Hybrid artificial genetic – neural network model to predict the transmission of vibration to the head during whole-body vibration training

In this work, Artificial Neural Network (ANN) modelling has been employed to investigate the effects of various factors on the biodynamic responses to vibration represented by the transmissibility and its phase. These factors include, height, weight, Body Mass Index (BMI), age, frequency and posture. Nine subjects stood on a vibrating plate and were exposed to vertical vibration at nine frequencies in the range 17-46 Hz while adopting four different standing postures; Bent Knee posture (BK), Locked Knee posture (LK), right foot to the Front and left foot to the Back posture (FB) and One Leg posture (OL). The accelerations of the vibrating plate and the head of the subjects were measured during the exposure to vibration in order to calculate the transmissibility between the vibrating plate and the head. Genetic Algorithm (GA) was used to choose ANN’s number of hidden layers and number of neurons in each layer to obtain the best performance for predicting the transmissibility. The GA compared the root mean square errors (RMSE) between the ANN outputs and the experimental outputs, and then choose the best results that could be achieved. The number of hidden layers and number of neurons tested in GA vary from one hidden layer to four hidden layers, and from one neuron per layer to one hundred neurons per layer. Several runs have been conducted to train and validate the ANN model. The results show that double hidden layer with 13 neurons in the first layer and 12 neurons in the second layer give the best candidate. The proposed model can be integrated with whole-body vibration machines in order to choose the suitable exposure based on the user’s characteristics

Thermodynamic analysis of humidification dehumidification desalination cycles

Humidification–dehumidification desalination (HDH) is a promising technology for small-scale water production applications. There are several embodiments of this technology which have been investigated by researchers around the world. However, from a previous literature [1], we have found that no study carried out a detailed thermodynamic analysis in order to improve and/ or optimize the system performance. In this paper, we analyze the thermodynamic performance of various HDH cycles by way of a theoretical cycle analysis. In addition, we propose novel high performance variations on those cycles. These high-performance cycles include multi-extraction, multi-pressure and thermal vapor compression cycles. It is predicted that the systems based on these novel cycles will have gained output ratio in excess of 5 and will outperform existing HDH systems.King Fahd University of Petroleum and MineralsCenter for Clean Water and Clean Energy at MIT and KFUP

Tri-axial forces at the seat and backrest during whole-body vertical vibration

During exposure of seated subjects to vertical whole-body vibration, forces in the fore-and-aft, lateral and vertical directions at the seat and backrest have been measured. The responses at the seat have been compared with those measured previously on a seat without a backrest. Twelve male subjects were exposed to random vertical vibration in the frequency range 0.25–20 Hz. The subjects sat on a rigid seat with a rigid backrest and were exposed to a 16 different conditions: four vibration magnitudes (0.125, 0.25, 0.625, and 1.25 m s?2 r.m.s.) and four sitting postures (with varying thigh contact with the seat). Although the excitation was vertical, considerable dynamic forces were found in the fore-and-aft direction on both the seat and the backrest. In the vertical direction on the backrest, and in the lateral direction on the seat and the backrest, the forces were low. At both the seat and the backrest, forces in all directions showed a non-linear behaviour. The presence of the backrest modified the forces on the seat in both the vertical and fore-and-aft directions: in all four postures there was an increase in the resonance frequency of the apparent mass when using the backrest. The effect of the backrest on fore-and-aft forces on the seat depended on whether the feet were supported or not. The results show the importance of considering the backrest when studying the response of the human body to whole-body vertical vibration

Effect of seat surface angle on forces at the seat surface during whole-body vertical vibration

Twelve male subjects have been exposed to whole-body vertical random vibration so as to investigate the effect of seat surface angle, vibration magnitude and contact with a backrest on the ‘vertical apparent mass’ (calculated from forces normal to the seat surface and vertical acceleration) and ‘fore-and-aft cross-axis apparent mass’ (calculated from forces parallel to the seat surface and vertical acceleration). At each of four seat surface angles (0°, 5°, 10°, and 15°), the subjects were exposed to four vibration magnitudes (0.125, 0.25, 0.625, and 1.25 m s?2 rms) in the frequency range 0.25–15 Hz.The ‘vertical apparent mass’ and ‘fore-and-aft cross-axis apparent mass’ on the seat surface suggested resonances in the vicinity of 5 and 4 Hz, respectively. At all seat angles, both with and without a backrest, the resonance frequency in the ‘vertical apparent mass’ was greater than the resonance frequency in the ‘fore-and-aft cross-axis apparent mass’. Within subjects, the two resonance frequencies were not correlated in any condition. Seat angles up to 15° had a negligible effect on the ‘vertical apparent mass’ but a considerable effect on the ‘fore-and-aft cross-axis apparent mass’ on the seat surface, where ‘cross-axis apparent mass’ increased with increasing seat angle. At all seat angles, increasing the vibration magnitude decreased the resonance frequency in both directions. The least significant decrease in resonance frequency with increasing vibration magnitude occurred in the ‘fore-and-aft cross-axis apparent mass’ at the maximum seat angle of 15°. At low frequencies, the backrest reduced the forces in both directions, with the reduction greatest in the ‘fore-and-aft’ direction. The ‘fore-and-aft cross-axis apparent mass’ at resonance was correlated with subject mass and subject stature

Non-linear dual-axis biodynamic response to fore-and-aft whole-body vibration

Seated subjects have participated in two experiments with fore-and-aft whole-body vibration to investigate dynamic responses at the seat and footrest in the direction of vibration and in other directions. In the first experiment, 12 males were exposed to fore-and-aft random vibration (0.25–20 Hz) at four magnitudes (0.125, 0.25, 0.625, and 1.25 m s?2 rms) while sitting on a seat with no backrest in four postures with varying foot heights to produce differing thigh contact with the seat (feet hanging, feet supported with maximum thigh contact, feet supported with average thigh contact, and feet supported with minimum thigh contact). In the second experiment, six subjects were exposed to three vibration magnitudes (0.125, 0.25, 0.625 m s?2 rms) in the average thigh contact posture, both with and without a rigid backrest. Forces were measured in the vertical, fore-and-aft, and lateral directions on the supporting seat surface (in the first experiment) and in the fore-and-aft and vertical directions at the footrest (in the second experiment).On the seat, there were three vibration modes in the fore-and-aft apparent mass on the seat at frequencies below 10 Hz in all postures (around 1 Hz, between 1 and 3 Hz, and between 3 and 5 Hz); large vertical forces were dependent on foot support while lateral forces were relatively small. At the feet, the fore-and-aft apparent mass showed a resonance between 3 and 5 Hz, which increased in frequency and magnitude when a backrest was used. The fore-and-aft vibration produced high vertical forces at the footrest. At frequencies below resonance, the backrest reduced vertical and fore-and-aft forces at the footrest. On the seat and the footrest, the forces showed a nonlinear characteristic that varied between postures.The presence of appreciable vertical forces indicate that during fore-and-aft excitation the body moved in two dimensions. It is concluded that forces in directions other than the direction of excitation should be taken into account when considering biodynamic responses to fore-and-aft whole-body vibration