scholarly journals Divergence and Vorticity from Aircraft Air Motion Measurements

2007 ◽  
Vol 24 (12) ◽  
pp. 2062-2072 ◽  
Author(s):  
Donald H. Lenschow ◽  
Verica Savic-Jovcic ◽  
Bjorn Stevens
Keyword(s):  
Wind Field ◽  
Numerical Models ◽  
Field Measurements ◽  
Air Velocity ◽  
Flow Distortion ◽  
Marine Stratocumulus ◽  
Least Squares Fit ◽  
Wind Measurements ◽  
Viable Approach ◽  
Field Systematic

Abstract This paper considers the accuracy of divergence estimates obtained from aircraft measurements of the horizontal velocity field and points out an error that appears in these estimates that has heretofore not been addressed. A procedure for eliminating this error is presented. The divergence and vorticity are estimated from the coefficients of a least squares fit to a wind field obtained from the Second Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II) circular flight legs. These estimates are compared with estimates from numerical models and satellites and with airplane estimates based on tracer budgets and the temporal changes in cloud-top height. The estimates are consistent with expectations and estimates using other methods, albeit somewhat high. Furthermore, significant differences occur among the cases, likely due to the large differences in the techniques. The results indicate that the wind field technique is a viable approach for estimating mesoscale divergence if the wind measurements are accurate. The largest source of wind field systematic error may be the result of flow distortion effects on the air velocity measurement and limitations of in-flight calibrations. Because of flow distortion, the only way the current systems can be calibrated is by flight maneuvers, which assume a steady-state homogeneous nonturbulent atmosphere. Analysis of the errors in this technique suggests that wind field measurements with minimal systematic errors should provide estimates of divergence with much greater accuracy than is now possible with other existing methods.

Hydrodynamic influences on sedimentology and geomorphology of nearshore parts of carbonate ramps: Holocene, NE Yucatán Shelf, Mexico

2021 ◽  
Vol 91 (10) ◽  
pp. 1040-1066
Author(s):  
Thomas C. Neal ◽  
Christian M. Appendini ◽  
Eugene C. Rankey
Keyword(s):  
Numerical Models ◽  
Remote Sensing Data ◽  
Field Measurements ◽  
High Energy ◽  
Tidal Range ◽  
Carbonate Platforms ◽  
Trade Winds ◽  
Tidal Forces ◽  
Carbonate Ramps ◽  
Geologic Record

ABSTRACT Although carbonate ramps are ubiquitous in the geologic record, the impacts of oceanographic processes on their facies patterns are less well constrained than with other carbonate geomorphic forms such as isolated carbonate platforms. To better understand the role of physical and chemical oceanographic forces on geomorphic and sedimentologic variability of ramps, this study examines in-situ field measurements, remote-sensing data, and hydrodynamic modeling of the nearshore inner ramp of the modern northeastern Yucatán Shelf, Mexico. The results reveal how sediment production and accumulation are influenced by the complex interactions of the physical, chemical, and biological processes on the ramp. Upwelled, cool, nutrient-rich waters are transported westward across the ramp and concentrated along the shoreline by cold fronts (Nortes), westerly regional currents, and longshore currents. This influx supports a mix of both heterozoan and photozoan fauna and flora in the nearshore realm. Geomorphically, the nearshore parts of this ramp system in the study area include lagoon, barrier island, and shoreface environments, influenced by the mixed-energy (wave and tidal) setting. Persistent trade winds, episodic tropical depressions, and winter storms generate waves that propagate onto the shoreface. Extensive shore-parallel sand bodies (beach ridges and subaqueous dune fields) of the high-energy, wave-dominated upper shoreface and foreshore are composed of fine to coarse skeletal sand, lack mud, and include highly abraded, broken and bored grains. The large shallow lagoon is mixed-energy: wave-dominated near the inlet, it transitions to tide-dominated in the more protected central and eastern regions. Lagoon sediment consists of Halimeda-rich muddy gravel and sand. Hydrodynamic forces are especially strong where bathymetry focuses water flow, as occurs along a promontory and at the lagoon inlet, and can form subaqueous dunes. Explicit comparison among numerical models of conceptual shorefaces in which variables are altered and isolated systematically demonstrates the influences of the winds, waves, tides, and currents on hydrodynamics across a broad spectrum of settings (e.g., increased tidal range, differing wind and wave conditions). Results quantify how sediment transport patterns are determined by wave height and direction relative to the shoreface, but tidal forces locally control geomorphic and sedimentologic character. Similarly, the physical oceanographic processes acting throughout the year (e.g., daily tides, episodic winter Nortes, and persistent easterly winds and waves) have more impact on geomorphology and sedimentology of comparable nearshore systems than intense, but infrequent, hurricanes. Overall, this study provides perspectives on how upwelling, nutrient levels, and hydrodynamics influence the varied sedimentologic and geomorphic character of the nearshore areas of this high-energy carbonate ramp system. These results also provide for more accurate and realistic conceptual models of the depositional variability for a spectrum of modern and ancient ramp systems.

Flow Fields Inside Stocked Fish Cages and the Near Environment

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Lars C. Gansel ◽  
Siri Rackebrandt ◽  
Frode Oppedal ◽  
Thomas A. McClimans
Keyword(s):  
Atlantic Salmon ◽  
Water Flow ◽  
Laboratory Tests ◽  
Numerical Models ◽  
Field Measurements ◽  
Flow Patterns ◽  
Fish Swimming ◽  
Swimming Depth ◽  
Starting Point ◽  
Fish Cages

This study explores the average flow field inside and around stocked Atlantic salmon (Salmo salar L.) fish cages. Laboratory tests and field measurements were conducted to study flow patterns around and through fish cages and the effect of fish on the water flow. Currents were measured around an empty and a stocked fish cage in a fjord to verify the results obtained from laboratory tests without fish and to study the effects of fish swimming in the cage. Fluorescein, a nontoxic, fluorescent dye, was released inside a stocked fish cage for visualization of three-dimensional flow patterns inside the cage. Atlantic salmon tend to form a torus shaped school and swim in a circular path, following the net during the daytime. Current measurements around an empty and a stocked fish cage show a strong influence of fish swimming in this circular pattern: while most of the oncoming water mass passes through the empty cage, significantly more water is pushed around the stocked fish cage. Dye experiments show that surface water inside stocked fish cages converges toward the center, where it sinks and spreads out of the cage at the depth of maximum biomass. In order to achieve a circular motion, fish must accelerate toward the center of the cage. This inward-directed force must be balanced by an outward force that pushes the water out of the cage, resulting in a low pressure area in the center of the rotational motion of the fish. Thus, water is pulled from above and below the fish swimming depth. Laboratory tests with empty cages agree well with field measurements around empty fish cages, and give a good starting point for further laboratory tests including the effect of fish-induced currents inside the cage to document the details of the flow patterns inside and adjacent to stocked fish cages. The results of such experiments can be used as benchmarks for numerical models to simulate the water flow in and around net pens, and model the oxygen supply and the spreading of wastes in the near wake of stocked fish farms.

Rainfall Anomaly over the Lee Side of Mount Carmel (Israel) and the Associated Wind Field

1997 ◽  
Vol 36 (6) ◽  
pp. 748-762 ◽  
Author(s):  
Yair Goldreich ◽  
Ariel Freundlich ◽  
Pinhas Alpert
Keyword(s):  
Wind Field ◽  
Rain Gauge ◽  
Rainfall Anomaly ◽  
Windward Side ◽  
Two Dimensional ◽  
Local Enhancement ◽  
Flow Disturbance ◽  
Model Simulations ◽  
Israel Experience ◽  
Wind Measurements

Abstract Yagur and other rain gauge stations located on the lee side of Mount Carmel in Israel experience much higher amounts of precipitation than those measured on the windward side of the mountain at a similar altitude and more rain than stations on the mountain itself. This phenomenon is consistently observed, and in the current study it is investigated primarily by means of simultaneous rain–wind observations and by using a two-dimensional simplified orographic model. Orographic model simulations suggest the existence of a flow disturbance at the lee of Mount Carmel, which might cause local rain enhancement. Results from the anemograph placed at Yagur, along with other wind measurements in the Carmel region, support the findings of this model. Observations depict the disturbed flow that occurred at the lee of Mount Carmel and was associated with rain enhancement. The channeled flow caused horizontal convergence, which is in accordance with the second hypothesis. Observations during the rainy periods indicate that the rain enhancement in Yagur is associated with the ridge-parallel flow on the lee side of the mountain. It is hypothesized that the horizontal convergence of the leeside flow with the flow over the mountain causes the local enhancement of precipitation.

Fish cage and mooring system dynamics using physical and numerical models with field measurements

2003 ◽  
Vol 27 (2) ◽  
pp. 117-146 ◽  
Author(s):  
David W. Fredriksson ◽  
M.Robinson Swift ◽  
James D. Irish ◽  
Igor Tsukrov ◽  
Barbaros Celikkol
Keyword(s):  
System Dynamics ◽  
Numerical Models ◽  
Field Measurements ◽  
Mooring System

scholarly journals Modeling Assessment of Tidal Energy Extraction in the Western Passage

2020 ◽  
Vol 8 (6) ◽  
pp. 411
Author(s):  
Zhaoqing Yang ◽  
Taiping Wang ◽  
Ziyu Xiao ◽  
Levi Kilcher ◽  
Kevin Haas ◽  
...  
Keyword(s):  
Cross Sections ◽  
Numerical Models ◽  
Three Dimensional ◽  
Energy Resource ◽  
Field Measurements ◽  
Tidal Energy ◽  
Resource Assessment ◽  
Ocean Model ◽  
Energy Extraction ◽  
Technical Specifications

Numerical models have been widely used for the resource characterization and assessment of tidal instream energy. The accurate assessment of tidal stream energy resources at a feasibility or project-design scale requires detailed hydrodynamic model simulations or high-quality field measurements. This study applied a three-dimensional finite-volume community ocean model (FVCOM) to simulate the tidal hydrodynamics in the Passamaquoddy–Cobscook Bay archipelago, with a focus on the Western Passage, to assist tidal energy resource assessment. IEC Technical specifications were considered in the model configurations and simulations. The model was calibrated and validated with field measurements. Energy fluxes and power densities along selected cross sections were calculated to evaluate the feasibility of the tidal energy development at several hotspots that feature strong currents. When taking both the high current speed and water depth into account, the model results showed that the Western Passage has great potential for the deployment of tidal energy farms. The maximum extractable power in the Western Passage was estimated using the Garrett and Cummins method. Different criteria and methods recommended by the IEC for resource characterization were evaluated and discussed using a sensitivity analysis of energy extraction for a hypothetical tidal turbine farm in the Western Passage.

scholarly journals Field Measurements of Wind Characteristics Using LiDAR on a Wind Farm with Downwind Turbines Installed in a Complex Terrain Region

Energies ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 5135
Author(s):  
Tetsuya Kogaki ◽  
Kenichi Sakurai ◽  
Susumu Shimada ◽  
Hirokazu Kawabata ◽  
Yusuke Otake ◽  
...  
Keyword(s):  
Wind Speed ◽  
Wind Farm ◽  
Field Experiments ◽  
Wind Farms ◽  
Field Measurements ◽  
Horizontal Wind ◽  
Flow Distortion ◽  
Horizontal Wind Speed ◽  
Vertical Profiling ◽  
Wind Characteristics

Downwind turbines have favorable characteristics such as effective energy capture in up-flow wind conditions over complex terrains. They also have reduced risk of severe accidents in the event of disruptions to electrical networks during strong storms due to the free-yaw effect of downwind turbines. These favorable characteristics have been confirmed by wind-towing tank experiments and computational fluid dynamics (CFD) simulations. However, these advantages have not been fully demonstrated in field experiments on actual wind farms. In this study—although the final objective was to demonstrate the potential advantages of downwind turbines through field experiments—field measurements were performed using a vertical-profiling light detection and ranging (LiDAR) system on a wind farm with downwind turbines installed in complex terrains. To deduce the horizontal wind speed, vertical-profiling LiDARs assume that the flow of air is uniform in space and time. However, in complex terrains and/or in wind farms where terrain and/or wind turbines cause flow distortion or disturbances in time and space, this assumption is not valid, resulting in erroneous wind speed estimates. The magnitude of this error was evaluated by comparing LiDAR measurements with those obtained using a cup anemometer mounted on a meteorological mast and detailed analysis of line-of-sight wind speeds. A factor that expresses the nonuniformity of wind speed in the horizontal measurement plane of vertical-profiling LiDAR is proposed to estimate the errors in wind speed. The possibility of measuring and evaluating various wind characteristics such as flow inclination angles, turbulence intensities, wind shear and wind veer, which are important for wind turbine design and for wind farm operation is demonstrated. However, additional evidence of actual field measurements on wind farms in areas with complex terrains is required in order to obtain more universal and objective evaluations.

scholarly journals Study of Current- and Wave-Induced Sediment Transport in the Nowshahr Port Entrance Channel by Using Numerical Modeling and Field Measurements

2020 ◽  
Vol 8 (4) ◽  
pp. 284 ◽  
Author(s):  
Ayyuob Mahmoodi ◽  
Mir Ahmad Lashteh Neshaei ◽  
Abbas Mansouri ◽  
Mahmood Shafai Bejestan
Keyword(s):  
Numerical Modeling ◽  
Caspian Sea ◽  
Recirculation Zone ◽  
Numerical Models ◽  
Field Measurements ◽  
Sediment Sources ◽  
The Caspian Sea ◽  
Access Channel ◽  
Negative Impacts ◽  
Wave Induced

The Nowshahr port in the southern coastlines of the Caspian Sea is among the oldest northern ports of Iran, first commissioned in the year 1939. In recent years, this port has been faced with severe sedimentation issues in and around its entrance that has had negative impacts on the operability of the port. The present study aims at identifying major reasons for severe sedimentation in the port entrance. First, field measurements were evaluated to gain an in-depth view of the hydrodynamics of the study area. Numerical models then were calibrated and validated against existing field measurements. Results of numerical modeling indicated that wind-induced current is dominant in the Caspian Sea. The numerical results also indicated that in the case of an eastward current direction, the interaction between current and the western breakwater arm would lead to the formation of a separation zone and a recirculation zone to the east of the port entrance region. This eddying circulation could transport suspend settled sediments from eastern shoreline towards the port entrance and its access channel. The results of this paper are mostly based on the study of current patterns around the port in the storm conditions incorporate with the identification of sediment sources.

scholarly journals Demonstration of an efficient interpolation technique of inverse time and distance for Oceansat-2 wind measurements at 6-hourly intervals

2017 ◽  
Vol 8 (3) ◽  
pp. 101-112 ◽  
Author(s):  
J Swain ◽  
P A Umesh ◽  
A S N Murty
Keyword(s):  
Wind Speed ◽  
State Of The Art ◽  
Numerical Models ◽  
Ocean Surface ◽  
The State ◽  
Wind Fields ◽  
Interpolation Technique ◽  
Ocean Surface Winds ◽  
Wind Measurements ◽  
Global Oceans

Indian Space Research Organization had launched Oceansat-2 on 23 September 2009, and the scatterometer onboard was a space-borne sensor capable of providing ocean surface winds (both speed and direction) over the globe for a mission life of 5 years. The observations of ocean surface winds from such a space-borne sensor are the potential source of data covering the global oceans and useful for driving the state-of-the-art numerical models for simulating ocean state if assimilated/blended with weather prediction model products. In this study, an efficient interpolation technique of inverse distance and time is demonstrated using the Oceansat-2 wind measurements alone for a selected month of June 2010 to generate gridded outputs. As the data are available only along the satellite tracks and there are obvious data gaps due to various other reasons, Oceansat-2 winds were subjected to spatio-temporal interpolation, and 6-hour global wind fields for the global oceans were generated over 1 × 1 degree grid resolution. Such interpolated wind fields can be used to drive the state-of-the-art numerical models to predict/hindcast ocean-state so as to experiment and test the utility/performance of satellite measurements alone in the absence of blended fields. The technique can be tested for other satellites, which provide wind speed as well as direction data. However, the accuracy of input winds is obviously expected to have a perceptible influence on the predicted ocean-state parameters. Here, some attempts are also made to compare the interpolated Oceansat-2 winds with available buoy measurements and it was found that they are reasonably in good agreement with a correlation coefficient of R > 0.8 and mean deviation 1.04 m/s and 25° for wind speed and direction, respectively.

Modelling seasonal evapotranspiration of arid lands in China

2011 ◽  
Vol 42 (1) ◽  
pp. 40-49 ◽  
Author(s):  
Yuanrun Zheng ◽  
Zhixiao Xie ◽  
Charles Roberts ◽  
Ping An ◽  
Xiangjun Li ◽  
...  
Keyword(s):  
Water Balance ◽  
Water Resource Management ◽  
Numerical Models ◽  
Field Measurements ◽  
Western China ◽  
Actual Evapotranspiration ◽  
Climate Data ◽  
Robust Model ◽  
Proposed Model ◽  
Local Soil

The measurement of actual evapotranspiration, a key term in the water balance equation, has become a very important issue. Many good methods exist for estimating actual evapotranspiration; however, most of these require complicated inputs. Here, a simple but robust model for estimation of actual evapotranspiration in arid areas of western China is proposed. This model is a visual system with a user-friendly interface in the STELLA (a commercial software package for building numerical models) environment combined with two existing water balance equations and local soil and climate data to ensure its easy application in developing areas. Validation with field measurements revealed that the estimated values of actual evapotranspiration obtained using the model are in agreement with the observed values. Both the established Choudhury model and the proposed model produced similar estimates when the actual annual evapotranspiration is below 200 mm, but the model proposed simulates real-world conditions more precisely when the actual annual evapotranspiration is greater than 200 mm. Another advantage of the proposed model is that it uses simple and reliable climate data that are readily available from the network of weather stations in China. The simulation results could serve as a relatively good reference for water resource management in this area.

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