Modeling North Atlantic nor'easters with modern wave forecast models

Author Posting. © Her Majesty the Queen in Right of Canada, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 123 (2018): 533–557, doi:10.1002/2017JC012868.Three state-of-the-art operational wave forecast model systems are implemented on fine-resolution grids for the Northwest Atlantic. These models are: (1) a composite model system consisting of SWAN implemented within WAVEWATCHIII® (the latter is hereafter, WW3) on a nested system of traditional structured grids, (2) an unstructured grid finite-volume wave model denoted “SWAVE,” using SWAN physics, and (3) an unstructured grid finite element wind wave model denoted as “WWM” (for “wind wave model”) which uses WW3 physics. Models are implemented on grid systems that include relatively large domains to capture the wave energy generated by the storms, as well as including fine-resolution nearshore regions of the southern Gulf of Maine with resolution on the scale of 25 m to simulate areas where inundation and coastal damage have occurred, due to the storms. Storm cases include three intense midlatitude cases: a spring Nor'easter storm in May 2005, the Patriot's Day storm in 2007, and the Boxing Day storm in 2010. Although these wave model systems have comparable overall properties in terms of their performance and skill, it is found that there are differences. Models that use more advanced physics, as presented in recent versions of WW3, tuned to regional characteristics, as in the Gulf of Maine and the Northwest Atlantic, can give enhanced results.NOAA-funded IOOS/SURA; BIO Grant Number: NA11NOS0120141; Canadian Panel on Energy R & D Grant Number: 1B00.003C; Fisheries and Oceans Canada's Aquatic Climate Change Adaptation Program Grant Number: MAR-92018-07-2

Analysis and inhibition of radial electromagnetic force in composite magnetic coupler

Abstract A new inhibition method was proposed for the problem of harmonic of radial electromagnetic force during the operation of the composite magnetic coupler. In order to suppress its radial electromagnetic force, a radial permanent magnet rotor eccentricity method is proposed, and a three‐dimensional finite element model is established. Based on the Maxwell tensor method, the radial electromagnetic force of the composite magnetic coupler is analysed, and the mathematical expression of its radial electromagnetic force is established, Maxwell stress tensor was used to analyse the radial electromagnetic force in a composite magnetic coupler and to establish the mathematical equation for the radial electromagnetic force. In order to suppress the radial electromagnetic force, a method based on rotor eccentricity in a radial permanent magnet was proposed. A prototype of a composite magnetic coupler with a rated power of 5 kW was designed to test its output torque under load. The results showed that the simulated curve was consistent with the tested curve, with a maximum numerical error of 8.9%. The tested values of the output torque before and after eccentricity were compared, and the results showed that the output torque remained basically unchanged after the eccentric structure was adopted and that the torque pulsation was significantly reduced

Discussion on Local Spark Sintering of a Ceramic-Metal System in an SR-CT Experiment during Microwave Processing

In this paper, local spark sintering of a ceramic-metal system (SiO2-Sn) during microwave processing was examinedby means of synchrotron-radiation-computed tomography technology. From the reconstructed 3-D and cross-section images of the specimen, adensification process was observed below the melting point of Sn, and then the specimen came into a rapid densification stage. These results may be due to the local spark sintering induced by the high-frequency alternating microwave electric fields. As the metallic particles Sn were introduced, the microstructure of “ceramic-metal” will lead to a non-uniform distribution and micro-focusing effect from electric fields in some regions (e.g., the neck). This will result in high-intensity electric fields and then induce rapid spark sintering within the micro-region. However, in the subsequent stage, the densification rate declined even when the specimen was not dense enough. The explanation for this is that as the liquid Sn permeated the gaps between SiO2, the specimen became dense and the micro-focusing effect of electric fields decreased. This may result in the decrease or disappearance of spark sintering. These results will contribute to the understanding of microwave sintering mechanisms and the improvement of microwave processing methods

A Novel Model for Evaluating the Operation Performance Status of Rolling Bearings Based on Hierarchical Maximum Entropy Bayesian Method

Information such as probability distribution, performance degradation trajectory, and performance reliability function varies with the service status of rolling bearings, which is difficult to analyze and evaluate using traditional reliability theory. Adding equipment operation status to evaluate the bearing operation performance status has become the focus of current research to ensure the effective maintenance of the system, reduce faults, and improve quality under the condition of traditional probability statistics. So, a mathematical model is established by proposing the hierarchical maximum entropy Bayesian method (HMEBM), which is used to evaluate the operation performance status of rolling bearings. When calculating the posterior probability density function (PPDF), the similarities between time series regarded as a weighting coefficient are calculated using overlapping area method, membership degree method, Hamming approach degree method, Euclidean approach degree method, and cardinal approach degree method. The experiment investigation shows that the variation degree of the optimal vibration performance status can be calculated more accurately for each time series relative to the intrinsic series

In situ Investigation of Titanium Powder Microwave Sintering by Synchrotron Radiation Computed Tomography

In this study, synchrotron radiation computed tomography was applied to investigate the mechanisms of titanium powder microwave sintering in situ. On the basis of reconstructed images, we observed that the sintering described in this study differs from conventional sintering in terms of particle smoothing, rounding, and short-term growth. Contacted particles were also isolated. The kinetic curves of sintering neck growth and particle surface area were obtained and compared with those of other microwave-sintered metals to examine the interaction mechanisms between mass and microwave fields. Results show that sintering neck growth accelerated from the intermediate period; however, this finding is inconsistent with that of aluminum powder microwave sintering described in previous work. The free surface areas of the particles were also quantitatively analyzed. In addition to the eddy current loss in metal particles, other heating mechanisms, including dielectric loss, interfacial polarization effect, and local plasma-activated sintering, contributed to sintering neck growth. Thermal and non-thermal effects possibly accelerated the sintering neck growth of titanium. This study provides a useful reference of further research on interaction mechanisms between mass and microwave fields during microwave sintering

Discussion on Microwave-Matter Interaction Mechanisms by In Situ Observation of “Core-Shell” Microstructure during Microwave Sintering

This research aims to deepen the understanding of the interaction mechanisms between microwave and matter in a metal-ceramic system based on in situ synchrotron radiation computed tomography. A special internal “core-shell” microstructure was discovered for the first time and used as an indicator for the interaction mechanisms between microwave and matter. Firstly, it was proved that the microwave magnetic field acted on metal particles by way of inducing an eddy current in the surface of the metal particles, which led to the formation of a “core-shell” microstructure in the metal particles. On this basis, it was proposed that the ceramic particles could change the microwave field and open a way for the microwave, thereby leading to selective heating in the region around the ceramic particles, which was verified by the fact that all the “core-shell” microstructure was located around ceramic particles. Furthermore, it was indicated that the ceramic particles would gather the microwaves, and might lead to local heating in the metal-ceramic contact region. The focusing of the microwave was proved by the quantitative analysis of the evolution rate of the “core-shell” microstructure in a different region. This study will help to reveal the microwave-matter interaction mechanisms during microwave sintering

Research on characteristics of air gap of speed-regulation magnet coupler under condition of constant load

Taking axial permanent magnet asynchronous speed-regulation magnetic coupler as research object, a mathematical model of output speed and air gap of speed-regulation magnetic coupler was built based on magnetic circuit method, characteristics of the air gap of magnetic coupler were analyzed, relation between the air gap and output speed of the magnetic coupler under condition of constant load was studied, and variation law of corresponding output speed with different air gaps of the magnetic coupler was obtained: with increasing of the air gap between copper disc and permanent magnet disc, output speed of the magnetic coupler decreases; when the air gap increases linearly from 2.5 mm to 12.5 mm, the output speed decreases gradually from 773 r/min to 723 r/min; when the load torque keeps constant, with increasing of the air gap, power loss increases gradually, and when the air gap increases linearly from 2.5 mm to 12.5 mm, the experimental power loss gradually increases from 565 W to 1 613 W. In actual operation, power loss can be reduced by reducing the air gap properly. The results of the research have a certain guiding significance for the output speed control of the speed-regulation magnetic coupler under condition of constant load