Tower Root Research Articles

Monitoring system framework design for floating wind turbine using the deep learning technology and tower response identification considering sensor optimization

Comparing with the fixed wind turbines, the dynamic characteristics of floating wind turbines (FWTs) are more complex and resulting in distinctions in the monitoring system for structural responses. An integrated monitoring system framework concept design for FWT is proposed combing the dynamic responses correlations of different structural parts and the deep learning technology, in which the intact and partial sensor failure operation modes are considered separately. The monitoring system consists of four vital structural components, including the rotor and nacelle, tower, floating foundation, and mooring system. In order to improve the tower response identification accuracy, a new method for the sensor optimization is proposed to utilize more structural information of the structure based on the effective independence method (EIM) and modal assurance criteria (MAC) methods. A multi-perception (MLP) neural network model based on the input-output coupling mechanism is established to identify the acceleration responses at the tower top and forces at tower root. The optimized identification model can greatly improve the identification accuracy of critical sensors by more than 50%, especially for bending moments.

Hybrid physical and data driven modeling for dynamic operation characteristic simulation of wind turbine

Accurate simulation of wind turbines is the key to achieve efficient control of wind turbines and optimal scheduling of wind power systems. Most of the existing methods are physical simulation models, which have heavy computational burden, especially for large-scale wind turbines, and the simulation accuracy is poor under complex dynamic operating conditions. In response, this paper proposes a hybrid physical and data driven model for dynamic operation characteristic simulation of wind turbines. Firstly, a database of dynamic characteristics of wind turbine operation under various wind conditions is constructed, and then the sequence learning (Seq2Seq) model is used to mine the time series characteristics of wind turbine operation parameters. Combining with long short-term memory (LSTM) network, the mapping relationship between various operating parameter time series to establish. On this basis, an attention mechanism is added to the model to learn the dynamic response characteristics of rotor inertia to natural wind process. Through numerical example analysis, the method proposed in this paper can accurately excavate and learn the time sequence dynamic characteristics of wind turbine operating conditions and parameters under various wind conditions, thereby improving the simulation accuracy and calculation efficiency of wind turbine output power and load dynamic characteristics. Taking the actual wind turbine operation data as an example, the simulation accuracy of wind turbine output power reaches 99.8%. Compared with traditional methods, and the simulation accuracy of tower root load reaches 88.5%.

An identification method of floating wind turbine tower responses using deep learning technology in the monitoring system

The acceleration at the tower top and the force on the tower root are the critical indicators for the structural safety of floating wind turbine (FOWT) towers. However, the corresponding monitoring sensors are prone to failure due to the harsh marine environment. Based on the coupling relationship between the tower force and the floating foundation motion responses, a method for identifying the tower top acceleration and the tower root force is proposed based on deep learning technology. Firstly, a 10 MW FOWT model is numerically simulated to obtain the corresponding responses through OpenFAST. Secondly, a multi-layer perception (MLP) model is constructed and trained. The process of determining the optimal sampling frequency is presented. Finally, the single-state and multi-state cases are studied to verify the feasibility of the proposed method. The results show that the proposed method has shown excellent performance in identifying the tower top acceleration and tower root force, which demonstrates its great promise in the field of smart health monitoring technology.

Aeroelastic load analysis of a co‐rotating quad‐rotor wind turbine

AbstractAn aeroelastic analysis is carried out to assess the loads on a selected quad‐rotor wind turbine vis‐à‐vis those on an equivalent rated single‐rotor turbine, with a specific focus on a comparison of support structure loads (e.g., tower root, yaw‐bearing, and boom loads). A quad‐rotor wind turbine with combined rated power of 6 MW and a single‐rotor with equivalent machine rating are modeled in SIMAPCK coupled with AerodynV15 (including turbulent wind input from TurbSim) to calculate the aerodynamic loads. A correction for tower/boom shadow is implemented in Matlab to account for reduction in (axial) incoming wind due to the presence of support structures that carry the rotors. The performance of the quad‐rotor wind turbine, with the single‐rotor as baseline, is carried out for load cases selected from wind turbine certification standard (IEC‐61400‐1) covering the following: nominal loads under normal wind speed profile, fatigue loads under normal turbulence, and ultimate loads under extreme turbulence. Results show that, comparing the quad‐rotor tower root loads to those of the single‐rotor turbine under extreme turbulence, the side‐side force is up to 31% higher, the force‐aft bending moment is up to 15% higher, and the normal force is up to 46% higher due to additional boom/nacelle inertial loads.

Structural responses of large-sized floating wind turbine with consideration of mooring-line dynamics based on coupled FEM simulations

ABSTRACT The dynamic response of a 5 MW floating wind turbine is examined using the coupled finite element simulations, and the dynamic effects of the catenary is considered, while the coupling between flexible components are included. The restoring performance of the mooring-line is analysed based on the vector equations and numerical simulations. The stiffness hysteresis and the influence of the catenary dynamics on the restoring performance are studied. Then the structural responses undergoing wind and wave loads, are examined. Our results show that the mooring-line tension significantly rise due to catenary dynamics, and the snap tension gets around three times larger. The mooring-line stiffness presents a hysteresis character, owing to the fluid/structural damping, which becomes more obvious with the increase of motion frequency/amplitude. Moreover, the structural response gets smaller principally because of the hysteresis effect. The spar displacement and the tower root stress become respectively 18.4% and 32.7% smaller.

Study on the length of cable-free zone of wide cantilever cable stayed bridge with low pylon

Low pylon cable-stayed bridge is a new type of composite bridge between girder bridge and traditional cable-stayed bridge. Because of its good mechanical properties, economic benefits and beautiful shape, low pylon cable-stayed bridge is widely used in highway and urban landscape bridges. In this paper, a wide and low pylon cable-stayed bridge under construction is taken as the research background, and the numerical simulation model is established by using the finite element analysis software MIDAS CIVIL. The influence of the length of the cable-free zone is studied. By changing the length of cable-free zone at the tower root and the length of cable-free zone in the middle of span, the influence of the length of non-cable zone on the deformation, bending moment, internal force and cable force of low pylon cable-stayed bridge at the completion stage is studied. The reasonable value range of non-cable zone length is obtained. The research results will provide theoretical guidance for the design and construction of similar projects.

System identification and controller design for individual pitch and trailing edge flap control on upscaled wind turbines

AbstractActive load reduction strategies such as individual pitch control (IPC) and trailing edge flap (TEF) actuation present ways of reducing the fatigue loads on the blades of wind turbines. This may enable development of lighter blades, improving the performance, cost effectiveness and viability of future multi‐megawatt turbine designs.Previous investigations into the use of IPC and TEFs have been limited to turbines with ratings up to 5 MW and typically investigate the use of these load reduction strategies on a single turbine only. This paper extends the design, implementation and analysis of individual pitch and TEFs to a range of classically scaled turbines between 5 and 20 MW. In order to avoid designing controllers which favour a particular scale, identical scale‐invariant system identification and controller design processes are applied to each of the turbines studied. Gain‐scheduled optimal output feedback controllers are designed using identified models to target blade root load fluctuations at the first and second multiples of the rotational frequency using IPC and TEFs respectively.The use of IPC and TEFs is shown in simulations to provide significant reductions in fatigue loads at the blade root. Fatigue loads on non‐rotating components such as the yaw bearing and tower root (yaw moment) are also reduced with the use of TEFs. Individual pitch performance is seen to be slightly lower on larger turbines, potentially due to a combination of reduced actuator bandwidth and movement of the rotational frequency of larger turbines into a more energetic part of the turbulent spectrum. However, TEF performance is consistent irrespective of scale. Copyright © 2015 John Wiley & Sons, Ltd.

Geometric Nonlinear Effect on Large Span Cable-Stayed Bridge

It is introduced that three main factors cause geometric nonlinear effects of long span cable-stayed bridge: large displacement effect, cable sag effect, and the combination of bending moment and axial force effect. The iteration method of geometrical nonlinear problem is also introduced. The bridge deformation was calculated by establishing a plane truss finite element model of a long-span single tower cable-stayed bridge under consideration of nonlinearity and compared with that done with linear method. It is concluded that nonlinearity influenced differently to the bending moment of main girder, the displacement of tower root and the vertical displacement of girder.

An assessment of the effectiveness of individual pitch control on upscaled wind turbines

The use of individual pitch control (IPC) based on loads transformed into nonrotating coordinates is explored on a range of wind turbines with ratings between 5MW and 15MW. Turbine models are generated using classical upscaling based on properties of the NREL 5MW reference wind turbine. The Ziegler-Nichols method is used with a low order linear model of each turbine to objectively tune a gain-scheduled, proportional-integral individual pitch controller. The performance of IPC is assessed by measuring reductions in blade and tower root damage equivalent loads from simulations at several wind speeds spanning Region 3. It is observed that the load reductions obtained with individual pitch control are maintained on upscaled turbines, with minimal impact on tower root loads, while actuator usage scales at a rate lower than expected with classical scaling.

The Damage Analysis of Usu Bridge under Seismic Load

In order to obtain the dynamic response of Usu bridge the compression damage model of concrete materials and the finite element method are used in this study. The frequency and the main vibration mode of Usu bridge are calculated. The damage distribution and the location of maximum damage of concrete structures under the four kinds of seismic load are obtained. The results show that the maximum damage of bridge deck occurs in close to support position, the maximum compression damage of the main tower occurs in the upper tower root place. Therefore, in the construction and maintenance process note the influence of seismic load of in these positions.

Low-Cost Tower Root Fatigue Load Estimation for Structural Health Monitoring of Grouted Connections in Offshore Wind Turbines

The sinking of wind turbines (WTs) with monopile foundations is one of the major issues in the offshore wind industry nowadays. Dynamic wind and wave loads act on the WTs causing vibrations of the structure. However, grouted connections in the monopiled WTs are not designed well enough to transfer bending moments from the wind loading. When the load capacity of the grouted connection is reached, stress cracks appear in the grout causing transition piece to slide down. Direct measuring of the fatigue load, called the tower bending moment, causing fatigue failures and sinking of the WTs is expensive and practically unfeasible. This paper suggests a low-cost, model-based algorithm for indirect measuring of the tower bending moments from the WT dynamic response measurements. The bending moment is estimated recursively using well-known Kalman filter theory. The method is validated using WT simulated data, assuming different measurement noise levels.

A New Dynamical Model of Flexible Cracked Wind Turbines for Health Monitoring

We develop a mathematical model of a large-scale cracked horizontal axis wind turbine (HAWT) describing the flapping flexure of the flexible tower and blades. The proposed model has enough fidelity to be used in health monitoring applications. The equations of motion account for the effect of the applied aerodynamic forces, modeled using the blade element momentum (BEM) theory, and the location and shape of a crack introduced into one of the blades. We first examine the static response of the HAWT in presence of the crack, and then we formulate the eigenvalue problem and determine the natural frequencies and associated mode shapes. We show that both shape and location of the crack influence the first four natural frequencies. The dynamic response of the HAWT subjected to wind and gravity is obtained using a Galerkin procedure. We conduct a parametric analysis to investigate the influence of the crack on the eigenstructure and overall dynamics. The simulations depict that the first four natural frequencies are reduced as the crack size become more important. We also conclude that the tower root moment may be considered as potential indicators for health monitoring purposes.

Experimental Study on Static Mechanical Behavior of Steel-Concrete Joint Section of Hybrid Girder Cable-Stayed Bridge

According to the structural characteristics of steel-concrete joint section of WuSu Bridge, a 1:3 reduced scale test model was designed to study the static mechanical behavior of the steel-concrete joint section. The test model is loaded according to the serviceability limit state and ultimate limit state separately, the stress of each members of the control sections of the test model is obtained. As shown in the results, the load from steel is smoothly delivered to concrete through the steel-concrete joint section, the stress values of the test model are generally less than the permissible value of the material given by the standard. The load-stress curve shows that the structural materials are in the elastic stage when being loading. All these show the steel-concrete joint section of WUSU Bridge has sufficient security reserve, the design of the steel-concrete joint section meets the security requirements. of the bridge is 140m+140m. The girder is consolidated with tower and pier. The main beam of the bridge is steel box beam with long cantilever while the beam at the tower root is made of concrete with two steel-concrete joint sections set up on both sides of main tower. Axial force, bending moment and torque from steel box beam are delivered to concrete beam through the bearing plate and the shear studs in steel-concrete joint section. The layout of the steel-concrete joint section of WuSu Bridge is shown in Fig. 1.

Research on Anti-Foundation-Displacement Performance and Reliability Assessment of 500 kV Transmission Tower in Mining Subsidence Area

The performance of resisting foundation displacement of typical single return circuit and double return circuit transmission towers under all kinds of load conditions including foundation horizontal displacement, foundation vertical uneven downward displacement were analyzed by finite element modeling. Results showed that stability failure of single steel angle represents tower's limit state under foundation displacement. The corresponding foundation displacement limits were calculated. And the towers' reliability were assessed by comparing the calculated earth surface deformation in advance to the towers' earth surface deformation permissibility. Result indicates that tower does not fail when foundation displacements are smaller than 0.5% of tower root distance. The assessment result revealed that under coal mining deformation conditions, complex foundation and measures adjusting the length of bolts between towers' legs and foundations can ensure all object towers' safety. The complex foundation is more effective than single foundation in resisting coal mining deformation.

Elastic-Plastic Time History Analysis of Self-Anchored Cable-Stayed Suspension Bridge

Base on the elastic-plastic analytical theory, an elastic-plastic time-history analysis of self-anchored cable-stayed suspension bridge, which engineering background is Dalian Gulf Cross-sea Bridge program, is performed by using general finite element software Midas/Civil. The material nonlinearity of structure is considered with reinforcement concrete fiber model, and distributed hinge type is adopted to simulate for plastic hinge. Compared with the results of an elastic time-history analysis, it is shown that for the structure into the elastic-plastic stage, because of the production of plastic hinge, the input seismic energy is dissipated partially, and the internal forces of structural elements are reduced. The bending moments and axial forces occur mainly in the main tower root. Furthermore, the rotation properties of the plastic hinge causes displacement increasing of certain parts of the structure, which assumes mainly the vertical displacement present on the top of main tower and the main beam. In conclusion, it is proposed that caging devices are set in the design.

Research on Performance of Resisting Foundation Displacement of High Voltage Electricity Transmission Tower in Mining Subsidence Area

The performance of resisting foundation displacement of a typical single return circuit transmission tower under all kinds of load conditions including foundation horizontal displacement, foundation vertical uneven downward displacement was analyzed by finite element modeling. Results showed that stability failure of single steel angle represents tower’s limit state under foundation displacement. And the corresponding foundation displacement limits were calculated. Results indicate that foundation pull condition is more dangerous than press condition. Under complex foundation displacement conditions, foundation horizontal displacement is primary factor leading to stability failure of towers. Under foundation press condition and pull condition, wind load is primary factor. Result also indicates that, tower does not fail when foundation displacements are smaller than 1.25% (under foundation press condition and pull condition) or 0.5% (under single foundation sink condition) of tower root distance.

Treatment of adult and obstetrical brachial plexus injuries.

Twenty-five percent of patients with injuries to the plexus require surgical intervention for optimal results. Patients with loss of serratus and rhomboids, Horner's syndrome, positive myelogram, or negative evoked potentials have a high incidence of lower root avulsions and a probability of upper root ruptures. These should be explored early. Results depend on the amount of remaining axonal input available for grafting. Using intraoperative electrical studies, elements which will recover spontaneously may be saved and improved function obtained by grafting only damaged elements. Obstetrical palsy patients should be immobilized for several weeks; passive stretching should then be done. Recovery within 2 months yields a normal arm; if recovery of the biceps or arm occurs within 3 months, the arm will be good. If biceps recovery has not begun by the third month, surgical intervention with appropriate repair will yield at least one grade higher function than in conservatively treated patients.