Variable Rotational Speed Research Articles

Rubbing characteristics of a rotating blade with cracks

A novel compound fault modeling (NCFM) method is proposed to provide a qualitative numerical characterization of the cracked blade with the rubbing fault. Firstly, the proposed NCFM method incorporated the effects of centrifugal stiffening and spinning softening on the rotating blade under aerodynamic force. Secondly, multiple factors including variable speed, crack depth, and multi-failures modes (i.e., crack fault, rubbing fault) are considered to establish the effect matrixes (i.e., the additional effect matrix introduced by rubbing fault and the nonlinear crack fault) of different failures. Beside, a modified rubbing force model of the cracked blade is established. Moreover, an in-depth comparative analysis of the obtained results with the variable contact friction coefficients, casing stiffness, rotational speed, and crack stiffness underlines the relevance of compound fault. On the one hand, the continuous increase of rotational speed or crack depth will intensifies rubbing, including a decrease in rubbing interval and an increase in rubbing displacement amplitude. On the other hand, crack fusion leads to earlier development of rubbing, with smaller rotational speeds corresponding to less severe rubbing.

Experimental study on performance predictions of pumps as turbine

Pumps as turbine can be utilized in water systems to convert waste energy into electricity and reduce leakage rates, offering an effective and affordable solution. Accurately estimating the energy production of a pump as turbine (PAT) is crucial for water stakeholders in order to calculate the payback period. Unfortunately, pump manufacturers do not provide pump characteristics in turbine mode, necessitating the development of experimental correlations by researchers to predict the characteristics. In this study, recent correlations are compared to experimental results obtained from a test rig. The use of a large database improves the accuracy of the predictions of characteristic curves and best efficiency points (BEP) in variable rotational speed. Finally, a prediction guideline is made to enable accurate prediction of the performance of a pump in turbine mode.

Wind Tunnel Testing and Analysis of a Rigid, Variable Speed Rotor for eVTOL Applications

Many electric vertical take-off and landing (eVTOL) aircraft intended for the urban air mobility (UAM) market are currently being designed with multirotor configurations using variable speed fixed-pitch, rigid rotors for lift. These types of rotors, which are similar in construction to general aviation airplane propellers, are simpler than helicopter rotors and have no moving parts in the rotating frame. This paper discusses wind-tunnel testing of a full-scale, UAM multirotor size, fixed-pitch, rigid rotor with a focus on vibratory blade loads and on the ability to predict these loads with comprehensive analysis. Test results show that vibratory loads are very high, with peak-to-peak magnitudes up to three times greater than the steady component. Correlation of test data to comprehensive analysis using geometrically exact composite beam structural elements and dynamic inflow wake modeling captures the trends in the steady and vibratory loads though it underpredicts the magnitudes; an expected result with the level of wake modeling fidelity used. The paper also discusses the physical sources of the observed vibratory loads and suggests potential options for mitigating their magnitude.

Analysis of Effect of Propeller Rotational Speed Variations on Torque and Power Using Computational Fluid Dynamics (CFD) Method

The speed on the ship is inseparable from a good propeller design in order to get the optimal thrust generated by the propeller motion. The propeller is a very important part in determining the ship's motion. The propeller itself is a tool used to generate thrust that comes from engine power transmitted through the shaft. Computational Fluid Dynamics (CFD) is a very suitable method for analyzing complex systems that are difficult to solve using manual calculations. With these advantages, CFD is often used to analyze a pattern of a system, one of which is the propeller, which in this study uses variations in flow velocity and propeller speed which can affect the value of the torque and power produced by the propeller.

Insights into the friction stir processing of fused filament fabricated polymers with multiple reinforcements

ABSTRACT Friction stir processing (FSP) is a most widely used severe plastic deformation (SPD) technique used for enhancement of mechanical properties and refinement of microstructure in metals, alloys and also in surface alteration, surface composites, and metal matrix composites. This work deals with the integration of FSP with fused filament fabrication (FFF), a popular additive manufacturing (AM) method. The research work comprises of four parts, first being 3d printing of poly lactic acid (PLA) and acrylonitrile butadiene styrene (ABS) parts through FFF, then multiple reinforcements like multi-walled carbon nanotubes (MWCNTs), aluminum oxide (Al2O3) and silicon dioxide (SiO2) are filled into the grooves, then in the third step FSP is performed on the 3D specimens with variations in rotational and travel speed of the tool with threaded pin profile. Finally, tensile strength is examined and the effect of different reinforcements is studied. The results indicate that MWCNTs reinforced PLA is found to have the highest strength (37.41 MPa) which is 72.6% more than the lowest strength (21.67 MPa) obtained for SiO2 reinforced PLA. However, in the case of other polymer, SiO2 reinforced ABS exhibited maximum strength (14.71 MPa) amongst other reinforcements for ABS. The ductility is decreased for all the FFF specimens after FSP and PLA composites exhibited improved surface profiling parameters as compared with ABS composites after FSP. Also, fractography is performed to understand the failure modes of specimens filled with different reinforcements.

Unveiling the effect of MnO/SiO2 ratios on the viscosity and structure of mold fluxes for high-Mn cryogenic steels

The serious reaction between Mn in molten steel and SiO2 in calcium silicate-based mold flux during continuous casting of Al-free high-Mn cryogenic steels could change the mold flux properties and in-mold performance. In this study, the combination of rotating viscometer, FTIR spectroscopy, Raman spectroscopy and O1s X-ray photoelectron spectroscopy (XPS) was employed to get a deep insight into the effect of the reaction levels characterized by MnO/SiO2 ratios on the viscosity and structure of mold fluxes. The results exhibit that the transformation of mold flux from Newtonian fluid to non-Newtonian fluid can be reflected by viscosity change with varying rotation speeds. The viscosity decreases continuously with increasing MnO/SiO2 ratio but the temperature dependence of viscosity decreases at high MnO/SiO2 ratio. Structural information from FTIR revealed the slag system is mainly a silicate structure. The deconvoluted results of Raman spectra show an increase in NBO/Si, amounts of Q0 ([SiO4]4–) and Q1 ([Si2O7]6–) units with increasing MnO/SiO2 ratio, whereas a decrease in amounts of Q2 ([SiO3]2–) and Q3 ([Si2O5]2–) units in the meantime, this indicates the depolymerization of the silicate structure with proceeding of the slag/steel reaction. According to semiquantitative analysis of XPS spectra, the relative proportion of bridge oxygen (O0) decreases at the cost of non-bridged oxygen (O–), which suggests that the silicate structure gradually depolymerizes. The structural analysis supports the change of viscous behavior of mold flux with slag/steel reaction.

A fault location method based on ensemble complex spatio-temporal attention network for complex systems under fluctuating operating conditions

Recently, traditional fault diagnosis methods achieve fault identification by establishing a sample set covering all fault degrees of different fault components in complex systems. However, the uncertainties including environmental stresses and own physical and chemical variations lead to an infinite number of fault degrees of fault components, and the fault identification of complex systems in practical engineering applications faces the challenge of fluctuating operating conditions due to variations of rotational speed and load. To address the above problem, a fault location method based on ensemble complex spatio-temporal attention network (ECSAN) is proposed in this paper, which can identify the critical fault components of complex systems by combining an ensemble learning mechanism with excellent basic estimators. A basic estimator consists of a feature extraction module, a feature enhancement module, and a classification module. In the first module, a complex spatio-temporal backbone network with strong generalization is developed to provide spatio-temporal features containing the inherent information of the sample data for complex systems. In the feature enhancement module, a lightweight complex attention layer is constructed to enhance the effective structural information of the features and reduce the interference of their redundant information. The classification module then adopts a Softmax layer to perform fault classification. Finally, an ensemble learning mechanism is designed to integrate the basic estimators. By constructing sample weights and introducing a knowledge transfer strategy, the generalization is further improved while saving training expenses. Two datasets from different experimental platforms are concerned to verify the effectiveness and superiority of this method under various operating conditions and fault degrees. The experimental results indicate that this method achieves 99.81% accuracy on a standard dataset of the mechanical system and 98.88% accuracy on a real dataset of the closed-loop control system of the water jet propulsion device, which is superior to comparison approaches.

P18: Improving Hydraulic Performance of the Left Atrial Assist Device Using Computational Fluid Dynamics

Purpose of Study: The purpose of this study was to refine the initial design of a new left atrial assist device (LAAD) using the results from computational fluid dynamics analyses (CFD). The CFD results would help guide design changes that could improve the hydraulic performance and flow patterns within the LAAD. The LAAD is a novel continuous-flow pump, implanted in the mitral plane, designed to treat patients with heart failure with preserved ejection fraction. Methods: Four different LAAD designs were evaluated. The key differences among the designs included changes to the shape and dimensions of the primary impeller blades, and the number, size, and curvature of the diffuser vanes. Steady state, frozen-rotor CFD simulations were run at flow rates and rotor speeds spanning the LAAD’s intended range of use. Of the four designs studied, the first and final designs were prototyped and underwent in vitro hydraulic performance testing. The in vitro studies were conducted by connecting a prototype LAAD to a mock circulatory loop system designed to simulate various levels of diastolic heart failure. Static pressure measurements, taken upstream, downstream, and at two other locations within the pump, were compared with CFD-predicted pressures to validate the CFD modeling approach and results. Results: The CFD-predicted static pressures agreed within 12% for design #1 and 10% for design #4 over a wide range of flow rate/rotor speed conditions providing confidence in the CFD modeling results. Regions of flow separation downstream of the impeller blade tips and the diffuser vanes were reduced for each design iteration. Increasing the impeller blade diameter, provided increased pump pressure rise at the expense of significantly higher torque and power requirements. A comparison of the hydraulic performance for the four designs, as shown in Figure 1, reveals that design #4 was able to provide the same pump pressure rise as design #1 at 3,800 vs. 4,400 rpm. Conclusions: Guided by the insight gained from each design iteration, the fourth design incorporated impeller blades with an improved alignment with the incoming flow and wider, more curved diffuser vanes that aligned with the approaching flow from the volute. These changes reduced flow separation within the impeller and diffuser regions which significantly improved the LAAD’s hydraulic performance and internal flow patterns. In vitro testing of this fourth generation LAAD design confirmed the predicted improvement in hydraulic performance.Figure 1. Comparison of the hydraulic performance for the four LAAD designs at a flow rate of 4.5 L/min and varying rotor speeds.

A Reinforcement Learning approach to the Optimal Torque MPPT problem in wind turbines

In this work, a torque controller for a variable rotational speed wind turbine has been modelled using Reinforcement Learning and considering the Optimal Torque - Maximum Power Point Tracking problem as one of optimization. The reward optimization function is designed as a non-linear function depending mainly on the rotor power variation. Based on this, an optimal action (electromagnetic torque variation) regulates the turbine rotational speed. A simulated 1.5 MW three bladed wind turbine operation is managed by the torque controller. It keeps the turbine working at optimal operational conditions after a successful training process, which is carried out using the Proximal Policy Optimization algorithm. For the controller training, the turbine confronts constant and then randomly staggered wind speed behaviour. Time series of rotor angular speed, torque and power are presented. Our results show that the modelled controller is able to reach and maintain the wind turbine operation at its optimal power generation conditions. This methodology avoids using some empirical parameter characteristic of the Optimal Torque - Maximum Power Point Tracking algorithm widely used in wind turbine control systems.

Improved prediction of coherent structure in an intermediate turbine duct

Modeling the unsteady flow in an intermediate turbine duct in an aero-engine is highly challenging partly owing to the complex physics subjected to unsteady vortical flow upstream. In this paper, the high-fidelity detached eddy simulations of an aggressive intermediate turbine duct are performed and validated against published data. The dominating coherent flow motions are then captured with sparsity-promoting dynamics mode decomposition under different tip gap sizes and rotating speeds of the rotor blade. Furthermore, a novel low-order spectrum reconstruction method based on selected flow modes and Gaussian fitting is proposed for fast prediction of the instantaneous flowfield in the intermediate turbine duct. The sources of error are discussed and a potential approach to improve the prediction accuracy is proposed. It reveals that the proposed method achieves accurate and generalized performance in reconstructing and predicting flow fields with periodic features for a small cost of calculation time. The maximum root mean squared error in the scenario of tip gap size and rotating speed variation is below 5.96 and 8.41, respectively. The error analysis shows that the variation of flow modes under different inflow conditions and nonlinearity of interacting flow structure accounts for the major part of prediction error. By applying a Proper orthogonal decomposition (POD) interpolation on the flow modes, the maximum root mean squared error in the scenario of tip gap size and rotating speed variation can drop to 4.76 and 2.69 without breaking the physical meaning of the representative modes. The novelty of the present work lies at the proposed prediction method combining DMDSP and POD-interpolation, of which the majority of the physical information are maintained and the prediction accuracy is improved. It may provide a promising approach for turbomachinery design, flow prediction, and investigating underlying mechanisms with low data requirements.

Mathematic Modelling of a Reversible Hydropower System: Dynamic Effects in Turbine Mode

Over the past few years, there has been significant interest in the importance of reversible hydro-pumping systems due to their favorable flexibility and economic and environmental characteristics. When designing reversible lines, it is crucial to consider dynamic effects and corresponding extreme pressures that may occur during normal and emergency operating scenarios. This research describes essentially the turbine operation, although various boundary elements are mathematically formulated and presented to provide an understanding of the system complexity. Different numerical approaches are presented, based on the 1D method of characteristics (MOC) for the long hydraulic circuit, the dynamic turbine runner simulation technique for the behavior of the power station in turbine mode and the interaction with the fluid in the penstock, and a CFD model (2D and 3D) to analyze the flow behavior crossing the runner through the velocity fields and pressure contours. Additionally, the simulation results have been validated by experimental tests on different setups characterized by long conveyance systems, consisting of a small scale of pumps as turbines (at IST laboratory) and classical reaction turbines (at LNEC laboratory). Mathematical models, together with an intensive campaign of experiments, allow for the estimation of dynamic effects related to the extreme transient pressures, the fluid-structure interaction with rotational speed variation, and the change in the flow. In some cases, the runaway conditions can cause an overspeed of 2–2.5 of the rated rotational speed (NR) and an overpressure of 40–65% of the rated head (HR), showing significant impacts on the pressure wave propagation along the entire hydraulic circuit. Sensitivity analyses based on systematic numerical simulations of PATs (radial and axial types) and reaction turbines (Francis and Kaplan types) and comparisons with experiments are discussed. These evaluations demonstrate that the full-load rejection scenario can be dangerous for turbomachinery with low specific-speed (ns) values, in particular when associated with long penstocks and fast guide vane (or control valve) closing maneuver.

Komparasi Kinerja AC Kendaraan dengan Menggunakan Refrigeran R-134a, dan R-290

The development of vapor compression refrigeration systems currently depends on the issue of environmental problems related to ozone layer depletion (ODP) and global warming potential (GWP). In addition to environmental issues, low energy use is also in the spotlight of researchers. To solve the problem of refrigeration development, natural refrigeration, especially hydrocarbons, is the focus of attention. Hydrocarbons are refrigerants that have excellent properties to be natural refrigerants. This study aims to compare the performance of refrigerant R-134a with R-290. The research used a standard vapor compression refrigeration system with a TEV-type expansion valve. The system performance is seen through compression, refrigeration effect, and COP with variations in compressor rotational speed of 1000 rpm, 1500 rpm, and 2000 rpm. The results showed that the compression work, refrigeration effect, and coefficient of performance (COP) of R-290 had a more excellent value. R-290 produces the highest compression work at a 2000 rpm compressor speed of 33.34 kJ/kg for the refrigeration effect at 1000 rpm of 353.33 kJ/kg and COP at 1500 rpm 12.32.

Semi Twisted Curve Blade Vortex Turbine Performance at Runner Rotation Speed Variation using CFD Simulation

Utilization of renewable energy potential continues to be developed at this time. One of them is a hydroelectric power plant with turbulent vortex technology. One of the vortex turbine blade designs that has been developed is the semi twisted curve. The blades shape of the blades and the position of the runners affect the performance of the vortex turbine. This research uses CFD simulation by varying the rotational speed of the runner, which is between 80 to 120 rpm. The position of the upper end of the runner is placed at a depth of 4.5 cm from the total depth of the cone basin of 33 cm, the maximum water power is set at 28.66 Watt obtained from the mass flow rate of water of 6.21 kg/s. The simulation results show that as the runner's rotational speed increases, the torque decreases, as well as the torque decreases slightly. The highest turbine power and efficiency occurred at 90 rpm runner rotation, which was 4.044 Watt and 14.11% respectively. This is because the turbine power calculation is the result of the multiplication between torque and runner rotation which produces the highest value at 90 rpm.

Harmonic vibration suppression of maglev rotor system under variable rotational speed without speed measurement

Harmonic vibration suppression of maglev rotor system under variable rotational speed without speed measurement

Transient thermal properties investigation for precision bearing-spindle system considering fixed-position preload and lubricant viscosity-temperature effect

Estimating the thermal properties of the precision bearing-spindle system is essential for machine tool operating accuracy and service life. To predict transient temperature field and related heat behavior exactly, an improved thermal network model for the spindle system considering fixed-position preload and lubricant viscosity-temperature effect was proposed. Firstly, the thrust load-axial displacement relationship of angular contact ball bearing was deduced, as well as the difference of bearing inner/outer ring thermal displacement in condition of Double O configuration, and the structural deformation for the spindle system subject to thermal-mechanical effect. Then, the bearing heat generation via the local approach and thermal resistances were calculated, and heat balance equations were derived and solved. Finally, the transient model coupled with heat generation/transfer and structural deformation in service was constructed, and the temperature field and related heat behaviors were obtained. Moreover, the results of theoretical model were compared with those of experiment test, indicating that the bearing temperature rise and spindle end deformation were in good agreement. Meanwhile, the bearing temperature rise, bearing and spindle deformation, and actual preload force were discussed, which had a nonlinear relationship and a positive correlation trend with rotation speed and initial preload. In addition, the assembly status might change with the variation of rotation speed.

Kriging-Based Surrogate Controller for Robust Control of a Flexible Rotor Supported by Active Magnetic Bearings

Abstract Vibration control in supercritical rotors is a challenging task due to the underlying complex dynamics that high-speed machinery undergoes. When taking into account both structural (e.g., structural integrity and material properties) and operational (e.g., rotational speed variation and environmental effects) uncertainties that can plague such systems, the task of designing and implementing a robust and reliable control system becomes increasingly daunting. In this contribution, a Kriging modeling approach is used to derive a representative surrogate-based controller applied to a flexible rotor supported by active magnetic bearings. The surrogate controller is formulated by considering the relationship between the shaft position and actuator current. This means that after proper training, the surrogate control takes the rotor position (proximity sensor readings) as input, and the output corresponds to the current levels for the actuators to control the system vibration amplitudes. Experimental tests considering a test rig composed of a flexible rotor supported by two active magnetic bearings were used to validate the proposed approach for different operational scenarios, namely, steady-state, run-up, and transient-state. In this case, the surrogate model was trained considering the shaft positions and the corresponding control currents measured with the rotor operating close to its first bending critical speed. The obtained results illustrate how the Kriging-based surrogate controller can reliably maintain acceptable vibration levels, even when exposed to unexpected constant rotation speeds and other operating conditions not manifested in previous sample sets.

Analysis on the dynamic characteristics of spiral groove dry gas seal based on the gas film adaptive adjustment model

PurposeThis study aims to acquire the influence mechanism of gas film adaptive adjustment (GFAA) acted on the dynamic characteristics of spiral groove dry gas seal (S-DGS) and then propose a sealing stability enhancement measure.Design/methodology/approachThe gas film dynamic stiffness and damping of S-DGS are obtained by numerically solving the transient Reynolds equation based on perturbation method and finite difference method. The dynamic coefficients in GFAA model and constant gas film thickness (CGFT) model are compared and analyzed.FindingsThere is the risk to misestimate the instability of DGS with rotational speed or medium pressure grows under the condition of CGFT assumption. Based on GFAA model, increasing balance ratio B properly is an effective measure to improve the stability of DGS. The balance ratio can stimulate the sensitivity of gas film dynamic coefficients to the variation of rotational speed. Increasing medium pressure in small balance ratio range will be conducive to reducing the risk of angular instability.Originality/valueThe influence mechanism of GFAA on S-DGS dynamic characteristics is analyzed. The interactions between rotational speed and balance ratio, medium pressure and balance ratio acted on gas film dynamic characteristics are explored based on the GFAA model.

OC6 project Phase III: validation of the aerodynamic loading on a wind turbine rotor undergoing large motion caused by a floating support structure

Abstract. This paper provides a summary of the work done within Phase III of the Offshore Code Comparison Collaboration, Continued, with Correlation and unCertainty (OC6) project, under the International Energy Agency Wind Technology Collaboration Programme Task 30. This phase focused on validating the aerodynamic loading on a wind turbine rotor undergoing large motion caused by a floating support structure. Numerical models of the Technical University of Denmark 10 MW reference wind turbine were validated using measurement data from a 1:75 scale test performed during the UNsteady Aerodynamics for FLOating Wind (UNAFLOW) project and a follow-on experimental campaign, both performed at the Politecnico di Milano wind tunnel. Validation of the models was performed by comparing the loads for steady (fixed platform) and unsteady (harmonic motion of the platform) wind conditions. For the unsteady wind conditions, the platform was forced to oscillate in the surge and pitch directions under several frequencies and amplitudes. These oscillations result in a wind variation that impacts the rotor loads (e.g., thrust and torque). For the conditions studied in these tests, the system aerodynamic response was almost steady. Only a small hysteresis in airfoil performance undergoing angle of attack variations in attached flow was observed. During the experiments, the rotor speed and blade pitch angle were held constant. However, in real wind turbine operating conditions, the surge and pitch variations would result in rotor speed variations and/or blade pitch actuations, depending on the wind turbine controller region that the system is operating. Additional simulations with these control parameters were conducted to verify the fidelity of different models. Participant results showed, in general, a good agreement with the experimental measurements and the need to account for dynamic inflow when there are changes in the flow conditions due to the rotor speed variations or blade pitch actuations in response to surge and pitch motion. Numerical models not accounting for dynamic inflow effects predicted rotor loads that were 9 % lower in amplitude during rotor speed variations and 18 % higher in amplitude during blade pitch actuations.

Fault diagnosis of low‐speed rolling bearing based on weighted reconstruction of vibration envelopes

AbstractThe main bearing supports the rotation of the main shaft of a wind turbine. It bears heavy dead weights as well as variable speed dynamic loading during operations; thus, it is a vulnerable part in a wind turbine drive train. Because of the low speed and time‐varying operations of the main bearing, vibrations generated by bearing faults are often weak in response amplitudes, low in frequency range, and smeared in damage feature energy. As a result, the applicability of the conventional acceleration envelope analysis (AEA) technique, a traditionally effective technology for bearing fault diagnosis, is limited in such cases. In order to resolve this, a modified AEA method specially designed for bearings with low and variable speed operation is proposed in this paper. First, the structural response is decomposed by means of variational mode decomposition (VMD) for the low frequency components to form a series of band‐limited intrinsic mode functions (BLIMFs). Next, weighting factors are determined for the BLIMFs by defined energy ratios. Finally, a new envelope is reconstructed by weighting the envelopes of each BLIMF for bearing fault diagnosis. The effectiveness and practicality of the proposed method for the diagnosis of main bearing faults in wind turbines is verified through the analysis of measured data from a wind turbine in the field. The proposed method provides an effective way for bearing fault diagnosis at low and variable rotational speeds.

Hover Dynamics and Flight Control of a UAM-Scale Quadcopter With Hybrid RPM and Collective Pitch Control

Hover analysis is performed on a 1200-lb gross weight UAM-scale quadcopter with both variable rotor speed and collective pitch control. With these redundant controls, the hover performance and flight dynamics are considered at three trim points, where power consumption can be increased to improve authority of the pitch inputs for changes in rotor thrust. An explicit model following control laws is optimized using CONDUITR to meet ADS-33E-PRF handling qualities specifications, with design margin optimization on each axis. The responses of the linearized system are examined with either control type, and pitch control is shown to outperform RPM-control in heave, while the opposite is true for yaw. Trim in axial climb is simulated, where the collective pitch can be scheduled with the climb rate to maintain effective stall margin. Hybrid control mixing is implemented using a complementary filter, allowing the aircraft to use pitch control for short-term responses and RPM control for trim. The benefits of this hybrid control scheme are demonstrated through simulation of hot/high/heavy conditions, where trimming with RPM control allows the pitch actuators to maintain margin for maneuvers. It is concluded that hybrid control allows the aircraft to reap the benefits of pitch control for maneuverability while maintaining stall margin by using RPM control for trim.