Numerical Modelling of the Effects of Vibration in Helicopters for Prediction and Analysis of Human Comfort Assessment

The pilot s situational awareness and the ability for decision making are affected by the vibration in helicopters. In addition, the vibration can also increase the metabolic rate, alveolar ventilation, blood cell velocity, anxiety and discomfort for any patients in helicopters during Emergency Medical Services (EMS). There is a necessity to understand and provide suitable inputs to the simulators for training and the designers to improve the comfort levels quality in helicopters. The integrated simulation of the pilot-helicopter and the patient-helicopter systems is proposed in this work. The Finite Element Method (FEM) model of Aérospatiale Gazelle is established in ABAQUS software. The structural modelling of the helicopter is undertaken to have the essential baseline model to generate the excitation forces at the cabin floor. These excitations form the input forces for the pilot seat and the stretcher with the patient. The structural model is integrated with the vibration forcing functions for six different flight conditions including two steady turn flights (V3109 and V3111) and four level flight conditions (V3101, V3103, V3105 and V3106) for Gazelle helicopter. The accelerations at the cabin floor for the two locations of the pilot seat and the stretcher are computed. These are integrated with the mathematical models of the pilot-seat and the patient-stretcher in MATLAB. The vertical vibration at the pilot s body that includes the head, the upper torso, the viscera and the pelvis are analysed. The translational and rotational vibrations at the patient s head, torso and pelvis are studied as well. Based on ISO 2631-1, the whole body vibration (WBV) and comfort assessment for the pilot and the patient are carried out during the six simulated flight conditions. The results on root mean square (r.m.s) of frequency-weighted acceleration at the centre frequencies of one-third octave band are obtained. The outputs on crest factor of frequency-weighted acceleration at the pilot seat and the interfaces at the stretcher with the patient s head, torso and pelvis confirm the fact that the basic evaluation method proposed by ISO 2631-1 is reliable enough. The comparison between the total frequency-weighted acceleration at the pilot s seat pan and approximate indication of comfort level shows (indicated by ISO 2631-1) that the pilot feels "a little uncomfortable" during V3101 flight condition that has relatively lower advance ratio compared to the three other level flight conditions (V3103, V3105, and V3106), in which the pilot is "not uncomfortable". The frequency-weighted acceleration shows that by increasing the advance ratio, the simulated vibration experiences a downward trend. However, this downward trend is not consistent and can change to an upward trend for advance ratios over a certain value (depending on the helicopter type and characteristics, the seat features, etc.). For the two steady turn flight conditions including V3109 and V3111, "uncomfortable" situation for the pilot is predicted. The higher total frequency-weighted acceleration for the V3111 (advance ratio of 0.26 ) than V3109 (advance ratio of 0.24) shows that increasing the advance ratio of steady turn flight conditions can increase WBV and worsen the pilot s discomfort. The total frequency-weighted acceleration for the patient s WBV shows that by increasing the advance ratio of level flight condition the WBV has decreased, considerably. For the low advance ratio of V3101 (0.14) and V3103 (0.26), it is predicted that the patient is "very uncomfortable" but for the higher advance ratio of level flight conditions of V3105 (0.35) and V3106 (0.37), the patient feels "fairly uncomfortable". The results show that an increase in patient s WBV when the advance ratio increases during steady turn flight conditions