Hydrodynamic and Hydrographic Modeling of Istanbul Strait

The aim of this study is to model hydrodynamic processes of the Istanbul Strait with its stratified flow characteristic and calibrate the most important parameters using local and global search algorithms. For that two open boundary conditions are defined, which are in the North and South part of the Strait. Observed bathymetric, hydrographic, meteorological and water level data are used to set up the Delft3D-FLOW model. First, the sensitivities of model parameters on the numerical model outputs are assessed using PEST toolbox. Then, the model is calibrated based on the objective functions focusing on the flowrates of upper and lower layers. The salinity and temperature profiles of the Strait are only used for model validation. The results show that the calibrated model outputs of Istanbul Strait are reliable and consistent with the in-situ measurements. The sensitivity analysis reveals that the Spatial Low-Pass Filter Coefficient, Horizontal Eddy Viscosity, Prandtl-Schmidt Number, Slope in log-log Spectrum and Manning Roughness Coefficient are most sensitive parameters affecting flowrate performance of the model. The agreement between observed salinity profiles and simulated model outputs is promising whereas the match between observed and simulated temperature profiles is weak showing that the model can be improved particularly for simulating the mixing layer.

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Hydrodynamic and Hydrographic Modeling of Istanbul Strait

Processes ◽

10.3390/pr7100710 ◽

2019 ◽

Vol 7 (10) ◽

pp. 710 ◽

Cited By ~ 1

Author(s):

Mehmet Koşucu ◽

Mehmet Demirel ◽

V.S. Kirca ◽

Mehmet Özger

Keyword(s):

Mixing Layer ◽

Flow Characteristics ◽

Open Boundary ◽

Roughness Coefficient ◽

Model Parameters ◽

Temperature Profiles ◽

Open Boundary Conditions ◽

Pass Filter ◽

Low Pass Filter ◽

Set Up

The aim of this study is to model the hydrodynamic processes of the Istanbul Strait with its stratified flow characteristics, and calibrate the most important parameters using local and global search algorithms. For that, two open boundary conditions are defined, which are in the northern and southern parts of the Strait. Observed bathymetric, hydrographic, meteorological, and water-level data are used to set up the Delft3D-FLOW model. First, the sensitivities of the model parameters on the numerical model outputs are assessed using Parameter EStimation Tool (PEST) toolbox. Then, the model is calibrated based on the objective functions, focusing on the flow rates of the upper and lower layers. The salinity and temperature profiles of the strait are only used for model validation. The results show that the calibrated model outputs of the Istanbul Strait are reliable and consistent with the in situ measurements. The sensitivity analysis reveals that the spatial low-pass filter coefficient, horizontal eddy viscosity, Prandtl–Schmidt number, slope in log–log spectrum, and Manning roughness coefficient are most sensitive parameters affecting the flow rate performance of the model. The agreement between observed salinity profiles and simulated model outputs is promising, whereas the match between observed and simulated temperature profiles is weak, showing that the model can be improved, particularly for simulating the mixing layer.

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Tidally induced lateral dispersion of the Storfjorden overflow plume

Ocean Science ◽

10.5194/os-9-885-2013 ◽

2013 ◽

Vol 9 (5) ◽

pp. 885-899 ◽

Cited By ~ 5

Author(s):

F. Wobus ◽

G. I. Shapiro ◽

J. M. Huthnance ◽

M. A. M. Maqueda ◽

Y. Aksenov

Keyword(s):

Ocean Circulation ◽

Circulation Model ◽

Bottom Layer ◽

Horizontal Resolution ◽

Open Boundary ◽

Coastal Current ◽

Fram Strait ◽

Open Boundary Conditions ◽

Shear Dispersion ◽

Set Up

Abstract. We investigate the flow of brine-enriched shelf water from Storfjorden (Svalbard) into Fram Strait and onto the western Svalbard Shelf using a regional set-up of NEMO-SHELF, a 3-D numerical ocean circulation model. The model is set up with realistic bathymetry, atmospheric forcing, open boundary conditions and tides. The model has 3 km horizontal resolution and 50 vertical levels in the sh-coordinate system which is specially designed to resolve bottom boundary layer processes. In a series of modelling experiments we focus on the influence of tides on the propagation of the dense water plume by comparing results from tidal and non-tidal model runs. Comparisons of non-tidal to tidal simulations reveal a hotspot of tidally induced horizontal diffusion leading to the lateral dispersion of the plume at the southernmost headland of Spitsbergen which is in close proximity to the plume path. As a result the lighter fractions in the diluted upper layer of the plume are drawn into the shallow coastal current that carries Storfjorden water onto the western Svalbard Shelf, while the dense bottom layer continues to sink down the slope. This bifurcation of the plume into a diluted shelf branch and a dense downslope branch is enhanced by tidally induced shear dispersion at the headland. Tidal effects at the headland are shown to cause a net reduction in the downslope flux of Storfjorden water into the deep Fram Strait. This finding contrasts previous results from observations of a dense plume on a different shelf without abrupt topography.

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Depth-averaged instantaneous currents in a tidally dominated shelf sea from glider observations

10.5194/bg-2016-118 ◽

2016 ◽

Author(s):

Lucas Merckelbach

Keyword(s):

Real Time ◽

North Sea ◽

Current Data ◽

Pass Filter ◽

Low Pass Filter ◽

Real Time Mode ◽

The North ◽

Shelf Sea ◽

The North Sea ◽

Better Than

Abstract. Ocean gliders have become ubiquitous observation platforms in the ocean in recent years. They are also increasingly used in coastal environments. The coastal observatory system COSYNA has pioneered the use of gliders in the North Sea, a shallow tidally energetic shelf sea. For operational reasons, the gliders operated in the North Sea are programmed to resurface every 3–5 hours. The glider's deadreckoning algorithm yields depth averaged currents, averaged in time over each subsurface interval. Under operational conditions these averaged currents are a poor approximation of the instantaneous tidal current. In this work an algorithm is developed that estimates the instantaneous current (tidal and residual) from glider observations only. The algorithm uses a second-order Butterworth low-pass filter to estimate the residual current component, and a Kalman filter based on the linear shallow water equations for the tidal component. A comparison of data from a glider experiment with current data from an ADCP deployed nearby shows that the standard deviations for the east and north current components are better than 7 cm s−1 in near-real time mode, and improve to better than 5 cm s−1 in delayed mode, where the filters can be run forward and backward. In the near-real time mode the algorithm provides estimates of the currents that the glider is expected to encounter during its next few dives. Combined with a behavioural and dynamic model of the glider, this yields predicted trajectories, the information of which is incorporated in warning messages issued to ships by the (German) authorities. In delayed mode the algorithm produces useful estimates of the depth averaged currents, which can be used in (process-based) analyses in case no other source of measured current information is available.

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Depth-averaged instantaneous currents in a tidally dominated shelf sea from glider observations

Biogeosciences ◽

10.5194/bg-13-6637-2016 ◽

2016 ◽

Vol 13 (24) ◽

pp. 6637-6649 ◽

Cited By ~ 1

Author(s):

Lucas Merckelbach

Keyword(s):

Real Time ◽

North Sea ◽

Current Data ◽

Pass Filter ◽

Low Pass Filter ◽

Real Time Mode ◽

The North ◽

Shelf Sea ◽

The North Sea ◽

Better Than

Abstract. Ocean gliders have become ubiquitous observation platforms in the ocean in recent years. They are also increasingly used in coastal environments. The coastal observatory system COSYNA has pioneered the use of gliders in the North Sea, a shallow tidally energetic shelf sea. For operational reasons, the gliders operated in the North Sea are programmed to resurface every 3–5 h. The glider's dead-reckoning algorithm yields depth-averaged currents, averaged in time over each subsurface interval. Under operational conditions these averaged currents are a poor approximation of the instantaneous tidal current. In this work an algorithm is developed that estimates the instantaneous current (tidal and residual) from glider observations only. The algorithm uses a first-order Butterworth low pass filter to estimate the residual current component, and a Kalman filter based on the linear shallow water equations for the tidal component. A comparison of data from a glider experiment with current data from an acoustic Doppler current profilers deployed nearby shows that the standard deviations for the east and north current components are better than 7 cm s−1 in near-real-time mode and improve to better than 6 cm s−1 in delayed mode, where the filters can be run forward and backward. In the near-real-time mode the algorithm provides estimates of the currents that the glider is expected to encounter during its next few dives. Combined with a behavioural and dynamic model of the glider, this yields predicted trajectories, the information of which is incorporated in warning messages issued to ships by the (German) authorities. In delayed mode the algorithm produces useful estimates of the depth-averaged currents, which can be used in (process-based) analyses in case no other source of measured current information is available.

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Non-linear model of the tides in the Gulf of Carpentaria

Marine and Freshwater Research ◽

10.1071/mf9810685 ◽

1981 ◽

Vol 32 (5) ◽

pp. 685 ◽

Cited By ~ 25

Author(s):

JA Church ◽

AMG Fobes

Keyword(s):

Open Boundary ◽

Open Boundary Conditions ◽

Kelvin Wave ◽

Rapid Phase ◽

North West ◽

The North ◽

Northern Half ◽

Non Linear ◽

Amphidromic Point ◽

Phase Variations

A non-linear barotropic model was used to evaluate the tidal regime in the Gulf of Carpentaria. The model was forced by open boundary conditions specified on a line joining Wessel Islands to False Cape and a volume flow through Torres Strait estimated from tidal constants on each side of the Strait. The model gives results in agreement with the available observations and in particular predicts mixed tides in the northern half of the Gulf and diurnal tides in the south-east corner of the Gulf. The diurnal tide consists of a Kelvin wave entering the Gulf in the north-west and propagating clockwise around the Gulf with one amphidromic point. The higher frequencies of the semidiurnal tides allow the generation of a first-mqde Poincare wave and the trapping of energy in the northern half of the Gulf. Amphidromes near Mornington Island and Groote Eylandt are also predicted, as is a region of low amplitude and rapid phase variations in the centre of the Gulf.

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The impact of sea-level rise on tidal characteristics around Australia

Ocean Science ◽

10.5194/os-15-147-2019 ◽

2019 ◽

Vol 15 (1) ◽

pp. 147-159 ◽

Cited By ~ 4

Author(s):

Alexander Harker ◽

J. A. Mattias Green ◽

Michael Schindelegger ◽

Sophie-Berenice Wilmes

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Open Boundary ◽

Open Boundary Conditions ◽

Tidal Dissipation ◽

North West ◽

The North ◽

Tidal Changes ◽

Tidal Characteristics ◽

The Impact

Abstract. An established tidal model, validated for present-day conditions, is used to investigate the effect of large levels of sea-level rise (SLR) on tidal characteristics around Australasia. SLR is implemented through a uniform depth increase across the model domain, with a comparison between the implementation of coastal defences or allowing low-lying land to flood. The complex spatial response of the semi-diurnal M2 constituent does not appear to be linear with the imposed SLR. The most predominant features of this response are the generation of new amphidromic systems within the Gulf of Carpentaria and large-amplitude changes in the Arafura Sea, to the north of Australia, and within embayments along Australia's north-west coast. Dissipation from M2 notably decreases along north-west Australia but is enhanced around New Zealand and the island chains to the north. The diurnal constituent, K1, is found to decrease in amplitude in the Gulf of Carpentaria when flooding is allowed. Coastal flooding has a profound impact on the response of tidal amplitudes to SLR by creating local regions of increased tidal dissipation and altering the coastal topography. Our results also highlight the necessity for regional models to use correct open boundary conditions reflecting the global tidal changes in response to SLR.

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Impact of the Incremental Analysis Updates on a Real-Time System of the North Atlantic Ocean

Journal of Atmospheric and Oceanic Technology ◽

10.1175/2008jtecho537.1 ◽

2008 ◽

Vol 25 (11) ◽

pp. 2055-2073 ◽

Cited By ~ 16

Author(s):

M. Benkiran ◽

E. Greiner

Keyword(s):

Real Time ◽

North Atlantic ◽

Weather Forecasting ◽

Incremental Analysis ◽

Real Time System ◽

Pass Filter ◽

Low Pass Filter ◽

The North ◽

The North Atlantic ◽

The Impact

Abstract Incremental analysis updates (IAUs) are a procedure by which analysis increments can be incorporated into a model hindcast and forecast in a smooth manner. It is similar to nudging but has a better response, particularly in regions of missing data. The IAU procedure was popular in the late 1990s in weather forecasting centers, because it acts as a low-pass filter. The impact of the IAU is examined in the context of a real-time, eddy-permitting ocean forecasting system in the North Atlantic from Mercator Océan. Forecast scores and ocean physics are compared for the following three companion runs: a forced mode, a sequential analysis, and IAU. These comparisons confirm that the IAU is beneficial because it removes spinup effects such as spurious waves and tropical convective cells. Forecast scores are also slightly improved. In addition, contrary to the weather forecasting case where the model and data are fairly unbiased, the IAU has the advantage of correcting the systematic biases in the ocean data assimilation system.

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Adaptive anti-disturbance control for a class of unknown pure feedback switched nonlinear systems

10.21203/rs.3.rs-170970/v1 ◽

2021 ◽

Author(s):

Longsheng Chen

Keyword(s):

Nonlinear Systems ◽

Design Method ◽

Tracking Error ◽

Average Dwell Time ◽

Switched Nonlinear Systems ◽

Pass Filter ◽

Low Pass Filter ◽

Control Scheme ◽

Low Pass ◽

Set Up

Abstract In this study, an adaptive anti-disturbance control scheme is investigated for a class of unknown pure feedback switched nonlinear systems subjected to immeasurable states and external disturbances. Radial basis function neural networks (RBFNNs) are employed to identify the switched unknown nonlinearities, and a Butterworth low-pass filter is adopted to remove the algebraic loop problem. Subsequently, a novel switched neural state observer and a novel switched disturbance are presented via the coupled design method to estimate the immeasurable states and compounded disturbances. Then, an improved adaptive control strategy for the studied problem is designed with the help of a filtering method to eliminate the “explosion of complexity” problem, and certain compensating signals are set up to compensate for the filter errors, where switched updated laws are constructed to lessen the conservativeness caused by adoption of a common updated law for all subsystems. By utilizing the Lyapunov stability theorem, the developed control scheme can guarantee that all signals in the closed-loop system are bounded under a class of switching signals with the average dwell time (ADT), while the tracking error can converge to a small neighbourhood of origin. Finally, simulation results are provided to demonstrate the effectiveness of the presented approach.

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Composite Hierarchical Anti-Disturbance Control with Multisensor Fusion for Compact Optoelectronic Platforms

Sensors ◽

10.3390/s18103190 ◽

2018 ◽

Vol 18 (10) ◽

pp. 3190 ◽

Cited By ~ 3

Author(s):

Yutang Wang ◽

Dapeng Tian ◽

Ming Dai

Keyword(s):

Sliding Mode ◽

Differential Evolution Algorithm ◽

Unmanned Aircraft ◽

Adaptive Mutation ◽

Model Parameters ◽

Phase Lag ◽

Multisensor Fusion ◽

Terminal Sliding Mode ◽

Pass Filter ◽

Low Pass Filter

In the aerospace field, compact optoelectronic platforms (COPs) are being increasingly equipped on unmanned aircraft systems (UAS). They assist UAS in a range of mission-specific tasks such as disaster relief, crop testing, and firefighting. However, the strict constraint of structure space makes COPs subject to multi-source disturbances. The application of a low-cost and low-precision sensor also affects the system control performance. A composite hierarchical anti-disturbance control (CHADC) scheme with multisensor fusion is explored herein to improve the motion performance of COPs in the presence of internal and external disturbances. Composite disturbance modelling combining the characteristic of wire-wound moment is presented in the inner layer. The adaptive mutation differential evolution algorithm is implemented to identify and optimise the model parameters of the system internal disturbance. Inverse model compensation and finite-time nonlinear disturbance observer are then constructed to compensate for multiple disturbances. A non-singular terminal sliding mode controller is constructed to attenuate disturbance in the outer layer. A stability analysis for both the composite disturbance compensator and the closed-loop system is provided using Lyapunov stability arguments. The phase lag-free low-pass filter is implemented to interfuse multiple sensors with different order information and achieve satisfactory noise suppression without phase lag. Experimental results demonstrate that the proposed CHADC strategy with a higher-quality signal has an improved performance for multi-source disturbance compensation.

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Deconstructing the subtropical AMOC variability

10.5194/egusphere-egu2020-20309 ◽

2020 ◽

Author(s):

Quentin Jamet ◽

William Dewar ◽

Nicolas Wienders ◽

Bruno Deremble ◽

Sally Close ◽

...

Keyword(s):

Time Scales ◽

North Atlantic ◽

Low Frequency ◽

Meridional Overturning Circulation ◽

Open Boundary ◽

Open Boundary Conditions ◽

Intrinsic Variability ◽

Linear Superposition ◽

The North ◽

Basin Scale

Mechanisms driving the North Atlantic Meridional Overturning Circulation (AMOC) variability at low-frequency are of central interest for accurate climate predictions. However, the origin of this variability remains under debate, complicating for instance the interpretation of the observed time series provided by the RAPID-MOCHA-WBTS program. In this study, we aim at disentangling the respective contribution of the local atmospheric forcing, the signal of remote origin and the ocean intrinsic dynamics for the subtropical low-frequency AMOC variability. We analyse for this a set of four ensembles of a regional (20oS - 55oN), eddy-resolving (1/12o) North Atlantic oceanic configuration, where surface forcing and open boundary conditions are alternatively permuted from fully varying (realistic) to yearly repeating signals.The analysis of the four ensemble mean AMOCs reveals predominance of local, atmospherically forced signal at interannual time scales (2-10 years), while signals imposed by the boundaries imprint at decadal (10-30 years) time scales. Due to this marked time scale separation, we show that most of the subtropical AMOC forced variability can be understood as a linear superposition of these two signals. Analyzing the ensemble spread of the four ensembles, we then show that the subtropical AMOC is also characterized by an intrinsic variability, which organizes as a basin scale mode peaking at interannual time scales. This basin scale mode is found to be weakly sensitive to the surrounding forced signals, suggesting no causal relationship between the two. Its spatio-temporal pattern shares however similarities with the atmospherically forced signal, which is likely to make the attribution from a single eddy-resolving simulation, or from observations, more difficult.

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