Search Results (20)

This study addresses the complex challenges associated with flexible mattress (soft mattress) installation in the sharply curved and deep-water sections of the Yangtze River, particularly in the Yaozui revetment reconstruction project. Under extreme hydrodynamic conditions—water depths exceeding 30 m and velocities over 2.5 m/s—the risk of structural failures such as displacement, flipping, or tearing of the mattress becomes significant. To improve construction safety and stability, the study integrates numerical modeling and on-site strain monitoring to analyze the mechanical response of flexible mattresses during deployment. A three-dimensional finite element model based on the catenary theory was developed to simulate stress distributions under varying flow velocities and angles, revealing stress concentrations at the mattress’s upper edge and reinforcement junctions. Concurrently, a real-time monitoring system using high-precision strain sensors was deployed on critical shipboard components, with collected data analyzed through a remote IoT platform. The results demonstrate strong correlations between mattress strain, flow velocity, and water depth, enabling the identification of high-risk operational thresholds. The proposed monitoring and early-warning framework offers a practical solution for managing construction risks in extreme riverine environments and contributes to the advancement of intelligent construction management for underwater revetment works. Full article

Nowadays, urban rail transit is expanding towards high-elevation zones, and the effect of the low air pressure environment on the pantograph-catenary system is becoming increasingly prominent. As a key indicator for evaluating the electrical contact performance of a pantograph-catenary system, research on the electrical characteristics of the pantograph-catenary arc is of great significance. For this reason, this paper established a plasma mathematical model applicable to the arc of the urban rail transit bow network based on the theory of magnetohydrodynamics. The mathematical model of the pantograph-catenary arc was used to set the relevant initial conditions. Based on COMSOL Multiphysics finite element simulation software, this study developed a multi-physics simulation model of the pantograph-catenary arc and systematically analysed its voltage characteristics and current density distribution under varying air pressure conditions. The results showed that as the air pressure decreases, the potential at the axial points declines, the pressure drop across the arc poles becomes more pronounced, and the current density decreases accordingly. This study provides theoretical and technical support for optimizing the design of and promoting the sustainable development of urban rail transit pantograph-catenary systems in high-altitude areas. Full article

This study experimentally evaluates the survivability and hydrodynamic performance of a moored oscillating water column (OWC) wave energy converter (WEC) subjected to extreme cyclonic wave conditions emulating tropical cyclone Oma (2019). Laboratory tests recreated realistic cyclonic sea states using focused wave groups through the NewWave theory, combining singular and embedded focused waves within irregular seas to simulate extreme crests, troughs, and transient slamming events. Three mooring systems, including catenary, vertical-taut, and taut with 45° tendons, were tested to quantify their influence on structural response, chamber pressures, mooring tensions, and motion dynamics. The results revealed a critical trade-off: mooring configurations optimised for energy capture efficiency (e.g., taut systems) exhibited reduced survivability during extreme waves, while survivability-focused designs (e.g., catenary) compromised operational performance. Slamming pressures and transient loads were highly sensitive to wave group and mooring stiffness, with vertical taut systems experiencing the largest peak tensions. By integrating localised slamming pressure data with global mooring load measurements, this work provides a novel framework for balancing energy production and storm resilience in OWC design. Full article

The mobile catenary is installed in the railway loading and unloading line, which could significantly increase the railway freight volume, provide a practical and efficient alternative to the traditional mobile catenary, and greatly improve the sustainability of electrified railroad freight transport. The increase in freight volume also leads to greater traction load and a more complex electromagnetic environment. To study whether the electromagnetic environment when the mobile catenary works meets the power frequency electromagnetic field exposure limit stipulated by the International Commission on Non-Ionizing Radiation Protection, this paper performed an experiment on the sunken mobile catenary. The results showed that the maximum magnetic induction intensity near the ground is 0.03 mT, and the peak electric field intensity on the ground is 1.1 KV/m. The finite element software is adopted to establish the pantograph–catenary model and mobile catenary model according to Principles of Electric Field Calculation and Finite Element Theory, and the space electric field is numerically simulated to study the changes in electric field intensity and distribution of electric field in catenary when the catenary arc occurs. The simulated results are basically consistent with the experimental results, to verify the reliability of the simulation model, which could effectively solve the difficulty and high cost of the experiment. The conclusion proves that the equipment meets the regulations and it highlights the potential, which provides a cost-effective and scalable solution for the electromagnetic environment when the mobile catenary works. Full article

Accurately simulating the deployment process of coupled systems in deep-sea environments remains a significant challenge. This study employs the Absolute Nodal Coordinate Formulation (ANCF) to dynamically model and analyze multi-body systems based on the Pendant Installation Method (PIM). Utilizing the principle of energy conversion, this study calculates the stiffness, generalized elastic forces, mass matrices, and Morison equation, formulating a motion equation for the dynamic coupling of nonlinear time-domain forces in cables during pendulum deployment, which is numerically solved using the implicit generalized-α method. By comparing the simulation results of this model with those from the catenary theory model, the advanced modeling capabilities of this model are validated. Lastly, the sensitivity of the multi-body system under various boundary conditions is analyzed. The results indicate that deployment operations are more effective in environments with strong ocean currents. Furthermore, upon comparing the impacts of structural mass and deployment depth on the system, it was found that deployment depth has a more significant effect. Consequently, the findings of this study provide a scientific basis for formulating subsequent optimization strategies. Full article

In the working process of the tethered unmanned aerial vehicle (UAV), there is interference from the tethered cable, which can easily lead to the instability of the UAV. To solve the above problems, a method based on the Lyapunov exponent is proposed to analyze the stability of tethered cables for tethered UAVs. The dynamics equation of the UAV platform is established using the Euler–Poincare equation. The tension formula of the tethered cable is derived from the catenary theory and the principle of micro-segment equilibrium. Based on the Lyapunov exponential method, the stability changes of the tethered UAV in the takeoff, hovering, and landing stages are simulated and analyzed in a MATLAB environment. Prototype tests are carried out to prove the correctness of the simulation model and calculation conclusions. The results show that with an increase in the density of the tethered cable, the stability of the tethered UAV tends to decrease. At the same time, stability is affected by the density of the tethered cable more often during takeoff than during landing. Full article

There is no analytical solution to the deflection influence line of catenary hingeless arches nor an explicit solution to the deflection influence line difference curvature of variable section hingeless arches. Based on the force method equation, a deflection influence line analytical solution at any location before and after structural damage is obtained, and then an explicit solution of the deflection influence line difference curvature of the structural damage is obtained. The indexes suitable for arch structure damage identification are presented. Based on analytical theory and a finite element model, the feasibility of identifying damage at a single location and multiple locations of an arch bridge is verified. This research shows that when a moving load acts on a damaged area of an arch structure, the curvature of the deflection influence line difference will mutate, which proves theoretically that the deflection influence line difference curvature can be used for the damage identification of hingeless arch structures. This research has provided theoretical support for hingeless arch bridge design and evaluation. Combined with existing bridge monitoring methods, the new bridge damage identification method proposed in this paper has the potential to realize normal health status assessments of existing arch bridges in the future. Full article

A periodic pigging operation performed to clean off sediment and provide operators with detailed health information for a pipeline is mandatorily required. The research on pigging-induced issues for the steel catenary riser (SCR), one of the key parts in offshore hydrocarbon recovery pipelines between the floating production system and the seabed, has been scarce until now. As a result, there is an urgent need for theories to guide the pigging operation to ensure safe pigging is achieved in deepwater risers. In this paper, a study aiming to determine the effects of the pigging impact load and the pigging-induced slugging load on the dynamic response of the riser is reported. A SCR pigging model was established and proposed based on the finite element analysis (FEA) method. The stress distribution and displacement of the SCR were investigated under the pigging conditions, with the consideration of the effects of waves, currents, and floating platform movements. It was found that the pigging load has large effects on the stress and displacement of the touchdown zone (TDZ), especially the touchdown point (TDP). The displacement of the TDZ in the Y (vertical) direction is more significant than that in the X (horizontal) direction under pigging conditions, and the maximum displacement of the TDZ in the Y direction is proportional to the weight of the pig, as well as the length of the pigging-induced slugging. Full article

At present, dry wellheads are usually adopted on small-storage TLP and SPAR platforms to develop offshore oil and gas because of the robust hydrodynamic performance under severe-wind seas. On the other hand, FPSO and FDPSO platforms that have a larger storage capacity can hardly use this cost-saving facility due to their relatively poor vertical motion performance. Cylindrical FPSOs are proposed to improve the heave performance of ship-type FPSOs, but their behaviors are still too large to adopt the dry wellheads. In the present work, a cylindrical FDPSO platform is proposed based on the FWPSO platform, adding an extension cylinder and a new damping structure at the bottom. Their hydrodynamic performances are calculated by the potential theory and compared in the frequency domain. Taking two particular mooring systems, including both catenary and ‘chain-polyester-chain’ types, and the survival sea scenario in the South China Sea into account, a time-domain coupling analysis was adopted to simulate the dynamic performance of the platform-mooring system. The feasibility of dry wellhead adoption on the FDPSO is discussed by investigating the platform motion and the mooring tension. The results show that the FCDS platform with the ‘chain-polyester-chain’-type mooring system can meet the motion response requirements, and the mooring system can also meet the requirements of the specification. Full article

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. Full article

This article presents a new method for the estimation of active power losses based on a “field” approach, i.e., on the theory of the electromagnetic field and the theory of propagation of electromagnetic waves in a dielectric medium. Electromagnetic waves are assumed to transmit energy from the traction substation to electric rolling stock through the airspace of the inter-substation zone (i.e., not through the wires of the traction network) and meet electrically conductive surfaces on their way. The waves are partially reflected from the surfaces and partially penetrate them, thus creating thermal losses, the determination of which is the main task of this article. The analytical expressions for specific losses of active power are obtained by solving the system of Maxwell’s equations. Calculations of specific power losses in the catenary, rails, roofs, and bottoms of carriages and electric locomotives are performed. Power losses in carriages and electric locomotives are found to be at least 7%. A comparative assessment of the magnitude of total power losses of different types obtained by the “field” and “circuit” approaches is provided, which has established that “conditional” losses correspond to losses in rails, train carriages, and electric locomotives. Full article

In this study, the problems of diffraction and radiation of water waves by a permeable vertical cylindrical body are formulated within the realm of the linear potential theory. The body, which is floating in constant water depth, is moored with a catenary mooring line system. The method of matched eigenfunction expansions for the prediction of the velocity potential in the fluid domain surrounding the body is applied. Furthermore, the static and dynamic characteristics of the mooring system are combined with the hydrodynamics of the body, to set up the coupled motion equations of the dynamical model, i.e., floater and mooring system, in the frequency domain. Numerical results obtained through the developed solution are presented. The results revealed that porosity plays a key role in reducing/controlling the exciting wave loads. As far as the mooring system is concerned, its quasi-static and dynamic characteristics, by employing several motion directions on the fairlead in accordance to varying environmental conditions, are examined, highlighting their effect on the body’s motions. Full article

The concept of multiline anchor, whose application is mainly considered in water depths beyond 100 m and analyzed only by numerical simulation, has been discussed for half a decade, yet previous studies have not conducted the wave basin experiment. Thus, this paper set this concept firstly with a shallow water mooring system designed for a Taiwan offshore water area, where the suitable water depth for floating offshore wind turbine is located from 50 to 100 m, and then conducted a 1:144 scaled model wave basin experiment to validate the results from numerical simulation. In this paper, the numerical model simulated and analyzed three identical DeepCwind OC4 semi-submersible platforms equipped with NREL 5MW wind turbines in OrcaFlex and the experiment carried out by using three 1:144 scaled semi-submersible platforms with equivalent disks which simulated different operations of wind thrusts. To consider the possible influence of the wake effect, the minimum turbines spacing was set at 750 m in a full scaled model and the length of mooring lines was redesigned according to the catenary theory. This paper utilized OrcaWave to calculate hydrodynamic parameters and input it into OrcaFlex to simulate the line tension and the three degrees of freedom (surge, heave, and pitch) of the platforms under regular and irregular wave tests, and coordinate with scaled model tests carried out in Tainan Hydraulics Laboratory (THL). In addition to the reduction in the number of anchors, the concept of multiline anchor was also discussed in this study for the spatial configuration of offshore wind farms. It shows that the wind farm composed of three floating wind turbines can reduce the ocean space by roughly 24% compared to that with a single-line anchor. According to the comparison of numerical and experimental results, this study finally optimized the mooring lines by changing the diameter to increase the stability and the threshold of Minimum Breaking Load (MBL) and proposed a multiline anchor configuration for shallow offshore water area in Taiwan based on the results obtained. Full article

This investigation focuses on the modelling of a floating oscillating water column (FOWC) wave energy converter with a numerical code (ANSYS AQWA) based on potential flow theory. Free-floating motions predicted by the numerical model were validated against experimental data extrapolated from a 1:36 scale model device in regular and irregular sea states. Upon validation, an assessment of the device’s motions when dynamically coupled with a four-line catenary mooring arrangement was conducted at different incident wave angles and sea states ranging from operational to survivable conditions, including the simulation of the failure of a single mooring line. The lack of viscosity in the numerical modelling led to overpredicted motions in the vicinity of the resonant frequencies; however, the addition of an external linear damping coefficient was shown to be an acceptable method of mitigating these discrepancies. The incident wave angle was found to have a limited influence on the magnitudes of heave, pitch, and surge motions. Furthermore, the obtained results indicated that the mooring restoring force is controlled by the forward mooring lines under the tested conditions. Full article

The purpose of the present paper is to propose installation curves for submarine cable deployment process for different water depths and tension deployment, emphasizing on the importance of modelling the “out of water” cable segment and the friction force between cable and overboard chute of the installation vessel. A custom-made analysis tool has been further expanded and used for the calculation of the cable hydraulic critical responses. Moreover, the concept of the critical water depth is proposed analytically for first time to define the cases in which the “out of water” cable segment can be ignored without denoting the accuracy of the minimum bending radius calculation. In addition, correction factors are proposed in relation to water depth and bottom tension values in order to eliminate the error of the safety factor calculation. Numerical formulation of the friction has been incorporated in the custom-made analysis tool as a further development. The analysis of various cable deployment cases proves that the inclusion of the “out of water” segment in the analysis is critical in shallow water areas. In contradiction, the modelling of the friction force is critical in deep water areas. However, both parameters are potential causes of important analysis errors. Full article