Tower Model Research Articles

Reliability Analysis of Transmission Tower Based on Unscented Transformation Under Ice and Wind Loads

Due to the complexity of the transmission tower structure and the correlation between wind and ice loads in the actual project, it is difficult to analyze the reliability of transmission towers with traditional methods. To solve this problem, the unscented transformation (UT) principle is presented concisely and used in the reliability analysis of transmission towers in this paper. Moreover, the finite element model of the target transmission tower is created. The reliability indices of the transmission tower under various loading cases are evaluated using UT and analyzed relative to the outcomes of the Monte Carlo method (MCS). Lastly, by analyzing and validating a wine-cup shape tangent tower, the simulation results show that the UT yields reliability indices with less than 6% relative error compared with MCS results for the transmission towers with lower reliability, which are more important in engineering. Variations in error caused by the change in correlation coefficients among variables are small. Consequently, the efficiency of calculations is improved by the UT-based reliability calculations for transmission towers in the case of correlated variables, which better meet engineering application requirements. It is proved that the method of reliability analysis for transmission towers based on the UT is applicable.

Introduction to cross-arm T pole tower of 110kV transmission line and design verification of double circuit T pole tower

Abstract With the development of various fields in China, users have higher and higher requirements for power reliability. In order to improve the reliability of 110 kV transmission lines, a new type of cross-arm T-connection technology came into being. This paper introduces the characteristics of the original T-connection technology and the new T-connection mode of the new T-connection technology, as well as the design verification of the double-circuit T-connection tower, and draws the conclusion that the new T-connection tower model is reasonable and the force of the rod can be effectively configured.

Theoretical analysis of heat and mass transfer characteristics of a counter-flow packing tower with different heating modes

Mass extraction/injection and multi-stage system have been proven to be effective approaches to improve the performance of humidification and dehumidification (HDH) desalination system. However, these two optimization schemes cause that the flow ratios of water to air at different positions of humidifier or that of different humidifiers have great difference. A single heating mode is inapplicable to all flow ratios of water to air. Hence, it is necessary to reveal the relationship among mass flow ratio, heating mode and thermal efficiency of humidifier for the selection of appropriate heating mode. A theoretical model of packing tower (typical kind of humidifier) which agrees well with experimental results was established in this paper, and the average relative errors of outlet air temperature, humidity and thermal efficiency are 2.3 %, 4.9 % and 5.8 %, respectively. A comparison among the thermal efficiencies of a counter-flow packing tower with different heating modes (I: solution heated, II: air heated, III: solution-air heated) was conducted. It is found that there exist two values of mass flow ratio (FRI-II and FRII-III) at which the thermal efficiencies of air heated and solution-air heated are equal and that of solution heated and solution-air heated are equal, respectively. However, the thermal efficiency of solution heated is always higher than that of solution-air heated (FRI-III does not exist). It seems clear that there is a relationship between FR and thermal efficiency (η) as follows: FR < FRI-II, ηI > ηIII > ηII; FRI-II < FR < FRII-III, ηI > ηII > ηIII; FR > FRI-II, ηII > ηI > ηIII. Additionally, the effects of inlet parameters on the FRI-II and FRII-III are also evaluated. The results show that the maximum temperature, inlet solution concentration and ambient temperature have positive effects on FRI-II and FRII-III, but ambient relative humidity has negative effect. In the final part, the selection of the heating mode of a counter-flow packing tower is taken as example to introduce the application of FRI-II and FRII-III proposed in this paper.

Route Planning Method of UAV Patrol Based on High Precision Tower Model

The high-precision positioning technology of industrial Unmanned Aerial Vehicle (UAV) plays a vital role in intelligent trajectory planning in power inspection. First, the information on power facilities is collected and processed to form a planning grid to optimize the flight path and correct the trajectory of UAV. However, the preparatory work is more complex, and the algorithm model which needs more detailed and complex terrain database data is not universal enough. To improve the safety of UAV and the efficiency of path planning, we establish a three-dimensional model of the power tower, calculate the coordinate position of the inspection work according to the information of the high-voltage transmission tower, and then determine the corresponding relationship between the inspection point and the flight trajectory combined with the safe distance. Based on the set of random interference semaphores and model rasterization, the discrete error strategy and Euler method are introduced to improve the performance. In each iteration, the best solution is first updated using the execution strategy. We continue to calculate the spatial coordinates of all reference points and provide the coordinate position distribution for the flight mission. The solution of equipment inspection trajectory optimization is realized by using dynamic obstacle perception. The proposed discrete measurement error self-correction algorithm is deployed on the flight platform to guide UAV inspection tasks according to the point cloud coordinate model of transmission equipment in the power system and to correct the flight route in time. To verify the research results, the Algorithm Artemisinin optimization and Whale Optimization Algorithm test verify that the ability of the proposed algorithm to get rid of local optimization is improved by 8.94% and, 12.42% respectively compared with other optimization algorithms. The convergence accuracy is 12.4% and 7.9% higher than other schemes, and it has a better effect in solving numerical problems. The research results using the embedded system to complete the task deployment and unloading provide a reference for trajectory planning and task design in different application scenarios.

Evaluation of wind-induced response of high-rise structure with TMD system by real-time hybrid simulation test with motor-driven shaking table

Due to the difficulty in constructing the small-scaled model of tuned mass damper (TMD) system to meet the requirement of dynamic similarity law, it is hard to evaluate the vibration control effect of passive TMD system on the wind-induced response of high-rise structure by wind tunnel test. The Real-Time Hybrid Simulation (RTHS) test could provide a suitable solution to this problem by increasing the size of the scaled TMD model to overcome the limitation in dynamic similarity law. A RTHS test system with a linear electric motor-driven shaking table was developed by the interface with model interface toolkit in general real time system operating environment. Taking the Guangzhou New TV Tower with a passive TMD system as an example, the Finite Element (FE) model of Guangzhou New TV Tower was selected as the numerical substructure and TMD system was selected as the experimental substructure, the RTHS test was conducted at a sampling frequency of 250 Hz to estimate the wind-induced response of this high-rise structure with a TMD system in various dynamic wind loading cases. To reduce the time delay effect generated by the nonlinear interaction between motion control system and experimental substructure, the adaptive time series (ATS) compensator for time delay compensation was proposed in the RTHS test. The RTHS results were also compared with the numerical simulation results using the FE model of the investigated object. The RTHS test with additional ATS time delay compensator can obtain more accurate experimental results. The effectiveness of the proposed RTHS test system was testified to be powerful test system to evaluate the wind-induced response of high-rise structures with complex passive TMD system.

Wake-induced vibration of ultra-long suspenders adjacent to bridge tower

The tower wake usually induces large-amplitude vibrations in adjacent suspenders of a long-span suspension bridge. In order to interpret the underlying mechanism of the significant wake-induced vibrations of ultra-long suspenders, the wake-induced vibration characteristics of tandem suspenders beside the bridge tower are investigated using computational fluid dynamics based simulation. First, the computational model of the bridge tower and suspenders is established. Subsequently, the effect of tower wake on suspender vibration is analyzed considering the inflow velocity and relative position between the tower and suspenders. Based on the proper orthogonal decomposition (POD), the flow characteristics behind the tower and around the suspenders are investigated, and the governing mechanism of wake-induced vibrations of the suspenders is revealed ultimately. The results indicate that the wake-induced vibration of the suspender exhibits a lock-in phenomenon with large cross-wind amplitudes at specific incoming wind velocities. The wind loads on the suspender in both along-wind and cross-wind directions exhibit components with frequencies that are multiples of the vortex shedding frequency. The flow field can be accurately constructed using the first four POD modes with the largest energy. The symmetric POD modes are the primary components that contribute to the significant wake-induced vibrations of the suspenders.

Failure intervention of transmission line tower primary legs using bi-angled cruciform retrofitting

Retrofitting has been suggested by researchers as an intervention measure against failure of transmission towers which needs to be done with minimal disruption. Retrofitting of the primary leg members of transmission line towers by bi-angled cruciform arrangement has been shown in literature to be effective. However, the influence of stresses and deformations existing in the leg member prior to retrofitting on the capacity of the final retrofitted member is not known. Therefore, this study assesses the effectiveness of bi-angled cruciform sections under preload conditions through experiment followed by a numerical study. The level of preload in the primary leg member with respect to its theoretical capacity, slenderness ratio and width-thickness ratio of the angle section were the parameters. The results suggest that bi-angled cruciform retrofit is more effective at lower slenderness and width-thickness ratios and the reduction in capacity of retrofitted member is more noticeable till 50 % preload after which the changes are not significant. While the former two parameters lead to lower load share in the retrofitting member, higher preloads however lead to more equal load share. The application of this retrofitting pattern is demonstrated numerically with a full-scale tower model simulated under code specified load cases. Critical load cases leading to tower failure before design loads were identified and the retrofitting was incorporated into the model for these load cases. The analysis showed that the final loads attained in these load cases improved by upto 70 % thus confirming the potential of this retrofitting technique in preventing tower failure.

Vibration modeling and simulation analysis of wind turbine flexible tower based on BP neural network

Vibration modeling and simulation analysis of wind turbine flexible tower based on BP neural network

Introduction to the design and verification of the cross-arm T pole for the 110kV transmission line and the single-loop T pole

Abstract With the development of various fields in China, users have higher and higher requirements for power reliability. In order to improve the reliability of 110 kV transmission lines, a new type of cross-arm T-connection technology came into being. This paper introduces the characteristics of the original T-connection technology and the new T-connection mode of the new T-connection technology, as well as the design verification of the new single-loop T-connection tower, and draws the conclusion that the new T-connection tower model is reasonable and the force of the rod can be effectively configured.

Tower loads characteristics of a semi-submersible floating wind turbine: An experimental study

For a Floating Wind Turbine (FWT), the tower emerges as a critical structure that connecting the Rotor-Nacelle Assembly (RNA) and the supporting platform, facilitating the transmission of both aerodynamic and hydrodynamic loads. This paper deduces the distinct responses of the bending moment generated by the motion of a FWT compared with a fixed wind turbine. Due to the complexity of the tower load responses, a comprehensive experimental investigation was conducted on a semi-submersible FWT. Stiffness-matched and geometry-matched tower models were designed and fabricated. These models accurately simulate the tower's flexibility and windward areas, impacting the global dynamic response. The model test precisely replicates the marine environmental conditions, incorporating the interactions between wind, waves, and current. It is particularly worth noting that, a multi-fans large-scale Wind Generation System (WGS) with rectifier networks was improved and fabricated to provide a reliable wind field. Results indicate that the tower load responses under the conditions with wind exhibit distinct nP component characteristics. Notably, 1P and 3P responses dominate most tower load responses, with the 3P response typically increasing with wind speed. The extreme value of My.b (y-axis moment at tower-base) is approximately 10 times larger than that of My.t (y-axis moment at tower-top), signifying a significant magnitude difference and reflecting the response characteristics of the tower loads. And the responses of My.b and Fx.t (x-axis force at tower-top) at the natural frequency of pitch motion are notably suppressed by the aerodynamic damping effect of wind. Furthermore, Fx.b (x-axis force at tower-base) and My.b exhibit obvious responses at the natural frequency of pitch motion. As the wave height increases, the wave-frequency response of the tower base load also strengthens, but the high-frequency response still accounts for a certain proportion of energy in the tower top load.

Investigation of the earthquake behavior of the historical Adana great clock tower using FEM updated based on environmental vibration data

In this study, the historical Adana great clock tower's dynamic characteristics (natural frequencies and mode shapes) were determined using the operational modal analysis (OMA) method. The finite element model (FEM) of the Clock Tower was updated based on the experimentally obtained dynamic characteristics. The update process was performed manually using the material properties of the Clock Tower. Linear dynamic analyses of the structures under earthquake loadings were performed using its updated finite element model. The acceleration records of the 1998 Adana-Ceyhan earthquake, scaled according to the horizontal elastic design spectrum defined in TBEC (2018) were used for dynamic input. The displacements, maximum and minimum principal stresses of the Clock Tower were obtained and evaluated. As a result of the analyses, it was determined that there was a potential for damage to the Clock Tower due to exceeding the tensile strength of the walls, but the potential for damage to the Clock Tower due to exceeding the compressive strength of the walls is weak.

Non-linear seismic behavior of historic Adana Great Clock Tower

In this study, the non-linear seismic behavior of the historic Adana Great Clock Tower was investigated. The dynamic characteristics (natural frequencies and mode shapes) of the Clock Tower were determined by operational vibration tests. The finite element model of the Clock Tower was manually updated in the light of the experimentally obtained dynamic characteristics. For the updated finite element model, pushover analyses and non-linear time history analyses were performed. Incremental pushover analyses were performed in the x and y directions proportional to the first lateral displacement modes of the Clock Tower in the x and y directions. The time history analyses took into account the Adana-Ceyhan (1998) earthquake acceleration records. Each of the two horizontal components of the earthquake acceleration records was separately scaled according to the design spectrum defined in TBEC-2018 for earthquake levels with a 10 % and 50 % probability of exceedance in 50 years. These scaled earthquake acceleration records were applied to the structure. The two scaled horizontal components for the same earthquake level were rotated 90° and reapplied to the structure. As the response quantities, displacement, base shear force and plastic strains were evaluated.

Fire resistance behavior and failure analysis of transmission tower exposed to wildfires

This paper deals with the fire resistance behavior and failure mode of transmission towers exposed to wildfires. A nonlinear thermo-mechanical coupling model of a latticed transmission tower was established by the finite element (FE) program ANSYS, which was validated from steel members’ perspectives. Wildfire analysis was conducted to determine the key parameters, including the number of legs in fire, fire intensity, and residence time, and the temperature–time curve was further proposed for parametric analysis. It reveals that the transmission tower may collapse under serviceability state loads in the wildfire, and the final failure mode was determined by the number of tower legs in the wildfire. A higher wildfire intensity will significantly reduce the wildfire resistance time of the transmission tower. Therefore, combustible materials around transmission towers need to be regularly cleaned to reduce the intensity and residence time of wildfires, which is an effective way to prevent wildfires. Moreover, a wildfire protection layer design process was proposed based on the environment surrounding the transmission tower, which proved reliable to provide valuable insights for the fire protection design of transmission towers in areas prone to wildfires.

Investigation of Nonlinear Effects in the Tower Structure of Wind Turbines and Their Influence on System Behavior

In multibody simulation (MBS) software, large structural components such as the tower are often modeled as flexible bodies using the Craig-Bampton method. While being very computationally efficient, nonlinear effects cannot be modelled in this way. The flange connections between the segments of tubular steel towers are one such source of nonlinearity. The magnitude of this nonlinearity increases with damages at the flanges as flange gaping becomes more common. The nonlinearities in the flanges lead to a changing stiffness and hence changing eigenfrequencies of the structure as a function of its deformation. In this paper, a nonlinear model of a tower with and without damages is being developed and validated based on an FEM model. The model is assembled from linear flexible bodies linked with nonlinear rotatory springs. The damages considered are broken bolts as well as axially symmetric angular flange gaps. It is shown that the MBS model closely emulates the FEM model including all nonlinear effects. The nonlinear tower model is incorporated into an existing MBS model of a commercial wind turbine in the 4 MW range. The eigenfrequencies of the full turbine model are being calculated using the build-in eigenvalue solver in Simpack. The results show a small but measurable decrease in eigenfrequencies compared to the linearized model, which scales with the extend of the damage.

Electromagnetic fields of lightning return stroke to wind turbines with discontinuous impedance model

This study introduces an electric field calculation model for wind turbine return strokes, incorporating impedance discontinuity within the turbine, a feature not considered in traditional tall tower models. The model introduces a reflection coefficient, ρx, at the connection between the blades and the tower. Disregarding the generation of upward leaders, this paper calculates the electric field of subsequent return strokes for different distances from the wind turbine and for different model parameters. The results demonstrate that changes in the reflection coefficient ρx affect oscillation amplitude and also slightly influence the pulse width, with a negative ρx leading to smaller and more frequent pulses. Contrasts with measured waveforms indicate that models with a constant reflection coefficient are inaccurate. Adopting variable reflection coefficient values yields a more accurate match. This approach offers a new perspective for electromagnetic field calculations in lightning-struck structures, emphasizing the significance of impedance dynamics of return stroke channel.

Passive Shunted Piezoelectric Systems for Vibration Control of Wind Turbine Towers: A Feasibility Study

Many countries have a variety of offshore and onshore wind turbines that face extreme aging challenges. Issues with harmful vibrations that must be minimized are addressed in this paper. A new method of wind turbine tower vibration control using piezoelectricity and shunt circuits is proposed in this paper. The passive vibration control method is shown to improve the tower’s structural performance under various environmental loads, like wind and seismic excitations. To examine the effectiveness of the suggested shunted piezoelectric system, a simple surrogate finite element model of a wind turbine tower is considered, and various investigations at the second eigenfrequency are carried out. An alternative way of modeling the studied structure is considered and the results demonstrate better performance. The advantages of setting up structural damping systems for decreasing tower vibrational loads and boosting their structural stability and resilience against extreme events are highlighted throughout this work.

Active vibration control for flexible towers based on displacement observation and reduced-order controller in modal space: Theory and experiment

Active vibration control is not only suitable but also urgently needed in order to mitigate excessive vibration for dynamic systems such as wind turbine towers. However, there is a challenge of directly observing displacement and developing an efficient reduced-order control strategy. With this in view, a reduced-order controller based on displacement observation is developed for the vibration mitigation of flexible high towers, where the problems of low signal-to-noise ratio (SNR) and intricate acceleration-based control algorithms are eliminated completely. The displacement can be measured by laser or modern videometrics technology. A reduced-order model with an active mass damper (AMD) at the top of the tower is created using modal truncation approach based on modal participation factor (MPF), which successfully preserves the dominant modes of the original structure, and reduces the influence of high-frequency uncertainties. Considering structure uncertainties caused by environmental factors and aging process, an unscented Kalman filter (UKF) is introduced to identify the modal stiffness of the reduced-order model. The present study, using a 5 MW onshore wind turbine as an example, investigates active vibration control under wind and seismic loads and compares it with traditional tuned mass damper (TMD). From a dynamic perspective, the simplified model of wind turbine tower takes the form of a multi-degree-of-freedom series model. Consequently, a six-story steel frame platform has been constructed to experimentally validate the efficacy of the reduced-order controller. According to numerical simulation and laboratory testing, the control effect of the reduced-order controller with a few displacement states as feedback can be utilized as an active control strategy for high-rise flexible towers.

Wind-Induced Response Analysis and Fatigue Life Prediction of a Hybrid Wind Turbine Tower Combining an Upper Steel Tube with a Lower Steel Truss

Based on the WindPACT-3MW wind turbine tower commonly used in wind power engineering, a finite element model (FEM) of a hybrid wind turbine tower combining an upper steel tube with a lower steel truss is designed and established. On this basis, a static optimization analysis, wind-induced vibration analysis, and fatigue life analysis of the hybrid tower structure are performed. The results show that under the same design parameters, the overall stiffness and static bearing capacity of the tower structure can be significantly improved by using subdivided truss webs, increasing the truss height as much as possible and increasing the width of the truss base appropriately. Under normal operation conditions, the response of the tower structure in the along-wind direction is significantly greater than the response in the crosswind direction, indicating that the aerodynamic thrust generated by the rotation of the blades is the main factor causing the wind-induced vibration of the tower structure. For the tower structure analyzed in this study, when considering the entire range of wind speeds from the cut-in wind speed to the cut-out wind speed, the fatigue life of the structure is 38.5 years.

Analysis of Vibration Characteristics of Horizontal Axis Wind Turbine Tower under Random Wind Action

As the main supporting structure of wind turbines, the service quality of towers directly affects the operational safety of wind turbines. Researching tower vibration characteristics, evaluating its service quality and early warning of damage is an important means to improve the operational safety of wind turbines. Firstly, the external load conditions of the wind turbine tower were determined through wind load calculation, and the load and dynamic theory of the variable pitch torque wind turbine tower were summarized. Secondly, based on the Euler-Lagrange energy equation, the Lagrange equation of the simplified dynamic model of the wind turbine tower is established, and the vibration characteristics of the tower under different wind speeds are analyzed. The research results can provide a theoretical basis for the research on the characteristics of the wind turbine tower.

Declined benefit of earlier spring greening on summer growth in northern ecosystems under future scenarios

Widespread spring warming and an earlier start of the growing season (SOS) compensated for spring vegetation productivity, simultaneously resulting in reduced retention of accessible nutrition and water resources in subsequent seasons. In this case, however, it is unknown whether the increased summer growth induced by earlier SOS will be sustained. Here, we analyzed the legacy effects of SOS on summer growth under historical and future scenarios, through combining remote sensing products, flux tower observations and model simulations. We observed that the background climate (summer temperature and summer precipitation) modulated the response of summer growth to SOS. In the past two decades, the advance of SOS promoted summer growth in most areas of the northern ecosystems, except for dry and hot regions. Moreover, the effects of SOS on plant growth reversed within the summer months, which may be related to the continued deterioration of moisture conditions. Models predicted a general shift from a negative to a positive correlation between SOS and summer growth under future warming and regionally uneven precipitation. In particular, under SSP370 and SSP585 scenarios, areas of positive correlation will exceed that of negative correlation by the end of the century. These results indicated the stimulation of summer growth by SOS advance may shift to inhibition in more regions in the future. Our findings highlighted the limited enhancement of plant carbon sink by altered spring phenology under future climate change.