Different Levels Of Vibration Research Articles

Effects of hydric stress on vibrational frequency patterns of Capsicum annuum plants

ABSTRACT Plants that experience a lack of sufficient irrigation undergo hydric stress, which causes the modification of their mechanical properties. These changes include a complex network of chemical and physical signals that interact between plant-plant and plant-environment systems in a mechanism that is still not well understood, and that differs among species. This mechanical response implies different levels of vibration when the plant experiences structural modifications from self-hydraulic adjustments of flux exchange at specific frequencies, with these carrying behavioral information. To measure these signals, highly sensitive instrumentation that allows the decoding of displacement velocity and displacement of plants, which is possible through calibrated equipment such as 3D scanning laser vibrometers, is necessary. Laser vibrometry technology allows for noninvasive measurements in real-time. Physiological changes could reasonably affect the biomechanical condition of plants in terms of the frequency (hertz) and intensity of the plant’s vibration. In this research, it is proposed that the frequency changes of a plant’s vibration are related to the plant’s hydric condition and that these frequency vibrations have the ecological potential to communicate water changes and levels of hydric stress. The peak of the velocity of plant displacements was found to vary from 0.079 to 1.74 mm/s, and natural frequencies (hertz) range is between 1.8 and 2.6 Hz for plants with low hydric stress (LHS), between 1.3 and 1.6 Hz for plants with medium hydric stress (MHS), and between 6.7 and 7.8 Hz for plants with high hydric stress. These values could act as preliminary references for water management using noninvasive techniques and, knowledge of the range of natural frequencies of hydric stress risk in chili pepper crops can be applied in precision agriculture practices.

MODELING OF ELECTRONIC SPEED PID-CONTROLLER OF INTERNAL COMBUSTION ENGINE

Describes the structure and working principle of electronic model PID speed controller, in conjunction with diesel fuel pump of high pressure. This model, together with a model of a diesel engine and given external load allows you to explore the influence of PID speed controller parameters for transients and the performance of the engine. Describes the electronic control unit that defines electronic pedal control, actuator, which affects the body dispensing fuel. Model may take into account the different levels of vibration, which are transmitted to the body dispensing fuel.

Research on deep hole drilling vibration suppression based on magnetorheological fluid damper

Based on the working principle of magnetorheological fluid damping, in this paper, a set of squeezing mode Magneto-rheological Fluid (MRF) dampers is designed for drilling vibration suppression in deep hole machines. Elaborate analysis of the correlativity between the dynamic morphology trajectory of the machined hole surface, the vibration of the drilling tool-shaft, and the theoretical derivation of the damping force, is put forward in accordance with the Bingham model and Euler-Bernoulli beam Equation. Simultaneously, the contrast analysis of the vibration suppression effect is carried out through the drilling experiments with and without an MRF damper. In addition, a series of measurements on the vibration characteristics of the drilling shaft, the drilling tool and the guide surface wear patterns, and the machine hole surface are analyzed, respectively. Both the drilling experiments and theory studies have revealed that the strength of the magnetic field changed with the drill shaft at different levels of vibration. The MRF damper could suppress the vibration with nonlinear characteristics initiatively and instantaneously, by variable damping, which can eventually improve the surface roughness. In addition, according to the phenomenon of tool tipping, the breakage of the guide bars and the machine hole surface deduces the condition of the vibration effect objectively.

On the Use of Machine Learning to Detect Shocks in Road Vehicle Vibration Signals

The characterization of transportation hazards is paramount for protective packaging validation. It is used to estimate and simulate the loads and stresses occurring during transport that are essential to optimize packaging and ensure that products will resist the transportation environment with the minimum amount of protective material. Characterizing road transportation vibrations is rather complex because of the nature of the dynamic motion produced by vehicles. For instance, different levels of vibration are induced to freight depending on the vehicle speed and the road surface; which often results in non‐stationary random vibration. Road aberrations (such as cracks, potholes and speed bumps) also produce transient vibrations (shocks) that can damage products. Because shocks and random vibrations cannot be analysed with the same statistical tools, the shocks have to be separated from the underlying vibrations. Both of these dynamic loads have to be characterized separately because they have different damaging effects. This task is challenging because both types of vibration are recorded on a vehicle within the same vibration signal.This paper proposes to use machine learning to identify shocks present in acceleration signals measured on road vehicles. In this paper, a machine learning algorithm is trained to identify shocks buried within road vehicle vibration signals. These signals are artificially generated using non‐stationary random vibration and shock impulses that reproduce typical vehicle dynamic behaviour. The results show that the machine learning algorithm is considerably more accurate and reliable in identifying shocks than the more common approaches based on the crest factor. Copyright © 2016 John Wiley & Sons, Ltd.

Transient flutter analysis of bluff bodies

This paper deals with the flutter theory for bridge decks and presents a new approach for the determination of 27 time domain dynamic force coefficients using forced motion of the deck section at either constant absolute speed (triangular wave form) or constant absolute acceleration (parabolic wave form). These coefficients are then introduced in a transient nonlinear flutter analysis where the wind speed is varied in order to predict the stability curve of a 3 degrees of freedom deck sections. This allows for considering the nonlinear nature of the flutter phenomenon, i.e. its variation according to multiple quantities (wind speed, frequency of motion, amplitude of motion, angle of attack, etc.), when predicting flutter amplitude at any wind speed. Results show good agreement with predictions from complex eigenvalue analysis and the stabilization of flutter was observed at different levels of vibration according to the wind speed. The effect of the aerodynamic mass is also studied and its non-inclusion is shown to lead to possible non-conservative results.

Effect of vibration during GTAW welding on microstructure and mechanical properties of Ti6Al4V

Grain growth in Ti6Al4V alloy during fusion welding decreases yield stress and tensile strength. This study examined the effect of mechanical vibration of the work piece during GTAW welding on the mechanical and metallurgical properties of Ti6Al4V. The structures of all welded specimens at different levels of vibration was examined and it was found that, during 330 Hz vibration, grain size in the welded metal zone decreased significantly over that of pieces welded without vibration. GTAW at 330 Hz significantly increased the mechanical properties and produced the highest yield strength, tensile strength and percentage of elongation. The highest level of hardness in the welded metal zone was achieved under this condition.

Quantification of changes in modal parameters due to the presence of passive people on a slender structure

This work proposes a method to predict changes in modal parameters of a generic structure due to the presence of passive people. The method requires to accurately know the modal model of the empty structure, i.e. natural frequencies, damping ratios and mode shapes. No restriction on the number of degrees of freedom of the structure is required. Each passive subject on the structure is modelled through his apparent mass and is introduced locally on the empty structure to obtain a model of the joint human–structure system. To include the apparent mass of the subjects in the model both measurements and models available in literature were used. The effect of using different models of the apparent mass was investigated and the effect of using apparent masses obtained with different levels of vibration was analysed.The proposed model was validated by means of experimental tests carried out on a lightly damped staircase. The empty structure was first tested to obtain its modal model in order to apply the proposed approach. After performing several tests with passive people standing on the structure, the experimental results showed small changes of natural frequencies (increase or decrease) and a high increase of damping ratios due to people׳s presence. Thus, the proposed approach was used to predict the above-mentioned changes. The measured and predicted frequency response functions, natural frequencies and damping ratios were compared. In all the cases taken into consideration, the predicted results fitted with the experimental evidence.

VIBRATION OF THE BICEPS BRACHII TENDON REDUCES TIME TO FAILURE WHEN MAINTAINING LIMB POSITION DURING A FATIGUING CONTRACTION.

Purpose/Hypothesis: Vibration reduces the tendon jerk, and the Hoffmann and stretch reflexes in the muscle exposed to the vibration (Bove et al, 2003;Cresswell and Ludieroscher et al, 2000;Lance et al, 1966), but does not alter the time to task failure when exerting a submaximal force against a rigid restraint (Cresswell and Ludieroscher 2000). Because the amplitude of the stretch reflex can be enhanced when the limb acts against a compliant load compared with a rigid restraint (Akazawa et al. 1983; De Serres et al. 2002), the purpose was to determine the influence of tendon vibration on the time to task failure when light loads were supported while maintaining limb position (position task) with the elbow flexor muscles. Number of Subjects: Twenty-five healthy adult men (22 ± 4 yr; range, 18–39 yr) performed the position task at 20% MVC force by maintaining a 90° elbow position until task failure. Materials/Methods: Subjects visited the laboratory for three sessions to perform the position task with two different levels of vibration (100 Hz, 2.5 N force, sub-threshold and supra-threshold for the tonic vibration reflex), and without vibration of the biceps brachii tendon. Results: MVC force prior to task performance was similar across the three sessions (313 ± 54 N, P = 0.83), indicating that the net torque exerted by the limb during the fatiguing contractions was similar. The EMG for the short and long heads of the biceps brachii, brachioradialis, and brachialis was similar across conditions (P > 0.05). Despite the similar criteria for task failure and a similar decline in MVC force (18.0 ± 8.0 %, P > 0.05), the time to task failure differed for each condition: supra-threshold vibration = 3.7 ± 1.4 min, sub-threshold vibration = 4.3 ± 2.1 min, and no-vibration conditions = 5.0 ± 2.2 min (P < 0 .001). The standard deviation (SD) for the vertical fluctuations in acceleration was greater at the start (0.27 ± 0.13 m/s2) and at 25% of task duration (0.28 ± 0.15 m/s2) for the supra-threshold condition compared with the no-vibration (0.13 ± 0.06 and 0.16 ± 0.09 m/s2;P = 0.03) condition, but was similar at task termination (0.83 ± 0.50 m/s2) for the three conditions. Conclusions: These findings indicate that both low and high levels of vibration applied to the biceps brachii tendon reduced the time to failure when maintaining limb position, which has implications for work-place activities. Clinical Relevance: Documenting evidence for early fatigue during tasks performed with prolonged vibration confirms the importance of afferent input during sustained tasks, and has implications for work and ergonomic environments.

Prolonged Vibration of the Biceps Brachii Tendon Reduces Time to Failure When Maintaining Arm Position With a Submaximal Load

Vibration reduces the amplitudes of the tendon jerk response and the Hoffmann and stretch reflexes in the muscle exposed to the vibration, yet does not alter the time to task failure when the task involves exerting a submaximal force against a rigid restraint. Because the amplitude of the stretch reflex is greater when a limb acts against a compliant load than a rigid restraint, the purpose was to determine the influence of prolonged tendon vibration on the time to failure when maintaining limb position with the elbow flexor muscles. Twenty-five healthy men performed the fatiguing contraction by maintaining elbow angle at 1.57 rad until failure while supporting a load equal to 20% of maximal voluntary contraction (MVC) force. The fatiguing contraction was performed on 3 separate days with different levels of vibration applied to the biceps brachii tendon: no vibration, subthreshold for a tonic vibration reflex (TVR), and suprathreshold for a TVR. MVC force before the fatiguing contraction was similar across the three sessions (mean of 3 sessions: 313 +/- 54 N, P = 0.83). Despite a similar decline in MVC force after the fatiguing contraction across conditions (-18.0 +/- 8.0%, P > 0.05), the time to task failure was 3.7 +/- 1.4 min for the suprathreshold TVR condition, 4.3 +/- 2.1 min for the subthreshold TVR condition, and 5.0 +/- 2.2 min for the no-vibration condition (P < 0 0.001). The average EMG of the elbow flexor muscles was similar (P = 0.22) during the fatiguing contractions. However, the fluctuations in limb acceleration at task onset were greater for the suprathreshold TVR condition (P < 0.01), but were not different between the subthreshold TVR and no-vibration conditions (P > or = 0.22). Furthermore, the difference in the SD of limb acceleration between the no-vibration and vibration conditions was correlated with the difference in time to failure for the no-vibration and subthreshold TVR conditions (P = 0.03; r2 = 0.22), but not for the no-vibration and suprathreshold TVR conditions (P = 0.90; r2 = 0.001). These findings indicate that prolonged vibration reduced the time to failure of a sustained contraction when subjects maintained limb position, suggesting that peripheral inputs to the motor neuron pool play a significant role in sustaining a contraction during tasks that require active control of limb position.

Control of a free-space adaptive optical interconnect using a liquid-crystal spatial light modulator for beam steering

This paper is a revision of a paper presented at the SPIE Conference on Micro-Optics, VCSELs, and Photonic Interconnects, Apr. 2004, Strasbourg, France. The paper appears (unrefereed) in SPIE Proceedings Vol. 5453. An adaptive beam position control system is reported, for use in alignment correction for free-space parallel optical interconnects at the board-to-board level. A liquid-crystal spatial light modulator (SLM) displaying binary phase gratings is used as a diffractive optical element to steer the beam. The design and implementation of a feedback controller for the SLM are presented, and shown in experimental results to completely correct for step disturbances within 1 to 2 sample periods. Extension of the system to tolerate random vibrations is considered, in terms of both the required SLM technology and the design of the control algorithms. The discussion highlights some of the trade-offs in choosing components when using this technology to correct for different levels of vibration.

EFFECTS OF VIBRATION, FEED FORCE AND EXPOSURE DURATION ON OPERATORS PERFORMING DRILLING TASK

It has been shown that vibration level, feed force, and exposure duration cause unfavourable effects on the work performance when hand-held vibrating tools are used by operators. Present study analyzed the effects of these variables on the heart rate and blood pressure of the operators carrying out the drilling task. Under three different levels of vibration (0.3, 0.5, and 1 m/s2), the operators performed the drilling for 3 minutes with three different levels of feed force (100, 200, and 300 N) in study 1, and for three different durations (10, 15, and 20 min) with a feed force of 200 N in study 2. Thirty male subjects participated in the two studies and data were analyzed on the basis of two factor repeated measure kind of experimental design. Results showed that in the kind of drilling task undertaken the level of vibration was statistically significant. However, the main effects of feed force and vibration exposure duration were statistically insignificant. These findings are discussed in the light of previous researches conducted on the subject.

Vibrationally mediated photolysis dynamics of H2O in the vOH=3 manifold: Far off resonance photodissociation cross sections and OH product state distributions

Vibrationally mediated photodissociation dynamics of water on the first excited electronic state surface (Ã) has been studied with slit jet-cooled H2O prepared in the complete polyad of vOH=3 overtone stretch levels (|03+〉, |12+〉, |12−〉, and |03−〉). (Notationally, |n1n2±〉 refers to symmetric/antisymmetric combinations of local mode OH stretch excitation, roughly corresponding to n1 and n2 quanta in the spectator and photolyzed OH bond, respectively.) At 248 nm photolysis wavelength the Condon point for bond cleavage occurs in the classically forbidden region, primarily sampling highly asymmetric H+OH exit valley geometries of the potential energy surface. Rotational, vibrational, spin orbit, and lambda doublet distributions resulting from this “far off resonance” photodissociation process are probed via laser induced fluorescence, exploiting the high efficiency laser excitation and light collection properties of the slit jet expansion geometry. Only vibrationally unexcited OH products are observed for both |12±〉 and |03±〉 initial excitation of H2O, despite different levels of vibration in the spectator OH bond. This is in contrast with “near-resonance” vibrationally mediated photolysis studies by Crim and co-workers in the |04−〉 and |13−〉 manifold, but entirely consistent with theoretical predictions from a simple two-dimensional quantum model. Photolysis out of the rotational ground H2O state (i.e., JKaKc=000) yields OH product state distributions that demonstrate remarkable insensitivity to the initial choice of H2O vibrational stretch state, in good agreement with rotational Franck–Condon models. However, this simple trend is not followed uniformly for rotationally excited H2O precursors, which indicates that these Franck–Condon models are insufficient and suggests that exit channel interactions do play a significant role in photodissociation dynamics of H2O at the fully state-to-state level.

Grip force in vibration disease.

In this experiment the hand grip force of 58 persons was measured. The study was carried out during a compulsory health examination. The subjects compressed with their left hand for 5 min fluctuating maximal force and with their right hand for 1 min with maximal constant force. The results were repeated with five different levels of vibration and without vibration. Individual forces varied in the 5-min experiment from 25 to 122 N. The strongest subjects were in a group affected by white fingers, but with no claim of diminished grip force. The weakest forces were seen in the group subjectively most-affected by vibration disease. On the basis of this examination, it seems that in some workers long-term exposure to vibration causes a diminution in grip force, which is a constant phenomenon, and it does not only manifest itself during their work. During exposure to vibration the force reduced from the resting level among the subjectively most-affected lumberjacks, but not in less-affected groups or in the reference group. No vibration frequency was found to be especially disadvantageous to grip force, and it was not possible to determine the normal limits of grip force.