Catenary Cables Research Articles

An Experimental Study on Vortex-Induced Vibration Suppression of a Long Flexible Catenary Cable by Using Vibration Dampers

In this paper, an experimental study is conducted to investigate the effectiveness of vibration dampers in suppressing vortex-induced vibration in a long, flexible catenary cable with a low mass ratio. The dampers, consisting of two small, symmetric, lightweight pipes clamped to the cable, are sparsely deployed along the cable to shape the vibration characteristics. The experimental results demonstrate that dampers significantly reduce the vibration amplitude by up to 60% and axial tension by up to 61% at high flow velocities, effectively suppressing the cable vibration in perpendicular flow. In addition, it is observed that the in-line and cross-flow vibration frequencies are approximately equal when the dampers are applied. This behavior contrasts with the conventional undamped catenary cable, where the in-line vibration frequencies are double those of the cross-flow frequencies.

Investigation of mooring breakage impact on dynamic responses of a 15 MW floating offshore wind turbine

The stability and integrity of the mooring system are some of critical factors affecting the safety and performance of floating offshore wind turbines (FOWTs). For this reason, it is necessary to investigate the dynamic responses of the rotor, platform, and the remaining cables of the FOWT subjected to mooring breakages. This is because a mooring breakage significantly increases the risk of damage to the FOWT, especially for a nonredundant mooring system. This study has analyzed the platform motions and mooring tension of a 15 MW FOWT, where each offset column connects to two and three mooring lines to enhance the redundancy of the mooring system. The fully coupled simulations of the FOWTs under mooring breakage scenarios are examined using the well-validated numerical framework, OpenF2A, to consider wind, wave and current loading combinations. The result reveals that the breakage of a single mooring has a minor impact on the aerodynamic performance and aeroelastic response of the FOWT for both mooring system configurations. Notably, the platform experiences significant surge and sway when the upwind mooring breaks, leading to a sharp increase in tension of the remaining mooring lines positioned in the same direction. Moreover, the occurrence of snap load events is another factor resulting in the abrupt increase in the mooring tension. However, the maximum tension in the remaining mooring lines has not exceeded the threshold of breaking stress for both redundant mooring systems. The mooring configuration with two catenary cables connected to each column is suggested for the station-keeping system of the 15 MW FOWT considering the dynamic behavior and manufacture cost.

A study on vortex-induced vibration of a long flexible catenary cable in perpendicular flow

In this paper, a numerical model based on Euler-Bernoulli beam theory and a single van der Pol wake oscillator model is proposed to study the vortex-induced vibration of a long flexible catenary cable with a low mass ratio. The wake model uses only one oscillator to describe the in-line and cross-flow vibration with consideration of their nonlinear coupling. An experiment on a flexible cable model in perpendicular flow is carried out to validate the proposed numerical model. Numerical results and experimental measurements are compared on the vortex-induced vibration responses including the maximum amplitude, axial tension, and vibration frequency. A sensitivity analysis of the parameters used in the numerical model has been carried out. Numerical simulations by the proposed numerical model with properly selected parameters have demonstrated that the vibration frequency and the axial tension can be well predicted, and the variation of the vibration amplitudes can also be properly captured. The lock-in phenomena and the axial tension variation of the long flexible catenary cable in perpendicular flow have been carefully studied both numerically and experimentally.

Study on Wind-Induced Response and Wind Deflection Control of Overhead Sealing Net Structure Spanning Transmission Lines

Sealing net structures are frequently used as protective devices for newly constructed transmission lines that intersect existing lines. They aim to ensure safety during the construction and operation of the intersecting lines. To explore the wind deflection response characteristics of sealing net structures under wind loads, a model of the sealing net structure was created using ANSYS/APDL software for finite element analysis. This model represents an overhead sealing net structure spanning an existing line. The results obtained from finite element simulations aligned well with the theoretical calculations, indicating the validity of the established finite element model for accurately analyzing the wind-induced response of the sealing net structure. Expanding on this foundation, the study analyzed the impact of various factors on the wind deflection of the sealing net. These factors encompass the span, wind speed, pretension of the catenary cable, wind direction angle, arrangement angle, and method of additional stay cables. The research investigated the influence of these factors on the wind deflection of the sealing net structure. Additionally, a proposal was presented for arranging the closure structure to mitigate wind deflection. This proposal provides valuable guidance for the design and safety considerations of transmission lines and sealing net structures.

Geometric Nonlinear Analysis of the Catenary Cable Element Based on UPFs of ANSYS

The catenary cable element has more advantages than other nonlinear truss elements but is less used in commercial programs. In this paper, the initial geometric configuration of the element is solved iteratively by the dichotomous method. Then the Updated Lagrangian (UL) Formulation for the two-node catenary cable element is combined with the element secondary development tool provided by ANSYS platform-User Programmable Features (UPFs) to develop a three- dimensional cable element—user101. The algorithm and procedure of this paper are verified through examples and a real bridge. The study shows that the developed cable element user101 is more accurate and faster than the ANSYS self-contained element. The method can effectively use the computational theory of nonlinear cable elements with catenary geometry and combine it with ANSYS commercial program, which saves computation time without reducing accuracy and has good practicality.

Development of a prototype autonomous inspection robot for offshore riser cables

The motion and large environmental loads experienced by riser cables connected to floating offshore wind turbines put them at higher risk of failure than grounded sections of cable. We propose an Autonomous Riser Inspection System (ARIS) to facilitate regular inspection of riser cables for early fault detection and gathering engineering data to improve future cable design. Novel robotic methods for automatic attachment, traversal and inspection of cables are described. We develop the sensing and intelligent processing needed to (i) enable autonomous traversal and position estimation, and (ii) gather information about the state and condition of riser cables. Information from an array of cameras and electric actuator current monitoring allows autonomous navigation around obstacles and identifying the end of the inspection. A visual processing algorithm identifies damage to the surface of the cable and sensing methods are developed to measures the cable catenary, where methods to estimate the robot’s position along the cable are developed to contextualise and efficiently re-locate observations. Technology concepts are verified through a combination of dry, lab-based experiments using a full-scale prototype and simulations. The results provide proof of concept that requirements for untethered, autonomous riser cable inspection can be met by the proposed system.

An adaptive variable-length cable element method for form-finding analysis of railway catenaries in an absolute nodal coordinate formulation

High-speed trains collect electric current from a railway catenary composed of metal cables. The current collection quality is affected by the geometric shape of the catenary. As catenary cables have large initial displacements and can exhibit strong vibration and undergo large deformations in train operation, a new method based on the cable element with an adaptive variable length in the absolute nodal coordinate formulation (ANCF) is proposed to accurately compute the initial equilibrium configuration of the catenary. The proposed method relies mainly on an installation simulation of a catenary structure with variable-length ANCF cable elements. The length variations of these elements are correlated with the assembly conditions of the structure. The governing motion equations of the variable-length cable elements are derived. In the proposed method, a railway catenary in a simple configuration is modeled with variable-length and constant-length cable elements that have initially straight shapes and are strain-free. By adjusting the element lengths, the structure is tensioned to reach the desired equivalence state. The proposed method essentially changes the structure from an arbitrary configuration to a constrained configuration using a dynamic simulation. The proposed method is insensitive to initial conditions and is easily implemented with complex railway catenaries. The validity and accuracy of the method were demonstrated by comparing the obtained results with results reported in the literature.

A Cost-Effective Approach to the Risk Reduction of Cable Fault Triggered by Laying Repeaters of Fiber-Optic Submarine Cable Systems in Deep-Sea

Long-distance submarine cable systems, such as the transoceanic system, generally consist of a series of cables and repeaters. Repeater units are spaced at regular intervals to boost the attenuated optical signal and presently contain optical amplifiers in a pressure vessel made of copper alloy. Since the repeater unit is more massive than the cable, it pulls the cable catenary locally toward the seabed. In the 1990s, several studies numerically simulated cable behavior in the water and showed that the seabed slack runs short, and the seabed cable tension increases just before the repeater reaches the seabed. Therefore, it has been pointed out that an unarmored cable with a polyethylene sheath can be easily damaged. However, no reports have been published regarding the actual situation of cable faults related to the laying of repeaters. This study quantitatively analyzes the mechanism of cable damage related to the laying of repeaters, based on experiments, simulations, maintenance records, and a comparative analysis between the simulation results and actual cable faults. Cost-effective methods to mitigate cable faults triggered by laying a repeater in the deep sea are also explored to ensure mechanical stability during the design lifetime.

Railway Overhead Contact System Point Cloud Classification.

As the railway overhead contact system (OCS) is the key component along the high-speed railway, it is crucial to detect the quality of the OCS. Compared with conventional manual OCS detection, the vehicle-mounted Light Detection and Ranging (LiDAR) technology has advantages such as high efficiency and precision, which can solve the problems of OCS detection difficulty, low efficiency, and high risk. Aiming at the contact cables, return current cables, and catenary cables in the railway vehicle-mounted LiDAR OCS point cloud, this paper used a scale adaptive feature classification algorithm and the DBSCAN (density-based spatial clustering of applications with noise) algorithm considering OCS characteristics to classify the OCS point cloud. Finally, the return current cables, catenary cables, and contact cables in the OCS were accurately classified and extracted. To verify the accuracy of the method presented in this paper, we compared the experimental results of this article with the classification results of TerraSolid, and the classification results were evaluated in terms of four accuracy indicators. According to statistics, the average accuracy of using this method to extract two sets of OCS point clouds is 99.83% and 99.89%, respectively; the average precision is 100% and 99.97%, respectively; the average recall is 99.16% and 99.42%, respectively; and the average overall accuracy is 99.58% and 99.69% respectively, which is overall better than TerraSolid. The experimental results showed that this approach could accurately and quickly extract the complete OCS from the point cloud. It provides a new method for processing railway OCS point clouds and has high engineering application value in railway component detection.

Seismic Design of Offshore Wind Turbines: Good, Bad and Unknowns

Large scale offshore wind farms are relatively new infrastructures and are being deployed in regions prone to earthquakes. Offshore wind farms comprise of both offshore wind turbines (OWTs) and balance of plants (BOP) facilities, such as inter-array and export cables, grid connection etc. An OWT structure can be either grounded systems (rigidly anchored to the seabed) or floating systems (with tension legs or catenary cables). OWTs are dynamically-sensitive structures made of a long slender tower with a top-heavy mass, known as Nacelle, to which a heavy rotating mass (hub and blades) is attached. These structures, apart from the variable environmental wind and wave loads, may also be subjected to earthquake related hazards in seismic zones. The earthquake hazards that can affect offshore wind farm are fault displacement, seismic shaking, subsurface liquefaction, submarine landslides, tsunami effects and a combination thereof. Procedures for seismic designing OWTs are not explicitly mentioned in current codes of practice. The aim of the paper is to discuss the seismic related challenges in the analysis and design of offshore wind farms and wind turbine structures. Different types of grounded and floating systems are considered to evaluate the seismic related effects. However, emphasis is provided on Tension Leg Platform (TLP) type floating wind turbine. Future research needs are also identified.

Influence of Clumps-Weighted Moorings on a Spar Buoy Offshore Wind Turbine

The spar buoy platform for offshore wind turbines is the most utilized type and the OC3 Hywind system design is largely used in research. This system is usually moored with three catenary cables with 120° between each other. Adding clump weights to the mooring lines has an influence on the platform response and on the mooring line tension. However, the optimal choice for their position and weight is still an open issue, especially considering the multitude of sea states the platform can be exposed to. In this study, therefore, an analysis on the influence of two such variables on the platform response and on the mooring line tension is presented. FAST by the National Renewable Energy Laboratory (NREL) is used to perform time domain simulations and Response Amplitude Operators are adopted as the main indicators of the clump weights effects. Results show that the clump weight mass is not as influential as the position, which turns out to be optimal, especially for the Surge degree of freedom, when closest to the platform.

Effect of selection criterion on the kineto-static solution of a redundant cable-driven parallel robot considering cable mass and elasticity

Cable mass and elasticity play a prominent role in analyzing large-scale cable-driven parallel robots (CDPR). However, for catenary cables (i.e., cables with mass and elasticity), the inverse kinematics of CDPR becomes a non-linear kineto-static problem. Furthermore, for redundant CDPR, this leads to multiple kineto-static solutions. This paper focuses on investigating various selection criteria to determine a unique kineto-static solution for the redundant over-constrained CDPR. For this investigation, the effect of the proposed selection criteria on sagging, elastic elongations and cable tensions are analyzed. Appropriate selection criteria, according to the application requirements, are proposed. Additionally, a rigorous study is done to analyze the effect of considering conventional cable models (i.e., massless rigid and massless elastic cable model) instead of the catenary cable model for various payloads, cables, and selection criteria. This helps in determining when a massless rigid/elastic cable model can be used as an alternative to the catenary cable model, which in turn, can avoid the additional computational complexity. The proposed analysis is beneficial in appropriate selection of actuators, cables, selection criteria and model complexity for a given redundant CDPR.

Motion Responses Analysis for Tidal Current Energy Platform: Quad-Spar and Catamaran Types

One approach to support floating tidal current turbines is by using a moored catamaran, a barge type platform. Considering its low draft, one might expect that it performs best at typical straits with sea states of small wavelets to small waves. The problem is that the high rotational motion responses of the catamaran due to wave loads tend to reduce the turbine performance. This paper looks for a possibility to deteriorate these rotational responses by introducing a platform with four buoyant legs referred to as a quad-spar considering its good stability performance. The platforms are moored by four catenary cables as their mooring system. The motion response modeling was undertaken by Computational Fluid Dynamic (CFD) simulation based on three-dimensional potential flow theory. Considering sea states of straits with typical tidal current energy potentials, the environmental load was set on random wave with the significant wave height, Hs, of about 0.09 to 1.5 m and the wave period, T, of about 1.5 to 6 s corresponding to the wave frequency, ω, of about 1.1 to 4.2 rad/s. This study found that lower motion responses can be satisfied by the quad-spar, in which its yaw, roll and pitch responses are on average about 5%, 44%, and 38%, respectively, compared to those of the catamaran. This result indicates that the quad-spar is more effective in reducing rotational motion responses needed to keep a high performance of the tidal current energy system.

Assessment of the Dynamic Behaviors of Submerged Floating Tunnel Under a High-Speed Train Loading

Submerged floating tunnels (SFTs) are innovative structural solutions to waterway crossings and are more economical compared to the conventional structures such as cable-supported bridges, underground tunnels or immersed tunnels. The dynamic behaviors of SFT under real train loads is the primary design requirement of an SFT, However, it is not investigated using realistic train models. In this study, the China-star high-speed train is used to evaluate the dynamic displacements, internal forces and cable tensions of SFT. The tunnel is modeled by FEM, the cables are modeled by elastic catenary cables, and ocean waves and currents are modeled by Airy’s wave theory. The SFT displacements, bending moments and cable tensions were significantly influenced by moving trains. The SFT experienced extreme vertical displacements and there was a large drop in the minimum cable tensions. The mooring cables were slacked both by magnitudes and speed of the moving trains, which should be avoided for the safety of SFT. This study recommends the additional buoyancies for the stability of SFT subjected to high speed trains.

Effect of Cable Stiffness and Waves Parameters on the Dynamic Responses of Submerged Floating Tunnel

Submerged floating tunnel (SFT) is a new structural solution for waterway crossings compared to the classical solutions such as cable supported bridge, immersed tunnel or underground tunnel. An SFT is subjected to extreme waves, currents, earthquakes and other environmental loadings. The effect of key structural and waves parameters are important from the design perspective for an SFT. This study, the dynamic responses of SFT are evaluated using truss and catenary cables to check the effect of cable stiffness. The second part of this study deals with the effect of wave height and wave period on the dynamic responses of SFT. 3D truss and 3D catenary cables give very similar dynamic responses under waves and vertical ground motions. The wave height and wave period mainly control the dynamic behavior of SFT.

Effect of Cable Stiffness and Waves Parameters on the Dynamic Responses of Submerged Floating Tunnel

Submerged floating tunnel (SFT) is a new structural solution for waterway crossings compared to the classical solutions such as cable supported bridge, immersed tunnel or underground tunnel. An SFT is subjected to extreme waves, currents, earthquakes and other environmental loadings. The effect of key structural and waves parameters are important from the design perspective for an SFT. This study, the dynamic responses of SFT are evaluated using truss and catenary cables to check the effect of cable stiffness. The second part of this study deals with the effect of wave height and wave period on the dynamic responses of SFT. 3D truss and 3D catenary cables give very similar dynamic responses under waves and vertical ground motions. The wave height and wave period mainly control the dynamic behavior of SFT.

Prediction of the Pantograph/Catenary Wear Using Nonlinear Multibody System Dynamic Algorithms

In this investigation, computational multibody system (MBS) algorithms are used to develop detailed railroad vehicle models for the prediction of the wear resulting from the pantograph/catenary dynamic interaction. The wear is predicted using MBS algorithms for different motion scenarios that include constant-speed curve negotiation and acceleration and deceleration on a tangent (straight) track. The effect of the vehicle vibration in these different motion scenarios on the contact force is further used to study the wear rates of the contact wire. The wear model used in this investigation accounts for the electrical and the mechanical effects. The nonlinear finite element (FE) absolute nodal coordinate formulation (ANCF), which is suitable for implementation in MBS algorithms, is used to model the flexible catenary system, thereby eliminating the need for using incremental-rotation procedures and co-simulation techniques. In order to obtain efficient solutions, both the overhead contact line and the messenger wire are modeled using the gradient-deficient ANCF cable element. The pantograph/catenary elastic contact formulation employed in this study allows for separation between the pantograph panhead and the contact wire, and accounts for the effect of friction due to the sliding between the pantograph panhead and the catenary cable. The approach proposed in this investigation can be used to evaluate the electrical contact resistance, contribution of the arcing resulting from the panhead/catenary separation, mechanical and electrical wear contributions, and the effect of the pantograph mechanism uplift force on the wear rate. Numerical results are presented and analyzed to examine the wear rates for different motion scenarios.

On the Cable Pseudo-Drag Problem of Cable-Driven Parallel Camera Robots at High Speeds

SummaryThis paper presents a control strategy for solving the cable pseudo-drag problem of cable-driven parallel camera robots at high speeds. The control strategy belongs to a hybrid position/tension control method based on cable tension optimization. The cable catenary model and cable pseudo-drag problem are considered firstly. Then, the dynamic model of the cable-driven parallel camera robot is established. The cable tension optimization is proposed. And then a control strategy is put forward and its stability is proved. Simulation results of a four-cable camera robot are presented and discussed.

Quantifying the Uncertainty of Identified Parameters of Prestressed Concrete Poles Using the Experimental Measurements and Different Optimization Methods

Prestressed concrete poles nowadays are widely used in supporting the catenary cables of train systems. Compared to their importance to the functionality of the train system, this type of structures have not yet received adequate attention from researchers. We have started tracing the changes in the dynamic behavior of these poles caused by the train passing and the degradation of the materials over a long-time period. In this aim, we installed a structural monitoring system on three of them along one of the high-speed train tracks in Germany. The efficient analysis of the recorded measurements by this system requires a well-known data covering the real material properties of the given structures considering uncertainties of the different parameters. In this paper, we inversely identify the material properties of the poles using deterministic and probabilistic approaches based on the experimental measurements of a full-scale structure and Finite Elements Models. In the deterministic approach, the parameters are identified using the simplex optimization algorithm. Uncertainty of the identified parameters is quantified using a Markov Estimator. In the probabilistic approach, Bayesian inference is utilized for better estimation of the probability distribution of the parameters. Both approaches are suitable for the estimation of mean values of the parameters. The Bayesian method, even though computationally more demanding, is additionally suitable for determining the probability distributions and quantifying the uncertainties of the identified parameters and the correlations between each pair of them. The results show the efficiency of each approach to identify the parameters of the poles. For a rough estimation of the mean values, we recommend the deterministic approach as a simple tool. Conversely, the Bayesian approach is recommended for more detailed and accurate estimation.

Transverse aeroelastic instability of guard cables with beacons excited by a longitudinal wind

Guard cables, also named ground cables, protect the overhead power lines from electrical discharges that occur during storms. They are installed above the power conductor and therefore, they are the highest cable installed. In some places they are provided with beacon spheres that are visible indicators used for identifying the overhead power lines, to warn low flying airplanes and helicopters of the obstructions. A new transverse aeroelastic instability that appears in guard cables with beacons when excited by a longitudinal wind (TILoW for short) has recently been reported to us. In some cases, a vertical or horizontal oscillatory motion takes place, whereas in other cases the beacon centers follow circular orbits placed also in the transverse plane, while each beacon follows the motion but remaining parallel to itself. The centers of the orbits seem to be close to the static equilibrium position of the guard cable catenary. This whirling motion can be identified as a kind of autorotation. In this work the instability is described, and vortex induced vibration (VIV) is suggested as a candidate responsible for the aerodynamic force exciting the oscillation modes. For the whirling (also could be denoted “revolving”) mode a parallel investigation is ongoing. In order to clarify the problem, a model of the elastic configuration that is excited by the aerodynamic loads is analyzed, the eigenmodes and eigenvalues are presented, and a preliminary order of magnitude assessment of the field data is performed. Frequencies and mode shapes derived from the elastic model and those from the video sequences are found to be in agreement. The oscillation results are compatible with the existence of an alternating force produced by vortex shedding from the sphere. Unfortunately, the assessment could not be pursued further due to the absence of data on the wind speed during the reported sequences.A simplified model of the cable with only one beacon (a swinging sphere) has been tested in a low speed wind tunnel, and the main modes (VIV oscillation and whirling autorotation) have been reproduced and characterized.