Motion Response Research Articles

Improving Ship Response Estimation using Neural Networks

The feasibility of a data-adaptive multi-fidelity seakeeping model is assessed for use in early stage design in this study. Data adaptive tuning (or correction) of lower-fidelity model predictions are implemented based on training with higher fidelity ship motion response data. Long Short-Term Memory (LSTM) neural networks are incorporated as part of a multi-fidelity approach for prediction of 6 degree of freedom (6-DOF) ship motion responses in waves. LSTM networks are trained and tested with Large Amplitude Motion Program (LAMP)simulations as a target, and SimpleCode simulations and wave time series as inputs. LSTM networks improve the fidelity of SimpleCode seakeeping predictions relative to LAMP, while retaining the computational efficiency of a lower-fidelity simulation tool.

Comparative Biomechanical Stability of the Fixation of Different Miniplates in Restorative Laminoplasty after Laminectomy: A Finite Element Study

A novel H-shaped miniplate (HSM) was specifically designed for restorative laminoplasties to restore patients’ posterior elements after laminectomies. A validated finite element (FE) model of L2/4 was utilized to create a laminectomy model, as well as three restorative laminoplasty models based on the fixation of different miniplates after a laminectomy (the RL-HSM model, the RL-LSM model, and the RL-THM model). The biomechanical effects of motion and displacement on a laminectomy and restorative laminoplasty with three different shapes for the fixation of miniplates were compared under the same mechanical conditions. This study aimed to validate the biomechanical stability, efficacy, and feasibility of a restorative laminoplasty with the fixation of miniplates post laminectomy. The laminectomy model demonstrated the greatest increase in motion and displacement, especially in axial rotation, followed by extension, flexion, and lateral bending. The restorative laminoplasty was exceptional in preserving the motion and displacement of surgical segments when compared to the intact state. This preservation was particularly evident in lateral bending and flexion/extension, with a slight maintenance efficacy observed in axial rotation. Compared to the laminectomy model, the restorative laminoplasties with the investigated miniplates demonstrated a motion-limiting effect for all directions and resulted in excellent stability levels under axial rotation and flexion/extension. The greatest reduction in motion and displacement was observed in the RL-HSM model, followed by the RL-LSM model and then the RL-THM model. When comparing the fixation of different miniplates in restorative laminoplasties, the HSMs were found to be superior to the LSMs and THMs in maintaining postoperative stability, particularly in axial rotation. The evidence suggests that a restorative laminoplasty with the fixation of miniplates is more effective than a conventional laminectomy due to the biomechanical effects of restoring posterior elements, which helps patients regain motion and limit load displacement responses in the spine after surgery, especially in axial rotation and flexion/extension. Additionally, our evaluation in this research study could benefit from further research and provide a methodological and modeling basis for the design and optimization of restorative laminoplasties.

Effect of Platform Configurations and Environmental Conditions on the Performance of Floating Solar Photovoltaic Structures

The growth and development of floating solar photovoltaic (FPV) power plants is a prominent topic within renewable energy technology. One reason contributing to this desired technology design concept is the possibility of land acquisition issues, whereas the usage of the ocean provides a greater technical alternative area. The objective of the research is to present an innovative design for a floating structure, focusing on investigating and comparing the seakeeping performance of several hull configurations: catamaran, trimaran, quadrimaran and pentamaran. The final computational simulation results indicate a linear negative trend in the motion response graphs, particularly in specific significant response values for heave (Global Z), roll (Global RX), and pitch (Global RY), as the hull configuration increases.

Coupling a nonlinear finite element mooring model with an overset CFD solver for dynamic analysis of floating structures in waves

An accurate prediction of motion responses of a moored floating structure requires high-fidelity coupled analysis between the structure and its mooring system in waves, which involves both mooring line dynamics and fluid dynamics. In this paper, we develop a nonlinear finite element dynamic mooring analysis module that allows large axial stretching of mooring lines under the open source CFD framework OpenFOAM, and couple it with an Overset CFD solver to establish a fully coupled finite element mooring-CFD analysis model for floating structures. The coupled model is advantageous over existing models in that it is able to deal with large axial mooring stretching and complex mesh motions induced by significant structure responses under severe operating conditions. The developed dynamic mooring analysis method is firstly validated against publicly available data. In order to validate the coupled model, a series of experimental tests were carried out for a semi-submersible platform moored by eight catenary lines under different operating conditions, including free decay, regular and irregular wave tests. The dynamic responses of the floating structure and mooring tension are analyzed and compared with experimental data. Results show that numerically predicted structure responses and mooring tension are generally in good agreement with experimental measurements. Meanwhile, the strongly nonlinear large-amplitude resonant motions generated by the interaction of irregular waves with the moored floating structure are also investigated. Comparisons reveal that the coupled model can accurately predict the resonant spectral peaks of the structure responses, indicating that the it is capable of simulating large-amplitude motions of moored floating structures. The coupled model developed in this paper can be further applied to study the survivability of moored floating structures under harsh sea conditions.

The performance of C-MAC videostylet versus D-Blade during tracheal intubation in patients with simulated cervical immobilization: A randomized comparative trial

ABSTRACT Background Concerning patients with suspected cervical spine (C-spine) fractures or other cervical pathologies, tracheal intubation must be done very carefully to avoid injury to the spinal cord. Methods Fifty-two patients within a range of 20–60 years old, and arranged for elective surgery, were indiscriminately allocated into two groups; Group S was intubated with the C MAC Videostylet (VS), whereas Group L was intubated by D blade Video Laryngoscope (VL) during cervical immobilization by Philadelphia collar. The first successful attempt duration, total number of intubation attempts, the total duration of the intubation, haemodynamic parameters, stress response of intubation, the degree of C-spine movement and complications were evaluated in both groups. Results Group L showed substantially shorter times for the first successful attempt (p-value <0.001) and the whole intubation procedure (p-value <0.001) compared to Group S. Group S had a significantly more total number of intubation attempts (p-value = 0.010). The haemodynamic parameters did not significantly differ throughout the measurements among groups. Regarding the blood cortisol measurements at different periods, there were statistically insignificant changes among the groups. Concerning the greatest alteration in C-spine angulation at the occiput-C1, C1-C2, and C2-C5 segments during laryngoscopy and intubation, there were statistically insignificant differences among groups. Conclusion The C MAC D-blade VL is superior to the VS in terms of the number and duration of intubation attempts during C-spine immobilization. Conversely, the VS showed comparable results to the D blade regarding C-spine motion and stress response.

Design strategy for resonance avoidance to improve the performance of tension leg platform-type floating offshore wind turbines

The objective of this study is to determine the effect of elasticity of the tower and blades of a large tension leg platform (TLP)-type FOWT on the eigenmodes of the entire system and suggest reference directions to be implemented in the conceptual design stage. Typically, TLP-type FOWTs are connected by a mooring system with strong tension and exhibit an extremely short natural period of motion compared with a semi-submersible platform. Furthermore, the wind turbine tower mounted on the floating platform is flexible in the fore-aft and side-to-side directions, forming a vibrating system in itself; therefore, it is coupled with the motion of the floating platform. In particular, the tower elasticity is known to influence the roll and pitch motions of the platform. In this study, the motion response characteristics of the platform were investigated according to the changes in the tower design parameter (bending stiffness). The influence of blade elasticity was also confirmed, verifying that the physical characteristics of both the tower and blade significantly affect the motion of the TLP. Additionally, the degree of influence based on environmental loads was identified to suggest a design direction for FOWTs while avoiding resonance.

Bistable response and quasi-periodicity excitation of the internal dynamics of soliton molecules.

Soliton molecules, a frequently observed phenomenon in most mode-locked lasers, have intriguing characteristics comparable to their matter molecule counterparts. However, there are rare explorations of the deterministic control of the underlying physics within soliton molecules. Here, we demonstrate the bistable response of intramolecular motion to external stimuli and identify a general approach to excite their quasi-periodic oscillations. By introducing frequency-swept gain modulation, the intrinsic resonance frequency of the soliton molecule is observed in the simulation model. Applying stronger modulation, the soliton molecule exhibits divergent response susceptibility to up- and down-sweeping, accompanied by a jump phenomenon. Quasi-periodic intramolecular oscillations appear at the redshifted resonance frequency. Given the leading role of bistability and quasi-periodic dynamics in nonlinear physics, our research provides insights into the complex nonlinear dynamics within dissipative soliton molecules. It may pave the way to related experimental studies on synchronization and chaos at an ultrafast time scale.

Integrated System of Semi-submersible Offshore Wind Turbine Foundation and Porous Shells

A novel semi-submersible platform is proposed for 5 MW wind turbines. This concept focuses on an integrated system formed by combining porous shells with a semi-submersible platform. A coupled aerodynamic–hydrodynamic–mooring analysis of the new system is performed. The motion responses of the novel platform system and the traditional platform are compared. The differences in hydrodynamic performance between the two platforms are also evaluated. The influence of the geometric parameters (porosity, diameter, and wall thickness) of porous shells on the motion response behavior of the new system is studied. Overall, the new semi-submersible platform exhibits superior stability in terms of pitch and heave degrees of freedom, demonstrating minimal effects on the motion response in the surge degree of freedom.

Numerical Simulation of Ship-added Resistance Based on a Numerical Wave Tank

The wave resistance increase of a ship during its actual voyage can affect its speed and safety. To design ships with excellent sailing performance, it is necessary to accurately predict the wave resistance increase of a ship in waves, as well as the motion response and wave resistance prediction of ships in waves, which involves complex hydrodynamic problems. This paper first establishes a physical model of the KCS vessel, then utilizes the numerical wave tank platform independently developed by our university. Based on viscous flow theory, it calculates the resistance of the KCS under calm water conditions. Using three-dimensional potential flow methods and spectral analysis, it computes the wave-induced resistance values for the KCS under six-degree sea states, analyzes the wave-induced resistance performance of the KCS, and ultimately, based on the calculation results of calm water resistance and wave-induced resistance combined with propeller efficiency parameters, calculates the effective power of the engine.

Study on the influence of ship waves on the dynamic response of floating tidal current power generation device

To study the influence of ship traveling waves on the hydrodynamic performance between the carrier platform and the turbine, the computational fluid dynamics method and the DFBI motion module of STAR CCM+ software were adopted. Under the condition of the coupling of the ship traveling wave and wave current generated at different speeds, the overall motion response of the power plant is simulated. What’s more, the influence of different wave conditions on the heave, pitch, and roll of the carrier platform and the energy efficiency of the turbine is analyzed. The results show that the ship speed has little effect on the carrier heave motion, but the maximum value of the carrier pitch motion increases with the increase in the ship speed. The value of turbine energy acquisition efficiency always decreases with decreasing lateral spacing and increases with decreasing speed. This paper has a certain reference value for the engineering application of floating tidal current power generation equipment.

Experimental study on evaluating hydrodynamic performance of a novel submerged floating tunnel

A submerged floating tunnel (SFT) is susceptible to significant vibrational responses when subjected to intricate and challenging conditions of the deep-water ocean environment. This is primarily due to the inherent attributes of large flexibility and lower damping exhibited by flexible components of an SFT. To the best of the authors' knowledge, a majority of the current SFT concepts do not completely satisfy the motion-limit values mandated by the relevant standards. In this study, a novel SFT concept is introduced to bolster its vibration suppression capacity through the optimization of the superstructure and substructure by using a three-tube structure and a rigid truss structure, respectively. To evaluate the efficacy of the novel SFT, a comprehensive series of experiments are conducted in a wave-current flume to scrutinize the vibration suppression performance of this novel SFT configuration, juxtaposed against conventional design concepts. The insights are revealed based on a comparative analysis in both the time and frequency domains, encompassing a range of key parameters, and by performing a sensitivity analysis specific to the present model. The results show that the superposition effect of wave and current coupling has a lower impact on the motion response of the proposed SFT with higher mooring stiffness. Despite the increase in cable tension (1–2 times) for the proposed SFT design, the corresponding vibration suppression performance is found to improve by 3–9 times. This experimental investigation holds profound theoretical and engineering significance, as it contributes pivotal knowledge to the field of vibration suppression for the SFT.

Optimization Analysis of the Arrangement of the Submerged Floating Tunnel Subjected to Waves

The motion responses, mooring tensions, and submergence depth are the dominant factors for the arrangement of the Submerged Floating Tunnel (SFT) subjected to waves. Generally, the maximum values of motion responses, mooring tensions, and absolute submergence depth are mainly focused on. In the present study, experiments are implemented to measure the motion responses and mooring tensions of the SFT with different mooring patterns and submergence depths under waves with different characteristic wave heights and periods. In order to evaluate the arrangement of the SFT more effectively and comprehensively, besides the maximum values, several new characteristic parameters are introduced. Such parameters account for the motion responses in the frequency domain, the uniformity of the tension distribution, the length of time during which the cable reaches a relaxed condition during wave action, the KC number, the dimensionless period, the wave height, and the submergence depth. The results from the optimization analysis show the following: according to the characteristic values of motion responses and mooring tensions, the pattern of diagonal cables is better than that of diagonal cables + vertical cables; and within the range of the present experiments, there are optimal dimensionless parameters—the dimensionless submergence depth d0/LP ≥ 0.15, the KC number ≤ 0.8, or the dimensionless wave height Hs/d0 ≤ 0.10—for the condition of which the dynamic responses and mooring tensions vary slightly.

Suppression of the vortex-induced vibration of the cylinder by the baffle plates at different submerged depths

In this paper, the suppression effect of baffle on VIV of cylinder at different depths is studied. According to two-dimensional transient model and RANS equation, VIV responses of a cylinder with two baffle plates at a fixed distance and a fixed Angle at different depths are numerically simulated. The submersion depth radio h* is mainly 1.2, 1.5, 2.5 and 5. The experimental data and predicting results are compared to display the accuracy of numerical method. When h* is 2.5, the baffle plates have the best suppression effect on VIV. Compared to the bare cylinder, the amplitude is decreased by 69%. Meanwhile, the vibration of the cylinder at different depths shows instability, and the motion response has great jitter. The lower baffle plate is subject to a unidirectional force when h* = 1.5 and 1.2.

A Simplified Method for the Evaluation of Floating-Body Motion Responses over a Sloping Bottom

Recently, many floating renewable energy platforms have been deployed in coastal regions, where sloping bottoms are an important factor when evaluating their safety. In this article, a simplified method coupling an eigenfunction matching method (EMM) and a finite-depth Green’s function (FDGF) is developed to evaluate floating-body motion responses over a sloping bottom for which bathymetry is homogeneous in the longshore direction. We propose an extended EMM to create an incident wave model over the sloping bottom, thereby obtaining the Froude–Krylov (F–K) force and Neumann data on the wet surfaces of the floating body for the diffraction problem. An equivalent depth is introduced to account for the interaction between the sloping bottom and floating bodies when dealing with the diffraction and radiation problems. The accuracy of the present method is validated through a comprehensive comparison with numerical and/or experiment results for a liquefied natural gas (LNG) ship and a floating hemisphere from the literature. Generally, the present, simplified method can give predictions with sufficient accuracy.

Effect of aircraft landing angle on hydrodynamics characteristics during wave landing

In order to study the effect of different courses on the landing performance of aircraft when landing in waves, a Computational Fluid Dynamics (CFD) method is developed to investigate the landing performance of the NACA TN 2929 A aircraft model. The solution of fluid flow is based on the Reynolds-averaged Navier-Stokes equations with the shear stress transport (SST) k−ω turbulence model, and the numerical scheme employed is the Finite Volume Method (FVM). The fifth-order Stokes wave is generated by using the velocity inlet wave-making method. In the work, the slamming load, pitch change and motion response of the aircraft landing at different wave positions are analyzed. The landing characteristics of aircraft landing parallel to the wave, perpendicular to the wave and at the yaw angle are studied. It is found that the landing characteristics of the aircraft at the 1/2 π phase are better than those at other ones, with the maximum load at the π phase. When the aircraft lands parallel to the wave, yaw displacement generated at 1/2 π phase and 3/2 π phase is equal in magnitude and opposite in direction in the initial short time. These results are important for reducing slamming loads and improving the airworthiness of the aircraft structure when landing on a wave surface.

Motion and Dynamic Responses Approach for WindFloat Structures under Marine Loads

Motion and Dynamic Responses Approach for WindFloat Structures under Marine Loads

Research on path following control of unmanned ship based on fast wave inversion disturbance compensation and preset performance

In this paper, wave inversion is innovatively applied to the path following control of unmanned ship for the first time. At the same time, the performance constraint problem and input saturation of the control system are considered, and the model uncertainty problem of the system is solved by improving the RBF algorithm. Firstly, the system identification method is used to obtain the wave information in real time and quickly based on the ship motion response under the current sea condition, and the disturbance compensation is carried out in the unmanned ship control system. Secondly, in order to ensure the safety and stability of the unmanned ship during navigation, the performance constraints of the unmanned ship path following control system are carried out. In addition, considering the external disturbance and model uncertainty, the RBF neural network control algorithm based on the predictor estimation error is designed, which greatly improves the transient performance of the controller. Finally, the stability analysis and simulation comparison test verify the correctness and feasibility of the proposed control strategy.

Hydrogels with Differentiated Hydrogen‐Bonding Networks for Bioinspired Stress Response

AbstractStress response, an intricate and autonomously coordinated reaction in living organisms, holds a reversible, multi‐path, and multi‐state nature. However, existing stimuli‐responsive materials often exhibit single‐step and monotonous reactions due to the limited integration of structural components. Inspired by the cooperative interplay of extensor and flexor cells within Mimosa's pulvini, we present a hydrogel with differentiated hydrogen‐bonding (H‐bonding) networks designed to enable the biological stress response. Weak H‐bonding domains resemble flexor cells, confined within a hydrophobic network stabilized by strong H‐bonding clusters (acting like extensor cells). Under external force, strong H‐bonding clusters are disrupted, facilitating water diffusion from the bottom layer and enabling transient expansion pressure gradient along the thickness direction. Subsequently, water diffuses upward, gradually equalizing the pressure, while weak H‐bonding domains undergo cooperative elastic deformation. Consequently, the hydrogel autonomously undergoes a sequence of reversible and pluralistic motion responses, similar to Mimosa's touch‐triggered stress response. Intriguingly, it exhibits stress‐dependent color shifts under polarized light, highlighting its potential for applications in time‐sensitive “double‐lock” information encryption systems. This work achieves the coordinated stress response inspired by natural tissues using a simple hydrogel, paving the way for substantial advancements in the development of intelligent soft robots.

Hydrogels with Differentiated Hydrogen-Bonding Networks for Bioinspired Stress Response.

Stress response, an intricate and autonomously coordinated reaction in living organisms, holds a reversible, multi-path, and multi-state nature. However, existing stimuli-responsive materials often exhibit single-step and monotonous reactions due to the limited integration of structural components. Inspired by the cooperative interplay of extensor and flexor cells within Mimosa's pulvini, we present a hydrogel with differentiated hydrogen-bonding (H-bonding) networks designed to enable the biological stress response. Weak H-bonding domains resemble flexor cells, confined within a hydrophobic network stabilized by strong H-bonding clusters (acting like extensor cells). Under external force, strong H-bonding clusters are disrupted, facilitating water diffusion from the bottom layer and enabling transient expansion pressure gradient along the thickness direction. Subsequently, water diffuses upward, gradually equalizing the pressure, while weak H-bonding domains undergo cooperative elastic deformation. Consequently, the hydrogel autonomously undergoes a sequence of reversible and pluralistic motion responses, similar to Mimosa's touch-triggered stress response. Intriguingly, it exhibits stress-dependent color shifts under polarized light, highlighting its potential for applications in time-sensitive "double-lock" information encryption systems. This work achieves the coordinated stress response inspired by natural tissues using a simple hydrogel, paving the way for substantial advancements in the development of intelligent soft robots.

Vibration control of a monopile offshore wind turbines under recorded seismic waves

The dynamics and vibration control of offshore wind turbines (OWTs) under wind, wave, and earthquake loads is an important but understudied topic, especially for fully coupled seismic analysis considering pile foundation flexibility of OWTs. In this work, we study the effect of multiple passive tuned mass dampers (MTMD) on a monopile OWT by using the fully coupled seismic analysis method. A combined shutdown procedures and MTMD vibration control strategy is proposed for the OWT. First, a state-of-the-art aeroelastic tool, FAST, is extended with a seismic load calculation module, and the numerically modeled monopile OWT addresses the effect of pile-soil interaction (PSI) by establishing ElasPile module in the updated FAST. Then, the focus is placed on the normal operation and emergency shutdown status of OWTs under the combined earthquakes, wind and wave conditions, and structural and motion responses are analyzed under various combination conditions through time-domain simulations, the dynamic characteristics of the OWT during realistic seismic events are shown. Sequentially, based on the proposed MTMD, the vibration migitation effects are evident for the operation OWT and the OWT with shutdown strategies during the combined loading conditions. The reduction in the extreme responses can be as high as 10.53% and 55.02% for the bending moment at the mudline in different OWT conditions, respectively. Therefore, the combined shutdown procedures and MTMD vibration control strategy of OWT is an effective vibration reduction method. Additionally, it is found that PSI has a significant impact on the dynamic characteristics and vibration control effects of OWT structures under wind, wave, and earthquake loads, and the coupled spring boundary condition on the basis of developed ElasPile module is recommended for seismic control analysis of OWT using the combined shutdown procedures and MTMD vibration control strategy.