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.

1. Workshop
CERI, UCD, Dublin
Wednesday 29th August 2018

2. Giulia Milana, Kian Banisoleiman and Arturo
González
Reduction of uncertainties
associated to the dynamic
response of a ship unloader

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. 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. 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. 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. 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. 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. 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. 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. DYNAMIC RESPONSE: single cycle

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. 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. 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. 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. FITTING

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. 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