Frequency Characteristics Of Waves Research Articles

Flexible Approximation Functions: Resonant Loads

Introduction. Patch antennas have found wide application in UAVs due to their numerous useful properties. However, since such an antenna system is essentially a resonator, the problem of its matching remains unresolved. The existing publications mostly deal with specific cases and report the typical values of the matching band of 5–7 %, which cannot be considered sufficient when there is a need to use the signal spectrum of up to hundreds of MHz. Therefore, research aimed at using more efficient methods of broadband matching could be of interest for engineers. Aim. To develop a broadband matching technique based on the generalized Darlington synthesis method using flexible approximating functions (AF) for load models with resonant properties. Materials and methods. The capabilities of the generalized Darlington synthesis method are extended AFs with increased variation properties. Flexible control of AF weight coefficients makes it possible to realize both smooth and wave frequency characteristics. The method is analytical and does not use iterative procedures. The mathematical apparatus of the method is based on an analysis of deductions in the zeros of the load resistance transfer function. Results. Flexible approximating functions were established to be effective for synthesis of matching circuits with resonant properties. Solutions for matching the loads with multiple transfer zeros both at the origin and in infinity were obtained. The opportunity of creating patch antennas with a matching layer up to 40 % and more was demonstrated. Conclusion. The results obtained for the SWR of patch antennas show that the potential estimates of matching limits are available only for analytical methods.

Three-phase adaptive reclosure technology for half-wavelength transmission lines using residual voltage frequency difference to identify fault existence

• The single-phase reclosing technique should not be used in half-wavelength transmission systems. • The residual voltage of half wavelength transmission system can be used to determine the existence of faults. • The frequency difference of residual voltage can be used to determine the existence of faults. • We propose a complete and feasible three-phase adaptive reclosure scheme for half wavelength transmission system. UHV AC transmission lines use adaptive reclosure technology not only to avoid reclosing in the permanent faults, but also effectively prevent the emergence of reclosing overvoltage, adaptive reclosure is of great significance, and its technical principle is based on the study and judgment of the existence of the fault. The reactive power of half-wavelength transmission lines along the line was self-balanced, no shunt reactor equipment, there is no "beat frequency" phenomenon, and very little information is available after the three-phase trip. In this paper, we analyze the fault traveling wave's frequency characteristics and identify the fault's characteristics based on the residual voltage frequency difference of the line after the three-phase trip. After the disappearance of the line fault, the stable frequency difference obtained by CVT reflects the entire length of the line, which is not affected by the system boundary conditions and can complete the reliable identification of the disappearance of the line fault. The two-terminal criterion is given for the short-line dead zone problem, and then a three-phase adaptive reclosure scheme for half-wavelength transmission lines based on the frequency difference to identify fault disappearance is proposed. Extensive RTDS digital-analog hybrid tests show that the method is correct and robust.

Flexible Approximation Functions for Broadband Matching

Introduction. Intensive use of broadband signals in RF devices for various purposes is associated with the need to develop broadband elements of RF systems. Iterative methods for designing such elements are frequently uninformative and ineffective, while analytical methods give solutions only for simple models. The problem is the small set of classical approximations, which impedes dealing with complex models of elements.Aim. Development of a wide-band matching technique based on generalized Darlington synthesis using flexible approximating functions (AF) for load models with zeros of transmission at infinity.Materials and methods. The paper is based on the generalized Darlington synthesis method. To extend the capabilities of the method, approximating functions with increased variation properties are used. In order to use the results in engineering practice, a synthesis algorithm was developed, which includes three stages: formation of the frequency response, control of analyticity of the used functions and limits of matching. The method is analytical and does not use iterative procedures. The mathematical apparatus of the method is based on the analysis of residues in the zeros of transfer function of load resistance.Results. Flexible approximating functions proved to be an effective tool for designing matching circuits with multiple transfer zeros in infinity. Variative properties of the function facilitate the realization of both smooth and wave frequency characteristics. A combination of both is also possible, ensuring the best properties of both. The proposed approximating functions allow a smooth change in the frequency response, while preserving the normalization characteristic of classical approximations. Application of such functions allowed us to virtually remove the limitations inherent in the classical AF on the minimum values of the load capacitance and more than 30 % of the limiting values of inductance in the above examples.Conclusion. The developed methodology makes the process of wideband matching physically transparent and can be applied to other classes of loads.

A new approach to predict dynamic mooring tension using LSTM neural network based on responses of floating structure

The prediction of dynamic mooring line tension using the responses of floating structures is of great significance for the safety monitoring of the station-keeping. Due to the mooring line tension usually has the typical low-frequency and wave-frequency characteristics, this paper proposes a method of Low-frequency adds wave-frequency responses (LAWR) to predict the mooring line tension. Firstly, the optimal Long-short term memory (LSTM) neural network structure is determined through conducting the parameter sensitivity analysis on the performance of the LSTM model. Secondly, the low-frequency and wave-frequency tension are predicted using the corresponding low-frequency and wave-frequency responses as the input data, respectively. Then, the total mooring line tension is predicted by superposing the low-frequency tension and wave-frequency tension. Finally, the feasibility of the LAWR method is verified by considering the different data relevance between the training sets and validating sets, including the sea state condition contains different current direction, wave height and spectral peak frequency. The method proposed in this paper could further improve the prediction accuracy of mooring line tension more than 30%, which has great engineering significance.

A new type of anti-heave semi-submersible drilling platform

Abstract A new type of semi-submersible drilling platform is designed. The numerical simulation software is used to analyze the heave response of the new platform in the frequency domain and time domain, and the semi-submersible drilling platforms with double-floating four-column structure and heave plate structure are compared with the new platform. This paper introduces the design principles of the new platform and the theoretical basis, mathematical model and boundary conditions during correlation analysis. The numerical simulation results show that the maximum and mean values of the heave response of the new platform are significantly reduced in the frequency domain analysis compared with the double-floating four-column and the heave-plate structure platform; and the new platform has a significant increase in the natural heaving period of the new platform, which can effectively prevent the occurrence of resonance. In the mooring time domain coupling analysis, the surge, sway and roll response of the new platform is small, and the heave response is greatly reduced. In the spectral analysis, the new platform has a smaller peak response and better wave frequency characteristics. The new platform has excellent anti-heave performance, reasonable structure and feasibility, and can provide reference for the design and selection of new generation semi-submersible drilling platform.

Theory of wave interaction in a magnetic field of arbitrary direction

A theory is developed for the interaction of electromagnetic waves and quantum systems subjected to a magnetic field of arbitrary direction in the two-mode (four-frequency) regime. Two versions of the theory are given: 1) for investigations of spectroscopic effects; 2) for studies of the physical processes in ring lasers having anisotropic resonators. Nonlinear differential equations are derived for the slowly varying amplitudes and phase differences of the modes. These can be used to study the amplitude and frequency characteristics of waves having arbitrary polarization vectors.