The Experts below are selected from a list of 6372 Experts worldwide ranked by ideXlab platform
Judith P Armitage - One of the best experts on this subject based on the ideXlab platform.
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the rhodobacter sphaeroides flagellar motor is a Variable Speed Rotor
FEBS Letters, 1997Co-Authors: Helen L Packer, Helen Lawther, Judith P ArmitageAbstract:The rotation rate of the unidirectional stop/start motor of Rhodobacter sphaeroides was investigated using computerised motion analysis of tethered cells. The R. sphaeroides motor was found to have a Variable rotation rate compared to the virtually constant-Speed motor of wild-type and CheR mutant (smooth swimming) Escherichia coli. In addition, the dynamics of the R. sphaeroides motor during stopping was analysed with no consistent correlation behaviour. The motor could go from full rotation to stop, or stop to full rotation within one video frame, i.e. 0.02 s, but it could also slow down into a stop or restart slowly, taking up to 0.25 s. The R. sphaeroides motor under chemokinetic stimulation was also analysed and was found to show increased torque generation and reduced variation in rotation rate.
Helen L Packer - One of the best experts on this subject based on the ideXlab platform.
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the rhodobacter sphaeroides flagellar motor is a Variable Speed Rotor
FEBS Letters, 1997Co-Authors: Helen L Packer, Helen Lawther, Judith P ArmitageAbstract:The rotation rate of the unidirectional stop/start motor of Rhodobacter sphaeroides was investigated using computerised motion analysis of tethered cells. The R. sphaeroides motor was found to have a Variable rotation rate compared to the virtually constant-Speed motor of wild-type and CheR mutant (smooth swimming) Escherichia coli. In addition, the dynamics of the R. sphaeroides motor during stopping was analysed with no consistent correlation behaviour. The motor could go from full rotation to stop, or stop to full rotation within one video frame, i.e. 0.02 s, but it could also slow down into a stop or restart slowly, taking up to 0.25 s. The R. sphaeroides motor under chemokinetic stimulation was also analysed and was found to show increased torque generation and reduced variation in rotation rate.
Rezaeiha A. - One of the best experts on this subject based on the ideXlab platform.
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Towards optimal aerodynamic design of vertical axis wind turbines: Impact of solidity and number of blades
2018Co-Authors: Rezaeiha A., Montazeri H., Blocken B.Abstract:The current study systematically analyzes the impact of solidity (σ) and number of blades (n) on the aerodynamic performance of 2-, 3- and 4-bladed Darrieus H-type vertical axis wind turbines (VAWTs). Solidity varies within the wide range of 0.09–0.36. A large number of operational parameters, i.e., tip Speed ratio (λ), Reynolds number (Re), turbulence intensity and reduced frequency (K) are investigated to provide a deeper insight into the impact of σ and n on the dynamic loads on blades, the turbine performance and the wake. High-fidelity unsteady Reynolds-averaged Navier-Stokes (URANS) simulations, extensively validated with experiments, are employed. The results show that the turbine optimal tip Speed ratio (λopt) is invariant to a newly-introduced parameter ‘’, regardless of the turbine geometrical and operational characteristics. In addition, a new correlation is derived to estimate λopt as a function of σ, which can also be employed to predict the optimal σ for a turbine with a given λ. It is also found that: (i) for constant-Speed urban VAWTs, which due to the low mean wind Speed in the urban environment, frequently operate at moderate to high λ, a relatively-low σ is optimal; (ii) an optimal VAWT is a moderately-high-solidity Variable-Speed Rotor maintaining a relatively-low λ, where due to the large blade chord length the resulting Re and K are favorably high; (iii) within the turbine optimal operational range, turbine power coefficient (CP) is almost independent of n. The present findings support the optimal aerodynamic design of small-to large-scale VAWTs
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Towards optimal aerodynamic design of vertical axis wind turbines: Impact of solidity and number of blades
Elsevier, 2018Co-Authors: Rezaeiha A., Montazeri H Hamid, Blocken, Bje BertAbstract:\u3cp\u3eThe current study systematically analyzes the impact of solidity (σ) and number of blades (n) on the aerodynamic performance of 2-, 3- and 4-bladed Darrieus H-type vertical axis wind turbines (VAWTs). Solidity varies within the wide range of 0.09–0.36. A large number of operational parameters, i.e., tip Speed ratio (λ), Reynolds number (Re), turbulence intensity and reduced frequency (K) are investigated to provide a deeper insight into the impact of σ and n on the dynamic loads on blades, the turbine performance and the wake. High-fidelity unsteady Reynolds-averaged Navier-Stokes (URANS) simulations, extensively validated with experiments, are employed. The results show that the turbine optimal tip Speed ratio (λ \u3csub\u3eopt\u3c/sub\u3e) is invariant to a newly-introduced parameter ‘σλ \u3csup\u3e3\u3c/sup\u3e’ regardless of the turbine geometrical and operational characteristics. In addition, a new correlation is derived to estimate λ \u3csub\u3eopt\u3c/sub\u3e as a function of σ which can also be employed to predict the optimal σ for a turbine with a given λ. It is also found that: (i) for constant-Speed urban VAWTs, which due to the low mean wind Speed in the urban environment, frequently operate at moderate to high λ a relatively-low σ is optimal; (ii) an optimal VAWT is a moderately-high-solidity Variable-Speed Rotor maintaining a relatively-low λ where due to the large blade chord length the resulting Re and K are favorably high; (iii) within the turbine optimal operational range, turbine power coefficient (C \u3csub\u3eP\u3c/sub\u3e) is almost independent of n. The present findings support the optimal aerodynamic design of small-to large-scale VAWTs. \u3c/p\u3
Edward C Smith - One of the best experts on this subject based on the ideXlab platform.
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lagwise dynamic analysis of a Variable Speed Rotor
Aerospace Science and Technology, 2013Co-Authors: Dong Han, Edward C SmithAbstract:Abstract An aeroelastic simulation of a Variable Speed Rotor in forward flight is conducted to investigate its dynamic characteristics in steady and transient states. The system equations of motion are derived based on the generalized force formulation by using Hamiltonʼs principle. The periodic and transient aeroelastic responses of a four bladed stiff in-plane Rotor are analyzed to investigate the loads transfer phenomenon in the lagwise direction. The transient lagwise moment increases sharply during the 2/rev resonance crossing. This high transient load in rotating frame is not transferred to the fixed frame. Flap motion has vital contribution to the periodic and transient lagwise loads. The 1/rev flapping motion in the rotating frame can excite the 4/rev Rotor torque in the fixed frame due to the Coriolis force. The faster the blade crosses the resonance area, the smaller the transient lagwise loads and the higher the Rotor torque. For the dissimilar Rotor with 5% reduction of one blade mass at 60% to 70% Rotor radius, the unbalanced 2/rev lag moment in the rotating frame is transferred to the fixed frame as the 2/rev Rotor torque. Increasing blade lag critical damping from 1% to 5% can reduce the peak–peak lagwise root bending moment by 64.9%, and the Rotor torque is reduced to the level without dissimilarity. The dynamics of a stiffer Rotor during the 4/rev resonance crossing is also addressed.
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transient loads control of a Variable Speed Rotor during lagwise resonance crossing
AIAA Journal, 2013Co-Authors: Dong Han, Edward C Smith, Joseph Wang, George A LesieutreAbstract:Varying Rotor Speed during operation is a potential way to improve Rotorcraft performance. The transient aeroelastic response of a stiff in-plane Rotor system undergoing Variable Speed operation in forward flight is considered. During crossing of the fundamental lag mode near 2/rev, high transient lag bending moments are observed. The flapping amplitude and duration of the resonance crossing event have a strong influence on the peak lagwise root bending moment. Embedded chordwise fluidlastic dampers are explored as a way to reduce the peak bending moments. Determination of the fluidlastic damper properties is based on the analysis of a two degree-of-freedom blade-damper system. Parametric studies show that tuning port area ratios, loss factors, and device mass can be modified to enhance damper performance, and control the stroke. Results indicate that more than 6% critical lag damping can be provided around the resonance Rotor Speed, and that approximately 65% peak-to-peak moment reduction can be achieved...
Helen Lawther - One of the best experts on this subject based on the ideXlab platform.
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the rhodobacter sphaeroides flagellar motor is a Variable Speed Rotor
FEBS Letters, 1997Co-Authors: Helen L Packer, Helen Lawther, Judith P ArmitageAbstract:The rotation rate of the unidirectional stop/start motor of Rhodobacter sphaeroides was investigated using computerised motion analysis of tethered cells. The R. sphaeroides motor was found to have a Variable rotation rate compared to the virtually constant-Speed motor of wild-type and CheR mutant (smooth swimming) Escherichia coli. In addition, the dynamics of the R. sphaeroides motor during stopping was analysed with no consistent correlation behaviour. The motor could go from full rotation to stop, or stop to full rotation within one video frame, i.e. 0.02 s, but it could also slow down into a stop or restart slowly, taking up to 0.25 s. The R. sphaeroides motor under chemokinetic stimulation was also analysed and was found to show increased torque generation and reduced variation in rotation rate.
