Relative Rotational Speed Research Articles

Optimal declutching control of hinged multiple floating bodies

In deep seas, there is an increasing utilisation of multiple floating structures as devices for harnessing renewable energy, such as hybrid wind-wave energy systems and multi-body wave energy converters. The control strategies have a great influence on the motion characteristics and energy conversion efficiency of these systems. The control technology brings more benefits to the system's performance, yet also introduces more complex challenges. This paper aims to fill the research gap in the control of multiple floating bodies and to propose a novel optimal declutching control method. Declutching control enables discontinuous loading and releasing of the force from power take-off system between bodies. It was found that the feasibility of the proposed method is highly dependent on the choice of objective functions, iteration numbers, and wave frequencies. With appropriate parameters, the declutching control can achieve a variety of objectives for a hinged floating multibody system, such as reducing pitch motion, improving extracted wave power, increasing relative rotational speed, and enhancing power extraction. The control effects on the velocity and the force-velocity phase relationship and how they benefit the objectives are discussed. All objective functions show a better control effect (at least 7.76%) on their respective performance indices than others.

Development of a wind turbine with two multidirectional wind wheels

The object of research is a wind generator with counter-rotating blades. A special feature of this design is the presence of two wind wheels that rotate in opposite directions. Wind wheels are on the same axis, between them there is a certain distance, which is determined based on research data. The problem of modern wind power is the low range of operating wind speeds, weak generation at low wind speeds. The upper speed limit is 25 m/s, exceeding which leads to breakdowns of various units of the wind station, especially this affects the integrity of the blades, rupture of the wind wheel, cracking of the metal parts of the bearings and their fasteners. The wind turbine presented in the article allows to achieve an increase in the generation of electric energy by 50–70 %. This is achieved by increasing the relative rotational speed of the rotor relative to the stator. Therefore, even at low speeds, the rotor speed relative to the stator increases, which leads to an increase in power generation. The design of the device includes: two wind wheels, one transmits its rotation to the stator, the second to the rotor axis, a metal base, a current collector mechanism. For conducting the research, an experimental model and a semi-industrial installation were used. Results studies have confirmed the theoretical increase in the generation of electrical energy by this design. The peculiarity of the obtained results is connected with the determination of the distance between two wind wheels, the optimal distance between them corresponds to the maximum energy generation. A distinctive feature of the results obtained can be considered an increase in the number of blades on the second wind wheel

Accounting for the Temperature Dependence of Hardness in Numerical Simulation of Wear in Pivot-Jewel Bearings

Pivot-jewel bearings are important components in rotor systems and flywheel energy storage systems; the relative rotation speed can reach about 10³ rps under nominal operating conditions, while the lifespan can amount to years. Wear calculations of the contact surfaces are necessary in such scenarios to assess the life cycle of friction joints. Accounting for the variation in the surface hardness due to friction heating can considerably affect the amount of wear in the contact surface.

The Relationship Between Kinematical Parameters of Trunk and Knee Injuries in Male Judo Players

Background and Aims The knee joint injury in judokas mostly occurs in the standing position. This study aims to investigate the relationship between kinematic variables of trunk and the occurrence of knee injuries in male judokas. Methods In this study, 15 male judokas aged 20-30 years (7 with a history of knee joint injury and 8 controls) were selected based on the inclusion and exclusion criteria. Then, after installing markers on their body, they were asked to stand on a 30-cm box and, after a jump upwards, land on the ground on one foot (the support foot). Cameras were used to measure the angles of the knee and trunk joints during the jump landing task. Shapiro-Wilk test was used to examine the normality of data distribution. ANCOVA was used to compare the groups. The ssignificance level was set at 0.05. Results Healthy judokas had lower knee flexion angle and higher knee valgus angle. Moreover, they had lower trunk flexion angle, higher internal knee rotation, and higher relative rotation speed between femur and tibia compared to the injured group (P<0.05). Conclusion Male Judo players with a history of knee injury have lower knee flexion and greater knee valgus, lower trunk flexion, higher internal knee rotation, and higher relative rotation between femur and tibia compared to their healthy peers. Professionals and coaches need to design injury prevention exercises for this group of athletes.

Attenuation control of gyrostat without energy supply

The motion by inertia of a system of two rigid bodies connected by a cylindrical hinge is considered. One of the bodies (platform) is arbitrary, and the second (rotor) is dynamically symmetrical, and the symmetry axis coincides with the hinge axis. The system does not possess any actuator capable of controlling the angular velocity of the rotor. As a control element, a “trigger” is used that prevents the relative rotation of the rotor. In the absence of external moments, the system initially moves about the center of mass as a rigid body in the case of Euler. After the rotor is released, it begins to rotate in such a way that the projection of its absolute angular velocity on the axis does not change. At that moment, when the relative rotation speed goes to zero, the latch can be turned on without losing energy. As a result, the original trajectory of the body changes. The possibilities of platform overturning and stopping its “tumbling” are studied.Previously, such systems (gyrostats) have been widely used to control the orientation of satellites or mobile robots. In most cases, the presence of a motor that changes the energy of the system was assumed. Unpowered gyrostats were used to stabilize the equilibrium orientations. Latched systems with two modes of motion do not appear to have been previously studied. The theory presented in this paper can be used to control the orientation of satellites or robots.

Numerical Study of Contra-Rotating Vertical Axis Wind Turbine H-Rotor Darrieus Type

The new Contra-rotating Darrieus turbine configuration has been invented to enhance the V ertical Axis Wind Turbine (VAWT) performance. This configuration increases the relative rotational speed of the generator, resulting in higher output power. It is well known that the increase can reach four times the output power. However, how the Darrieus turbine VAWT contra- rotating configuration influences its aerodynamic performance still needs to be discovered. This study investigates the aerodynamic performance of the contra-rotating configuration by comparing it to the single-rotating Darrieus turbine VAWT under the same conditions. The freestream speed is 5 m/s, with TSR varying from one to two intervals of 0.2. This research is being completed using Computational Fluid Dynamics (CFD) 3D cases with an Unsteady Reynold Average Navier-Stokes (URANS) equation as the turbulent model equation. The results of this study show that in terms of output power or Power coefficient (Cp), the contra-rotating has a greater value than the single- rotating configuration. However, in all TSR variations, contra-rotating outperforms single-rotating in terms of aerodynamic performance or moment coefficient (Cm). This is due to the fact that the aspect ratio of stage 1 contra-rotating rotor is lower than the single-rotating rotor, resulting in more significant blade tip losses in contra-rotating. Theflow was discovered through the gap between stages 1 and 2 contra-rotating, providing additional momentum. This phenomenon increases Cm at an azimuth angle of 200°-255°.

Wear Analysis of Support Spring of Sprag Clutch during State of Overrunning

This paper analyzes the wear of the support spring of sprag clutches for different structural parameters during overrunning state. Specifically, the stiffness model of the support spring is established based on the characteristics of the variable helix angle, and also the supporting force model is established according to the energy conservation law during the working process of the sprag clutch. Meanwhile, the relative rotation speed between the support spring and the wedge is analyzed by dynamic simulation method. Furthermore, the wear model of the support spring in process of overrunning is established based on Archard wear theory. The results show that there is a linear relationship between supporting force and spring radial displacement compression. In addition, increasing free length and wire diameter of springs will aggravate the wear of springs, whereas enlarging pitch diameter of springs will reduce it. When free length is increased from 270 to 290 mm, the wear time is reduced by 20.88%; when wire diameter is increased from 0.5 to 0.7 mm, the wear time is reduced by 42.75%; when pitch diameter is increased from 2 to 2.4 mm, the wear time is increased by 3.35%. The degree of influence of the structural parameters on the spring wear from large to small is free length, wire diameter, and pitch diameter. Exactly speaking, when wear time is 100 hr, the relative sensitivity of structural parameters affecting the wear of the support spring is in order of free length (2.2), wire diameter (0.97), and pitch diameter (0.08). The research provides a reference for the design and optimization of the support spring for highly reliable sprag clutches.

Improving the efficiency of the coal grinding process in ball drum mills at thermal power plants

Ensuring the reliable operation of the dust fuel preparation system at thermal power plants (TPP) is a topical issue since it determines the energy strategy of any country that fires coals for thermal energy production. This unit is one of the most energy-intensive units in TPP. Those systems are outdated, poorly automated and high energy-intensive. Furthermore, they must ensure efficient and safe operation of the facility while being environmentally friendly. The current work focuses on the process of grinding coals in ball drum mills for further pulverized combustion. An experimental study was performed in order to determine the main factors (rotational speed of the drum mill, the degree of loading with the grinding balls, and the velocity of the supplied air) that affect the efficiency of the fuel preparation system. The obtained experimental data and performed mathematical modeling resulted in regression equations describing the energy performance of the mill. Three regression equations for mill productivity, power consumed, and specific surface area of the final product were obtained and validated. The study reveals that the lowest specific energy consumption is achieved when the relative rotational speed of the mill is between 0.81 and 0.87; the weighted average diameter of the balls ranges from 33.5 up to 34.5 mm; the load factor of the grinding media ranges from 0.325 up to 0.335, the supplied air velocity is between 0.2 and 0.3 m/s. The proposed methodology allows adjustment of the operating parameters of the grinding process to achieve the lowest energy consumption. The power consumption for the preparation can be reduced up to 5 % for the selected operation mode of the grinding facility.

Action and Contribution of the Iliopsoas and Rectus Femoris as Hip Flexor Agonists Examined with Anatomical Analysis.

To evaluate the difference in action between the iliopsoas and rectus femoris muscles in hip flexion by estimating the relative contribution to the maximal hip flexion torque and relative rotation speed. We examined 22 lower limbs of 10 male and 12 female formaldehyde-fixed adult Japanese cadavers. Using morphometric data from cadaver dissections, we calculated the moment arm length and physiological cross-sectional area for each muscle. We considered moment arm length and physiological cross-sectional area as indices of the maximal torque and compared them among the muscles at various hip joint angles. To evaluate the relative rotation speed, we calculated the increase of the hip joint angle for a 1% reduction of the muscle fiber length in each muscle. The rectus femoris contributed approximately 2/3 to the flexion torque in mild flexion up to 60°, whereas the iliopsoas contribution increased sharply beyond 60°. The relative iliopsoas rotation speed was 2.5- to 3-times higher than that of the rectus femoris in mild flexion up to 60° under the specific condition that each muscle had the same muscle contraction speed. We found that the iliopsoas served as a rapid flexor, while the rectus femoris was a powerful flexor.

Studying phase formation of 12Х18Н10Т alloy and copper after friction welding

The technology of joining alloy 12X18H10T and copper has been studied. The use of friction welding is proposed. Modern development of technology requires the use of new technologies and materials. Despite the increase in the use of composite materials, and especially on the basis of the polymer matrix, metal alloys remain indispensable. Due to their physical and mechanical properties, metal-based alloys are used in rocket and space technology, mechanical engineering, and other industries. Goal. The aim of this work is the reason for the decrease in the mechanical properties of the connection 12Х18Н10Т – М1, which were obtained under suboptimal conditions. Friction welding was developed in early 1956 in the USSR. Since the 1960s, other countries have also begun to develop friction welding. This tool is a type of pressure welding, during which the metal is heated by friction of one of the parts of the product. At the end of the process, the final connection takes place. This type of welding is used in aircraft construction, rocketry, machine building, etc. In Ukraine, research in this direction is conducted at the Eugene Paton Institute of Electric Welding. The parameters of the friction welding technological process are considered. Results. The samples of welded joints 12Kh18N10T + M1 were studied. The following methods were used: mechanical tests; metallographic and electro-microscopic studies; hardness measurements; micro-X-ray spectral study. Originality. Welding joints with low strength were investigated; they were obtained for the following parameters: relative rotation speed 0.4 m/s, pressure during heating 80 MPa, pressure during forging 80 MPa, upset value 9 * 10-3 m samples with low strength varied in the deformed layer of steel from the joint surface to the base metal from 3240 MPa to 2450 MPa; in a deformed copper layer from 1020 MPa to 690 MPa. On samples that had high strength, the microhardness varied on the steel side from 2260 MPa in the contact surface to 2160 MPa, and in copper from 590 MPa to 460 MPa. Fig. 1 shows the microstructure of the deformed zones of the welded joint 12X18H10T, obtained according to the optimal parameters. Practical value. The reason for the decrease in the mechanical properties of the 12Х18Н10Т – М1 joint was established.

Gear‐shifting control of non‐synchronizer electric‐driven mechanical transmission with active angle alignment

AbstractNon‐synchronizer electric‐driven mechanical transmission (EMT) has advantages of low cost and simple mechanical structure, which is a key assembly in electric vehicles. In such an system, as the synchronizer is removed from the mechanical transmission, big impacts between the sleeve and clutch gear arise during a gear shift, which cause a long power‐off interruption. In this article, our contribution is to propose a novel control strategy to avoid impacts by achieving both zero relative rotational speed and angle differences between the sleeve and clutch gear. To obtain this strategy, we first derive the dynamic model of the gear‐shifting process as a hybrid automaton (HA) model. Based on the HA model, we can see that impacts can be eliminated when the rotational speed and angle differences become zeros. Then, to obtain zero rotational speed and angle differences and reduce the gear‐shifting time, a time‐optimal control law to synchronize the rotational speed and angle is first solved based on Pontryagin's minimum principle. Meanwhile, to resolve the solution difficulty brought by the period‐varied rotational angle difference, we introduce an optimal initial angle difference, and then use an incremental angle difference to replace the period‐varied one. Based on that, a model tracking strategy is proposed to enhance the system's antidisturbance capacity. For the gear‐shifting actuator, a dual bang‐bang control law is solved to save the gear‐shifting time. Finally, we carry out simulations and bench tests to validate the control strategy. Results show that the control strategy can indeed reduce impacts and power‐off time.

Super‐Durable, Low‐Wear, and High‐Performance Fur‐Brush Triboelectric Nanogenerator for Wind and Water Energy Harvesting for Smart Agriculture

AbstractThe triboelectric nanogenerator (TENG), as a promising energy harvesting technology, provides a new approach for the realization of the Internet of Things (IoTs). However, material abrasion severely limits its practical applications because of the deterioration in mechanical durability and electrical stability. Here, naturally available animal furs are introduced, owing to their superiorities of extremely low wear, high performance and humidity resistance. More than 10 times the electric output is observed relative to the conventional TENG, even at low driving torque. The transferred charge of fur‐brush TENG (FB‐TENG) exhibits only 5.6% attenuation after continuous operation for 300 000 cycles, maintaining high output performance even if the relative humidity increases up to 90%. Furthermore, a counter‐rotating structure is first designed to further increase the output by doubling the relative rotation speed. Based on this mechanism, a significantly elevated output current of 36.6% is obtained in ambient conditions. Finally, self‐powered automatic irrigation, weather monitoring and wireless water level warning multifunctional management systems are realized by collecting the wind and water flow energy. This work provides a strategy of reducing wear on the premise of high performance, which lays a foundation for effective environmental energy harvesting toward practical applications in big data and the IoTs.

Автоматизований контроль механічних параметрів дводвигунового електропривода похилого дифузійного апарата

The article is devoted to the mechanical parameters automated control method development. Control object is the two-engine electric drive of an inclined diffusion apparatus. It is shown that in production conditions, the traditional automated control system, equipped with only electrical parameters control system, does not meet the requirements for the reliability of the two-engine electric drive with elastic bonds in the kinematic circuit. Structural schemes of two-motor electric drive`s relative rotation angle and speed control methods are developed. Theoretical evaluation of metrological characteristics of the proposed measuring channels was carried out, its static characteristics were constructed, and quantization errors were determined. It was established that the quantization error of the measuring channel is directly proportional to the mark number of engine shaft rotation sensors. Therefore, the optimal number of marks for means of mechanical parameters control was determined, which would ensure the necessary reliability of control. The algorithms of two-motor electric drive`s relative rotation angle and speed automated control are developed, the production implementation results of developed control means based on theoretical research are presented. Experimental studies of the two-motor electric drive`s relative rotation angle and speed automated control work, which showed the complete adequacy of measurement, both the speed of engines rotation and their shafts relative rotation angle, were carried out. The real metrological characteristics of these means correlate with theoretical developments. With the help of developed control means, experimental time charts were obtained that illustrate the operation of an inclined diffusion apparatus two-engine electric drive, in transient gear modes associated with the presence of an elastic-dissipative connection between the drive engines and the uneven distribution of torque between them. Preliminary theoretical studies of the dynamic properties of such an electric drive system have been experimentally confirmed.

Design development of technological complex for friction welding of thin-walled products made of armlen

In this paper, we present the results of engineering design of a technological complex for friction welding of thin-walled products from armlen. We have also analyzed welding methods for plastic details. The main technological parameters of friction welding are: relative speed of welded surfaces rotation or linear velocity of the planes relative to each other; melting pressure for creating of a friction force; heating time; sediment pressure; cooling time of the weld. Each of these parameters depends on the material type and the shape of welded surfaces, assuming that absolutely flat surfaces are considered, since flatness does not strongly affect these parameters for thin-wall products. Further, welding technology of thin-walled parts from mineral-filled polypropylene (armlen) is offered, calculations of technological parameters of welding process are carried out and an electronic model of the complex is developed. On the basis of the electronic model and drawings, a prototype of the technological complex was made. Approbation of the complex on the example of gas-proof boxes production showed its high efficiency and prospects of its use for the whole class of thin-walled products from armlen.

The efficiency analysis of the SH-25A ball drum mill when grinding industrial products of fossil fuels

The working characteristics of a laboratory ball drum mill during grinding of Karaganda coal products were studied in order to apply the results obtained to industrial installations. The performed analysis shows that the most complicated and energy-intensive stage of preparation of coal dust is the grinding of fuel. The operational characteristics of the mill productivity, consumed electric power and specific energy consumption in terms of the relative rotational speed of the drum as well as the optimal values of the relative velocity determining the qualitative grinding of the fuel have been determined. The performance of the processed drum mill reaches its maximum at a relative speed of rotation of the drum 0.71 ensuring a waterfall mode of grinding of fuel related to the high-speed mode of a coal-grinding mill. The estimated specific energy consumption for fuel grinding varies in the range from 0.11 kWh/kg up to 0.23 kWh/kg at fuel milling coefficient of Kl = 1.2.

Theoretical Model and Experimental Research on Friction and Torque Characteristics of Hydro-viscous Drive in Mixed Friction Stage

The hydro-viscous drive (HVD) has been widely used in fan transmission in vehicles, fans, and scraper conveyors for step-less speed regulation or soft starting. In the mixed friction stage, the contact, friction, and torque characteristics of friction pairs are very complex and change at any time. The characteristics of the frictional and hydrodynamic lubrication states were studied in order to calculate and predict the friction and torque characteristics of the friction pairs in the mixed friction stage. The fluid torque was calculated by applying the average shear stress model and the load-carrying capacity of asperity was determined on the basis of the fractal contact theory. In addition, the contact friction coefficient of the friction pairs was taken into consideration and measured by using the MM1000-III friction and wear testing machine. The asperity friction torque and total torque in the mixed friction stage were obtained and finally, the test rig for the torque characteristics was set up. The results show that the contribution to the total torque is shared by the oil film and the asperity friction. The friction coefficient decreases sharply at first and then increases with a change in the relative rotational speed, following the Stribeck curve closely, and the contact frictional coefficient slowly decreases with increase in the pressure between the friction pairs. The torque between the friction pairs is provided by the asperity friction, and the torque due to the oil film reduces to zero. When the thickness of the oil film is small, a major contribution to the total torque is due to the asperity friction. The total torque also increases with the decrease in the film thickness ratio. Therefore, by theoretical analysis and experimental verification, the torque of the friction pairs in the mixed friction stage can be accurately calculated using the average shear stress model and asperity friction torque model.

Evaluation of microgeometry of cylindrical parts after cross-rolling in smooth plates

Hardening and finishing processing of cylindrical parts by transverse rolling in smooth plates was studied. The effect of the relative deformation and rotational speed of the workpiece on the main quality characteristics of the surface layer of hardened parts, such as diameter accuracy, roughness and ripples of the surface layer was determined experimentally. The results of the work offer a means for adopting the described method of cross-rolling for manufacturing of machine parts. The process in question can be implemented without the use of environmentally hazardous lubricating cooling technological means, which makes it possible to attribute it in the future to one of the types of green mechanical processing technologies.

Experimental research on cage dynamic characteristics of angular contact ball bearing

The dynamic performance and life of the precise bearing, even abnormal operation and early failure are affected directly by the complex and unstable motion of the cage. Based on the cage dynamic performance test device with controllable motion of inner and outer rings, respectively, the dynamic characteristics of the cage were studied under different rotating speeds and loads, while inner ring rotated with outer ring fixed and inner–outer rings rotated reversely. Then the trajectory of the cage mass center was drawn through experimental study. The three-dimensional space motions of cage reveal that, when only inner ring rotates, the trajectories of cage mass center are approximately circular under axial load, and the amplitude of the axial displacement raises with the increase of the rotation speeds. With the increase of radial loads, the cage mass center trajectories are shaking from a circle to a small area on the side of the bearing center. When the inner–outer rings rotate in the opposite direction, the rotation speed of the cage is greatly reduced, and the mass center trajectories of the cage oscillate irregularly on side of the bearing center. As the relative rotation speed of rings increases, the axial displacement fluctuation enlarges. With the increase of the radial loads, the axial fluctuation decreases.

Research on a rotational speed control strategy of the mandrel in a rotary steering system

AbstractRotary steering systems are cutting-edge, intelligent oil drilling and steering equipment developed at the end of the twentieth century. The core function of the bit pointing rotary steering system is to control the eccentric shaft with bit pointing function to track the outer drill collar for reverse rotation [1]. When the relative speed thereof is offset, the mandrel tool face remains stationary, and the directive function of the drill bit is realized [2]. Therefore, it is important to precisely control mandrel rotational speed and make it follow the outer drill collar to conduct face-to-face rotation at all times. A double closed loop control method for realizing rotational speed loop and position loop through controlling mandrel rotational speed is proposed in this paper. Relative rotational speed of drill bit shaft (or mandrel) and drill collar of zero can be realized within the shortest time, thereby realizing rapid and precise rotational speed tracking. Relative positions of mandrel and drill collar at several angles on 360° circumferences, thereby proving the feasibility of the method. The method can provide a technical reference and basis for prototype production of directional rotary steering system [3].

Matching Performance Prediction Between Core Driven Fan Stage and High Pressure Compressor

Abstract Based on the aerodynamic matching configuration between a core driven fan stage (CDFS) and high pressure compressor (HPC), matching state point correlation equations have been established in this paper. The radial nonuniformity of the CDFS outlet flow and the aerodynamic loss caused by complex flow structure between these two components are taken full account in the equations, and a high-accuracy prediction program for matching performance has been developed. Based on the experimental performance data of two components, matching performance prediction at given bypass ratio is made and compared with experimental results. The results show that: 1) The outlet temperature of CDFS varies with its state points change, which makes the relative corrected rotation speed of HPC in matching environment change, and the characteristic line of HPC is not based on the same relative corrected rotation speed. 2) The difference exists between the matching performance prediction results and experimental results. One reason is that CDFS performance varies in the component environment and the matching environment due to the different back pressure regulation modes; another reason is that this prediction method doesn’t consider the effect of the CDFS’s outlet flow nonuniformity on the HPC’s performance, but the maximum relative deviation of the flow rate is only 0.74 %.