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"Reduction of uncertainties associated to the dynamic response of a ship unloader" presented at CERI2018 by Giulia Milana

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Here, the TRUSS (Training in Reducing Uncertainty in Structural Safety) ITN (Innovative Training Network) Horizon 2020 project (http://trussitn.eu, 2015-19) demonstrates how the accuracy of residual life assessment predictions can be improved by achieving a good agreement between measured and predicted dynamic responses of a crane structure. Existing records of measured strain data are often missing information such as the weight of the payload, the hoisting speed and acceleration that are relevant for structural assessment purposes. This paper aims to reduce uncertainties associated with the recorded data in an aged grab ship unloader by comparing measured and non-linear transient finite element analyses results for a loading/unloading cycle. The speed pattern is determined from a best match to the measured record. The moving load consisting of ‘trolley + grab + payload’ is modelled with parameters that are derived from minimizing differences between measured and simulated responses. The determination of these loading parameters is central to accurately assess the remaining life of ship unloaders.

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"Reduction of uncertainties associated to the dynamic response of a ship unloader" presented at CERI2018 by Giulia Milana

  1. 1. Workshop CERI, UCD, Dublin Wednesday 29th August 2018
  2. 2. Giulia Milana, Kian Banisoleiman and Arturo González Reduction of uncertainties associated to the dynamic response of a ship unloader
  3. 3. STRUCTURE • 34 year-old grab ship unloader • Located in Scotland • used to unload coal Data continuously acquired at 125 Hz • 48 channels of strain • strain gauges in a full bridge configuration • 16 locations Outer Ties Inner Ties Lifting Boom Monitoring system
  4. 4. DYNAMIC RESPONSE: lifting boom • Young’s modulus, E, equal of 207 GPa • Noise removed applying a low-pass filter with cut-off frequency equal to 10 Hz (8th order Chebyshev Type I) 55 s Single Cycle
  5. 5. EQUIVALENT MODELS Lifting Boom Moving System Data continuously acquired at 125 Hz • mT = mass of the trolley • mP = mass of the payload (grab+payload) • kS = stiffness of the lifting system TRANSIENTDYNAMICANALYSIS 𝑀 ሷ𝑢 + 𝐶 ሶ𝑢 + 𝐾 𝑢 = 𝐹(𝑡) Adapted from Zrnic et al. 2009
  6. 6. DEFINING MODEL PARAMETERS • A = area of boom section • I = inertia of boom section • r = boom density • M1 = first lumped mass • M2 = second lumped mass • k1 = stiffness of the first spring • k2 = stiffness of the second spring known unknown
  7. 7. RECONCILED 3D MODEL MODE OMA* Frequencies (Hz) 3D MODEL Frequencies (Hz) Error (%) I 0.78 0.74 5.1 II 0.91 0.86 5.5 *Eight PCB 352C42 and six B&K 4507 B004 accelerometers were positioned at 12 location on the upper substructure. OMA Mode shapes characterised by a lateral/twisting motion 3D MODEL
  8. 8. DEFINING PARAMETERS: k1 and k2 Comparisons, in terms of vertical bending stress, were conducted between static results from 3D model and those from the 2D model of the boom. The scenario with gravity off was assumed. k1 = 4.69 107 N/m k2 = 3.1 107 N/m
  9. 9. DEFINING PARAMETERS: r, M1 and M2 Comparisons, in terms of vertical displacement, were conducted between static results from 3D model and those from the 2D model of the boom. The scenario with gravity on was assumed. r = 1.57 104 kg/m3 M1 = 8.34 104 kg M2 = 1.23 105 kg
  10. 10. MODALANALYSIS: comparison MODE 2D MODEL (Hz) 3D MODEL (Hz) Error (%) I 2.33 2.32 0.43 II 3.39 3.44 1.45 III 6.30 6.30 0.0 3DMODEL2DMODEL
  11. 11. DYNAMIC RESPONSE: single cycle
  12. 12. TRAVELLING: assumptions • For the travelling phases the dynamic response is comparable to the static one • The value of the deceleration/acceleration, aT, does not influence the structural response significantly aT= ± 3 m/s2 • Constant travelling speed with final breaking (same parameters for travelling empty grab and travelling full grab) vT := travelling speed xT := distance, from the left pinned end, at which the trolley stops to conduct hoisting operations unknown
  13. 13. TRAVELLING: definition parameters Static analyses: load applied at each node of the boom and the stress at the transducer location obtained Dynamic measured response xT = 26 m 5.3 s17.5 m vT = 3.3 m/s
  14. 14. HOISTING: assumptions vl := lowering speed tb := breaking time tfilling := filling time vh := hoisting speed ta := acceleration time mP := payload mass unknown h := range of lift (61 m) known
  15. 15. HOISTING: definition parameters vl := 5.8 m/s tb := 3.5 s tfilling := 10 s vh := 4.8 m/s ta := 6 s mP := 12500 kg
  16. 16. FITTING
  17. 17. CONCLUSIONS • A simplified finite element of the lifting boom was used to carry out transient dynamic analysis, in order to simulate an unloading cycle • The parameters of the simplified model were defined based on static analysis, in terms of vertical bending stresses and displacements, and natural frequencies • The response obtained was then compared with the measured stresses obtained from the monitoring system • Matching the responses, some parameters, often not recorded while acquiring data, were estimated • These parameters, especially xT and mP, should be used for a more accurate estimation of the stress ranges used for carrying out a fatigue life assessment, also at locations where the transducers were not installed
  18. 18. The TRUSS ITN project (http://trussitn.eu) has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 642453 Thanks for your attention

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