Tower Deflection Research Articles

Reliability evaluation of reinforced concrete arch bridges during construction based on LGSSA‐SVR hybrid algorithm

AbstractDuring the cantilever casting process of reinforced concrete arch bridges with cantilever cast‐in‐situ method, it is difficult to select representative training samples for reliability analysis due to its complex structural system. Many random variables and large computational sample size, this paper proposes to solve the reliability indexes based on the combination of the improved sparrow search algorithm (LGSSA) and the support vector regression (SVR) method. Firstly, random variables are selected according to the actual situation of the bridge structure. Then representative training samples are designed to be substituted into the finite element model through the homogeneous method. The resultant data samples are used to fit the functional function by the support vector regression. Then combined with the penalized function method to transform the nonlinear optimization into the problem of solving the extreme value of the function. Based on the improved SSA to solve the extreme value of the final function. Finally the reliability index of the structure is obtained. With the background of reinforced concrete arch bridge of 200 m, the method is used to analyze the reliability of its buckling cable stress, arch stress, buckling tower deviation and structural system reliability during the cantilever casting process. The results show that the overall structural reliability of the arch ring during cantilever casting is 3.502–3.608. The indexes of buckling cable stress reliability are 3.806–6.784. The indexes of arch ring stress reliability are 4.379–7.562, and the indexes of buckling tower deflection reliability are 3.608–8.123.

Comparison of Floating Offshore Wind Turbine Tower Deflection Mitigation Methods Using Nonlinear Optimal-Based Reduced-Stroke Tuned Vibration Absorber

Tower fatigue and strength are crucial operational concerns of floating offshore wind turbines (FOWTs) due to the escalation of the vibration phenomena observed on these structures as compared to land-based ones. FOWT towers are excited by wave and wind polyperiodic disturbances yielding continual transient states of structural vibration that are challenging for vibration mitigation systems. Thus, the paper investigates a novel implementation of nonlinear optimal-based vibration control solutions for the full-scale, tension leg platform (TLP)-based, NREL 5MW wind turbine tower-nacelle model with a 10-ton tuned vibration absorber (TVA), equipped with a magnetorheological (MR) damper, located at the nacelle. The structure is subjected to excessive wave and wind excitations, considering floating platform motions derived from model experiments in a wave tank. The MR damper operates simultaneously with an electromagnetic force actuator (forming a hybrid TVA) or independently (a semiactive TVA). The study includes both actuators’ nonlinearities and dynamics, whereby the former are embedded in the Hamilton-principle-based nonlinear control solutions. The TVA is tuned either to the NREL 5MW tower-nacelle 1st bending mode frequency (TVA-TN) or to the TLP surge frequency (TVA-TLP). The optimal control task was redeveloped concerning the TVA stroke and transient vibration minimisation, including the implementation of the protected structure’s acceleration and relative displacement terms, as well as the nonzero velocity term in the quality index. The regarded model is embedded in a MATLAB/Simulink environment. On the basis of the obtained results, the TVA-TN solution is by far superior to the TVA-TLP one. All the regarded TVA-TN solutions provide a tower deflection safety factor of ca. 2, while reference systems without any vibration reduction solutions or with a passive TVA-TLP are at risk of tower structural failure as well as the hybrid TVA-TLP system. The obtained TVA stroke reductions of 25.7%/22.0% coincide with 3.6%/10.3% maximum tower deflection reductions for the semiactive/hybrid TVA-TN case (respectively) with regard to the previously developed approaches. Moreover, these reductions are obtained due to the sole control algorithm enhancement; thus, no additional resources are necessary, while this attainment is accompanied by a reduction in the required MR damper force. The lowest obtained TVA stroke amplitude of 1.66 m is guaranteed by the newly introduced semiactive control. Its hybrid equivalent ensures 8% lower primary structure deflection amplitude and reduced nacelle acceleration levels thanks to the utilisation of the force actuator of the relatively low power (ca. 6 kW); the trade-off is an increased TVA stroke amplitude of 2.19 m, which, however, is the lowest among all the tested hybrid solutions. The analysed reference passive TVA systems, along with a modified ground-hook hybrid solution, can hardly be implemented in the nacelle (especially along the demanding side–side direction). The latter, being the well-proven hybrid solution for steady-state tower deflection minimisation, yielded unsatisfactory results. The achievements of the study may be used for an effective design of a full-scale vibration reduction system for the TLP-based floating wind turbine structure.

Impact of climate change on the design of multi-megawatt spar floating wind turbines

Increased frequency and intensity of extreme events can make offshore constructions unsafe due to the rapidly shifting wind-wave pattern. The consequences of climate change are disregarded by the current performance-based design of offshore wind turbines (OWT). The Statistical Downscaling Model (SDSM) and Artificial Neural Network (ANN) algorithm are used to present a simplified approach to enable the inclusion of future climatic projections in the design of spar-floating wind turbines. A two-variable statistical equation employing an Artificial Neural Network is established for calculating wind-induced wave height for the North Sea and West Coast of India, which is a valuable parameter for the site-specific design of offshore constructions. Under the SSP2-4.5 scenario, the North Sea's most likely wind speed is anticipated to decrease by 11 %, whereas the west coast of India experiences a slight decrease in wind speed. Serviceability responses, such as tower deflection, rotation, and nacelle acceleration, are expected to rise by 8–10 %. In contrast, a decrease in these responses is projected in the North Sea due to a decrease in future wind speed and wave height. Climate change has a greater impact on shutdown conditions than on normal operations, primarily due to the pronounced shifts in extreme climate conditions.

A New Method for Correcting the Deviation of a Middle Pier Tower of a Long-Span Intermediate Arch Bridge

To control the deviation of a long-span concrete-filled steel tube (CFST) arch bridge during construction monitoring, a practical method for controlling tower deviation is studied and established. The form of construction of this bridge is an intermediate double-arch bridge, which differs from conventional bridges, thus requiring the urgent resolution of the issue of unbalanced middle piers. Therefore, the mechanical characteristics and construction process of an intermediate long-span, dual-coupled steel pipe arch bridge are meticulously examined by using a 1:10 scale model, with particular focus on discussing the deflection of the buckle tower during the installation of the arch rib segments. Construction control is implemented using a novel tower deflection control method that addresses unilateral torsion problems and difficulties in controlling the deflection of the tower. The model results are compared with the finite element analysis output, demonstrating that this new approach can resolve unbalanced tower deviations by maintaining absolute values within 0.5 mm. After correcting these deviations, the measured results from the model bridge tower align with the calculated analytical results and even surpass the theoretical expectations for tower deviation. This remarkable new method accurately resolves real-world bridge tower deviations.

Simplified Calculation Method of Middle Tower Effect of Multi-tower Suspension Bridge

In accordance with the “middle tower effect” design problem of multi-tower suspension bridges, the finite element method is currently used to find the reasonable range of the longitudinal stiffness of the middle tower through trial calculations. This method has disadvantages such as complex modeling and large calculation workload. Based on the principle of stiffness distribution, a simplified analysis method of the mid-tower effect of the multi-tower suspension bridge is proposed with the coordination of unbalanced force at the tower top and tower offset as the convergence target. By this method, the mid-span deflection-span ratio parameter and the anti-slip safety factor of the main cable at the saddle under the most unfavorable vehicle live load can be quickly obtained. Relying on the Oujiang River North Estuary Bridge project, the applicability of the method is verified, and the result has a slight deviation from the finite element solution, and the calculation accuracy meets the requirements. The influence of the longitudinal stiffness of the center tower and the friction coefficient between the main cable saddle slots on the middle tower effect of multi-tower suspension bridge is studied. (1) For an 800 m main span multi-tower suspension bridge, when the longitudinal stiffness of the middle tower is greater than 4 MN.m-1, the structure can basically satisfy the requirements of the vertical rigidity of the specification, and the deflection-span ratio is greater than 1/300; when the longitudinal rigidity of the middle tower is greater than 20 MN.m-1, the structure can meet the design requirements of the deflection-span ratio of 1/400. (2) When the longitudinal tower stiffness of the middle tower is 4 MN.m-1, the maximum tower deflection reaches 0.95 m; when the stiffness of the middle tower is greater than 80 MN.m-1, the maximum tower deflection of the middle tower is less than 0.3 m, but the unbalanced force at the top of the tower is greater than 27000 kN, which is unfavorable for the anti-skid requirements of the main cable at the top of the middle tower. (3) Increasing the friction coefficient of the cable saddle from 0.15 to 0.3 can effectively reduce the limiting effect of the middle tower effect on the value of the longitudinal stiffness of the bridge tower. Finally, through the response surface analysis method, based on the independent variable parameters such as the span of the main span, the number of lanes, the friction coefficient of the saddle groove, etc., the recommended formula for the longitudinal stiffness of the middle tower is given, which provides a quick solution method and check basis for the preliminary design of the middle tower of a multi-tower suspension bridge.

Effective wind speed estimation based on a data-driven model of wind turbine tower deflection

The deflection of the wind turbine tower can provide us with rich information about the effective wind speed. In this paper, a new method for effective wind speed estimation is proposed based on tower deflection. The tower vibration model is derived and a subspace identification method is used to identify the model parameters. An online estimator of aerodynamic thrust force based on the identified tower model is designed and then implemented using a Kalman filter together with a recursive least squares algorithm. The estimated aerodynamic thrust force is then used as an input to a neural network estimator, which is trained to invert the aerodynamic thrust force equation and estimate the effective wind speed. In order to show the performance of the proposed estimator, the estimated thrust force and wind speed are compared and verified with a third-party simulation data of a 1.5 MW wind turbine. The comparison shows close agreement between their values.

Analytical Displacement Model of Wind Turbine Towers under Loading Conditions

The goal of this work is in twofold: 1) to determine the directional deformation (deflection) and bending stress of 1.25 MW Suzlon wind turbine tower under loading conditions for different cross-sections through finite element analysis method; 2) to develop and validate the analytical model allowing to estimate same for different cross-sections. Wind shear force has been calculated in the prevailing direction of the wind for tower structures through integral equations, are then used as input for 3-dimensional finite element model to compute the tower deflection and bending stress. To improve the estimation of tower deflection, a mathematical model is developed based on cantilever beam theory. Results are then compared with those obtained from numerical analysis method. The wind turbine tower deflection is found maximum at the tip of the structure and increasing with the hub height. Results indicate that the square cross-section tower is superior with respect to tower deflection with a maximum deflection of 0.064 mm. Numerical analysis method is used to verify the results of mathematical tower deflection model showing very less percentage of error. Thus, the new mathematical model has the advantage of estimating the tower deflection by just knowing the average wind speed of a wind farm for any wind turbine tower structure.

Simplified joint-slippage model of bolted joint in lattice transmission tower

Joint-slippage models are key parameters in structural deflection prediction of angle steel transmission towers. Depended by number of bolts, bolt diameter, bolt arrangement, cross section dimensions of angle steel and so on, there are so many different bolted joints with various joint-slippage characteristics in which only a few angle steel bolted joints were experimental tested. To determine the load-deformation relationship of bolted joints, a simplified joint-slippage model was proposed based on the component method. Then, the load-deformation relationship of two specimens of single-leg bolted joints and two specimens of lap-splice bolted joints were predicted by the proposed model and the finite element method in ABAQUS. Compared with the corresponding experimental results of other researchers, the validation of the proposed model and the finite element method were all verified. Furthermore, the load-deformation relationship of a single-leg bolted joint and a lap-splice bolted joint of a full-scale test tower were also predicted by the proposed model to further verify the validation of the model. Finally, structural deflection prediction of the test tower was conducted in ANSYS based on the proposed joint-slippage model. The predicted tower deflections were in good agreement with the test results.

Designing Video Measuring Device for Monitoring Ice Deposits on Overhead Power Lines

The diagnosis of icing of overhead power lines (OHPLs) by the optical technique involves controlling the linear gap according to video surveillance data. During operation, the wire is exposed to mechanical and thermal strains. This article reveals the need for controlling the wire heating process and suggests an algorithm for calculating the procedure error caused by deflections of modern flexible towers. A conclusion is made that it is important to monitor tower deflections at wind loads. The procedure for correcting the resulting error is considered.

An optical method of registration of line tower deflection for diagnosis of OHL state

An optical method of registration of line tower deflection for diagnosis of OHL state

Generalized analytical displacement model for wind turbine towers under aerodynamic loading

The goal of this work is two-fold: 1) to determine the angular deflection and displacement of the NREL 5 MW reference wind turbine tower under different atmospheric thermal stratifications, and under overlapping wind turbine wake effects using a comprehensive numerical analysis; 2) to develop and verify a generalized analytical model allowing to efficiently estimate wind turbine tower displacements under a variety of flow conditions. Large-eddy simulations are used to generate atmospheric flows similar to those of a characteristic diurnal cycle. One hour periods are selected and inputted into an aero-elastic simulation code which resolves the rotor-disk aerodynamic loading components, which are then used as inputs to a 3-D finite element model of the tower to compute the angular deflection and displacement. To improve efficiency in tower displacement predictions, a generalized analytical model is developed based on a simplified 2-D cantilever beam and 1-D momentum theory. Results are compared with those obtained from the numerical simulations. Results indicate that the tower deflection standard deviation increases with increasing atmospheric turbulence and wake superposition. Also, differentiated tower displacements are experienced under different atmospheric stratifications. Interestingly, lone standing wind turbines undergo larger tower deflections compared to those located within very large wind farms. The wind turbine rotor thrust and the aerodynamic thrust on the tower are found to have the greatest and least influence, respectively, on tower deflection. Displacement results from the finite element analysis are used to verify the accuracy of the new generalized analytical model showing a very good agreement. This new model has the advantage of estimating the tower deflection by just knowing the inflow velocity for any wind turbine, independent of the atmospheric stratification and wind farm arrangement.

Joint stress based deflection limits for transmission line towers

Experimental investigations have revealed significant mismatches between analytical estimates and experimentally measured deflections of transmission towers. These are attributed to bolt slip and joint flexibility. This study focuses on effects of joint flexibility on tower deflections and proposes criterions for permissible deflection limits based on the stresses in joints. The objective has been framed given that guidelines are not available in the codes of practices for transmission towers with regard to the permissible limits of deflection. The analysis procedure is geometric and material nonlinear with consideration of joint flexibility in the form of extension or contraction of the cover plates. The deflections due to bolt slip are included in the study by scaling up the deflections obtained from analysis by a factor. Using the results of the analysis, deflection limits for the towers are proposed by limiting the stresses in the joints. The obtained limits are then applied to a new full scale tower to demonstrate the application of the current study.

Failure analysis of lattice tower like structures

The Experimental investigations have revealed significant mismatches between analytical estimates and experimentally measured deflections of tower structures. Conductor and groundwire tension and sag are influenced by the peak and cross-arm deflections and hence accurate estimates of the tower deflections at service loads are of key interest. This paper presents a nonlinear formulation for analysis of tower structures in an attempt to close the mismatch. The analysis includes geometric nonlinear behaviour of the tower, material nonlinearity as well as leg member buckling in compression. The nonlinear analysis reveals that the ultimate collapse loads of the towers tested to failure can be predicted. However the, deflections continue to have a mismatch despite nonlinear analysis. This demonstrates the need for inclusion of other parameters to be able to reduce the error of analytical deflection estimates.

Measurements of tower deflections on full-scale wind turbines using an opto-mechanical platform

In this study tower deflections of a full-scale turbine are measured with an opto-mechanical platform. This measurement approach is advantageous as no modification to the turbine is required. The tower deflections are measured simultaneously with measurements of wind speed and turbulence upstream of the turbine and of turbine parameters (blade pitch angle, rotor torque and rotor speed). Measurements show that tower deflections during normal operation are sensitive to the yaw misalignment of the rotor, and the tower deflections with negative yaw misalignment are seen to be larger than with positive yaw misalignment. The tower deflections during power cut-off and normal operation are, respectively, modeled with free and forced vibration single-degree-of-freedom models to calculate the damping ratio. The damping ratio during power cut-off, 6.8%, is in the lower range of damping ratios that are measured during normal operation, 5.5%–13.2%. These findings suggest that blade pitch and rotor torque can be used to alleviate the unsteady structural loads caused by the lightly damped oscillations during transition to power cut-off. Additionally, positive yaw misalignments can be used as a strategy for load alleviation during normal operation of wind turbines.

Joint slip investigation based on finite element modelling verified by experimental results on wind turbine lattice towers

Slippage corresponds to the relative displacement of a bolted joint subjected to shear loads since the construction clearance between the bolt shank and the bolthole at assembly can cause joint slip. Deflections of towers with joint slippage effects is up to 1.9 times greater than the displacements obtained by linear analytical methods. In this study, 8 different types of joints are modelled and studied in the finite element program, and the results are verified by the experimental results which have been done in the laboratory. Moreover, several types of joints have been modelled and studied and load-deformation curves have also been presented. Finally, joint slip data for different types of angles, bolt diameter and bolt arrangements are generated. Thereupon, damping ratios (ζ) for different types of connections are reported. The study can be useful to help in designing of wind turbine towers with a higher level of accuracy and safety.

Dynamics and optimal control of flexible solar updraft towers

The use of solar chimneys for energy production was suggested more than 100 years ago. Unfortunately, this technology has not been realized on a commercial scale, in large part due to the high cost of erecting tall towers using traditional methods of construction. Recent works have suggested a radical decrease in tower cost by using an inflatable self-supported tower consisting of stacked toroidal bladders. While the statics deflections of such towers under constant wind have been investigated before, the key for further development of this technology lies in the analysis of dynamics, which is the main point of this paper. Using Lagrangian reduction by symmetry, we develop a fully three-dimensional theory of motion for such towers and study the tower's stability and dynamics. Next, we derive a geometric theory of optimal control for the tower dynamics using variable pressure inside the bladders and perform detailed analytical and numerical studies of the control in two dimensions. Finally, we report on the results of experiments demonstrating the remarkable stability of the tower in real-life conditions, showing good agreement with theoretical results.

Case Study on 4000 m-span Cable-stayed Suspension Bridge

This study describes the case studies for a cable-stayed suspension bridges proposed over the Tsugaru Strait, Japan. Center Bridge is designed as a compound bridge of suspension bridges and cable-stayed bridges with 4000 m super-long-span. Case studies about the effects of cable-stayed bridge length, the design of sub-cable, height and stiffness of main tower, type of foundation and length of side span on displacement were carried out. With appropriate design of above parameters, the compound bridge can reduce horizontal displacement of main tower and vertical deflection in the central portion and enhance resistance to partial loading. The study reports the results based on these case studies.

Floating Wind Turbines

This article discusses the functioning of floating wind turbines. The engineering requirements for the design of floating offshore wind turbines are extensive. Wind turbine design tools usually consist of an aerodynamic model (for flow around the blades) coupled with a structural code. Aero-elastic models used in the design of fixed turbines calculate all the necessary loading parameters, from turbine thrust and power generation, to blade and tower deflections. The design of floating structures usually involves hydrodynamics tools such as WAMIT Inc.’s software for studying wave interactions with vessels and platforms, or Principia’s DIODORE, to predict the hydrodynamic quantities, such as added mass, damping and wave exciting forces, which are used as a kernel in the time domain simulations. In marine projects, design tools typically need to be validated against model tests in a wave tank or basin. Such work is performed frequently, and scaling laws are very well defined.

Testing of lattice towers for Ontario Hydro transmission line refurbishment program

As part of the ongoing transmission-line refurbishment study, three single-circuit, 115 kV, Kingston-type suspension towers on rock-anchor foundations were tested to failure. The types of loads applied to the towers were chosen to represent unbalanced loads due to broken skywire and conductor, heavy-ice, strong-wind and wind-on-ice loads. Selected tower members and foundations were instrumented to measure the member loads, tower deflections, and foundation movement during various stages of testing. The measured values were compared with the corresponding predicted values. The correlation between the predicted and actual tower-failure loads is good. The tower tests confirmed that there is reserve strength available for upgrading the conductor on this line. The measured tower member loads and functions loads correlated fairly satisfactorily with the corresponding calculated values. The rock-anchor foundation did not show any movement at all. The test towers, the tower loading schedule, instrumentation, and tower-testing procedures are described. Measured and predicted failure load are presented. Measured and predicted deflections at selected joints just prior to failure and loads on members just prior to failure are also included.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Interferometric Recording of the Deflections of Towers and Telescopes

Wind generates vibrations in towers and in telescopes placed in the open air. Interferometers for measuring these vibrations were developed. Applications to scale models of a telescope led to improvements of the telescope design. An optoelectronic system using three photocells for scanning the interferometer fringes allows the application of an inexpensive laser with several longitudinal modes as a light source for the interferometers.