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In this contribution, we employ a recurrent neural network (RNN) architecture in a variational optimization to obtain the ground state of linear chains of planar, dipolar rotors. We test different local basis sets and discuss their impact on the sign structure of the many-body ground state wavefunction. It is demonstrated that the RNN ansatz we employ is able to treat systems with and without a sign problem in the ground state. For larger chains with up to 50 rotors, accurate properties, such as correlation functions and Binder parameters, are calculated. By employing quantum annealing, we show that precise entanglement properties can be obtained. All these properties allow one to identify a quantum phase transition between a paraelectric and a ferroelectric quantum phase. [ABSTRACT FROM AUTHOR]

A number of internal rotation codes can deal with the combination of one or two internal rotors with one 14N quadrupole nucleus, but once it comes to two 14N nuclei, no such code is available even for the case of one internal rotor. We present here the extension of our internal rotor program called BELGI-2N using the rho-axis method global approach to deal with compounds containing one methyl rotor and two weakly coupling 14N nuclei. To test our new code, we applied it to the microwave data recorded for N-methylimidazole, 2-methylimidazole, 4-methylimidazole, and 5-methylimidazole using a chirped-pulse Fourier transform microwave spectrometer in the 7.0–18.5 GHz frequency range. Compared to the previously published study, BELGI-2N was able to (i) significantly increase the number of assigned and fitted lines, (ii) fit the complete datasets considering both the internal rotation and the 14N nuclear quadrupole coupling effects simultaneously, and (iii) achieve standard deviations within the measurement accuracy for all methylimidazole isomers. [ABSTRACT FROM AUTHOR]

In this work, we perform a density matrix renormalization group study of chains of planar rotors interacting via dipolar interactions. By exploring the ground state from weakly to strongly interacting rotors, we find the occurrence of a quantum phase transition between a disordered and a dipole-ordered quantum state. We show that the nature of the ordered state changes from ferroelectric to antiferroelectric when the relative orientation of the rotor planes varies and that this change requires no modification of the overall symmetry. The observed quantum phase transitions are characterized by critical exponents and central charges, which reveal different universality classes ranging from that of the (1 + 1)D Ising model to the 2D classical XY model. [ABSTRACT FROM AUTHOR]

This study investigates the efficiency evaluation of a compressor rotor designed for drive units requiring compressors with a power demand of less than 30 kW. The primary aim of the research presented in this article is to assess the feasibility of utilizing axial compressors to maintain high efficiency across a broad range of rotor speeds. A critical challenge in the considered power range is the occurrence of low Reynolds numbers, specifically those below 250,000. This research seeks to identify the underlying causes of efficiency degradation at low Reynolds numbers and determine the rotor's geometric parameters which most significantly influence the localized efficiency drop. Compressor efficiency was evaluated through numerical simulations. The numerical model was validated using experimental data and subjected to a grid independence study. Simulations were conducted for nine geometric configurations of the axial compressor rotor, with modifications to parameters such as the blade angle, blade thickness, blade solidity, and hub-to-tip ratio. For each configuration, a series of simulations was performed at rotor speeds ranging from 400 RPM to 2400 RPM. The simulation results indicated that the blade angle solidity was the most influential parameter affecting efficiency. A reduction in the blade angle led to approximately a 20% decrease in efficiency, primarily due to localized flow separation near the blade tip. Additionally, altering the number of blades caused a 20% efficiency reduction attributed to hub corner separation. The findings enabled the identification of optimal parameters, which will serve as a foundation for efficiency testing in the multistage configuration. [ABSTRACT FROM AUTHOR]

Flexibility plays a crucial role in the design and performance of modern rotors. Its impact on rotor performance and its ability to adapt to external flow disturbances are well-established. In this study, we employ numerical simulations to explore the behavior of a flexible rotor submerged in a turbulent flow, aiming to forecast the influence of its flexibility on performance metrics. The rotational motion of the rotor and the forces imposed by the flow induce deformations in the blades, including bending and twisting. These deformations not only disrupt the flow patterns (vortices) in the turbulent wake but also modify the aerodynamic profiles, thereby affecting essential performance aspects such as thrust, drag, and lift. Our objective is to uncover the relationships between blade deformations, rotation frequencies, and rotor performance in a turbulent flow with a Reynolds number, R e = O (1 0 4) , and for a tip speed ratio in the range [ 0 , 18 ]. We demonstrate that the mean blade bending angle can be effectively expressed using a modified Cauchy number, revealing a scaling law. We also examined how the aerodynamic performance of the rotor blade is affected by variations in the tip speed ratio, either amplifying or reducing it. Through this research, we advance our understanding of the interplay between rotor flexibility, deformation, and performance, contributing to the optimization of rotor design and operational efficiency. [ABSTRACT FROM AUTHOR]

Detecting Broken Rotor Bars (BBFs) in induction motors is critical for ensuring their reliable operation. While conventional methods, such as Fast Fourier Transform analysis of stator current spectra, have been widely used for BBF detection, they suffer from limitations like spectral leakage and low-frequency resolution. The Welch Transform is known for effectively reducing spectral leakage and noise when analyzing finite data. This paper presented an innovative FPGA-based architecture for real-time implementation of Welch transform for BBFs in induction motor diagnostics accompanied by a novel right-band-based detection technique, and the architectures are explained in detail. We conducted experiments to verify the effectiveness of the proposed architectures, including applying BBF faults under varying loads and severity levels. The results demonstrated the efficiency of our proposed architectures, as it was found that resource consumption rates were meagre, and error indicators were obvious. The results were displayed in real-time through a user-friendly graphical interface, demonstrating the practical effectiveness of the FPGA-based solution. [ABSTRACT FROM AUTHOR]

This paper presents a method of rotor position estimation for switched reluctance motors suitable for saturation. The effects of saturation as well as voltage changes are taken into account at the same time. It is based on the inductance in the unsaturated region. When the phase inductance is equal to the threshold, it is defined as a characteristic point. Meanwhile the characteristic pulse signal is triggered. Different inductance intersection thresholds are determined when the phase current and bus voltage change. The rotor position is estimated by interval speed. Compared with the traditional inductance method, the position estimation error is smaller. Finally, the correctness and effectiveness of the proposed method are verified by simulation and experiments. [ABSTRACT FROM AUTHOR]

To increase the accuracy of an analytic method based on the concentrated-mass approach for solving the mechanical operating modal characteristics of complete impellers and impellers with balancing holes in a centrifugal-pump rotor system, we establish a mathematical model and a three-dimensional simulation model for a double-supported three-stage centrifugal-pump rotor system. By comparing the modal results obtained from the two models, we propose a mathematical model that integrates the optimization of mass-distribution methods and bending stiffness correction coefficients, and we derive an optimized mathematical model for rotors with balancing holes. The effectiveness of the optimized mathematical model is validated via three-dimensional simulation, and the influence of balancing holes on the wet modes is analyzed. The results show that the wet natural frequencies are lower than the dry ones and that the wet natural frequencies obtained from analytical calculations are consistently higher than those obtained from three-dimensional simulation results. The optimized mathematical model significantly improves the accuracy of the wet modal characteristics for both complete impellers and impellers with balancing holes, with the errors in the low-order natural frequencies reduced by more than 50%. Under the same hole spacing, the natural frequencies of the three-stage centrifugal pump rotor system decrease with increasing hole diameter slightly. Under the same hole diameter, the natural frequencies of the rotor system increase slightly with the hole spacing. The effect of stiffness changes caused by balancing holes on the natural frequencies is larger than the effect of mass changes. [ABSTRACT FROM AUTHOR]

Steel–concrete hybrid towers (SCHTs) have been adopted as a popular supporting structure for wind turbines with the increasing hub height and rotor diameter. The excessive transverse vibration of the supporting tower adversely compromises the turbine’s operation and leads to structural deteriorations. The tuned mass damper (TMD) has been validated as an efficient device integrated with high-rise structures in vibration suppressions. This study aims to provide a reliable method for determining the key parameters of the TMD to obtain the optimal performance in vibration suppressions. This study begins with a rigorous theoretical analysis to investigate the dynamic responses of the SCHT. The dynamic analysis serves as a basis for developing a dynamics model of the SCHT integrated with a TMD, which provides a programmable method to analyze the effect of the TMD on the dynamic responses of the SCHT. Then, an optimization model based on the genetic algorithm (GA) is established to obtain the optimal parameters of the TMD. Finally, a numerical test comprising 12 loading conditions is conducted to analyze the vibration mitigation effect of the TMD. The validation process also provides discussions about the influence of the wind turbine operation states and the fitness function adopted in the GA on the efficiency of the TMD. Those findings demonstrate the effectiveness and limitations of the TMD for mitigating vibrations of the SCHT. It thereby contributes to the understanding and improvement of vibration control strategies for SCHT structures and can guide future design and optimization efforts. [ABSTRACT FROM AUTHOR]

Dynamic loads are inevitably generated during the operation of rotating machinery. In situ monitoring the dynamic loads is of great significance for assessing shafting health. Triboelectric nanogenerator (TENG) is sensitive to motion but not suitable for load monitoring, while piezoelectric nanogenerator (PENG) is just the opposite. Therefore, the combination of the two can complement each other. From this, a dynamic load monitoring smart bearing (DLMSB) integrated with TENG and PENG is proposed. The specially designed TENG can produce an "M‐waveform", which can be used to extract rotation frequency and distinguish the quadrant of the rotor. Meanwhile, applying PENG to capture the load condition of the bearing, and referring to the main frequency of M‐waveform, it is convenient to obtain the dynamic loads of shafting. Furthermore, a real‐time monitoring system is developed, which can realize not only real‐time monitoring of the rotation speed and dynamic loads magnitude but also the quadrant discriminating of dynamic loads. The results have shown that the monitoring error for dynamic loads is 3 N or 5.5%, and the accuracy rate for determining the quadrant of the dynamic loads can reach 93%. This study provides a novel approach for the in situ monitoring of mechanical operating status via nanogenerators. [ABSTRACT FROM AUTHOR]

The axial misalignment and tip clearance of the double spiral seals are important indexes affecting the sealing performance of the double spiral seals. In practical engineering applications, the sealing ability of double spiral seals is greatly affected by axial misalignment and tip clearance, and the coupling of assembly parameters and structural parameters of double spiral seals leads to the difficulty of seal design and use. A numerical model of spiral seals was established, and the velocity field, pressure field and critical sealing ability of double spiral seals were simulated and calculated. The influence of different axial misalignment displacements and different tip clearances on the sealing ability of double spiral seals was analyzed. The influence of axial misalignment displacement, tip clearance and rotor speed on the sealing performance of double spiral seals is obtained. The above research results provide a design basis for the engineering application of double spiral seals. [ABSTRACT FROM AUTHOR]

The magnetic bearing rotor system is affected by internal uncertainties and various forms of external disturbances, which will affect the stability of the active magnetic bearing system. To address this issue, a composite hierarchical anti-disturbance strategy is used to improve the anti-disturbance ability of the magnetic bearing rotor system. The disturbance observer is used to compensate the system's external disturbances, and the controller is used to suppress the system's internal uncertainties. For this purpose, H ∞ controller, disturbance observer (DOB), and linear extended state observer (LESO) are designed, respectively. Then, H ∞ controller is combined with DOB and LESO to form H ∞-DOB and H ∞-LESO composite controllers and prove their stability. Finally, simulation and experiments show that H ∞ -DOB and H ∞ -LESO have better disturbance suppression effects than the H ∞ controller for external disturbances. And when the disturbance frequency or rotor rotation frequency of the system is high, H ∞ -LESO controller has better disturbance suppression effect than H ∞ -DOB. [ABSTRACT FROM AUTHOR]

The design and technological scheme of a small-sized forage harvester with a capture width of 1.35 m equipped with a device oriented along the length of the stems was developed in this study. As a result of theoretical studies, the process of the movement of mass into the chamber of the mowing rotor due to centrifugal forces was revealed. The speed of mass movement and the average size of crushed particles with the mowing rotor were determined. The oriented feeding process of stems in the chamber of the chopping rotor is mathematically described in this paper. An analytical expression is obtained for determining the average size of crushed particles by the forage harvester, that is, a mathematical model of the processes of mowing, oriented feeding, and the chopping of stem fodder by the forage harvester. Laboratory and field tests of a forage harvester equipped with a device oriented along the length of the stems were conducted. The combine harvester's productivity was 6.14 t/h when mowing alfalfa. Special experiments were conducted to determine the average size of crushed particles after the mowing rotor. The average size of crushed particles with the mowing rotor was 147.4 mm, while the theoretical value was 144 mm. The difference between these values was only 2.31%. A special experiment was conducted on the combine without an orienting device to compare the quality indicators. The mass fractions of crushed particles of up to 50 mm in length when the combine was operating with and without an orienting device were 79.3 and 46.7, respectively. Accordingly, the average length of crushed particles was 33.79 mm and that without an orienting device was 77.07 mm. The theoretical value of the average length of crushed particles was 34.9 mm (i.e., the difference between the theoretical and actual value of the average size of the crushed particles was only 3.25%). All this proves that when the combine harvester was operated with an orienting device, there was a significant increase in the quality indicators of the chopped feed, and the reliability of the theoretical studies and the resulting mathematical model were determined. [ABSTRACT FROM AUTHOR]

In order to solve the problem of difficult simulation of the bolted joint structure of rotors, this study proposes an improved sub-regional thin-layer element method (ISRTL) and applies it to the equivalent simulation of the joint interface in the presence of bolt deviations. The theory introduces the fractal theory and Hertz contact theory to calculate the thin-layer parameter for the region with weak influence of bolt preload. The trend of dynamic response under different loosening deviation conditions is investigated. The experimental study of bolt deviation under axial tension and transverse vibration was carried out using a drum-disk rotor. The frequency and stiffness with bolt loosening position conform to M-type trend. The error of the eigenfrequencies calculated by the proposed method is within 3 % from the experimental results. The results demonstrate that ISRTL method has high accuracy and efficiency in the simulation study for the assembly deviation of rotor bolt connections. [ABSTRACT FROM AUTHOR]

This study investigates the prediction of the aerodynamic characteristics of Flettner rotors through three deep learning models. Various numbers of Flettner rotors, arrangements, and spin ratios are employed to consider these effects in the dataset. For the training of deep learning models, a dataset of aerodynamic force coefficients and flow fields is generated using Computational Fluid Dynamics (CFD). Three deep learning architectures (U-net, Encoder-Decoder, and Decoder models) are employed and trained to predict the aerodynamic characteristics of Flettner rotors. Three deep learning models are established through a training stage with a hyperparameter study and by altering the number of layers. The aerodynamic force coefficients and flow fields are predicted by established deep learning models and show small absolute errors compared to those from the CFD analysis. Moreover, predicted flow fields reflect the flow characteristics according to the difference of spin ratio and arrangement of Flettner rotors. In conclusion, the established deep learning models demonstrate rapid and robust predictions of aerodynamic force coefficients and flow fields for Flettner rotors under varying arrangements and spin ratios. Furthermore, a significant reduction in computational time is measured when comparing the analysis time of CFD simulations to the training and testing time of the deep learning models. [ABSTRACT FROM AUTHOR]

The flux observer method is widely utilized as a sensorless control technique in which the stator or rotor flux of IPMSM can be measured with a closed-loop observer or an integrator. However, DC-offset (DCoff), the ramp signal, and harmonics are consistently present in the acquired rotor flux because of an unidentified starting value, errors in the integral computation's current detection, and the inverter's nonlinearity. The aforementioned interference signals will drastically reduce the sensorless control efficacy. This work introduces an enhanced flux estimator with a negative feedback loop and PI controller to overcome the DC drift problem resulting from a pure integrator and a low-pass filter. Moreover, an optimal design approach of flux estimator structures with a broad range of speeds for Interior permanent magnet synchronous motor (IPMSM) drives is proposed, which utilizes an integrated topology of the voltage and current models incorporating a DC-offset PI-correction loop, actual and estimated flux magnitude's correction error. The flux vector's initial inaccuracy is eliminated, together with the DCoff and drift in the acquisition channel. A phase-locked-loop state estimator is utilized to derive the speed and position from the actual and estimated flux. The effectiveness and superiority of the suggested approach were proven by simulation and experimental findings for the IPMSM drives, which displayed high dynamic performances over varying scenarios. This reliable approach, including sensorless control, is suitable for all AC motors with sinusoidal flux distributions over a wide speed range. [ABSTRACT FROM AUTHOR]

Tip loss correction is necessary for all aerodynamic computations based on the blade-element momentum theory (BEMT) that plays an essential role in wind turbine design. Glauert tip-loss correction, which is most widely used, assumes the rotor is lightly loaded and thus lose some accuracy for modern wind turbines that are highly loaded. In the present work, a new g-function involving the rotor's thrust-coefficient is introduced, which connects the tip loss correction with the rotor's load condition and reduces the error of the tip loss correction. Computational tests are performed on two rotors that are distinct in size and tip shape. The new g-function results in good consistency between the computed forces and the reference data, exhibiting excellent role in improving the accuracy of the BEMT computations. In general, the new g-function combines good effectiveness and applicability, and thus has great potential for engineering applications. [ABSTRACT FROM AUTHOR]

Lobe pumps are used in many different sectors because of their versatility and effectiveness for managing multiphase flows. In this study, three-dimensional unsteady numerical simulations are performed to evaluate the vortex cavitation phenomenon in these pumps. The work combines dynamic meshing techniques, advanced vortex recognition methods, and a full cavitation model to provide insight into the genesis, evolution, and influence of vortex cavitation on pump performance. The results of the study demonstrate that under high-speed and high-pressure conditions, vortex flow occurs at the edge of the rear of the rotor lobe in the suction chamber of the lobe pump, resulting in the production of vortex cavitation. Cavitation is most strong at the core of the vortex, while the degree of cavitation at the edge of the vortex gradually diminished. The gas volume fraction reduces from 0.135 to 0.0832, and this makes the pressure decrease from 1.055 to 1.02 MP. The process of genesis, development, and removal of vortex cavitation is cyclic. At different levels of cavitation, the degree of pulsation in pump outlet flow, pressure, and radial force increases with increasing cavitation. Periodic vortex cavitation leads to periodic changes in pump output pressure, flow rate, radial force, and axial force. [ABSTRACT FROM AUTHOR]

The possibility of wobbling mode in the A ≈ 80 mass region is investigated by using the constrained triaxial covariant density functional theory and quantum particle rotor model for rubidium isotopes. Several states with the obvious triaxial deformation and high-j particle configuration are obtained in 79 , 81 , 83 , 85 Rb, which are suitable for establishing the wobbling mode. Taking the nucleus 81 Rb as an example, the available experimental energy spectrum with the π g 9 / 2 configuration is described well. The decreased energy difference between the partner bands, the enhanced B (E 2) out / B (E 2) in values, the angular momentum components and the azimuthal plots indicate that 81 Rb can be transverse wobbling candidate. The present work provides a promising basis for future experimental research on the wobbling mode in the A ≈ 80 mass region. [ABSTRACT FROM AUTHOR]

Understanding the aerodynamics of multi-rotor systems under temporally varying discrete gusts is the focus of this work. Axial and edgewise 1-minus-cosine profiles of varying amplitude (0.1 Ω R – 0.3 Ω R) and gust durations (0.3 – 15 s) were studied for the rigid, unarticulated Harrington single and coaxial rotors, and the Advanced Precision Composites (APC) 12x6E (a commercial off-the-shelf propeller) quad-rotor in hover. An in-house free vortex method (FVM) was utilized to study the time and frequency domain of thrust, span-wise angle of attack distribution, and the rotor wake structure across the gust event. It was observed that edgewise gusts produced higher frequency components in the thrust signal compared to axial gusts for all rotor systems. Strong wake–wake and blade–vortex interactions (BVI) were observed particularly for edgewise gusts, leading to strong variations in the sectional angle of attack and the thrust values. The wake interactions are more pronounced in the APC quad-rotor system, which operates at a low reduced frequency, essentially resulting in a quasi-steady response of the wake to the gust, resulting in a considerably higher number of BVI events, increased peak rotor loads, and higher frequency content. This study can aid in the understanding of the gust response of small- and medium-scale rotors. [ABSTRACT FROM AUTHOR]

For long flight duration and low noise emission, efficient and quiet quadcopters have a continuous demand. The toroidal rotor, which is ring-shaped with each blade forming a closed loop, is recognized for its potential to reduce tip vortex intensity, thereby improving aerodynamic efficiency and reducing noise levels. However, existing studies provide limited and sometimes controversial results of toroidal rotor performance relative to conventional rotors. This study aims to conduct a more comprehensive and systematic evaluation by employing a multi-objective optimization framework to design toroidal and conventional rotors for fair comparison. The optimization under the constraint of a required thrust considers objectives of aerodynamic efficiency and noise emission, with the design variable of blade twist angle. The study compares a toroidal 2-blade rotor with conventional 2-blade and 4-blade rotors. The results show that, while the toroidal rotor generates lower noise than conventional 2-blade rotors, it shows lower aerodynamic efficiency. Compared to conventional 4-blade rotors, the toroidal rotor has lower aerodynamic efficiency and larger noise emission. The trend is determined by the effect of rotational speed and blade–vortex interaction, as revealed by flow field analysis. Noise spectrum analysis allows to identify loading and thickness noise contributions and locate the primary noise sources of the toroidal rotor. [ABSTRACT FROM AUTHOR]

The shock wave/boundary layer interaction at the tip of transonic shrouded rotor blades usually leads to severe flow separation, which seriously affects aerodynamic performance. In this paper, the effect of part-shroud treatment on the shock wave/boundary layer interaction was numerically investigated. The part-shroud treatment suppresses the shock wave/boundary layer interaction-induced flow separation by introducing the tip leakage vortex at an optimal location. Parametric studies reveal that positioning the tip leakage vortex onset upstream the shock wave effectively reduces flow separation on the suction side, with the best outcomes achieved when the onset is slightly upstream of the shock wave. Based on these findings, the optimal shroud range extends from the leading edge to just upstream of the shock wave under a near stall condition. In National Aeronautics and Space Administration Rotor 35, the 30% shrouded rotors demonstrate a 2.4% improvement in the stall margin over 100% shrouded rotors with little reduction in peak efficiency. [ABSTRACT FROM AUTHOR]

The advantages of vertical axis wind turbines (VAWTs) have increasingly been recognized as effective turbomachines. Nonetheless, significant challenges remain regarding their efficiency and operational range. One promising approach to enhance their aerodynamic performance is the integration of vortex cavities, which can contribute to improved operational efficiency. This study utilizes computational fluid dynamics (CFD) to analyze the placement of vortex cavities systematically. The research investigates different configurations, such as suction side layout (SSL) and pressure side layout within single, double, triple, and quadruple arrangements to forecast their effect on H-type Darrieus VAWT aerodynamic performance. The findings show that the optimal configuration, with a concentration of 0.2 and 0.8 C in SSL, led to a 25% increase in power coefficient ( C p ) at the tip speed ratio (TSR) of 3.3. Conversely, the suboptimal configuration, with a concentration of 0.2 and 0.4 C in SSL, resulted in a substantial 54% decrease in C p at the same TSR due to issues with flow separation and lack of flow attachment after the vortex cavity. To optimize efficiency within the high-TSR range, a double, top, and bottom deflector configuration has been developed. Findings indicate that incorporating the double deflector has broadened the rotor's operational range from TSR 3.5 to 4.2 and concurrently elevated the rotor efficiency to 86%. [ABSTRACT FROM AUTHOR]

We conduct experimental investigations of the effect of the tip air injection as a stability control method on a low-speed axial-flow compressor experiencing severe circumferential total pressure distortion. Eight Coanda-shaped injectors, uniformly distributed upstream of the rotor blade leading edge, were employed to counteract stall margin degradation caused by a flat-baffle circumferential distortion. Unsteady pressure data from the tip clearance and rotor wake regions were captured using time-resolved sensors and probes and analyzed through time-frequency transformation and proper orthogonal decomposition (POD) techniques. POD investigation under distorted inflow conditions reveals that the third-order POD mode, which characterizes unsteady tip leakage flow (TLF), plays a dominant role in triggering stall. Based on this insight, tip air injection with varying momentum ratios was applied to enhance the stall margin. The positive correlation between the injected momentum ratio and stall margin improvement was established, demonstrating the stabilizing effect of tip air injection under the circumferential distortion. The results indicate that tip air injection primarily acts on the rotor blade tip region to suppress the unsteady TLF at the center and downstream areas of the distortion, leading to an increase in tip blade load and a reduction in both the scale and number of pre-stall disturbances. However, the injection has a minimal impact on the unsteady TLF frequency band in the rotor wake region. Additionally, the POD analysis confirms that as the injection rate is increased, the energy percentage, flow field intensity, and power spectral density amplitude of the third-order POD mode are decreased, further reflecting the mitigation of unsteady TLF. The present work provides important insight into the stability control mechanisms of a tip air injection under circumferential distortion, offering design guidance for the implementation of active stability control strategies in axial-flow compressors. [ABSTRACT FROM AUTHOR]

We report remarkable pattern formation of quasiperiodic domains in the two-dimensional parameter space of an intrinsically coupled system, comprising a rotor and a Duffing oscillator. In our analysis, we characterize the system using Lyapunov exponents, identifying self-similar islands composed of intricate regions of chaotic, quasiperiodic, and periodic behaviors. These islands form structures with an accumulation arrangement, denominated here as metamorphic tongues. Inside the islands, we observe Arnold tongues corresponding to periodic solutions. In addition, we surprisingly identify quasiperiodic shrimp-shaped domains that have been typically observed for periodic solutions. Similar features to the periodic case, such as period-doubling and secondary-near shrimp with three times the period, are observed in quasiperiodic shrimp as torus-doubling and torus-tripling. [ABSTRACT FROM AUTHOR]

One major problem affecting rotor blade aerodynamics is dynamic stall, characterized by a series of events where transient vortex shedding negatively affects drag and lift, leading to abrupt changes in the wing's pitching moment. The present work focuses on the mitigation of such effects by using a modified NACA0012 airfoil—the NACA0012-IK30 airfoil—previously used for thrust enhancement in flapping propulsion. An experimental rig is designed to study the advantages of a deflectable leading edge on a plunging and pitching wing, more specifically its influence on the aerodynamic coefficients over time. In the first stage, results indicate that the proposed IK30 mechanism does mitigate the stall effects under static conditions, with stall visualization data corroborating it. Regarding time-varying conditions, the data presents the adequacy of the proposed geometry under different plunging and pitching conditions, which, when correctly used, can mitigate or even eradicate the adverse effects of dynamic stall experienced, leading to significant drag reductions and modest lift enhancements. In the absence of a dynamic stall, the movable leading edge can also provide operational advantages, where it does not negatively affect drag or lift but can reduce the pitching moment intensity by indirectly shifting the pressure center. This study contributes to the long-standing discussion on how to mitigate the adverse effects of dynamic stall by providing an innovative yet simple solution. [ABSTRACT FROM AUTHOR]

Shock is the main characteristic of supersonic compressors. There are relatively few studies of the control of shock structure and secondary flow in supersonic compressors by nonaxisymmetric endwall optimization. The lack of understanding of the mechanism of flow structure changes in supersonic compressors by the nonaxisymmetric endwall limits the application of this technique in supersonic compressor interiors. In this paper, the effects of nonaxisymmetric endwall on the supersonic compressor and flow mechanism were studied using the numerical simulation method and verified by experiment. The results showed that the optimized nonaxisymmetric endwall design increased the peak isentropic efficiency of the supersonic compressor by 0.6%, verifying the effectiveness of the nonaxisymmetric endwall in improving the supersonic compressor. By comparing the flow fields at the peak efficiency points before and after optimization, it was found that the shock loss in the rotor was reduced by the change of shock structure induced by the nonaxisymmetric endwall, and the secondary flow loss was controlled by the change of shock structure in the rotor. Moreover, the rotor's nonaxisymmetric endwall changed the downstream stator's inlet conditions, reducing the stator's total pressure loss. Therefore, the nonaxisymmetric endwall has a wide range of applications for regulating the internal shock structure of supersonic compressors. [ABSTRACT FROM AUTHOR]

The chiral iridium rotors Ir(ppy)2(pyX)Cl (X = C≡C-SiR3, R = alkyl) remarkably contain two distinct rotational conformers in the ground (S0) and excited (T1) states that can be detected by NMR and emission measurements respectively at variable temperatures. The observed phosphorescent emissions, vibronic (involving L = ppy) and broad (L = pyX), arise from different triplet ligand to metal charge transfers from the two rotational conformers at distinct ³MLCT excited states. Both conformers exist in these Ir(ppy)2(pyX)Cl rotors due to the electron-withdrawing, conjugated substituent X. [ABSTRACT FROM AUTHOR]

The high-performance vector control technology of permanent magnet synchronous machines (PMSMs) relies on high-precision rotor position. The Hall-effect sensor has the advantages of low cost, simple installation, and strong anti-interference ability. However, it can only provide six discrete rotor angles in an electrical cycle, which makes high-precision vector control of PMSMs difficult. Hence, to obtain the necessary rotor position of PMSMs, a rotor position fitting method combining the Hall signal and machine flux information is proposed. Firstly, the rotor position signal output by the Hall-effect sensors is used to calibrate and update the stator flux obtained under pure integration. Then, based on the corrected stator flux and its relationship with current and angle, the rotor position and speed are obtained. Experimental verification shows that the rotor position observer combining Hall signal and flux information can reduce the initial value bias and integral drift caused by traditional average speed method hysteresis and pure integration method calculation of flux and can quickly and accurately track and estimate the rotor position, achieving high-performance vector control of PMSMs. [ABSTRACT FROM AUTHOR]

AbstractRotor unbalance presence is very dangerous, because it may cause the rotor operational deflection and thus, high vibrations of the engine. There are many experimental procedures decreasing the operational rotor deflection, but nowadays mathematical modeling approach is becoming widely used. In mathematical models unbalances are needed to be applied, but there are some effects increasing these loads. One of these effects is dual stiffness effect. In this article partial differential equations modeling operational deflection of a shaft with dual stiffness are considered. Theoretical solution is obtained in the case of a simply supported beam with a constant distributed load exerted. The method of applying load accounting for dual stiffness in a general case of three-dimensional shaft is proposed. In a test task it is showed, that the method gives the results having a good comparison with an experiment. Moreover, accounting for dual stiffness leads to results being closer to the one. [ABSTRACT FROM AUTHOR]

The internal flow field of the hydrogen circulation pump becomes more complex and flow process becomes more intense during the stopping process, strong vibration is generated to the pump and the working life of the pump is shortened. Therefore, the pressure pulsation at the inlet and outlet section, the radial force characteristics of the active rotor and the transient flow mechanism of the internal flow under different stopping modes are studied in this paper. The results show that the intake pressure and exhaust flow change greatly in exponential stopping mode, while the pressure pulsation amplitude decreases with the increase of stopping time in linear stopping mode. In addition, the radial force value of the active rotor in the exponential stopping mode is significantly smaller than that in the linear stopping mode, and the direction of the radial force F x and F y point to the negative direction of their respective axes. In this paper, the dynamic mesh technology is used to design the corresponding rotating speed UDF according to different stopping functions, and then the transient simulation of the hydrogen circulation pump under different stopping modes is completed. Finally, the change law of pressure and flow pulsation, radial force characteristics and internal flow field under different stopping modes are analyzed. [Display omitted] • Effects of different stopping modes on flow characteristics are studied. • Pressure variation under different stopping modes are discussed. • Radial force of the rotor under different stopping modes are analyzed. • Working process is researched from the pressure and velocity distribution. [ABSTRACT FROM AUTHOR]

Accurate dynamic parameters are essential for precise control of model-based manipulators. Due to the direct connection between the joint axis and the motor rotor of the direct drive manipulator, using additional joints would increase the disturbance of the system, leading to substantial trajectory tracking errors, which could potentially harm the manipulator if the tracking error exceeds the limited position of joints, and it also curtails the comprehensive parameter excitation and affects the identification accuracy. Restricting joint movement to a narrow area can prevent this injury, but it also curtails the comprehensive parameter excitation and affects the identification accuracy. To address these challenges, this paper presents a novel method for identifying dynamic parameters of multiple degree-of-freedom (DOF) series direct drive manipulators. Specifically, an open-loop gravity torque compensation strategy with spatial geometric characteristics is introduced to ensure secure operation during manipulator identification processes. Meanwhile, an improved model reference adaptive identification (MRAI) method is presented to estimate the nominal inertia quickly and accurately. Finally, a disturbance observer (DOB) based on minimum model perturbation bound is proposed to compensate for significant variations in model disturbances, enabling stable and precise tracking of planned exciting trajectories. This proves advantageous for fully exciting dynamic parameters and improving identification accuracy. Simulation experiments demonstrate that the tracking error of each joint's exciting trajectory is within 0.07 radians, and the maximum absolute error of identifying dynamic parameters is 0.099169409, which verifies the feasibility and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In May 1945 an Imperial Japanese Army Green cipher machine was captured at Baguio in the Philippines. The machine was unlike any previous Japanese cipher machine that was known to U.S. codebreakers; GREEN made use of multiple irregularly stepping rotors and a fractionating matrix. The U.S. Army's Signal Security Agency began an urgent effort to understand the machine and its weaknesses, design an attack, and construct an analog. However, three months after the capture of a Green Machine, the war with Japan ended without any messages enciphered by GREEN having been intercepted. Six months after the war ended, construction of a GREEN analog was completed, and the analog was delivered to the museum. [ABSTRACT FROM AUTHOR]

Given the presence of various non‐ideal conditions, such as detection errors, converter non‐linearity, noise, and parameter mismatches, the flux model experiences the introduction of DC bias and high‐frequency harmonics, which subsequently deteriorate the accuracy of flux estimation. To dispose these issues, an improved non‐linear flux observer (FOIFFO) using a second‐order generalised integrator as an in‐loop filter is proposed for the sensorless control of permanent magnet synchronous motors. The observer demonstrates robust performance in eliminating DC bias and having a strong filtering ability for high‐order harmonics even without amplitude and phase compensation to accurately estimate the rotational speed and rotor position. The performance of the method is analysed by transfer functions and bode plots, while the discretisation method of the FOIFFO is proposed. Finally, the new sensorless control strategy is verified by synthesising the experimental results. [ABSTRACT FROM AUTHOR]

The high-speed permanent magnet motor has been widely used in the industrial field because of its high-power density, fast dynamic response, and wide speed range. High efficiency and stable operation are the premises for the high-speed permanent magnet motor to exert its advantages. Firstly, this article analyzes the problems existing in the drive technology of high-speed permanent magnet motors from three aspects: current harmonics, rotor position detection, and low carrier ratios. Aiming to address the above problems, the status of the latest research is summarized from the aspects of harmonic suppression, position sensorless, and control strategies. In addition, future research trends for high-speed permanent magnet motors are discussed. [ABSTRACT FROM AUTHOR]

Centrifugal pump rotor system is a complex vibration system due to the unsteady multi-scale fluid–solid interactions (FSIs). In order to explore the coupling vibration of the rotor system between the multi-scale fluid domain and different flow conditions, the bidirectional fluid–solid interaction (BFSI) was carried out, and the numerical and experimental results of the centrifugal pump performance were compared. The transient forces of the impeller and vibration characteristics of rotor system considering BFSI for different flow rates, wear-ring clearances, and axial movements were also studied in detail. The results show that the maximum errors of head and efficiency between the simulation and experiment are only 5.41% and 2.33%, respectively. The radial force of impeller is smallest at 1.0Qd and the axial force decreases with the increase in flow rate. The average deformation and stress of the rotor system reaches to 0.35 mm and 70.7 MPa, respectively, when the axial movement increases to +1.5 mm. The vibration acceleration on the blades increases gradually from the root to the top, and the vibration acceleration on the shaft is greater than that at the impeller. [ABSTRACT FROM AUTHOR]

In this research, a variable-camber inlet guide vane (VIGV) is applied to a highly loaded counter-rotating fan for the first time at variable working conditions. Additionally, internal flow analysis of the highly loaded counter-rotating fan is performed to reveal the essential flow mechanism and determine its impact on overall performance. It is found that the through-flow capacity is improved with a decrease in the camber angle. At −10°VIGV, the through-flow capacity increases by 3.1% at the design speed, while the through-flow capacity is only increased by 0.7% at the low corrected speed. The main reason for this is that the through-flow capacity along the blade span of the high-pressure rotor can be increased at the design speed, while only part of the blade span can be increased at the low corrected speed. At the low corrected speed, with the increase in the camber angle, the isentropic efficiency can be effectively improved by the counter-rotating fan, and the isentropic efficiency increases by 1.43% at +20°VIGV. This is mainly due to the decrease in the camber angle reducing the low-pressure rotor's incidence angle along the blade span, which suppresses the flow separation of the low-pressure rotor's suction surface. [ABSTRACT FROM AUTHOR]

Airflow-assisted manufacturing holds significant promise across various applications, including rotor spinning, where airflow is crucial for fiber transfer and ultimately affects yarn performance. This study introduces a three-dimensional model of flexible fiber motion within the flow field of a rotor spinning unit. The fiber is modeled as cylindrical segments connected by rigid joints, with the segments experiencing fluid torques and the joints subjected to fluid forces. The model accounts for the fiber bending and torsional deformation. Fiber motion is determined by solving the translational and rotational equations, alongside the fiber–wall interactions. Emphasis is placed on the fiber stripping process from the opening roller. Supported by the numerical methods validated through visualization experiments and further corroborated by spinning examinations, we advance the understanding of the motion behavior of fibers released from different initial positions in the rotor spinning unit, and specifically, delve into the impact of airflow patterns on fiber movement. The developed numerical methodology and findings are vital for optimizing rotor spinning unit design and effectively harnessing airflow technology in processing. [ABSTRACT FROM AUTHOR]

An interesting feature in dissipative nonlinear systems is the emergence of characteristic domains in parameter space that exhibit periodic temporal evolution, known as shrimp-shaped domains. We investigate the parameter space of the dissipative asymmetric kicked rotor map and show that, in the regime of strong dissipation, the shrimp-shaped domains repeat themselves as the nonlinearity parameter increases while maintaining the same period. We analyze the dependence of the length of each periodic domain with the nonlinearity parameter, revealing that it follows a power law with the same exponent regardless of the dissipation parameter. Additionally, we find that the distance between adjacent shrimp-shaped domains is scaling invariant with respect to the dissipation parameter. Furthermore, we show that for weaker dissipation, a multistable scenario emerges within the periodic domains. We find that as the dissipation gets weaker, the ratio of multistable parameters for each periodic domain increases, and the area of the periodic basin decreases as the nonlinearity parameter increases. [ABSTRACT FROM AUTHOR]

Foil bearings for high speed turbomachinery are and have been studied in terms of load capacity and lift‐off speed, stability, thermal behaviour and manufacturing. This paper focuses on a modular rotor‐bearing test rig, with which design changes can easily be experimentally investigated. An exemplary design change is undertaken and its effects are studied. Furthermore, a simple procedure is introduced, with which rigid body modes of the rotor can be extracted from phase information derived from experimentally obtained time series data. [ABSTRACT FROM AUTHOR]

Constant temperature anemometry and background-oriented schlieren (BOS) measurements on a CH-53G helicopter (takeoff mass ≈14t) are used to investigate the rotor wake including the vortex breakdown to statistical turbulence. Hovering flights at a range of hub heights 0.50 < h < 0.83 were investigated. The position of the rotorcraft was optically tracked using markers affixed to the fuselage. A complete breakdown of the tip vortices was noted within 0.3R of the rotor plane, in stark qualitative contrast to small-scale experiments which show the tip vortices persisting to the ground plane. The large (37m2) BOS field of view showed a small effect of vortex pairing and blade vortex interaction, which was overshadowed by the rapid wake breakdown. Vortex pairing was found to result from varying vortex convection velocities rather than from initial differences in the vortex spacing due to the blade track. [ABSTRACT FROM AUTHOR]

During helicopter air-to-air refueling, the aircraft propeller's jet can engage with the helicopter rotor. The impact on the helicopter rotor thrust and aerodynamic hub moments is solved analytically for the first time, based on blade element momentum theory. The collective and cyclic blade pitch controls needed for disturbance rejection are computed for a typical air-to-air refueling scenario. A propeller jet affecting the retreating side of the rotor requires much more pilot controls to retrim than an impingement on the advancing side. [ABSTRACT FROM AUTHOR]

Measurements were made using flow visualization to track the blade tip vortices of a 1.108-m radius stacked rotor in hover. Vortex measurements of an isolated, two-bladed rotor were also made and correlated with the Landgrebe wake model. When a second rotor was introduced to the system, the interaction between the upper and lower rotor vortices resulted in deviations from the Landgrebe wake model. Changing the azimuthal spacing revealed large changes in the trajectory of the upper and lower rotor vortices, particularly at small, negative azimuthal spacings. The miss distance, or distance between a rotor blade and vortex, was measured. Positive miss distances where the lower rotor blade passed below the upper rotor tip vortex were associated with greater noise between 1 and 5 kHz, possibly from turbulent boundary layer noise or blade-vortex interaction noise. The greatest performance and lowest broadband noise corresponded with large miss distance and minimal vortex-vortex interaction, which occurred at an azimuthal spacing of -45°. The tip vortex trajectory, and thus miss distance, could be modified by utilizing differential collective. This resulted in a 4.5-dB reduction in broadband noise at negative differential collectives by allowing the lower rotor blade to pass above the upper rotor vortex and achieving negative miss distances. At azimuthal spacings where the miss distance was always negative, the airfoil self-noise dictated the broadband noise level. [ABSTRACT FROM AUTHOR]

High-fidelity computational fluid dynamics (CFD) simulations of seven rotors in compact configuration at three different flight scenarios are performed. The cases are hover as well as 50 and 100 km/h forward flights. For comparison, each rotor is simulated as an isolated rotor with the same RPM and pitch angle as in the configuration. Additionally, a bigger isolated rotor with the same diameter as the complete configuration is simulated. For the configuration as well as the bigger rotor a flight mechanics trim is performed using the flight mechanics tool VFAST. The CFD simulations are performed with FLOWer. In hover, only the center rotor showed a significant figure of meritdrop of 16% compared to the isolated rotor. The thrust of the outer rotors is increased at the tip areas facing outwards, while the tip areas towards the center and the tip areas of the center rotor showed reduced thrust compared to the isolated rotor. The wake contraction at the outer rotors is increased compared to the bigger rotor. For the 50 km/h forward flight, the efficiency of the front rotors is increased (10-17%) and the rear ones decreased (11-16%). In this case, the wake is directly convected from the front rotors into the rear rotor planes and strong vortex interactions occur. For the 100 km/h case, the efficiency of the front rotors increases by 3-11%, while it decreases by 5-9% for the rear rotors. Due to the higher pitch, the wake of the rotors flows away from the rotor plane and the rotor-rotor interactions are reduced. [ABSTRACT FROM AUTHOR]

Owing to their high specific energy capabilities, ultramicrogas turbines (UMGT) are a high-potential technology to provide portable electric power supply for applications with demand of less than 1 kW. UMGT conceptual design is challenged by small-scale effects augmenting interdisciplinary dependencies leading to highly coupled, nonlinear component interactions. This work provides a novel approach to conceptual UMGT design by combining reduced order component and system modeling with constrained multi-objective optimization. Hereby, Part I presents integrated design and performance modeling of compressor, turbine, combustor, and generator. In Part II, the heat engine and generator modules are merged into a system framework by establishing conceptual UMGT rotor geometry and engine design. Following bearing selection and lifetime assessment, experimentally validated reduced order models are developed for heat transfer and rotordynamic analysis. Using the elaborated framework, a constrained multi-objective system optimization of a 300 W engine is performed based on ten design parameters and comparing SiAlON and Inconel 718 as potential rotor materials available for additive manufacturing. Hereby, bearing lifetime, system efficiency, and specific power are maximized while meeting rotordynamic, structural, and thermal requirements. Evaluating the results, interdisciplinary effects are highlighted, and two optimum engine configurations are suggested. [ABSTRACT FROM AUTHOR]

Ultramicrogas turbines (UMGTs) for electric power generation up to 1 kW are a viable replacement technology for lithium batteries in drones due to their high energy density. Previous research has shown that small-scale effects disqualify conceptual design practices applied to larger gas turbines owing to highly coupled, nonlinear component interactions. To fill this gap, we propose an interdisciplinary conceptual design and analysis framework based on reduced order models. To this end, the current work is divided into two parts covering component design and system integration, analysis, and optimization. In Part I, automated conceptual design of all engine subcomponents is elaborated facilitating interdependent reduced order models for compressor, turbine, combustor and high-speed generator while also considering additive manufacturing constraints. In a second step, the reduced order performance models are compared to computational fluid dynamics (CFD) Reynolds-averaged-Navier-Stokes (RANS) simulations of various turbomachinery geometries as well as experimental data of combustor and high-speed generator prototypes, showing good agreement and thus validating the component modules. In conclusion, the first part of this work elaborates an automated and efficient method to conceptual design of all components required for a functional UMGT. Since the strategy is applicable independent of component arrangement and engine layout, the proposed methods offer a universal framework for small gas turbine generators. [ABSTRACT FROM AUTHOR]

In view of the cost and reliability issues caused by mechanical position sensors, position sensorless control (PSC) of permanent magnet synchronous motors (PMSMs) has received widespread attention. A series of rotor position estimation (RPE) schemes have been developed, in which the phase‐locked loop (PLL) plays an important role. However, the conventional phase‐locked loops face two thorny issues, one is the degradation of RPE performance under motor acceleration and deceleration conditions, and the other is high noise sensitivity. To this end, an adaptive gain PLL (AG‐PLL) is proposed for PSC of PMSM drives. The gains of the loop filter in the proposed AG‐PLL are adaptively adjusted with the estimation error in order to find a compromise between the estimation performance under motor acceleration and deceleration conditions and the noise sensitivity. Moreover, the proposed scheme avoids increasing the order of the PLL, so its dynamic performance is also guaranteed. The proposed scheme is tested based on the hardware‐in‐the‐loop platform. [ABSTRACT FROM AUTHOR]

A rotor speed signature analysis‐ (RSSA‐)based inter‐turn short circuit (ITSC) fault diagnostic method is proposed, which is robust with regard to speed‐ and current‐loop bandwidths of permanent magnet synchronous machine (PMSM) drive systems. Conventional ITSC fault detection solutions that rely on current signals or extra devices. Thus, an initial step of investigation on the validity of RSSA is taken for residual insulation capacity monitoring of the ITSC fault at the incipient stage. The Vold–Kalman filtering order tracking method is employed for the real‐time extraction of fault features. Besides, the impact of speed‐ and current‐loop controller bandwidths on ITSC fault diagnosis is also analysed and an Adaline estimator is designed to decouple their impacts. Finally, the effectiveness of the proposed method is verified on a faulty PMSM, which exhibits satisfying results in tracking the degradation of residual insulation, even if the phase currents are significantly distorted due to low switching frequency of the inverter. [ABSTRACT FROM AUTHOR]