Draglines are the most expensive pieces of equipment used in coal mines at a cost of $50 M to $100M each. Improving their productivity will produce major benefits to the coal mining industry. The dynamic behaviour of the dragline structure has a significant effect on the fatigue life of the main components of a dragline and related maintenance costs. This paper describes the field tests conducted on the dragline DRE23 at the Peak Down coal mine, Queensland, Australia. Sixteen accelerometers were installed on the dragline boom and mast. Three different excitation methods were used in the test: 5.4-kg impact hammer, dragline bucket impulse and ambient excitations produced during normal operation. The aim of the modal testing was set to explore the six global modes for the dragline boom structure. The results showed that the impact hammer excitation was not adequate to excite any of the global modes. The excitation produced by bucket impulse was powerful but was difficult to control. The output-only identification using the response to the ambient excitation was promising but it was difficult to identify all targeted global modes

Faruquee, Zakir

Guan, Zhiqiang

Gurgenci, Hal

Horton, Bradley

University of Queensland eSpace

 
 
DRAGLINE FIELD TESTING 
 
 
 
 
 
Zhiqiang Guan, Zakir Faruquee and Hal. Gurgenci 
 
Centre for Mining Technology & Equipment, Department of Mechanical Engineering,  
The University of Queensland, Qld 4072, Australia. 
 
 
 
 
ABSTRACT 
 
Draglines are the most expensive pieces of equipment used 
in coal mines at a cost of $50 M to $100M each. Improving 
their productivity will produce major benefits to the coal 
mining industry. The dynamic behaviour of the dragline 
structure has a significant effect on the fatigue life of the 
main components of a dragline and related maintenance 
costs. This paper describes the field tests conducted on the 
dragline DRE23 at the Peak Down coal mine, Queensland, 
Australia. Sixteen accelerometers were installed on the 
dragline boom and mast. Three different excitation methods 
were used in the test: 5.4-kg impact hammer, dragline 
bucket impulse and ambient excitations produced during 
normal operation. The aim of the modal testing was set to 
explore the six global modes for the dragline boom structure. 
The results showed that the impact hammer excitation was 
not adequate to excite any of the global modes. The 
excitation produced by bucket impulse was powerful but was 
difficult to control. The output-only identification using the 
response to the ambient excitation was promising but it was 
difficult to identify all targeted global modes. 
 
 
INTRODUCTION 
 
Draglines are used in surface coal mines to remove the 
overburden before mining the coal.  Overburden depths up 
to 60 m are typically excavated by using draglines. 
Overburden removal is usually the critical process in the 
mine and the dragline is the key piece of machinery. Any 
improvement in the productivity of a dragline would directly 
result in more coal being exposed at a higher rate, and 
hence more coal that could be mined and shipped out. 
Conversely, a major breakdown on the dragline may cause 
the whole mining process to stop in single-pit mine sites.  
 
Most failure on draglines occurs through fatigue. Dynamic 
characteristics of a dragline structure have a significant 
effect on the fatigue life of its major components. In 
particular, an improved understanding of the dynamic 
coupling between the structures and the rest of the machine 
is important to prevent catastrophic failures, as has 
happened recently in an Australian coal mine. 
 
A series of tests were carried out on a dragline. The primary 
objective of these tests was to characterise the loads acting 
on the dragline during normal operation and the resultant 
stresses on critical components. As part of the testing 
program it was decided to investigate the feasibility of using 
different techniques to determine the modal properties of the 
dragline boom in the field. This paper describes these modal 
tests and some preliminary analysis of the test data. 
 
Fig. 1 shows the operation of a dragline in a coal mine. 
During the digging operation, the motion of the bucket is 
controlled using the drag and hoist ropes. After the bucket is 
filled, it is hoisted to the dump height and swung to the dump 
position by swinging the house and the boom. Hoisting and 
swing operations occur concurrently. One full cycle is 
achieved after the bucket swings back to the digging 
position. 
 
 
 
Fig.1 Dragline working in Peak Downs coal mine. 
 
The tests were part of a project concerned with the relation 
between the bucket size and the machine component 
reliabilities. The objective of the modal component of the 
field tests was to identify the first few natural frequencies of 
the dragline boom-mast structure. Sixteen accelerometers 
were installed on the dragline boom and the mast. Three 
different excitation sources were used in the test: a 5.4-kg 
impact hammer, the dragline bucket itself, and the normal 
dig-swing-dump operation. 
 
 
 
LOCATIONS OF THE ACCELEROMETERS 
 
A finite element model was constructed to calculate the 
modal parameters of the dragline. The predicted frequencies 
for the first ten modes were less than five Hertz. Most 
importantly, these modes were very closely spaced 
presenting a serious challenge to modal analysis of this kind 
of machine. The first ten predicted natural frequencies of the 
dragline boom, mast and A-frame are listed in Table 1 and 
the first two modal shapes are plotted in Fig. 2. 
 
Table 1  First ten modes of the dragline DRE23. 
Mode No Freq. 
(Hz) 
Component 
1 0.981 Boom 
2 0.998 Boom 
3 1.72 Boom & mast 
4 2.169 Boom & mast 
5 2.208 Boom & mast 
6 2.281 Boom & mast 
7 2.445 Boom & mast 
8 2.548 Boom, mast & A-frame 
9 3.17 Mast 
10 3.43 Boom 
 
  
 
 
Fig. 2  First and second modal shapes of DRE23. 
 
An optimum set of sensor locations was identified based on 
the results of finite element calculation. The optimum 
locations of the sixteen accelerometers were identified from 
a two stage process. In the first stage a Guyan Reduction 
exercise was applied to the Dragline FE model – this allowed 
the ranking of the best master degrees of freedom according 
to the Guyan Reduction process. The second stage involved 
the selection of 16 of the highest ranking master dofs. In 
choosing these 16 dofs the Modal Assurance Criteria 
(MAC)[1] was used to assess how uniquely identifiable the 
first 10 FE modes were according to their representation by 
the 16 selected dofs. In making the final selection of the 16 
dofs, consideration was also given to the practicality of 
instrumenting certain regions of the dragline. Figure 3 shows 
the 16 accelerometer locations used for the dragline modal 
tests. Among these sixteen accelerometers, eight are strain 
gauge based (TML type) accelerometers (AB_1 to AB_5, 
AB_8, AB_9 & AB_11) and the other eight are the 
piezoelectric type (PCB type) accelerometers. 
 
AB_1
AB_2
AB_3
AB_4
AB_5
AB_6
AB_12
AB_8
AB_9
AB_10
AB_11
AF_17
AF_15
AF_16
AF_13
AF_14
TML accelerometers:
AB_1:AB_5, AB_8, AB_9 &
AB_11
PCB accelerometer: AB_6, AB_10,
AB_12 & AF_13:AF17  
 
Fig. 3  Locations of the sixteen accelerometers. 
 
 
MODAL IMPACT RESPONSE TESTS WITH IMPACT 
HAMMER 
 
A 5.4-kg impact hammer was used to hit the boom tip (near 
the location of AB_1) and the middle of the boom (near the 
location of AB_5 and AB_8, see Fig. 3 for the locations of 
the accelerometers) in both vertical and horizontal directions. 
The output of the impact hammer and the response of each 
accelerometer were recorded. Fig. 4 shows a plot of the 
outputs of the impact hammer and the accelerometers AB_1 
and AB_2 when the hammer was hit at the location near the 
accelerometer AB_1 vertically. Fig. 5 shows the output of the 
hammer and the accelerometers AB_1, AB_2 and AB_5 
when the hammer hit near the accelerometer AB_5 
horizontally. 
 
 
 
Fig.4  Outputs with the hammer hit near AB_1 vertically. 
 
Fig.5 Outputs with the hammer hit near AB_5 horizontally. 
 
As shown in the above figures, even at locations very close 
to the hammer impact the excitation was not enough during 
the hammer impact test. This indicates that with the type of 
accelerometers used on the dragline, the 5.4-kg hammer is 
not heavy enough to excite the dragline. Other methods 
such as the dragline bucket impulse and normal operation 
were used as exciting sources in the rest of our modal test. 
 
 
MODAL RESPONSE TESTS WITH THE DRAGLINE 
BUCKET IMPLUSE 
 
A short bucket lift-and-drop operation was used to excite the 
structure with the empty, half-full and full bucket. The time of 
lifting-and-dropping the bucket was controlled as short as 
possible in practice. The operations of these tests included: 
• Start with the bucket lying on the ground under the boom 
point. 
• Start the hoist but stop immediately before the bucket is 
lifted. 
 
Figs. 6 and 7 show the outputs of accelerometers AB_1 to 
AB_5 with empty and full bucket impulse test, respectively. 
The signals from all PCB accelerometers were filtered with a 
user constructed 30 Hz low-pass filter and the signals from 
all TML accelerometers were filtered with 20 Hz low-pass 
filter of the dynamic strain gauge amplifier. 
 
 
Fig. 6  Outputs of the four accelerometers with empty bucket 
impulse. 
 
 
Fig. 7  Outputs of the four accelerometers with full bucket 
impulse. 
 
 
MODAL RESPONSE TESTS WITH NORMAL 
OPERATIONS 
 
The tests were carried out under normal dig-swing-dump 
operations. During the normal operations, the signals of all 
 
sixteen accelerometers were recorded continually. As in the 
case of the bucket impulse tests, the signals from all PCB 
accelerometers were filtered with 30 Hz low-pass filter and 
the signals from all TML accelerometers were filtered with 20 
Hz low-pass filter. 
 
Fig. 8 shows five minutes data of all accelerometers on the 
boom (AB_1 to AB_6, and AB_8 to AB_12) during the 
normal operation tests.  Fig. 9 shows the same time record 
of all accelerometers on the mast (AF_13 to AF_17). 
 
 
 
 
 
 
 
 
Fig. 8  Five minutes output of the accelerometers  
on the boom during normal operations. 
 
 
Fig. 9  Five minutes data of the accelerometers on the mast 
during normal operations. 
 
 
MODAL IDENTIFICATION 
 
The difficulty with the conventional FRF based modal 
analysis approach however is measuring the input excitation 
applied to the boom. Because of this problem a more 
promising approach to identifying the dragline’s modal 
parameters is an identification algorithm based purely on the 
acceleration outputs [2,3]. A preliminary investigation of the 
method discussed by Abdelghani et al has been used to 
process accelerometer data acquired during the normal dig-
dump operation of the dragline. The results of this analysis 
(which are still being conducted) are shown in Fig. 10 with 
Power Spectral Density (PSD) plots and the identified 
frequency stabilisation plot for the accelerometers of setup1 
(AB1 AB3 AB4 AB6 AB8 AB12). The most likely undamped 
frequencies are those peaks in the PSD plots and they are 
summarised in Table 2. 
 
Table 2: Undamped natural frequencies from Output only 
identification algorithm 
Undamped 
natural frequency  
[Hz] 
Paired FE  
model frequency  
[Hz] 
0.878 0.981 
2.1478 No conclusive pairing at this 
stage 
2.540 No conclusive pairing at this 
stage 
3.200 No conclusive pairing at this 
stage 
3.63 No conclusive pairing at this 
stage 
3.320 No conclusive pairing at this 
stage 
4.6862 No conclusive pairing at this 
stage 
 
The problem with the preliminary results shown in Table 2 
however has been the difficulty pairing the identified mode 
shapes with the FE mode shapes – for example using the 
 
MAC pairing metric. It was observed that with the exception 
of the first mode, the identified modes had MAC values of 
0.5 or less and on many occasions multiple identified modes 
paired equally well with a single FE mode. Work is 
continuing on this problem. 
 
 
[dB]
Frequency [Hz]
0 3 6
-60
-30
0
30
Magnitude of Power Spectral Density -  'setup1'
CVA
9
 
 
Figure 10 (a): Average Power Spectral Density of Setup1 
accelerometers reading 
 
counts
Frequency [Hz]
0 10 20 30 40 50
10
20
30
40
50
60
70
 
 
Figure 10( b): Stabilisation diagram of CVA method  for 
setup1 accelerometers reading 
 
 
CONCLUSIONS 
 
The following conclusions are based on the preliminary 
analysis of the test data.  
 
1. 5.4-kg impact hammer is not heavy enough to excite the 
dragline structure. The excitation with dragline bucket 
appears to have the potential to be an effective 
excitation tool in the modal testing of this kind of 
machines. 
2. Output only modal identification method is probably the 
best method to identify the modal parameters of such 
machines. 
 
 
ACKNOWLEDGEMENTS 
 
This work was conducted as part of the research program of 
dragline bucket load optimisation in the Cooperative 
Research Centre for Mining Technology and Equipment 
(CMTE) and funded by ACARP. The authors would like to 
thank CMTE and ACARP for support of this project. 
 
 
 
 
 
REFERENCES  
 
[1]  Allemang, R. J., Brown, D. L., A correlation coefficient 
foe modal vector analysis, Proceedings of the 1st 
International Modal Analysis Conference (IMAC I), Orlando, 
Florida, U.S.A., pp. 110-116 (1982). 
 
[2]  Benveniste, A., Fuchs, J.J., Single Sample Modal 
Identification of a Nonstationary Stochastic Process, IEEE 
Transactions on Automatic Control, Vol(30), No(1), pp. 66-
74, (1985) 
 
[3]  Abdelghani, M., Goursat, M., Biolchini, T., Hermans, 
L., Van der Auweraer, H., Performance of Output only 
Identification Algorithms for Modal Analysis of Aircraft 
Structures, 17th International Modal Analysis Conference, pp 
224-230 (1999). 
 


Dragline Field Testing

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Dragline Field Testing

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