Differences in Gait Stability and Acceleration Characteristics Between Healthy Young and Older Females

Our aim was to evaluate differences in gait acceleration intensity, variability, and stability of feet and trunk between older females (OF) and young females (YF) using inertial sensors. Twenty OF (mean age 68.4, SD 4.1 years) and 18 YF (mean age 22.3, SD 1.7 years) were asked to walk straight for 100 meters at their preferred speed, while wearing inertial sensors on their heels and lower back. We calculated spatiotemporal measures, foot and trunk acceleration characteristics, their variability, and trunk stability using the local divergence exponent (LDE). Two-way ANOVA (such as the factors foot and age), Student's t-test and Mann–Whitney U test were used to compare statistical differences of measures between groups. Cohen's d effects were calculated for each variable. Foot maximum vertical (VT) acceleration and amplitude, trunk-foot VT acceleration attenuation, and their variability were significantly smaller in OF than in YF. In contrast, trunk mediolateral (ML) acceleration amplitude, maximum VT acceleration, amplitude, and their variability were significantly larger in OF than in YF. Moreover, OF showed lower stability (i.e., higher LDE values) in ML acceleration, ML, and VT angular velocity of the trunk. Even though we measured healthy OF, these participants showed lower VT foot accelerations with higher VT trunk acceleration, lower trunk-foot VT acceleration attenuation, less gait stability, and more variability of the trunk, and hence, were more likely to fall. These findings suggest that instrumented gait measurements may help for early detection of changes or impairments in gait performance, even before this can be observed by clinical eye or gait speed.

Analysis on the Seismic Performance of Shock Absorption Layer Applied in Tunnel Lining Structure Using Shaking Table Model Tests

Shock absorption layer is a relatively simple and effective aseismic measure, which can bear the adverse effects of surrounding rock deformations and buffer the forces acting on lining structure with seismic action. This paper conducts a series of shaking table model tests to analyze and compare the aseismic performances of tunnel lining structure with and without shock absorption layer in different grades of surrounding rocks, in which the superior thickness of shock absorption layer is determined. Therein, it is concluded that the shock absorption layer has prominent influence on reducing the acceleration responses of surrounding rock and lining structure with seismic excitation. The setting of the shock absorption layer can reduce the acceleration amplitude of tunnel lining with seismic excitation by about half. Furthermore, the setting of 1 cm shock absorption layer will increase the Fourier amplitudes and change the vibration frequencies of surrounding rock and lining structure with seismic excitation, while the setting of 2 cm shock absorption layer can significantly decrease the Fourier amplitudes and keep the vibration frequencies of surrounding rock and lining structure with seismic excitation. Therefore, the aseismic effect of 2 cm shock absorption layer is better than the aseismic effect of 1 cm shock absorption layer, which can both reduce the acceleration amplitude and Fourier amplitude of tunnel lining with seismic excitation while keep its characteristics in frequency domain. This research on the aseismic performance of shock absorption layer can contribute to the construction of tunnel engineering and improve the safety of tunnel lining structure.

Cutting force, Vibration, and Temperature in Drilling on a Thermoplastic Material of PEEK

Polyetheretherketone (PEEK) is one of the semi-crystalline thermoplastic polymers with excellent machinability and chemical stability applied to precise structural plates and electronic components. This study installed multiple sensors to analyze the machining characteristics in the PEEK drilling. According to the time domain signals, the effects of spindle speed and feed rate on the machining characteristics of cutting force and vibration were investigated. In addition, an infrared thermography was installed to record the temperature variation within the drilling area. The experimental hole was 2-mm diameter with a 4.5-mm depth. Experimental results showed that the effect of the feed rate on thrust force is greater than the spindle speed; drilling by a low-level spindle speed with a low-level feed rate can obtain the smallest cutting force and acceleration amplitude in the spindle axis; the temperature within the drilling area is inverse to the feed rate and a high-level feed rate is helpful for forming regular curl chips. When adequate airflow was applied during the drilling operation, the hole’s shrinkage ratio and roundness can be decreased. The data presented in this paper provide valuable references for realizing the drilling of the thermoplastic—PEEK.

A Magnetoelectric Hybrid Hydraulic Damper for the Mining Robot Suspension System

In order to improve the damping and controllability of the mining robot suspension system, a new magnetoelectric hybrid suspension hydraulic damper, which is a semiactive suspension damper, is proposed based on the traditional hydraulic damper by introducing the magnetic-electric hybrid suspension structure. The structure and working principle of the damper are introduced, respectively, and the mathematical models of the equivalent stiffness and equivalent damping of the system are calculated by the magnetic circuit method and the oil circuit method, while AMESim/Simulink cosimulation is carried out. In order to test the damping performance, a prototype of the magnetoelectric hybrid suspension hydraulic damper was fabricated. The results show that the vibration displacement amplitude can be reduced by 20% and the vibration acceleration amplitude can be reduced by 10% by adjusting the stiffness and damping of the system due to the magnetoelectric hybrid suspension structure. Moreover, the experimental results are consistent with the simulation results, which verify the effectiveness and superiority of this type of damper.

SUBSTANTIATION OF DESIGN PARAMETERS OF COAL DUST EXPLOSION CONTAINMENT SYSTEM

The aim of the paper is to identify the qualitative and quantitative parameters of seismic waves and accelerations on the mine working contour after an explosion of the gas-and-dust mixture. Information about the formation of seismic waves in the rock mass accommodating the mine working was received using modelling in order to improve the means of containment of explosion of further developed dust-air mixture. The parameters of seismic waves, such as propagation velocity and acceleration, amplitude, and frequency of oscillations of mine working walls, were established for the conditions of the experimental structure, which allows to scientifically substantiating the design parameters of the systems protecting the miners against explosion. The energy of the explosion propagates in the rock mass in the form of a series of peak-like pulses and oscillations with smaller amplitude. Modulus of acceleration is an informational indicator, which suits the most for registration by seismic sensors responding, specifically, to the most powerful peak pulses formed by seismic waves. By revealing the qualitative and quantitative indicators of seismic wave propagation on the mine working contour and in the rock mass, the parameters of seismic sensors of the systems protecting the miners against explosion can be substantiated.

Vibration Characteristics Diagnosis and Estimation of Fault Sizes in Rolling Contact Bearings: A Model Based Approach

A novel model based technique is presented in this paper for the estimation of the fault size in different components of rolling contact bearings. A detailed dimensional analysis of the problem is carried out and experimental methodology using Box-Behnken design is applied to generate the experimental data set. First, analysis of the vibration acceleration amplitude at the fault frequency, its dependence on the bearing operating and fault parameters using the obtained vibration data set is carried out by statistical analysis of variance. Numerical equations are developed then using the experimental data set for the correlation of the vibration acceleration amplitude in frequency domain with the fault sizes based on the developed dimensionless terms. A hybrid Back propagation neural network integrating genetic algorithms is also developed so as to check the computational performance of the developed model equations. Validation of the proposed method is carried experimentally also for three seeded defect sizes on outer race, inner race and rolling element. The maximum model accuracy observed is for inner race defect case with predictive accuracy of 99.44 percentage and for the roller defect case it is 98.77 percentage. The deviance observed for the model predictive performance is maximum for outer race defect case with least accuracy of 90.47 percentage amongst all.

Acceleration Breaks the Cells Defense Mechanisms against Vibration in Anthemis gilanica Calli

Vibration is a mechanical stress which happens in nature and affects many biological aspects of plants. In this research, the effect of acceleration and vibration was investigated on some physiological and biochemical responses of Anthemis gilanica in vitro. Calli were induced from leaf (LS) and root segments (RS) and were applied to different frequencies of vibrations (0, 50, and 100 Hz) and accelerations (1, 2, and 4 g) on the A. gilanica calli for 30 min. Results showed that vibration significantly increased relative water content (RWC), growth parameters, protein and proline contents, ascorbate peroxidase (APX), peroxidase (POX), and superoxide dismutase (SOD) activities and decreased total carbohydrate, malondialdehyde (MDA), H2O2 contents, and polyphenol oxidase (PPO) activity in both LS and RS calli. Inversely, increase of acceleration in vibrated calli decreased growth parameters, RWC, protein content, and POX activity and induced proline and carbohydrate accumulations, SOD, APX, and PPO activities as compared to vibration alone. Different responses of two callus types were observed, and the highest growth, protein content, and membrane stability were observed in LS calli as compared to RS calli. It found that high acceleration amplitude intensified the resonance effect of vibration by induction of lipid peroxidation and oxidative stress damage in A. gilanica.

Control parameter optimization of a nonlinear vehicle suspension system with time-delayed acceleration feedback

A time-delayed acceleration feedback control is proposed to improve the vibration performance of a nonlinear vehicle suspension system. First, the harmonic balance method is applied to obtain the vertical acceleration amplitude of the system excited by simple harmonic road excitation. Then, taking the amplitude of the sprung mass acceleration and control force into account, the single-objective and multiple-objective optimization problems of time-delayed feedback control parameters, respectively, are discussed. Finally, the mathematical simulation is provided to verify the correctness of the optimization results. It is concluded that the nonlinear suspension with optimal time-delayed feedback control has better vibration control performance compared to passive one. The acceleration amplitude of the sprung mass is significantly reduced by the single-objective optimization of the control parameters. Moreover, when the optimal time delay is introduced, the active control force input is fewer than that without time delay. The phenomenon of energy transfer between the sprung mass and the unsprung mass is observed in some road-excitation frequencies.

ERGONOMIC ASPECTS RELATED TO MOBILE AGRICULTURAL MACHINERY OPERATORS

Ergonomics is the key to make the machine “worker friendly”. In this paper, the humble effort is carried out to present the outline of the tractor industry of India as well as Ukraine for the subsequent analysis of the operator's working conditions and negative production factors that affect his health. Experiment was conducted in Ukraine for three different tractor models i.e. HTZ-181, HTZ-200, HTZ-200B. Vibrations were measured at frame between cab brackets (on left side member), cab floor at the operator's feet and cab frame (on rear crossmember at the rear window base) for plowing and harrowing operations. Research of structural elements vibration parameters of some tractor models (for harrowing and plowing operation) showed that the cab frame has the highest vibration activity in the vertical direction with a peak in the octave band with a geometric mean frequency of 16 Hz. In the transverse direction, the tractor frame has the highest vibration acceleration amplitude, while the maximum vibration acceleration amplitude falls on the octave band of 16 Hz, but its value is two times lower than in the vertical direction. It was also observed that the amplitudes of vibration accelerations of the elements of the tested tractors during plowing the field had higher values than during harrowing, but these excesses were not significant. Analysis of the test results shows that the tractors' suspensions have practically the same vibration characteristics, and therefore, it is recommended to conduct further studies of the parameters of general vibration (on the operator's seat) and local vibration (on the steering wheel) in order to assess the tractor operator' working conditions, his safety and develop technical solutions to improve the devices/machines. The study practical value and originality consists in identifying the structural elements of mobile agricultural machinery (for example, tractors) that have the highest vibrations, which affect the operator for their further improvement, but not for replacing the machinery. This approach to improving the working conditions of mobile agricultural machinery operators is driven by the country's weak economy and can be beneficial for developing countries in the face of a lack of funds to purchase new ergonomic machines.

Analysis and visualisation of tremor dynamics in deep brain stimulation patients

Deep brain stimulation (DBS) is an established therapy for movement disorders such as in Parkinson's disease (PD) and essential tremor (ET). Adjusting the stimulation parameters, however, is a labour-intensive process and often requires several patient visits. Physicians prefer objective tools to improve (or maintain) the performance in DBS. Wearable motion sensors (WMS) are able to detect some manifestations of pathological signs, such as tremor in PD. However, the interpretation of sensor data is often highly technical and methods to visualise tremor data of patients undergoing DBS in a clinical setting are lacking. This work aims to visualise the dynamics of tremor responses to DBS parameter changes with WMS while patients performing clinical hand movements. To this end, we attended DBS programming sessions of two patients with the aim to visualise certain aspects of the clinical examination. PD tremor and ET were effectively quantified by acceleration amplitude and frequency. Tremor dynamics were analysed and visualised based on setpoints, movement transitions and stability aspects. These methods have not yet been employed and examples demonstrate how tremor dynamics can be visualised with simple analysis techniques. We therefore provide a base for future research work on visualisation tools in order to assist clinicians who frequently encounter patients for DBS therapy. This could lead to benefits in terms of enhanced evaluation of treatment efficacy in the future.