Gravitational Lensing of Continuous Gravitational Waves

Continuous gravitational waves are analogous to monochromatic light and could therefore be used to detect wave effects such as interference or diffraction. This would be possible with strongly lensed gravitational waves. This article reviews and summarises the theory of gravitational lensing in the context of gravitational waves in two different regimes: geometric optics and wave optics, for two widely used lens models such as the point mass lens and the Singular Isothermal Sphere (SIS). Observable effects due to the wave nature of gravitational waves are discussed. As a consequence of interference, GWs produce beat patterns which might be observable with next generation detectors such as the ground based Einstein Telescope and Cosmic Explorer, or the space-borne LISA and DECIGO. This will provide us with an opportunity to estimate the properties of the lensing system and other cosmological parameters with alternative techniques. Diffractive microlensing could become a valuable method of searching for intermediate mass black holes formed in the centres of globular clusters. We also point to an interesting idea of detecting the Poisson–Arago spot proposed in the literature.

Integrated rupture mechanics for slow slip events and earthquakes

Slow slip events usually occur downdip of seismogenic zones in subduction megathrusts and crustal faults, with rupture speeds much slower than earthquakes. The empirical moment-duration scaling relation can help constrain the physical mechanism of slow slip events, yet it is still debated whether this scaling is linear or cubic and a fundamental model unifying slow slip events and earthquakes is still lacking. Here I present numerical simulations that show that slow slip events are regular earthquakes with negligible dynamic-wave effects. A continuum of rupture speeds, from arbitrarily-slow speeds up to the S-wave speed, is primarily controlled by the stress drop and a transition slip rate above which the fault friction transitions from rate-weakening behaviour to rate-strengthening behaviour. This continuum includes tsunami earthquakes, whose rupture speeds are about one-third of the S-wave speed. These numerical simulation results are predicted by the three-dimensional theory of dynamic fracture mechanics of elongated ruptures. This fundamental model unifies slow slip events and earthquakes, reconciles the observed moment-duration scaling relations, and opens new avenues for understanding earthquakes through investigations of the kinematics and dynamics of frequently occurring slow slip events.

EFFECTS OF MARINE CONDITION ON THE SPEED AND FUEL CONSUMPTION OF A FULLY – LOADED VLCC

Minimizing fuel consumption is a priority for ship-owners seeking to reduce their vessel costs due to sea conditions. One of the most reliable methods used to estimate fuel consumption is to identify field investigations for future voyages. The VLCC Salina was used based on daily field data collected over a proper period and year of 2014 was identified as a period of optimal performance after its periodic dry dock repair. According to verified results for Beaufort scales of 2, 3 and 4, the vessel exhibited an average speed loss of 2.2% due to wind and wave effects for a Froude number of 0.15 while its greatest speed loss was observed at angles of 30‒60° relative to its longitudinal axis. The results were finally used to develop a methodology for estimating fuel consumption of Salina and 3 other sister-ships, during future voyages, in the fleet of the National Iranian tanker company.

Numerical investigations of the free surface flow around a surface piercing hydrofoil

Starting with January 2013, naval architects faces new challenges, as all ships greater than 400 tons must comply with energy efficiency index (MPEC 62, 2011). From ship hydrodynamics point of view one handy solution is using Energy Saving Devices (ESD), with the main purpose to improve the flow parameters entering the propeller. For ballast loading condition the ESD may intersect the free surface disturbing and complicating the flow due to free surface /boundary layer interaction, turbulence and breaking wave effects that coexist and which are not completely clarified so far. Therefore, a free surface flow around a NACA 0012 surface piercing hydrofoil is numerically investigated and the results are compared to experimental results obtained in the Towing Tank of the Naval Architecture Faculty, “Dunarea de Jos” University of Galati. The comparison includes drag and free surface elevation on hydrofoil surface together with numerical uncertainty.

Grid-characteristic numerical method for medical ultrasound

Grid-characteristic method (GCM) is a fast and reliable numerical method that allows to model wave effects in viscoelastic media with high accuracy, including surface and contact waves. This research is dedicated to the application of GCM to the problem of medical ultrasound. Calculations for High-Intensity Focused Ultrasound (HIFU) were performed on 3D model statements for homogenous and inhomogeneous media, and a qualitative correspondence with experimental data was achieved. Numerical results include estimation of consumed energy (based on Maxwell viscosity model), velocity vector and stress tensor components. Various material parameters were considered, including relaxation time and inclusions of different types.

Optimal control of fluctuations of the “liquid substance - pipeline” system in terms of speed during transportation of a liquid substance

The process of transporting a liquid substance (oil, petroleum products, gas mixtures) the pipeline network and related engineering facilities, being a dynamically non-equilibrium physical system, are often carried out in extreme modes, which can form dangerous wave phenomena accompanied by various instabilities, generating undesirable consequences and even catastrophes. Similar phenomena can occur in technical devices and apparatuses containing in their design hydraulic networks for the transfer of continuous media (aircraft, energy objects). Eliminate (extinguish or reduce the intensity) such phenomena are possible in the shortest possible time by making additional structural changes to the pipeline network, which make it possible to use external devices for dynamic influence on the “liquid substance – pipeline” system and eliminate (or minimize) the possibility of negative wave effects. The paper is devoted to the problem of eliminating dangerous vibrations initiated by a liquid substance transported through a pipeline network, provided that time resources are spent minimally. A mathematical model of the wave process and the problem of optimal control over the speed of such a model are considered. The control effect on the “liquid substance-pipeline” system is carried out at the initial and final points of the pipeline network, while the necessary information about the state of the system is used in a finite number of points distributed along the entire length of the pipeline, which makes it possible to calculate external influences on the system. In order to simplify the presentation of the results, a linear carrier of a liquid substance is used (in applications, a pipeline without branches) and a one-dimensional wave equation – the length of the pipeline is much larger than its diameter.