Values Of Current Velocity Research Articles

Tidal turbine wake characterization by vessel-mounted ADCP data analysis

Wakes generated downstream turbines are one of the key points to be considered for tidal stream energy farm layout design. Distance between consecutive turbines must be optimized considering available resource spatial distribution and the current velocity reduction caused by upstream turbines. Tidal turbine wake characteristics have been analyzed experimentally and numerically, however, there is still a lack of studies presenting data measured in the wake of large-size turbines in tidal sites.
 In this paper, the wake generated downstream of a SIMEC Atlantis Energy 0.5 MW turbine in Naru Strait (Nagasaki Prefecture, Japan) is analyzed using data measured with a vessel-mounted ADCP. This analysis is based on the comparison between data measured before turbine installation (September 2020) and during turbine operation (March 2021, May 2021, and September 2021). 
 Due to the difficulties that measuring at the same position and the same tide moment with a vessel-mounted ADCP would mean, a direct comparison between these four datasets is unviable. To solve this issue, data were pretreated to calculate a ratio (RD) resulting from the division of current velocity values at every vertical layer by the current velocity measured at the shallowest layer. After that, this ratio is interpolated to a regular 3D mesh. Assuming that the current velocity profile shape for one point does not change with time, resulting RD values interpolated from data measured in different fieldworks can be compared.
 The impact of tidal turbine operation on the current velocities is quantified with a variation ratio RV calculated by dividing RD during turbine operation (RD*) by RD before turbine installation (RD). These results show a clear velocity deficit even at 18D from the turbine, which clearly contrasts with results from other similar studies available in the literature, which may be related to the low turbulence intensity measured at the turbine installation point.

Verifying Measurements of Surface Current Velocities by X-Band Coherent Radar Using Drifter Data

Introduction. Conventional contact measurements of hydrographic parameters frequently fail to provide the necessary accuracy of data in the field of water area monitoring. This problem can be solved using coherent radars enabling direct measurements of surface current velocities.Aim. To establish the accuracy of surface current velocities measured by a Doppler radar using drifter data.Materials and methods. In June 2022, coastal operational oceanography studies were conducted at the hydrophysical test site of the Institute of Oceanology of the Russian Academy of Sciences in the Black Sea near Gelendzhik. Measurements were carried out using a coherent X-band radar installed on the Ashamba research vessel simultaneously with drifter experiments using Lagrangian drifters of the near-surface layer with an underwater 0.5 m sail. Coordinates were transmitted via mobile communication. The drifter data on the current velocity and direction were used to verify radar measurements. Measurements were taken onboard of the research vessel at a low speed and different distances from the shore, near the drifters. The tracks of the vessel and drifters were recorded simultaneously. Processing of the radar data involved obtaining Doppler spectra of signals to estimate the dynamic processes on the sea surface, including the current velocity.Results. Radial components of the near-surface current velocity were calculated. Then, the current velocity values obtained based on the drifter and radar data were compared.Conclusion. The present work makes a contribution to the advancement of methods for measuring surface currents from the board of a moving ship by Doppler radars. The obtained results confirm the suitability of the radar hardware and software and signal processing algorithms for measuring currents. The radar measurement data were found agree well with drifter data in the velocity range from 15 cm/s.

Study of Hydrodynamic Patterns of Tanjung Pasir Banten Waters to Support the NCICD Sea Wall Development Plan

Numerical modeling of hydrodynamics (HD) around the Tanjung Pasir Waters was carried out using MIKE 21 HD Flexible Mesh software to get the current velocity pattern conditions during the west and east monsoons. This activity is to support the NCICD sea wall construction plan. In addition, the results that will be obtained in this modeling are the conditions of the speed and direction of the current in various tidal conditions during spring and neap. The data used in this modeling include wind speed and direction, wave height, wave period, and wave direction. Based on the research that has been done, the validation value of Naotide tidal data on tidal field data is 93.8 %. HD MIKE 21 modeling results on field data have a validation value of 93.4 %. Extract points 4 and 5 which are the northernmost, have the highest current velocity values compared to the other points. In addition, when heading to the high tide phase, both spring and neap conditions, the current velocity value has the highest value.

An Analytical Study on Wave-Current-Mud Interaction

This study aims at providing analytical investigations to the first and second-order on the wave–current–mud interaction problem by applying a perturbation method. Direct formulations of the wave–current–mud interaction could not be found in the literature. Explicit formulations for the particle velocity, dissipation rates, and phase shift in the first order and the mass transport in the second-order have been obtained. The findings of the current study confirmed that by an increase in the current velocity (e.g., moving from negative to positive values of current velocity), the dissipation rates and mud (instantaneous and mean) velocity decrease. The proposed assumption of a thin mud layer (boundary layer assumption) matches with the laboratory data in the mud viscosity of the orders of (0.01 N/m2) in both wave dissipation and mud mass transport leading to small ranges of discrepancies. The results from the newly proposed model were compared with the measurements and the results of an existing model in the literature. The proposed model showed better agreements in simulating the mud (instantaneous and mean) velocity compared to the existing one.

VARIATION OF VOLUME TRANSPORT AND VARIABILITY OF CURRENT IN KARIMATA AND GASPAR STRAITS DURING 2010-2014 BASED ON NUMERICAL MODELING

Karimata Strait located between Kalimantan and Bangka Islands, while Gaspar Strait located between Bangka and Belitung Islands. Volume transport variations through Karimata and Gaspar Straits during 2010-2014 were studied using three-dimensional numerical model of HAMburg Shelf Ocean Model (HAMSOM). Simulated area is located in 1°0′0′′N - 4°30′0′′N and 104°0′15′′E - 110°30′0′′E with a horizontal resolution of 0.5′ (about 0.94 km). The correlations value of current velocity from model with observation is quite high i.e. 0.85 for zonal component (u) and 0.89 for meridional (v) with 95% of significance level. The results of signal analysis showed that the volume transport is strongly influenced by the seasonal period. In addition to seasonal wind, there was also weak and medium phase of El Niño and La Niña during 2010 - 2014 that affected volume transport. The average volume transport from 2010-2014 through Karimata and Gaspar Straits are -2.75 Sv and -1.98 Sv, respectively (1 Sv = 106 m3/s). The negative value shows the southward volume transport, while positive to north. Total transport to south indicates that there are may be due to parts of Indonesia Through Flow (ITF) flow through South China Sea, Karimata Strait, and Gaspar Strait to the Java Sea.Keywords: volume transport, Karimata Strait, Gaspar Strait

Pola Arus Permukaan dan Kondisi Fisika Perairan di Sekitar Pulau Selayar pada Musim Peralihan 1 dan Musim Timur

<strong>Surface Current Pattern and Physics Condition of Waters Around Selayar Island in the First Transitional and Southeast Monsoons. </strong> Seasonal observations of the flow of surface water and physics conditions around Selayar Island adjacent to Arlindo throughflow pathways of Makassar Strait have been conducted with a focus on the first transitional season and the southeast monsoon season. The purpose of this research is to obtain the pattern of seasonal surface current and physics characteristics of water column, i.e. temperature and salinity in Selayar Island waters during those seasons. The observations conducted on 22–27 May 2015 and 7–10 August 2015 illustrated the successive periods of the first transitional season and the southeast monsoon season. The methods used for taking oceanographic data such as temperature, salinity, and current were the stationary oceanographic measurement using CTD and currentmeter at 29 stations located in surrounding waters of Selayar Island. The surface current pattern generated from the interpolation process of the overall observation stations indicated that during the first transitional season the current moved eastward with an average velocity of 0.25 m/s. During the southeast monsoon season, the same pattern was still observed with a slightly higher average velocity of 0.26 m/s. The temperatures and salinity of Selayar Island waters during the southeast monsoon season were 2°C lower and 0.5 psu higher than during the first transitional season. Differences in mean current velocity values tended to be more affected by local tidal conditions. Different salinity was thought to be influenced by upwelling phenomena and local climatic factors such as rainfall, wind, and river flow discharge.

Estimation of extreme marine hydrodynamic variables in western Laizhou Bay

Laizhou Bay and its adjacent waters are of great importance to China’s marine oil and gas development. It is therefore crucial to estimate return-period values of marine environmental variables in this region to ensure the safety and success of maritime engineering and maritime exploration. In this study, we used numerical simulations to estimate extreme wave height, sea current velocity and sea-level height in western Laizhou Bay. The results show that the sea-level rise starts at the mouth of the bay, increases toward west/southwest, and reaches its maximum in the deepest basin of the bay. The 100-year return-period values of sea level rise can reach 3.4–4.0 m in the western bay. The elevation of the western part of the Qingdong Oil Field would remain above the sea surface during extreme low sea level, while the rest of the oil field would be 1.6–2.4 m below the sea surface. The return-period value of wave height is strongly affected by water depth; in fact, its spatial distribution is similar to the isobath’s. The 100-year return-period values of effective wave height can be 6 m or higher in the central bay and be more than 1 m in the shallow water near shore. The 100-year return-period values of current velocity is about 1.2–1.8 m s−1 in the Qingdong Oil Field. These results provide scientific basis for ensuring construction safety and reducing construction cost.

Potential impacts of the mean sea level rise on the hydrodynamics of the Douro river estuary

Numerous studies based on tide gauge records demonstrated the sea level rise on the Portuguese coast during the last century. Different climatic models predict a mean sea level rise for this coast ranging between 0.28 m and 0.42 m, for the period 2091–2100 relative to 1980–1999. Thus, the potential evaluation of the sea level rise impact on the Portuguese coast becomes critical, especially in sensitive areas as estuaries. The main aim of this work is to evaluate hydrodynamic changes in the Douro estuary induced by the sea level rise. A baroclinic finite volume numerical model was implemented to the Douro estuary in a 2D mode. The model calibration was performed comparing predicted and observed sea surface elevation time series for several stations. The tidal input at the ocean open boundary forces the 2D hydrodynamic model considering actual and future mean sea levels. At the landward boundary the model is forced with the freshwater discharge. The research explores changes in current velocity and amplitude and phase differences of the main diurnal and semi-diurnal tidal constituents along the estuary. The results suggest local significant changes in the Douro hydrodynamics in response to the sea level rise. Nevertheless, the differences don't affect the general estuary’s circulation. Concerning the main tidal constituents, the amplitude increases and the phase decreases, revealing that the tide tends to propagate faster upstream and with higher tidal ranges. Owing to the increasing of the amplitude and the water level, the current velocity values tend to decrease in the estuary, mainly near the low-lying areas.

Physical factors influencing immature-fish communities in the surf zones of sandy beaches in northwestern Kyushu Island, Japan

We aim to understand the relationships between physical conditions and characteristics of the immature-fish community in surf zones of sandy beaches. Therefore, we obtained fish samples between March 2007 and February 2008 and analyzed certain physical conditions in the surf zones of 21 sandy beaches on the coastline of the northwestern Kyushu Island, Japan. We collected a total of 83 species and 6458 immature individuals. In a BIO-ENV analysis, the highest correlation was observed between fish assemblage and S20 (i.e., the slope from the shoreline to the sites where the depth was 20 m) and current velocity (CV) values. Stepwise multiple linear regression analyses revealed that the number of species and individuals decrease with an increase in the S20 and CV values. These results show that species richness and the abundance of immature-fish increase under shelving and calm conditions. Thus, immature-fish assemblages are strongly influenced by the prevailing physical conditions. Moreover, in six of the 10 dominant species, a negative correlation was observed between CV and abundance. On the other hand, S20 was found to be the explanatory variable only in the case of the most dominant species, i.e., Gymnogobius breunigii. Furthermore, a positive correlation was observed between S1 (i.e., the slope from the shoreline to the sites where the depth was 1.0 m at the mean tidal level) and median particle size (i.e., MPS of the sediments) and the abundances of Sillago japonica and Favonigobius gymnauchen, respectively, and a negative correlation with salinity, in the case of Acanthogobius lactipes. We conclude that the characteristics of the fish community in surf zones on sandy beaches are determined by not only the shelving and calm conditions, which influence fish assemblages and abundances, but also the habitat diversity, which influences the diversity of fish species.

A cellular automaton model of traffic considering the dynamic evolution of velocity randomization probability

Few cellular automaton models of traffic have taken the relationship between the randomization probability of velocity and the specific value of current velocity into account. On the basis of Nagel-Schreckenberg model, this paper presents a modified cellular automaton model in which the randomization probability evolves with the driver’s remembering to historic experience and with the traffic condition around. Numerical simulation results show that the proposed model can reveal the influence of driver’s remembering on the traffic and generate higher average velocity and flux.

Mathematical modeling of mineral nitrogen, mineral phosphorus transfer and water current in the Curonian Bay

4 Laboratory of Nuclear Hydrophysics, Vilnius Gediminas Technical University, Saulėtekio 11, LT-10223 Vilnius, Lithuania E-mail: linasg@dtiltas.lt Monitoring of mineral nitrogen, mineral phosphorus concentrations and water current ve­ locities in the northern part of the Curonian Bay was carried out on April 10 and 11, 2002. Investigations of the mentioned parameters were carried out in the Lithuanian part of the Curonian Bay between Kaliningrad Region and the Klaipėda Strait, and the hydrometeoro­ logical situations were considered simultaneously. Mineral nitrogen concentration in the period of observations were varied within 1.240 and 1.711 mg/l, and mineral phosphorus concentrations ranged from 0 to 0.009 mg/l. Wa­ ter current velocity values ranged between 0.01 and 0.3 m/s. Nitrogen and phosphorus promote biological water pollution. Transfer of these admix­ tures depends on water stream velocities and direction. Therefore, mathematical modeling of the processes of admixture transfer and water current was proposed. The method of objective analysis was used for calculating the concentration field of mineral nitrogen, mineral phosphorus and the field of water current velocities. Because of the lack of measurement results, repeated calculations were carried out to find an optimum coincidence of the calculation and measurement data. Autocorrelation functions of mine­ ral nitrogen, mineral phosphorus and water current velocities were calculated. The agreement between the measurement and calculation results was satisfactory.

Development of large fish farm numerical modeling techniques with in situ mooring tension comparisons

A study is conducted to validate a numerical model for calculating mooring system tensions of a large fish farm containing 20 net pens in the absence of waves. The model is forced using measured current velocity values obtained outside of the farm. Mooring line tensions calculated with the numerical model are compared with load cell field data sets. The approach considers current velocity reduction and load characteristics that occur through the net pen system for both clean and fouled net conditions. Without accounting for the reduction, the numerical model produces excessively conservative results. With reduction, a substantial improvement occurs. Understanding these differences will help to establish appropriate safety factors when designing large marine fish farms using the model. Additional validation studies should be conducted with wave and current forcing to investigate the modeling of large fish farms for exposed or open ocean sites.

STIRRING-UP OF SOFT SEA BED MATERIAL DUE TO ACTIONS OF WAVES AND CURRENTS IN OSAKA BAY

Stirring-up of soft sea bed material in Osaka Bay were investigated through field observations and hydraulic experiments. Field observations were carried out at the point of 14m-deep and 15km apart from Kansai International Airport. The bed material size at the filed is 0.01mm in mean diameter. Echo Intensity data of ADCP were used to detect the stirring-up of bottom material induced by wave and current. The threshold value of current velocity for stirring-up has been estimated to be about 20-cm/s. The different properties of stirring-up between fine sand and silt were has experimentally been checked in wave oscillatory flow in t e wave channel. In less than 10cm/s flow condition, the fine sand was stirried-up easily with ripple formation. The silt needs fas er current for stirring-up because it could not move individually.

Hydraulic Microdistribution of Cased Caddis Larvae in an Austrian Mountain Brook

AbstractWater velocity acting at the upper edge of the case opening was measured at the locations of 1074 cased caddis larvae along a cross section of the Seebach near Lunz Biological Station (Lower Austria). In addition, Froude number, boundary Reynolds number, bottom shear stress and thickness of the viscous sublayer were measured at the center of contagious sampling squares of 30 × 30 cm over the same cross section. Measurements were made at monthly intervals from 2 November 1993 to 24 October 1994 using an impeller‐meter (Ott C2; propeller diameter = 30 mm) and a set of FST hemispheres. A total of 16 species was recorded with Drusus biguttatus Pictet, Allogamus auricollis Pictet and Potamophylax cingulatus Stephens being most abundant. Maximum values of current velocity and hydraulic stress parameters (e.g. Froude numbers up to 0.90) were recorded for D. biguttatus. P. cingulatus and Glossosoma conformis Neboiss, whereas lowest values of hydraulic stress parameters were observed in Sericostoma flavicorne Schneider. In addition, up to 40% of the population in Drusinae species and P. cingulatus was over‐represented in high stress areas at the streambed, whilst up to 36% of the population in S. flavicorne and Allogamus spp. were over‐represented in low stress areas.

Avoiding stick-slip through PD control

Addresses the question of how to achieve steady motion at very low velocities using proportional-derivative (PD) control. Most prior work in control has used friction models which depend only on the current value of velocity. This type of analysis indicates that stick-slip can be avoided only through velocity feedback. The tribology literature, however, indicates that friction also depends on the history of motion. By including this dependence, a second regime of stable motion is revealed which is associated with position feedback gains above a critical value. Two experimentally-based dynamic friction models are compared using a linearized stability analysis. In accord with experiment, a state variable friction model exhibits asymptotically stable motion for any system stiffness (position feedback gain) exceeding a critical value. This property is not exhibited by a time-lag friction model. >

Optoelectronic system for the measurements of ship models trajectory

When using self-propelled ship models, it is necessary to observe and record a trajectory of actual movement and also to determine a current value of velocity and acceleration. An optoelectronic system for determining and recording the trajectory of the model has been developed. It operates over an 150 m*150 m area with a fundamental error of less than 0.1 m and consists of an optical transmitter aboard the model and two stations ashore connected to a computer placed in a remote operational room. The directional angles are measured by two receiving telescopes (one for each station ashore), which are rotating with an angular velocity approximately 15 rad/s. The coordinates of the model are obtained by simple arithmetic. Errors of measurements and the maximum range of operation are also discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ciliated Colonization of Artificial Substrates in Different Saprobic Conditions in a Running Water

AbstractThis work investigates the effect of water current velocity and organic load on the colonization rate of ciliated Protozoa in periphyton communities. Artificial substrates (glass slides) were placed at three stations in a small mountain stream which runs through urban and industrial areas. The first station was located in an oligosaprobic to beta‐mesosaprobic zone, the second in an alfa‐mesosaprobic zone, and the third station in an alfa‐mesosaprobic to polysaprobic zone. At each station three substrates were placed in biotopes of different current velocity values (5… 20 cm/ sec., 20… 40 cm/sec. and 50… 70 cm/sec.). With such a distribution of artificial substrates it was possible to study the effect of the water current velocity on the colonization dynamics of ciliates in particular saprobic zones.