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Body motions associated with walking exhibit irregular and complex patterns with time. Chaos analysis methods have been developed to clarify nonlinearity of the lower extremity motions. No research has been reported on chaos analysis of the upper extremity joints. The purpose of this study was to investigate chaotic characteristics of movements of the upper body as well as the lower extremity during level walking. Gait experiments were carried out for eighteen young males. Each subject was instructed to walk on a treadmill at his own natural speed. Flexion-extension angles of eleven joints were obtained by using eight video cameras. To evaluate joint characteristics in a quantitative way, the largest Lyapunov exponent (LLE) was calculated from a reconstructed state space created by time series and embedding dimension. The mean LLE ranged from 0.080 to 0.137 for the upper body, and from 0.090 to 0.182 for the lower extremity joints. The mean LLE of the upper extremity joints was statistically different from that of the lower extremity joints (p<0.05). The results obtained can be used as a valuable reference for the normal gait for further studies of abnormal walking.

Artificial intelligence (AI) is a modern approach which has the ability to capture nonlinear relationships and interaction effects. Frequently, AI methods have been used by researchers to predict output responses of the Resistance spot welding (RSW) due to the complex- ity during the welding process and numerous interferential factors, especially the short-time property of the process. The present study is to investigate the weld strength of spot weld for high strength steel sheets of CR780 using the Adaptive neuro fuzzy inference system (ANFIS). These results were compared with those obtained by conventional Artificial neural network (ANN). The input parameters were extracted through the dynamic resistance signal which was obtained from the primary circuit of the welding machine. Both the ANN and ANFIS models were utilized for the formulation of mathematical model with an off-line dynamic resistance response of the RSW at a particular parameters setting. The performances of both models were compared in terms of correlation coefficient value (R), Root mean squared error (RMSE), and Mean absolute percentage error (MAPE). While both methods were capable of predicting the weld strength, it was found that ANFIS model could predict more precisely than ANN.

In general, to send out natural gas via a pipeline network across the nation in LNG terminal, high-pressure cryogenic pump supply highly compressed LNG to high-pressure vaporization facilities. The Number of cryogenic pumps determined the send-out amount in LNG receiving terminal. So it is main equipment at LNG production process and should be maintained on best conditions. In this paper, to find out the cause of high vibration at cryogenic pumps-motor system in LNG terminal, vibration spectrum analysis and motor current signature analysis have been performed together. Through the analysis, motor rotor bar problems are estimated by the vibration analysis and confirmed by the current analysis. So, it is demonstrated through the case study in this paper, how performing vibration analysis and current signature analysis together can reliable diagnosis rotor bar problems in pump-motor system.

Seat tightness at the fully shut position should be a consideration in the development of a butterfly valve for use in a liquefied natural gas (LNG) vessel. A flexible solid metal seal offers sufficient tightness of the butterfly valve and meets the specifications for cryogenic temperature. In the present study, characteristics for a cryogenic butterfly valve, such as the flow coefficient and the pressure loss coefficient, were estimated by numerical fluid analysis carried out to simulate 3-D flow and to study performance as it was affected by the opening angles of the valve disc. A design criterion to ensure the seat tightness of the butterfly valve at the fully shut position was proposed, in which the contact pressure between the metal seal and the valve disc would be compared with the fluid pressure. Numerical structural analysis showed that the contact pressure can be calculated by simulation of the frictional contact behavior on the surface of the metal seal and the valve disc. As a result, an adequate flexibility of the metal seal and the valve disc was required in order to accomplish a contact pressure that would be high enough to satisfy the seat tightness requirement. Under cryogenic temperature, thermal shrinkage caused the metal seal to adhere closely to the valve disc periphery at both sides and raised the contact pressure to a relatively high value, though there was no contact across a small area at the center position, which is susceptible to leakage. An additional displacement of the metal seal and the valve disc appeared at an operating fluid pressure of 6.9 bar and produced sufficient contact pressure at the no-contact area. This was verified by experimental leakage tests performed at room and cryogenic temperatures.

We have proposed a new method to predict the state of bolt fastening connection using time-domain structural vibration signal and experimentally validated its effectivness. To obtain the structural vibration signal, non-contact type laser displcement sensor and contact type piezo film sensor were used, respectively. Two-beam structures with holes were prepared and fastened with a set of bolt and nut. By applying a random initial displacement at the free end of the cantilever beam structure, vibration signals were measured for three different bolt fastening states: fully fastened, half-loosened and 90 %-loosened. After extraction of features from the obtained vibration signals, the bolt fastening state was classified based on the k-nearest neighbor (k-NN) algorithm. It is experimentally verified that the bolt fastening state can be accurately predicted by using the structural vibration signals and machine learning algorithm.

In this study, we investigated the heat transfer characteristics of kerosene for various fuel flow rates in the regenerative cooling heat exchanger of scramjet engines. We used hydrogen for combustion and kerosene for the heat exchanger regenerative cooling. The internal combustor wall surface temperature was measured using a phosphor thermometer. The fuel pressure and temperature were also measured. Significant changes were observed when kerosene flow rate changed from 6 to 8 g/s. The fuel boiling point at specific pressures and temperatures was obtained using differential scanning calorimetry; at the kerosene boiling point, they were found to be consistent with the temperature and pressure values between 6 and 8 g/s fuel flows, which confirmed that the fuel changes from liquid to gas under these circumstances, leading to considerable changes in the surface and fuel temperature tendencies. These findings could help in the optimal design of scramjet engines regenerative cooling heat exchangers.

In the present study, the mechanical model of section element in tube bulging area was established through the stress conditions of hydraulic bulging. Based on the mechanical model, the equivalent stress and equivalent strain equations of the section element in the bulging area were derived, respectively. Combined with the experimental data, the equivalent stress and strain of the section element in the bulging area were fitted by polynomial, and the plastic hardening model of thin-walled tube under pulsating loading was obtained. In order to verify the model precision, the plastic hardening models obtained from pulsating hydroforming and non-pulsating hydroforming were taken as the material model by finite element simulation respectively. The experimental results were compared with the simulation results which showed that as a pulsating hydraulic loading material parameters, the model established in this paper had higher precision.

Even though many techniques have been used in the research for the quality of a surface, the effect of each cutting condition on the surface roughness has yet to be definitely determined. In the present study, the cause of the contradictory effect of the cutting condition was explained. As a result, the cutting velocity was found to be an improper cutting parameter for explaining variations in surface roughness. It was also discovered that the depth of cut could affect the surface roughness, contrary to the claims of most publications. Consequently, the optimum cutting conditions were determined for the finest surface roughness, and were proven to be significantly better than those obtained using the Taguchi method and methods described in the literature.