Cycloidal Motion Research Articles

Study on hydrodynamic performance of multi-link cycloidal propeller

Cycloidal propellers are special propellers that can obtain a wide range of thrust in any direction without changing the propeller rotation speed or requiring the assistance of a rudder. They are typically installed on ships with high-mobility requirements. The implementation of pure cycloidal blade pitch control is complex, and there are a few control mechanisms capable of realizing these blade pitch motions. In this paper, a multi-link mechanism is designed to control the movement of the blades, and the relationships between blade pitch angle, linkage lengths, and their adjustment angles are established. The linkage lengths and their adjustment angles are solved using a genetic algorithm. The blade pitch angle controlled by the multi-link mechanism matches well with the pure cycloidal pitch angle after adjusting the linkage lengths and adjustment angles. The layout of linkages for the six-blade cycloidal propeller is designed to ensure that there is no motion interference between the linkages and their supporting shafts during operation. The open water hydrodynamic performance of the cycloidal propeller controlled by the multi-link mechanism and pure cycloidal pitch motion is analyzed using computational fluid dynamics. The simulation results indicate that the cycloidal propeller can achieve similar performance with different control mechanisms.

Kinematics Analysis and Gait Study of Bionic Turtle Crawling Mechanism.

Longer distance water delivery culverts pose obstacles such as deposited silt, stones, and dead trees. In this paper, a crawling robot is designed to mimic the joint structure of a turtle using bionic design principles. The mechanism and gait of the robot are analyzed. The kinematics model of the robot is established using the D-H method and analytical approach, while the dynamics model is established using Lagrange's method. Based on kinematics and dynamics analysis theory, compound cycloid and cubic polynomial motion trajectories for the robot foot are planned along with a crawling gait resembling that of a turtle's abdomen. Simulation experiments and scale prototype experiments confirm that when gait parameters are identical, the energy consumption of compound cycloid trajectory exceeds that of cubic polynomial foot trajectory. When planning these two types of foot trajectories, it was observed that energy consumption ratio decreases with increasing step length but increases with increasing step height.

Nomograms for maximum pressure angles in radial cams with follower eccentricity for cycloidal and harmonic motion curves

For an adequate design of radial cams with translating roller followers, it is necessary to maintain the constraint that maximum pressure angle cannot exceed the empirically accepted value of 30°. The direct calculation of this parameter is difficult and it is usually sought to reduce it by trial and error. Nomograms that exist so far only calculated this angle for cams with no eccentricity between follower and cam. This research presents two nomograms with this additional parameter, which allows for greater design freedom using all available variables. The charts are for cycloidal and harmonic motion curves, and can be used for their full and half curves. The study discusses the advantages of using nomograms and the methods to obtain low values of maximum pressure angle by satisfactorily combining available parameters. Although nomograms are no longer a widely used tool in the industry, they still have didactic functions in textbooks and could be useful for preliminary analysis in engineering projects.

Investigation of Surface Residual Stress for Medium Carbon Steel Quenched by YAG Laser with Extended Cycloidal Motion

This study investigated the surface residual stress for AISI 1045 steel quenched by a YAG laser. A coaxial laser spindle was installed on a CNC machine for the experiment. The laser motion was arranged to follow the path of an extended cycloid which widened the quenching area on the steel surface. Both the temperature distribution and the residual stresses were measured by thermocouples and a portable X-ray diffractometer, respectively. When the temperature distribution was cooled down near the value of the room temperature, the residual stresses were then measured after the laser quenching process. The diffractometer used a single exposure of X-ray with a two-dimensional detector to calculate the Debye–Scherrer ring (D-S ring) for the determination of the normal and shear stresses. Different laser powers were exploited for the measurement of residual stresses, including 500, 600, 700, and 900 watts. In addition to the experiment, an analytic model for the investigation of residual stresses was built by the finite element analysis for which MSC Marc was used. The assumption for the FEA was that the laser spot had a circular shape of uniform energy distribution and the thermal–elastic–plastic model was applied to the simulation for the laser quenching process. The analytic and experimental results for the surface residual stresses had excellent consistency with a maximum difference of 10.5% from the normal stresses. The numerical results for the residual stresses also revealed that the normal stresses were compressive for the laser-quenching treatment and the shear stress could be neglected compared to the normal stress.

Electron Population Analysis Techniques for Understanding Fundamental Cross-Field Electron Device Physics

Two techniques have been developed to analyze and visualize electron populations in particle-in-cell (PIC) simulations. One generates normalized probability distributions of the electron population’s position and velocity and shows the changes in these distributions over time. The second generates radial and azimuthal breadth ratios of the electron population. In the magnetron studied, these ratios quantify the electron population’s internal support for charge transfer and the level of cycloidal motion of the electron population. These techniques reveal information not seen in conventional electron distribution and history plots, including insights into magnetron startup.

A Novel Fish-Inspired Robot with a Double-Cam Mechanism

Fishes have evolved different excellent swimming strategies. To study the influence of tail fin swing on the swimming performance of bionic robot fish, with one joint under the same tail swing frequency and amplitude, we designed a novel robot fish, driven by a double-cam mechanism. By designing the profile of the cam in the mechanism, the robot fish can achieve different undulatory motion trajectory of the caudal fin under the same tail swing frequency and amplitude. The mechanism simulated the undulatory motion of crucian carp. We studied the influence of undulatory motion on the swimming speed of robot fish, which was analyzed by dynamic analysis of the undulatory motion and experiments. According to the experimental results, we can find that the swimming speed of the robotic fish is different under various wave motions. When other conditions are the same, the speed that the robot fish can achieve by imitating the swing motion of the real fish is 1.5 times that of the robot fish doing the cycloid motion. The experimental results correspond to the kinetic analysis results. Furthermore, it is proven that the robot fish with a low caudal peduncle stiffness swims faster under a low swinging frequency, and the speed of a robot fish with a high caudal peduncle stiffness is higher under a high tail swinging frequency.

Development of the shape of the cam profile of mechanical yam vibrator using cycloid motion

At a high frequency of vibration; the cam of a vibrator always encounters the issue of jamming or the follower rolling off or losing contact with the cam when the appropriate design is not carried out. This study, therefore, developed the shape of the cam profile of mechanical yam vibrator using cycloid motion in the South. Displacement equations from the base circle to the cam profile were developed to obtain the shape of the cam using cycloid motion. A vibrometer was used to evaluate the developed 5 mm, 10 mm, and 20 mm cam sizes installed in a mechanical yam vibrator. The maximum displacement recorded for 5 mm, 10 mm and 20 mm cam sizes were 4.47 mm, 8.71 mm, and 14.54 mm respectively for low (1 – 5 Hz) frequency; 4.58 mm, 8.84 mm and 16.34 mm respectively for medium (60 – 100 Hz) frequency; and 4.66 mm, 9.09 mm and 17.30 mm respectively for high (150 – 200 Hz) frequency. This study shows that a cycloid cam would operate smoothly at low, medium, and high frequencies of vibration and function properly for frequency and displacement of vibration up to 200 Hz and 20 mm respectively without jamming and failing. A cycloid cam is therefore recommended for low, medium, and high frequencies motion of vibration.

Sensor-less and time-optimal control for load-sway and boom-twist suppression using boom horizontal motion of large cranes

Load-sway and boom-twist should both be considered in motion control given that a large crane typically has a long lattice boom. Hence, this study first analyzes the load-sway and boom-twist (vibration) of an actual crawler crane, and proposes a new dynamics model considering the above vibration. To ensure safety, sudden acceleration/deceleration is prohibited while controlling the motion of large crane. In addition, real time measurement and feedback of vibration is generally difficult. Hence, this study proposes a vibration sensor-less control based on a cycloidal motion trajectory with smooth acceleration/deceleration. Two-dimensional load-sway can be suppressed only by boom horizontal motion for simple implementation. Time optimality is also considered in the motion trajectory design in order to ensure operational efficiency. Experimental results demonstrate the effectiveness of the proposed approach.

Analytical solutions and computational nomograms for maximum pressure angle for cam mechanisms for full and half cycloidal and harmonic motion curves

High pressure angles in cams with roller followers still pose as a problem in cam projects. The main objective of this work is to deduce the maximum pressure angle equations for full and half cycloidal and harmonic motion curves for translating roller followers in radial cams and create nomograms that can calculate this parameter by simply connecting two points by a straight line in a chart. The nomograms were made for the mentioned curves via an open source software and it is discussed the limitations of the given charts and the advantages of using the current method. Additionally, the paper reinforces the need for authors to make it clear that another well known and frequently used nomogram cannot be used as is for half curves. Although use of nomograms has fallen into disuse, it still has applications in textbooks and quick preliminary analysis in real life projects.

An experimental and numerical analysis of the dynamic variation of the angle of attack in a vertical-axis wind turbine

Simulation methods ensuring a level of fidelity higher than that of the ubiquitous Blade Element Momentum theory are increasingly applied to VAWTs, ranging from Lifting-Line methods, to Actuator Line or Computational Fluid Dynamics (CFD). The inherent complexity of these machines, characterised by a continuous variation of the angle of attack during the cycloidal motion of the airfoils and the onset of many related unsteady phenomena, makes nonetheless a correct estimation of the actual aerodynamics extremely difficult. In particular, a better understanding of the actual angle of attack during the motion of a VAWT is pivotal to select the correct airfoil and functioning design conditions. Moving from this background, a high-fidelity unsteady CFD model of a 2-blade H-Darrieus rotor was developed and validated against unique experimental data collected using Particle Image Velocimetry (PIV). In order to reconstruct the AoA variation during one rotor revolution, three different methods-detailed in the study-were then applied to the computed CFD flow fields. The resulting AoA trends were combined with available blade forces data to assess the corresponding lift and drag coefficients over one rotor revolution and correlate them with the most evident flow macro-structures and with the onset of dynamic stall.

How to extract the angle attack on airfoils in cycloidal motion from a flow field solved with computational fluid dynamics? Development and verification of a robust computational procedure

One of the key problems faced by researchers dealing with Computational Fluid Dynamics simulations and rotating machines is represented by how to extract the angle attack from a numerically computed flow field. If this issue has been addressed successfully for some applications, in case of airfoils moving in cycloidal motion (i.e. having a rotational motion within a rectilinear flow field, like in Darrieus Vertical-Axis Wind Turbines) some proposals do exist, but always affected by some arbitrary choices on the velocity probing that are not supported by a proper verification. The aim of the present study is to try finding a robust computational procedure tailored for the scope. To this end, three different post-processing methods - detailed in the study – were considered and applied to the flow fields of 2-blade H-Darrieus rotor, coming from a high-fidelity unsteady model based on Computational Fluid Dynamics; the resulting blade angle of attack trends over one rotor revolution were then combined with available blade forces data to assess the corresponding lift and drag coefficients. In order to assess the actual accuracy of these approaches for a stable tip-speed ratio, the post-processed force coefficients were compared to the ones computed via a numerical pitching airfoil model, which received the sampled angle of attack trends as input; eventually, the pitched lift and drag values have been used to reconstruct the blade forces over one rotor revolution and compare them with the ones coming from full turbine simulations. Results show large scattering of obtained data, remarking the importance of the proper selection of the angle of attack sampling strategy for the analysis of turbine performance. Overall, the “LineAverage” approach, i.e. the use of multiple sampling points around the airfoil for velocity probing, has proved to be the most accurate method.

Numerical Analysis on the Effectiveness of Gurney Flaps as Power Augmentation Devices for Airfoils Subject to a Continuous Variation of the Angle of Attack by Use of Full and Surrogate Models

The disclosing of new diffusion frontiers for wind energy, like deep-water offshore applications or installations in urban environments, is putting new focus on Darrieus vertical-axis wind turbines (VAWTs). To partially fill the efficiency gap of these turbines, aerodynamic developments are still needed. This work in particular focuses on the development of a mathematical model that allows predicting the possible performance improvements enabled in a VAWT by application of the Gurney flaps (GFs) as a function of the blade thickness, the rotor solidity and geometry of the Gurney flap itself. The performance of airfoil with GFs was evaluated by means of detailed simulations making use of computational fluid dynamics (CFD). The accuracy of the CFD model was assessed against the results of a dedicated experimental study. In the simulations, a dedicated method to simulate cycles of variation of the angle of attack similar to those taking place in a cycloidal motion (rather than purely sinusoidal ones) was also developed. Based on the results from CFD, a multidimensional interpolation based on the radial basis functions was conducted in order to find the GF design solution that provides the highest efficiency for a given turbine in terms of airfoil and solidity. The results showed that, for the selected study cases based on symmetric airfoils, the GF positioned facing outwards from the turbine, which provides the upwind part of the revolution, can lead to power increments ranging from approximately 30% for the lower-solidity turbine up to 90% for the higher-solidity turbine. It was also shown that the introduction of a GF should be coupled with a re-optimization of the airfoil thickness to maximize the performance.

Reference-frames in vision: Contributions of attentional tracking to nonretinotopic perception in the Ternus-Pikler display.

Perception depends on reference frames. For example, the "true" cycloidal motion trajectory of a reflector on a bike's wheel is invisible because we perceive the reflector motion relative to the bike's motion trajectory, which serves as a reference frame. To understand such an object-based motion perception, we suggested a "two-stage" model in which first reference frames are computed based on perceptual grouping (bike) and then features are attributed (reflector motion) based on group membership. The overarching goal of this study was to investigate how multiple features (i.e., motion, shape, and color) interact with attention to determine retinotopic or nonretinotopic reference frames. We found that, whereas tracking by focal attention can generate nonretinotopic reference-frames, the effect is rather small compared with motion-based grouping. Combined, our results support the two-stage model and clarify how various features and cues can work in conjunction or in competition to determine prevailing groups. These groups in turn establish reference frames according to which features are processed and bound together.

Numerical analysis on effects of blade number on hydrodynamic performance of low-pitch marine cycloidal propeller

Marine cycloidal propeller, as a special type of marine propulsion system, is used for ships that require high maneuverability, such as tugs and ferries. In a marine cycloidal propeller, the thrust force is generated by rotation of a circular disk with a number of lifting blades fitted on the periphery of the disk, so that the propeller axis of rotation is perpendicular to the direction of thrust force. Each blade pitches about its own axis, and the thrust magnitude and direction can be adjusted by controlling the pitching angle of the blades. Therefore, the propulsion and maneuvering units are combined together and no separate rudder is needed to maneuver the ship. Two configurations of marine cycloidal propeller have been studied and developed based on propeller pitch: low-pitch propeller (designed for advance coefficient less than one, means λ < 1) and high-pitch propeller (designed for λ > 1). Low-pitch marine cycloidal propellers are used in applications with low-speed maneuvering requirements, such as tugboats and minesweepers. In this study, the effects of blade number on hydrodynamic performance of low-pitch marine cycloidal propeller with pure cycloidal motion of the blades are investigated. The turbulent flow around marine cycloidal propeller is solved using a 2.5D numerical method based on unsteady Reynolds-averaged Navier–Stokes equations with shear-stress transport k–ω turbulent model. The presented numerical method was validated against experimental data and showed good agreement. The results showed that the thrust coefficient of marine cycloidal propeller generally decreases by increasing the blade number, whereas the torque coefficient increases. Consequently, the hydrodynamic efficiency of marine cycloidal propeller drops as the blade number increases.

Efficacy of proposed 2DEG-based photoconductive antenna using magnetic bias-controlled carrier transport

An externally applied magnetic field was used to induce increased photocarrier transport along the high mobility channel in GaAs/AlGaAs modulation-doped heterostructures (MDH). The terahertz (THz) emission from GaAs/AlGaAs MDH increases with increasing magnetic field, applied parallel to the heterojunction. The THz emission enhancement factors due to the magnetic field in MDH are higher than in undoped GaAs/AlGaAs heterojunction and in bulk SI-GaAs. This demonstrates that properly utilizing the high-mobility channel for carrier transport promises to be a viable design consideration for efficient THz photoconductive antenna (PCA) devices. Moreover, it was observed that for MDH, as well as for an undoped GaAs/AlGaAs heterojunction, the enhancement for one magnetic field direction is greater than the enhancement for the opposite direction. This is in contrast to the symmetric enhancement with magnetic field direction observed in a bulk SI-GaAs. An analysis of photocarrier trajectories under an external magnetic field supports the explanation that the enhancement asymmetry with magnetic field direction in MDH is due to the cycloid motion of electrons as affected by the GaAs/AlGaAs interface.

Exchange Processes Induced by Large Horizontal Coherent Structures in Floodplain Vegetated Channels

AbstractMangrove forests along the Mekong delta estuaries are usually observed to degrade together with the increasing extension of fish farms. In this limited‐width condition, the formation of coherent structures, their interactions with mangroves, the role of the width of the mangrove forest, and their effects on the exchange processes between the open channel and the adjacent floodplain are still not well examined. In order to obtain more insight, a unique laboratory experiment of a vegetated compound channel mimicking estuarine mangroves has been conducted. The results show that in a compound vegetated channel with a very gentle transverse slope, the vegetated shear layer dynamics resembled that associated with vegetation rather than that associated with a depth differential. Furthermore, the flow field under the effect of large horizontal coherent structures (LHCSs) shows a spatially and temporally cycloid motion with associated flow events, namely, sweep, ejection, stagnant, and reverse flows. It is also suggested that the coherent structures can have an influence on a broader area than the vegetation area into which the eddy structures can penetrate. In terms of the exchange processes, the momentum transfer and the intensity of transverse fluctuations induced by the LHCSs can be related to this phenomenon. Consequently, decreasing the mangrove width can significantly affect the pattern of the LHCSs, disturb the transverse exchange processes induced by these structures, and thereby changing the shear layer, creating unfavorable conditions for sedimentation inside forests and for river bank stability.

On the use of Gurney Flaps for the aerodynamic performance augmentation of Darrieus wind turbines

Gurney Flaps (GFs) can enhance the aerodynamic performance of airfoils, making them generate more lift and delaying the onset of stall. Since their potential was discovered in the early ‘70 s, GFs have been applied in several fields, including wind turbines. Here, the research has been focused mostly on the use of GFs in Horizontal Axis Wind Turbines (HAWTs), whereas a lack of studies involving the application of these devices on Darrieus Vertical-Axis Wind Turbines (VAWTs) is apparent in the literature. The benefits induced by GFs could actually be particularly interesting for this type of wind turbines, which are presently receiving a renewed attention from the industry.In the present work, an extended numerical analysis using Computational Fluid Dynamics (CFD) was carried out with the aim of evaluating the potential of using Gurney Flaps for the power augmentation of Darrieus wind turbines.After a validation of the numerical approach using wind tunnel experimental data on a static airfoil, the simulations have assessed the impact of different GF mounting and height on board airfoils moving in the cycloidal motion typical of Darrieus wind turbines. The results on a single rotating airfoil allowed the analysis to highlight the physical phenomena taking place past the rotating blades, including the delay of stall and the modifications induced on the surrounding flow field; power enhancements higher than 20% were shown for some configurations. Then, impact of GFs on a real three-blade turbine was analyzed. The best configuration resulted in a 2%c GF installed in the inner side of the airfoil, so to have a better torque extraction in the downwind half of the revolution. The GF benefits were apparent especially at lower tip-speed ratios, suggesting its use both for newly-designed turbines and even as a retrofitting solution in existing rotors.

A 2.5D numerical study on open water hydrodynamic performance of a Voith-Schneider propeller

Marine cycloidal propeller (MCP) is a special type of marine propulsors that provides high maneuverability for marine vessels. In a MCP, the propeller axis of rotation is perpendicular to the direction of thrust force. It consists of a number of lifting blade. Each blade rotates about the propeller axis and simultaneously pitches about its own axis. The magnitude and direction of thrust force can be adjusted by controlling the propeller pitch. Voith-Schneider propeller (VSP) is a low-pitch MCP with pure cycloidal blade motion allowing fast, accurate, and stepless control of thrust magnitude and direction. Generally, low-pitch cycloidal propellers are used in applications with low speed maneuvering requirements, such as tugboats, minesweepers, etc. In this study, a 2.5D numerical method based on unsteady RANS equations with SSTk-ωturbulent model was implemented to predict the open water hydrodynamic performance of a VSP for different propeller pitches and blade thicknesses. The numerical method was validated against the experimental data before applying to VSP. The results showed that maximum open water efficiency of a VSP is enhanced by increasing the propeller pitch. Furthermore, the effect of blade thickness on open water efficiency is different at various advance coefficients, so that the maximum efficiency produced by the VSP decreases with increasing blade thickness at different propeller pitches.

Gamma-ray vortices emitted from nonlinear inverse Thomson scattering of a two-wavelength laser beam

We develop a classical theory of nonlinear inverse Thomson scattering of a two-wavelength laser beam, which is valid for laser beams with linear or circular polarization and arbitrary intensity and wavelength. We reveal that an electron inside a circularly polarized two-wavelength laser field undergoes a cycloid motion in the transverse plane and radiates an electromagnetic wave forming a spiral phase structure. Its photon energy is proportional to a linear combination of the product between the initial laser photon energies $\ensuremath{\hbar}{\ensuremath{\omega}}_{01}$ and $\ensuremath{\hbar}{\ensuremath{\omega}}_{02}$, and their harmonic numbers ${n}_{1}$ and ${n}_{2}$, namely, ${n}_{1}\ensuremath{\hbar}{\ensuremath{\omega}}_{01}+{n}_{2}\ensuremath{\hbar}{\ensuremath{\omega}}_{02}$. The orbital angular momentum of a photon due to the spiral phase structure is given by $({n}_{1}+{n}_{2}\ifmmode\pm\else\textpm\fi{}1)\ensuremath{\hbar}$. We show that a combination of two wavelengths differing by one order of magnitude or more is advantageous for producing gamma rays carrying a large orbital angular momentum of $\ensuremath{\sim}10\ensuremath{\hbar}$. Moreover, this work indicates that a helical undulator with two magnetic periods is capable of producing photons with a large orbital angular momentum. This radiation process plays an important role in the development of optical vortex beams and even in astrophysical environments.

Implementation of the “Virtual Camber” Transformation into the Open Source Software QBlade: Validation and Assessment

Thanks to the renewed interest in vertical-axis wind turbines, research efforts are devoted at improving the accuracy of present simulation tools, many of which are underdeveloped if compared to those for horizontal-axis turbines. In particular, recent studies demonstrated that a correction for the “virtual camber” effect has a major impact on the simulation. In cycloidal motion indeed the blade aerodynamics are equivalent to those of a virtually-transformed airfoil with a camber line defined by its arc of rotation. In this study, the implementation of a specific module to account for the virtual camber effect in the Open-Source code QBlade is presented. The effectiveness of the model is then validated by four 1-blade and a full 3-blade H-Darrieus turbines, for which both experimental measurements and detailed CFD calculations were available. A sensitivity analysis on the impact of the virtual camber correction on the accuracy of a low-order simulation model has been carried out as a function of the chord-to-radius ratio and the airfoil thickness-to-chord ratio. Reference thresholds for the model applicability are presented for both variables.