Motion Response Research Articles

Coupling dynamic characteristics of installation vessel - Multi buckets jacket foundation lowering system

Precise control of the splash zone lowering process of the multi-bucket jacket foundation for an offshore wind turbine can save time during the entire construction period, thereby reducing construction and installation costs. This paper focuses on the “installation vessel - multi buckets jacket foundation” coupled dynamic system during the lowering process of the multi-bucket jacket foundation. Taking the three-bucket jacket foundation (TBJF) and the four-bucket jacket foundation (FBJF) as the research objects, four different sling layout types were proposed. The influence of the slings layout types on the motion response of the installation vessel and foundation and the slings' tension in this system were comparatively studied through numerical simulation. Research shows that through the lowering of Type 1 conditions, that is, each chord corresponds to a vertical sling and is directly connected to the crane's lifting point, the motion performance of the foundation and installation vessel can be reduced, ensuring the smooth progress of the lowering process of the structure. Under the same conditions, the FBJF has greater motion response due to the large wave force bearing area and large water plane area. Under different conditions, the DAF value and failure factor of the slings of the two structures during the lowering process all meet the specification requirements.

An Experimental and Numerical Study of Motion Responses of Multi-Body Arrays with Hinge Connections

Hinged multi-body systems are gaining popularity in the field of ocean engineering. Their performance is commonly evaluated using numerical simulations, but comparisons with experimental data are required to ensure the accuracy of the computational tools. However, there is a dearth of experimental studies on the motion performance of hinged multi-body systems, particularly those involving more than two hinged floating bodies. This study aims to fill this gap in experimental data for hinged multi-body systems beyond two bodies. The rectangular box was chosen as the test model due to its stable hydrodynamic properties and ease of numerical modelling. Five identical boxes were prefabricated and subsequently tested in the pool in a sequence ranging from one to five boxes to capture the motion performance. Additionally, a numerical programme based on potential flow theory was developed for mutual validation with the experimental data. Firstly, the physical properties of each box were determined through equations calculation and a free decay test, enabling the acquisition of all parameters for conducting numerical simulations. Then, the response amplitude operator (RAO) curves for the heave and pitch motion of a single box were depicted, and the results indicated that the resonant frequency in pitch direction obtained from the regular wave test was consistent with that obtained from the free decay test. Finally, the motion RAO curves of hinged multi-body systems were presented and analysed. The agreement between the measured and computed results confirms the suitability of the experimental data presented in this study as benchmark data for validating numerical simulations.

Multi-objective model predictive control for ship roll motion with gyrostabilizers

Ships are prone to significant roll motion while sailing in adverse conditions, posing a serious threat to ship safety and maneuverability. Therefore, effective ship motion control is crucial. Integrating the MPC control algorithm with a gyrostabilizer can effectively achieve this goal. To evaluate and compare control strategies, a multi-objective model predictive control is proposed that integrates considerations of ship motion, safety, and energy consumption to conduct the operation concurrently. By assigning different weights to these factors, the study aims to discern the varying impacts on control effectiveness. The response of ship roll motion in beam waves is evaluated through roll hydrodynamic modelling, accounting for wave memory effects. A state-space model of ship and gyrostabilizers is proposed to represent their dynamic interaction and response to external moment. Subsequently, the influence of different weightings in the multi-objective model predictive control is compared, and the control performances of a frigate under different wave conditions are analyzed respectively. The multi-objective model predictive control, with varied weight assignments, leads to distinct reductions in roll motions. This investigation offers valuable insights into controlling roll motion in beam wave conditions, effectively reducing motion under varying sea conditions, and providing alternative guidance tailored to user preferences.

Hydrodynamic performance characteristics of small-scale in-situ buoys with critical motion requirements

As the accuracy of high-precision oceanographic measurement instruments increases, the operational requirements for buoy motion become critical. This study focuses on the small-scale in-situ buoy, optimizing buoy configuration to ensure stability and performance. Aiming at the special structure which consists of a large floating column and several small tube connectors, a method for evaluating the hydrodynamic performance is proposed which combines potential flow theory with Morison equation. And the method validity is confirmed using experimental data. The performances analysis of different type buoy with catenary or taut mooring system are developed. According to the critical motion requirements for the long-term stability, the cylindrical type buoy equipped with a catenary mooring system is regarded as the most stable and economical choice, exhibiting a surge motion response of 4.07 m, a heave motion response of 2.89 m, and a pitch motion response of 9.37°. Furthermore, the anchor chain acts as an elastic damper which can mitigate the transient impact of the environmental loads, greatly limiting the amplitude of the longitudinal and heaving motions. And the maximum mooring line tension is 249.28 kN, which is significantly lower than other schemes. The evaluation method offers a technical support for engineering applications.

Experimental and numerical study on dynamic responses of a TLP-type modular floating structure system

This paper explores a proposed TLP-type modular floating structure system, incorporating both central TLP modules and peripheral floating artificial reef modules. The outermost floating artificial reef module can function as a floating breakwater, and also serving as a habitat for surrounding marine organisms. To assess the system's multi-body coupling dynamics under various wave conditions, both scale model tests (1:80) and time-domain numerical simulations were performed. The simulations accounted for hydrodynamic interactions among the bodies and the mechanical coupling effects. During the scale model test, a survival strategy has been proposed to prevent collision risks between reef modules and adjacent TLP modules, which involving a hinge connector with additional linear spring. A preliminary stiffness recommendation was suggested by a trade-off between the pitch of the reef module and the spring force. Numerical and experimental results have been widely compared and discussed, including the multi-body motion responses and the tension leg loads. A good agreement has been achieved, although responses are slightly overestimated by numerical simulation due to the neglect of the viscous damping effect. In addition, the responses of the proposed system, connected with and without the outermost floating artificial reef module, have been compared and analyzed. The results suggest that the connection of the reef module can significantly reduce the system's surge response and enhance its survivability under severe sea conditions. The validated numerical model can serve as a valuable reference for subsequent system optimization and further engineering applications.

Analysis and research on the hydrodynamic performance of offshore floating photovoltaic systems under large tidal variations

Abstract This paper focuses on the multi-module connected offshore floating photovoltaic system, designing a mooring system with buoys, considering the effects of buoy size, position on the motion response of the photovoltaic system, mooring cable tension, and photovoltaic air gap. Based on the three-dimensional potential flow theory, optimal parameters for buoys were selected using regular waves at an average depth of 10 meters. Subsequently, factors such as tidal differences, randomness of waves, wind, and currents were taken into account, and the motion response, mooring tension, and photovoltaic air gap were calculated separately at water depths of 8 m, 10 m, and 12 m. The analysis results indicate that the offshore floating photovoltaic system with a buoy mooring system, under the influence of tidal differences, does not show significant differences in the minimum air-gap height of the photovoltaic system, ensuring safe and stable operation.

Numerical simulation and analysis of motion responses and added resistance of a KRISO container ship in regular waves

Abstract In order to explore the influence of vessel speed on seakeeping characteristics and provide valuable insights for ship performance evaluation, the accurate prediction of ship motion and resistance in wave conditions is essential. In this study, the variations in ship motion and resistance with respect to ship speed are analyzed during navigation in regular waves. The results suggest that the added resistance coefficient of the KCS demonstrates an initial rise, succeeded by a subsequent decline, with the expansion of wavelength. Moreover, the peak non-dimensional resistance coefficient, observed at different ship speeds, demonstrates an upward trend with the augmentation of ship velocity. This research methodology provides a valuable tool for numerically predicting the hydrodynamic performance of vessels in regular wave conditions.

Self-Repeatable snapping liquid–crystal-elastomer actuator

Liquid crystal elastomers (LCEs) show potential for use in sensors and robotics owing to their reversible stimuli response. However, current actuators have limitations such as low power and slow recovery. Incorporating snap-through transitions induced by mechanical instability into motion can enhance the speed and power of soft actuators. However, the snap-through transitions’ single-shot motion response without external assistance at complicates their application to continuous and self-repeatable actuation. This study introduces a promising and simple approach for creating a rapid and self-repeatedly regulated snapping motion in an LCE actuator by confining the LCE film in a frame. We explore the confinement effect of a freestanding pre-curved LCE film that smoothly changes its bending direction and shows anticlastic buckling. Interestingly, a self-repeating snapping motion is generated by attaching a rigid film onto the LCE film, thereby inducing synclastic deformation. Remarkably, the up-and-down bending snapping motion occurs at a very high speed (within 30 ms) and is self-regulated depending on the temperature of the bottom surface. By utilizing this thermally responsive snapping LCE actuator, we successfully demonstrate an organic-based novel fire alarm and a self-propelled soft-walk mechanism.

Layout Optimization of Wave Energy Park Based on Multi-Objective Optimization Algorithm

Abstract In this paper, both semi-analytical method and numerical simulation is applied to investigate the hydrodynamic behavior of large arrays of point-absorber wave energy converters (WECs). To analyze wave interactions among multiple WECs within an array, a semi-analytical model is developed based on the potential flow theory and the matched eigen-function expansions method. The fluid domain is divided into two kinds of regions: interior regions underneath the cylinders and an exterior region surrounding all the cylinders. The matched eigenfunction expansions method is employed to solve the radiation potential problem in each domain, and the hydrodynamic coefficients and motion response of the cylinders in the array are evaluated. To validate the accuracy of the semi-analytical method, WAMIT is adopted to simulate the wave energy park numerically and compared with the results by the semi-analytical model. The hydrodynamic characteristics and power absorption performance of the WECs within the wave energy park are analyzed. The power performance of a wave energy park is studied as functions of layout geometry, incident wave direction and separation distance between WECs respectively. Finally, MOPSO based on a surrogate model is used to optimize the layout of wave energy array.

Deviceization of high-performance and flexible Ag2Se films for electronic skin and servo rotation angle control

Ag2Se shows significant potential for near-room-temperature thermoelectric applications, but its performance and device design are still evolving. In this work, we design a novel flexible Ag2Se thin-film-based thermoelectric device with optimized electrode materials and structure, achieving a high output power density of over 65 W m−2 and a normalized power density up to 3.68 μW cm−2 K−2 at a temperature difference of 42 K. By fine-tuning vapor selenization time, we strengthen the (013) orientation and carrier mobility of Ag2Se films, reducing excessive Ag interstitials and achieving a power factor of over 29 μW cm−1 K−2 at 393 K. A protective layer boosts flexibility of the thin film, retaining 90% performance after 1000 bends at 60°. Coupled with p-type Sb2Te3 thin films and rational simulations, the device shows rapid human motion response and precise servo motor control, highlighting the potential of high-performance Ag2Se thin films in advanced applications.

Flow memory effects on the nonlinear hydrodynamic load of an ROV in translational maneuvering

This paper describes experimental and numerical investigations of the flow memory effect on the nonlinear hydrodynamic load response of a work-class remotely operated vehicle (ROV) under surge, sway, and heave impulse motions. The hysteresis loops of the dynamic drag coefficients during impulse motion tests are analyzed by comparing them with those obtained in steady drag tests. The areas of the loops and differences between the maximum and minimum dynamic and steady coefficients are used to quantify the flow memory effect. A novel unsteady hydrodynamic model for ROVs in translational maneuvering is established. This model considers the flow memory effect in terms of the unsteady hydrodynamic load response obtained from impulse motion response tests. The results given by the unsteady model are found to be in good agreement with those from CFD simulations. The unsteady hydrodynamic characteristics (including the asymmetric forces, force magnitude, and phase delay), motion amplitude, and frequency effect on the hydrodynamic forces of the ROV are analyzed by comparing the unsteady model results with those obtained from the steady model, revealing the rules governing the flow memory effect.

Coupled Motion Response Analysis for Dynamic Target Salvage under Wave Action

The strategic recovery of buoys is a critical task in executing deep-sea research missions, as nations extend their exploration of marine territories. This study primarily investigates the dynamics of remotely operated vehicle (ROV)-assisted salvage operations for floating bodies during the recovery of dynamic maritime targets. It focuses on the hydrodynamic coefficients of dual floating bodies in this salvage process. The interaction dynamics of the twin floats are examined using parameters such as the kinematic response amplitude operator (RAO), added mass, damping coefficient, and mean drift force. During the “berthing stage”, when the double floats are at Fr = 0.15–0.18, their roll and yaw Response Amplitude Operators are diminished, resulting in smoother motion. Thus, the optimal berthing speed range for this stage is Fr = 0.15–0.18. During the “side-by-side phase”, the spacing between the ROV and FLOAT under wave action should be approximately 0.4 L to 0.5 L. The coupled motion of twin floating bodies under the influence of following waves can further enhance their stability. The ideal towing speed during the “towing phase” is Fr = 0.2. This research aims to analyze the mutual influence between two floating bodies under wave action. By simulating the coupled motion of dual dynamic targets, we more precisely assess the risks and challenges inherent in salvage operations, thus providing a scientific basis for the design and optimization of salvage strategies.

Effect of electromagnetic middle-ear implant simulating sites on the stapes spatial motion: A finite element analysis.

The electromagnetic middle-ear implant (MEI) is a new type of hearing device for addressing sensorineural and mixed hearing loss. The hearing compensation effect of the MEI varies depending on the transducer stimulation sites. This paper investigates the impact of transducer stimulation sites on MEI performance by analyzing stapes spatial motion. Firstly, we constructed a human-ear finite element model based on micro-CT scanning and inverse molding techniques. This model was validated by comparing its predictions of stapes spatial motion and cochlear response with experimental data. Then, stimulation force was applied at four common sites: umbo, incus body, incus long process and stapes to simulate the electromagnetic transducer. Results show that at low and middle frequencies, stapes-stimulating and incus-long-process-stimulating produce similar spatial motion to normal hearing; at high frequencies, incus-body-stimulating produces similar results to normal hearing. The equivalent sound pressure level generated by the stapes piston motion is less sensitive to the stimulation direction than that deduced by the stapes rocking motion.

Dynamic analysis of multi-module floating photovoltaic platforms with composite mooring system by considering tidal variation and platform configuration

Floating Photovoltaics (FPV) are emerging as an innovative technology to utilizing solar energy which advances the exploration of renewable energy technologies in the deep sea. This investigation proposes a novel methodology to verify the feasibility of the designed models in time-domain analysis via the motion responses, the mooring analysis based on the finite element method (FEM) and the airgap analysis, considering a comparison of dynamic responses between the regular hexagon shape and rectangle shape semi-submersible floating photovoltaic platform (FPVP) both combinate the cables and the tensioners mooring system to adapt the tidal variation. Initially, the response amplitude operators (RAOs) of the two configurations of the FPVP numerical models established in AQWA are derived from the frequency-domain analysis. Then, the method of rectifying the RAOs by incorporating additional damping essential to compensating the fluid viscosity due to the limitation of the potential flow theory is verified through comparison with the Computational Fluid Dynamics (CFD) solver. Subsequently, the motion responses of the two conceptualized FPVPs with the composite mooring system under different depths of water are assessed in time-domain analysis through OrcaFlex which regards the cables and tensioners as Morison type based on the FEM theory. Simultaneously, the variations in the air gap of platforms with dissimilar stiffness tensioners are compared to assess the safety of FPV systems under different water depths. The long-term extreme forecast of effective tension force for various return periods derived from the Weibull distribution model is verified. Finally, considering the factors that influence the design and safety of multi-module floating photovoltaics in variable-depth water, this study provides essential guidance for the safe construction technology of semi-submersible FPVPs, serves as a valuable reference for promoting reliable and cost-effective FPV technologies for offshore environments.

Influence of Damping Plate Size on Pitch Motion Response of Floating Offshore Wind Turbine

For floating offshore wind turbines, a significant pitch and roll motion response of the platform can affect the acceleration and power generation of the nacelle. The damping plate is considered a type of attachment that can be used to reduce rotational motion, but research on its anti-rotational effect is limited. The objective of this work is to analyze the impact of installing damping plates and varying their sizes on the pitch motion response of semi-submersible platforms, while also proposing optimization strategies for damping plate design. Firstly, a comparison between numerical simulations and experimental measurements validates the accuracy of the CFD calculations. Subsequently, different sizes of damping plates are proposed for the platforms, followed by simulations under various conditions. Finally, comprehensive data analysis is conducted. The findings suggest that installing damping plates enhances both the platform’s added moment of inertia and damping coefficients while simultaneously amplifying its motion response in regular waves. Furthermore, increasing the size of damping plates leads to an increase in both the added moment of inertia and motion response for the platform, whereas the damping coefficient exhibits an initial increasing trend followed by a subsequent decrease. Ultimately, it is found that increasing the distance between damping plates and the free surface significantly reduces wave-induced loads on the platform.

Characterisation of the Rigid Body Vibration Spectra of Road Transport Vehicles

ABSTRACTFor decades, numerous attempts at re‐creating realistic (vertical) vibrations that purport to represent typical conditions during road transport have been proposed and published. This has and continues to result in a significant number of target power density spectra (PDS) for use in laboratory simulation of vibrations despite the fact that the underlying parameters that influence the vibrations (road surface unevenness and vehicle dynamics) remain largely unchanged. This paper seeks to address this situation by analysing published and measured PDS (129 in total) from a variety of vehicles and road types with the aim of establishing typical PDS. Through the analysis of the frequency of the first natural mode of these PDS, it was found that there exist five typical response PDS (three for steel leaf suspension and two for air ride suspension) that can be considered as representative vibration response PDS for road transport in general. These representative PDS were matched with a two degree‐of‐freedom quarter‐car model representing the heave response of the rigid body motion of the vehicles. The analysis suggests that the higher frequency content of the measured data is not related to rigid body motion but emanates from drivetrain and, in some cases, structural vibrations. These usually comprise numerous harmonics of fixed and varying frequencies as well as transients. As these vibrations are impossible to classify based on vehicle type, it is recommended that the five quarter‐car representative spectral models proposed in this paper—namely, for steel leaf spring suspended vehicles with heavy, moderate and light loads and air ride type vehicles with heavy and light loads—be used for laboratory simulation for the purpose of evaluating the vibration resistance of products and packaged systems. It is suggested that, for most packaged product, this is sufficient to test their ability to survive road transport vibrations. These will yield more realistic vibrations than those endorsed by standards organisations and should have a positive impact on the optimisation of packaging designs and a corresponding reduction in packaging waste. Finally, the need for further work aimed at developing methods to identify and extract fixed and varying discrete frequency vibration as well as transient vibrations was identified.

Study on aerodynamic and coupled motion response characteristics of floating vertical axis wind turbine

ABSTRACT To improve the efficiency of a floating VAWT (FVAWT), the aerodynamic and coupled motion response characteristics of 5MW Φ-type FVAWT are studied in fully coupled system. Based on the computational fluid dynamics (CFD) method, the dynamic fluid body interaction (DFBI), overlapping grid and dynamic mesh technique are adopted for numerical simulations. Under wind-wave coupling conditions, the power coefficient (Cp) and motion response of FVAWTs with different tip speed ratios (TSR) and height-todiameter ratios (η) are analysed. The mechanism of platform heave motion on torque Q generation of VAWT is explored. The results show that the FVAWT with height-to-diameter ratio of 1.2 and tip speed ratio of 5 has optimal aerodynamic and motion performance. Under the optimal tip speed ratio, the Cp of the offshore FVAWT is 5.21% higher than that of the land VAWT. As the floating platform rises, the torque of wind turbine decreased correspondingly, and vice versa.

Motion and Mooring Load Responses of a Novel 12-MW Semi-Submersible Floating Wind Turbine: An Experimental Study

Abstract Due to the complexity of the integrated Floating Wind Turbine (FWT) system, obtaining reliable results necessitates extensive experiments. This paper conducts a comprehensive study on the motion performance and mooring load responses of a novel 12-MW semi-submersible FWT through model tests carried out in a wave basin. A multi-blade large-scale wind-generation system, equipped with a rectifier network, was enhanced and constructed to provide a dependable wind field. And a flexible tower was designed and fabricated, achieving an accurate simulation of the tower's stiffness characteristic and its impact on the overall dynamic response. The marine environmental conditions encompass various combinations of wind, waves, and currents. Rigorous calibration and identification tests were undertaken to validate the environmental conditions and the model system. The findings reveal that, under mild wave parameters, the mooring load is primarily influenced by the resonance response with platform motions, particularly surge resonance. The load effect of wind and current induces mean surge and pitch motions, while their damping effect reduces the standard deviation of responses, notably suppressing the pitch response peak at its natural motion frequency. Wave loads predominantly dictate the vibration range of motion responses. When the current velocity reaches a sufficient magnitude, the coupling effect between current and wave in the wave–frequency region significantly amplifies the mooring response. Notably, motions and mooring loads in the 60-deg and 90-deg directions surpass those in the 0-deg direction, with the maximum responses occurring at 60 deg.

Hydraulic Model Tests for a Pontoon-Type Floating Structure with a Horizontal Damping Plate

In this study, hydraulic model tests were conducted to investigate the effect of a horizontal damping plate on the motion of the pontoon-type floating structure. The floating structures with and without the horizontal damping plates were fabricated with the scale of 1/20 and their motion responses to the regular and irregular wave conditions were investigated. From the comparison for the responses of each model with 16 wave conditions, it could be known that the damping plate made the response of the the pontoon to be smaller by about 5 to 10 % compared with the normal rectangular pontoon.

Study on the relationships between particle shapes and motion responses in the geotechnical coarse-grained system subjected to vibration loads

The vibration-induced deformation of coarse-grained soil originates from the internal particle motions, which are reflected in translational and rotational behaviors controlled by particle shapes. However, the mechanism by which particle shapes affect particle motions in granular systems remains unclear, and diverse shape parameters make it difficult to accurately express the motion behaviors through a single shape parameter. Leveraging the advantages of the discrete element method (DEM) and machine learning methods, therefore, the relationships between shape features and motion behaviors were explored in complex-shaped granular systems. Firstly, a shape database containing hundreds of gravel particles was constructed, from which 10 representative shape parameters were selected to characterize the Form, Sphericity, and Roundness features through hierarchical clustering and principal component analysis. Then, three DEM models, established based on the shape database, were simulated to obtain particles’ translational and rotational indicators. Following, a regression relationship between representative shape parameters and motion indicators was established through the XGBoost model, and the SHAP values were utilized to explore the main shape parameters influencing particle motions. The results indicate that particle motions in the upper layer are primarily influenced by the Form parameter, and the equiaxial shape can promote the vertical displacement. The particle motions in the middle layer are mainly controlled by the Sphericity and Roundness parameters, and the flatness or angular shape has a suppressing effect on the vertical displacement.