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Simulator trial data

In the series of simulator trials in WP4.1, 28 subjects were exposed to low-frequency sway and heave motion, and combinations of both. The purpose was to investigate perceived comfort and motion sickness as a function of motion magnitude, as well as the interference of ship motion with passenger activities.

To this end, we used the TNO ship motion simulator, a sea-container with inner dimensions of (L x W x H) 3.8 x 2.2 x 2.4m, mounted on a piston of 2.5m above the roll and pitch axes based in a gimbals system. Maximum roll and pitch angle is limited to +/-15°, respectively +/-20°. The gimbals system could additionally be translated vertically with a stroke of 1 m. The motions were controlled by a hydraulic system.

Eight artificial motion profiles were used, ordered in a Latin square design to account for randomness and a balanced order of conditions. A total of eight motion conditions was the maximum that could be carried out during one day. As described below, subjects performed four different tasks during each trial, according to a rotating scheme. During each trial only one of the eight motion conditions was presented. For several reasons a simulator trial should not exceed 15 minutes, and each trial consequently comprised of four periods of three minutes: two minutes of which was reserved for the execution of a task (see below), and the remaining minute was reserved for filling in a task-related questionnaire.

During each motion condition, subjects were asked to perform a set of psychomotor tasks that encompassed a range of passenger-related activities aboard ships. Passenger activities were divided in five categories:
- Cognitive activities,
- Physical activities,
- Recreational activities,
- Provocative activities, and
- Eating and drinking.

The first three categories (cognitive, physical, recreational) were explicitly covered in experimental tasks that were performed during each motion condition. Cognitive aspects were examined in a reading task that also involved some arithmetic. Physical aspects were investigated in a manual task (writing), and in a locomotor task (walking). As recreational activity a dart game was employed. The effects of head movements were examined implicitly during a letter acquiring task. The order of the tasks was digram balanced to avoid order effects. Instead of investigating the disturbing effects of ship motion on eating and drinking during all eight motion conditions, this was done during separate lunch and coffee breaks inside the simulator using a motion profile with increasing amplitude over time. It may be noticed, that sleeping and resting is not listed in the essential passenger activities. For practical reasons this was considered beyond the scope of this study.

Comfort was rated in three ways:
- Objectively by rating task performance (e.g. the number of missteps during the walking task),
- By means of task specific questions answered just after each task, and
- By means of a general questionnaire just after each trial.

A total of 1120 questionnaires were returned in this trial.

Within-subject analyses of variance (ANOVA) were used to analyse the data statistically. Separate tests were used to analyse for effects of sway only, heave and sway in combination, and the regularity of sway motion.

The results showed that sway motion affected comfort more than heave motion, and that the effects of both motion components added linearly. Performance on motor tasks was impaired during motion, in contrast to the performance on cognitive tasks, which was hardly affected. For all activities, however, perceived effort increased considerably with increasing motion amplitude, even though the performance itself did not always suffer from the motion. Since also motion sickness symptoms increased with motion amplitude, an important conclusion is that subjective ratings discriminate more than objective scores.

The general questionnaire revealed that comfort ratings were strongly related to discomfort ratings, and that all mental and physical comfort parameters behaved in a similar way. This leads to another conclusion that, principally, discomfort can be described by one general subjective rating. However, the results indicated that in an operational questionnaire special attention should be given to aspects of enjoyment, fatigue, motion sickness, and postural balance. Three subjects had to quit the experiment due to motion sickness, which implies a motion sickness incidence of 10%. The findings of this study are of relevance for the design of questionnaires to be used in the sea trials (WP2 and WP3), and to quantify the overall relationship between comfort and ship motion (WP5).

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