Oceanic Motions Research Articles

Heat transfer and stratification behaviors of internally heated double-layer fluids systems under swinging conditions

To evaluate the safety designs aimed at the stratified corium pools for nuclear reactors applied in the marine environment, it’s important to carry out research on the convection related phenomena inside a layered fluids system under motion conditions. Thus, in this paper, the macroscopic characteristics of heat transfer and stratification for the double-layer fluids systems with internal heat source under motion conditions were studied through visualization experiments, and due to the complexity of actual ocean motions, only swinging motions were considered. In this research, a new dimensionless number Ris was proposed to quantify the effects of swinging motions, which represents the ratio of the characteristic buoyancy to the characteristic centrifugal force caused by swinging motions. Based on experimental results, swinging motions exert the most significant impacts on the layered systems when Ris is less than 1. In this case, the ratio of maximum temperature fT and the ratio of temperature difference between the two layers fΔT both dropped below 0.5, while the ratio of peak heat transfer capacity fQ-peak raised above 1.5, with the ratio of stable heat transfer capacity fQ-stable most probably lying within the range of 1.06 to 1.2. Additionally, several representative types of macroscopic interface deformation or stratification instability was observed, and phenomenon of mixing could appear between the double-layer fluids under intense-enough swinging conditions. These phenomena imply the significantly intensified forced convection inside the layered systems, which explains the sharply decreased temperature difference and the greatly enhanced heat transfer capacity during high-intensity swinging motions. By contrast, when Ris becomes larger than 10, the values of fΔT、fΔT and fQ-peak will be approaching to 1.0, and relatively stable stratification of the layered systems can be maintained, which indicates the increasingly negligible impacts of swinging motions in such cases. Besides, it was found that an increase in the thickness of either the lower-layer or the upper fluid also helped restrain interface deformation and enhanced the stratification stability of the layered systems.

Development of a liquid metal subchannel code applied to ocean conditions and study on the effect of core geometry parameters and ocean motions on flow and heat transfer characteristics

The Generation IV International Forum (GIF) proposes a type of liquid metal reactor, due to its thermal properties and efficient heat transfer in a relatively small system. This special heat transfer characteristic allows the liquid metal reactor to be modular in design and flexible in installation on a nuclear-powered ship. Accurate prediction of the coolant temperature and flow distribution between subchannels is important to ensure nuclear safety in the complex ocean environment. In this study, an ocean version of subchannel code is developed by adding the motion terms in the momentum equations for the liquid metal reactor core based on the previously land-based subchannel code. Since the research on the characteristics of flow resistance and heat transfer mechanism under ocean conditions is not mature, the original empirical model is still used in the ocean version code. The constitutive models of the liquid metal are analyzed and incorporated into the ocean code. The code has been verified and validated by comparing with Computational Fluid Dynamics (CFD) simulation results, and experimental data. The effect of geometric parameters such as rod Pitch to Diameter ratio (P/D), Rod to Wall gap (RTW) is studied in the liquid metal lead 7 rod bundles. In addition, the effect of heaving start-up and shutdown motions between liquid metal lead and water is discussed in the 5 × 5 bare rod bundles. In general, the modified subchannel analysis code can well complete the calculation of liquid metal reactor under ocean conditions, as well as provide support for the design and safety analysis of a liquid metal cooled fast reactor.

Surface wave generation from a constant-slope-inducing asymmetric ocean floor motion: influence of compressible ocean

Surface wave generation from a constant-slope-inducing asymmetric ocean floor motion: influence of compressible ocean

Prediction and positioning of UWSN mobile nodes based on tidal motion model

As the node positioning of underwater wireless sensor networks is easily affected by tidal motion, ocean current motion and multipath effect, the node positioning accuracy is low. In order to better improve the positioning accuracy of moving nodes of underwater wireless sensor networks, a method of locating mobile nodes of underwater wireless sensor based on tidal motion model is proposed. Firstly, the Time Difference of Arrival (TDOA) localization optimized by niche genetic algorithm is used to initialize each node. The integration of niche technology can effectively find multiple excellent solutions in the solution space, thus providing more abundant solution choices. This algorithm has excellent performance in multi-modal optimization problems, and can avoid the algorithm falling into local optimal solutions, so as to obtain more comprehensive optimization results. The simulation results show that the proposed algorithm has better positioning accuracy than the traditional Chan algorithm and Taylor algorithm. Then, each node is updated in real time by the optimized tidal movement model formula predicted by Kalman filter algorithm. The prediction algorithm is used to compare the real-time predicted update position of the node with the actual position. The positioning distance error of the prediction algorithm is also enough to meet the practical application requirements.

Fewer tropical cyclones yield more near-inertial wind work to the global ocean over the past four decades

In general, tropical cyclones (TCs) will inject energy into oceanic inertial motion‒a prevalent phenomenon in the ocean. Under global warming, the intensity of TCs is on the rise, while their frequency has exhibited a decline since 2000. However, the long-term trend of this energy infusion is an underexplored problem in this context. Using a damped-slab model, we computed the wind work exerted by TCs on the ocean’s mixed-layer inertial motions. Our results show that the global wind work has increased by approximately 50% from 1979 to 2023. The wind work increase of strong TCs (Saffir–Simpson levels 4–5) is the major contributor to the increasing trend of global wind work, primarily due to their increasing frequency and substantial wind stress. At basin scale, the wind work input of the North Atlantic TCs has increased by 2 times, owing to an increase in both their intensity and frequency. Specifically, in the South Indian and the eastern North Pacific basins, the rise in wind work is primarily attributed to the enhanced wind energy of TCs within the inertial bands.

Effect of inclination on SB LOCA transient of a floating nuclear reactor in MARS-KS analysis using moving reactor model

As the imperative to reduce Green House Gas emissions grows within the maritime sector, nuclear power emerges as a promising solution. Especially, offshore floating nuclear power plants have garnered significant attention and development efforts from various institutions and nations. These types of reactors provide unique benefits such as extended refueling periods for advanced safety and exceptional mobility, facilitating access to remote regions. However, the external forces are induced by operating on a moving condition, that can impact the thermal–hydraulic characteristics of various hydraulic components in the entire reactor system. Addressing the safety issues of offshore floating reactors requires conducting thermal–hydraulic analyses under diverse oceanic motions. To achieve this objective, this study centered on analyzing accidents in an offshore floating reactor, specifically the BANDI-60, targeting the Small Break Loss of Coolant Accident induced by a double-ended guillotine break in the Direct Vessel Injection line. This study utilizes the system thermal–hydraulic code MARS-KS moving reactor model considering various tilting conditions and a BANDI-60 nodalization with a quarter-divided reactor pressure vessel and containment vessel volumes in the circumferential direction. The inclination conditions include static inclination along the x and y directions. Significantly, static inclination, particularly when the break aligned downward with the inclination direction, emerged as the most critical condition affecting reactor core integrity. Additionally, the containment vessel volume affects the equilibrium pressure after a break occurs, with smaller volume resulting in smaller peak cladding temperature values in static inclined conditions.

An innovative dry-lab test rig for mechanical-hydraulic power take-off of wave energy conversion system

A dry-lab test rig is a powerful means to reduce costs in the design process of a wave energy conversion system (WECs). A dry-lab test rig technique allows the use of real components inside a simulation of a mathematical model. This paper presents the development of an innovative dry-lab test rig for the mechanicalhydraulic power take-off (MHPTO) unit of WECs. The development of a drylab test rig of MHPTO involves several processes, such as three-dimension (3D) modelling, component purchasing, structure fabrication, component installation, and operational testing. The developed dry-lab test rig consists of two main parts, such as the simulated wave emulator plant and the real MHPTO unit plant. The simulated wave emulator plant was developed in this test rig to replicate the interaction motion between the ocean wave motion and the wave absorber device. The developed dry-lab test rig was tested using five different irregular wave input conditions to ensure it could perform under the five different wave input conditions. The overall results demonstrate that the developed dry-lab test rig was successfully performed in all sea states. From the results, the profile of electrical power produced by the real MHPTO unit can be clearly obtained in each sea state.

REPRESENTATION OF A NON-STATIONARY MODEL OF BAROCLINIC OCEAN MOTION USING THE FICTITIOUS DOMAIN METHOD

This paper presents a groundbreaking non-stationary model, intricately crafted using the fictitious domain technique, to delve into the complex dynamics of baroclinic ocean motion. This study marks a significant leap in our understanding of water mass interaction, shedding light on the profound impact of temperature and salt gradients on sea currents.The methodology uses modified Navier-Stokes equations for viscous, incompressible flow, considering advection, diffusion, and Coriolis force.The results of this study underscore the immediate and tangible implications of our research. The solutions unveiled the pivotal role of pressure and temperature differentiation in the genesis of ocean currents. The analysis demonstrated that by integrating nonlinear terms and detailed modeling of initial and boundary conditions, we can markedly improve the precision of water mass movement forecasts. This work underscores the urgent necessity for further research into dynamic ocean modeling to enhance our ability to predict climate change.This article introduces truly innovative approaches to numerical modeling, which hold immense potential for the future of the field. These approaches have the power to transform existing models of sea currents and pave the way for the development of more efficient methods for monitoring and predicting the state of the marine environment.

Dynamic 3-D Visualization System of Sea Flow Field Based on Virtual Reality Technology in the Environment of Internet of Things

Abstract Ocean 3-D dynamic visualization is a method to analyze the law of ocean motion by processing complex and changeable ocean data by importing and visualizing. Through 3-D visualization design, the ability to analyze and reconstruct 3-D visualization characteristics of sea area flow field can be improved. To improve the 3-D dynamic visualization effect of ocean flow field and reveal the law of ocean motion, this paper designs a 3-D dynamic visualization system of ocean flow field based on virtual reality technology. Firstly, the framework of the dynamic 3-D visualization system of sea area flow field was designed. On the basis of defining the system development environment, the system software was developed and designed from the aspects of information acquisition module, database model, 3-D reconstruction module, visual simulation module, etc. So far, the design of the 3-D dynamic visualization system of sea area flow field was realized. The simulation results show that the output stability of the design system is good, the visualization ability is strong, and it has certain application values.

Theoretical study on pressure oscillation dominant frequency of bubbles submerged jet under rolling condition

Steam direct contact condensation is a highly efficient heat and mass transfer phenomenon, usually accompanied by strong mass, momentum and energy exchanges at the water-steam interface, which can rapidly realize cooling and pressure relief, but also accompanied by pressure oscillations. When the relevant equipment is used in offshore nuclear power plants and naval non-energetic systems, the additional inertial force field caused by ocean motion may cause greater harm to the safe operation of the relevant devices. Therefore, a theoretical study is conducted to investigate the effect of rolling motion on dominant frequency of steam submerged jets pressure oscillation with low mass fluxes. Firstly, based on bubble dynamics theory, a theoretical model of bubble condensation oscillations under rolling motion with low mass flux is established. Then, the mechanism of the rolling conditions on the dominant frequency of pressure oscillation is analyzed from the aspect of theoretical derivation. Finally, on the basis of the potential flow function theory and small perturbation theory, the predicted correlation of pressure oscillation dominant frequency under the rolling motion with low mass flux is derived, and compared with the numerical simulation results, the prediction deviation is within ±10%.

Heat transfer behaviors in corium pools under swinging conditions

As an effective severe accident mitigation strategy, in-vessel retention (IVR) of molten corium is one of key research objects in the realm of nuclear safety analysis. However, relevant studies on this topic are currently very limited for ocean floating reactors (OFRs), which are inevitably influenced by ocean motion conditions. Thus, in this paper, both experimental and numerical study were performed on the heat transfer behaviors in corium pools under swinging conditions for OFRs. Experimental results showed that swinging motions generally weakened the thermal stratification in the liquid region of corium pools. When swinging motions were intense enough, the dimensionless temperature decreased by 7.1 % at the top of corium pool, while it increased by 30.7 % at the bottom. Accordingly, remelting of the solid crust at the bottom was found in this case. Moreover, a surge of heat flux was observed in the middle and upper parts of corium pool contacting the vessel wall soon after swinging motions started. The peak heat flux could be about 2.57 times higher than that before the starting of swinging motion. But in the stable state of swinging motions, thermal focusing effect was alleviated by more than 18 % within the test conditions. Based on the numerical simulation, the convection inside corium pools was enhanced under swinging conditions, with the bulk flow velocity reaching the magnitude of 1 cm/s. Additionally, high heat flux was mainly concentrated in the symmetric two directions perpendicular to the axis of swinging motion in the free surface nearby region. The peak heat flux ratio was about 2.3 in the azimuth angle 0° and 180°, 25.7 % higher than that in the azimuth angle 90° and 270°. This work is supposed to provide valuable references to evaluate the safety designs for ocean floating reactors during postulated severe accidents.

Ocean-Current-Motion-Model-Based Routing Protocol for Void-Avoided UASNs

An increasing number of scholars are researching underwater acoustic sensor networks (UASNs), including the physical layer, the protocols of the routing layer, the MAC layer, and the cross-layer. In UASNs, the ultimate goal is to transmit data from the seabed to the surface, and a well-performed routing protocol can effectively achieve this goal. However, the nodes in the network are prone to drift, and the topology is easily changed because of the movement caused by ocean currents, resulting in a routing void. The data cannot be effectively aggregated to the sink terminal on the surface. Thus, it is extremely important to determine how to find an alternative node as a relay node after node drift and how to rebuild a reliable transmission path. Although many relay routing protocols have been proposed to avoid routing voids, few of them consider the relay node selection between the outage probability and the ocean current model. Therefore, we propose an ocean current motion model based routing (OCMR) protocol to avoid the routing void in UASNs. We predicted underwater node movement based on the ocean current motion model and designed a protection radius to construct a limited search coverage based on the optimal outage probability; then, the node with the best fitness value within the protection radius was selected as the alternative relay node using an improved WOA. In OCMR, the problem of the routing void caused by ocean current motion is effectively suppressed. The simulation results show that, compared with VBF, HH-VBF, and QELAR, the proposed OCMR platform performs well in terms of the PDR (packet delivery ratio), average end-to-end delay, and average energy consumption.

Analysis of coolant flow distribution characteristics at core inlet of small pressurized water reactor under rolling condition

The flow distribution characteristics at core inlet directly determines the thermal and hydraulic characteristics in the core, and it is closely related to the safety of nuclear reactor. The primary coolant is subjected to additional inertial force in ocean motion, which influence the flow distribution characteristics at core inlet. In the present paper, numerical simulation method is adopted to analyze the coolant flow distribution characteristics at core inlet of the Reactor Pressure Vessel (RPV) of a Small Reactor under rolling condition. Then the results of the flow distribution characteristics were compared with those under steady state. The results show the variation range of flow distribution factors in each channel under rolling condition is within 5%. And the uneven distribution of coolant at the core inlet increases with the increase of rolling amplitude, and decrease with the rolling period in short period. Standard deviation of flow distribution factor at the core inlet changes little under rolling condition, which indicates the flow distribution at the core inlet keeps good uniformity.

A Dynamic Coupling of Ocean and Plate Motion

A Dynamic Coupling of Ocean and Plate Motion

SBLOCA analysis of a floating nuclear reactor under ocean conditions using MARS-KS moving reactor model

With increasing demands to reduce greenhouse gas emissions from the maritime industry, nuclear power has emerged as a potential solution. Among these options, offshore floating reactors have been demonstrated and developed by various organizations and countries. The offshore floating reactors offer advantages such as a long refueling period for enhanced safety and high mobility, enabling access to remote areas. However, when operating on a moving platform, offshore floating reactors are exposed to external forces that can affect the thermal-hydraulic properties within the reactor core and various hydraulic components. To address the safety concerns associated with offshore floating reactors, evaluating their thermal-hydraulic performance under different ocean motions is necessary. Therefore, this study focused on conducting accident analyses in an offshore floating reactor called BANDI-60, specifically investigating a Small Break Loss of Coolant Accident caused by a double-ended guillotine break in the Direct Vessel Injection line using the system analysis code MARS-KS. Various ocean conditions were considered, including static inclination, combined inclination with heaving, and rolling motion. Among these conditions, static inclination, especially when the break was aligned downward with the inclination direction, was identified as the most significant factor affecting the integrity of the reactor core.

Satellite Velocity Correction Method of Ocean Current Retrieval for a Spaceborne Doppler Scatterometer

For a spaceborne pencil-beam rotating Doppler scatterometer, its precision in measuring the ocean surface motion depends on the Doppler centroid of the received signals. The Doppler centroid is determined by the relative motion between the scatterometer and the ocean surface. This relative motion includes contributions from satellite velocity, the phase velocity of resonant Bragg waves, the orbital motions of ocean waves, and the ocean surface current. Subtracting the contribution of the satellite platform velocity from the complex Doppler information is important for the application of a spaceborne Doppler scatterometer in ocean surface current retrieval. In this research, we propose a method for the platform velocity correction influenced by the Doppler centroid offset and analyze the accuracy of this correction method. The method is based on the echoed signal model of a Doppler scatterometer. Our results show that the offset could lead to a measurement offset of up to 0.02 m/s when the beam width was 0.3°. For a 0.6° beam width, the maximum offset was 0.07 m/s. Thus, with the high accuracy of the current spaceborne sensors’ measurement, the offset can be accurately eliminated. In future applications and data processing algorithms, this effect should be considered.

On the Quartic Korteweg–de Vries hierarchy of nonlinear Rossby waves and its dynamics

A long-standing challenge in exploring the dynamics of large-scale atmospheric or oceanic motions is to find more appropriate theoretical models. This paper aims at the mechanisms of nonlinear Rossby waves by a new obtained nonlinear evolutionary equation hierarchy approach. The multiple scales method and weak nonlinear perturbation method are adopted based on the quasi-geostrophic potential vorticity conservation law for large scale atmospheric or oceanic motions. It is the first time that a Quartic Korteweg–de Vries model equation is derived to describe the propagation of nonlinear Rossby waves amplitude, which provides a new acceptable theoretical model for the study of atmospheric blocking phenomena. Qualitative and quantitative analysis for the new Quartic KdV model are finished to disclose the evolutionary mechanisms of nonlinear Rossby waves. The corresponding results declares that the β effect, topographic features and detuning parameter are all important factors on the nonlinear Rossby waves.

Kinetic Energy Exchanges between a Two-Dimensional Front and Internal Waves

Abstract Fronts and near-inertial waves (NIWs) are energetic motions in the upper ocean that have been shown to interact and provide a route for kinetic energy (KE) dissipation of balanced oceanic flows. In this paper, we study these KE exchanges using an idealized model consisting of a two-dimensional geostrophically balanced front undergoing strain-induced semigeostrophic frontogenesis and internal wave (IW) vertical modes. The front–IW KE exchanges are quantified separately during two frontogenetic stages: an exponential sharpening stage that is characterized by a low Rossby number and is driven by the imposed strain (i.e., mesoscale frontogenesis), followed by a superexponential sharpening stage that is characterized by an Rossby number and is driven by the convergence of the secondary circulation (i.e., submesoscale frontogenesis). It is demonstrated that high-frequency IWs quickly escape the frontal zone and are very efficient at extracting KE from the imposed geostrophic strain field through the deformation shear production (DSP). Part of the extracted KE is then converted to wave potential energy. On the contrary, NIWs remain locked to the frontal zone and readily exchange energy with the ageostrophic frontal circulation. During the exponential stage, NIWs extract KE from the geostrophic strain through DSP and transfer it to the frontal secondary circulation via the ageostrophic shear production (AGSP) mechanism. During the superexponential stage, a newly identified mechanism, convergence production (CP), plays an important role in the NIW KE budget. The CP transfers KE from the convergent ageostrophic secondary circulation to the NIWs and largely cancels out the KE loss due to the AGSP. This CP may explain previous findings of KE transfer enhancement from balanced motions to IWs in frontal regions of realistic ocean models. We provide analytical estimates for the aforementioned energy exchange mechanisms that match well the numerical results. This highlights that the strength of the exchanges strongly depends on the frontal Rossby and Richardson numbers. Significance Statement Fronts with large horizontal density and velocity gradients are ubiquitous in the upper ocean. They are generated by a process known as frontogenesis, which is often initialized by straining motions of mesoscale balanced circulations. Here we examine the energy exchanges between fronts and internal waves in an idealized configuration, aiming to elucidate the mechanisms that can drain energy from oceanic balanced circulations. We identify a new mechanism for energy transfers from the frontal circulation to near-inertial internal waves called convergence production. This mechanism is especially effective during the later stages of frontogenesis when the convergent ageostrophic secondary circulation that develops is strong.

Machine Learning Provides a Clearer Window into Ocean Motion

A new method could translate satellite information about sea surface heights into insights on current, heat flow, and—ultimately—climate change.

Fatigue damage assessment methodology for a deepwater subsea wellhead based on monitoring data

ABSTRACT Deepwater subsea wellhead system is subjected to the various cyclic loads transmitted from the drilling riser due to ocean waves, currents and platform motion during drilling operation; therefore, the fatigue damage is accumulated. A fatigue damage assessment methodology and its detailed analysis procedure for subsea wellheads utilising transfer function theory based on monitoring acceleration data at the drilling riser are developed. Studies on an actual monitoring case for a subsea wellhead under drilling operation with 336 h of monitoring events are conducted and a verification method by comparison of the measured fatigue results and predicted fatigue results based on wave and current data are introduced. The results for wave and vortex-induced vibration (VIV) fatigue life based on measured acceleration data are calculated, and the fatigue bias with predicted results are summarised. The developed fatigue damage assessment method and monitoring case studies can be valuable references for deepwater drilling engineering.