7/28/2019 VDV SG27

1/1

Trade

www.southampton.ac.uk

Human factors in the design of high speed marine craftD.Nikoli1, R.Allen1, R.Collier2, L.Collier2, D.Taunton3, D.Hudson3, R.A.Shenoi3

Description of the research

Aim of the study

The main objective of this study was to establish if there is arelationship between boat motion during transits and measures ofhuman physiology.

A secondary objective was to establish if exposure of a human torandom and shock vibration affected a measure of spinal musclefatigue and a participant's rating of perceived exertion (RPE).

Methodology

An experiment was conducted in order to establish if synchronisedmeasures could be used to establish relationships between boatmotion during transits and measures of human physiology duringexposure to random whole-body vibration in a dynamic environmentand to analyse its influence on human physiology.

The experiment was undertaken during a sea trial with a RIB-X ExpertXT650. A male participant (26 years old, 170 cm tall and 72 kg weight)participated in this study. The time duration of the trial wasapproximately 30 minutes at an average boat speed of 25 knots. Seaconditions were moderate (sea state 3) with the average wave height of

0.84 m and zero-crossing period of 4 s taken at the closest waverecorder.

The data measured during the trial (Figure 1) were:

boat vibration and motion (LCG acceleration and heading),

human whole-body vibration (head and seat acceleration),

human physiological data (electromyography (EMG) activity ofspinal muscles and electrocardiographic (ECG) changes).

Perceived exertion using the Borg Rating of Perceived Exertion (RPE)scale was recorded following the trial.

Collaboration

This multi-disciplinary project was carried out as a collaborativeendeavour involving:

1. Institute of Sound and Vibration Research (ISVR),University of Southampton

2. School of Health Sciences, University of Southampton

3. School of Engineering Sciences, Ship Science,University of Southampton

4. The Royal National Lifeboat Institution (RNLI)

5. University College Chichester

The research was funded by EPSRC (grant no. EP/C525728/1).

Impact of the research

Designers of high speed marine craft, biomedical engineers and

human performance specialists aim to establish guidelines for designof such craft that take into account the need of the crew to maximiseperformance.

It is anticipated that this translational methodology could be used toenable a better understanding of:

how fatigue develops as a result of exposure during transits,

fatigue characteristics of spinal muscles,

how fatigue impacts human performance,

how to reduce fatigue through preventative exercise measures.

Results and discussionWhole-body vibration

The total Vibration Dose Value (VDV) of 12.28 calculated from seatacceleration was dominated byy-axis (12.19) with a contribution from

x and z-axes (2.08 and 4.92). This exceeded the Exposure ActionValue (EAV) of 9.1 ms1.75 19 minutes into the trial. Plot of thefrequency-weighted seat acceleration in the most prominent axis along

with the corresponding VDV is given in Figure 2, where the EAV andExposure Limit Value (ELV) are marked by dotted lines.

ECG analysis

Plots of boat speed, normalised frequency-weighted LCG and seat rmsacceleration magnitudes with a plot of normalised instantaneous heartrate recorded during the trial are given in Figure 3. Results showed astatistically significant correlation between boat vibrations and theheart rate variations. The relationship is evident in the three vibrationaxes. The influence of the boat vibration with the correlationcoefficient of 0.52 is larger than the seat vibration with the correlationcoefficient of 0.45. The delay between the heart rate and vibrationsignals was estimated to be approximately 2 s.

EMG analysis

Median frequencies (MDFs) calculated for the whole duration of trial

Figure 1. Experimental setup (A LCG Accelerometer, G LCG RateGyroscope, H Head Accelerometer, S Seat Accelerometer)

Figure 2. Vibration dose value in y-direction for sitting posture

Figure 3. Boat speed, frequency-weighted seat and LCG rmsacceleration magnitudes and heart rate during trial

Figure 4. Median frequencies of the four EMG signals recordedduring trial

are shown in Figure 4. It can be seen from these plots that the MDFsof the lower back spinal muscles, i.e. Left Multifidus and Right

Multifidus, decrease with time showing a cumulative effect consistent

with muscle fatigue.

Summary

The EMG and ECG changes during vibration exposure were used as abasis for evaluation of fatigue. RPE measures indicated that theparticipant rated the exertion as somewhat hard during the transitand changes in the EMG and ECG signals indicated that fatigue wasassociated with the transit. This experiment demonstrated that it is

feasible to simultaneously measure human performance and boatdata, and that there is a relationship between the boat motion andsubsequent fatigue.