Motion Analysis Case Study

Transcription

1 Motion Analysis Case Study

2 Very often, complex motions are desired as part of a solution to some engineering problem. Machines and mechanisms are then designed to produce these motions.

3 Motion generation can be accomplished in two general ways: 1. Classic mechanisms that for a constant input will produce a predictable and constant output (coupler curve): Scotch yoke constant rotary input, reciprocating linear output Geneva wheel constant rotary input, indexed intermittent rotary output Four bar (or multi-bar) linkages complex interactions between input & output 2. New mechanical designs employing state-of-the-art motion control technologies that can produce any motion: Multi-axis motion systems Stepper Motor Driven Servo Motor Driven Hydraulically Driven Linear output Rotary output Combinations

4 Scotch Yoke

5 Geneva Wheel

6 Regardless of the method used, each design must be synthesized and then fine tuned using a number of methods available to engineers: Hand calculations Manual sketching/drafting CAD Finite Element Analysis Numerical Modeling and Simulation Iteration

7 Case Study Steel Catenary Risers (SCR) are long flexible pipes used to carry produced hydrocarbons from the wellhead to processing facilities or transport vessels. Interactions between the risers and seafloor are not well understood. Implications for catastrophic failure are great environment, lost revenue.

8 SCR Configuration

9 Engineering Problem Pipe stresses are high/complex at the touchdown point Motion (input) of the pipe is generated by floating structure in various sea-states Engineers wish to understand the SCR stress response to input motion for various sea bottom conditions

10 Engineering Solution Simulate input motion (sea/vessel motions) by numerical simulation This can be verified by full scale floating structure responses Generate a SCR response by numerical simulation (FEA) Numerical SCR response can be tuned by analyzing an instrumented model test and comparing results to FEA results When SCR models have been tuned, slightly different input motions or new scenarios can be tested numerically

11 Model Test Design, build SCR scale model Install strain gauges to measure model pipe induced strains Design and build a machine to move the model pipe in the correct manner Run a test

12 Centre for Cold Ocean Resource Engineering (C-CORE)- Centrifuge Facility Used in geotechnical based experiments Keeps stress and strain responses in models the same as the prototype (full scale) Centrifuge at C-CORE is second largest in North America 200g testing capability

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15 The Role of CAE and Motion Analysis in SCR Testing Motion of SCR was numerically solved for at one POINT The movement envelope of this POINT was considered at a model scale An appropriate g-level was calculated for the model scale Motion generating equipment (X-Z Actuator) designed using CadKey

16 Elements of the Motion Analysis Determine Extents of Movement Envelope Volume in which machinery must move to actuate the model pipe In this case 2D Determine Clearance Envelope Interior clearance space of the Centrifuge Chamber which must not be entered by machinery In this case 3D Consider maximum VELOCITY, ACCELERATION and FORCES at the input POINT Machinery must be able to provide these parameters Another consideration SCR model must be held in a position for many hours in addition to the motion of the test to account for consolidation of clay Consider g-level (40g) in the design of the equipment along with V,A and F All components of the assembly will now weigh 40 times as much self weight becomes problematic Forces and stresses on load bearing surfaces and bolted connections are very large Inertial loads are high in the direction of high g-level

17 Methods used in this program Careful measurement of the centrifuge facility and drawing upon previous industrial experience CAD to design the components of the assembly Hand calculations used: Design for minimum stress Bolted connection design CAD used to remove unnecessary mass CAM in mind minimum tool radius in machining pockets Quick calculation of part volumes for mass calculations Iteration Some unexpected problems encountered Example counter-balance cable pulley support shaft and bearing failure

18 Considerations Actuation provided by hydraulic power 2000 psi 30 gpm hydraulic power available Because of high inertial loads at 40g, a counterbalance system was needed Because of 3D space constraints material properties and fatigue characteristics of cables became important Hydraulic cylinder mounted on one side only, a system to prevent roll of the assembly needed

19 Hydraulic Actuation Hydraulic cylinders offer many advantages: Compact design Few moving parts Very reliable Produce large forces Fast response Wide range of motion profiles, with added ADVANTAGE of LOAD HOLDING

20 2D Motions Surge direction X Heave direction Z A hydraulic cylinder needed in X and Z

21 Model SCR & Clay, POINT Pickup Assembly and Surge Movement (X-axis) Components

22 Surge Movement Components & Hydraulic Cylinders

23 Support Structure for Heave (Z-axis) Movement

24 Structural Considerations Maximum Section Modulus (Z) Maximum moment of inertia of section in strong direction divided by distance to neutral axis Support of structure in weak axis Minimum Bending Stress Minimum number of bolts to carry load Shear Keys on joints where possible Consideration of failure scenarios consequences of failure

25 Support Structure for Heave & Surge Assemblies, Hydraulic Cylinders and Counter-Balance System

26 Anti-Roll Cable Support Structure

27 X-Z Actuator Assembly with SCR Clay Box

28 POINT Pickup Truss

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34 The Role of Iteration Sometimes forces or interactions of forces can be unforeseen When problems arise an analysis must take place and a solution found

35 Counter-Balance Pulley Support Shaft Assembly

36 Thoughts Original Shaft deflected Choice of bearing New selection Maximum Section Modulus

37 Questions? END Thank-you!