scholarly journals Hydrodynamic and Hydrographic Modeling of Istanbul Strait

Processes ◽  
2019 ◽  
Vol 7 (10) ◽  
pp. 710 ◽  
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.

scholarly journals Hydrodynamic and Hydrographic Modeling of Istanbul Strait

2019 ◽  
Author(s):  
Mehmet Melih Koşucu ◽  
Mehmet Cüneyd Demirel ◽  
V.S. Ozgur Kirca ◽  
Mehmet Özger
Keyword(s):  
Mixing Layer ◽  
Open Boundary ◽  
Roughness Coefficient ◽  
Model Parameters ◽  
Temperature Profiles ◽  
Open Boundary Conditions ◽  
Pass Filter ◽  
Low Pass Filter ◽  
The North ◽  
Set Up

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.

scholarly journals Tidally induced lateral dispersion of the Storfjorden overflow plume

Ocean Science ◽  
2013 ◽  
Vol 9 (5) ◽  
pp. 885-899 ◽  
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.

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

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.

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

Sensors ◽  
2018 ◽  
Vol 18 (10) ◽  
pp. 3190 ◽  
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.

Nonlinear joint model updating of strong column-weak beam type frames based on instantaneous characteristics of the responses under earthquake excitations

2017 ◽  
Vol 20 (5) ◽  
pp. 682-693 ◽  
Author(s):  
Ping-Ping Yuan ◽  
Zuo-Cai Wang ◽  
Wei-Xin Ren ◽  
Wen-Yu He
Keyword(s):  
Objective Function ◽  
Simulated Annealing Algorithm ◽  
Model Updating ◽  
Element Model ◽  
Joint Model ◽  
Model Parameters ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Nonlinear Joint ◽  
Instantaneous Frequencies

In this article, a novel method based on the instantaneous frequencies and amplitudes of the principal response components is presented for nonlinear joint model updating. The instantaneous frequencies and amplitudes are first extracted by a low-pass filter with Hilbert transform. Then, limited point values of the extracted instantaneous frequencies and amplitudes are applied to represent the response of the nonlinear structure. Finally, an objective function based on the residuals of instantaneous frequencies and amplitudes between experimental structure and finite element model is established using the response surface method. The optimal values of the nonlinear joint model parameters are obtained by minimizing the objective function using simulated annealing algorithm. To verify the effectiveness of the proposed method, a three-story frame with bilinear moment–rotation relationship at the beam-column joints under earthquake excitations is simulated as a numerical example. The accuracy of the proposed nonlinear joint model updating procedure is quantified using the defined error indices. The effects of the selected data point number and the weight factors in the objective function are also discussed in the article. The results indicate that the proposed method can effectively update the nonlinear joint model with high accuracy even with noise effect.

scholarly journals Can turbulent reconnection be fast in 2D?

2010 ◽  
Vol 6 (S271) ◽  
pp. 385-386
Author(s):  
K. Kulpa-Dybeł ◽  
G. Kowal ◽  
K. Otmianowska-Mazur ◽  
A. Lazarian ◽  
E. Vishniac
Keyword(s):  
Three Dimensional ◽  
Open Boundary ◽  
Initial Vector ◽  
Spectral Space ◽  
Two Dimensional ◽  
Open Boundary Conditions ◽  
Random Forcing ◽  
Potential Perturbation ◽  
Set Up ◽  
External Driving

AbstractTurbulent reconnection is studied by means of two-dimensional (2D) compressible magnetohydrodynamical numerical calculations. The process of homogeneous turbulence is set up by adding two-dimensional random forcing implemented in the spectral space at small wave numbers with no correlation between velocity and forcing. We apply the initial Harris current sheet configuration together with a density profile calculated from the numerical equilibrium of magnetic and gas pressures. We assume that there is no external driving of the reconnection. The reconnection develops as a result of the initial vector potential perturbation. We use open boundary conditions. Our main goal is to find the dependencies of reconnection rate on the uniform resistivity. We present that the reconnection speed depends on the Lindquist number in 2D in the case of low as well as high resolution. When we apply more powerful turbulence the reconnection is faster, however the speed of reconnection is smaller than in the case of our three-dimensional numerical simulations.

scholarly journals Convolution Integral: How a Graphical Type of Solution Can Help Minimize Misconceptions

2021 ◽  
Vol 3 (2) ◽  
pp. 103
Author(s):  
Hendra J. Tarigan
Keyword(s):  
Impulse Response ◽  
Physical System ◽  
Convolution Integral ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Convolution Integrals ◽  
Low Pass ◽  
Simulation And Experiment ◽  
Rc Circuit ◽  
Set Up

A physical system, Low Pass Filter (LPF) RC Circuit, which serves as an impulse response and a square wave input signal are utilized to derive the continuous time convolution (convolution integrals). How to set up the limits of integration correctly and how the excitation source convolves with the impulse response are explained using a graphical type of solution. This in turn, help minimize the students’ misconceptions about the convolution integral. Further, the effect of varying the circuit elements on the shape of the convolution output plot is presented allowing students to see the connection between a convolution integral and a physical system. PSpice simulation and experiment results are incorporated and are compared with those of the analytical solution associated with the convolution integral.

scholarly journals Tidally-induced lateral dispersion of the Storfjorden overflow plume

2013 ◽  
Vol 10 (2) ◽  
pp. 691-726
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 setup 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 deep Fram Strait. This finding contrasts previous results from observations of a dense plume on a different shelf without abrupt topography.

A Test System for Pressure Pulsation and Hydrodynamic Noise in Centrifugal Pump Based on Virtual Instrument Technology

2011 ◽  
Author(s):  
Yin Luo ◽  
Shouqi Yuan ◽  
Yue Tang ◽  
Jianping Yuan ◽  
Jinfeng Zhang
Keyword(s):  
Centrifugal Pump ◽  
Virtual Instrument ◽  
Pressure Pulsation ◽  
Test System ◽  
Real Time System ◽  
Pump System ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Hydrodynamic Noise ◽  
Set Up

A system based on virtual instrument was set up to test and analyze the pressure pulsation and hydrodynamic noise in centrifugal pump. It has adjustable sampling time length and frequency which can avoid the disadvantages of data loss and redundancy caused by fixed sampling parameters. A signal preprocessing toolkit compiled by LabVIEW was set up, which can anti the aliasing of the signal by use of the low pass filter, decrease the noise in the concerned frequency by the wavelet de-noising and efficiently reduce the error caused by test system. Meanwhile, the data analysis toolkits in this system not only include signal power spectrum and octave for obtaining the frequency characteristic, but also include correlation analysis between the measured waveforms and wavelet analysis for detecting the signature of the signal. All of the toolkits could be used as an automatic real-time system. The feasibility of this system has already been evaluated in a centrifugal pump system, and it is testified that this system can realize and analyze the pressure pulsation and inner hydrodynamic noise automatically.

scholarly journals Velocity Field and Turbulence Structure around Spur Dikes with Different Angles of Orientation under Ice Covered Flow Conditions

Water ◽  
2021 ◽  
Vol 13 (13) ◽  
pp. 1844
Author(s):  
Rahim Jafari ◽  
Jueyi Sui
Keyword(s):  
Flow Characteristics ◽  
Ice Cover ◽  
Roughness Coefficient ◽  
Turbulence Structure ◽  
Flow Conditions ◽  
Spur Dike ◽  
Turbulence Structures ◽  
Scour Hole ◽  
Spur Dikes ◽  
Set Up

Spur dikes are well-known structures that are widely used in rivers and coastal regions. Depending on their types, sizes, and orientation angles, spur dikes can substantially change flow characteristics. Results of previous studies indicate that the presence of an ice cover in rivers can cause complicated flow structures. The present experimental study investigates velocity fields and turbulence structures in the vicinity of spur dikes under ice cover with different roughness coefficients. The spur dikes were set up at the following three angles of orientation, 90°, 60°, and 45°. Our results show that the strongest velocity fluctuation occurs immediately above the scour hole surface and very close to the dike tip. The increase in the dike angle toward upstream, the velocity component values increase, leads to a larger scour hole. Results show that an increase in dike angle of each 10° (from 45° to 90°) increases the scour depth between 5% and 10%, depending on flow conditions. Furthermore, the increase in the cover roughness coefficient and the blockage ratio of a spur dike leads to a further increase in turbulence kinetic energy and 3D velocity components values. The findings of this study imply that the appearance of an ice cover can increase turbulence intensities up to nearly 30%.

Sign in / Sign up

Export Citation Format

Share Document