Identifying the turbulent flow developing inside and around the bottom trawl by Electromagnetic Current Velocity Meter approach in the flume tank

The Knowledge of turbulent flow developing inside and around the bottom trawl net is of great importance not only for improving the hydrodynamic performance of the gear but also for the selectivity via the fish response,such as the herding response or escape behavior.The 3-D Electromagnetic Current Velocity Meter(ECVM)measurements were performed to investigate the effect of turbulent flow on the bottom trawl net performance and to analyze the turbulence intensity and velocity ratio inside and around different parts of the trawl net.Proper orthogonal decomposition(POD)method was applied in order to extract the phase averaged mean velocity field of turbulent flow from each available ECVM instantaneous velocity.The results demonstrated the existence of turbulence flow,consisting of turbulent boundary layer flow and the turbulence due to the trawl wake developing all inside and around the bottom trawl net.Increasing input streamwise velocity results in faster trawl movement and a significant turbulent flow.The maximum turbulence intensity inside and around trawl wing,square part,first belly,second belly,third belly,cod-end is 0.95%,1.34%,3.40%,4.10%,4.25%and 3.80%,respectively.It was found that the mean velocity field in a turbulent flow inside and around trawl net cod-end recovered on the average was~77.58%of the input streamwise velocity.It is~12.92%,~13.07%,~11.40%,~13.00%and~0.45%less than that inside and around trawl wing,square part,first belly,second belly,and third belly of the bottom trawl net,respectively.The turbulent flow behavior depends strongly on the structure oscillation,input streamwise velocity and,porosity of the net structure.It is necessary to take into account the velocity reduction inside and around a different part of the trawl net to improve the entire drag force determination,cod-end design,and further selectivity control of the fishing gear.

Inverse problem of pulsed eddy current field of ferromagnetic plates

To determine the wall thickness, conductivity and permeability of a ferromagnetic plate, an inverse problem is established with measured values and calculated values of time-domain induced voltage in pulsed eddy current testing on the plate. From time-domain analytical expressions of the partial derivatives of induced voltage with respect to parameters,it is deduced that the partial derivatives are approximately linearly dependent. Then the constraints of these parameters are obtained by solving a partial linear differential equation. It is indicated that only the product of conductivity and wall thickness, and the product of relative permeability and wall thickness can be determined accurately through the inverse problem with time-domain induced voltage. In the practical testing, supposing the conductivity of the ferromagnetic plate under test is a fixed value, and then the relative variation of wall thickness between two testing points can be calculated via the ratio of the corresponding inversion results of the product of conductivity and wall thickness. Finally, this method for wall thickness measurement is verified by the experiment results of a carbon steel plate.

Electromagnetic backscattering from one-dimensional drifting fractal sea surface Ⅱ：Electromagnetic backscattering model

Sea surface current has a significant influence on electromagnetic（EM） backscattering signals and may constitute a dominant synthetic aperture radar（SAR） imaging mechanism. An effective EM backscattering model for a one-dimensional drifting fractal sea surface is presented in this paper. This model is used to simulate EM backscattering signals from the drifting sea surface. Numerical results show that ocean currents have a significant influence on EM backscattering signals from the sea surface. The normalized radar cross section（NRCS） discrepancies between the model for a coupled wavecurrent fractal sea surface and the model for an uncoupled fractal sea surface increase with the increase of incidence angle,as well as with increasing ocean currents. Ocean currents that are parallel to the direction of the wave can weaken the EM backscattering signal intensity, while the EM backscattering signal is intensified by ocean currents propagating oppositely to the wave direction. The model presented in this paper can be used to study the SAR imaging mechanism for a drifting sea surface.

Electromagnetic processes in a χEFT framework

Recently,we have derived a two–nucleon potential and consistent nuclear electromagnetic currents in chiral effective field theory with pions and nucleons as explicit degrees of freedom.The calculation of the currents has been carried out to include N 3 LO corrections,consisting of two–pion exchange and contact contributions.The latter involve unknown low-energy constants （LECs）,some of which have been fixed by fitting the np Sand P-wave phase shifts up to 100 MeV lab energies.The remaining LECs entering the current operator are determined so as to reproduce the experimental deuteron and trinucleon magnetic moments,as well as the np cross section.This electromagnetic current operator is utilized to study the nd and n 3 He radiative captures at thermal neutron energies.Here we discuss our results stressing on the important role played by the LECs in reproducing the experimental data.

A systematical study of the chiral magnetic effects at the RHIC and LHC energies

Considering the magnetic field response of the QGP medium,we perform a systematical study of the chiral magnetic effect（CME）,and make a comparison with the experimental results for the background-subtracted correlator H at the energies of the RHIC Beam Energy Scan（BES） and the LHC energy.The CME signals from our computations show a centrality trend and beam energy dependence that are qualitatively consistent with the experimental measurements of the charge dependent correlations.The time evolution of the chiral electromagnetic current at the RHIC and LHC energies is systematically studied.The dependence of the time-integrated current signal on the beam energy s1/2with different centralities is investigated.Our phenomenological analysis shows that the time-integrated electromagnetic current is maximal near the collision energy s1/2≈39 GeV.The qualitative trend of the induced electromagnetic current is in agreement with the CME experimental results at the RHIC and LHC energies.