scholarly journals Estimation of Open Boundary Conditions Based on an Isopycnic-Coordinate Internal Tidal Model with Adjoint Assimilation Method

2013 ◽  
Vol 2013 ◽  
pp. 1-11 ◽  
Author(s):  
Yanqiu Gao ◽  
Guangzhen Jin ◽  
Haibo Chen ◽  
Xianqing Lv
Keyword(s):  
Boundary Conditions ◽  
Internal Tide ◽  
Open Boundary ◽  
Open Boundary Conditions ◽  
Tidal Model ◽  
Good Ability ◽  
Order Of Magnitude ◽  
Adjoint Assimilation ◽  
Spatially Varying ◽  
Group 1

The isopycnic-coordinate internal tidal model with adjoint assimilation method is developed into a three-layer version. Two groups of ideal experiments are carried out in order to investigate the estimation of spatially varying open boundary conditions (OBCs). In group 1, different independent point schemes (IPSs) are used to invert 6 kinds of prescribed distributions of OBCs. Results show that, after assimilation, the cost functions and their gradient norms are reduced by about 2 orders of magnitude and by about 1 order of magnitude, respectively; the mean absolute errors (MAEs) in OBCs and the vector differences of horizontal current are reduced by 1 order of magnitude and by more than 23.53% compared with the values before assimilation, respectively. The results demonstrate that the three-layered model has a good ability in estimating the spatially varying OBCs; the use of IPSs can effectively improve the estimation precision; fewer independent points are feasible when the distribution is simpler, and appropriately more independent points are required when the distribution is more complex. In group 2, by using the optimal IPSs in group 1, the model is also able to successfully invert the OBCs on a real topography in the Luzon Strait area. The results are important to the study of the internal tide in the South China Sea.

scholarly journals Optimization of Open Boundary Conditions in a 3D Internal Tidal Model with the Adjoint Method around Hawaii

2013 ◽  
Vol 2013 ◽  
pp. 1-11 ◽  
Author(s):  
Anzhou Cao ◽  
Haibo Chen ◽  
Jicai Zhang ◽  
Xianqing Lv
Keyword(s):  
Boundary Conditions ◽  
Adjoint Method ◽  
Internal Tide ◽  
Descent Method ◽  
Steepest Descent Method ◽  
Open Boundary ◽  
Open Boundary Conditions ◽  
Tidal Model ◽  
Open Boundaries ◽  
Surface Manifestation

Based on the theory of inverse problem, the optimization of open boundary conditions (OBCs) in a 3D internal tidal model is investigated with the adjoint method. Fourier coefficients ofM2internal tide on four open boundaries, which are regarded as OBCs, are inverted simultaneously. During the optimization, the steepest descent method is used to minimize cost function. The reasonability and feasibility of the model are tested by twin experiments (TEs). In TE1, OBCs on four open boundaries are successfully inverted by using independent point (IP) strategy, suggesting that IP strategy is useful in parameter estimation. Results of TE2 indicate that the model is effective even by assimilating inaccurate “observations.” Based on conclusions of TEs, theM2internal tide around Hawaii is simulated by assimilating T/P data in practical experiment. The simulated cochart shows good agreement with that obtained from the Oregon State University tidal model and T/P observations. Careful inspection shows that the major difference between simulated results and OSU model results is short-scale fluctuations superposed on coamplitude lines, which can be treated as the surface manifestation modulated by the internal tide. The computed surface manifestation along T/P tracks is comparable to the estimation in previous work.

scholarly journals Parameter Estimation for a 2D Tidal Model with POD 4D VAR Data Assimilation

2016 ◽  
Vol 2016 ◽  
pp. 1-14 ◽  
Author(s):  
Shouguo Qian ◽  
Xianqing Lv ◽  
Yanhua Cao ◽  
Fenjing Shao
Keyword(s):  
Data Assimilation ◽  
Altimeter Data ◽  
Open Boundary ◽  
Phase Lag ◽  
Open Boundary Conditions ◽  
Control Variables ◽  
Tidal Model ◽  
Reduced Order ◽  
Spatially Varying ◽  
Proper Orthogonal

Combining the proper orthogonal decomposition (POD) reduced order method and 4D VAR (four-dimensional Variational) data assimilation method with a two-dimensional (2D) tidal model, a model is constructed to simulate theM2tide in the Bohai, Yellow, and East China Seas (BYECS). This model consists of two submodels: the POD reduced order forward model is used to simulate the tides, while its adjoint model is used to optimize the control variables. Numerical experiment is carried out to assimilate the harmonic constants, which are derived from TOPEX/Poseidon (T/P) altimeter data, into the 2D tidal model through optimizing the initial values and the temporally and spatially varying open boundary conditions (OBCs). The absolute mean difference between the model results and observations is 3.2 cm and 2.9∘for amplitude and phase-lag, respectively, better than the results of Lu and Zhang (2006), suggesting that the construction of the POD reduced order model and the inversion of control variables are successful.

scholarly journals Estimating Smoothly Varying Open Boundary Conditions for a 3D Internal Tidal Model with an Improved Independent Point Scheme

2018 ◽  
Vol 35 (6) ◽  
pp. 1299-1311 ◽  
Author(s):  
Dong Jiang ◽  
Haibo Chen ◽  
Guangzhen Jin ◽  
Xianqing Lv
Keyword(s):  
Boundary Conditions ◽  
Adjoint Method ◽  
Spline Interpolation ◽  
Northern South China Sea ◽  
Altimeter Data ◽  
Open Boundary ◽  
Open Boundary Conditions ◽  
Independent Point ◽  
Tidal Model ◽  
Point Scheme

AbstractAn improved independent point (IP) scheme was proposed to estimate the open boundary conditions (OBCs) for a 3D internal tidal model through assimilating the TOPEX/Poseidon (T/P) altimeter data. Under the assumption that the OBCs were spatially and smoothly varying, values at a set of independent points along the open boundary were inverted using the adjoint method and values at other points were interpolated by the spline method. The scheme was calibrated through idealized experiments where the M2 tidal constituent in the northern South China Sea was simulated. The OBCs can be successfully inverted with the improved scheme and were better in spatial smoothness than the results obtained with the Cressman interpolation when embedded in the IP scheme. Simulations in realistic domains showed that the errors between simulations and observations were smaller when the spline interpolation was employed instead of the Cressman interpolation. Three boundary conditions of spline interpolation were used in simulations in realistic domains, and the result of the periodic boundary condition had the smallest error compared with the first and second boundary conditions.

scholarly journals Estimation of Open Boundary Conditions for an Internal Tidal Model with Adjoint Method: A Comparative Study on Optimization Methods

2013 ◽  
Vol 2013 ◽  
pp. 1-12 ◽  
Author(s):  
Haibo Chen ◽  
Chunbao Miao ◽  
Xianqing Lv
Keyword(s):  
Boundary Conditions ◽  
Line Search ◽  
Adjoint Method ◽  
Optimization Methods ◽  
Optimization Techniques ◽  
Open Boundary ◽  
Unknown Boundary ◽  
Bfgs Method ◽  
Open Boundary Conditions ◽  
Tidal Model

Based on an internal tidal model, the practical performances of the limited-memory BFGS (L-BFGS) method and two gradient descent (GD) methods (the normal one with Wolfe’s line search and the simplified one) are investigated computationally through a series of ideal experiments in which the open boundary conditions (OBCs) are inverted by assimilating the interior observations with the adjoint method. In the case that the observations closer to the unknown boundary are included for assimilation, the L-BFGS method performs the best. As compared with the simplified GD method, the normal one really uses less iteration to reach a satisfactory solution, but its advantage over the simplified one is much smaller than expected. In the case that only the observations that are further from the unknown boundary are assimilated, the simplified GD method performs the best instead, whereas the performances of the other two methods are not satisfactory. The advanced L-BFGS algorithm and Wolfe’s line search still need to be improved when applied to the practical cases. The simplified GD method, which is controllable and easy to implement, should be regarded seriously as a choice, especially when the classical advanced optimization techniques fail or perform poorly.

scholarly journals Inversion of Tidal Open Boundary Conditions of the M2 Constituent in the Bohai and Yellow Seas

2017 ◽  
Vol 34 (8) ◽  
pp. 1661-1672 ◽  
Author(s):  
Haidong Pan ◽  
Zheng Guo ◽  
Xianqing Lv
Keyword(s):  
Boundary Conditions ◽  
Adjoint Method ◽  
Spline Interpolation ◽  
Altimeter Data ◽  
Open Boundary ◽  
Open Boundary Conditions ◽  
Tidal Constituent ◽  
Spatially Varying

AbstractOpen boundary conditions (OBCs) of the M2 tidal constituent in the Bohai and Yellow Seas (BYS) were inverted successfully through assimilation of TOPEX/Poseidon (T/P) altimeter data. An improved independent points (IPs) scheme was employed in the inversion. Under the assumption that the OBC was spatially varying, values at a set of IPs along the open boundary were inverted using the adjoint method and those at other points were calculated by the spline interpolation. The OBC inverted with the improved scheme was closer to reality in terms of smoothness than that inverted with the Cressman interpolation. The scheme was calibrated in twin experiments. Practical experiments showed that the misfits between simulated results and observations were smaller when the spline interpolation was used.

scholarly journals Impurity induced scale-free localization

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Linhu Li ◽  
Ching Hua Lee ◽  
Jiangbin Gong
Keyword(s):  
Boundary Conditions ◽  
Skin Effect ◽  
Reciprocal Lattice ◽  
Periodic Boundary Conditions ◽  
Open Boundary ◽  
Open Boundary Conditions ◽  
Translational Invariance ◽  
Scale Free ◽  
Special Cases ◽  
Simulation Results

AbstractNon-Hermitian systems have been shown to have a dramatic sensitivity to their boundary conditions. In particular, the non-Hermitian skin effect induces collective boundary localization upon turning off boundary coupling, a feature very distinct from that under periodic boundary conditions. Here we develop a full framework for non-Hermitian impurity physics in a non-reciprocal lattice, with periodic/open boundary conditions and even their interpolations being special cases across a whole range of boundary impurity strengths. We uncover steady states with scale-free localization along or even against the direction of non-reciprocity in various impurity strength regimes. Also present are Bloch-like states that survive albeit broken translational invariance. We further explore the co-existence of non-Hermitian skin effect and scale-free localization, where even qualitative aspects of the system’s spectrum can be extremely sensitive to impurity strength. Specific circuit setups are also proposed for experimentally detecting the scale-free accumulation, with simulation results confirming our main findings.

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