sensor
More recently, the University of Exeter wanted to measure the displacement of the mooring rope under test up to 1m.
So, we recommended the outdoor K100 draw-wire sensor from Micro-Epsilon. It measures displacement from 0-1500mm up to 0-5000mm and comes with an IP69K steam jet protection rating making it ideal to use in this wet environment.
Its reinforced glass-fibre plastic enclosure and separate drum and spring spaces promise high protection against environmental influences.
K100 Draw Wire Key Features
- Measuring Ranges: 0-1500mm & 0-5000mm
- IP69K Dust Tight & Steam-Jet Cleaning Protected
- Potentiometer & Analogue Outputs
- Ideal for Outdoor Use & Wash-Down Applications
- Dust-Tight & Reinforced Glass-Fibre Enclosure
- Non-Linearity: <±0.25% of Full-Scale Output
Thank you to Ed Hartgill, DMaC Project Engineer, for allowing us to write about this innovative mooring rope testing application.
Thank you to Dr Sam Weller, Mor Engineering Ltd, for the above images of the DMaC testing rig.
Read more about the DMaC testing rig here https://renewable.exeter.ac.uk/facilities/dmac/
