Oceanic Motions Research Articles

Research on thermal hydraulic characteristics of integrated reactor in natural circulation operation under ocean motions

The modified one-dimensional thermal hydraulic program RELAP5/MOD3.3 was developed to simulate the natural circulation characteristics of an integrated reactor. The ocean motions were realized by adding additional acceleration in the source term of momentum equation. The pressure drop and heat transfer correlations of helically coiled tubes were adopted. The effect of natural circulation characteristics on integrated reactor was studied under rolling, heaving and inclined motions. Simulation results show that the core inlet temperature has no significant change under those three ocean conditions. The average fluctuation value of core mass flow rate is less than the steady-state value and decreases with the increasing rolling angle under the rolling motion. Besides, critical period was observed. In the heaving motion, the average fluctuation value of core mass flow rate is equal to the steady-state value which is different from the rolling motion. The steam equilibrium quality changes slightly in different heaving acceleration. In the inclined condition, the core mass flow rate is decreased with the increasing inclined angle and excessive inclined angle will cause the steam unsuperheated and this may affect the performance of the turbine.

Effect of single and combined ocean motions on a small OFNP under SBO accidents

In view of the safety characteristics of the offshore floating nuclear plant (OFNP), an ocean condition available analysis code based on RELAP5 MOD3.3 is developed and the influences of single heaving, single rolling and combined motion of heaving and rolling on a OFNP were analyzed under station blackout accident (SBO). The results indicate that heaving motion accelerates the drop in the reactor pressure. The flow fluctuation caused by heaving motion promoted the derivation of residual heat after SBO; Rolling motion accelerates the declination of the reactor pressures and the coolant temperature after SBO, and also causes a large flow oscillation in pipes. The results also shows that the combined motion is more severe than these two single conditions. The parameters variation under the combined motion is more similar to that under its rolling condition. The residual heat can be removed effectively under all these conditions and the security will not be threatened.

Carbonate imaging with magnetotellurics in a shallow-water environment, South Yellow Sea, China

Complex structure distribution and wide-spread Meso-Paleozoic carbonate strata have limited the use of the seismic investigation in the South Yellow Sea, China. To figure out the carbonate strata distribution, we conducted magnetotelluric data acquisition in the Central Uplift of the South Yellow Sea Basin at a water depth of ~20 m. Novel Ocean Bottom Electromagnetic (OBEM) receivers with a smaller size and a lower center of mass were used to reduce the instability caused by the shallow water motions. Magnetic fields associated with the ocean motions, mainly tides and gravity waves, were identified and segmentation multi-station processing was applied to the data. We conducted 1-D and 2-D inversions to derive the resistivity models. Significantly elevated resistivity zone is obtained at depths between 3 and 8 km. Combining the seismic data, drilling well and local geology, we concluded that the marine carbonate strata at the Central Uplift hold a thickness of over 7 km, which starts from the Indo-Chinese unconformity interface at a depth of ~650 m and extends to the metamorphic basement at a depth of ~8 km.

A New Concept of Full Ocean Current Vector Retrieval With Spaceborne SAR Based on Intrapulse Beam-Switching Technique

Synthetic aperture radar (SAR) has proven to be an important tool for the retrieval of ocean surface currents. However, existing spaceborne SAR systems can usually measure only one component of an ocean current vector. In this article, we propose a new concept of dual-look spaceborne SAR system for ocean surface motion remote sensing. The key of the proposed SAR system lies in the use of a technique called intrapulse beam switching (IPBS) implemented by a phased array antenna. One example for the application of the proposed IPBS-based SAR system is its combination with the Doppler centroid anomaly (DCA) method. Through the combination, the DCA method, which in its conventional version can measure only the radial component of a current vector, is generalized to measure full ocean current vectors. A system design example and its performance evaluation demonstrate that the accuracies for ocean surface velocity vector measurement better than 5 cm/s in both azimuth and range, and better than 10° in velocity direction for a mild current, and a swath width of about 100 km, can be achieved. A comparison with other beam-generating schemes indicates that a relatively large swath width, without compromising the current-measuring accuracy, can be achieved by the proposed SAR system with one single antenna array and one single physical output channel—a feature that means a high level of integration which in turn allows for the flexibility to operate this system in multiple SAR modes.

The natural circulation flow characteristic of the core in floating nuclear power plant in rolling motion

In recent years, the FNPP (Floating Nuclear Power Plant) has got more and more attention and rapid development due to very wide prospect application on remote areas or islands. In general, the IPWR (Integral Pressurized Water Reactor) is adopted to meet the requirements of the limited space, the nuclear safety and the maneuverability in marine. The IPWR could depend on natural circulation operation to remove the residual heat of core under accident conditions or low load operation condition. Because the driving head is low, the natural circulation flow in many parallel channels is likely to be influenced by ocean motion and thermonuclear coupling effect. Among various kinds of ocean motions, the rolling motion will introduce the additional force pressure drop and change the gravity pressure drop with time, so the force acting on coolant in the assemblies will be more complex. In order to clarify the natural circulation flow characteristics of the core in FNPP in rolling motion, based on the modified RELAP5 code by adding the ocean motion module and spatial coordinate convert module, the neutron physics and thermal-hydraulic coupled model of IPWR was been established. The core three-dimensional distribution, the radial cross-section and axial distribution of main thermal-hydraulic parameters were obtained. The effect of the tangential force pressure drop, the centripetal force pressure drop and the gravity pressure drop on the coolant in the core in rolling motion were discussed. The results showed that the natural circulation flow rate fluctuates periodically with the rolling motion. And the time-varying gravity pressure drop is the main effect factor of fluctuation. Because of the structure of IPWR is compact, the rolling radius is relatively short, the effect of the general rolling motion on the natural circulation flow distribution of the core is not obvious. The coolant temperature and the fuel power distribution of the core periphery fluctuates slightly, and the reactivity feedback introduced by the coolant temperature and the fuel temperature fluctuation is relatively small. In consequence, the FNPP in the movable marine platform in natural circulation mode operation is safety in general rolling motion.

Simulation investigation of ocean motion on small reactor based on modified system code

Offshore nuclear small reactor is a promising research direction during recent years. In order to carry out system simulation and safety analysis under accident conditions for marine reactors, the classic thermal-hydraulic system analysis code RELAP5 is modified by taking heaving, inclining and rolling motion into consideration in this paper. Additional forces are added to the momentum equation for heaving and rolling, and control volume coordination are transformed for inclining and rolling. Then, a simplified small reactor with two loops is simulated by the modified code and the effect of ocean motion is investigated. Generally, heaving leads to the periodic fluctuation of mass flow rate, inclining would cause the decrease of total mass flow through the core, and the effect of rolling is more complex. Simulation analysis is also performed on two design basis accident LOCA and LOFA in this study. Safety related conclusions are obtained about the impacts of various ocean motion.

On zero-dimensional ocean dynamics

How to study the effect of the Sun or the Moon?s gravity on ocean motion? Of course, Newton?s gravity should be considered. However, Newton?s law considers the Earth as a 0-D point, the ocean motion inside of a 0-D point of the Earth is negative 3-D, and Newton?s law becomes invalid in a negative space. In order to solve the problem, we divide the Earth into two parts, one part is the studied ocean, the other is the left Earth without the ocean. A mechanics model can be then established for the 0-D ocean dynamics.

Reconstructing the Ocean Interior from High-Resolution Sea Surface Information

AbstractWhen evaluated against the 1/30°-resolution, submesoscale-resolving OFES model outputs, the previously published “interior + surface quasigeostrophic” method (from the 2013 study by Wang et al., denoted W13) for reconstructing the ocean interior from sea surface information is found to perform improperly in depicting smaller-scale oceanic motions (associated with horizontal scales smaller than about 150 km). This could be attributed to the fact that the W13 method uses only the barotropic and first baroclinic modes for the downward projection of sea surface height (SSH), while SSH at smaller scales significantly reflects other higher-order modes. To overcome this limitation of W13, an extended method (denoted L19) is proposed by employing a scale-dependent vertical projection of SSH. Specifically, the L19 method makes the projection via two gravest modes as proposed in the W13 method only for larger-scale (>150 km) signals, but for smaller scales (≤150 km) it exploits the framework of the “effective” surface quasigeostrophic (eSQG) method. Evaluation of the W13, eSQG, and L19 methods shows that the proposed L19 method can achieve the most satisfactory subsurface reconstruction in terms of both the flow and density fields in the upper 1000 m. Our encouraging results highlight the potential applicability of L19 method to the high-resolution SSH data from the upcoming Surface Water and Ocean Topography (SWOT) satellite mission.

О РОЛИ ТЕРМИЧЕСКОГО И ВЕТРОВОГО ФАКТОРОВ В ФИЗИЧЕСКОЙ МОДЕЛИ ОБЩЕЙ ЦИРКУЛЯЦИИ ВОД МИРОВОГО ОКЕАНА

The main content of the work consists of certain systematization and addition of longexisting, but eventually deformed and partly lost qualitative ideas about the role of thermal and wind factors that determine the physical mechanism of the World Ocean’s General Circulation System (OGCS). It is noted that the conceptual foundations of the theory of the OGCS in one form or another are contained in the works of many well-known hydrophysicists of the last century, but the aggregate, logically coherent description of the key factors determining the physical model of the OGCS in the public literature is not so easy to find. An attempt is made to clarify and concretize some general ideas about the two key blocks that form the basis of an adequate physical model of the system of oceanic water masses motion in a climatic scale. Attention is drawn to the fact that when analyzing the OGCS it is necessary to take into account not only immediate but also indirect effects of thermal and wind factors on the ocean surface. In conclusion, it is noted that, in the end, by the uneven flow of heat to the surface of the ocean can be explained the nature of both external and almost all internal factors, in one way or another contributing to the excitation of the general, or climatic, ocean circulation.

Impacts of subtidal motions and the earth rotation on modal characteristics of the semidiurnal internal tide

Subtidal motions, such as large-scale circulations and mesoscale eddies, frequently occupy on the propagation path of internal waves in the ocean. Through solving a modified Taylor–Goldstein equation with subtidal currents, density stratification, and the earth rotation, this study investigates the impacts of subtidal motions and the earth rotation on the modal characteristics of the semidiurnal internal tide (SIT) based on long-term mooring measurements in the northern South China Sea (SCS). It is shown that the modal characteristics of the SIT are significantly influenced by the time-varying subtidal current and density stratification associated with energetic subtidal motions in the northern SCS. The earth rotation plays a minor role in modulating the modal characteristics of the SIT in the northern SCS, but it becomes effective at middle and high latitudes when strong subtidal current shear associated with subtidal motions is present. Moreover, the strong subtidal current associated with subtidal motions may significantly affect the critical latitude of the SIT. The observational results reported here will help to improve our understanding of the modal characteristics of internal tides under the influence of subtidal motions in global oceans.

Sensitivity analysis based on Morris method of passive system performance under ocean conditions

Passive safety systems, which do not require external input to operate, are widely used to enhance the inherent safety in new generation nuclear power plants. A challenging issue still to be resolved is the quantification of the functional failure probability of passive safety systems. The evaluation of functional failure relies on repeated thermal-hydraulics simulations which is usually time-consuming in practice. Response surface method has been proposed to tackle this issue. However, the number of input parameter limits its efficiency to a great extent. Therefore, it is necessary to identify the uncertain input parameters that have an important impact on the system performance, which helps reduce the dimension of the input parameters. Especially in marine nuclear power plants, the complex ocean motions will introduce more uncertainties in the passive system behavior. It’s of great significance to screen key parameters for passive safety systems under ocean conditions. In this paper, the Morris method is used to perform an efficient sensitivity analysis to identify key parameters for a passive residual heat removal system in IPWR200. Twenty-four parameters related to passive system behavior are screened and ranked for their sensitivity. The results demonstrated that four of the twenty-four parameters have a more significant influence on the passive system performance.

The Simulation and Experimental Study of Hydraulic Transmission with Constant-pressure Scheme for Wave Energy Converter Application

This paper presents the simulation and experimental results of the hydraulic system for wave energy converter application. The different input force applied from the pump unit will imitates the force of wave energy converter (WEC) produced by the ocean waves motion. The simulation conducted using the Hydraulic FluidSIM® 5th version, while the experiment was conducted at Festo-Hydraulic Laboratory. In FluidSIM®, the role of wave floater represented by a set of pump unit that will provide desired pressure to the hydraulic piston. The pump unit consists of a motor, pump, tank and pressure relief valve. The input pressure at the pump unit was adjusted in twelve different levels in the range of 5 Bar to 60 Bar. The different pressure will create a different oil velocity that caused the extension and retraction of the piston. The different pressure also will create a different speed (measured in RPM) of a hydraulic motor. An accumulator and four units of check valves used to drive the moving oil in unidirectional at a smooth flow rate. As a result, the rise of input pressure at the pump unit will increase the speed of a hydraulic motor. For this reason, to achieve the optimal electrical generation by a generator that mounted with hydraulic motor, the higher input pressure is needed. Furthermore, the simulation is validated by the physical experiment to determine the accuracy of generating data. The averaged accuracy of simulation data compared to experimental is 89.92%. After all, the finding from this study will be utilised as a reference in the estimation of the optimal dimension for the actual scale of a hydraulic system for application in the WEC.

Flow instability in a vertical boiling channel under ocean conditions

Two-phase flow instability is a very common phenomenon in two-phase systems. However, there are a few studies on flow instability characteristics under ocean motions especially the resonance phenomenon induced by combined actions of thermal hydraulic and ocean motions. The flow instability is harmful to the operation of two-phase flow systems. Therefore, more researches are needed for in depth understanding of this phenomenon. In this paper, an ocean condition version thermal-hydraulic system code is briefly introduced. The source term for additional acceleration is added into the momentum equation in a conventional system code. The system code possesses the capability to assess flow instability under ocean conditions. The quantitative analysis of system stability is performed based on stability boundary, phase change number (Npch) line and scale of flow oscillation (SFO). The effects of rolling and heaving motions on flow instability in a vertical boiling channel are analyzed. There is resonance phenomenon which induces oscillations with relatively large amplitude and makes the system more unstable.

The influence of geostrophic strain on oceanic ageostrophic motion and surface chlorophyll

Oceanic submesoscale ageostrophic processes have been progressively recognized as an important upwelling mechanism to close the nutrient budget and sustain the observed primary production of phytoplankton in the euphotic layer. Their relatively small spatio-temporal scales (of 1~10 km and a few days) have hindered a systematic observational quantification of the submesoscale ageostrophic flow variability and its impact on ocean biogeochemistry. By combining surface drifters, satellite altimetry and satellite ocean-color data, we detect that when the strain rate of mesoscale surface geostrophic flow is strong, it favors a higher ageostrophic kinetic energy level and an increase in surface chlorophyll concentration. The strain-induced frontal processes are characterized by a surface chlorophyll increase and secondary ageostrophic upwelling along the light side of the oceanic density front. Further analysis indicates that the balanced ageostrophic motions with longer time scales are more effective in inducing chlorophyll increase than the unbalanced shorter time-scale wave motions.

Slingshot Resonance for Ocean Wave Energy Conversion

The slingshot effect and its application to converting ocean wave energy are discussed. It is shown that, owing to the large inertia transported by ocean waves and their periodicity, the slingshot effect can result in the transmission of significant kinetic energy to a puck colliding elastically with a pusher plate driven by ocean wave motion. A simplified geometrical model is used to demonstrate that, despite the stochastic nature of the collisions (whereby collisions occur at random times in the wave cycle), head-on collisions occur more frequently, yielding a net average gain of energy. However, the most promising configuration for applying the slingshot effect to ocean wave energy conversion is that which matches, through appropriate design, the travel time of the puck between collisions with the wave period. Then, only head-on collisions occur, resulting in a significant magnification of the puck kinetic energy. Further research will be required before this slingshot effect can be practically implemented for ocean wave energy conversion.

Numerical study of laminar flow and friction characteristics in narrow channels under rolling conditions using MPS method

Abstract Modern small modular nuclear reactors can be built on a barge in ocean, therefore, their flow characteristics depend upon the ocean motions. In the present research, effect of rolling motion on flow and friction characteristics of laminar flow through vertical and horizontal narrow channels has been studied. A computer code has been developed using MPS method for two-dimensional Navier-Stokes equations with rolling motion force incorporated. Numerical results have been validated with the literature and have been found in good agreement. It has been found that the impact of rolling motions on flow characteristics weakens with increase in flow rate and fluid viscosity. For vertical narrow channels, the time averaged friction coefficient for vertical channels differed from steady friction coefficient. Furthermore, increasing the horizontal distance from rolling pivot enhanced the flow fluctuations but these stayed relatively unaffected by change in vertical distance of channel from the rolling axis. For horizontal narrow channels, the flow fluctuations were found to be sinusoidal in nature and their magnitude was found to be dependent mainly upon gravity fluctuations caused by rolling.

Effects of ocean motions on density wave oscillations under natural circulation

The study of natural circulation is attracting more and more attention of researchers and engineers for the improvement of the system safety. A lot of natural circulation systems are applied to new generation reactors which make reactor systems safer and more compact because there are fewer components and no circulation pump in the natural circulation systems. The residual heat can be removed passively from the reactor by the natural circulation system which prolongs the response time for operators and reduces the potential accident because of human error. With the application of nuclear reactors under the ocean conditions, the study on flow oscillation characteristics in natural circulation system under ocean condition becomes very significant.Usually, flow oscillation is harmful to the operation of natural circulation systems which can affect the cooling capability of natural circulation systems in some extreme situations. In this paper, the classification of flow instability is introduced for systems under ocean conditions. Characteristics of density wave oscillations (DWO) under natural circulation are studied, including oscillation characteristics, stability boundary and subcooling effect. The characteristics of DWO under rolling and heaving motions are compared with those under the normal condition. The effects of rolling and heaving characteristics are analyzed, including maximum rolling angle, rolling period, rolling center location, maximum acceleration and heaving period. The resonance phenomenon is found, and resonant behaviors are analyzed.

A magnetically driven equatorial jet in Europa’s ocean

During recent decades, data from space missions have provided strong evidence of deep liquid oceans underneath a thin outer icy crust on several moons of Jupiter, particularly Europa. But these observations have also raised many unanswered questions regarding the oceanic motions generated under the ice, or the mechanisms leading to the geological features observed on Europa. By means of direct numerical simulations of Europa's interior, we show here that Jupiter's magnetic field generates a retrograde oceanic jet at the equator, which may influence the global dynamics of Europa's ocean and contribute to the formation of some of its surface features by applying a unidirectional torque on Europa's ice shell.

Verification and improvement of dynamic motion model in MARS for marine reactor thermal-hydraulic analysis under ocean condition

Abstract Unlike land-based nuclear power plants, a marine or floating reactor is affected by external forces due to ocean conditions. These external forces can cause additional accelerations and affect each system and equipment of the marine reactor. Therefore, in designing a marine reactor and evaluating its performance and stability, a thermal hydraulic safety analysis code is necessary to consider the thermal hydrodynamic effects of ship motion. MARS, which is a reactor system analysis code, includes a dynamic motion model that can simulate the thermal-hydraulic phenomena under three-dimensional motion by calculating the body force term included in the momentum equation. In this study, it was verified that the dynamic motion model can simulate fluid motion with reasonable accuracy using conceptual problems. In addition, two modifications were made to the dynamic motion model; first, a user-supplied table to simulate a realistic ship motion was implemented, and second, the flow regime map determination algorithm was improved by calculating the volume inclination information at every time step if the dynamic motion model was activated. With these modifications, MARS could simulate the thermal-hydraulic phenomena under ocean motion more realistically.

Characterizing the Transition From Balanced to Unbalanced Motions in the Southern California Current

AbstractAs observations and models improve their resolution of oceanic motions at ever finer horizontal scales, interest has grown in characterizing the transition from the geostrophically balanced flows that dominate at large‐scale to submesoscale turbulence and waves that dominate at small scales. In this study we examine the mesoscale‐to‐submesoscale (100 to 10 km) transition in an eastern boundary current, the southern California Current System (CCS), using repeated acoustic Doppler current profiler transects, sea surface height from high‐resolution nadir altimetry and output from a (1/48)° global model simulation. In the CCS, the submesoscale is as energetic as in western boundary current regions, but the mesoscale is much weaker, and as a result the transition lacks the change in kinetic energy (KE) spectral slope observed for western boundary currents. Helmholtz and vortex‐wave decompositions of the KE spectra are used to identify balanced and unbalanced contributions. At horizontal scales greater than 70 km, we find that observed KE is dominated by balanced geostrophic motions. At scales from 40 to 10 km, unbalanced contributions such as inertia‐gravity waves contribute as much as balanced motions. The model KE transition occurs at longer scales, around 125 km. The altimeter spectra are consistent with acoustic Doppler current profiler/model spectra at scales longer than 70/125 km, respectively. Observed seasonality is weak. Taken together, our results suggest that geostrophic velocities can be diagnosed from sea surface height on scales larger than about 70 km in the southern CCS.