Wave-triggered breakup in the marginal ice zone generates lognormal floe size distributions

Fragmentation of the sea ice cover by ocean waves is an important mechanism impacting ice evolution. Fractured ice is more sensitive to melt, leading to a local reduction in ice concentration, facilitating wave propagation. A positive feedback loop, accelerating sea ice retreat, is then introduced. Despite recent efforts to incorporate this process and the resulting floe size distribution (FSD) into the sea ice components of global climate models (GCM), the physics governing ice breakup under wave action remains poorly understood, and its parametrisation highly simplified. We propose a two-dimensional numerical model of wave-induced sea ice breakup to estimate the FSD resulting from repeated fracture events. This model, based on linear water wave theory and viscoelastic sea ice rheology, solves for the scattering of an incoming time-harmonic wave by the ice cover and derives the corresponding strain field. Fracture occurs when the strain exceeds an empirical threshold. The geometry is then updated for the next iteration of the breakup procedure. The resulting FSD is analysed for both monochromatic and polychromatic forcings. For the latter results, FSDs obtained for discrete frequencies are combined appropriately following a prescribed wave spectrum. We find that under realistic wave forcing, lognormal FSDs emerge consistently in a large variety of model configurations. Care is taken to evaluate the statistical significance of this finding. This result contrasts with the power-law FSD behaviour often assumed by modellers. We discuss the properties of these modelled distributions, with respect to the ice rheological properties and the forcing waves. The projected output will be used to improve empirical parametrisations used to couple sea ice and ocean waves GCM components.

Research of Power Distribution System Dynamic Simulation Based on Grid’s Harmonic Current

Harmonic current in power grid will cause extra power consumption of electrical equipment and affect the stable operation of power grid. Based on the dynamic model experiment system of 10kV distribution network, a working platform for parallel operation of charging pile was built, which studied the harmonic current components and analyzed the simulation waveform. The results show that with the increase of number of charging piles, the content of harmonic current will decrease correspondingly, the main components are low frequency odd harmonics; When 16 charging piles are connected in parallel, three harmonics are the main components; the waveform of the simulation calculation curve and the actual measurement curve are basically consistent, and the current amplitude of each frequency harmonic wave is basically the same , so it is proved that the dynamic model test platform is reasonable and feasible to test grid’s harmonic current. The dynamic model can provide technical support for harmonic suppression research.

Effects of the Rates on the Performance and Pressure Pulsations of a High-Speed Pump with Straight Blade

Along with the crucial requirement for efficiency improvement in the cutting-edge petrochemical technology, the evaluation of the dynamic performance characteristics of high-speed pump is becoming increasingly important. It has become a main topic in the research of high-speed pump to minimize the pressure pulsation induced by the fluid in the pump body, so as to reduce the mechanical vibration. Although the research on the transient flow characteristic and pressure fluctuation of a high-speed pump with straight blades is of great significance, it has been seldom explored. In this work, the flow instability of a 16 straight-blade high-speed centrifugal pump is studied numerically at a rotational speed of 8500 rpm and flow rate of 3 m3/h. Results show that with the influence of rotor-stator interaction, time-domain pressure signals at the tongue show double peak characteristic, whereas a single peak characteristic exists at the diffuser wall. The pressure fluctuation near the tongue is reduced to approximately half of that at the volute wall by the water ring effect accompanied with the high-pressure factor. At the tongue region, the amplitude of the blade passing frequency is reduced by the unsteady flow, whereas the harmonic wave was increased at 2–4 times of the blade passing frequency.

Tailoring linear and nonlinear surface plasmon response in borophene nanostructure

A newly reported 2D material “borophene” provides a novel building block for nanoscale materials and devices. In this work, the linear and nonlinear plasmonic response of electric dipole moment in the metallic borophene is theoretically investigated. In our proposed model, the borophene nanostructure is deposited on the top of the dielectric layer sandwiched with the silver layer acting as a mirror. It was found that the scattering at the scattering peak originates mainly from the exciting total electric dipole. Our calculations demonstrated that scattering in the proposed model can be tuned well with carrier relaxation time, effective electron mass, and free carrier density. The strongly localized fundamental field induces the desired increase of second harmonic wave, which is discussed in detail by introducing the second-order nonlinear source. In addition, the evolution of the lifetime of linear and nonlinear plasmonic modes is also investigated which helps us to study the underlying mechanism of micro process in the borophene plasmonic-photonic interaction. The manipulation of plasmonic behavior and lifetime evolution makes the borophene an excellent platform for tunable plasmonic-photonic devices.

Novel internal measurements of ion cyclotron frequency range fast-ion driven modes

Novel internal measurements and analysis of ion cyclotron frequency range fast-ion driven modes in DIII-D are presented. Observations, including internal density fluctuation (ñ) measurements obtained via Doppler Backscattering, are presented for modes at low harmonics of the ion cyclotron frequency localized in the edge. The measurements indicate that these waves, identified as coherent Ion Cyclotron Emission (ICE), have high wave number, _⊥ρ_fast ≳ 1, consistent with the cyclotron harmonic wave branch of the magnetoacoustic cyclotron instability (MCI), or electrostatic instability mechanisms. Measurements show extended spatial structure (at least ~ 1/6 the minor radius). These edge ICE modes undergo amplitude modulation correlated with edge localized modes (ELM) that is qualitatively consistent with expectations for ELM-induced fast-ion transport.

Modeling of Harmonic Wave Propagation Through a Metasurface with Helmholtz Resonator Shaped Cells

Harmonic wave propagation through a novel metasurface design is presented in this paper. The metasurface is formed by using the Helmholtz resonator as the cells shape design since such resonator has uniqueness and advantageous performances. The study is conducted both numerically using the finite element method and experimentally using specific measurements to validate the numerical results. Parametric studies of the selected variables are also conducted to obtain broader information on the performance. From the result, it is found that the new proposed metasurface design has the potential to be implemented in future engineering practices.

Topological sensitivity analysis revisited for time-harmonic wave scattering problems. Part II: recursive computations by the boundary integral equation method

PurposeThe purpose of this paper is to revisit the recursive computation of closed-form expressions for the topological derivative of shape functionals in the context of time-harmonic acoustic waves scattering by sound-soft (Dirichlet condition), sound-hard (Neumann condition) and isotropic inclusions (transmission conditions).Design/methodology/approachThe elliptic boundary value problems in the singularly perturbed domains are equivalently reduced to couples of boundary integral equations with unknown densities given by boundary traces. In the case of circular or spherical holes, the spectral Fourier and Mie series expansions of the potential operators are used to derive the first-order term in the asymptotic expansion of the boundary traces for the solution to the two- and three-dimensional perturbed problems.FindingsAs the shape gradients of shape functionals are expressed in terms of boundary integrals involving the boundary traces of the state and the associated adjoint field, then the topological gradient formulae follow readily.Originality/valueThe authors exhibit singular perturbation asymptotics that can be reused in the derivation of the topological gradient function in the iterated numerical solution of any shape optimization or imaging problem relying on time-harmonic acoustic waves propagation. When coupled with converging Gauss−Newton iterations for the search of optimal boundary parametrizations, it generates fully automatic algorithms.

Transient processes in a gas/plate structure in the case of light loading

The problem of a pulse excitation in an acoustic half-space with a flexible wall described by a thin plate equation is studied. The solution is written as a double Fourier integral. A novel technique of estimation of this integral is developed. The surface of integration is deformed in such a way that the integrand is exponentially small everywhere except the neighbourhoods of several ‘special points’ that provide field components. Special attention is paid to the pulse associated with the coincidence point of the branches of the dispersion diagram of the acoustic medium and the plate. This pulse is shown to be a harmonic wave of a finite duration.