Tower Axis Research Articles

A new shape reconstruction method for monitoring the large deformations of offshore wind turbine towers

Offshore wind turbine (OWT) upsizing has become an inevitable trend. Compared with small OWTs, large OWT rotors exert greater horizontal loads and bending moments on the tower. These factors make a large OWT tower more prone to geometric nonlinear deformations, which can affect the normal operation of a wind turbine and even lead to damage to the wind turbine tower. Therefore, monitoring the deformation of large OWT towers is necessary. Shape sensing is a technique that uses surface strains to reconstruct deformed shapes. Currently, there is a lack of effective methods for geometric nonlinearity deformation shape sensing. In addition, the tower of OWT is a variable cross-section structure. The influence of varying cross-sections further increases the difficulty of developing a large deformation reconstruction algorithm. To solve this problem, this paper proposes a new method called rotation angle approximation (RAA). This method establishes a least-squares error functional using analytic curvature and section curvature. The rotation angles of the tower axis are obtained via this function. The deformed shape is then predicted via the boundary conditions and the rotation angles along the tower axis. Numerical simulations demonstrated this method can accurately predict the large deformations of a tower under different load conditions.

Deformation of High Rise Cooling Tower through Projection of Coordinates Resulted from Terrestrial Laser Scanner Observations onto a Vertical Plane

The appearance and development of new construction materials, technology and accurate geodetic instruments have led to the necessity of their inevitable use in the health monitoring, maintenance, and restoration of civil structures and special structures such as high-rise cooling towers. This paper presents an accurate practical and analytical method for determining the structural deformation and axis inclination of high rise cooling towers using terrestrial laser scanner (TLS) observations through the projection of tower surface points coordinates on a vertical plane. Four cooling towers in El-Mahla El-Kubra city, Egypt are observed and studied. Two of them with height 56 m, and the others were 36 m height. The studied four towers have different cross-section diameters along the tower height. Each tower has a cone shape with a curved wall. The equation of the tower wall is determined using TLS observations and least squares adjustment techniques. The equations of cone projection with a curved wall are derived and presented in this paper. From TLS observations, the radii and accuracy of each 2 m tower height are determined with center coordinates, and then the inclination of the tower axis is calculated and drawn. From the results of TLS observations, data processing, and analysis using the suggested techniques, it is deduced that there is a deformation in tower walls with small values. The specified technique for observations collection and TLS data analysis through projection on a vertical plane is significant and valuable for determining the structural deformation of circular high rise buildings and towers. From the results, there are obvious deformation values in some cooling towers, so maintenance work must be included. The towers also must be checked and monitored several times at brief intervals.

Assessing historical church tower asymmetry using point cloud spatial expansion

Church towers are key cultural heritage. In theory, towers are vertical, while facade elements are symmetrically positioned around the tower axis. However, during service of a structure, building and lifetime conditions cause deviations, with associated risks. Laser scanning point clouds can be used to assess the structural state but a universal approach was missing. The proposed algorithm first estimates the tower inclination, and tests which multi-axis representation best represents the course of the tower. Next, point cloud spatial expansion recovers relative distances and deviations of facade elements. The resulting procedure was applied to assess two Dutch medieval towers including the Old Church in Delft and the St. Bavo Church in Haarlem, respectively. As results of analysis, significant asymmetry was found with a 1.4° deviation of the multi-modal axis of the St. Bavo Church tower together with variations of 0.1%–1.5% for facade slopes, while 0.1°–3.1° radial deviations were found in the position of the turrets of the Old Church tower.

Thermoeconomic Analysis of Concentrated Solar Power Plants Based on Supercritical Power Cycles

Solar thermal power plants are an alternative for the future energy context, allowing for a progressive decarbonisation of electricity production. One way to improve the performance of such plants is the use of supercritical CO2 power cycles. This article focuses on a solar thermal plant with a central solar receiver coupled to a partial cooling cycle, and it conducts a comparative study from both a thermal and economic perspective with the aim of optimising the configuration of the receiver. The design of the solar receiver is based on a radial configuration, with absorber panels converging on the tower axis; the absorber panels are compact structures through which a pressurised gas circulates. The different configurations analysed keep a constant thermal power provided by the receiver while varying the number of panels and their dimensions. The results demonstrate the existence of an optimal configuration that maximises the exergy efficiency of the solar subsystem, taking into account both the receiver exergy efficiency and the heliostat field optical efficiency. The evolution of electricity generation cost follows a similar trend to that of the exergy efficiency, exhibiting minimum values when this efficiency is at its maximum.

Rapid approach for structural design of the tower and monopile for a series of 25 MW offshore turbines

The goal of further reducing the Levelized Cost of Energy (LCOE) has driven the investigation of large-scale wind turbines. This work presents a simple, rapid and detailed approach for the structural design of the tower and monopile without a controller, but with frequency and high fidelity structural verification. The approach uses an optimization to reduce the mass of the structures while meeting strength, buckling and geometric constraints by using analytical equations. A verification of frequency constraints is performed with BModes, and ANSYS Mechanical APDL is used for high fidelity verification of stress and buckling. The approach is applied to study the design space of three 25 MW offshore wind turbines with different rotor diameters and cone angles, and to evaluate the nacelle center of mass fore-aft location effect. Results obtained show that the tower and monopile are more susceptible to changes in the rotor thrust than the overturning moment even for designs with high pre-cone angle and large distance of the nacelle center of mass from the tower axis. But it is possible to obtain structurally feasible tower and monopile designs for the three 25 MW turbines studied while not exceeding diameter and wall thickness limits. However, mass penalties can be decreased by 0.8-14%, to further reduce the cost of energy, by increasing the diameter limit which may require manufacturing technology development. The approach applied and studies serve to understand the design space of the tower and monopile for a 25 MW turbine, and provide baseline designs that can be used in the development of a controller and evaluation of a full suite of design load cases.

Design Optimization of 10MW Downwind Turbines with Flexible Blades and Comparison with Upwind Turbines

Downwind turbines can adopt light and flexible blades because of limited risk of tower-strike. We investigate superiority of a downwind configuration in large-scale wind turbines with high extreme wind speed through comparison of optimized 10 MW downwind and upwind turbines. Blades and towers of these turbines are optimized to minimize their levelized cost of energy (LCoE) with steady state aero-structural analyses considering tower shadow and potential flow effects on power production and fatigue damage. Comparison shows that the optimized downwind turbines have an advantage in LCoE due to their lighter and more flexible blades than the upwind turbines with conventional prebend of 6 [m]. This advantage is derived from smaller thrust force, lighter rotor-nacelle-assembly, and a small distance between a tower axis and center of gravity of the rotor-nacelle-assembly. The upwind turbine requires 11 [m] prebend to obtain the comparable LCoE to the downwind turbine.

MITIGASI KEGAGALAN INSULATION UDARA DI ZONA RIGHT OF WAY (ROW) PADA KETINGGIAN POHON PARASERIANTHES-FALCATARIA

Abstract
 Total blackouts (on August 04, 2019) in the Special Capital Region of Jakarta have an impact to daily the economy and the cessation of MRT (Mass Rapid Transit) public transportation services, as well as public communication systems. The determination of the value of the voltage gradient for knowing of the black-out was used the method of analyses to the exposure of the electric fields under the Extra High Voltage (EHV) transmission lines 500 kV, at the span of the tower T.434 and T.435 in Malon hamlet, Gunung-Pati village, districts of Gunung-Pati, Semarang city - central Java. The analysis of the electric field exposured has been carried out in a simulation using a Matlab softwere by solving the simultaneous equations model that corresponding to the tower configuration system and how many conductors were used. The results of the simulation showed that there was a failure of air insulation between phase conductors and the trees of Sengon (Paraserianthes-Falcataria) at a value of voltage gradient of 32 448.10 kV / m, 66 861.13 kV / m, and 33 129.75 kV / m, each were for the lateral distance of 10 m, 12 m, and 14 m from the tower axis T.434 and T.435.
 Keywords: Mitigation, ROW, Paraserianthes-Falcataria, Transmission-lines

A Solar Chimney for renewable energy production: thermo-fluid dynamic optimization by CFD analyses

This paper analyzes the performance of a solar tower designed for renewable energy production. The Solar Chimney Power Plant (SCPP) involves technology that converts solar energy by means of three basic components: a large circular solar collector, a high tower in the center of the collector and a turbine generator inside the chimney. SCPPs are characterized by long term operational life, low maintenance costs, zero use of fuels, no use of water and no emissions of greenhouse gases. The main problem of this technology is the low energy global conversion coefficient due to the presence of four conversions: solar radiation > thermal energy > kinetic energy > mechanical energy > electric energy. This paper defines its starting point from the well known power plant of Manzanares in order to calibrate a numerical model based on finite volumes. Following that, a solar tower with reduced dimensions was designed and an analysis on various geometric parameters was conducted: on the inlet section, on the collector slope, and on the fillet radius among the SUPP sections. Once the optimal solution was identified, a curved deflectors able to induce a flow swirl along the vertical tower axis was designed.

Structural Analysis of Tension Tower Subjected to Exceptional Loads During Installation of Line Conductors

The paper presents results of study dealing with verification of the impact of different installation options (defined by the distance and tilt of anchoring cables from the tower axis and the distance and tilt of winch from the tower axis) to meet the limit state conditions for the tension tower subjected to exceptional loads during installation of overheads lines. 36 optional positions of anchor and winch have been considered. In current practice both the winch and the anchor are mounted at the distance from the axis of tower equal to 2 times H (where H - the distance above ground level on which an anchor or cable are fixed to the tower). It has been shown that the anchor as well as the winch can be fixed to the temporary foundations at the distance equal to H without any hazard to the safety of the structure.

Equivalent nonlinear beam model for the 3-D analysis of shear-type buildings: Application to aeroelastic instability

Tower buildings can be very sensitive to dynamic actions and their dynamic analysis is usually carried out numerically through sophisticated finite element models. In this paper, an equivalent nonlinear one-dimensional shear–shear–torsional beam model immersed in a three-dimensional space is introduced to reproduce, in an approximate way, the dynamic behavior of tower buildings. It represents an extension of a linear beam model recently introduced by the authors, accounting for nonlinearities generated by the stretching of the columns. The constitutive law of the beam is identified from a discrete model of a 3D-frame, via a homogenization process, which accounts for the rotation of the floors around the tower axis. The macroscopic shear strain in the equivalent beam is produced by the bending of columns, accompanied by negligible rotation of the floors. A coupled nonlinear shear–torsional mechanical model is thus obtained. The coupling between shear and torsion is related to a non-symmetric layout of the columns, while mechanical nonlinearities are proportional to the slenderness of the columns. The model can be used for the analysis of the response of tower buildings to any kind of dynamic and static excitation. A first application is here presented to investigate the effect of mechanical and aerodynamic coupling on the critical galloping conditions and on the postcritical behavior of tower buildings, based on a quasi-steady model of aerodynamic forces.

A shear–shear torsional beam model for nonlinear aeroelastic analysis of tower buildings

In this paper, an equivalent one-dimensional beam model immersed in a three-dimensional space is proposed to study the aeroelastic behavior of tower buildings: linear and nonlinear dynamics are analyzed through a simple but realistic physical modeling of the structure and of the load. The beam is internally constrained, so that it is capable to experience shear strains and torsion only. The elasto-geometric and inertial characteristics of the beam are identified from a discrete model of three-dimensional frame, via a homogenization process. The model accounts for the torsional effect induced by the rotation of the floors around the tower axis; the macroscopic shear strain is produced by bending of the columns, accompanied by negligible rotation of the floors. Nonlinear aerodynamic forces are evaluated through the quasi-steady theory. The first aim is to investigate the effect of mechanical and aerodynamic coupling on the critical galloping conditions. Furthermore, the role of aerodynamic nonlinearities on the galloping post-critical behavior is analyzed through a perturbation solution which permits to obtain a reduced one-dimensional dynamical system, capable of capturing the essential dynamics of the problem.

Earthquakes and ancient leaning towers: Geodetic monitoring of the bell tower of San Benedetto Church in Ferrara (Italy)

Abstract In May–June 2012, several seismic events took place in the Po River Plane in northern Italy, with a maximum magnitude of M W 5.86 (M L 5.9)] and the epicentre located about 32 km from the centre of Ferrara. Many historical buildings were seriously damaged and others showed marked deformations or differential settlements. Therefore, it was necessary to place many of them under monitoring, using fast and safe measurement techniques to quickly obtain accurate information on ongoing structural deformation. This paper presents the case study of the bell tower of San Benedetto Church in Ferrara (17th century), which was already under monitoring at the time of the earthquake because of its remarkable leaning angle. Immediately after the seismic events, monitoring of the bell tower was repeated. Digital levelling indicated a marked differential settlement of the foundations with regard to the trend of secular movement, while terrestrial laser scanning (TLS) revealed a significant increase of the inclination of the tower's axis, confirming the results from levelling and showing good integration of both monitoring techniques.

The Variable Geometry Central Receiver System Concept. First Results and Comparison with Conventional Central Receiver Systems

In line with the global trend for improving efficiency of existing solar power plants, the CTAER has developed and built a variable geometry central receiver facility, in which the solar field rotates around the tower axis following the sun's position during the day. The goal of this new approach is to increase the optical efficiency of the field by significantly reducing the angle of incidence of the Sun on the heliostats. This paper presents the advantages of this new variable geometry design and describes the main features of the experimental facility based on this approach as built by CTAER in Almeria. It also compares a conventional solar central receiver plant (i.e., with stationary heliostats and receiver) and an equivalent variable geometry power plant. For this study we employed published data from a real solar central receiver plant with known production (Abengoa's PS10). The results of the study show an increase in annual energy collection and distribution by the variable geometry plant, leading to a potential reduction in the number of heliostats required compared to a conventional central receiver plant for the same annual energy collection.

The key role of the surface membrane in why gastropod nacre grows in towers

The nacre of gastropod molluscs is intriguingly stacked in towers. It is covered by a surface membrane, which protects the growing nacre surface from damage when the animal withdraws into its shell. The surface membrane is supplied by vesicles that adhere to it on its mantle side and secretes interlamellar membranes from the nacre side. Nacre tablets rapidly grow in height and later expand sideways; the part of the tablet formed during this initial growth phase is here called the core. During initial growth, the tips of the cores remain permanently submerged within the surface membrane. The interlamellar membranes, which otherwise separate the nacre tablet lamellae, do not extend across cores, which are aligned in stacked tablets forming the tower axis, and thus towers of nacre tablets are continuous along the central axis. We hypothesize that in gastropod nacre growth core formation precedes that of the interlamellar membrane. Once the core is complete, a new interlamellar membrane, which covers the area of the tablet outside the core, detaches from the surface membrane. In this way, the tower-like growth of gastropod nacre becomes comprehensible.

水平軸風車ロータ空力負荷に及ぼすタワーの影響に関する数値解析(流体工学,流体機械)

The existence of tower in horizontal axis wind turbine system has sometimes a large effect on its surrounding fluid flow. In case of upwind turbines, the unsteady aerodynamic loads occur when the blades of a wind turbine are passing in front of the tower. The fluctuation of load causes a variation of power output and affects a fatigue life of the wind turbine, directly concerning the cost problems. The present paper describes a numerical method for calculation of the tower effects on aerodynamic loads, and shows the calculation results. For the calculation of aerodynamic loads on the rotor blades, an inviscid aerodynamic model based on the asymptotic acceleration potential method is adopted, which is capable of calculating the unsteady aerodynamic loads. In the model, the rotor blades are represented by spanwise and chordwise pressure distributions. The tower is represented by pressure distribution, in order to adapt the numerical model to that for calculation of aerodynamic loads on the blades. The calculation results show that the tower effects on aerodynamic loads depend on the distance between rotor plane and tower axis, and the tower radius, along with the operating wind condition.

A model for yawing dynamic optimization of a wind turbine structure

A novel design optimization model for placing frequencies of a wind turbine tower/nacelle/rotor structure in free yawing motion is developed and discussed. The main aim is to avoid large amplitudes caused by the yawing-induced vibrations in the case of horizontal-axis wind turbines or rotational motion of the blades about the tower axis in case of vertical-axis wind turbines. This can be a major cause of fatigue failure and might severely damage the whole tower/nacelle/rotor structure. The mathematical formulation considers a single pole tower configuration having thin-walled circular cross section with constant taper along the tower height. The nacelle/rotor combination is modeled as a rigid mass elastically supported at the top of the tower by the torsional spring of the yawing mechanism. Adequate scaling and non-dimensionalization of the various parameters and variables are given in order to make the model valid for a variety of wind turbine configurations and types of the material of construction. The resulting governing differential equation of motion is solved analytically by transforming it into a standard form of Bessel's equation, which leads to the necessary exact solutions for the frequencies and mode shapes. Several cases of study are examined for different values of the yawing stiffness and inertia parameters by considering both conditions of locked and unlocked yawing mechanism. Useful design charts are developed for placing the frequencies at their needed target values with no penalty of increasing the total structural weight of the system. In all, the developed model guarantees full separation of the system frequencies from the critical exciting yawing frequencies by proper choice of the optimization design parameters.

TORSIONAL DYNAMIC OPTIMIZATION OF WIND POWER GENERATORS

ABSTRACTThe present paper develops an appropriate optimization model for placingfrequencies of a typical wind rotor/tower structure in free torsional motion. The aim isto avoid large amplitudes caused by the yawing-induced vibrations in the case ofhorizontal-axis machines or rotational motion of the blades about the tower axis incase of vertical-axis machines. This can be a major cause of fatigue failure and mightseverely damage the whole structure of the wind generator. The mathematicalformulation considers a single pole tower configuration having thin-walled circularcross section with constant taper along the tower height. The nacelle/rotorcombination is modeled as a rigid mass elastically supported at the top of the towerby the torsional spring of the yawing mechanism. The resulting governing differentialequation of motion is solved analytically by transforming it into a standard form ofBessel’s equation, which leads to the necessary exact solutions for the frequenciesand mode shapes. Several cases of study are examined for different values of theyawing stiffness and damping parameters by considering both conditions of lockedand unlocked yawing mechanism. Useful design charts are developed for placing thefrequencies at their needed target values with no penalty of increasing the totalstructural weight of the system. In all, the developed model guarantees fullseparation of the system frequencies from the critical exciting torsional frequenciesby the appropriate choice of the optimization design parameters.

Dynamic gust response of inclined towers

The classical stochastic dynamic analysis of line-like structures is extended to the case of a lattice tower with axis inclined to the vertical, for example an inclined flare tower. Attention is concentrated on the quasi-resonant response which is expressed in terms of geometric influence factors applicable to the spectral ordinates of a set of orthogonal turbulence components, together with effective length scales of the respective normalised co-spectra for separations along the tower axis. The turbulence can be regarded as isotropic in the relevant frequency range. The effective length scales for general inclination to the mean wind direction are considered in detail. The implications for fatigue checking a typical tower are considered in conclusion.

Dynamic gust response of inclined towers

The classical stochastic dynamic analysis of line-like structures is extended to the case of a lattice tower with axis inclined to the vertical, for example an inclined flare tower. Attention is concentrated on the quasi-resonant response which is expressed in terms of geometric influence factors applicable to the spectral ordinates of a set of orthogonal turbulence components, together with effective length scales of the respective normalised co-spectra for separations along the tower axis. The turbulence can be regarded as isotropic in the relevant frequency range. The effective length scales for general inclination to the mean wind direction are considered in detail. The implications for fatigue checking a typical tower are considered in conclusion.

DETERMINATION OF THE SECULAR MOVEMENT OF THE AXIS OF THE CIVIC TOWER AT MODENA

Three different survey methods have been performed to determine the historical components of the movement of the Civic Tower at Modena. The comparison between the results obtained in this survey and the data of measurements carried out at the beginning of this century has permitted the determination of the variation of tower axis inclination.