Tower Structure Research Articles

A Fourier‐series numerical approach for the analysis of tubular members

AbstractThis paper provides an efficient and robust numerical solution for the linear buckling analysis of tubular members, such as the supporting tower structures of wind turbines. The method uses Fourier‐series approximations for the displacement functions. Longitudinal discretization can optionally be applied, i.e., the member can be divided into segments. The strain‐displacement relationship directly considers the curved geometry. The implementation allows for arbitrary support conditions. Four pure loading situations are considered, uniform – in each segment – along the length: normal force, bending moment, torque, and shear force; however, they can arbitrarily be combined, as is commonly occurring in wind turbine towers. The applied methodology results in a computational advantage compared to the shell finite element method, while still maintaining much more generality and applicability compared with common analytical solutions. Furthermore, the method is supplemented with features, as spectral analysis and buckling length calculation.

Behavioral Analysis of a Mast with a Combined Prestressed Stayed Columns System and Core of a Spun Concrete Circular Cross-Section

Widely used telecommunication structures are usually of the tower or mast type. For medium and tall telecommunications structures, tower-type constructions become less efficient compared to mast-type structures. The goal of our article is to discover a new, efficient telecommunication structure. For relatively low heights, tower systems can be designed with a continuous cross-section, in most cases using reinforced concrete elements. Among them, efficient spun concrete elements, whose load-bearing capacity is higher than that of ordinary solid reinforced concrete elements due to the technological features of their production, should be mentioned. A significantly higher efficiency of masts can be achieved by employing various combined structural systems that utilize a prestressed stayed columns system. It should be noted that there are not many solutions for prestressed stayed columns systems with spun concrete core elements and that research into their design and behavior is not yet sufficiently developed. The behavior of this combined structure is analyzed with regard to the geometric and physical nonlinearity of its elements. The strength and stability of the spun concrete core of such a combined system are evaluated. The impact of the prestressing of this prestressed stayed column structure on the internal forces and displacements of the reinforced concrete core is analyzed. The performance of the new structure compared to conventional tower and mast structures is presented. In the article, it has been determined that by applying the prestressed stayed columns system to telecommunication structures, the innovative structural system becomes 2.5 times more efficient than the classic mast and 5 times more efficient than the typical tower system on the mass criterion.

Nonlinear energy sink-based study on vortex-induced vibration and control of foil-cylinder coupled structure

The interference of blade wake flow can pose a threat to the safety of flexible tower structures. In order to investigate the influence of airfoil position parameters on the VIV characteristics and the vibration reduction effect of nonlinear energy sinks (NES) on the cylinder, a flexible tower under the influence of blade wake flow is used as a reference, and a dynamic simulation model of an airfoil-twin degree-of-freedom cylindrical coupled structure is established based on computational fluid dynamics (CFD), structural dynamics, and nested grid techniques. The accuracy of the numerical model established in this paper is verified by comparing it with experimental data from foreign literature. The calculation results indicate that airfoils in different positions cause changes in the amplitude and frequency ratios of the cylinder and can either delay or enlarge the frequency lock-in interval of the cylinder. Under the influence of airfoil wake, the column experiences more severe vibrations. The NES can absorb the vibrational energy of the cylinder, and setting appropriate NES parameters can reduce the resonance response between the cylinder and the shedding vortices in the wake of the airfoil. This helps to change the shedding mode of the vortex and effectively suppress the VIV of the cylinder.

Experimental Study on the Influence of Incoming Flow on Wind Turbine Power and Wake Based on Wavelet Analysis

Taking a wind farm in the Qinghai–Tibet Plateau as the experimental site, the ZephiR Dual Mode (ZDM) LiDAR and ground-based laser LiDAR were used to scan the incoming flow and wake of the wind turbine separately. Based on wavelet analysis, the experimental study was conducted on the influence of different incoming wind speeds on the power and wake of the wind turbine. It is found that the incoming wind speeds have a great influence on the wind turbine power, and the fluctuation frequency of the wind speed is obviously higher than that of the power, that is, the scale effects of turbulence are magnified. The rotation of the wind wheel can accelerate the collapse of the large-scale turbulent structures of the incoming flow, and large-scale vortices continue to collapse into small-scale vortices, that is, the energy cascade evolution occurs. And in the wake diffusion process, the dissipation degree of the upper blade tip vortex is greater than that of the lower blade tip vortex caused by the rotation of the wind turbine. Under the same incoming flow conditions, due to the influence of tower and ground turbulence structure, the energy level connection phenomenon of the measuring points below the hub height is stronger than that above the hub height, and it weakens with the increase of the measuring distance. That is, the energy cascade of the measuring points below the hub height at 1.5 D (D is the diameter of the wind wheel) of the wake is weaker than that at 1 D of the wake. With the increase of the measuring distance of the wake, the influx of the external flow field further aggravates the momentum exchange and energy transport between the vortex clusters, that is, the influence of the external flow field gradually increases in the wake vortex pulsation.

Numerical analysis of insulated and conventional cross arms for transmission line tower

The development of the world power industry has led to studies focused on high-performance materials to enhance the durability and prolong the service life of existing structures. In this context, cross arm is one of the main components of an electricity-transmission structure. The application of composite units (insulated cross arm) on lattice transmission towers was evaluated using the software Ansys 2020 R2 in terms of efficiency, cost, and mechanical performance, compared to conventional transmission towers. Finite-element analysis results demonstrated reductions in internal forces, displacements, and support reactions when the insulated cross-arm (IC) tower structure was employed instead of the conventional cross-arm (CC) tower structure. This could lead to minor structural costs. The IC tower exhibited a better stability under free vibrations owing to its higher stiffness than that of the CC tower. The main reason for these results was the height reduction proportioned by IC structures.

A simplified analytical method for lateral dynamic responses of a transmission tower due to rockfall impact

Transmission tower structures support high-voltage power lines that carry electricity over long distance and rockfall is one of critical disasters during its safe operation. This paper presented a simplified analytical methodology for lateral dynamic responses of a transmission tower structure due to rockfall impact. At first, the lateral dynamic displacement of a lattice transmission tower structure can be represented by a second-order partial differential equation and half sine wave was used for rockfall impact. Then, the solution can be approximated by a set of specified shape functions multiplied by time-dependent generalized coordinates. And the partial differential equation is discretized into a set of single degree of freedom system. And then the shape function can be determined by solved an eigenvalue function and the fundamental frequency of a transmission tower can was derived based on the energy method and combination synthesis method. Finally, the lateral dynamic displacements can be approximately obtained. A numerical study of a transmission tower was conducted. Parametric study of the effect of impact location height, impact duration, peak impact force, as well as the distribution of cross-arms on dynamic responses were also carried out. And the results show that the discrepancy between the analytical and the computed of fundamental frequency is less than 3%, the error of dynamic displacement is within 10%, and the fundamental frequency of the structure decreases with the increase of the tower top additional mass ratio.

Performance evaluation of high-rise reinforced concrete buildings under dynamic loading considering different structural systems

With the growing construction of towering structures owing to modernisation and growth in land use, tackling the height and stiffness concerns are now essential. Several structural systems have been developed to withstand various loading scenarios, including framed systems, shear wall systems, braced framed systems, outrigger systems, and diagrid systems. The present investigation employs E-tabs software to accomplish dynamic analyses on a G + 16 story RCC building with regard to every structural system. The variables studied were base shear values, storey shear force values, maximum displacement values, maximum storey drift values, stiffness of storey levels, and time periods. The major goal was to find the most appropriate system among those examined. This study can add to our knowledge concerning building dynamics and helps to make well-versed assessments about prospective high-rise constructions and the findings can be useful in the design of high-rise structures. After accomplishing the study, it was demonstrated that for numerous response parameters, the diagrid structural system proved to be the most successful in managing lateral forces, functioning similarly to the shear-walled model. The diagrid structural system's efficiency in optimising stability and resistance against dynamic loads demonstrates its potential for improving the safety as well as the performance of these structures. Finally, the diagrid system offers potential as a feasible high-rise building choice, providing an efficient and effective response to the issues faced by urbanization-driven vertical expansion.

Application of BPNN Optimized by Fireworks Algorithm on Structural Bearing Capacity Analysis of Transmission Tower under Icing Conditions

With the increasing power demand in city development, the construction and application of transmission towers need to meet higher requirements. Icing is an extreme meteorological condition in the world, and icing disasters cause various accidents such as tower collapse and line disconnection of large-area lines every year. Therefore, it is of great significance to study the ultimate bearing capacity of transmission towers under icing conditions. The structural bearing capacity under icing is greatly affected by meteorological conditions and environmental factors, which has strong randomness and complexity, and brings a series of urgent problems to the structural stability of transmission towers. In the paper, the ultimate bearing capacity analysis and failure path research are conducted on the 500 kV linear cathead tower structure, and a structural bearing capacity prediction model based on the fireworks algorithm (FWA) is established. In order to accurately predict the structural bearing capacity, reduce the adverse effects of line icing, and ensure the structural stability of the transmission tower, the FWA is introduced into the neural network model. The self-adjusting mechanism of the local search ability and global search ability of the FWA is used to optimize the optimization process of weights and thresholds in the neural network, and a structural bearing capacity prediction model based on the FWA improved backpropagation neural network (BPNN) is proposed. Through the analysis and calculation of the measured data of the transmission tower in a certain area, and the comparative study with the traditional BPNN and the BPNN optimized by other common algorithms, the analysis and calculation results of the FWA-BPNN model used in this paper are closer to the actual value, the multiple indicators are more superior, and the model is more stable, which can realize the rapid and accurate analysis of the axial stress of tower members and maximum displacement between member nodes of the transmission tower under the icing condition.

Centrifuge testing of improved monopile foundation for offshore wind turbines

Large fixed vertical offshore wind turbine (OWT) tower structures are typically used to transfer complex loads to the foundations from a combination of wind, waves, and self-weight. These loads must be accommodated within a very small rotation envelope and natural frequency bands to allow the turbines to operate effectively. These challenging loading conditions and strict operational requirements can lead to extremely costly foundation designs. Several foundation options are available to support these turbines, with monopiles currently accounting for 80% of the installed capacity with routinely used diameters of 5–8 m and depths of penetration of 30–80 m. To limit monopile diameters and penetration depths, an improved monopile design: the ‘hybrid foundation’ comprising a plate and centrally located pile, is proposed as an alternative to monopiles. A series of scaled physical model centrifuge tests were conducted to investigate the benefits of the hybrid foundation system and compare its behavior with the typically used monopiles. This type of foundation system can enhance the performance of an OWT since the turbines are subjected to high lateral loads and overturning moments. Centrifuge modeling has been used to investigate the lateral capacity and stiffness of the foundations under lateral monotonic and cyclic loading conditions. Two models were tested: a standard monopile (MP) and a hybrid foundation (HF). Lateral loads were applied with eccentricity for both models to replicate prototype (field) conditions. Models were tested at 50g in over-consolidated clay beds. These soil samples were prepared using inflight consolidation and subjected to a sand surcharge, to increase the shear strength in the zone of influence of the model foundations. Monotonic lateral loading results indicated that the addition of a plate improves the relative lateral ultimate capacity, whilst enabling a reduction of monopile penetration depth and diameter for similar capacities. Specifically, similar capacity/stiffness was realized for the HF system compared to the MP. One-way cyclic lateral loading indicated both the HF and the MP had a shakedown response under fatigue loading of up to 10000 cycles, which indicates the potential use of this novel system for future developments.

Analysis of the Temperature Field Effect on the Thermal Stress of the Main Tower of Long-Span Suspension Bridges

To investigate the temperature field variation of the main tower of large-span suspension bridges, the Nanjing Xinshengwei Yangtze River Bridge was selected as the objective of the present study. The finite element model of the main tower was developed, and the analysis of the effect of the temperature field on the structure of the main tower was carried out. The calculation parameters of the temperature field of the main tower were determined, and the influence of the solar radiation temperature of the main tower within 24 h was investigated. Differences in the temperatures inside and outside the wall of the tower column were analyzed, and the thermal stress of the tower wall under the most unfavorable temperature difference was calculated. Results show that under the positive temperature difference, the area of tensile stress is mainly concentrated on the inner wall, the maximum value is located at the corner of the intersection of the tower wall, and the range of tensile stress is mainly diffused along the vertical wall. Under the action of negative temperature difference, the area of tensile stress is mainly concentrated in the outer tower wall, the maximum value is located in the upper part of the western outer tower wall, and the range of tensile stress is mainly diffused along the center of the tower wall to both sides. The maximum tensile stresses in the inner and outer tower wall are 2.8 MPa and 1.3 MPa, respectively, which meets the standard value of 2.85 MPa for the tensile strength of C60 concrete specified in the Chinese national standard.

Design of Temperature Monitoring System for Air Cooled Radiators Based on LoRa

Air cooling technology is widely used in the north. When the winter temperature in the north is too low, the cooling radiator is prone to freezing, leading to the inability of air cooling units to operate normally and causing huge economic losses. In response to the above issues, this article designs a monitoring system for air cooled radiators based on LORA communication, based on Internet of Things technology. Analyze the A-type tower structure and heat dissipation principle of the air-cooled condenser, reasonably select the temperature measurement point position, and achieve temperature data transmission through LoRa communication and Ethernet communication technology. The monitoring software is programmed in C # language, which can visually display the temperature distribution information of the air-cooled condenser and store data in real time. The experimental results indicate that the system has certain guiding significance for preventing the freezing phenomenon of air cooled condensers and optimizing operation.

Optimal design of corona ring in composite insulator considering the effects of tower structure, conductor, hardware and mutual phases

One of the key elements in lowering the electric field intensity (EFI) on the creepage distance of composite insulators is the usage of the corona ring and its ideal design. First, using the Finite Element Method (FEM) in the 3D COMSOL Multiphysics program, this paper investigated and calculated the changes in the EFI of the creepage distance of the 230-kV composite insulator with and without taking into account the effects of the corona ring, tower structure, conductor, hardware, and mutual phases. Next, the ideal goal function is chosen in order to minimize the insulator creepage distance's maximal EFI. Nelder-Mead (NM) and Bound Optimization by Quadratic Approximation (BOBYQA), two optimization techniques, are used for the best design of corona ring parameters on the 230 kV insulator. Finally, the diameter, thickness, and installation position of the ideal corona ring are determined using the suggested methodologies and different restrictions. The obtained results demonstrate that, in contrast to previous studies that have only focused on a few of the aforementioned constraints, taking into account the tower structure, conductor, hardware, and mutual phases will have a significant impact on the distribution of the EFI on the insulator creepage distance.

Deformations of a three-dimensional model of a trihedral double lattice rod tower

Introduction. The calculation of deformations of spatial structures, as a rule, is carried out numerically on the basis of the finite element method. With the development of computer mathematical systems for regular systems an opportunity to obtain analytical solutions appeared. Such solutions can be used as test ones to evaluate numerical solutions and for preliminary calculation of a structure at design stage. The task has been set to derive deformation dependences of a spatial truss under various loads from its size and number of panels.
 
 Materials and methods. The truss of the tower structure is statically determined. The calculation of force values in the bars is performed by cutting out nodes in a Maple symbolic mathematics system. The Maxwell – Mohr formula is used to determine the displacement of a node at the top of the frame, considering only the longitudinal deformations of the rods. From the generalization of a series of analytical solutions for trusses with consecutively increasing number of panels onto an arbitrary number of panels the sought formula is derived by the induction method.
 
 Results. An algorithm of derivation of formulas for the deflections of a building along two mutually perpendicular horizontal axes under the action of lateral uniformly distributed nodal loads is presented. Effort distribution patterns are obtained for the truss rods and analytical stress dependences of some rods on the number of panels are found. Linear asymptotics of the solutions for the number of panels and the points of extremum are found and computed.
 
 Conclusions. The considered model of the spatial statically determined tower truss allows deriving exact formulas for deformations under the action of various loads within the limits of the adopted model. It is possible to use derived formulas for a preliminary estimation of designed structure and to apply as test ones for numerical calculations. The extremum points and analytical expressions for asymptotes allow the derived formulas to be used for solving stiffness optimization problems of a structure.

Undrained cyclic loading behavior of stiff Eocene-to-Jurassic plastic, high-OCR clays

Assessing foundation response to cyclic loading is vital when designing transport infrastructure, such as road pavements and rail tracks, as well as offshore, port, and tall tower structures. While detailed guidance is available on characterizing many soil types’ cyclic behavior, relatively few studies have been reported on stiff, geologically aged, plastic clays. This paper addresses this gap in knowledge by reporting cyclic loading experiments on three natural stiff UK clays that were deposited and buried between the Jurassic Age and Eocene Epoch before geological unloading to their currently heavily over-consolidated states. High-quality samples taken at relatively shallow depths were reconsolidated to nominally in situ K0 stresses in triaxial and hollow cylinder apparatus before imposing cyclic loading. The completely stable, metastable, or unstable outcomes invoked by different levels of undrained cyclic loading are interpreted within a kinematic yielding framework that is compatible with monotonic control experiments’ outcomes. The cyclic limits marking the onset of significant changes in permanent strain accumulation, pore pressure development, and stress–strain hysteresis demonstrate that the weathered Gault clay offers the lowest cyclic resistance. The experiments show that energy considerations provide a promising way of evaluating undrained pore pressure generation and stiffness degradation. They also provide a basis for developing cyclic constitutive models and analysis procedures for cyclic foundation design in stiff, high-OCR, plastic clay strata.

Data set from shaking table tests of a slender MDOF structure with base-rocking mechanisms

Numerical models of seismic-resistant structures are typically validated by comparing numerically predicted key seismic response parameters to those obtained from benchmark shake table experiments. However, studies have shown that for structures rocking on rigid foundations, the seismic response can be unrepeatable in experiments and deterministically unpredictable by numerical models. Therefore, researchers have proposed to validate rigid rocking models using statistical approaches, yet no experimental study has examined whether the same observations apply to slender multi-degree-of-freedom (MDOF) free-rocking structures or controlled rocking structures with positive post-rocking stiffness and dedicated energy dissipation. This data paper describes the now publicly available data obtained from a series of 254 shaking table tests of a slender MDOF tower structure with two base-rocking mechanisms, which can be used to examine the predictability of the seismic response of an MDOF rocking structure and to statistically validate different approaches aiming to model tall and slender structures that utilize base-rocking mechanisms to mitigate the dynamic response due to higher-mode effects.

Integration of high-precision UAV laser scanning and terrestrial scanning measurements for determining the shape of a water tower

This study was aimed at integrating surveys from terrestrial laser scanning (TLS) and high-precision scanning performed by a drone (ULS) for a tower structure. This will allow a complete point cloud to be obtained for the entire object. Integrated measurements will eliminate gaps in the point cloud, characteristic of TLS or ULS separate measurements. Existing studies report ULS accuracy of a few cm, but the precision may be about 10 mm. Assuming that the ULS point cloud will be matched to the TLS cloud, which has higher accuracy, the high accuracy of the whole integrated model can be expected. The integration of the surveys was carried out for the water tower and a coherent model of the structure was obtained, with a mean merge error of 13 mm. Detailed comparative analyses were carried out in selected cross-sections, obtaining mostly a several-millimetre compliance of the results in the analysed categories.

Modeling and modal analysis of the structure of long-span transmission tower

The structure of the long-span transmission tower is a typical nonlinear structure with the characteristics of great height, large line span, heavy overall weight and flexible tower body. The current design code only analyzes the traditional tower types, but the analysis of the truss structure of transmission tower is limited. Aiming at improving the design defects of the structure of long-span transmission towers, this paper uses the finite element software APDL to build the three-dimensional finite element model of a long-span transmission tower, to carry out the modal finite element analysis as well as to extract the specific parameters of each modal finite element mode: Modality, Natural frequency of vibration, Periodicity. The results show that the natural vibration period of the main machinery of this type of steel transmission tower is about 0.37–1.37 s; The structure of the long-span transmission tower has certain displacements in six degrees of freedom, in which the value of the X-dimensional displacement is the largest. There are some large displacements and local torsion in the high-order mode, combined with the results of modal analysis, so it is suggested to consider the structural improvement or external reinforcement of the weak parts of the long-span transmission tower.

How to Fold a Triangle: The Connection between the Grashof Fourbar Linkage and Pythagorean Triangles

Summary This paper presents two different methods for folding a triangle onto a flat line by converting it into a Grashof Special Case fourbar linkage. Foldable triangles have many applications, ranging from space structures to collapsible furniture. In the first method, a generic triangle with positive real side lengths is shown to be foldable inward and outward by adding a pin joint at a specific location to one of the sides. The second method shows how to create a collapsible linkage using a Pythagorean triangle; we demonstrate that all four links in the Pythagorean fourbar have integer length and can be easily built using rods with uniformly spaced holes (e.g., LEGO bricks, Unistrut, etc.). Next, the formulas for finding the interior angles of the Pythagorean fourbar are presented, for the purpose of plotting collapsible structures with mathematical software. We conclude with a demonstration of a sample application of Pythagorean fourbars to collapsible arch or tower structures and a surprising proof that some types of collapsible arch structures are unrealizable with Pythagorean fourbars.

Coupled analysis of monopile offshore wind turbine under modified three-dimensional seafloor ground motions

The safe operation of offshore wind turbines (OWTs) is significantly influenced by the combined effect of wind, waves, and offshore earthquakes. However, limited seafloor ground motion data have been used to determine the dynamic characteristics and responses of OWTs subjected to offshore earthquakes. Hence, synthetic seafloor ground motions are particularly important for seismic analysis of OWTs. This paper proposes a new method to simulate seafloor ground motions. In the study, the dynamic shear modulus of the water-bearing soil layer and the damping effect of the soil–seawater layers were introduced to modify the simple Crouse and Quilter (C-Q) model in seawater and P-SV and SH transfer function models at offshore sites. Further, three-dimensional seismic waves were synthesized based on the modified transfer function models at a typical offshore site with bedrock–soil–seawater layers, and a fully coupled numerical analysis model of OWTs, including the rotor nacelle assembly, tower structure, and substructure with pile–soil interaction (PSI) under wind, wave, and seafloor ground motion, was established by incorporating the earthquake module and PSI module into the updated FAST v8 software. Moreover, based on the established coupled OWT model, the measured seafloor ground motion records and the seafloor ground motions synthesized using the proposed method were compared, and a coupled analysis of the OWT under wind, wave, and offshore earthquake loadings was carried out. Furthermore, the coupled mechanisms of the OWT under synthesized and recorded seafloor ground motions were determined.

Health monitoring of ultra high fiber performance reinforced concrete communication tower using machine learning algorithms

Within the last decades, the needed for communication towers has accelerated with the requirements for effective communication, especially for radio, radar, and television. The complexity configuration of the tower and limit access to the structure body especially inner part of the tower with hollow section is led the health monitoring of tower as the main challenging issue to maintenance during its function. The change of natural frequencies can be considered as one of the prevalent damage detection methods in structural assessment procedures. Therefore, the main aim of present research is to develop health monitoring system for Ultra High Fiber Performance Reinforced Concrete (UHPFRC) communication tower based on frequency domain response. Since the frequency data of tower is mostly noisy and interpreting of frequency in different modes in variant case of tower damage. The hybrid algorithm based on the Adaboost, Bagging and RUSBoost algorithms are implemented to identify the damage in the UHPFRC communication tower using frequency domain data. The training samples for the algorithm are obtained from a finite element simulation and full-scale experiment testing is also performed to generate the testing samples. The finite element simulation dynamic frequency results are verified through conducting a full-scale experimental test on 30 m height UHPFRC communication tower. For this propose, frequency Response Functions (FRF’s), for healthy and damaged structures were obtained by exciting of tower by an impact hammer and the acceleration response recorded by three accelerometers sensors attached in suitable positions. The developed hybrid algorithm to identifying the damage is tested and verified by considering the part of tower segments 2–3 and conducting experimental testing on the healthy structure as well as a damaged structure which caused using dynamic actuator. The testing results proved the accuracy of the developed optimized hybrid algorithm to identify damage in the tower structure in variant condition.