Relative rotor phasing for multicopter vibratory load minimisation

This study focuses on vibration reduction for quadcopters and octocopters with elastic, two-bladed, fixed-speed, variable-pitch rotors through the use of relative rotor phasing. The study defines phase modes such as a pitch phase mode with relative phasing between the front and aft rotors, a roll phase mode with relative phasing between the left and right rotors, and a differential phase mode with relative phasing between the clockwise and counter-clockwise spinning rotors for both the quadcopter and the octocopter, as well as additional higher harmonic phase modes for the octocopter. Parametric studies on individual phase modes indicate that, for the quadcopter in forward flight, the pitch and roll phase modes can almost entirely eliminate the 2/rev vibratory forces (at the aircraft level), but the 2/rev vibratory moments cannot be minimised at the same time. By simultaneously using multiple phase modes, a Pareto front can be generated and a solution selected based on the relative emphasis on force or moment vibration reduction. For the octocopter, it was observed that individual higher harmonic modes (specifically the 2c or 2s modes) could almost entirely eliminate both the 2/rev vibratory forces and moments, simultaneously. Compared with vibration levels in forward flight that might, on average, be expected if the rotors were randomly phased, a 62% reduction of a composite vibration index can be achieved on a quadcopter, and complete elimination of vibration was achievable on an octocopter, with appropriate rotor phasing.

Application of non-metallic composite reinforcement for contact line supports

The technology for pre-stressing and anchoring of the composite rebar was developed. It makes possible to reinforce concrete products and produce the contact line supports of high quality, which possesses advantages in comparison with the steel reinforced concrete. The prototypes of supporting structures with the use of the composite BFRP reinforcement were developed. They were tested for strength, rigidity and crack resistance. In the course of testing, the value of a pole deflection in the plane of the application of the control load was determined. Poles with composite reinforcement (with vibratory load and after vibratory load) and steel reinforced poles were tested and compared. Results obtained show that the vibratory load had no significant impact on the properties of supports reinforced with pre-stressed composite rebars and confirm the practical possibility to use them. In the future, it is necessary to develop the working drawings for the replacement of the steel reinforcement by a composite polymer rebar and the technical requirements for supports of the contact lines of Russian Railways as well as the technical regulations for their design and manufacturing.

Visual Performance Evaluation of Helicopter Pilots in Vibrating Cockpit

Rotorcraft are known to suffer from relatively high levels of vibration as compared to their fixed-wing counterpart, due to exposure to significant vibratory load levels. Pilots usually operate in a vibrating cockpit, and hence can suffer from degradation of their instrument reading performance. Therefore, the expected level of degradation in visual performance should be estimated when there is room for design changes. The present work demonstrates the evaluation of visual vibration degradation of helicopter pilots using a modular analysis environment. Core elements are an aeroelastic helicopter model, a seat-cushion model, a detailed human biodynamics multibody model, and a simplified model of ocular dynamics, which are assembled into an overall model. The contribution of each component is examined using a figure of merit that includes both eye and instrument panel vibration.

The Theory of Concrete Mixture Vibratory Compacting

Purpose. The creation of the compacting vibratory process theoretical basis enabling the assessment of the efficiency and the choice of rational modes of the vibration influence on the concrete mixture, based on the minimal energy input in the process of its compacting.Methodology. The paper contains the description of the mechanism of compacting under the action of external vibration forces whereat a variable tensely deformed condition occurs in the concrete mixture. In this case the primary structural links break, the links between its separate elements weaken, the final movements of mineral particles result in the creation of a more compact packing. As the basic factor determining the character of the compacting process, the authors propose to use the product of voltage and the velocity of the vibratory action, which presents the power of the vibratory action on the compacted medium.Results. The authors have obtained analytical expressions enabling the determination of the growth of the concrete mixture density in time function depending on the type of the vibratory load and the power of the applied vibratory action on the compacted medium. The paper contains the theoretical and experimental values of the specific work that provides compacting up to the values required by the technological norms depending on the consistence of the concrete mixture at vertical and horizontally directed vibrations.Conclusions. The authors have specified the existing hypothesis and proposed a more general power hypothesis of the process of vibratory compacting of concrete mixtures, applicable to the description of the vibration process and concrete media treatment by various vibratory mechanisms, tools and machines. One can use the obtained results to set the rational modes and duration of the vibratory action on the compacted medium depending on the amount and type of the specific work of compacting and also to determine the basic parameters of vibration machines of various technological purpose.

Fatigue Analysis of the Structural Bottom of an Aluminum Planing Craft through Vibratory Load of the Propeller System

This work analyzed the structural fatigue of a high-speed craft, which has a propeller system formed by two 493-hpengines connected through speed multipliers to water jet systems. Its aluminum alloy structure has combined-typeframing. The useful life of the boat bottom’s structure was determined considering the cyclical loads generatedby the propulsion system, using the Finite Elements method and applying the effort-number method of cycles tofailure. For this, a structural model was developed of the selected zone, which was analyzed with the SAP2000program, to obtain complex amplitudes of the stress supported by the structure. Thereafter, with these results thestress range was determined and, then, using S-N curves for Aluminum the number of cycles that needed to becarried out by six structural details selected was determined, for its failure. Using Miner’s Rule, combined with thecraft’s assumed work modes, the time of the useful life time of the referential details selected during an hour wasdetermined. Finally, if the craft operates for three hours per day, the bottom structure of the boat analyzed wouldhave a useful life of 14.5 years, when working principally in low speed rating.

Study on Vibratory Loads of Rotor with Trailing Edge Excitation

To investigate the vibratory load of rotor with trailing edge excitation, and to study the relationship between TEF motion and hub vibratory load, a comprehensive model is built based on a conventional rotor modeling. Both the inertial force and aerodynamic force of TEF are considered. Effects of frequency, phase and amplitude of the excitation on hub vibration are discussed. The results indicate that with proper phase, hub vibration can be reduced with any of 2-5/rev trailing edge excitation. Within a reasonable range, the change in 4/rev hub vibration is more obvious with larger flap deflection. Control laws of several vibration directions are different, so various directions should be considered overall for optimal vibration control. Light TEFs are beneficial for vibration control.

Experimental Validation of Fretting Fatigue Strength and Fretting Wear Rate at Contact Surface of Turbine-Blade-Shroud Cover

In continuously coupled blade structures, fretting fatigue and wear have to be considered as supposed failure modes at the contact surface of the shroud cover, which is subject to steady contact pressure from centrifugal force and the vibratory load of the blade. We did unique fretting tests that modeled the structure of the shroud cover, where the vibratory load is only carried by the contact friction force, i.e., a type of friction. What was investigated in this study are fretting fatigue strength, wear rate, and friction characteristics, such as friction coefficient and slip-range of 12%-Cr steel blade material. The friction-type tests showed that fretting fatigue strength decreases with the contact pressure and a critical normal contact force exists under which fretting fatigue failure does not occur at any vibratory load. This differs from knowledge obtained through pad-type load carry tests that fretting fatigue strength decreases with the increase of contact pressure and that it almost saturates under a certain contact pressure. Our detailed observation in the friction-type tests clarified that this mechanism was the low contact pressure narrowing the contact area and a resulting high stress concentration at a local area. The fretting wear rate was explained by the dissipated energy rate per cycle obtained from the measured hysteresis loop between the relative slip range and the tangential contact force. It was found that the fretting wear rate is smaller than the wear rate obtained by one-way sliding tests, and the former is much smaller than the latter as the dissipated energy decreases. Finally, to prevent fretting fatigue and wear, we propose an evaluation design chart of the contact surface of the shroud cover based on our friction-type fretting tests.