Galloping Amplitude Research Articles

Performance-based ice engineering framework: A data-driven multi-scale approach

Ice storms are one of the most devastating natural hazards which have the potential to inflict significant damage to the built environment. The multi-hazard nature of ice events complicates the analysis of their induced risk due to their inherent nonlinear interactions. In addition, the concurrent and interacting hazards are often responsible for several aerodynamical/dynamical instabilities such as the galloping mechanism. Moreover, the existing risk approaches are usually not suited for large-scale risk evaluation over extended geographical regions due to the involved high-computational costs. Therefore, in this study, a novel data-driven multi-scale performance-based ice engineering (PBIE) framework is developed to support the design of new structures subjected to ice storms or the rehabilitation of existing ones. In addition, the proposed PBIE is capable of rapidly estimating the real-time risk over an extended region due to an ice event. Specifically, it leverages the superior capabilities of state-of-the-art data-driven techniques (e.g., machine learning) to efficiently generate the corresponding risk maps and identify the high-risk areas. The proposed PBIE framework is applied to a simplified example in which the galloping-induced risk on iced conductors, in terms of the galloping amplitude, is evaluated for both local and regional scales. The resulting PBIE framework can be readily applied for design or retrofitting purposes or integrated within an emergency response management system to inform preventive actions that can mitigate the ice storm-induced damages and save lives.

Anti-galloping analysis of iced quad bundle conductor based on compound damping cables

Based on the strain displacement relationship of spatial curved beam theory, a nonlinear dynamic equation for a hybrid model of iced bundle conductor galloping analysis with three translational degrees of freedom and one rotational degree of freedom was established. The element independence is numerically studied, and the impact of modal truncation on the galloping response is analyzed to verify the accuracy of the model. In addition, the compound damping cable is applied to transmission lines for the first time to prevent galloping, and a corresponding nonlinear vibration control finite element equation for the iced quad bundle conductor with a compound damping cable structure under wind load is developed. The study also examines the influence of various parameters on galloping amplitude. The results show that the hybrid model accurately predicts the galloping response of transmission lines. The compound damping cable can effectively suppress the galloping of the quad bundle conductor, and the vibration reduction effect reaches more than 85%. Increasing the installation height of the compound damping cable improves its damping effect. At the same installation height, when the horizontal installation position is close to the mid-span of the conductor, the damping effect first increases and then decreases, suggesting an optimal installation position exists. Moreover, properly increasing the stiffness of the primary cable and reducing the stiffness of the return spring can improve the vibration reduction effect of the compound damping cable. Additionally, if the damping coefficient and the mass of the primary cable are properly increased, the vibration reduction effect of the compound damping cable will be better.

Suppression of Railway Catenary Galloping Based on Structural Parameters’ Optimization

Railway catenary galloping, induced by aerodynamic instability, poses a significant threat by disrupting the electric current connection through sliding contact with the contact wire. This disruption leads to prolonged rail service interruptions and damage to the catenary’s suspension components. This paper delves into the exploration of optimizing the catenary system’s structure to alleviate galloping responses, addressing crucial parameters such as span length, stagger dropper distribution, and tension levels. Employing a finite element model, the study conducts simulations to analyze the dynamic response of catenary galloping, manipulating structural parameters within specified ranges. To ensure accurate and comprehensive exploration, the Sobol sequence is utilized to generate low-discrepancy, quasi-random, and super-uniform distribution sequences for the high-dimensional parameter inputs. Subsequent to the simulation phase, a genetic algorithm based on neural networks is employed to identify optimal parameter settings for suppressing catenary galloping, taking into account various constraints. The results gleaned from this investigation affirm that adjusting structural parameters can effectively diminish the galloping amplitude of the railway catenary. The most impactful strategy involves augmenting tension and reducing span length. Moreover, even when tension and span length are fixed, adjusting other parameters demonstrates efficacy in reducing galloping amplitudes. The adjustment of messenger-wire tension, dropper distribution, and stagger can achieve a 22.69% reduction in the maximum vertical galloping amplitude. Notably, maintaining a moderate stagger value and a short steady arm–dropper distance is recommended to achieve the minimum galloping amplitude. This research contributes valuable insights into the optimization of railway catenary systems, offering practical solutions to mitigate galloping-related challenges and enhance overall system reliability.

Study on the Effect of Anti-galloping Device with Cubic Stiffness and Particle Damping

The galloping of iced conductors is a common disaster of overhead conductors. Most traditional anti-galloping devices lack a nonlinear dynamic vibration absorber; hence, they have a limited anti-galloping effect. In this study, we designed, optimized, and tested an electric power fitting and an anti-galloping device with cubic stiffness and particle damping for ultra-high-voltage (UHV) transmission lines. We built a nonlinear dynamic model of the coupling galloping system comprising split conductors and anti-galloping devices. The harmonic balance method obtained the steady-state analytical solutions and corresponding averaged equations. The test spans in the laboratory were used to design the test program and equipment. We verified the accuracy of the nonlinear dynamic model and the harvesting effect of the anti-galloping device with cubic stiffness and particle damping. The theoretical and experimental results were highly consistent, and in the range of (0, 2] Hz, the anti-galloping device reduced the galloping amplitude. Therefore, cubic stiffness and particle damping can effectively improve the anti-galloping ability of UHV transmission lines, prolonging their service period.

Thermal and vibratory response of sprung square cylinder with four nature-inspired fin-shaped bumps

Nature provides man with various interesting structures, offering him a constant source of manufacturing tools and invention. The main purpose of the present paper is to investigate the effect of shark-inspired fins, which are installed on the top and bottom plates of a sprung cylinder on the vibration response and heat transfer of square cylinder. Two fin sizes, i.e. small and big, are used. Three configurations for the fins on the top and bottom plates of the square cylinder are considered: at the corners of the square cylinder, spaced from the corners, and in the middle of the plates. The results indicate that adding fins increases the amplitude of vortex-induced vibrations and extends the lock-in region which is both intensified as the size of fins increases. In particular, for the cylinder equipped with small fins in configurations 1–3, the maximum VIV amplitude increases by, respectively, 36 %, 57 % and 52 % compared with the plain cylinder. In contrast, shark fins can lower the galloping amplitude by as much as 87 % and shrink the galloping zone such that for big fin size in the second and third configurations, the galloping zone and its corresponding vortex-shedding mode are not observed. Adding fins to the cylinder augments heat transfer. The increase in mean Nusselt number depends on vortex-shedding mode, and the rise in Nusselt number is higher in the 2P + 2S mode.

Study on Aerodynamic Instability and Galloping Response of Rail Overhead Contact Line Based on Wind Tunnel Tests

The overhead contact line is a tensioned cable structure erected along the railroad to power the electric train. Under the wind load, the galloping of OCL caused by aerodynamic instability may form a large amplitude, which is a big potential threat to the normal operation of the electric railway. In this paper, a wind tunnel test is performed to investigate the aerodynamic coefficients of the contact line with two levels of wear. The aerodynamic instability of the contact line can be observed on a worn contact wire at around an 8° wind angle of attack. Employing a nonlinear finite element model of the OCL, the galloping is reproduced and analysed via several numerical simulations. The effect of the wear level and angle of attack on the galloping response is analysed. The galloping amplitude of the contact line spikes at the angle of attack of 8° and 9° at 20% and 30% wear levels, respectively. Then damping dropper is included in the model, and its effect on the suppression of the OCL galloping is quantified. The results indicate that a damping dropper of 100 Ns/m is recommended to be mounted on the railway OCL to reduce the detriment of galloping under a strong wind field.

The Design and Experiment of a Spring-Coupling Electromagnetic Galloping Energy Harvester.

In order to improve the output characteristics of the electromagnetic energy harvester in a high-speed flow field, a spring-coupling electromagnetic energy harvester (SEGEH) is proposed, based on the galloping characteristics of a large amplitude. The electromechanical model of the SEGEH was established, the test prototype was made, and the experiments were conducted using a wind tunnel platform. The coupling spring can convert the vibration energy consumed by the vibration stroke of the bluff body without inducing an electromotive force into the elastic energy of the spring. This not only reduces the galloping amplitude, but it also provides elastic force for the return of the bluff body, and it improves the duty cycle of the induced electromotive force and the output power of the energy harvester. The stiffness of the coupling spring and the initial distance between the coupling spring and the bluff body will affect the output characteristics of the SEGEH. At a wind speed of 14 m/s, the output voltage was 103.2 mV and the output power was 0.79 mW. Compared with the energy harvester without a coupling spring (EGEH), the output voltage increases by 29.4 mV, with an increase of 39.8%. The output power was increased by 0.38 mW, with an increase of 92.7%.

Experimental study on the galloping characteristics of single ice-coated transmission lines under oblique flows

Galloping of ice-coated transmission lines is occasionally observed under oblique wind directions. However, most current investigations on the galloping mechanisms are for flow perpendicular to the span of the transmission lines. In order to address this gap, this research studies the galloping characteristics of ice-coated transmission lines under oblique flows based on wind tunnel tests. The wind-induced displacement of an aero-elastic iced-coated transmission line model was measured with a noncontact displacement measurement equipment in a wind tunnel at different wind speeds and directions. The results show that galloping is characterized by elliptical trajectories and negative damping, which is more likely to occur under oblique flows than the direct flow (0°). At 15° wind direction, a galloping in vertical direction was observed at wind speeds above 5 m/s. At 30° wind direction, galloping was observed over the entire range of the tested wind speeds. Moreover, the galloping amplitudes under oblique flows are observed to be larger than that at the direct flows. Consequently, when the wind direction between the major winter monsoon azimuth and the lateral direction of transmission line route is between 15° and 30°, appropriate anti-galloping devices are highly recommended in practice.

Hydrokinetic energy harvesting from flow-induced vibration of a hollow cylinder attached with a bi-stable energy harvester

This paper proposes an electromagnetic bi-stable energy harvester (EBEH) with tunable stiffness for scavenging the hydrokinetic energy from flow-induced vibration (FIV) scenarios. A mathematical model of the magneto-mechanical–electrical coupling system is established considering vortex-induced forces, wake oscillator effect, negative linear stiffness and hybrid excitations. The bi-stable system with adjustable barrier height is employed to enhance state-of-the-art energy scavenging performance of vortex-induced vibration (VIV). Preliminary verification with regard to VIV within a lock-in wind speed range has been implemented by means of CFD simulation. The nonlinear energy transfer capacity and energy conversion performance of the FIV based EBEH are evaluated under solitary vortex-induced vibration (VIV) and hybrid excitations. Simulation results show that EBEH with larger negative linear stiffness has higher energy conversion efficiency and target energy transfer capacity in a wide range of inlet velocities. The large amplitude and low frequency vibration of the VIV of the cylinder is mainly caused by the lift pulsation, meanwhile the small amplitude and high frequency galloping are caused by the perpendicular component pulsation of the drag force. The fluctuations of the lift/drag coefficient at different inflow velocities are directly related to the VIV or galloping amplitude of the cylindrical bluff body. Specifically, the frequency fD is approximately twice the frequency fL in a wide inflow velocity range; The amplitude of fluctuating lift exceeds 2.0 in a wide range of inflow velocity from 1.0 m/s to 20 m/s. The nonlinear energy transfer efficiency of the FIV based EBEH with smaller barrier height is greater than 60% when the inflow velocity ranges from 20 m/s to 30 m/s. The nonlinear energy transfer capability of EBEH with appropriate negative stiffness outperforms its counterpart of cubic stiffness more than ten times. The maximum mean harvested power achieved from EBEH can be increased over 900% than that of the cubic stiffness case. Regardless of negative stiffness alteration, the optimal external load that maximizes the EBEH output power is around 50 Ω. Additionally, when the vortex-induced vibration cannot be woken, intervention of base excitation causes considerable chaotic motion consisting of aperiodic intra-well and inter-well snap-throughs at low inflow velocities. Nevertheless, nonlinear energy transfer efficiency of bi-stable energy harvester is slightly crippled with the increase of the base excitation intensity.

Aerodynamic Force and Aeroelastic Response Characteristics Analyses for the Galloping of Ice-Covered Four-Split Transmission Lines in Oblique Flows

In order to study the galloping mechanism of ice-covered four-split transmission lines in oblique flows, the aerodynamic forces and aero-elastic response characteristics of the crescent-shaped four-split ice-covered transmission lines are investigated through wind tunnel tests on rigid and aero-elastic models. According to Den Hartog and Nigel’s galloping theories, the damping coefficients are calculated based on the experimental data. The results show that the crescent-shaped ice-covered four-split transmission lines usually suffer from torsional galloping. Furthermore, based on the aero-elastic wind tunnel data, the galloping is characterized by an elliptical trajectory, negative damping ratio, and a negative strain at hanging position. In addition, the galloping appears to be more prone to occur under oblique flows, with a larger galloping amplitude and a lower critical wind speed. This might be because an out-of-plane vibration of the third-order mode is excited at a lower wind speed, leading to a coupled resonance between in-plane and out-of-plane vibrations at the third-order mode with a frequency ratio of 1:1. The experimental results in this paper can also be used to verify the fluid-structure interaction simulation method of ice-covered transmission lines.

Aerodynamic performance of a sinusoidal wavy cylinder at subcritical and critical Reynolds numbers

Previous studies have shown that in the subcritical regime, wavy circular cylinders exhibit less wind-induced drag than standard circular cylinders. However, the aerodynamic performance of wavy cylinders at higher Reynolds numbers is still unknown. Hence, a series of wind tunnel tests including measurement of the surface pressure, vortex-induced vibration (VIV) and dry galloping were conducted for a wavy cylinder and a corresponding standard cylinder at Re = 1.00 × 105-3.86 × 105. The results indicate that the aerodynamic characteristics, including the mean and fluctuating pressure distributions, mean and fluctuating aerodynamic force coefficients, Strouhal number, flow regime classification, and non-Gaussian characteristics, are significantly modified when shifting from the standard cylinder to the wavy cylinder. Furthermore, these modifications highly depend on the Reynolds number. Regarding the wavy cylinder, related parameters obviously vary along the spanwise direction, indicating three-dimensional aerodynamic characteristics. Moreover, the maximum VIV amplitude of the wavy cylinder is 40% lower than that of the standard cylinder. The velocity corresponding to the maximum amplitude is increased by 11% for the wavy cylinder. Additionally, the maximum dry galloping amplitude is reduced by 11%.

Risk assessment of the iced transmission line galloping based on fuzzy and cluster algorithms

A risk assessment method for transmission line galloping in mountainous areas is proposed based on meteorological conditions, environmental factors and line parameters to timely and effectively assess the risk level of stable and reliable power supply of iced transmission lines in galloping and ensure its normal operation. The galloping amplitude is obtained through cluster algorithm by use of three factors, i.e., icing, line and wind, on the premise of entering the key meteorological factors by fuzzy algorithm to predict the ice thickness. Then the galloping amplitude is used as the risk evaluation standard, and the risk is graded accordingly. Taking the historical galloping monitoring data and meteorological record parameters collected by a certain power grid as samples, upon analysis, it shows that the proposed method can perform more accurate assessment on the risk of transmission lines, reveal the weak links of lines through the risk assessment results, ensure that the risk points or sections can be controlled, provide the decision-making basis and enhanced decision-making support ability for power grid dispatchers and line operators and maintainers, realize the shift from passive hazard prevention to active risk avoidance, effectively improve the ability of power grid to prevent, reduce and cope with severe meteorological hazards, reduce the impact of galloping on the safe operation of power grid, and decrease unnecessary hazards and losses.

Triboelectric–electromagnetic hybridized module for energy harvesting of power transmission lines galloping and self-powered galloping state monitoring

With the vigorous advancement of smart power grid, online monitoring is essential for a stable operation of overhead transmission lines. The energy supply that drives the monitoring system has become one of the bottlenecks restricting the development of distributed sensing systems. In view of the self-excited vibration with the characteristics of low-frequency and large-amplitude generated in the conductor galloping, a hybridized generator has been designed to be composed of an electromagnetic generator (EMG), a horizontal TENG (H-TENG), and a vertical TENG (V-TENG) to provide an alternative approach for capturing mechanical energy derived from conductor galloping. Based on triboelectric–electromagnetic working principal, a sophisticated-designed stator and rotor structure oriented to the application scenarios of transmission lines successfully achieved self-power through the designed EMG and galloping state sensing through the designed H-TENG and V-TENG, respectively. The output performance, feasibility and durability of the hybridized generator was well validated on the linear motor platform and the conductor galloping test platform, and the output current was used to realize the characterization of the conductor galloping amplitude and galloping trajectory. This work not only provides an effective and sustainable solution to the self-powered intelligent sensor nodes in the complex surroundings of power transmission system, but also reveals TENG promising potential on the sensing applications in low-power monitoring sensors for conductor galloping.

Integrated numerical simulation of an electromagnetic transmission line galloping excitation test system

PurposeThis paper aims to establish the mathematical model and solve the complex calculation multi-field coupling problem for an electromagnetic overhead transmission line galloping excitation test system.Design/methodology/approachAn electromagnetic excitation test system is introduced. To calculate the vibration response of the transmission line, a transient coupled finite element model containing electromagnetic repulsive mechanism and transmission line system was established. Considering the advantages of Newmark-ß algorithm and fourth-order Runge–Kutta algorithm, the two algorithms are combined to solve the model. Compared with the simulation results of existing commercial finite element software, the accuracy of the calculation model of electromagnetic force and wire vibration response are verified.FindingsComparison results show that the proposed calculation model can accurately obtain the force of electromagnetic mechanism and the vibration response of the overhead power lines, and improve the calculation efficiency. The calculation results show that vibration under electromagnetic excitation presents a double half-wave mode, and the galloping amplitude varies according to the charging voltage.Originality/valueThis paper built the transient simulation model for a galloping test system. The Newmark-ß algorithm and the fourth-order Runge–Kutta algorithm are used to solve the model. The research results are of great significance for the actual galloping test system design.

Galloping behaviors of ice-coated conductors under steady, unsteady and stochastic wind fields

This paper addresses the similarities and differences between the galloping behaviors of ice-coated conductor transmission lines under steady, unsteady and stochastic wind fields. A finite element model of crescent-shaped ice-coated conductor is first established by using the 3-node isoparametric cable element. The analysis model and numerical integration scheme used in this study are then verified by comparison with the existing experimental data and numerical simulations. In order to efficiently simulate two-dimensional unsteady and stochastic wind fields acting on the ice-coated conductor, the newly-developed spectral representation method based on wavenumber-frequency joint power spectrum is adopted. The probability density evolution method (PDEM) is introduced to explore the statistical characteristics of conductor galloping under stochastic wind field. It is revealed that the unsteady wind field stimulates the self-excited vibration of the ice-coated conductor and further leads to an unstable galloping. However, under the stochastic wind field, the galloping variance of ice-coated conductor is steady and periodic, and the galloping probability density propagates alternately as uni- and bi-modals. These properties are quite different from those exhibited in simplified nonlinear models excited by Gaussian white noises in existing literature. Moreover, the galloping amplitude under stochastic wind field is greatly larger than that under steady wind field. Therefore, an extensive attention should be paid to the safety design of conductor transmission lines in cold regions considering the influence of stochastic wind field.

A New Method of Conductor Galloping Monitoring Using the Target Detection of Infrared Source

Because the galloping of iced conductors is one of the main disasters in the State Grid, resulting in huge economic and property losses every year, the research on relevant monitoring methods is of great significance. The existing galloping monitoring technology is mainly based on the contact detection method, which presents potential electrical hazards and power supply problems. In this paper, a conductor galloping monitoring method based on the target detection of infrared sources is put forward to overcome the shortcomings of existing methods. In other words, an infrared source label is installed on the conductor spacer, high-definition night vision infrared cameras are installed on electric power towers to take video of the infrared source labels, and the characteristic amplitude of conductor galloping is calculated by an image recognition and tracking algorithm. The practical application results indicate that the method has the advantages of non-contact detection, safety and reliability, and high detection accuracy.

Nonlinear modelling of unsteady wake galloping forces on a circular cylinder in the wake of a fixed cylinder

This paper aims at developing a nonlinear mathematical model for the unsteady wake galloping forces (UWGF) acting on a circular cylinder in the wake of a fixed identical circular cylinder, which is always neglected in quasi-steady analysis. Numerical simulations are conducted to obtain the synchronous unsteady aerodynamic lift forces and displacements of wake galloping at Reynolds numbers (Re) of 1640–8420. The downstream cylinder is free to vibrate in the cross-flow direction with a mass-damping m*ζ = 0.267. The spacing ratio is fixed at L/D = 4 (where L is the center-to-center distance between the cylinders and D is the cylinder diameter). The UWGF model is built by combining the self-excited force and the vortex-induced force based on the spectra of the aerodynamic lift forces. Using an energy equivalent principle, the self-excited force can be divided into three parts: aerodynamic damping terms, aerodynamic stiffness terms and pure force terms. The identified aerodynamic parameters show that the aerodynamic damping terms are key factors determining the stable amplitude of wake galloping. The vortex-induced forces trigger an initial displacement to excite vibration in the early stage and have no influence on the stable amplitude. The proposed UWGF model is verified by experimental results and can calculate wake galloping responses better than the quasi-steady theory.

Multi-ball rotative nonlinear energy sink for galloping mitigation

Galloping is a destructive type of flow-induced vibration (FIV) affecting engineering structures subjected to wind. In this paper, we introduce a simple, low-cost device able to passively absorb the energy of vibrating structures and reduce the galloping amplitudes. This purely nonlinear energy sink (NES) consists of multiple balls rotating freely in a circular track without direct mechanical coupling with the primary system. We assess the benefit of the proposed NES in mitigating the galloping of a square prism through wind tunnel tests and explain the main factors affecting its behaviour. The NES balls rotate due to dynamic interaction with the prism, exhibiting a way of nonlinear energy absorption, which is enhanced by ball collisions. We test different NES configurations varying the number of NES balls to highlight the number of balls’ effect on shifting the mass centre and changing the dynamics of the NES. Whereas a single ball NES with a mass 8% that of the prism can increase the critical reduced velocity by 68%, a 2 or 3-ball NES of equivalent mass increases this speed by 87%.

A Wind Tunnel Study on the Aerodynamic Characteristics of Ice-Accreted Twin Bundled Conductors

Galloping of twin bundled overhead conductors accreted by ice is a frequent phenomenon during freezing weather, which may damage the operation of transmission lines. To analyze the galloping behavior of iced conductors, their aerodynamic characteristics must be studied. In this study, models with two different outlines were designed and tested to determine a more suitable ice-accreted conductor testing model. Subsequently, the influences of the conductor type, ice thickness, wind turbulence intensity, and wake effect of the windward conductor on the aerodynamic coefficients of the conductors with crescent-shape ice are investigated. The results show that the strand outline of overhead conductors must be considered to improve the accuracy of aerodynamic tests. With increasing ice thickness, the aerodynamic stability becomes rapidly deteriorated. Under the wind turbulence intensity of 4%, the aerodynamic stability gets the most enhancement. Moreover, different conductor types have little impact on the aerodynamic coefficients. The wake caused by the windward conductor is the leading cause for the twin bundled iced conductors to have weaker aerodynamic stability than a single conductor. The aerodynamic coefficients determined in this study are essential for predicting the galloping amplitudes of ice-accreted twin bundled overhead conductors under different weather conditions.

Characteristic Analysis and Prevention of Ice Galloping of Transmission Lines Based on Finite Element Method

Ice galloping is one of the disasters that have the greatest impact on the safe operation of transmission lines in winter. This article analyze the characteristics and prevention method of ice galloping of electric grid transmission lines based on finite element method. The amplitude and time response of transmission line during ice galloping can be obtained. A new type of efficient anti-galloping interface spacer is proposed, which can reduce the galloping amplitude. The effectiveness of the proposed method and model is verified by application examples.