High Altitude Wind Research Articles

カイト型テザー係留飛行ロボットを用いた小型風力発電システムの試み

This research aims at realizing a high altitude wind power generation system, we have proposed a kite-based tethered flying robot.In order to lift up heavy wind power generator and monitoring sensors with the robot, we have also proposed that the kite is lifted up first to acquire enough lifting power, and then, the wind power generator and monitoring sensors are lifted along the tether line later. In this paper, we report the improved wind power generation system by lifting up wind power generator using kite-based tethered flying robot with lifting mount.

Reduced Image Aliasing With Microwave Radiometers and Weather Radar Through Windowed Spatial Averaging

Microwave remote sensing instruments detect and image physical phenomena such as brightness temperature and volume reflectivity. The spatial resolution of these measurements is limited by the physical properties of the instrument such as the antenna size, the spatial scan pattern, and temporal sampling. Analysis shows that common sampling schemes undersample the spatial information present at the antenna. Here, we address methods to better capture the spatial information available by applying the Nyquist–Shannon sampling theory to the spatial averaging and sampling of remote sensing data. The use of overlapping windows for spatial averaging rather than treating pixels independently improves the image fidelity while maintaining the system sensitivity. Additionally, the sensitivity to spatially small targets can be maximized by matching the window shape to the antenna pattern. The spatial imaging of scanning radiometers, radars, and phased-array systems is addressed. These principles are demonstrated with the theory and data from the National Aeronautics and Space Administration Goddard Space Flight Center's High-Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP) radar.

복합재 로터 블레이드의 차원축소와 복원해석을 위한 블레이드 해석 라이브러리 개발

본 논문에서는 블레이드 해석 라이브러리를 통해 단면해석 및 응력복원 해석 결과를 VABS의 결과와 비교하였다. 강성 행렬로 연결된 1차원 보 모델을 가상일의 원리에 의해 계산된 에너지를 복원 이론에 기반한 차원 복원해석 과정을 통해 계산된 응력과 3차원 해석모델과 비교하였다. 블레이드 해석 라이브러리의 구성, 입력 및 출력 형태, 차원 축소와 복원을 통한 로터 블레이드의 구조해석 프로시져를 기술하고, 블레이드 해석 라이브러리의 검증은 고형모델, 박 벽 모델의 단면해석, 3차원 복합재료 유한요소 모델로 구성하여 VABS를 통하여 검증하였다. 차원 축소와 복원해석을 통하여 블레이드 해석 라이브러리는 복합재료 블레이드의 전후처리 프로그램와 연계되어 고고도 무인기, 로터 블레이드, 풍력 블레이드 및 틸트로터 블레이드의 모델링에 활용될 수 있을 것이다. In this paper, numerical results of sectional analysis and stress recovery were compared with the results of VABS through the blade analysis library. The results of recovery analysis for one-dimensional model including the stiffness matrix is compared with the calculated three-dimensional stress results of three-dimensionial FEM based on the principle of virtual work. We discuss the configuration of the blade analysis library and compare verifications of numerical analysis results of VABS. Blade analysis library through dimensional reduction and stress recovery is intended to be utilized in conjunction with pre- and post-processing of the analysis program of the composite blade, high-altitude uav's wing, wind blades and tilt rotor blade.

Experimental studies on the dynamic behaviour of a robot cable-detecting system

A cable-detecting robot usually works in a high-altitude environment that spans hundreds of meters. Thus, the stability and safety of the system are very important. To analyse further the dynamic performance of the robot–cable system, similar experimental models of cables on the Junshan Highway Bridge over the ChangJiang River are set up and vibration experiments are conducted. To study the effects of high-altitude wind load on the safe performance of the cable and on the climbing ability of the robot, transverse wind load is simulated and wind-load equivalent experiments on cable vibration are performed. The experimental results indicate that, under Grade 7 wind (wind velocity is less than 61 km/h), the vibration amplitude of the cable is significantly less than 2.5 D ( D is the diameter of the cable), although the vibration slightly increases. Under the circumstances, the cable cannot be damaged; therefore, the safety of the cable–robot system is demonstrated.

Design space exploration of gyrocopter‐type airborne wind turbines

AbstractThis paper presents a multidisciplinary framework for the design and analysis of gyrocopter‐type airborne wind turbines. In this concept, four rotary wings provide lift to a flying vehicle, and excess power is extracted using gearboxes and generators before being transferred to the ground through electrical conductors embedded in a structural tether. A physical breakdown of the system was performed, and five models were constructed: wind model, rotor aerodynamics, structural mass, electrical system, and tether (structures and aerodynamics). A stochastic optimizer in the framework enforces interdisciplinary compatibility and maximizes electrical power transmitted to the ground under various operating conditions. The framework is then used to explore the design space of this advanced concept in numerous flight conditions. The effect of implementing new technologies was also studied in order to evaluate their effect on the overall performance of the system. It is shown through a 1.3MW design that a gyrocopter‐type airborne generator could provide more power than a ground‐based wind turbine for a given blade radius, although only a fraction of the available wind power can be harvested using off‐the‐shelf technologies and components. The work presented in this study demonstrates the challenges of designing a high altitude wind generator and shows that performance is affected by complex interactions between each subsystem. Copyright © 2015 John Wiley & Sons, Ltd.

Generation and Transmission of Electrical Energy in High-Altitude Wind Power Generating System

This paper presents a high-altitude wind power generating system supported by a light gas filled blimp/aerostat that extracts electrical energy from high-altitude streamlined wind. The optimal generation and transmission mechanisms that give suitable power-to-weight (P/W) ratio and efficiency of the overall system are investigated. The variations in weight and total losses of the permanent magnet synchronous generator with changes in generation voltage and pole-pair number (frequency) have been analyzed. The design of the tether that transmits electrical power to the ground-based station is also presented. AC and dc transmission mechanisms using aluminum/copper-based conductors are studied and compared to find optimal weight of the tether. It is found that aluminum conductor gives better P/W ratio than using copper conductor. From the detailed analysis of generation and transmission mechanisms, it is concluded that the optimal electrical power architecture is medium voltage (MV) ac generation as well as transmission. It exhibits better P/W ratio and efficiency in comparison with low-voltage ac generation and MV dc transmission. The selected optimal electrical architecture simplifies electric system by transferring the power electronic converter from the airborne unit to the ground-based station and thereby improves the overall P/W ratio by a factor of 7% approximately.

Kite Model with Bridle Control for Wind-Power Generation

A compact flight dynamics model of a kite is developed by using Lagrangian formulation. The lengths of the three ropes of the bridle and the tether of the kite depend on time and are used to implement an open-loop control scheme of the kite system. By imposing simple time-periodic control laws, two pumping strategies for wind-energy generation are explored. Periodic trajectories of the system and their stability properties (Floquet characteristic multipliers) are computed numerically. As the amplitudes of the figure-eight paths are increased, the system becomes more efficient but less stable. A cyclic-fold bifurcation is detected for a very large lateral displacement of the kite. The impact of the control-law parameters on the generated power, including the period and the amplitude, is investigated. The results indicate that a correct design of the control could provide an optimal energy-generation system and a robust scheme to exploit high-altitude winds.

The Coplane Analysis Technique for Three-Dimensional Wind Retrieval Using the HIWRAP Airborne Doppler Radar

AbstractThe coplane analysis technique for mapping the three-dimensional wind field of precipitating systems is applied to the NASA High-Altitude Wind and Rain Airborne Profiler (HIWRAP). HIWRAP is a dual-frequency Doppler radar system with two downward-pointing and conically scanning beams. The coplane technique interpolates radar measurements onto a natural coordinate frame, directly solves for two wind components, and integrates the mass continuity equation to retrieve the unobserved third wind component. This technique is tested using a model simulation of a hurricane and compared with a global optimization retrieval. The coplane method produced lower errors for the cross-track and vertical wind components, while the global optimization method produced lower errors for the along-track wind component. Cross-track and vertical wind errors were dependent upon the accuracy of the estimated boundary condition winds near the surface and at nadir, which were derived by making certain assumptions about the vertical velocity field. The coplane technique was then applied successfully to HIWRAP observations of Hurricane Ingrid (2013). Unlike the global optimization method, the coplane analysis allows for a transparent connection between the radar observations and specific analysis results. With this ability, small-scale features can be analyzed more adequately and erroneous radar measurements can be identified more easily.

Potential of Offshore Wind Energy and Extreme Wind Speed Forecasting on the West Coast of Taiwan

It is of great importance and urgency for Taiwan to develop offshore wind power. However, relevant data on offshore wind energy resources are limited. This study imported wind speeds measured by a tidal station and a buoy into the software WAsP to estimate the high-altitude wind speeds in the two areas. A light detection and ranging (Lidar) system was set up near the tidal station and buoy. High-altitude wind speeds measured by the Lidar system were compared with the WAsP-estimated values, and it was discovered that the two data sets were consistent. Then, long-term wind speed data observed by buoys and tidal stations at various locations were imported into WAsP to forecast wind speeds at heights of 55–200 m on the west coast of Taiwan. The software WAsP Engineering was used to analyze the extreme wind speeds in the same areas. The results show that wind speeds at 100 m are approximately 9.32–11.24 m/s, which means that the coastal areas of west Taiwan are rich in wind energy resources. When a long-term 10-min average wind speed is used, the extreme wind speed on the west coast is estimated to be between 36.4 and 55.3 m/s.

Design Assistant Decision Model for Parafoil Precise Airdrop

Decision capacity and command level is essential for accurate aerial delivery of parafoil. In this paper, we according to the system theory and the modular scheme, put forward the parafoil precision airdrop aided decision model consist ofaircraft flight route model,parafoil maneuvering performance model,high altitude wind field characteristic model, landing terrain environment model, the enemy threat situation model, complex electromagnetic environment simulation mode. Andwe focuses on the aircraft flight route model, landing terrain environment model and the simulation model of high altitude wind. The model can providecertain auxiliary decision information to airdrop commander; can also be used to other specific precision airdrop work.

Ensemble Kalman Filter Assimilation of HIWRAP Observations of Hurricane Karl (2010) from the Unmanned Global Hawk Aircraft

Abstract This study utilizes an ensemble Kalman filter (EnKF) to assess the impact of assimilating observations of Hurricane Karl from the High-Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP). HIWRAP is a new Doppler radar on board the NASA Global Hawk unmanned airborne system, which has the benefit of a 24–26-h flight duration, or about 2–3 times that of a conventional aircraft. The first HIWRAP observations were taken during NASA’s Genesis and Rapid Intensification Processes (GRIP) experiment in 2010. Observations considered here are Doppler velocity (Vr) and Doppler-derived velocity–azimuth display (VAD) wind profiles (VWPs). Karl is the only hurricane to date for which HIWRAP data are available. Assimilation of either Vr or VWPs has a significant positive impact on the EnKF analyses and forecasts of Hurricane Karl. Analyses are able to accurately estimate Karl’s observed location, maximum intensity, size, precipitation distribution, and vertical structure. In addition, forecasts initialized from the EnKF analyses are much more accurate than a forecast without assimilation. The forecasts initialized from VWP-assimilating analyses perform slightly better than those initialized from Vr-assimilating analyses, and the latter are less accurate than EnKF-initialized forecasts from a recent proof-of-concept study with simulated data. Likely causes for this discrepancy include the quality and coverage of the HIWRAP data collected from Karl and the presence of model error in this real-data situation. The advantages of assimilating VWP data likely include the ability to simultaneously constrain both components of the horizontal wind and to circumvent reliance upon vertical velocity error covariance.

Modular Interleaved Soft-Switching DC-DC Converter for High-Altitude Wind Energy Application

High-altitude wind power (HAWP) generating system uses dc-dc converter to transform the dc link voltage to an optimal medium voltage dc for efficient transmission to ground-based station. This paper presents a comparative study of current-fed and voltage-fed (VF) isolated dc-dc converters for HAWP application. VF converters (VFCs) with inductive and capacitive filters are compared with current-fed converters for a 100-kW rated power. The power electronic converters used maintain zero-voltage switching on the primary side switches to reduce switching losses. The current and voltage ratings of the components used are provided to realize higher power-to-weight (P/W) ratio. Losses and P/W ratio are assessed using the components' datasheets and compared with evaluate the converters that exhibit higher P/W ratio and efficiency. It is observed that VFC with capacitive filter exhibits higher P/W ratio and efficiency. Small signal modeling of VFC with capacitive filter is carried out to obtain the state-space model. Transmission voltage is controlled at optimal value using voltage control loop for efficient power transmission. Simulation studies of VFC with capacitive filters are carried out to verify the steady state analysis and performance using the software PSIM-9 at 100-kW power level that converts 600-8000 V. A 1-kW scaled down laboratory prototype is designed, built, and tested using modular devices and accessed to validate the performance. It yields an efficiency of 94.2% at full load converting a ten-times scaled down voltage of 60-800 V.

Spectrum analysis of wind profiling radar measurements

Unlike previous studies on wind turbulence spectrum in the planetary boundary layer, this investigation focuses on high-altitude (1–5 km) wind energy spectrum and turbulence spectrum under various weather conditions. A fast Fourier transform (FFT) is used to calculate the wind energy and turbulence spectrum density at high altitudes (1–5 km) based on wind profiling radar (WPR) measurements. The turbulence spectrum under stable weather conditions at high altitudes is expressed in powers within a frequency range of 2 × 10−5–10−3 s−1, and the slope b is between −0.82 and −1.04, indicating that the turbulence is in the transition from the energetic area to the inertial sub-range. The features of strong weather are reflected less obviously in the wind energy spectrum than in the turbulence spectrum, with peaks showing up at different heights in the latter spectrum. Cold windy weather appears over a period of 1.5 days in the turbulence spectrum. Wide-range rainstorms exhibit two or three peaks in the spectrum over a period of 15–20 h, while in severe convective weather conditions, there are two peaks at 13 and 9 h. The results indicate that spectrum analysis of wind profiling radar measurements can be used as a supplemental and helpful method for weather analysis.

Research on the Optimization Design of Gas-Solid Coupling of Wind Turbine Blades

The effects of high-altitude wind shear of wind speed should be considered, the appropriate number of distribution group should be determined and the distribution of wind speed hybrid model parameters and solving should be loaded onto the blades. When the stress of rotor blade is analyzed, the elastic deformation of the blades and the effects of the vibration of oscillating flow field on reaction of the blades must be considered during the operation. Thus the laws of blade load distribution and the corresponding deformation can be accurately calculated to analyze the interplay between deformation vibration airflow and paddle, to determine the law of deformation of rotor blades, the surface pressure distribution, stress distribution and blade design safety factors. When wind load changes with the wind speed, the adaptive blades are powered by aeroelastic, the law of wielding and flapping of the blade will be studied. The torsion coupling effects of adaptive blade, blade bending ,the law of torsional deformation variation of the angle of attack and the impact on aeroelastic blades structural strength will be explored. The results of this study design will be optimized as the power factor, improving the stability of the design of wind turbine power output, reducing material consumption blades absorb vibration and reducing wind load maneuvering to avoid blade stall achieve pitch control. Thus it provides a theoretical basis for optimal design of strength and stiffness of the elongated paddles.

Multi-mass dynamic model of a variable-length tether used in a high altitude wind energy system

This paper presents a multibody approach to dynamics modelling of a variable-length tether moving through air, in a system where an airborne module generates aerodynamic lift and uses the tether to cyclically drive the winch-generator unit fixed on the ground. The rope is modelled as a series of straight, massless, elastic segments with the rope mass fragments lumped to the segment joints. Individual segment length is constant, with the exception of segment being wound out from the winch, while the number of segments is variable. For the segment being wound out, a special modelling approach is derived. The forces acting on the rope are also concentrated at the joints, thus simplifying computations and facilitating rope aerodynamic drag modelling. The proposed tether dynamics model is integrated into the overall model of controlled power production system and verified by computer simulation. The model is compared with two simpler tether dynamics models also proposed in the paper.

Energy storage systems sizing study for a high-altitude wind energy application

As the ground-based wind-turbine systems have steadily reached their performance peak due to turbine blade size limitations, generator size constraints, high investment costs, and relatively unpredictable nature of near-surface winds, the possibility of harnessing the energy of steady, high-altitude/high-speed winds has become increasingly attractive within the last decade. However, due to the intermittent nature of power production of a considered high-altitude wind energy system utilizing an airborne module tethered to a ground station, sufficiently large energy storage is required in order to provide steady power supply to the electrical power grid. This paper focuses on the sizing of typical low-to-medium scale energy storage systems (up to 10 MW), such as those based on flywheels, compressed air, batteries and ultracapacitors, considering the intermittent power production cycle, airborne module altitude range and ground-station generator power ratings. The assessment results are summarized in terms of investment/running costs, storage system size, and durability, thus providing practical guidelines for the selection of appropriate energy storage system.

Open Function Analysis on the Electro Hydraulic Coupling System of Cabin Door in the Flight Environment

In order to study the performance simulation of the aircraft cargo door electrohydraulic system in the flight environment, the electrohydraulic co-simulation method is put forward to analysis the influence of the stochastic wind field on the aircraft cargo door electrohydraulic system. To work it out, the numerical simulation of the turbulent wind field and the discrete gust makes the high-altitude wind stochastic field have the random amplitude and time, then use the high-altitude wind stochastic field and the aircraft cargo door electrohydraulic simulation system to build the virtual prototype system. Use the virtual prototype system to get the relationships of data transfer among the electronic-controlled system, hydraulic system and the wind load. Since the aircraft must complete the open function in the different velocities, the cargo door must be put in the different flight velocities to get the functional examinations. At last, use the relationships of data transfer to finish the functional examinations, and get the opening time distribution under the different velocities.

Utilizing Versatile Transmission Waveforms to Mitigate Pulse-Compression Range Sidelobes With the HIWRAP Radar

The NASA Goddard Space Flight Center (GSFC) High-altitude Imaging Wind and Rain Airborne Profiler (HIWRAP) is a solid-state dual frequency Doppler radar funded by the NASA Instrument Incubator Program. It uses direct-digital-synthesizer devices to generate versatile waveforms including conventional pulses and linear frequency modulation (LFM) chirps. This letter describes a waveform used by the GSFC and the Remote Sensing Solutions to address the critical limitations of range sidelobes and blind ranges in airborne pulse-compression radar. By utilizing a frequency diversity waveform consisting of two pulses and an LFM chirp at each transmit cycle, this system provides the improved sensitivity and range resolution benefits of pulse compression on targets within the middle and high altitudes while maintaining conventional pulsed data near the radar and the surface. The data obtained by the HIWRAP during the NASA Midlatitude Continental Convective Clouds Experiment using this waveform scheme are presented.

Experimental Study of the Dynamic Performance of a Cable with a Detecting Robot

To analyze further the dynamic characteristics of the robotcable system, similar experimental models of cables on the Junshan Highway Bridge are constructed. To study the effect of high-altitude wind load on the safe performance of the cable and the robots climbing ability, transverse wind load is simulated and wind-load equivalent experiments on cable vibration are performed on the robot to simulate high-altitude conditions. Vibration amplitude and acceleration of the cable slightly increase under Grade 7 wind, which demonstrates the stability of the cablerobot system.

Harmonic buffeting in a high-altitude ridge-mounted triblade Horizontal Axis Wind Turbine

In the context of high-altitude mountain ridges, harvesting energy with wind turbines presents new challenges. The results of a computer model solving the Reynolds-Averaged Navier–Stokes equations for incompressible flows above such a ridge are presented in the context of a case study. A theoretical blade-element model of a triblade Horizontal-Axis Wind Turbine (HAWT) was implemented. By combining both models we show that a wind turbine placed at such a location may receive less dense incoming air with repercussions on power output, as well as other unforeseen effects due to airflow negative vertical incidence such as the appearance of harmonic cyclic torque both in the turbine main shaft and nacelle yaw-control system.