Current Circulation Research Articles

Effects of detached breakwaters on drowning due to rip and circulation currents

Effects of detached breakwaters on drowning due to rip and circulation currents

Topological visualization of the plasmonic resonance of a nano C-aperture.

The plasmonic response of a nano C-aperture is analyzed using the Vector Field Topology (VFT) visualization technique. The electrical currents that are induced on the metal surfaces when the C-aperture is excited by light is calculated for various wavelengths. The topology of this two-dimensional current density vector is analyzed using VFT. The plasmonic resonance condition is found to coincide with a distinct shift in the topology which leads to increased current circulation. A physical explanation of the phenomenon is discussed. Numerical results are presented to justify the claims. The analyses suggest that VFT can be a powerful tool for studying the physical mechanics of nano-photonic structures.

INTERPRETATION OF CURRENT AND TIDAL PATTERN AT SELANGOR RIVER, KUALA SELANGOR

Abstract. Tidal data has been used to determine long-term water level alterations. Tides are high-powered and notoriously hard to ascertain. Tidal analysis and prediction need substantial study with the requisite approaches, techniques, and tools in conjunction with weather parameters and natural calamities. TOtal TIde Solution (TOTIS) software, which is rooted in harmonic analysis, is one of the most often used software in Malaysia. This study aims to interpret the current circulation and tidal pattern at the Selangor River, Kuala Selangor, Selangor Darul Ehsan. A period of one-month data is retrieved via Valeport 740 Tide Gauge from tide gauge station, whereas the current data are retrieved via Valeport Current Meter 105, which are used to analysed. The latest updated data period for the tide gauge station utilised are based on the availability of data. Therefore, tides are predicted using 33 resolved constituents for two years, starting from January 2021 until December 2022. Tidal analysis generates tidal constituents, which are then used for tidal prediction. Root Mean Square Error (RMSE) and datum offset are used to evaluate software's output. It signifies that TOTIS software is trustworthy and reliable in terms of tidal analysis and prediction accuracy. The highest river current records with high speed occur during high tide phenomenon. The output data for magnitude of river current speed are derived satisfactorily with high precision. It aids in monitoring and analyse of an appropriate method to prevent or reduce additional river erosion.

Assessing the Projected Changes in European Air Stagnation due to Climate Change

Abstract Air pollution is a major environmental threat to human health. Pollutants can reach extreme levels in the lower atmosphere when weather conditions permit. As pollutant concentrations depend on scales and processes that are not fully represented in current global circulation models (GCMs), and it is often too computationally expensive to run models with atmospheric chemistry and aerosol processes, air stagnation is often used as a proxy for pollution events with particular success in Europe. However, the variables required to identify air stagnation can have biases in GCM output, which adds uncertainty to projected trends in air stagnation. Here, the representation of air stagnation in GCMs is assessed for Europe in the historical period and in end-of-century projections based on a high-emission scenario using three methods for identifying air stagnation. The monthly frequency of stagnation during summer and autumn is projected to increase with climate change when stagnation is identified by a well-established index. However, this increase is not present when air-stagnation frequency is estimated using a statistical model based on the synoptic- to large-scale atmospheric circulation. This implies that the projected increases in air stagnation are not driven by an increase in frequency or severity of large-scale circulation events that are conducive to stagnation. Indeed, projected changes to the atmospheric circulation in GCMs, in particular a reduction in atmospheric block frequency, would suggest a reduction in future air stagnation. Additional analyses indicate that the projected increases in stagnation frequency follow the trend toward more frequent dry days, which is apparently unrelated to the large-scale drivers of air stagnation.

A New Topology and Modulation Strategy to Suppress the Leakage Current in Transformerless Cascaded H-Bridge Inverters in PV Application

The use of transformerless inverters is common due to the lower cost, lighter weight, and higher efficiency. The lack of the transformer leads to the leakage current circulation through the parasitic capacitors, which increases the power losses, electromagnetic interferences, and safety issues. In this article, first, the proposed cascaded H-bridge (CHB) -based inverter’s equivalent common-mode (CM) model is determined. Then, a new multicarrier pulsewidth modulation strategy is proposed to suppress the leakage current. In the presented method, new redundancy states are provided due to the use of just one blocking switch. These extra redundancy states and the proposed modulation strategy help to keep the CM voltage (CMV) constant and suppress the leakage current. The validity of the proposed solution is verified by simulation in the MATLAB/Simulink environment. In addition, a universal prototype with a power rating of 600 W is built and tested, and the experimental results are presented to confirm the theoretical and simulation results. The experimental results show a maximum efficiency of 98.5% and a European efficiency of 98.3%. The proposed topology is also compared to the existing transformerless topologies to show its effectiveness.

Laboratory Study of Surfactant Film Compression and Boundary Transformation under the Action of Surface Waves

In this paper we present the results of a laboratory experiment simulating the mechanisms of a surfactant film localization under the action of periodic surface waves. It is shown that the film compressed by a surface wave, can be conditionally divided into three sections — the dense film region as the most distant from the wave source, the area of a diluted film and the region of relatively clean water. The paper is focused on the processes occurring in the diluted film region characterized by the transition from clean water to the dense film, where horizontal circulation currents are registered. The character of currents is varying depending on the wave amplitude so that the divergent circulation cells occur at small and large wave amplitudes, but at medium amplitudes the roller currents forming a convergence zone on the basin axis are observed. The experimentally obtained stationary distribution of surfactant concentration is compared with the previously developed model of film compression due to surface tension induced by waves. The comparison shows good agreement between the theory and the experimental results at small and large wave amplitudes. Their discrepancy at medium wave amplitudes in the diluted film region is presumably related to the presence of convergent cells which are not considered in the model.

Evaluation of the readership of the times of India newspaper and magazine in the hospitality segment in Madurai district

The study examines the factors that influence the readership of daily newspapers and magazines in guests staying at hotels. The study attempts to gain a granular understanding of the Times of India newspaper’s performance within the changing consumer behaviour trends observed in the hospitality market in Madurai District. The major factors which directly shift the satisfaction of the readers are determined, these factors are then assessed on their interactional nature with other decision variables to implement the best strategies to create increased readership. The tests are conceptualized to offer objective functions to improve the current circulation system of the Times of India daily newspaper. The linear relationship of the major factors was determined using the PLUM ordinal regression analysis. The results give clarity into the sales & marketing efforts needed to succeed in the hotel segment for the print media industry. The major criteria for enriching the target market characteristics of the hospitality segment by print media sales & marketing initiatives are studied in the results.

진동감소 및 감쇠력 확보를 위한 와전류형 EM댐퍼 구조 설계

In this paper, we propose an eddy current type EM damper that can have the simple structure of an existing mechanical damper and the effective damping force of a magnetic fluid fluid damper at the same time. The proposed eddy current type EM damper has a structure similar to that of a mechanical damper, in which a permanent magnet is attached to a plunger and a conductor (copper) is provided on the outer wall of the cylinder to generate and generate an eddy current cutoff. Damping force. When the permanent magnet attached to the plunger vibrates up and down, an eddy current is generated, and a magnetic field having the opposite polarity to the magnetic field acting by the circulation of the eddy current is generated. In order to verify the reliability of the damping force of the eddy current type EM damper, analysis is performed using a finite element analysis method that applies axial symmetry analysis technology, and the direction in which the damping force is generated acts in the opposite direction to the vibration characteristics to generate external vibration. The damping ability to suppress was verified.

Ramp Design Standards for Carporch at Housing Sector in Double Storey House to Accommodate Low Clearance Vehicle

This research aims to evaluate and propose effective gradient at car porch area for the housing sector. The dependent variable that acts as presumed effect is vehicle to stuck and become lodged but the independent variable is referring to the car clearances dimension, design of the ramp and guidelines in ramp design. In other words, the situation of the vehicles to stuck and lodged depends on the car clearances dimension, design of the ramp and guidelines in ramp design. Interview sessions were held with the professional architects and engineers in the engineering department at Majlis Bandaraya Seremban, DBKL, Majlis Bandaraya Melaka, Majlis Bandaraya Johor Bahru, Jabatan Kerja Raya (JKR) and consultant firms. During the interview session, four aspects of this matter were discussed to explore the existing standards and guidelines in ramp design for car porch at housing sector in double storey house to accommodate low-clearances vehicles. The feedback from the professionals was analysed by narrative analysis method and the result of the study will be valuable to the construction industry and tools for future design. These data can be used to estimate the suitable degree and percent for different categories of ground clearances which is useful for current development and current technology circulation.

Weak grid integrated solar photovoltaic‐based distributed generation system proficient in supplying VAR requirement with current restriction

AbstractThis study presents a grid interactive solar photovoltaic (PV) system proficient with low voltage ride through capability. When the supply voltage drops more than 10%, the solar PV system remains connected and continues to supply the active power to the loads as well as to the grid. Along with the active power supply, the solar PV array system supplies the reactive power for stabilising the system. Due to the supply of both the active and reactive powers, there is a chance for a grid fed inverter (GFI) current to exceed the maximum current limit. It may result in the tripping of inverter protection. Therefore, a current limiting logic is incorporated to keep the inverter current within the safe limit. The unbalanced voltages are responsible for circulation of negative sequence currents in the system. As the prime aim of the present work deals with the supply of positive sequence currents to the grid, it is required to estimate the positive and negative sequence voltages separately. Intending the estimation of sequence voltages from unbalanced supply voltages, a frequency adaptive higher order complex filter (FAHOCF) is used. A MATLAB model of grid interactive solar PV array is developed and simulated results are verified with test results.

Forecast Sensitivity-based Observation Impact (FSOI) in an analysis–forecast system of the California Current Circulation

Forecast Sensitivity-based Observation Impacts (FSOI) in an analysis–forecast​ system of the California Current System (CCS) are quantified using an adjoint-based approach. The analysis–forecast system is based on the Regional Ocean Modeling System (ROMS) and a 4-dimensional variational (4D-Var) data assimilation approach. FSOI was applied to four different metrics of forecast skill that target important features of the CCS circulation along the central California coast. A particular focus of the FSOI analysis is the impact of assimilation of measurements of the radial component of surface currents from a network of high frequency (HF) radars since this is a new data stream in the near-real-time system considered here. On average, ∼50–60% of all observations assimilated into the model yielded improvements in the forecast skill. Conversely, the remaining ∼40–50% of data degrade the forecasts, in line with similar findings in numerical weather prediction systems. Much of the improvement in forecast skill arises from remotely sensed observations, including HF radar data; on average only ∼50% of in situ measurements contribute to a reduction in forecast error. This is partly due to the large volume of remote sensing observations compared to in situ observations. However, in situ observations are an order of magnitude more impactful than remotely sensed data when viewed in terms of the average impact per observation.

Basin-scale gyres and mesoscale eddies in large lakes: a novel procedure for their detection and characterization, assessed in Lake Geneva

Abstract. In large lakes subject to the Coriolis force, basin-scale gyres and mesoscale eddies, i.e. rotating coherent water masses, play a key role in spreading biochemical materials and energy throughout the lake. In order to assess the spatial and temporal extent of gyres and eddies, their dynamics and vertical structure, as well as to validate their prediction in numerical simulation results, detailed transect field observations are needed. However, at present it is difficult to forecast when and where such transect field observations should be taken. To overcome this problem, a novel procedure combining 3D numerical simulations, statistical analyses, and remote sensing data was developed that permits determination of the spatial and temporal patterns of basin-scale gyres during different seasons. The proposed gyre identification procedure consists of four steps: (i) data pre-processing, (ii) extracting dominant patterns using empirical orthogonal function (EOF) analysis of Okubo–Weiss parameter fields, (iii) defining the 3D structure of the gyre, and (iv) finding the correlation between the dominant gyre pattern and environmental forcing. The efficiency and robustness of the proposed procedure was validated in Lake Geneva. For the first time in a lake, detailed field evidence of the existence of basin-scale gyres and (sub)mesoscale eddies was provided by data collected along transects whose locations were predetermined by the proposed procedure. The close correspondence between field observations and detailed numerical results further confirmed the validity of the model for capturing large-scale current circulations as well as (sub)mesoscale eddies. The results also indicated that the horizontal gyre motion is mainly determined by wind stress, whereas the vertical current structure, which is influenced by the gyre flow field, primarily depends on thermocline depth and strength. The procedure can be applied to other large lakes and can be extended to the interaction of biological–chemical–physical processes.

Grain-size analysis of the Late Pleistocene sediments in the Corinth Rift: insights into strait-influenced hydrodynamics and provenance of an active rift basin

Abstract Grain-size analysis of the sediments in borehole M0079A, located in the Corinth Rift, was used to explore hydrodynamic conditions and provenance in the Late Pleistocene Corinth Rift. Grain-size populations that were sensitive to the sedimentary environments were characterized by frequency distribution, particle size–standard deviation and probability cumulative curves. Our results indicate the grain-size population component in the range 0.15–0.25 µm may be used as a sensitive proxy for hyperpycnal flows, which have commonly been triggered by river floods from the southern margin of the rift since c. 0.593–0.613 Ma. The high-density plumes derived from the longer rivers of the southern rift that were prevalent before c. 0.593–0.613 Ma. When sediment is supplied as hemipelagic deposition, the proportion of the total grain-size population that is in the 0.3–0.5 µm range becomes an index for suspension fall-out deposits. The core shows coarser sediments during the marine periods, and this may be linked to the current circulation related to the Ishtmia Strait opening. The study thus illustrates how the establishment of interbasinal straits can influence the details of sedimentary hydrodynamics in the deep-water axis of an adjacent depocentre.

Integral backstepping-ILC controller for suppressing circulating currents in parallel-connected photovoltaic inverters

In big solar plants where the use of a single inverter is neither economically or technically feasible, parallel linked photovoltaic inverters are necessary. For parallel-connected operation, the most significant issue is that even a slight variation in the output voltages of particular inverters results flow of circulating currents. A high level of circulation current causes inverter power losses to increase, which lowers the system's overall performance by decreasing its efficiency. In this paper, a novel simple and effective controller for parallel-connected inverters is proposed to ovoid the circulating currents among the inverters. Convergence efficiency and low computational cost of the suggested controller based on integral backstepping method are the primary motivations of this work. The simulation and experimental findings show that the suggested control system achieves the required power quality and reduces circulation current under various loading situations.

Modeling and Suppression of Circulating Currents Among Parallel Single-Phase Three-Level Grid-Tied Inverters

T-type three-level inverters have attracted extensive attention for their utility in many applications, especially photovoltaic power generation. For these inverters, parallel operation offers superior performance in capacity, reliability, and scalability. However, the introduced circulating current (CC) may cause overcurrent in line, which seriously threatens the safety and stability of the system. The mechanism of CC lacks detailed analysis in single-phase modular inverters. Thus, an accurate mathematical model is established and a CC suppression method is proposed in this article for parallel-operated single-phase T-type three-level inverters. First, the characteristics of port degradation are analyzed, and an improved equivalent circuit is introduced based on the findings. Then, according to the improved equivalent circuit, a detailed mathematical model is established. Using this model, excitation sources of CC are analyzed and divided into three parts. After that, a CC suppression method involving carrier-based pulsewidth modulation with offset voltage injection is proposed, and a deadbeat controller is designed to calculate the offset voltage. Moreover, the proposed method can balance the neutral-point voltage across dc-link capacitors as well. Simulation and experimental results validate the theoretical analysis and effectiveness of the proposed scheme.

North Atlantic Current and European Slope Current Circulation in the Rockall Trough Observed Using Moorings and Gliders

AbstractThe Rockall Trough (RT) accommodates the warmest and saltiest branch of the North Atlantic Current, which delivers water from the Gulf Stream into the marine environment around western Europe. In addition, the European Slope Current (ESC) carries warm water northward along the eastern boundary of the RT, and exchange between the ESC and the continental shelf is a dominant factor in determining the oceanographic conditions around the British Isles. However, the picture of the mean circulation and variability in the RT is still emerging, with a continuous observational campaign still in its relative infancy. The ESC, in particular, is poorly constrained by ship‐based, mooring, and satellite observations. In this paper, we examine the RT circulation and volume transport using a temporally extended and spatially expanded observing network. Six years of continuous mooring occupation reveal that a large‐amplitude, basin‐scale freshening event, previously detected south of Iceland around 2015, impacted the RT around 2017. Geostrophic transport was greatly reduced during this period, driven by a concurrent subsurface temperature increase at the western boundary. The circulation regained strength during the latter part of the record. We gathered 110 glider transects over 22 months which capture the ESC velocity field in unprecedented detail. The data are sufficient to characterize both the mean state and the emergent seasonal variability of the ESC, and reveal the year‐round presence of a southward countercurrent at depth. Variability in the strength and structure of this previously unstudied feature modulates net northward transport in the eastern boundary current system.

Synchronized I/V droop method for islanded microgrid

Islanded microgrids mainly adopt master-slave and peer-to-peer control. The master-slave control is relatively simple but requires the capacity of the master power source is large enough to support the voltage of the micro-grids. Once the master source is out of operation, the whole microgrid can't maintain its regular operation. The peer-to-peer control method simulates the droop characteristics of active power-frequency (P/f) and reactive power-voltage (Q/V) of the bulk power grid, which can achieve plug-and-play of the distributed generations. However, the peer-to-peer control method is complicated and has the inherent frequency stability problems that exist in the bulk power systems. A current-voltage (I/V) droop control method for islanded microgrids with 100% inverters is presented based on the synchronization of outputted current phasors. Satellites based timing signals are used to synchronize standard-frequency current phasors generated by inverters, which can suppress the current circulation and free from frequency stability problems. The I/V droop control is employed to share the inverter's power outputs according to their capacities and maintain the grid voltage in a normal range. Small signal analysis shows the proposed method has a faster response and better stability than traditional methods. The effectiveness and feasibility of the proposed method are verified by digital simulations and laboratory experiments. Since the frequencies and phase angles of the outputted currents of inverters are consistent, the synchronous control of active and reactive power is archived by adjusting the current amplitude. The method makes the AC microgrids' control process similar to that of the DC grids; therefore, it is simple and has better stability and power distribution accuracy.

New Indicators ‘Acircularity’ and ‘Resource Efficiency Account’ to Evaluate the Efforts of Eco-Design in Circular Economy

This study proposes new indicator, Resource Efficiency Account (REA). REA represents the effects of eco-design efforts in achieving a circular system. The key concept of REA is “acircularity.” “Acircularity” is the distance to the ideal circular system to be achieved. REA is given as material efficiency (service per total value of constituent materials) divided by acircularity. Acircularity is the sum of the value of resources that the techno-sphere demands from the eco-sphere, and the value of resources that are dissipated within the techno-sphere. If an utterly circular state is reached, the acircularity value is zero. Additionally, this study proposes a new method to quantify the decline of the quality of scrap provided to the market as a decline in the value of the material to calculate the dissipation. The calculation focuses on the control level of impurities in scrap. The validity of these indicators is discussed using an automobile case. Differences in the current circulation level, eco-design for recycling, and refurbishment efforts can be quantitatively evaluated using REA and acircularity.

A Planar Switching Integrated Quadrant Coil Antenna to Form Widespread Switched Polarized H-Field for Misalignment Resilient WPT System

This article presents a planar switching integrated quadrant coil antenna to mitigate lateral and angular misalignment problems in near-field wireless power transfer (WPT) applications. To allow a completely free receiver movement, both the misalignment problems are concurrently addressed by forming widespread distributions of switched polarized H-field in the receiver region. To achieve this, current circulations through the four quadrant coils composing the proposed antenna are judiciously controlled to form three orthogonal H-field components. For lateral misalignment mitigation, the widespread field distributions are obtained by using a field-forming approach for optimizing the antenna parameters. To produce the switched polarized H-field for angular misalignment mitigation, time-switching of the orthogonal H-field components is performed. This switching operation is realized by three double pole double throw (DPDT) switches interconnecting the coils and integrated within the design for a cost-effective planar antenna solution. The fabricated prototype is measured and the experimental results are corroborated with the analysis. The results demonstrate the potential of the proposed antenna to simultaneously mitigate both the misalignment problems for medium-range WPT of small devices, such as medical implants, wireless endoscopy capsules, and wearable devices, which are allowed to freely rotate and displace.

Deciphering the diversity and distribution of chromophytic phytoplankton in the Bohai Sea and the Yellow Sea via RuBisCO genes (rbcL).

Present study investigated composition and distribution of chromophytic phytoplankton in the Bohai Sea (BS) and the Yellow Sea (YS) by using rbcL genes. Bacillariophyceae, Haptophyceae and Pelagophyceae were the most abundant phytoplankton groups. Distinct phytoplankton communities were observed in the BS and the YS: offshore stations were dominated by bloom forming genera Thalassiosira and Skeletonema, while brown tide-forming species including Chrysochromulina spp. and Aureococcus anophagefferens were commonly found in the nearshore areas. Redundancy analysis showed that phosphate, temperature and silicic acid play key roles in structuring chromophytic phytoplankton, such as phytoplankton at nearshore stations were affected by nutrient runoff from adjacent rivers (Yellow River). Anthropogenic activities in the Bohai Sea and seasonal circulation of ocean currents may also contribute to shaping chromophytic phytoplankton communities. This study provides data support and foundational observations of chromophytic phytoplankton in the BS and the YS, and their responses to environmental gradients and human activities.