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In this research, the fault-tolerant pitch angle control of a horizontal axis wind turbine in region 3 (where the wind velocity is greater than rated wind speed) is investigated. The effective wind velocity (EWV) is one of the necessary information for each control system. Wind speed is measured by the anemometers on the top of the nacelle however, the measurement is not precise and is only applicable for one point in the rotor. To address this issue, we have developed a novel hybrid approach. The approach is based on a sliding mode observer to estimate the aerodynamic torque and an adaptive neuro-fuzzy inference system (ANFIS) is introduced for obtaining the EWV. The estimated aerodynamic torque, pitch angle, and rotor speed are the inputs to this system and EWV is the output. New super twisting sliding mode control is introduced to overcome the faulty actuator case and control optimally the output power. Pitch sensitivity is further necessary information that is determined by another ANFIS system. The estimated EWV, pitch angle, and rotor speed are inputs of this system. Thus, the only information that is needed for this control approach is the pitch angle and rotor speed. The full aeroelastic simulations demonstrate excellent performance in comparison to the gain schedule PI control approach in tracking the output power and can reduce both the fore-aft vibration of the tower and the flapwise vibration of the blade significantly.

Lightning is a sudden release of electrostatic energy that plays a significant role in the ionospheric-magnetospheric coupling process. A short-term increase in the particle count rates (CR) in the Van Allen Radiation Belt (VAB) is known as the particle bursts. Due to lightning events, the increase in the number of high-energy particles in the inner region of the VAB (L 2) is a fascinating research to implement. This paper tries to determine the number of lightning-induced particles, which can successfully establish a connection between the two regions of the atmosphere (the ionosphere and the magnetosphere). Lightning-generated electromagnetic radiation propagates through the Earth Ionosphere Waveguide (EIWG), where some energy leaks through and scatters particles in the radiation belt. By lowering the pitch angle, some particles precipitate into the ionosphere and cause secondary ionization. This excess particle count caused by lightning strokes is detected using data from the NOAA-15 satellite and data from the World Wide Lightning Location Network (WWLLN) is used to verify the relationship between lightning stroke and particle count. In this paper, we process our work by using lightning locations over a specific region of India and the geographic/geomagnetic conjugate locations. The monthly variation shows a high correlation between the lightning stroke number and the particle counts within the conjugate geomagnetic location, while the correlation with the particle counts within the conjugate geographic location is significantly lower. In the second half of the paper, we use an automated energy filtration method, for the computation of the particle counts induced by maximum energetic lightning (having lightning energy value > 104 J and the particle counts induced by minimum energetic lightning (having lightning energy value 104 J). The results of this analysis demonstrate that the variation of PCs in the conjugate geomagnetic location is more closely related to the maximum energetic lightning variation than the lowest energetic lighting variation. This paper will demonstrate the coupling process between the ionosphere and the magnetosphere based on counting the particles produced by lightning.

This article aims to understand the pitch angle distributions (PADs) of the charged particles in the Earth’s inner magnetosphere using test-particle simulations. The emphasis is on characterizing the variation in pitch angle of the charged particles trapped along the Earth’s magnetic field lines. These charged particles undergo gyration, bounce, and azimuthal drift motions in the Earth’s inner magnetosphere. They are trapped until their pitch angle falls into the loss-cone to get lost into the upper atmosphere. We have developed a three-dimensional test-particle simulation model in which the relativistic equation of motion is solved numerically to track these trapped particle’s trajectories. We have examined the pitch angle distributions of the electron, proton, and oxygen for the cases where adiabatic invariants are conserved and non-conserved. For this purpose, we have considered the particle’s trajectory in the latitudinal range of [ - 40 ° , 40 ° ] for one complete drift around the Earth. We found that when adiabatic invariants are conserved, the particles possess butterfly-type pitch angle distributions. Whereas, when adiabatic invariants are not conserved, the particle’s pitch angle distribution bunches toward the 90°-peaked distribution. The situation of non-conservation of adiabatic invariants demonstrated in the present simulation is arising due to larger gyro-radius (few Earth radii) over which the ambient magnetic field is not constant. We have noticed that in the static dipolar magnetic field, all three, 1st, 2nd, and partly 3rd adiabatic invariants are non-conserved when gyro-radius is larger. The information on the change in the pitch angle distribution pattern from butterfly-type to 90°-peak distribution will be useful to understand the pitch angle distributions observed by the recent spacecraft in the Earth’s radiation belts.

Solar energy is one of the emerging technologies and the use of concentrating power technology is increasing in solar power plants. Parabolic trough collector is a concentrating solar power technology that is situated in the open terrain and subjected to wind loads. The structural stability of these devices under such loads determines the ability to accurately concentrate the rays at the absorber tube, which affects the overall optical and thermal efficiencies. A detailed numerical analysis is carried out at different wind loads and design conditions. It is observed that for a change in velocity from 5 m/s to 25 m/s, slope deviations increase from 1.21 mrad to 3.11 mrad at the surface of the reflector exceeding the shape quality of the mirror panels. Higher yaw angles and pitch angles of 60° and 120° are observed to be decisive in the design of collectors. Roof-mounted collectors experience a 40% higher drag force than ground-mounted collectors at a 0° pitch angle. For the Aluminium trough, the slope deviation at the surface of the reflector is higher by 4.62% than glass. The study will be helpful for engineers and scientists in the design of the parabolic trough collectors.

Offshore wind energy is one of the most important sources of renewable energy to make sure supplying enough electricity for the world in the future. The floating offshore wind turbine (FOWT) operates under many influences such as both the aerodynamic force, the hydrodynamic force and coupled motion between the two. Therefore, in this paper about the effect of collective pitch control and cyclic pitch control on power and loads of FOWT are discussed under the uniform wind velocity of 10 m/s with wind tunnel and numerical investigation. FAST tool (Fatigue, Aerodynamics, Structures, and Turbulence) is used to simulate FOWT under the same wind conditions as wind tunnel experiments. A two-bladed downwind turbine model is used for this experiment to estimate the fluctuations of the power coefficient, thrust coefficient and moments. The pitch moment and the yaw moment are measured at the top of the tower and the fluctuation of loads is compared. The phase angle of the pitch angle is controlled by three actuators through a swash plate equipment. From the simulated results, the effect of the pitch angle change on the power coefficient is higher than the yaw angle change. For the yawed wind condition, the load of the wind turbine at the phase angle of ξ = 60° was equal to the optimum operating point. Thence, the load of the wind turbine was decreased when the cyclic pitch control method was applied.

In this study, flow and heat transfer characteristics of binary hybrid nanofluid (CuO / MgO-water) through new configuration channel, namely: the curved-corrugated channel, are evaluated numerically using the multi-phase mixture model. The binary hybrid nanofluid is experimentally prepared with average diameters of 40 nm and three volume fractions of nanoparticles of 1%,3%, and 5%. Measured thermophysical properties are employed to simulate the complex flow within the tested configurations of channel with presence of E-shaped baffles. Various geometric parameters such as gap ratio (GR = 0.2,0.3,0.4, and 0.5), blockage ratio (BR = 0.2,0.25,0.3, and 0.35), and pitch angle (β = 10°, 12.5°, and 15°) at different Reynolds number (8000–28,000) and volume fraction (φ) of CuO / MgO particles (0–5%) are considered to serve the purpose. The findings uncover that the binary hybrid nanofluid improves the thermophysical properties of the base fluid and thereby boost the thermal performance of the system. It is found that the thermal-hydraulic performance (THPF) of binary hybrid nanofluid enhances with increasing volume fraction, and this enhancement is close to 38% when Re = 28,000 and φ = 0.05. Regards the geometric parameters, THPF enhances by increasing the blockage ratio and decreasing the pitch angle while recording the best improvement at the particular gap ratio, i.e. 0.3.

The mechanism of nanoparticle transport inside carbon nanotubes is taken into account to investigate the dynamics of single-walled carbon nanotubes carrying a nanoparticle. The motion of the nanoparticle is on helical tracks, which is induced by temperature difference in the nanotube, with main characteristics such as axial, and angular velocities and pitch angle. The helical motion is modeled based on constrained and unconstrained simulations. In the case of the former, the axial velocity is constant, however, in the latter simulation, the axial velocity is time-variant and stop-and-go events with simultaneous changes in the rotation direction are considered as random uncertainty in the system. Once the helical motion is clarified, the dynamic behavior of the nanotube acted upon by a moving nanoparticle is investigated for simply supported boundary conditions and stability analysis is performed to obtain the critical velocities as well as critical temperature differences based on Floquet theorem. For the case of the system with random uncertainty, the statistical properties as well as confidence and prediction intervals of the dynamic response are also studied by Monte-Carlo simulation. The results highlight the importance of the helical motion mechanism of the moving nanoparticle and the random uncertainty in the system.

Regions outside the reach of traditional propulsion systems or the ones that require significant propellant, may be reached by harnessing the solar radiation pressure and leveraging coupled dynamics to maneuver a sail-based spacecraft. Earth-trailing orbits have recently been investigated for getting a unique perspective of the Sun while maintaining the spacecraft in close proximity to Earth. Vertical orbits trailing the Earth exhibit the additional capability to view the Sun from above and below the ecliptic plane. In this work, families of sail-based orbits are explored for varying Earth-trailing angles and Z amplitudes in the Sun-Earth circular restricted three-body problem. Optimization is carried out to ensure that the non-traditional vertical orbits exhibit a constant pitch angle control history, as well as symmetry across the X-Y plane. The stability of the resulting orbit families is assessed using an extension of Flouquet theory to Differential Algebraic Equations. Results indicate that sail-based Earth-trailing vertical orbits can be more stable than traditional sub-L1 sail-based vertical orbits.

Pitch angle greatly affects the performance of VAWT. Aiming at the maximum value of CT, this study first obtains the theoretical optimal angles of attack, i.e., 17.7° and −18.4° in upwind and downwind zones. A 2.5D model is simulated using Fluent to determine the magnitude and direction of induced velocity, and an initial pitch angle adjustment law is obtained combining the proposed local TSR. Compared with a prototype wind turbine, CP is increased by 2.69% after applying the initial adjustment law. The fitting curve angle δ at the abrupt part of pitch angle is analyzed. The smaller the angle δ is, the more evident the performance improvement of VAWT becomes. CP is increased by 11.68% when the angle is δ = 0°. On this basis, the adjustment law corresponding to δ = 0° of 100°

Wind power is one of the cheapest and direct methods to alleviate negative impacts on environment therefore the demand of efficient wind energy conversion system is increasing. Uneven distribution of wind impacts the performance of Wind Turbine (WT) system so constant and noise free power at output is required. The pitching angle varies according to the Wind Speed (WS), and the power output equation of the entire WT system depends upon WT pitch angle. Pitch control is widely used to optimize power above rated WS. This paper proposes an efficient adaptive pitch control controller to maintain the output power of a 5 MW WT in dynamic wind conditions. Compared to low level control loops (such as PI), this illustrates the effectiveness of the proposed controller. The model was tested in a 5 MW WT GH bladed system.

As the lighter-than-air (LTA) flight vehicle, the stratospheric airship is a desirable platform to provide communication and surveillance services. During the ascent from sea-level to the mission altitude, the volume of the lifting gas may change significantly, which will result in the change of the center-of-buoyancy (CB). A general calculation method is developed to specify CB for the stratospheric airship with a double-ellipsoid hull and an arbitrary number of the gas cells. The cross-section-integral (CSI) method is used as a basic calculation scenario to specify CB. Considering the complexity in determining the boundary between the helium and air in the gas cell, a searching algorithm is put forward and the specification of CB can be conducted by the iterative calculation. As an important application, the stable condition of the pitch angle is analyzed when the change of CB is involved. Under different initial configurations, the stable pitch angle of the stratospheric airship during the ascent is specified and compared, which shows the advantages of the multi-gas-cell configuration. The results of this paper may provide an important reference for the engineering application of the stratospheric airship.

An uncertain ocean environment demands robust control to manoeuvre autonomous underwater vehicle (AUV) to achieve the control objectives. The desired depth of the vehicle can be achieved by implementing an efficient pitch angle control law to satisfy the longitudinal motion of AUV. In this paper, a linearized pitch channel model of MAYA AUV is used. A norm-based robust controller is designed to achieve the design requirements in the presence of parametric uncertainty and disturbance. The efficacy and feasibility of control laws demonstrated through a computational tool MATLAB.

Wind turbines are usually designed to withstand extreme winds statically so that they can survive a storm. In order to deal with power control and safety in operation during high wind speed, a pitch angle control system is proposed and has been employed in commercial wind turbines. In the present study, a small pitch-controlled wind turbine model with 0.8 m rotor diameter has been designed, constructed and tested in the wind tunnel. A linkage mechanism has been used to control the pitch angle by using a DC servo-motor as an actuator; this proved to be efficient and convenient for small wind turbines and worked perfectly. This study covers two main tasks. First, carefully extract the characteristic of the small wind turbine model under study at different wind velocities and pitch setting angles. Second, a pitch angle control system is implemented to control the power output of the turbine at wind speeds above the rated speed. The neural network fitting function provides a suitable and good controlling action in pitch angle control system which can achieve wind turbine the required power curve. All measurements and control actions were achieved by using the Arduino Mega board supported with MATLAB SIMULINK.

The current study evaluates the performance of magnetic sails as a function of the incoming velocity and flow direction. A particle model is employed for the simulation of multiple angle-velocity combinations for the incoming ion flow, leading to a relationship between the drag force and the sail properties. Apart from the drag force, the model is able to predict lift and side forces on the sail. The importance of the non-axial forces is evident when designing plane-change maneuvers within the solar system. Using the solar wind and the correct magnetic sail pitch angle, a change in the inclination of the orbital plane can be achieved. A study is therefore presented using a single-coil magnetic sail starting in the ecliptic plane and employing a bang–bang control for the pitch angle. An increase of more than 30°in the orbital inclination is achieved within a 20 year time-frame.

This paper investigates a novel control strategy that reduces the fatigue load of wind turbines during active power control. Based on the analysis of the reference power tracking of wind turbines, the proposed new control strategy considers simultaneous control of rotor speed and pitch angle. For this goal, a two-degree-of-freedom wind turbine active power control model based on the small-signal method is established, and the linearized fatigue load calculation is also completed in the model. For the effective control under this two-degree-of-freedom control framework, a model predictive control method suitable for multi-objective optimization is applied. Simultaneously, with the help of simulation tools, adaptive weight selection for multi-objective optimization is discussed and implemented. Simulation results show that the two-degree-of-freedom control system proposed in this paper can accurately implement reference power tracking and significantly reduce the fatigue load of wind turbines. The proposed method is valid not only on a single wind turbine but also in the wind farm’s active power dispatching process.

Smoothed particle hydrodynamics (SPH) is adopted to simulate the peak impact load, the water entry process and the water entry characteristics of a re-entry capsule with the complex capsule motions modelled by a developed six degrees of freedom fluid-solid coupling model. Diffused particle distribution is developed and used in the simulations to decrease memory and computational cost. The results show that the six degrees of freedom model and diffused particle distribution are valid. The results obtained by the improved SPH method match well with experimental results, and the maximal impact load of the capsule may reach more than 10 G, even tens of G. In addition, the peak impact loads are significantly affected by the capsule vertical velocity, the capsule mass, and the pitch angle, while are slightly affected by the horizontal velocity. More concretely, the peak impact load increases with the increase of vertical velocity, and decreases with the increase of mass. However, there is no definite law between the peak load and the pitch angle. These results can provide a foundation for guiding capsule design.

This paper proposes a new collective pitch controller for wind turbine systems to maintain the generator speed constant at the rated value in the region above the rated wind speed. It provides the command of the collective pitch angle to the wind turbine system, and one can impose explicit limits on the magnitude and the rate-of-change of the pitch angle command. In addition, the controller involves a variable gain that realizes non-overshooting convergence from the large errors in the generator speed and accurate regulation of the generator speed near the rated value. This controller is an extension of an amplitude- and rate-saturated controller previously proposed by the authors. It is combined with a state and disturbance observer and a lookup table-based feedforward. The proposed controller is validated through a software simulator FAST emulating a three-bladed horizontal-axis wind turbine system.

Roll-isolation is an effective way for spinning vehicle to greatly reduce the roll gyro range of strapdown Inertial Navigation System (SINS) and increase the accuracy of inertial navigation. However, during a recent flight test, the roll-isolated control system failure was observed under a large pitch angle ( 70 ° ⩽ θ ⩽ 85 ° ), which introduces a sharply increase in the roll angular velocity, the saturation of roll gyro and the inertial navigation failure. To address this issue, the governing equation of the roll-isolated system is derived with the consideration of various disturbance factors. The control failure is reproduced by numerical simulation. And the results show that the pitch and yaw angular velocity can cause a dramatic increase in roll rate under the large pitch angle, resulting in the roll-isolated control failure. Meanwhile, an improved roll-isolated control system is developed using PI controller, which is verified by mathematical simulation.

Parabolic trough collector (PTC) is a mature concentrating solar power technology that has been commercialized for the recent decades. However, in the operation experience, it is found that the wind load introduces a considerable threat on its performance and safe operation. In this paper, the deformation, vibration and corresponding optical efficiency loss (optical efficiency difference between non-wind and wind conditions) of parabolic trough collectors induced by wind load are systematically studied. A three-dimensional multiphysics-coupled (fluid dynamics-elastic mechanics-geometrical optics) transient model is firstly established in COMSOL Multiphysics and validated by benchmark data. Then, the wind load effects are investigated and the following conclusions have been drawn: (1) The maximum displacement increases with the increase of wind speed and quadratic fitting curve exhibits better agreement compared with exponential curve used in previous study. When wind speed is 14 m s−1, the maximum displacement reaches 9.55 mm and the corresponding optical efficiency loss is 19.83%. (2) Pitch angle significantly affects flow fields and deformations. When the pitch angle varies from 0° to 270°, the maximum deformation and minimum deformation are obtained at θ = 0° and θ = 270°, respectively. Besides, more precise flow fields with more details have been obtained compared with early studies. (3) By comparative investigation, it is proved that replacing time-varying wind speed with mean speed is inaccurate, which may underestimate the practical deformation and optical efficiency loss. (4) By elastic investigation, it is proved that aeroelastic response could occur locally while self-excited vibrations are not likely to occur under most practical operation conditions.

In this paper, passive reinforcement learning (RL) solved by particle swarm optimization policy (PSO–P) is used to handle an adaptive neuro-fuzzy inference system (ANFIS) type-2 structure with unsupervised clustering for controlling the pitch angle of a real wind turbine (WT). The proposed control scheme is based on gain-scheduled reinforcement learning recurrent ANFIS type 2 (GS-RL-RANFIST2) pitch angle controller to maintain the rotor speed at its rated value while smoothing the output power and the performance of the pitch angle system. The practical application of the proposed controller is evaluated by using FAST tool for a real 600 kW WT equipped with a synchronous generator with a full-size power converter (CART3, located at the National Renewable Energy Laboratory, NREL), whose results are compared with those obtained by a gain corrected proportional integral (GC-PI) controller. The results demonstrate that the GS-RL-RANFIST2, which sets the nonlinear characteristics of the system automatically and waves more uncertainties in the windy conditions, allows to increase the energy capture and smooth the output power fluctuation, and therefore, to improve the control and response of the WT.

In the present research, the performance of a prototype tidal turbine is evaluated via towing tank tests. The examined model is a three-bladed horizontal axis with a 1.15 m diameter. Previously, we studied the hydrodynamic behavior of this turbine and calculated the hydrodynamic coefficients using a numerical approach. Thus, this work concentrates on overwhelming the challenges, from manufacturing and assembling to data acquisition and power storage. The turbine is tested under various conditions namely: pitch angle, electrical load, carriage speed, and immersion depth to improve efficiency. Our experiment indicated the turbine performance to be the best being close to the surface of the water at different flow speeds. The optimum electrical load was found to be 20 Ω adding 16–40% to efficiency. By fixing the optimum load and tip immersion depth, the maximum efficiency of the whole rotor achieved around 0.265 at less than 0.56 m/s as towing speed while at the speed of 1.1 m/s, the maximum output power was more than 120 W having the pitch of the blades fixed at 20.4°.

The power performance of twin vertical axis wind turbines (VAWTs) is believed to surpass that of their individual counterparts. In this study, the power performance of twin VAWTs was investigated via computational fluid dynamics (CFD) simulations by changing their configuration parameters, including the airfoil section (NACA), solidity ratio (σ), pitch angle (β), rotational direction (φ), and turbine spacing (S/D). The CFD model was validated against wind tunnel test data from the literature. An L16 (45) orthogonal table was adopted to optimize the power performance using the Taguchi method. The rated power coefficient (CP) and rated tip speed ratio (TSR) were calculated for the 16 cases in the table. The extent of impact of the five parameters on the rated TSR ranked as σ ˃ β ˃ NACA ˃ φ ˃ S/D. In comparison, the extent of impact of these parameters on CP ranked as β ˃ S/D ˃ σ ˃ NACA ˃ φ. The optimal and worst configurations of the twin VAWTs were determined and their CP values increased by 13% and 8%, respectively, from that of their standalone counterparts. Moreover, the rated TSRs of the twin VAWTs differed from those of their standalone counterparts.

This paper proposes an adaptive control scheme for hypersonic vehicle with external disturbances, parametric uncertainties, actuator failures, input saturation and state constraints. Firstly, the longitudinal model of generic hypersonic vehicle is divided into velocity subsystem and altitude subsystem. Secondly, based on the tangent barrier Lyapunov function and auxiliary system, two adaptive fault tolerant controllers are designed for velocity subsystem and altitude subsystem, respectively, which can solve the problem of input saturation. By using the controllers, the flight states containing the angle of attack, flight path angle, pitch angle and pitch angle rate can be guaranteed in prospective ranges. Finally, the Lyapunov stability theory and numerical simulations are adopted to verify the effectiveness of the presented controllers.

Wind energy is clean form of energy which is abundantly available. A great deal of study has been carried out lately in order to utilize the wind energy available on a large scale as it does not affect the environment and it is a sustainable source of energy. The modelling and simulation of wind turbine system supports mainly in improving the design and performance of the wind turbine. In the past few years, MATLAB©-Simulink© became one of the most common software, which is important for modelling, and simulation of dynamic systems. The use of MATLAB© in modelling and simulation of dynamic real-world systems is unprecedented. As the MATLAB© provides graphical interface, it gives clear picture about the performance of wind turbine in a real-world scenario and model accordingly. In this study, a horizontal axis wind turbine with variable pitch mechanism is considered and simulated it in MATLAB©-Simulink© by varying the wind speed and pitch angle. The active power output of the turbine varies with the wind speed and the angle of attack (β). Based on the results, it is found out, the optimum characteristics of wind turbine like pitch angle and turbine speed is obtained at various wind speed. Therefore, by simulating and analysing the results, it is found out that the maximum active power output of the turbine is achieved at the optimum pitch angle.

The use of hydraulic pressure drive unit as actuator element in the pitch control scheme of a large wind turbine plant introduces inevitable time-delay in the feedback loop. This delay has an adverse impact on the performance and stability of the closed-loop system; nevertheless, if the delay magnitude exceeds a critical margin, the closed-loop system is driven to instability. In a large wind turbine plant, owing to its massive tower structure and enormous blade span, unstable, or for that matter, even marginally stable operation is highly detrimental. If the unboundedly evolving or sustained oscillations in pitch angle, signifying unstable or marginally stable operation respectively, are not curtailed using efficient braking systems, it might lead to the loss of whole structure. Hence, in this paper, the problem of delay-dependent stability of time-delayed pitch control system of a large wind turbine plant has been addressed using the classical Lyapunov-Krasovskii functional approach combined with Wirtinger inequality. The derived stability criterion which is in LMI framework, is tested on a benchmark wind turbine plant. In the sequel, simulation results are also provided to validate the effectiveness of the presented analytical results.

Agricultural vehicles are typically unable to maintain a level position and therefore unable to guarantee the quality of work when operated on uneven terrain. Current levelling methods mostly depend on adjustments that are passive or delayed with adjustment taking place after the bodywork has tilted. The objective of this research was to propose a rapid active levelling method, in which levelling starts as soon as the vehicle platform begins to tilt, thus actively preventing or reducing vehicle body inclination. The design relies on a ground detection device installed in front of each wheel of the four-wheels of the agricultural vehicle, which senses ground information ahead of the vehicle in its normal direction of motion. This information combined with the agricultural vehicle's driving condition is then used to determine the instantaneous adjustments necessary for moving the levelling actuator ensuring that the work platform remains level. The principle of coordinated deformation of four-wheel vehicle chassis suspension was studied by using virtual prototyping technology. By using the coordinate transformation method, a calculation formula between the platform adjustment angle and variations in pitch or roll angle was derived, as well as the required formula relating the displacement of the adjustment device and the platform adjustment angle. Experiments showed that the designed levelling system based on the rapid active levelling method could maintain the pitch angle and roll angle of the platform within less than ±0.5° for more than 80% of the duration of the tests.

In this article a wind turbine performance enhancement is studied numerically using two type of tip plates. A three dimensional finite volume code is developed to simulate the wind turbine flow field periodically at different wind speeds and pitch angles. The well-known Menter's Shear Stress Transport ( k ω − S S T ) turbulence modelling is incorporated into the code to investigate the turbulent flow field that occurs in wind turbines. Here we show that using tip plates for wind turbines performance improvement can only occur if the turbine blade pitch angle is set at the maximum output power based on the given wind speed. Otherwise, using the tip plates play negative role and reduce the wind turbine output power. This physical effect is related to the wind turbine working condition at which both the blade span-wise flow as well as the tip blade trailing vortices stay at their minimum amount.

This work aims to investigate the availability of a tip-jet on a ducted fan under large blade pitch angle and high solidity conditions. The aerodynamic performance and flow field of a ducted fan in hover are numerically investigated over a range of blade pitch angles at three operating speeds. A numerical experiment is conducted using the shear-stress transport k-omega turbulence model with a refined high-quality structured grid. The maximum thrust, peak efficiency, and stall margin of the ducted fan with tip-jet are the main interests of this investigation. Results indicate a 30% increase in the thrust of the fan with tip-jet near stall margin condition. This aerodynamic improvement seems to increase with the blade pitch angle because the separation flow at the front part of the blade becomes uniform and reattaches to the blade surface due to the entrainment effect of the tip-jet. The nozzle with an angle in downwash direction can improve tip-jet efficiency at a large blade pitch angle. The tip-jet is applicable to a fan with a large pitch angle and high solidity.

There are many cycling events undertaken in a velodrome which involve close interactions between cyclists. During a single race, particularly the team pursuit, a cyclist can alternately be ahead of or behind another rider; two positions which have very different flow fields. Additionally, as a cyclist travels around a level corner, the relative flow experienced by the cyclist becomes curved. Due to the lean angle of the cyclist, this resolves into a change in both the yaw and pitch angle as well as the flow speed relative to the cyclist. An experimental investigation was conducted with a bicycle fitted with a three-component velocity probe placed anterior to the rider in a simulated team pursuit race. The results demonstrate a reduction in the airspeed-to-wheel speed ratio for each drafting cyclist, down to 46% for the 4th rider. The turbulence intensity increased for each drafting position, from 1.5% to 18.5%. A yaw angle of up to 7° and pitch angle of −3° were observed on the velodrome bends. In addition, a fluctuation in the yaw angle due to the cadence cycle was observed. The results demonstrate the aerodynamic conditions experienced in track cycling and can be used to inform further investigations.

In the monitoring of greenhouse gas emission from industrial smoke-stacks, the most common device used to measure the stack gas velocity is the S-type Pitot tube in South Korea, which is used to estimate the volumetric flow rate by what is termed the Continuous Emission Monitoring System (CEMS). The S-type Pitot tube installed in the stack is inevitably affected during velocity measurements by velocity changes, yaw and pitch angle misalignments due to the harsh environments. Various geometries of the S-type Pitot tube can affect the characteristics of the S-type Pitot tube coefficients, including the degree of sensitivity to velocity changes and yaw and pitch yaw angle misalignments. Nevertheless, there are no detailed guidelines pertaining to the S-type Pitot tube geometry considering accurate and reliable measurements in the ISO, EPA and ASTM international standards. In the present study, S-type Pitot tubes with various geometric parameters, in this case the distance between the impact and wake orifices and the bending angle of the orifices, were manufactured by a 3D printer. Wind tunnel experiments were conducted in the Korea Research Institute of Standards and Science (KRISS) air speed standard system to determine the optimal geometry of an S-type Pitot tube for the accuracy velocity measurements in actual smokestacks which undergo velocity changes and yaw and pitch angle misalignments. Particle image velocimetry was also used to understand the flow phenomena around an S-type Pitot tube under various geometric and misalignment conditions by means of qualitative visualization. The results indicate that S-type Pitot tubes with a long effective length have more constant distributions of the S-type Pitot tube coefficients when the velocity changes from 2 m/s to 15 m/s. The error indexes for yaw angle misalignments show that S-type Pitot tube models with large effective lengths are less affected by yaw angle misalignments. The S-type Pitot tube coefficients were mostly insensitive to the both positive and negative pitch angle misalignments regardless of the velocity and geometry of the various models tested.

This paper first deals with the control and dynamic modeling of full converter based wind turbines (WTs) with squirrel cage induction generator (SCIG) and then studies stability and dynamic behavior of WT considering the pitch angle control and drive train dynamics. In this way, WT system is divided into several single-input–single-output subsystems with several PI controllers, and control loops related to stator current, rotor flux, generator speed and pitch angle are extracted. Then, at the first stage, pitch angle control design based on the single-mass drive train model is presented, and WT dynamic performance is investigated by the modal and frequency response analyses of the whole WT system. It is shown that the control design based on the single mass model may result in unstable modes and thus unstable WT response. Next, theoretical analyses are developed for the elaborate pitch angle controller design using two-mass drive train model to consider torsional dynamics associated with the multi mass drive train model. Further, the paper examines the WT stability and interaction of the pitch control system with the speed control loop at different pitch control bandwidths. Finally, WT responses are studied by time domain simulations in the MATLAB-SIMULINK environment.

Vertical-axis wind turbines (VAWTs), which are considered an important wind energy conversion device, have recently received renewed attention. Researchers are investigating the pitch angle control method to improve the wind energy utilization efficiency of VAWTs. In this study, ANSYS Fluent is used to investigate the aerodynamic performance of two-dimensional VAWTs. Different pitch angles are investigated using unsteady Reynolds-averaged Navier–Stokes calculations, and turbulence is modeled with the shear stress transport k–ω model. Four quartiles are defined for the azimuthal angle of a rotation period: upwind (45 ° θ ° ), leeward (135 ° θ ° ), downwind (225 ° θ ° ), and windward (315 ° θ ° ). Furthermore, the sliding-mesh technique and a user-defined function are applied to adjust the pitch angle of the wind turbine blades in different azimuthal zones. This study proposes a pitch angle control method that effectively improves the efficiency of VAWTs by comprehensively analyzing the aerodynamic performance of the wind turbine and power coefficient ( C p ) variation in each zone. The results indicate that an appropriate pitch angle control solution can significantly improve the efficiency of the wind turbine. Compared to a fixed pitch angle of 0°, an approximately 17.0% increase in C p can be achieved and, compared to the optimal fixed pitch angle −1°, an approximately 12.0% increase in C p can be achieved.

In previous study (Chen et al., 2018), performances of a fixed pitch and a sinusoidal pitch H-Darrieus vertical-axis turbine (VAT) are compared by numerical simulations. With an appropriate amplitude of sinusoidal pitching, the power efficiency could be improved by 33%, and the fluctuation in power output, rotation speed and shaft torque are suppressed meanwhile. In this study, to reduce the hydrodynamic resistant torque, the original sinusoidal pitching is modified to keep the pitch angle at zero or at a small initial angle in the downstream half of rotation cycle. Numerical simulation results show this modification increases power efficiency by 20% over that of an original sinusoidal pitch turbine. Furthermore, systemically study confirms that as rotational inertia of rotor increases, the power coefficient and tip-speed ratio do not change much, and the fluctuation in output torque can be dramatically reduced. However, a very large rotational inertia turbine would perform very poor unless the rotor be accelerated over a threshold speed with exterior assistance.

Spiral-wound heat exchangers (SWHEs) are the important equipment for the industry development, however, the non-uniformity of flow medium in the shell side seriously decreases their heat transfer performance. The maldistribution is more critical when SWHEs are used in the floating production storage & offloading system (FPSO) and this restricts the application of SWHEs in the FPSO system. To make SWHEs more suitable for the FPSO, it is necessary to study their distribution performance of gas-liquid mixture under sloshing conditions. A novel distributor named “tubes distributor” was designed and a gas-liquid two-phase experimental bench was built to process the investigation via air and water as the mediums. The influence of sloshing amplitude, sloshing period and sloshing form was investigated. The results show that the increase of heave amplitude makes the two-phase distribution performance better which is in contrast with that in roll condition. At the same time, the increasing pitch angle results in the better gas uniformity and worse liquid uniformity. Different from sloshing amplitude, the longer sloshing periods lead to the worse two-phase distribution uniformity. It is also got that roll condition can provide the worse two-phase distribution performance under complex practical offshore sloshing condition than the experimental condition.

This paper developed a horizontal axis micro-hydrokinetic river turbine (HAMHRT) technology for local renewable energy applications. Firstly, a hydrofoil shape was selected, and the hydrodynamic and cavitation characteristics of the hydrofoils were analyzed, then the chord length and twist angle for different blade location were optimal, and finally a 2 m diameter with 3-bladed HAMHRT was designed. Then, the numerical computational model of a hydrodynamic analysis for the prototype HAMHRT was carried out to determine force distributions along the blade under normal and extreme operating conditions, including the non-designed conditions, different tip speed ratios as well as the different pitch angles. The rotor has a maximum efficiency of 25.2% at the river current speed of 0.8 m/s, pitch angle of 4° and TSR of 6. It is ensured that the rotor performance does not deteriorate in a relative large scope even if the current speed changes or if the TSR deviates from the design values. Finally, the unsteady behaviors of hydrodynamics of this HAMHRT were analyzed farther. From the output performance of this turbine, the designed rotor was found to have stable power output and good efficiency at current speeding conditions.

This work focuses on the hydrodynamic performance analyses of three different types of flapping hydrofoils, in this case the pitch-heave (PH), left-swing (LS), and right-swing (RS) types, in their power extraction regimes via two dimensional CFD simulations. The power extraction performance is presented in an isocontour parametric map and is investigated from a comparison of the kinematics parameters and the development of unsteady vortices among the three types. It is found from the parametric analysis and comparison that the LS-type of flapping hydrofoil outperforms the PH and RS-types due to relatively high forces as well as the good synchronization of the forces and moment with the translational velocity and pitch angular rate, respectively upon the different aspects of the vortex development. Consequently, the power extraction performance improves from the LS to the PH and then to the RS-types. It is also recognized from another isocontour parametric map that the maximum power-extraction efficiency is achieved at a similar maximum effective angle of attack, at the maximum effective angle of attack rate, and at the maximum pitch angle rate for the LS and RS types, while the range of the maximum effective angle of attack rate is lower in the PH-type hydrofoil.

After more than a decade of operation at Titan and Saturn, the Cassini RADAR instrument is considered well understood and calibrated. In light of the recent Juno mission which is exploring the inner magnetosphere and the atmosphere of Jupiter, it is worthwhile to reconsider the original measurements of Cassini at Jupiter. The better instrument knowledge in combination with a better understanding of the ammonia distribution of Jupiter has allowed for revising the synchrotron flux density to 1.10 ± 0.07 Jansky, a factor of 2.5 larger than the initial estimate (Bolton et al., 2002). The forward model reduced uncertainties pertaining to the spacecraft pointing using a Markov-Chain Monte Carlo algorithm and constrained simultaneously a brightness model of Jupiter with a disk-averaged brightness temperature of 158.6 ± 2.4 K and depletion of ammonia at the poles (limb darking coefficient, p = 0.05). The flux density spectrum for the 2001 measurement campaign reveals a depletion of energetic electrons (>30 MeV) in contrast to an undisturbed electron population at lower energies. Comparing the Cassini radio maps to Very Large Array maps revealed a redistribution of energetic particles to higher latitudes, indicating enhanced pitch angle scattering for energetic particles. This kind of behavior has been observed in the terrestrial Van Allen belts and could be caused by the resonance of energetic electrons with electromagnetic ion cyclotron waves. We used a simplified analytic expression to determine the feasibility of this process at Jupiter. Although this process is not feasible under nominal conditions, a 10-fold enhancement of the cold plasma density, caused for example by extreme UV events, or volcanic eruptions on Io, could lead to rapid pitch angle scattering of electrons, and the subsequent removal of these particles by the atmosphere.

We report three ring current aurora events that are conjugated in the two hemispheres observed by satellite and ground imagers on May 16, 2005, August 26, 2018 and September 5, 2005. The ring current auroras appeared as auroral spots or arcs in the day, dusk or night side. These events confirm that the particle sources are in the equatorial ring current ions and pitch angle diffusion of the ions lead to the ion precipitation in the both hemisphere on the same field lines, thus the auroras are conjugated.

The dish solar thermal power generation system is widely used due to the high efficiency. The mechanism of the whole system must meet stringent structural deformation requirements. In this work, the dish concentrator model is developed by the CFD software STAR-CCM+ and the finite element software of ABAQUS, respectively. The pressure fields obtained in the STAR-CCM+ environment are mapped to the ABAQUS model. The validated finite element (FE) model is employed to predict the amplitude and frequency of the vibration. The effects of different pitch angle, azimuth angle and wind velocity on the amplitude and frequency of the vibration are also considered in the process of calculation. The simulated calculation of fluid-structure coupling model is used for the analysis of harmonic response of four hinge nodes vibration. The vibration period of sinusoidal wind excited is 2 s. The results show that the vibration of the dish concentrator will occur with the sinusoidal wind load and reaches the maximum in a short time, then gradually becomes flatter. Moreover, the change of the height angle has a little influence on the modal frequencies of the system and the modal natural frequency is only changed a little when the wind load increases. Thus, the information obtained from the FE model can serve as a reference for subsequent analyses mechanism design such as wind-induced response dynamics analysis.

The efficiency of a vertical axis wind turbine (VAWT) can be improved by placing a shield or deflector upstream of the turbine to reduce the negative torque on the blade. However, previous studies mainly focused on fixed shields or deflectors, and the performance of the VAWT was significantly affected by the wind direction. Considering this, this paper proposed a novel passive-pitch shield (PPS) which consists of two simple plates and could passively adjust its pitch angle according to the wind direction, so that the VAWT could operate with high efficiency under any wind directions. Two-dimensional transient CFD simulations were carried out to quantitatively analyze the influence of the PPS on the performance of the VAWT. The influence of PPS on the VAWT was explained in depth from the perspective of flow structures. Simulations were also performed to verify the passive pitch capability of the PPS and good results were obtained. To further improve the performance of the VAWT, several types of PPSs were compared. It was found that the power coefficient of the VAWT was increased by 46.32%.

There is always a risk of destruction of man-made satellites by the energetic electrons trapped in Van Allen radiation belts in space. These energetic electrons also pose a biological danger to astronauts. The cyclotron resonance interaction is studied between the whistler-mode waves in the frequency range of ELF (Extremely Low Frequency 300 – 3000 HZ) and VLF (Very Low Frequency 3 – 30 kHz) propagating along geomagnetic field line and counter streaming energetic electron. During this process the pitch angle of energetic electrons reduces. This results in the dumping of these electrons into the lower ionosphere. This makes electrons unable to strike the satellites orbiting in low Earth orbit, Geosynchronous, Sun-synchronous or polar orbit. It is shown that the lifetime values of energetic electrons vary from 2.03 to 227.68 hours at low latitudes. It is shown that these waves can remove these energetic electrons from their path and ensure the safety of satellites.

Experimental investigation of large amplitude yaw-roll coupled oscillations was conducted in a low-speed wind tunnel using an aircraft configuration model. A special test rig was designed and constructed to provide different coupled motions from low to high angles of attack. A parameter “coupling ratio” was introduced to indicate the extent of yaw-roll coupling. At each pitch angle, seven coupling ratios were designed to study the yaw-roll coupling effects on the lateral-directional aerodynamic characteristics systematically. At high angles of attack, the damping characteristics of yawing and rolling moments drastically varied with coupling ratios. In the coupled motions with the rotation taking place about the wind axis, the lateral-directional aerodynamic moments exhibited unsteady characteristics and were different from the “quasi-steady” results of the rotary balance tests. The calculated results of the traditional aerodynamic derivative method were also compared with the experimental data. At low and very high angles of attack, the aerodynamic derivative method was applicative. However, within a wide range of angles of attack, the calculated results of aerodynamic derivative method were inconsistent with the experimental data, due to the drastic changes of damping characteristics of lateral-directional aerodynamic moments with yaw-roll coupling ratios. Keywords: High angles of attack, Hysteresis, Lateral-directional aerodynamic characteristics, Unsteady, Yaw-roll coupling

This paper discusses the stability, transition and control of displaced non-Keplerian orbits by the spacecraft using low-thrust propulsion. The two-body dynamical model developed in the polar coordinates is parameterized by the thrust pitch angle, and then two of the hyperbolic and elliptic equilibria are solved from it. The bounded motions near two equilibria are investigated by dynamical system techniques to find out all the stable and unstable periodic trajectories, and two scenarios of the resonant periodic trajectory are presented. Regardless of the thrust pitch angle, all the transit orbits are numerically demonstrated to be restricted inside the invariant manifolds of Lyapunov orbit near the hyperbolic equilibrium. Then the transit orbits can be distinguished from non-transit ones by the restriction of three-dimensional invariant manifolds projected onto the Poincare section or position space. Based on the influence of thrust direction on the system topology, operating the thrust pitch angle is an effective tool to achieve the transfer within different types of KAM tori, or even transfer beyond the KAM tori.

In this paper, the effects of side trailing edge tapering on the wake of a simplified square-back vehicle are investigated. The tapered surfaces are reported to trigger a switch from a laterally asymmetric bi-stable wake to a vertically asymmetric stable wake. The wake structure reported in the literature for lateral symmetry breaking states is seen to rotate by 90 ∘ as the angle of the tapered surfaces ϕ s is increased. A 6 % drag reduction over the simple square-back case is reported for 6 ∘ ϕ s 12 ∘ . This gain is found to be the result of the stretching of the circular vortex responsible for the suction zone visible in any symmetry breaking state. A downwash dominated wake is observed in these conditions. The sensitivity of such a wake to small variations of the model pitch angle (for ϕ s = 12 ∘ ) is also assessed. As the pitch angle α is reduced from 0 ∘ to − 2 ∘ , the time averaged wake is reported to switch from a downwash dominated topology to an upwash dominated topology. A strengthening of the long-time instability is observed when the symmetry in the vertical direction is recovered and is accompanied with a 4.9 % reduction in base drag over the same model tested at α = 0 ∘ .

The tracing control problem of hypersonic vehicle subject to external disturbances, parametric uncertainties, input saturation and state constraints. Firstly, the longitudinal model of the hypersonic vehicle is converted to the velocity subsystem and altitude subsystem based on the functional decomposition. Secondly, two adaptive anti-saturation controllers are proposed for the velocity subsystem and altitude subsystem with the unknown upper bound of external disturbances. By using the asymmetric barrier Lyapunov function, the two controllers can make flight path angle, angle of attack and pitch angle rate keep within the certain ranges. Meanwhile, the auxiliary system is introduced to deal with the problem of input saturation and a low-pass filter is designed to avoid the “explosion of terms” in traditional backstepping control caused by the complicated differentiations of the virtual control signals. Finally, the effectiveness of the presented control strategy is verified by the Lyapunov stability theory and numerical simulations results.

The attitude of Near-space airship including yaw, roll and pitch angle is important to the output performance of airship solar array. The yaw angle of airship can be controlled without affecting airship mission execution in the quasi-zero wind layer of near-space. This paper aims to improve solar energy system of near-space airship by optimizing airship yaw angle. Based on the solar radiation model and solar array energy model, a MATLAB program is established to calculate the output power. For model validation, solar radiation and output power are simulated and compared with experimental results. The optimum yaw angle for a whole year is obtained with optimization model based on genetic algorithm. The effect of airship shape parameters including the slenderness ratio and the ratio of forebody length to total length ( L 1 /L) is elaborated. The results show that the effect of yaw angle on output power is greater at higher latitude than that at lower latitude and the solar array output energy can be remarkable increased after adjusting yaw angle of airship according to the optimization result. Although the optimal yaw angle is different with the change of working date and latitude, the optimum values mainly lie in 0° and 180°. Moreover, the optimal yaw angle is barely changed, when the slenderness ratio and L 1 /L of airship are greater than 0.3 and 0.25, respectively. The result has great valuable engineering reference in attitude planning of near-space airship and other aerospace vehicle for energy improvement.

Most of the low-cost NanoSats, which run on the low-earth orbits and have no severe pointing requirement, usually adopt magnetic-based attitude control scheme as an important or even the dominant attitude control strategy to de-tumble and stabilize themselves. The attitude control components regularly equipped include magnetic torquers and magnetometer, and sometimes even a miniaturized momentum wheel. The primary task of the attitude control system of the NanoSats is to achieve rate damping and the famous B-dot control algorithm is widely adopted to de-tumble the satellites. However, when the initial angular velocity is significantly fast and an obvious lag exists in the control system, the wide-spread B-dot control algorithm would fail to de-tumble the satellite. Oppositely, the angular velocity would be controlled to a large-scale one. In this paper, one novel rate damping algorithm is proposed to deal with this case. For momentum satellites, during de-tumbling control process based on B-dot algorithm, their attitude motion is analyzed in detail. Analysis indicates that the roll-yaw control channel is stable and the pitch angle tumbles from 180 deg down to −180 deg in about one orbit period. In addition, the optional range of the bias moment has been specified. Simulation results indicate that the proposed novel damping algorithm is effective and the momentum satellite's attitude motion during B-dot damping process is coincided with the resulted attitude motion characteristics, which is benefit for the satellites, which are running in dawn-dusk orbits, to obtain solar energy for the positive/negative Y-body axis is always pointing at the negative normal direction of the orbital plane.

With advances in incremental non-linear flight control, new challenges and possibilities for incorporating efficient flight envelope protections arise. Investigation of a phase plane based command and virtual control limiting pitch angle protection in the reference model of a cascaded incremental backstepping controller is performed for a commercial aircraft model. This provides an almost model free design of a combined flight control law and envelope protection. Verification through simulation shows that accurate predictable response behaviour is obtained close to the limit, which permits a protection that minimizes the interference into the nominal control.

The wake of upstream wind turbines is known to affect the operation of downstream turbines and the efficiency of the wind farm. In this study, a systematic experimentation on performance and wake spatial evolution was carried out using a wind turbine model varying tip speed ratio, pitch and yaw angles. The change of pitch angle was observed to induce a greater effect on the wake velocity as compared to the tip speed ratio. This is interpreted in terms of “force viewpoint”, which describes more quantitatively the relationship between the turbine performance and the wake, as compared to the “power viewpoint”, based on the sole energy conversion. The turbine yaw angle is observed to cause not only a decrease in power and thrust, but also an offset and an asymmetry in the wake. The offset, quantified using the spatial distribution of the velocity minima, is modeled analytically. Comparisons of model estimations with the experimental measurements show that the proposed model can acceptably predict the wake offset of a yawed turbine. The observed dependencies of the mean velocity deficit and wake turbulence on power, thrust, and yaw angle, may suggest new derating strategies for wind farm optimization.