scholarly journals Stability Constraints on Practical Implementation of Parity-Time-Symmetric Electromagnetic Systems

Photonics ◽  
2021 ◽  
Vol 8 (2) ◽  
pp. 56
Author(s):  
Josip Lončar ◽  
Josip Vuković ◽  
Igor Krois ◽  
Silvio Hrabar
Keyword(s):  
Electromagnetic Radiation ◽  
Time Domain ◽  
Stability Criterion ◽  
System Stability ◽  
Symmetric System ◽  
Practical Implementation ◽  
Time Symmetry ◽  
Transient Simulations ◽  
Form Stability ◽  
Symmetric Systems

Recently, several applications leveraging unconventional manipulation of electromagnetic radiation based on parity-time symmetry have been proposed in the literature. Typical examples include systems with unidirectional invisibility and asymmetric refraction. Such applications assume an inherent system stability and no occurrence of unbounded signal growth or unwanted self-oscillations. Here, a general instability issue of parity-time-symmetric systems is investigated, with particular emphasis on a recently proposed system based on resistive metasurfaces. Explicit closed-form stability criterion is derived, crosschecked and verified by both time-domain transient simulations and the measurements on an experimental demonstrator operating in a lower radiofrequency range. Results of this study lead to the conclusion that any parity-time-symmetric system is necessarily marginally stable. Finally, it is shown that such a marginally stable system may easily become unstable if not designed carefully.

Frequency-Dependent Resistances and Inductances in Time-Domain Transient Simulations of Power Transformers

2019 ◽  
Vol 55 (9) ◽  
pp. 1-5
Author(s):  
Matthias K. Bucher ◽  
Thomas Franz ◽  
Michael Jaritz ◽  
Jasmin Smajic ◽  
Jens Tepper
Keyword(s):  
Time Domain ◽  
Power Transformers ◽  
Frequency Dependent ◽  
Transient Simulations

Time-Domain Flooding Simulation of a Damaged Warship

2020 ◽  
Vol 54 (2) ◽  
pp. 69-78
Author(s):  
Li-fen Hu ◽  
Hao Wu ◽  
Qingtao Gong ◽  
Xiangyang Wang ◽  
Wenbin Lv
Keyword(s):  
Experimental Data ◽  
Time Domain ◽  
Stability Criterion ◽  
Vof Method ◽  
Navier Stokes ◽  
Ship Motions ◽  
Fluid Interface ◽  
Complex Dynamic ◽  
Turbulence Effect ◽  
Mesh Update

AbstractUnderstanding of the complex dynamic behavior of damaged ships and floodwater remains limited for ship designers and safety authorities. In this work, a Navier-Stokes (NS) solver that combines the volume of fluid (VOF) method with overset mesh techniques is developed to simulate the flooding process of a damaged ship. The VOF method captures the fluid interface, and the turbulence effect on flows is considered with the k-ω model. The overset mesh techniques are employed to handle the mesh update following transient ship motions. Then, the results of a damaged barge with dynamic and overset mesh are compared with the experimental data. On the basis of this validation, the solver is applied to the flooding problems of a damaged warship. This research is intended to be a useful step toward the establishment of a stability criterion for damaged ships in the future.

scholarly journals Parity–Time Symmetry in Bidirectionally Coupled Semiconductor Lasers

Photonics ◽  
2019 ◽  
Vol 6 (4) ◽  
pp. 122 ◽  
Author(s):  
Andrew Wilkey ◽  
Joseph Suelzer ◽  
Yogesh Joglekar ◽  
Gautam Vemuri
Keyword(s):  
Semiconductor Lasers ◽  
Electric Fields ◽  
Single Mode ◽  
Equation Model ◽  
Rate Equations ◽  
Symmetric System ◽  
Time Symmetry ◽  
Complicating Factors ◽  
Future Work ◽  
Coupled Semiconductor

We report on the numerical analysis of intensity dynamics of a pair of mutually coupled, single-mode semiconductor lasers that are operated in a configuration that leads to features reminiscent of parity–time symmetry. Starting from the rate equations for the intracavity electric fields of the two lasers and the rate equations for carrier inversions, we show how these equations reduce to a simple 2 × 2 effective Hamiltonian that is identical to that of a typical parity–time (PT)-symmetric dimer. After establishing that a pair of coupled semiconductor lasers could be PT-symmetric, we solve the full set of rate equations and show that despite complicating factors like gain saturation and nonlinearities, the rate equation model predicts intensity dynamics that are akin to those in a PT-symmetric system. The article describes some of the advantages of using semiconductor lasers to realize a PT-symmetric system and concludes with some possible directions for future work on this system.

scholarly journals Testing a differential-algebraic equation solver in long-term voltage stability simulation

2006 ◽  
Vol 2006 ◽  
pp. 1-13
Author(s):  
José E. O. Pessanha ◽  
Alex A. Paz
Keyword(s):  
Power System ◽  
Algebraic Equation ◽  
Time Domain ◽  
Voltage Stability ◽  
Power System Stability ◽  
System Stability ◽  
Variable Order ◽  
Differential Algebraic Equation ◽  
Short Period

This work evaluates the performance of a particular differential-algebraic equation solver, referred to as DASSL, in power system voltage stability computer applications. The solver is tested for a time domain long-term voltage stability scenario, including transient disturbances, using a real power system model. Important insights into the mechanisms of the DASSL solver are obtained through the use of this real model, including control devices relevant to the simulated phenomena. The results indicate that if properly used, the solver can be a powerful numerical tool in time domain assessment of long-term power system stability since it comprises, among several important features, suitable and very efficient variable order and variable step-size numerical techniques. These characteristics are very important when CPU time is a great concern, which is the case when the power system operator needs reliable results in a short period of time. Prior to the present work, this solver has never been applied in power system stability computer analysis in time domain considering slow and fast phenomena.

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