Measured Flow Data Research Articles

Rheology of self-compacting concrete containing silica fume and recycled aggregates

Rheology of Self-Compacting Concrete (SCC) containing selected silica fume dosages (0% (control mix), 5%, 10% and 15%) in a binary binder has been investigated using the flow-curve test protocol implemented on a co-axial cylinder rheometer. At each silica fume dosage, coarse recycled concrete aggregate volumetric replacement levels were 0%, 50% and 100%. Calibration of selected flow models with the measured flow data showed that rheology transitioned from shear thickening to shear thinning as the silica fume dosage increased from 0% to 15%, other mix constituents remaining unchanged. Similar flow behaviour was noted in the SCCs made with the recycled concrete aggregates (SCRACs) across all replacement levels though for a given silica fume dosage, degree of shear thinning decreased with increasing contents of the coarse recycled aggregates. The experimental results have been used to propose a workability box containing bounds for acceptable rheology of the SCCs and the SCRACs.

Turbulent flow interacting with flexible trawl net structure including simulation catch in flume tank

The interaction between fluid and the midwater trawl with stocked catches is extremely complex, but essential to improve the understanding of the drag force acting on the trawl, the behavior of the fishing structure during a trawling process, and to predict its selectivity process. The present study assesses the turbulent characteristics inside and around the midwater trawls with catch and without catch linked to its fluttering motion. The analysis is based on three-dimensional electromagnetic current velocity meter measurements performed in the multiple points inside and outside different parts of a 1/35 scaled midwater trawl model with the aim of access the main turbulent flow structure inside and around the gear. Time-averaged normalized flow velocity fields and turbulent flow parameters were analyzed from the measured flow data. Furthermore, Fourier analysis was conducted by watching the time–frequency Power spectrum content of instantaneous flow velocities fields, the fluttering trawl motions, turbulent kinetic energy, and momentum flux. Based on successive analyzes of mean flow characteristics and turbulent flow parameters, it has been demonstrated that the presence of catch inside the trawl net impacts the evolution of unsteady turbulent flow by creating large trawl fluttering motions that strongly affect the flow passage. The results showed that the time-averaged normalized streamwise and transverse flow velocities inside and around the trawl net with catch were 12.41% lower compared with that obtained inside and around the trawl without catch. The turbulent length scale and turbulent Reynolds number obtained in the different part of the trawl net with catch were about 33.05% greater than those obtained on the trawl net without catch, confirming that the unsteady turbulent flow developing inside and around the midwater trawl is influence by the catch and liner. It is observed that the motions of both the trawl without catch and the trawl with catch are mainly of a low-frequency activity and another component related to unsteady turbulent flow street. A complex fluid–structure interaction is then demonstrated where the fluttering motions of the trawl net affect the fluid flow inside and around trawl net, the fluid force, turbulent pattern, and simultaneously, the periodic unsteady turbulent flow influence the trawl motions.

Model and application of inversion data cleaning for flow monitoring stations in the middle route of the South-to-North Water Diversion Project

For a long-distance open-channel water transfer project, the correctness of the hydrological state study and hydrodynamic numerical simulation is impacted directly by the spatiotemporal and consistency of the flow monitoring data along the project. Reported here is an inverted data cleaning model for flow monitoring stations based on the principle of water dynamic balance and the longest sequence method of interval flow, targeting the abnormal phenomenon of unequal flow at monitoring stations in the dispatching operation and using the middle route of the South-to-North Water Diversion Project in China as the research object. As an example, a hydrodynamic model is built for verification using flow and water level data after model cleaning as the upper and lower boundaries, respectively, for the middle-route project from the Baihe River to Huangjin River. The findings indicate that the cleaning model enhances the accuracy of flow monitoring data and reduces both the mean absolute error of the water level in front of the gate and the root-mean-square error by 0.0757 and 0.0895 m, respectively. In terms of data spatial consistency and logic, the cleaned flow data are superior to the measured flow data.

Comparison of the SCS-CN and Hydrograph Separation Method for Runoff Estimation in an Ungauged Basin: The Izmit Basin, Turkey

The separation of surface runoff and base flow is a very specific problem in water balance calculations, particularly if there is not enough measured flow data. In this study, the SCS-CN method is used to estimate the surface runoff in the ungauged Izmit Basin. The CNs are estimated using the Hydrologic Soil Groups map, based on soil data of the General Directorate of Rural Services of Turkey and land use obtained from the CORINE-2006 database for different AMCs. The surface runoff was computed using the SCS-CN method for the ungauged Izmit Basin that corresponds to 17% and 21% of the rainfall, i.e. 134 mm (for Kocaeli Meteorological Station; rainfall=804 mm) and 171 mm (for Sakarya Meteorological Station; rainfall=820 mm). According to SCS-CN method estimates, approximately 41-42% of the annual rainfall in the Izmit Basin directly contributes to the total streamflow, and 21-25% of it contributes to base flow and unmeasured infiltration. To compare the results of the SCS-CN method along with hydrograph separation method, the gauged Yuvacık Dam Sub-Basin, which is hydro-meteorologically similar to the Izmit Basin, was selected. The results showed that 16% of the rainfall in the Yuvacık Dam Sub-Basin became surface runoff. Also, it was found that about 42% of the annual rainfall in the Yuvacık Dam Sub-Basin directly contributes to the total streamflow and 23% of it contributes to the base flow and unmeasured infiltration. These results confirm that the ratio of surface runoff obtained by the hydrograph separation method in the Yuvacık Dam Sub-Basin matches with the ratio of surface runoff calculated using the SCS-CN method for the entire Izmit Basin.

A hybrid hierarchical strategy for registration of 7T TOF-MRI to 7T PC-MRI intracranial vessel data

Purpose7T time-of-flight (TOF) MRI provides high resolution for the evaluation of cerebrovascular vessels and pathologies. In combination with 4D flow fields acquired with phase-contrast (PC) MRI, hemodynamic information can be extracted to enhance the analysis by providing direct measurements in the larger arteries or patient-specific boundary conditions. Hence, a registration between both modalities is required.MethodsTo combine TOF and PC-MRI data, we developed a hybrid registration approach. Vessels and their centerlines are segmented from the TOF data. The centerline is fit to the intensity ridges of the lower resolved PC-MRI data, which provides temporal information. We used a metric that utilizes a scaled sum of weighted intensities and gradients on the normal plane. The registration is then guided by decoupled local affine transformations. It is applied hierarchically following the branching order of the vessel tree.ResultsA landmark validation over Monte Carlo simulations yielded an average mean squared error of 184.73 mm and an average Hausdorff distance of 15.20 mm. The hierarchical traversal that transforms child vessels with their parents registers even small vessels not detectable in the PC-MRI.ConclusionThe presented work combines high-resolution tomographic information from 7T TOF-MRI and measured flow data from 4D 7T PC-MRI scan for the arteries of the brain. This enables usage of patient-specific flow parameters for realistic simulations, thus supporting research in areas such as cerebral small vessel disease. Automatization and free deformations can help address the limiting error measures in the future.

Understanding Hydrological Processes under Land Use Land Cover Change in the Upper Genale River Basin, Ethiopia

The expansion of cultivated land in place of natural vegetation has a substantial influence on hydrologic characteristics of a watershed. However, due to basin characteristics and the nature and intensity of landscape modification, the response varies across basins. This study aims to evaluate the performance of a soil and water assessment tool (SWAT) model and its applicability in assessing the effects of land use land cover (LULC) changes on the hydrological processes of the upper Genale River basin. The results of satellite change detection over the past 30 years (between 1986 and 2016) revealed that the landscape of the basin has changed considerably. They showed that settlement, cultivated, and bare land areas had increased from 0.16% to 0.28%, 24.4% to 47.1%, and 0.16% to 0.62%, respectively. On the contrary, land cover units such as forest, shrubland, and grassland reduced from 29.6% to 13.5%, 23.9% to 19.5%, and 21.8% to 18.9%, respectively. Based on monthly measured flow data, the model was calibrated and validated in SWAT-CUP using the sequential uncertainty fitting (SUFI-2) algorithm. The result showed that the model performed well with coefficient of determination (R2) ≥ 0.74, Nash–Sutcliffe efficiency (NSE) ≥ 0.72, and percent bias (PBIAS) between −5% and 5% for the calibration and validation periods. The hydrological responses of LULC change for the 1986, 2001, and 2016 models showed that the average annual runoff increased by 13.7% and 7.9% and groundwater flow decreased by 2.85% and 2.1% between 1986 and 2001 and 2001 and 2016, respectively. Similarly, the total water yields increased from 324.42 mm to 339.63 mm and from 339.63 mm to 347.32 mm between 1986 and 2001 and 2001 and 2016, respectively. The change in hydrological processes, mainly the rise in runoff and total water yield as well as the reduction in lateral and groundwater flow in the watershed, resulted from LULC changes. This change has broader implications for the planning and management of the land use and water resource development.

Impacts of Land-Use Change, Associated Land-Use Area and Runoff on Watershed Sediment Yield: Implications from the Kaduna Watershed

An uncontrolled sediment influx from the watershed upstream is a known threat to dam stability, while the pattern and amount of sediment yield are influenced by the predominant upstream land-use and land cover (LULC) types, precipitation amount, and intensity. Hence, the need to monitor sediment yield accumulation and its controlling factors in dam operation becomes crucial. In this paper, the Soil and Water Assessment Tool (SWAT) was used to assess the roles of land-use change, land cover area, and runoff on watershed’s sediment yield based on change detection analysis between 1975 and 2013 in the Kaduna Watershed (Nigeria), Western Africa. The SWAT standard procedures for the simulation of hydrological characteristics and sediment yields prediction were adopted. The datasets were calibrated for a period of 46 years and validated using 2015–2017 measured flow data, and suspended sediments concentration (SSC) acquired between March and October 2018. The model function was statistically determined using the Nash-Sutcliffe (NS), the coefficient of determination (r2) and the percentage of observed data (p-factor). The evaluation results of the SWAT model yielded NS, r2 and p-factor of 0.71, 0.80, and 0.86, respectively. These data suggest that the model performed satisfactorily for streamflow and sediment yield predictions. Findings suggest that the extinction of evergreen forests and a significant change in land-use from range grasses and forest to agriculture generic and residential types between 1975 and 2013, which resulted in surface runoff, sediment yield, and flow alteration. Evapotranspiration increased by 22.40% between 1975 and 2013. These changes have negatively impacted the watershed runoff by 56.00% and model sediment yield by 68.00% at the end of 2013. Thus, these variations can influence various human activities in the watershed, such as food security, livestock, energy production and water supply. It is hypothesized from the presented data that land use types exact a more dominant control on runoff and sediment yield than land cover area, although climatic influence may not be ruled out.

Comparison of the SCS-CN and Hydrograph Separation Method for Runoff Estimation in an Ungauged Basin: The Izmit Basin, Turke

The separation of surface runoff and base flow is a very specific problem in water balance calculations,particularly if there is not enough measured flow data. In this study, the SCS-CN method is used to estimate the surfacerunoff in the ungauged Izmit Basin. The CNs are estimated using the Hydrologic Soil Groups map, based on soil data ofthe General Directorate of Rural Services of Turkey and land use obtained from the CORINE-2006 database for differentAMCs. The surface runoff was computed using the SCS-CN method for the ungauged Izmit Basin that corresponds to17% and 21% of the rainfall, i.e. 134 mm (for Kocaeli Meteorological Station; rainfall=804 mm) and 171 mm (forSakarya Meteorological Station; rainfall=820 mm). According to SCS-CN method estimates, approximately 41-42% ofthe annual rainfall in the Izmit Basin directly contributes to the total streamflow, and 21-25% of it contributes to baseflow and unmeasured infiltration. To compare the results of the SCS-CN method along with hydrograph separationmethod, the gauged Yuvacık Dam Sub-Basin, which is hydro-meteorologically similar to the Izmit Basin, was selected.The results showed that 16% of the rainfall in the Yuvacık Dam Sub-Basin became surface runoff. Also, it was foundthat about 42% of the annual rainfall in the Yuvacık Dam Sub-Basin directly contributes to the total streamflow and 23%of it contributes to the base flow and unmeasured infiltration. These results confirm that the ratio of surface runoffobtained by the hydrograph separation method in the Yuvacık Dam Sub-Basin matches with the ratio of surface runoffcalculated using the SCS-CN method for the entire Izmit Basin.

Evaluation of hydrological modeling using climatic station and gridded precipitation dataset

The conventional rainfall data estimates are relatively accurate at some points of the region. The interpolation of such type of data approximates the actual rainfield however in data scarce regions; the resulted rainfield is the rough estimate of the actual rainfall events. In data scarce regions like Indus basin Pakistan, the data obtained through remote sensing can be very useful. This research evaluates two types of gridded data i.e., European Reanalysis (ERA) interim and Japanese Reanalysis 55 years (JRA-55) along with the climatic station data for three small dams in Pakistan. Since no measured flow data is available at these dams, the nearest possible catchments where flow data is available are calibrated and the calibrated parameters of these catchments are then used in actual dams for simulating the flow from all the three types of data using Soil and Water Assessment Tool (SWAT). The results of the comparison of gridded and rainguage precipitation shows that gridded data highly overestimates the climatic station data. Similar results were observed in the comparison of flow simulated by SWAT model. The Peak flood calculated from JRA-55 overestimates while the Era-Interim peak floods are comparable to that of climatic stations in two of the three catchments.

Elucidating the performance of hybrid models for predicting extreme water flow events through variography and wavelet analyses

Accurate prediction of extreme flow events is important for mitigating natural disasters such as flooding. We explore and refine two modelling approaches (both separately and in combination) that have been demonstrated to improve the prediction of daily peak flow events. These two approaches are firstly, models that aggregate fine resolution (sub-daily) simulated flow from a process-based model (PBM) to daily, and secondly, hybrid models that combine PBMs with statistical and machine learning methods. We propose the use of variography and wavelet analyses to evaluate these models across temporal scales. These exploratory methods are applied to both measured and modelled data in order to assess the performance of the latter in capturing variation, at different scales, of the former. We compare change points detected by the wavelet analysis (measured and modelled) with the extreme flow events identified in the measured data. We found that combining the two modelling approaches improves prediction at finer scales, but at coarser scales advantages are less pronounced. Although aggregating fine-scale model outputs improved the partition of wavelet variation across scales, the autocorrelation in the signal is less well represented as demonstrated by variography. We demonstrate that exploratory time-series analyses, using variograms and wavelets, provides a useful assessment of existing and newly proposed models, with respect to how they capture changes in flow variance at different scales and also how this correlates with measured flow data – all in the context of extreme flow events.

Hydrological Modeling: A Better Alternative to Empirical Methods for Monthly Flow Estimation in Ungauged Basins

Water resource is required for agricultural, industrial, and domestic activities and for environmental preservation. However, with the increase in population and growth of urbanization, industrialization, and commercial activities, planning and management of water resources have become a challenging task to meet various water demands globally. Information and data on streamflow hydrology are, thus, crucial for this purpose. However, availability of measured flow data in many cases is either inadequate or not available at all. When there is no gauging station available at the site of interest, various empirical methods are generally used to estimate the flow there and the best estimation is chosen. This study is focused on the estimation of monthly average flows by such methods popular in Nepal and assessment of how they compare with the results of hydrological simulation. Performance evaluation of those methods was made with a newly introduced index, Global Performance Index (GPI) utilizing six commonly used goodness-of-fit parameters viz. coefficient of determination, mean absolute error, root mean square error, percentage of volume bias, Nash Sutcliff Efficiency and Kling-Gupta Efficiency. This study showed that hydrological modeling is the best among the considered methods of flow estimation for ungauged catchments.

A mock circulation loop for in vitro haemodynamic evaluation of aorta

Haemodynamic conditions play a crucial role in the pathological development of aortic dissection (AD). However, it is challenging to quantitatively and precisely capture the flow features in vivo. In this study, a mock circulation loop (MCL) embedded with patient-specific aortic phantoms was proposed. In order to evaluate perfusion characters, a normal aortic model and an AD model were established with twelve main branches. The system is capable of replicating the aortic geometry, vascular compliance, characteristic resistance, and peripheral resistance of the cardiovascular system. By altering controlling parameters, it can mimic various cardiovascular conditions. The physiological healthy rest cardiac condition was reproduced and the rationality and accuracy of the system was confirmed by comparing the measured flow data from the MCL with a normal aortic phantom and the in vivo ultrasound velocimetry of healthy volunteers (maximum discrepancy was 4.69%). Different flow features between the normal and AD phantoms were quantitatively compared by pressure sensors and ultrasonic flow sensors under the same condition. Therefore, the proposed MCL can be applied as a research tool for in vitro haemodynamic analysis of the aorta. Moreover, it can be applied to evaluate the performance of interventional devices and to provide a realistic platform for trainings on interventional treatments.

Investigating the hydrological performance of green roofs using storm water management model

The green roof, also known as vegetated roof covers, or eco-roofs or natural roofs, is one of the recently developed low impact development (LID) techniques, which significantly increases water retention and thus helps to mitigate the urban flooding. In the present study, the installation of green roofs is assumed as a hypothetic retrofitting scenario according to a sustainable storm water mitigation strategy for a selected urban catchment and performance has been evaluated using Storm Water Management Model (SWMM). The model has been calibrated for the measured flow data of eight events using Nash-Sutcliffe Efficiency (NSE) Coefficient. The lowest and highest value of NSE was found 0.67 and 0.93 respectively. The hydrologic performance of the green roof was conducted under event-based as well as continuous simulation. Based on simulation results, peak flow has been reduced from 7.13 ltr/sec to 6.36 ltr/sec for Green Roof – 1 (GR-1) and 1.45 ltr/sec to 1.30 ltr/sec for Green Roof – 2 (GR-2). The simulation results point out that the integration of green roof LID contributes to the reduction of the quantity of storm water runoff by increasing the retention period. However, the hydrological behavior of a green roof is site-specific, and therefore the site-specific conditions and parameters like characteristics of the vegetation, physical properties of its layers, etc. have to be considered in the evaluation of its performance. Further, the research at the micro-level is necessary to evaluate the role of the green roof slope, the effect of vegetation cover, and the antecedent period on the performance of the green roofs for more reliable results.

Optimal design and operation of River Basin Storage

The State of Colorado’s Stream Simulation Model (StateMod) provides comparative analysis for historical and future water resource decisions and policies along the Lower South Platte River. In order to identify locations for increased water storage, our research uses simulated data produced by StateMod as input to a mixed integer-linear optimization model. This model minimizes the cost of meeting unmet demands by assigning network flow of, and designing additional storage for, excess water while adhering to constraints that force the physical and topographical structures of the river. Using historical, measured flow data from 1962 through 2012, we extend the capability of StateMod by considering solutions with the following characteristics: (1) a single-reservoir solution, (2) a solution in which we only expand existing reservoirs, and (3) a solution without the constraints in (1) or (2). We conclude that, for the time horizon considered, the optimal method to mitigate shortages is with the construction of a combination of smaller surface and sub-surface reservoirs, and a corresponding prescribed flow. The total increased storage volume is 25,378 acre-feet (AF). Our work can be used as a strategic analysis tool by planners and engineers to quickly identify the most effective reservoir locations and the order in which to build them, rather than examining every potential storage site and the time at which it should be built, if at all.

Calibration of Midstream Buoy Coefficient Based on Flow Measurement

The midstream float method is a standby flow measurement method adopted by hydrological stations when the river floods are rising and falling sharply and the flow meter is difficult to measure or special water regime occurs. In this paper, based on the Years of measured flow data of Xiaolongtan Hydrological Station of Nanpanjiang River, the Midstream Buoy Coefficient in the natural river course of Nanpanjiang River Basin is calculated and analyzed. The average buoy coefficient is calculated by measuring the actual flow divided by the imaginary flow and the average value is 0.76 and the maximum variation is less than 14%. This method can solve the actual needs of high flow measurement. The results can provide technical basis for sudden flood, special water regime, emergency monitoring, flood prevention and early warning. The flow measurement under the condition of insufficient testing personnel.

Short term traffic flow prediction based on multiple time series data and improved Elman neural network

To improve the short term traffic prediction precision, this paper proposes an improved Elman neural network (ELMNN) model for the prediction work. The model input includes two parts: the measured flow data and the theoretical flow data obtained by traffic occupancy and speed. Furthermore, in order to capture the inner regularity of the time series data, the theoretical flow data and the measured flow data are both reconstructed using a phase space reconstruction method. Finally, the reconstructed data are put into the improved ELMNN model, which is developed by employing the mind evolution algorithm (MEA). Compared with the original models, the results of the case study show that the proposed model can obviously improve the prediction accuracy.

SIMULATION OF SEDIMENT YIELD AT THE UPSTREAM WATERSHED OF JEBBA LAKE IN NIGERIA USING SWAT MODEL

In this study, we focused on the applicability and suitability of Soil and Water Assessment Tool (SWAT) embedded in Geographical Information Systems (GIS) environment in the prediction of sediment yield of a watershed (12,992km2 ). The watershed is drained by Rivers Niger, Kontagora, Awun and Eku and is located at the upstream of Jebba Reservoir in north central Nigeria . SWAT was run daily for 26 years (1985 to 2010 ) using climatic data representing three weather stations located within the watershed. The model was calibrated and validated using measured flow data from 1990 to 1995. Also due to the unavalilability of observed sediment data for the area, sediment samples were collected from three locations in the watershed from May to December, 2013 using suspended sediment sampler USDH-2A. The sediment samples were analysed and used to spatially calibrate and validate the model. The model was statistically evaluated using coefficient of determination, R 2 and Nasch-Sutcliffe Efficiency, NSE. Evaluation of the model revealed that it performed satisfactorily for stream flow and sediment yield predictions in the watershed. The model predicted the annual sediment yield in the watershed as 255.8 tons/ha/yr producing about 8.31x 109 tons of sediment between 1985 and 2010. Sediment concentration (mg/l) in the reach during the period of simulation showed that the highest sediment concentration was obtained in subbasins 29, 20 and 19 with values 446.3, 376.8 and 365.4 mg/l respectively. However, lowest sediment concentration occurred in subbasin 73 with a value of 108.6 mg/l. The results from the study showed that a properly calibrated SWAT embedded in GIS environment is suitable for modelling the hydrology and predicting the sediment yield in a watershed. In the light of this, SWAT can be adopted by water engineers and hydrologists in Nigeria and other sub sahara Africa countries in the region as a decision support tool to assist policy makers in achieving sustainable sediment and water management at watershed level.

An experimental study of a flow-accelerating hydrokinetic device

Tidal energy researchers and developers use experimental testing of scaled devices as a method of evaluating device performance. Much of the focus to date has been on horizontal axis turbines. This study is focused on a novel vertical axis turbine which incorporates variable-pitch blades and a flow accelerator. The research involves laboratory testing of scale model devices in a recirculating flume. Computational fluid dynamic modelling is used to reproduce the measured flow data to investigate disparities in experimental data. The results show that the device is capable of achieving localised flow acceleration of up to a factor of 2 above the freestream velocity and achieved a mechanical power efficiency of 40%.

Tools for managing hydrologic alteration on a regional scale: Estimating changes in flow characteristics at ungauged sites

Abstract Hydrologic alteration is a predominant stressor for biological resources in streams. This stress is further aggravated by competing human and ecological demands for limited water resources. Understanding flow–ecology relationships and establishing relevant and implementable flow targets are essential to protect biological communities. Estimating degree of ecologically relevant hydrologic alteration depends on the availability of long‐term flow data at sites with biological information. However, measured flow data are seldom available at sufficient density to support large‐scale analyses of the biological effects of hydrologic alterations. The ability to accurately simulate flows and estimate flow metrics at many ungauged locations across a broad geographical area remains a fundamental challenge. We address this challenge by applying a novel technique to simulate flow regimes at any stream reach of interest by first developing an ensemble of regionally calibrated and validated hydrological models, and then using a selection tool to match the “best‐fit” model to ungauged stream reaches. An ensemble of 26 HEC‐HMS rainfall–runoff models were calibrated to represent the range of catchment conditions in the southern California region. We developed current and historical flow regimes and a suite of flow metrics at 572 ungauged sites in southern California with bioassessment monitoring data. The flow metrics represent hydrograph characteristics of magnitude, timing, frequency, duration and variability. The flow metrics were estimated under three precipitation conditions—dry, wet and average. In addition, we estimated aggregated flow metrics for (dry + wet + average) condition. Hydrologic alteration was estimated as the deviation between the modelled current and historical flow metrics. Approximately 79% of the region shows some degree of hydrologic alteration, and approximately 40% of the sites are estimated to be severely altered. Magnitude metrics tend to increase in response to urban and agricultural land uses, whereas the timing and duration metrics are mostly unchanged. This mechanistic modelling approach demonstrates the feasibility of estimating flow alterations for ungauged catchments with relative ease of transferability over a broad geographical region. The continuous granular flow data allow for computation and consideration of metrics that may be applicable to a variety of ecological endpoints and consideration of a range of management trade‐offs.

Transient LES of an offshore wind turbine

Abstract. The estimation of the cost of energy of offshore wind farms has a high uncertainty, which is partly due to the lacking accuracy of information on wind conditions and wake losses inside of the farm. Wake models that aim to reduce the uncertainty by modeling the wake interaction of turbines for various wind conditions need to be validated with measurement data before they can be considered as a reliable estimator. In this paper a methodology that enables a direct comparison of modeled with measured flow data is evaluated. To create the simulation data, a model chain including a mesoscale model, a large-eddy-simulation (LES) model and a wind turbine model is used. Different setups are compared to assess the capability of the method to reproduce the wind conditions at the hub height of current offshore wind turbines. The 2-day-long simulation of the ambient wind conditions and the wake simulation generally show good agreements with data from a met mast and lidar measurements, respectively. Wind fluctuations due to boundary layer turbulence and synoptic-scale motions are resolved with a lower representation of mesoscale fluctuations. Advanced metrics to describe the wake shape and development are derived from simulations and measurements but a quantitative comparison proves to be difficult due to the scarcity and the low sampling rate of the available measurement data. Due to the implementation of changing synoptic wind conditions in the LES, the methodology could also be beneficial for case studies of wind farm performance or wind farm control.