Unidirectional Rotation Research Articles

Numerical analysis and wave tank validation on the optimal design of a two-body wave energy converter

To improve the performance of a ‘point absorber’ type wave energy converter (WEC), an additional submerged body can be deployed. The submerged body can be used to increase the equivalent excitation force on the WEC, as well as provide resonance tuning. This paper presents numerical analysis and experimental validation of a two-body point absorber type WEC using a mechanical motion rectifier (MMR) based power takeoff. The two-body point absorber consists of a floating buoy connected to a neutrally buoyant submerged body via the power-takeoff. The mechanical motion rectifier and a ball screw translate the relative heave motion of the two bodies into unidirectional rotation, which in turn spins a generator. Frequency domain analysis suggests there is an optimal submerged body mass for maximum WEC power absorption. Regular wave simulations in the time domain are compared to the results obtained in the frequency domain. While the time domain and frequency domain results predict the same optimal mass ratio, time domain analysis provides a more complex and accurate power result. To validate the time domain model, experimental wave tank testing is conducted using a 1:30 scale model WEC. The experiment shows the two-body WEC can produce twice the amount of power as the single-body WEC with same floating buoy and can be further increased by PTO design and power electronics optimization. Wave tank testing also shows the two-body WEC has a capture width ratio up to 58% at 59 kW/m and 51% at 36 kW/m.

Analysis of particle movement in the velocity layer on rotating surfaces

Experiments on rotating in the air cones with vertex angle β=120∘ and the flat disc (i.e. a cone with β=180∘) show that for frequencies Ω ≥ 150 rpm projections of the particles' trajectory on a horizontal plane are close to a logarithmic spiral. The analysis of this approximating function and the results of the physical modeling, which helped to determine the coefficient dependence of the particles’ near-surface resistance CD* when moving in the viscous fluid (air), demonstrated that the particles do neither slide nor roll on the surface of the rotary heat exchangers. The average distance between a single particle and the surface is less than but comparable to the thickness of the stationary near-surface velocity layer of the viscous fluid, the thickness of which is at least 10 times greater than the size of the particles. When subjected to the gravity field and the centrifugal force, particles are “jumping” on the surface, the height of these “jumps” being approximately equal to the displacement thickness of the velocity layer. The movement of the particles alongside the normal to the surface as well as their unidirectional rotation under the influence of the velocity gradient in the velocity layer lead to the mass exchange between the layers of the viscous fluid; consequently they intensify the heat abstraction from the hot surface and its transfer to the air and the particles. These factors lead to the reduction of the heating time of the particles and the increase the quality of the flash-products.

Design of energy harvester using rotating motion rectifier and its application on bicycle

The energy harvester has been employed to transform mechanical vibration into electrical power in the field of road transportation. An electromagnetic energy harvester for bicycle application to recycle low-frequency vibration is proposed. The input of up-down motion is transformed into bidirectional rotation by the transmission part, and then translated into unidirectional rotation by the rotating motion rectifier. The rectifier outputs rotation to the generator, and the electrical energy generated can be stored in super capacity at the charging mode or light up the LED at the discharging mode. Lab experiments are conducted to test the proposed harvester on Instron servo-hydraulic machine. A power of 0.491 W and a total efficiency of 52.8% are achieved with sinusoidal displacement inputs from 1.0 Hz to 2.5 Hz and external resistors from 50 Ω to 200 Ω. Field tests of applying the harvester onto the bicycle are carried out and a power of 0.313 W is obtained when riding through the speed bump. Above tests demonstrate potential applications of the harvester in self-powered devices.

A Prospective Ultrafast Hemithioindigo Molecular Motor

AbstractThe maximum speed of light‐driven molecular motors is an important key‐property governing not only their overall performances but also many advanced functions. Currently, special emphasis lies on increasing the rate of unidirectional rotations to surpass natural systems and harness the full potential of artificial motors. Herein, we report a new molecular setup for a prospective light‐powered three‐step motor based on the hemithioindigo chromophore. Comprehensive quantum chemical treatment predicts a very low energy barrier for the only thermal ratcheting step in the unidirectional 360° rotation. Thus an ultrafast motion in the THz range could be possible with this motor at high light intensities and consequently a precise control of rotation speeds solely by light intensity variations could potentially be achieved. Experimental analyses using X‐ray crystallography and solution spectroscopy deliver first insights into the working mechanism and show that visible‐light photoswitching is feasible in both stable switching states. Additionally, significant alterations of the ground‐state energies can be induced by pH changes without hampering photoswitching capabilities.

An inspection path optimization of impeller for balancing efficiency and accuracy

On-machine inspection becomes a trend for obtaining the real shape of the workpiece in adaptive machining. Troubled by the overlapping structure of the impeller, and the positioning error from the rotary axes of the machine tool, it is a challenge to generate an on-machine inspection path to balance efficiency and accuracy. Reducing inspection path helps to reduce the occupied time of the machine tool. Thus, to let the stylus needn’t leave the impeller’s channel during the inspection, the accessible space of whole inspection path is addressed in path generation. In order to improve accuracy, the inspection error affected by the positioning errors of the rotary worktable is discussed. Furthermore, the error differences of the unidirectional and bidirectional rotations of the rotary axes are considered in path generation. By the stylus orientation optimization, the bidirectional rotations of rotary axes are prevented as much as possible. At last, the effectiveness of improving inspection efficiency and accuracy is verified by the impeller on-machine inspection. The inspection time can be reduced to less than 40% of traditional inspection, and the inspection error can be decreased 0.008 mm at least.

Modeling and field-test of a compact electromagnetic energy harvester for railroad transportation

To enable the smart technologies and safe operation of transit and rail transportation, such as hot box detector, track health monitoring and wireless communication on the railroad side, a cost-effective energy source is in need. This paper presents the design, modeling, in-lab experiment and field-test results of a compact ball-screw based electromagnetic energy harvester with a mechanical motion rectifier (MMR) mechanism for smart railway transportation. The MMR mechanism is realized by the embedded one-way clutches in the bevel gears, which converts the bi-directional track vibration into the unidirectional rotation of the generator. Compared to previous designs, the proposed harvester has reduced backlash and thus can harvest energy from a small input of the track deflection induced by the moving train. Two prototypes with different key design parameters were built and tested. A comprehensive model considering the train-rail-harvester interaction was developed to analyze the dynamic characteristics of the coupled system and predict the energy harvesting performance of the harvesters at different train speeds. Both in-lab and field tests were carried out to examine the energy harvesting performance of the harvesters and validate the model. Field test results illustrated that an average power of 1.12 W and 2.24 W were achieved for two prototypes respectively when a Type A rapid transit passed by with a 30 km/h vehicle speed.

Molecular Crankshaft Effect Converting Piston-like Molecular Motion to Continuous Rotation of Macro Objects.

A molecular system inducing an accumulative unidirectional rotation motion of glass flakes with about 100 μm in size is introduced. The molecular system is a chiral nematic liquid crystal containing a chiral azobenzene derivative which shows a reversible E- Z photoisomerization accompanying a large helical twisting power change. A film of the molecular system shows different texture change paths upon UV and visible light irradiations inducing " E to Z" and " Z to E" photoisomerizations, respectively, of the chiral azobenzene dopant. Namely, a polygonal fingerprint texture inducing the rotation of glass flakes on the film surface was maintained during UV irradiation, while a focal conic texture inducing no rotation of glass flakes emerged during visible light irradiation. As a result, cycles of the alternative irradiation of UV and visible lights afforded many rotations toward a single direction of the glass flakes which can be considered as a continuous conversion of light energy to mechanical work. We may compare the effect of this molecular system converting "back and forth" structural change between E and Z isomers of the chiral azobenzene to a continuous rotational motion of glass flakes with the crankshaft effect converting a piston-like motion to a rotational motion seen in engines in the real world.

Unidirectional rotary motion in a metal-organic framework.

Overcrowded alkene-based light-driven molecular motors are able to perform large-amplitude repetitive unidirectional rotations. Their behaviour is well understood in solution. However, Brownian motion precludes the precise positioning at the nanoscale needed to harness cooperative action. Here, we demonstrate molecular motors organized in crystalline metal-organic frameworks (MOFs). The motor unit becomes a part of the organic linker (or strut), and its spatial arrangement is elucidated through powder and single-crystal X-ray analyses and polarized optical and Raman microscopies. We confirm that the light-driven unidirectional rotation of the motor units is retained in the MOF framework and that the motors can operate in the solid state with similar rotary speed (rate of thermal helix inversion) to that in solution. These 'moto-MOFs' could in the future be used to control dynamic function in crystalline materials.

Towards molecular motors in unison.

Built-in molecular motors in a porous crystal show unidirectional rotary motion fuelled by light.

Blends of polycarbonate with polyethylene terephthalate glycol: compatibility of components, rheological and mechanical properties

The influence of the component ratio in the stabilized binary blends of amorphous polycarbonate (PC) and polyethylene terephthalate glycol (PET-G) on the compatibility of components, relaxation, rheological and mechanical properties was studied. The materials were prepared by reactive mixing of the components in the melt in a mixing rectifier based on a twin-screw extruder with unidirectional screw rotation. It is established that the components in the blends are mutually soluble over the entire range of their concentrations. The temperature of the а -process of relaxation (the glass transition temperature, Tg, in the mixtures) is in the interval between the values of Tg PC = 148.3 °C, Tg PET-G = 82.0 °C and obeys the Fox equation for single-phase blends. The mechanical characteristics of the mixtures change in a non-additive way when the concentration of the components is varied. In particular, in blends in which the PC content prevails, a significant increase in the upper yield limit is observed in comparison with the additive values, which, according to the relaxation spectrometry, is due to intense intermolecular interactions.

Needle Insertion Control Method for Minimizing Both Deflection and Tissue Damage

Because fine needles can easily be deflected, accurate needle insertion is often difficult. Lower abdominal insertion is particularly difficult because of less imaging feedback; thus, an approach for allowing a straight insertion path by minimizing deflection is beneficial in cases of lower abdominal insertion. Although insertion with axial rotation can minimize deflection, the rotational insertion may cause tissue damage. Therefore, we established a novel insertion method for minimizing both deflection and tissue damage by combining rotation and vibration. Using layered tissues, we evaluated the effect of a combination of rotation and vibration in terms of deflection and tissue damage, which were measured by the insertion force and torque, and the area of the hole created by the needle using histological tissue sections to measure tissue damage. The experimental results demonstrated that insertion with unidirectional rotation is risky in terms of tissue wind-up, while insertion with bidirectional rotation can decrease deflection and avoid wind-up. We also found that insertion with vibration can decrease the insertion force and torque. Therefore, insertion with a combination of bidirectional rotation and vibration can minimize needle deflection and tissue damage, including the insertion force and torque and the hole area.

USING SIMULATION TO STUDY CUTTING FORCE IN BIOPSY NEEDLE INSERTION WITH BI-DIRECTIONAL ROTATION

The rotational motion has been utilized in several medical needle technologies to enhance the capability of cutting tissue. The needle rotation helps significantly reduce the tissue cutting force, which improves procedure outcome and pain. However, the needle rotation can also incur tissue winding that intensifies tissue damage, which results in complications of bleeding and hematoma. Some histological observations showed that bidirectional needle rotation could reduce the tissue damage caused by tissue winding. In this study, we established a cohesive surface based finite element model to evaluate the cutting force in needle insertion with unidirectional and bidirectional rotation. The simulation results suggested that the frequency of switching direction of needle rotation insignificantly influences the cutting force. The Latin Hypercube method was used to generate a response surface of cutting force and locate the minimum at the insertion speed of 1[Formula: see text]mm/s combined with the slice/push ratio of 1.9. In clinical use, we suggested that the needle speeds can be first selected to optimize the cutting force according to the type of target tissue. If the desired needle rotation is high, a proper switching frequency can be applied to reduce the tissue winding damage without increasing the cutting force.

Current-induced rotations of molecular gears

Downsizing of devices opens the question of how to tune not only their electronic properties, but also of how to influence ‘mechanical’ degrees of freedom such as translational and rotational motions. Experimentally, this has been meanwhile demonstrated by manipulating individual molecules with e.g. current pulses from a Scanning Tunneling Microscope tip. Here, we propose a rotational version of the well-known Anderson-Holstein model to address the coupling between collective rotational variables and the molecular electronic system with the goal of exploring conditions for unidirectional rotation. Our approach is based on a quantum–classical description leading to effective Langevin equations for the mechanical degrees of freedom of the molecular rotor. By introducing a time-dependent gate to mimic the influence of current pulses on the molecule, we show that unidirectional rotations can be achieved by fine tuning the time-dependence of the gate as well as by changing the relative position of the potential energy surfaces involved in the rotational process.

Research on the Sea Surface Vertical Spar Buoy Power Installation Driving by Double-Sided Rack

Based on the analysis of engineering examples of current domestics and foreign wave energy conversion device and wave energy power generation principle, in this paper, a buoy wave power device was proposed and the principles were explored. The device mainly uses mechanical transmission devices for wave energy conversion to mechanical power. In the paper, the overall design of the buoy wave power device was carried, and directional reversing gearbox was developed, it can convert the vertical reciprocating movement of the wave to unidirectional rotation. According to Froude-Krylov hypothesis method, the paper analyses the perpendicular wave force of the vertical cylinder and the action of the ups and downs of displacement under the force. On the basis of the above work, the overall design of the device was completed.

Rebalancing the Vestibular System by Unidirectional Rotations in Patients With Chronic Vestibular Dysfunction.

Introduction: Vestibular dysfunction is a common disorder that results in debilitating symptoms. Even after full compensation, the vestibulo-ocular reflex (VOR) could be further improved by using rehabilitation exercises and visual-vestibular adaptation. We hypothesized that in patients with asymmetric vestibular function, the system could be rebalanced by unidirectional rotations toward the weaker side (i.e., a pure vestibular stimulation).Methods: Sixteen subjects (5 female and 11 male, 43.2 ± 17.0 years old) with chronic vestibular dysfunction that was non-responsive to other types of medical treatment were recruited for the study (ClinicalTrials.gov Identifier: NCT01080430). Subjects had VOR asymmetry quantified by an abnormal directional preponderance (DP) with rotation test and no previous history of central vestibular problems or fluctuating peripheral vestibular disorders. They participated either in the short-term study (one session) or the long-term study (7 visits over 5 weeks). Rehabilitation consisted of five trapezoid unidirectional rotations (peak velocity of 320°/s) toward the weaker side. Care was taken to slowly stop the rotation in order to avoid stimulation in the opposite direction during deceleration. To study the short-term effect, VOR responses were measured before and 10, 40, and 70 min after a single unidirectional rotational rehabilitation session. For long-term effects, the VOR gain was measured before and 70min after rehabilitation in each session.Results: We observed a significant decrease in VOR asymmetry even 10 min after one rehabilitation session (short-term study). With consecutive rehabilitation sessions in the long-term study, DP further decreased to reach normal values during the first 2 sessions and only one subjects required further rehabilitation after week 4. This change in DP was due to an increase in responses during rotations toward the weaker side and a decrease in VOR responses during rotations in the other direction.Conclusion: Our results show that unidirectional rotation can reduce the VOR imbalance and asymmetry in patients with previously compensated vestibular dysfunction and could be used as an effective supervised method for vestibular rehabilitation even in patients with longstanding vestibular dysfunction.

Chiral crystal-like droplets displaying unidirectional rotational sliding.

The self-assembly of organic molecules into supramolecular materials with structural ordering beyond the nanometre scale is challenging. Here, we report the spontaneous self-assembly of a chiral discotic triphenylene derivative into millimetre-sized droplets. The structure of the droplets is characterized by high positional and orientational ordering and a three-dimensional integrity similar to that of single crystals. Notwithstanding, these assemblies slide when placed on a vertical substrate demonstrating their fluid nature. X-ray imaging shows that during the sliding process the internal crystal-like structure is maintained and that the droplets undergo clockwise or counterclockwise unidirectional rotation, depending on the chirality of their molecular components. Rheological measurements suggest that this rotational behaviour might result from the distinct yield stress between the (R)- and (S)-enantiomers. Overall, our findings demonstrate that molecular chirality can determine the movement direction of a supramolecular structure, thus expanding the fundamental understanding of the structure and dynamics of soft materials.

Parameter Optimisation of Power Regeneration on the Hydraulic Electric Regenerative Shock Absorber System

With the increasingly prominent energy issues, regenerative shock absorber has attracted intensive attention in last two decades for the development of structure design. However, the researchers sometimes concentrate on conceptual designs without considering optimal parameter refinements. This paper proposes a regenerative shock absorber called the “hydraulic electric regenerative shock absorber (HERSA)” which includes an analytical regeneration performance parameters optimisation approach to promote the regeneration efficiency and regenerated power. The developed HERSA model is able to convert oscillatory motion into unidirectional rotary motion through the alteration of hydraulic flow while recovering power by a generator. The proposed model is also capable of obtaining the optimal parameters at certain condition, as well as providing the flexibility of different component combinations to match specific system need. The results demonstrate that the proposed model can effectively decide the optimal parameters in the system, and also the recoverable power can achieve average power of 331 W at 1 Hz‐25 mm sinusoidal excitation in the system, which is approximately 65% efficiency. This study can be further used to guide prototype design in future study.

A hemithioindigo molecular motor for metal surface attachment.

Functionalization of surfaces with responsive molecular entities is currently an important research field allowing the organization of molecular functions in space in a defined way and thus accessing emergent properties not observed in solution. Herein we report on the synthesis of a hemithioindigo molecular motor bearing thioether feet for surface attachment on its thioindigo fragment. We also give a full theoretical description of its ground state energy profile together with an experimental evaluation of the visible light driven unidirectional rotation in solution. Comparison with the corresponding unsubstituted original motor shows that after feet-attachment the hemithioindigo molecular motor is fully operative with a similar maximum attainable speed and degree of unidirectionality.

Spontaneous rotation of ratchet wheel with soft boundary in active particle bath

Self-propelling motionisubiquitous in the biological world, ranging from the molecular-level transportation of motor proteins along the microtubules, to the swimming of bacteria on a micrometer scale. An intriguing topic is to design microdevices or micromotors that can rectify the random motion and convert the energy into mechanical work. Here we design a soft microdevice, which may possess the advantages such as damage resistance, durability and adaptability, by utilizing two-dimensional Langevin dynamics simulation. We use a flexible chain to mimic the soft boundary of microdevice. We investigate the dynamical behaviors of microdevice when it is immersed in a thin film of active particle suspension. We find that the microdevicecan rotateunidirectionally and hence output the work. To uncover the physical mechanism of unidirectional rotation, we calculate the pressure distribution along the soft boundary. The spontaneous symmetry breaking of flexible boundary is the origin of the unidirectional rotation, which can lead to the inhomogeneous pressure distribution and hence torque on ratchet. It is because the persistent motion drives the particles to accumulate near the boundary and induce the soft boundary to deform. Further, we focus on the effect of active force and particle density on the angular velocity. With the increase of active force, the average angular velocity increases monotonically due to the increase of torque. With the increase of the number density of active particles, the average angular velocity increases. This is because the aggregation of a large number of particles is beneficial to the increase of ratchet torque. Additionally, we pay attention to the effect of rotational diffusion rate, <i>D</i><sub>r</sub>, of active particles and the number of ratchet wheels. We find the average angular velocity decreases with the increase of rotation diffusion <i>D</i><sub>r</sub> because ofthe ability of particles to weakly accumulate at high <i>D</i><sub>r</sub>s. The average angular velocity also decreases with the increase of the number of ratchet wheels. This is because a large number of ratchet wheels weaken the asymmetry of pressure distribution and hence reduce the torque on wheel. Our work provides a new insight into the design of soft microdevices for studying the non-equilibrium system.

Polarization-based tachometer for measuring spinning rotors.

We report on the polarization analysis of shortpulse ultraviolet radiation produced by third-harmonic generation in a gas of coherently spinning molecules. A pulse of twisted linear polarization imprints a unidirectional rotational motion to the molecules leading to an orientation of their rotational angular momenta. A second pulse, time-delayed with respect to the first one, circularly polarized in the plane of rotation of the molecules, acts as a driving field for third-harmonic generation. The angular momentum and energy conservation applied to this process foresees the generation of two Doppler-shifted circularly-polarized harmonics of opposite handedness. Our analysis reveals that spinning molecules enable the generation of a well polarized third-harmonic radiation exhibiting a high degree of ellipticity. Tracking the orientation of the latter allows a time-capture of the molecular axis direction from which the average angular velocity of the rotating molecules is inferred. This method provides a user-friendly polarization-based tachometer for measurement of the rotational speed of spinning nonlinear rotors.