Oceanic Motions Research Articles

An investigation of characteristics of flow and heat transfer in the two-layer molten pool under swing motion condition

In-Vessel Retention (IVR) of molten corium is an important strategy for management of severe accidents adopted by some active service generation II plus reactors and advanced generation III reactors like AP1000, Hualong one and APR1400. One of the most important factors contributing to IVR analysis can be attributed to the characteristics of heat transfer in the molten pool in the lower head of reactor pressure vessel (RPV), which directly determines the heat load imposed on the vessel wall of the RPV lower head. Besides, IVR is also an important strategy for management of severe accidents of Ocean Floating Reactor (OFR), whose flow and heat transfer characteristics are influenced by the ocean motion conditions. However, since all previous molten pool experiments were conducted under static condition, characteristics of the heat transfer in the molten pool thus obtained may be different from those under ocean motion conditions, thus not applicable to the latter. To address this issue, in this study, an experimental system was established, which includes a two-layer molten pool test facility and a swing motion platform. Based upon the system, the effects of the swing angle and swing period on the characteristics of heat transfer in the two-layer melt pool were investigated. In addition, a scaling method was proposed to select simulant materials for the two-layer corium pool. Results of the experiment show that the swing period and angle have a significant effect on the temperature field of the molten pool and the rate of heat transfer. We thus suggest that, in future studies, new heat transfer correlations, models and IVR analysis method for ocean floating reactors should be researched and developed to evaluate the IVR design of ocean floating reactors, which is critical for management of severe accidents of the ocean floating reactors.

Experimental study of pool boiling heat transfer under rolling condition

Many heat exchangers inside ocean nuclear power plants (ONPPs) adopt pool boiling, and the additional inertial forces derived from complicated ocean motion will induce some unique thermohydraulic characteristics, which are still remaining to be further elucidated. In this paper, effects of rolling condition on pool boiling heat transfer are experimentally investigated by using the six-freedom platform. The variation of inertial forces during rolling periods are analyzed, and observations of bubble unique behaviors about nucleation, growth, coalescence, departure and wagging under rolling condition are implemented to verify the rolling effects on pool boiling heat transfer. The results show that rolling motion enhances pool boiling in both regions of natural convection and nucleate boiling. Maximum 23.9 % higher heat transfer coefficient (HTC) and 8.1 % higher critical heat flux (CHF) are obtained under rolling condition with amplitude A = 26° and period tp = 5 s. Bubble nucleation is improved by the rolling motion, which decreases the superheat degree at onset of nucleate boiling (ONB) and increases the nucleation site four times at this moment. Small bubbles grow and coalesce more drastically under rolling condition, and bubble departure is accelerated, with 11 %–19 % reduction of departure diameter and 23 %–32 % increase of departure frequency. This work can not only present fundamental mechanism for pool boiling heat transfer under rolling condition, but also serve as useful guidelines for designing pool boiling heat exchangers inside ONPPs.

Marine Drifting Trajectory Prediction Based on LSTM-DNN Algorithm

In this paper, the long short-term memory with dense neural network (LSTM-DNN) is first introduced to calculate marine drifting trajectory. Based on the Internet of Things technology and the LSTM-DNN algorithm, the marine drifting trajectory model is established. In this model, the information such as wind field, temperature field, ocean current motion field, and target attributes are included, and the influences of the above information on the trajectory model are studied in detail. In order to verify the proposed model, the marine experiments are carried out in the end. The results show that the predicted trajectory data matches well with the experimental trajectory data. By introducing DNN into the algorithm, computational accuracy of drifting trajectory can be significantly improved compared with the conventional LSTM-based prediction model. A detailed comparison of the two algorithms has also been given in the paper. The proposed remote sensing of marine drifting trajectory model can provide a high accurate trajectory prediction and will lead an important guidance in the marine search and rescue work.

Experimental study on thermal performances of flat-plate pulsating heat pipes under static and swing conditions

Pulsating heat pipe (PHP), as an efficient heat transfer component, can be used for waste heat recovery and electronic cooling. The influences of typical ocean motions, such as inclination and swing, on thermal performances of PHPs are inevitable for practical offshore applications. In this study, surfactant-free functionalized multi-walled carbon nanotubes (f-MWCNTs) nanofluids with long-term stability were prepared. Thermal performances of PHP with f-MWCNTs nanofluids and mixed fluids under static and swing conditions were comparatively investigated. Results indicate that 0.25 mg/ml f-MWCNTs nanofluids (base fluid, 1:1 ethanol-DI water) shows the lowest thermal resistance among all working fluids. Thermal performances of flat-plate PHP with ethanol-DI water mixed fluids are better than that of ethanol-based f-MWCNTs nanofluids, and HFE-7100-DI water mixed fluids are more suitable for performance enhancements at the lower heat loads. As for effects of swing motion, the increased swing amplitudes and decreased swing periods will reduce thermal performances. In the worst case, swing motions can reduce thermal performances by 5.85%. Moreover, frequencies of temperature difference fluctuations increase with the decrease of swing periods. Although the change of swing amplitudes has a certain effect on frequencies and amplitudes of temperature difference fluctuations, but the influence seems negligible as well. These results can be used to guide practical offshore applications of PHPs.

Comparison and optimization of heat transfer models in reactor channel under the rolling condition

The convective heat transfer characteristics of reactor system under ocean condition affect the reliability and safety of its operation. The modification of system code applied to marine reactor mainly focuses on momentum equation and geometry position, but rare of improvement on heat transfer model. Therefore in this paper, a series of single-phase flow experiments in circular and rectangular channels under ocean motion are summarized. Then the related heat transfer models are analyzed and compared with experiment data. The results show that the existing models have limited application in different intervals of Reynolds Number. In order to optimize the heat transfer model, time average and pulsation amplitude of Nusselt number is taken into consideration and modified based on mechanism and best fit of existing experiments.

Interpreting consequences of inadequate sampling of oceanic motions

AbstractInadequate sampling of oceanic motions, which commonly occurs for both oceanic measurements and simulations, can cause peculiar spectral features and potentially leads to misinterpretations. Here, we combine an extremely high‐frequency moored velocity record and a high‐resolution numerical simulation with the basic signal‐processing theory to quantitatively explore how varying sampling rates affect the ability to represent oceanic motions, especially internal gravity waves (IGWs). The moored measurements and simulations demonstrate that hourly sampling is sufficient to capture horizontal internal tidal velocities, but inadequate to faithfully characterize the vertical velocity for nearly all frequencies. The daily‐sampled model simulation shows a complicated frequency‐wavenumber spectral pattern of IGWs. Due to contrasting periodicities in time and space, temporal subsampling tends to retain the total variance of original IGWs, while spatial subsampling directly induces spectral energy loss. This study sheds light on data applications of the upcoming satellite altimetry missions.

Bi‐Directional Energy Cascades in the Pacific Ocean From Equator to Subarctic Gyre

AbstractOcean circulation receives its energy input at basin scales while dissipates at microscopic mixing scale. How this energy is transferred across different lengthscales is of paramount importance for understanding the ocean circulation equilibration and variability. Advancement in high‐resolution numerical simulations in recent years has significantly improved our understanding of kinetic energy (KE) cascades from basin to kilometer scales, although observational evidence to verify the simulated processes remains limited. Using repeat ship‐board velocity measurements along 165°E across the equatorial, subtropical and subarctic Pacific Ocean, we show that the length scale separating the inverse and forward cascades, LS, falls in the 8 ∼ 300 km range and it does not scale straightforwardly with the baroclinic deformation radius. Balanced and unbalanced oceanic motions co‐exist in this range but contribute oppositely to the directional energy cascades. LS is observed to depend on the relative strengths of these motions, as well as by their interaction.

A Characteristics Set Computation Model for Internal Wavenumber Spectra and Its Validation with MODIS Retrieved Parameters in the Sulu Sea and Celebes Sea

The quasi-linear or nonlinear interactions among different ocean motions dominate the system internal structure and appearance feature presented in spatial and temporal evolution. However, deficiency of the characteristics set computation model for internal wavenumber spectra proves to be a serious barrier to derive interaction mechanisms of internal waves with large or small scale ocean motions. In this study, a characteristics set computation model for internal wavenumber spectra is proposed for complicated offshore environments. The refraction of current shear instability, bottom topography and the reflection at surface and bottom are attentively considered in the complicated characteristics inlaid scheme. Model results are validated with MODIS retrieved internal wave parameters in the Sulu Sea and Celebes Sea. This original characteristics set computation model for internal wavenumber spectra can be used widely and can further improve the understandings of generation, dissipation, nonlinear wave-wave interaction and mixing process of internal waves.

Interdecadal Modulation of ENSO‐Related Anomalous Equatorial Intermediate Currents in the Western Pacific by the PDO

AbstractAs the most prominent decadal variability in the Pacific Ocean, the Pacific Decadal Oscillation (PDO) can influence the El Niño‐Southern Oscillation‐related atmospheric and upper oceanic motions. Based on results from ocean reanalysis products and linear continuously stratified model experiments, we reveal that the PDO can further extend its interdecadal modulation effect to the equatorial intermediate currents below the thermocline. For the maximum El Niño‐related intermediate eastward transport anomaly in the western Pacific, its magnitude during the warm PDO is nearly twice as large as that during the cold PDO, and its occurrence time in the warm PDO leads that in the cold PDO by about 2 months. Such modulation is achieved through westward and downward propagation of the reflected Kelvin‐to‐Rossby waves, triggered by enhanced and eastward‐displaced anomalous westerly wind. The decisive wind forcing region for the modulation is located over the equatorial central Pacific of 5°S–5°N and 180°–140°W.

Structured pathways in the turbulence organizing recent oil spill events in the Eastern Mediterranean

The chaotic nature of ocean motion is a major challenge that hinders the discovery of spatio-temporal current routes that govern the transport of material. Certain material, such as oil spills, pose significant environmental threats and these are enhanced by the fact that they evolve in a chaotic sea, in a way which still nowadays is far from being systematically anticipated. Recently such an oil spill event has affected the Mediterranean coast of several Middle Eastern countries. No accidents were reported for these spills previous to their arrival at the coast, and therefore there was no hint of their origin. Modelling such an event, in which uncertainties are increased due to the lack of information on where and when the spills was produced, stretches available technologies to their limits, and requires the use of novel ideas that help to understand the essential features of oil and tar transport by ocean currents. In this regard Lagrangian Coherent Structures enable us to find order within ocean chaos and provide powerful insights into chaotic events and their relationships over different locations and times like the one addressed. Using the observed locations of the oil impacting the coast at specific times, we seek to determine its original location and the time it was released in the open ocean. We have determined both using a combination of earlier satellite observations and computational modelling of the time evolution. The observed agreement between modeled cases and satellite observations highlights the power of these ideas.

Parametric analysis of hybrid tribo-piezoelectric energy harvester

Energy harvesters are widely used in various fields for environmental energy harvesting purposes. Due to the less power output of a single energy harvester, researchers are working on hybridizing energy harvesters. This paper presents a hybrid model of d33 mode piezoelectric energy harvester (PEH) and vertical contact mode triboelectric energy harvester (TEH). A Polyvinylidene fluoride (PVDF) composite film is used for the PEH unit, and a Polydimethylsiloxane (PDMS) composite film is used for the TEH unit. The effect of various design parameters like material, structural and experimental parameters are numerically investigated for a periodic motion of hybrid tribo- piezoelectric energy harvester (HTPEH). A genetic algorithm has been used to maximize the harvested energy. This study will help design the prototype of HTPEH according to applications. The HTPEH can generate a significant amount of energy which can be helpful in the applications like designing self-powering electronic devices, robotics, sensors, and harvesting the vibration energy from human, wind, or ocean motion.

Optimal Precursors Identification for North Atlantic Oscillation Using the Parallel Intelligence Algorithm

The North Atlantic Oscillation (NAO) with abnormal sea level pressure (SLP) differences influence the westerly wind strength and storm tracks in the North Atlantic, which further affects the winter climate in the northern hemisphere. The predictability of NAO has become an important area of climate research in recent years. The identification of optimal precursors (OPRs) would help to investigate the dynamics of atmospheric and oceanic motions, as well as the nonlinear characteristic. The conditional nonlinear optimal perturbation (CNOP) method has been widely used in research on the OPR of the climatic event to explore which kind of initial perturbation is most likely to trigger climate events. However, the previous works on NAO’s OPR are based on a simple ideal model, which cannot describe the evolution process of NAO. Moreover, the commonly used algorithms that rely on the adjoint model are not suitable for the large complicated numerical models that do not have corresponding adjoint models, like Community Earth System Model (CESM). To break through the limitation, this paper proposes the parallel principal component analysis (PCA)-based particle swarm optimization (PSO) and genetic algorithm (GA) hybrid algorithm (PGAPSO) algorithm to identify the OPR of NAO using CESM. For different initial conditions, OPRs identified by the proposed method can always make the basic state develop into NAO events with corresponding phases. Compared with other adjoint-free approaches, the proposed method has relatively better fitness values and more mature patterns. The results also reveal that the proposed method can avoid falling into a local optimum and has strong robustness. In terms of performance, the proposed method searches in feature space with a much lower number of dimensions, thus improving efficiency. In addition, the proposed method is accelerated with multiple parallel frameworks to enhance performance, and it achieves the speedup ratio of 40.2.

Effect of rolling motion with large radius on flow and heat transfer characteristics of supercritical methane in a mini channel

• Rolling results in the violent fluctuation of flow and heat transfer in supercritical methane. • Additional force along the flow direction is the key to affect the flow and heat transfer. • Hysteresis exists in the coupling of rolling, flow fluctuation and temperature fluctuation. • Rolling produces greater fluctuation in the near-wall area than that in the inner center area. The offshore floating storage and regasification unit (FSRU) is developing rapidly as a new type of storage and gasification system for liquefied natural gas (LNG), and the heat transfer and system stability of offshore LNG vaporizers are greatly affected by ocean rolling. To reveal the regular pattern and mechanism of supercritical methane heat transfer performance under ocean motion, this research numerically studied the flow and heat transfer characteristics of supercritical methane in a 1 × 1 × 100 mm mini channel under the additional inertial force by large radius rolling. Based on the non-inertial coordinate system, the normal inertial acceleration, radial inertial acceleration and Coriolis inertial acceleration were considered. Moreover, Nusselt number, degree of fluctuation and friction factor were investigated. The ranges of Reynolds number and Nusselt numbers are 15,000 to 45,000 and 35 to 130 respectively. The results show that the Nusselt number and friction factor violently fluctuate under rolling motion, and the fluctuation period is similar to the rolling period. Besides, the fluctuation degree of Nusselt number is greater than that of friction factor, and the largest fluctuation degree of Nusselt number is 27.9%. The effect of the fluctuation increases with the decrease of the rolling period and the increase of the rolling amplitude. Hysteresis exists in the coupling of rolling, flow fluctuation and temperature fluctuation. In addition, the degree of fluctuation is reduced with the increase of fluid temperature and mass flux. For the effect of rolling, the additional force in the mainstream direction plays a leading role. Besides, the influence of radial force is greater than that of normal force for horizontal flow condition.

Kelp inspired bio-hydrogel with high antibiofouling activity and super-toughness for ultrafast uranium extraction from seawater

Highly efficient extraction of uranium from seawater is vital for meeting the growth demands of uranium resources for the development of nuclear energy industry. However, currently available uranium adsorbents encounter multiple challenges, including the ultralong extraction period, severe marine biofouling, and violent impact of ocean motions. Targeting on these challenges and inspiring by the high tolerance of kelp to marine biofouling and motions, a kelp inspired super-toughness (KIST) bio-hydrogel is fabricated for uranium extraction from seawater. The hydrogel KIST is prepared by compositing the biofriendly and low-cost bacterial cell debris with polyvinyl alcohol, making the KIST hydrogel possesses high environment friendly. Attributing to the fast uranium adsorption rate of the bacterial cell debris, the KIST hydrogel realizes a uranium extraction capacity of 1.18 mg g−1 in biofouling-containing natural seawater with an ultrafast equilibrium adsorption time of 28 h, which is the shortest among all available uranium adsorbents in natural seawater. The antimicrobial activity of the bacterial cell debris empowers KIST hydrogel with as high as 99.21% inhibition rate to the growth of a broad range marine biofouling microorganisms, including the marine bacteria and marine algae. The KIST hydrogel also possesses outstanding tensile ability, flexibility, and rheological property, endowing the hydrogel with high resistance to the ocean current. Taking into consideration these advantages, the KIST hydrogel would be a promising adsorbent for practical uranium extraction.

Effects of ocean turbulence on photon orbital angular momentum quantum communication

The effect of the turbulent motion of ocean on the quantum communication based on the orbital angular momentum in an underwater quantum channel is studied in this work. Based on the power spectrum model of ocean turbulence proposed by Elamassie, the quantitative relationships of different ocean turbulence parameters with the single photon detection probability of orbital angular momentum photons, the channel capacity, the key generation rate, the concurrence of two entangled photons are proposed. The maximum entanglement distance of the orbital angular momentum entangled photon-pairs in the ocean turbulence is further studied by the universal entanglement decay of the concurrence of entangled photon-pairs in the ocean turbulence. The results show that the detection probability of single photon, the channel capacity, the key generation rate, and the concurrence of entangled photon-pairs decrease with the increase of the dissipation rate of turbulent kinetic energy and the decrease of the rate of dissipation of mean-squared temperature. The influence of the temperature and salinity balance parameter of ocean turbulence on the performance of underwater quantum communication are significantly different under the condition of whether the stable stratification of seawater is assumed or not. In the ocean turbulent environment, the increasing of the initial orbital angular momentum quantum number of signal photons can improve the key generation rate of quantum key distribution and the resistance of entangled photons to entanglement decay.

Flow and Heat Transfer of Supercritical CO2 in a Vertical Tube Under Ocean Rolling Motion

Abstract This paper explores the fluid flow and heat transfer behaviors of supercritical carbon dioxide (SCO2) in a tube. The application is utilization of waste heat from a marine gas turbine. The effects of ocean rolling motion on the thermofluid characteristics of SCO2 in a circular tube are numerically investigated based on a verified turbulence model. It is found that the time-averaged heat transfer capacity over a rolling period is improved over static conditions by 7.9%. However, the onset of heat transfer recovery is postponed, and the range of heat transfer deterioration is extended. Under the action of inertial forces due to the rolling motion, heat exchange between cooler/denser and warmer/lighter fluids is enhanced. Secondary circulation is formed when t/tc = 0.325, and the section-averaged heat transfer coefficient is improved by a maximum of 71%. For various periods, a parabolic can be distinctly found in terms of the variation trend of time-averaged heat transfer coefficient, which behaves differently from conventional fluids. Regarding the instantaneous thermal performance, a polarization phenomenon can be observed under severe rolling. With the rise of the layout height, the time-averaged heat transfer performance of the tube increases monotonously, and the maximum increment is 10.64% in studied range.

Tracking deep-sea internal wave propagation with a differential pressure gauge array

Temperature is used to trace ocean density variations, and reveals internal waves and turbulent motions in the deep ocean, called ‘internal motions.’ Ambient temperature detected by geophysical differential pressure gauges (DPGs) may provide year-long, complementary observations. Here, we use data from four DPGs fixed on the ocean bottom and a high-resolution temperature sensor (T-sensor) 13 m above the seafloor as a square-kilometer array deployed offshore ~ 50 km east of Taiwan facing the open Pacific Ocean to examine the impact of temperature on DPG signals related to internal motions. The DPG signals correlate with T-sensor temperature variations between 0.002 and 0.1 mHz, but have time shifts partially caused by slow thermal conduction from the ambient seafloor to the DPG chamber and partially by internal motion propagation time across the array. Applying beamforming-frequency-wavenumber analysis and linear regression to the arrayed T-sensor and DPG data, we estimate the propagating slowness of the internal motions to be between 0.5 and 7.4 s m−1 from the northwest and northeast quadrants of the array. The thermal relaxation time of the DPGs is within 103–104 s. This work shows that a systematic scan of DPG data at frequencies < 0.1 mHz may help shed light on patterns of internal wave propagation in the deep ocean, especially in multi-scale arrays.

Impact of Different Wind Representations on Resonant Ocean Near-inertial Motions in the Gulf of Mexico

This study investigates the resonated diurnal impact of the surface wind forcing from several atmospheric wind products, including CCMP (Cross-Calibrated Multi-Platform), ERA Interim, NCEP-2 (NCEP-DOE AMIP-II Reanalysis), MERRA (Modern-Era Retrospective analysis for Research and Application), NARR (Northern American Regional Reanalysis) and NAM (North American Mesoscale Forecast System), on the wind-driven near-inertial ocean motions in the northern Gulf of Mexico by numerical simulation, and in comparison, with NDBC buoy surface observed winds. Our analyses show that the near-inertial wind power input, which can affect vertical mixing in the water column, is closely associated with the variability of land-sea breeze by various wind products. In comparison with buoy observations in the northern Gulf of Mexico, the MERRA has the worst land-sea breeze representation, while the NCEP2 and CCMP, which are chosen to represent the coarsest and medium–high horizontal resolution, have the best performance. We further show that by comparison of the buoy data, that the near-inertial wind power input derived from all the wind products is underestimated by 30–50% approximately.

Ocean mass, sterodynamic effects, and vertical land motion largely explain US coast relative sea level rise

Regional sea-level changes are caused by several physical processes that vary both in space and time. As a result of these processes, large regional departures from the long-term rate of global mean sea-level rise can occur. Identifying and understanding these processes at particular locations is the first step toward generating reliable projections and assisting in improved decision making. Here we quantify to what degree contemporary ocean mass change, sterodynamic effects, and vertical land motion influence sea-level rise observed by tide-gauge locations around the contiguous U.S. from 1993 to 2018. We are able to explain tide gauge-observed relative sea-level trends at 47 of 55 sampled locations. Locations where we cannot explain observed trends are potentially indicative of shortcomings in our coastal sea-level observational network or estimates of uncertainty.

Study on LOFA and LOHS Accidents with Passive Safety System for Integrated Marine Reactor

To simulate the complex accident phenomena of a marine reactor, the thermal-hydraulic system code RELAP5 is modified to perform the analysis under ocean conditions. An integrated reactor with a passive residual heat removal system (PRHRS) is modeled by the improved code, and the effects of different ocean motions under a total loss-of-flow accident (LOFA) and a loss-of-heat-sink (LOHS) accident are analyzed with respect to safety characteristics. The results indicate that for LOFA, the primary loop can form an effective natural circulation to cool the core, and for LOHS, the PRHRS can effectively remove the residual heat from the core to ensure the core safety. The results also show that heaving motion accelerates the drop of the first-loop temperature and enhances the heat transfer capacity of the PRHRS. Inclining motion reduces the natural circulation flow in the core. A rolling condition causes fluctuations in the mass flow rate, the variations of which are not strictly sinusoidal, and increasing the rolling period also improves the heat exchange capacity of the PRHRS.