scholarly journals THEORETICAL FORMS OF SHORELINES

2011 ◽  
Vol 1 (7) ◽  
pp. 11
Author(s):  
W. Grijm
Keyword(s):  
Simple Relation ◽  
Mathematical Treatment ◽  
Physical Processes ◽  
Wave Characteristics ◽  
Wave Approach ◽  
Real Value ◽  
Detailed Picture ◽  
Made In

In previous publications Pelnard-Considere, Bruun and larras have d.erived theoretical shore formations. When doing so, it is necessary to idealize the conditions, such as a lxttoral transport by waves only, unvarying wave characteristics and a simple relation between the angle of wave approach and the littoral transport. Moreover various other simplifications have to be made in order to make it possible to handle the equations. The question may arise whether results, obtained from such an idealized situation, have any value for practical cases, where the conditions are much more complex and variable. The answer is no when we expect to obtain a true and detailed picture of the development of any particular stretch of coast. Such theoretical exercises can be of real value, however, because they help us to understand why and how certain formations come into being and how they are influenced by certain physical processes* This is the case for instance with such formations as deltas, spits and tombolos. We cannot say that we really know the function which determines the littoral transport. Up to now one of the simplifications in the mathematical treatment has been the restriction to stay within an area in which the values of

scholarly journals A NuSTAR confirmation of the 36 ks hard X-ray pulse-phase modulation in the magnetar 1E 1547.0 − 5408

2021 ◽  
Vol 502 (2) ◽  
pp. 2266-2284
Author(s):  
Kazuo Makishima ◽  
Teruaki Enoto ◽  
Hiroki Yoneda ◽  
Hirokazu Odaka
Keyword(s):  
Time Lapse ◽  
Phase Behaviour ◽  
Modulation Amplitude ◽  
Axial Deformation ◽  
Physical Processes ◽  
Arrival Times ◽  
Pulse Phase ◽  
Phase Variations ◽  
Complex Phenomena ◽  
Made In

ABSTRACT This paper describes an analysis of the NuSTAR data of the fastest-rotating magnetar 1E 1547 − 5408, acquired in 2016 April for a time lapse of 151 ks. The source was detected with a 1–60 keV flux of 1.7 × 10−11 erg s−1 cm−2, and its pulsation at a period of 2.086710(5) s. In 8–25 keV, the pulses were phase-modulated with a period of T = 36.0 ± 2.3 ks, and an amplitude of ∼0.2 s. This reconfirms the Suzaku discovery of the same effect at $T=36.0 ^{+4.5}_{-2.5}$ ks, made in the 2009 outburst. These results strengthen the view derived from the Suzaku data, that this magnetar performs free precession as a result of its axial deformation by ∼0.6 × 10−4, possibly caused by internal toroidal magneti fields (MFs) reaching ∼1016 G. Like in the Suzaku case, the modulation was not detected in energies below ∼8 keV. Above 10 keV, the pulse-phase behaviour, including the 36 ks modulation parameters, exhibited complex energy dependencies: at ∼22 keV, the modulation amplitude increased to ∼0.5 s, and the modulation phase changed by ∼65° over 10–27 keV, followed by a phase reversal. Although the pulse significance and pulsed fraction were originally very low in >10 keV, they both increased noticeably, when the arrival times of individual photons were corrected for these systematic pulse-phase variations. Possible origins of these complex phenomena are discussed, in terms of several physical processes that are specific to ultrastrong MFs.

Bridging the Gap Between Continuum Mechanical Microrotation Viscosity and Lagrangian Point-Particles

2013 ◽  
Vol 135 (12) ◽  
Author(s):  
Helge I. Andersson ◽  
Lihao Zhao
Keyword(s):  
Fluid Dynamics ◽  
Simple Relation ◽  
Lagrangian Point ◽  
Flow Variable ◽  
Particle Loading ◽  
Carrier Fluid ◽  
Point Particles ◽  
Fluid Property ◽  
Dilute Suspension ◽  
Made In

The microrotation viscosity is an essential fluid property in micropolar fluid dynamics. By considering a dilute suspension of inertial spherical point-particles in an otherwise Newtonian fluid, an explicit analytical expression for the microrotation viscosity is derived. This non-Newtonian continuum mechanical fluid property is seen to be proportional with the viscosity of the carrier fluid and the local particle loading. A number of assumptions were made in order to arrive at this simple relation, which implies that the microrotation viscosity should be considered as a flow variable rather than as a constant fluid property.

scholarly journals Wave Propagation on Microstate Geometries

2019 ◽  
Vol 21 (3) ◽  
pp. 705-760 ◽  
Author(s):  
Joe Keir
Keyword(s):  
Wave Equation ◽  
Decay Rates ◽  
Mathematical Treatment ◽  
Linear Wave ◽  
Local Energy ◽  
Linear Wave Equation ◽  
Uniform Decay ◽  
Uniformly Bounded ◽  
Kaluza Klein ◽  
Made In

AbstractSupersymmetric microstate geometries were recently conjectured (Eperon et al. in JHEP 10:031, 2016. 10.1007/JHEP10(2016)031) to be nonlinearly unstable due to numerical and heuristic evidence, based on the existence of very slowly decaying solutions to the linear wave equation on these backgrounds. In this paper, we give a thorough mathematical treatment of the linear wave equation on both two- and three-charge supersymmetric microstate geometries, finding a number of surprising results. In both cases, we prove that solutions to the wave equation have uniformly bounded local energy, despite the fact that three-charge microstates possess an ergoregion; these geometries therefore avoid Friedman’s “ergosphere instability” (Friedman in Commun Math Phys 63(3):243–255, 1978). In fact, in the three-charge case we are able to construct solutions to the wave equation with local energy that neither grows nor decays, although these data must have non-trivial dependence on the Kaluza–Klein coordinate. In the two-charge case, we construct quasimodes and use these to bound the uniform decay rate, showing that the only possible uniform decay statements on these backgrounds have very slow decay rates. We find that these decay rates are sublogarithmic, verifying the numerical results of Eperon et al. (2016). The same construction can be made in the three-charge case, and in both cases the data for the quasimodes can be chosen to have trivial dependence on the Kaluza–Klein coordinates.

scholarly journals Nearshore Wave Transformation Domains from Video Imagery

2019 ◽  
Vol 7 (6) ◽  
pp. 186 ◽  
Author(s):  
Umberto Andriolo
Keyword(s):  
Sediment Transport ◽  
Intensity Variation ◽  
Wave Transformation ◽  
Physical Processes ◽  
Pixel Intensity ◽  
Wave Characteristics ◽  
Wide Range ◽  
Different Types ◽  
Propagation Properties ◽  
Wave Properties

Within the nearshore area, three wave transformation domains can be distinguished based on the wave properties: shoaling, surf, and swash zones. The identification of these distinct areas is relevant for understanding nearshore wave propagation properties and physical processes, as these zones can be related, for instance, to different types of sediment transport. This work presents a technique to automatically retrieve the nearshore wave transformation domains from images taken by coastal video monitoring stations. The technique exploits the pixel intensity variation of image acquisitions, and relates the pixel properties to the distinct wave characteristics. This allows the automated description of spatial and temporal extent of shoaling, surf, and swash zones. The methodology was proven to be robust, and capable of spotting the three distinct zones within the nearshore, both cross-shore and along-shore dimensions. The method can support a wide range of coastal studies, such as nearshore hydrodynamics and sediment transport. It can also allow a faster and improved application of existing video-based techniques for wave breaking height and depth-inversion, among others.

A Review of Nonsteady Flow Models for Compressor Stability

1994 ◽  
Vol 116 (2) ◽  
pp. 202-215 ◽  
Author(s):  
J. P. Longley
Keyword(s):  
Fluid Dynamics ◽  
Flow Field ◽  
Rotating Stall ◽  
Time Development ◽  
Mathematical Treatment ◽  
Two Dimensional ◽  
Nonsteady Flow ◽  
Physical Processes ◽  
Flow Models ◽  
Modeling Techniques

This paper presents a review of the different approaches to modeling the nonsteady fluid dynamics associated with two-dimensional compressor flow fields. These models are used to predict the time development of flow field disturbances and have been found useful in both the study of rotating stall and the development of active control. The opportunity to digest the earlier investigations has now made it possible to express the modeling ideas using only a very simple mathematical treatment. Here, the emphasis is on the underlying physical processes that the models simulate and how the assumptions within the models affect predictions. The purpose of this work is to produce, in a single document, a description of compressor modeling techniques, so that prospective users can assess which model is the most suitable for their application.

Fluid-structure Interactions

1998 ◽  
Vol 120 (04) ◽  
pp. 66-68 ◽  
Author(s):  
Klaus-Ju¨rgen Bathe
Keyword(s):  
Finite Element ◽  
Fluid Structure Interactions ◽  
Physical Processes ◽  
Fluid Structure ◽  
Modeling And Analysis ◽  
Structure Interaction ◽  
Design And Manufacturing ◽  
Physical Phenomena ◽  
Acoustic Fluid ◽  
Made In

This article reviews finite element methods that are widely used in the analysis of solids and structures, and they provide great benefits in product design. In fact, with today’s highly competitive design and manufacturing markets, it is nearly impossible to ignore the advances that have been made in the computer analysis of structures without losing an edge in innovation and productivity. Various commercial finite-element programs are widely used and have proven to be indispensable in designing safer, more economical products. Applications of acoustic-fluid/structure interactions are found whenever the fluid can be modeled to be inviscid and to undergo only relatively small particle motions. The interplay between finite-element modeling and analysis with the recognition and understanding of new physical phenomena will advance the understanding of physical processes. This will lead to increasingly better simulations. Based on current technology and realistic expectations of further hardware and software developments, a tremendous future for fluid–structure interaction applications lies ahead.

scholarly journals Advances in understanding and parameterization of small-scale physical processes in the marine Arctic climate system: a review

2014 ◽  
Vol 14 (17) ◽  
pp. 9403-9450 ◽  
Author(s):  
T. Vihma ◽  
R. Pirazzini ◽  
I. Fer ◽  
I. A. Renfrew ◽  
J. Sedlar ◽  
...  
Keyword(s):  
Sea Ice ◽  
Arctic Sea Ice ◽  
Surface Fluxes ◽  
Climate System ◽  
Arctic Climate ◽  
The Arctic ◽  
Small Scale ◽  
Climate Modelling ◽  
Physical Processes ◽  
Made In

Abstract. The Arctic climate system includes numerous highly interactive small-scale physical processes in the atmosphere, sea ice, and ocean. During and since the International Polar Year 2007–2009, significant advances have been made in understanding these processes. Here, these recent advances are reviewed, synthesized, and discussed. In atmospheric physics, the primary advances have been in cloud physics, radiative transfer, mesoscale cyclones, coastal, and fjordic processes as well as in boundary layer processes and surface fluxes. In sea ice and its snow cover, advances have been made in understanding of the surface albedo and its relationships with snow properties, the internal structure of sea ice, the heat and salt transfer in ice, the formation of superimposed ice and snow ice, and the small-scale dynamics of sea ice. For the ocean, significant advances have been related to exchange processes at the ice–ocean interface, diapycnal mixing, double-diffusive convection, tidal currents and diurnal resonance. Despite this recent progress, some of these small-scale physical processes are still not sufficiently understood: these include wave–turbulence interactions in the atmosphere and ocean, the exchange of heat and salt at the ice–ocean interface, and the mechanical weakening of sea ice. Many other processes are reasonably well understood as stand-alone processes but the challenge is to understand their interactions with and impacts and feedbacks on other processes. Uncertainty in the parameterization of small-scale processes continues to be among the greatest challenges facing climate modelling, particularly in high latitudes. Further improvements in parameterization require new year-round field campaigns on the Arctic sea ice, closely combined with satellite remote sensing studies and numerical model experiments.

scholarly journals A modification of the CABARET scheme for numerical simulation of one-dimensional detonation flows using a one-stage irreversible model of chemical kinetics

2017 ◽  
pp. 1-10
Author(s):  
А.В. Данилин ◽  
А.В. Соловьев ◽  
А.М. Зайцев
Keyword(s):  
Numerical Simulation ◽  
Chemical Kinetics ◽  
Order Of Approximation ◽  
Governing Equations ◽  
Physical Processes ◽  
Cabaret Scheme ◽  
One Dimensional ◽  
One Stage ◽  
The Right ◽  
Made In

Представлен алгоритм для численного моделирования задач одномерной детонации с использованием одностадийной необратимой модели химической кинетики. Дискретизация уравнений движения произведена согласно балансно-характеристической методике ``кабаре''. Аппроксимация источниковых членов выполнена без расщепления по физическим процессам с использованием неявного подхода с регулируемым порядком аппроксимации. Показано точное согласование параметров моделируемой детонации Чепмена--Жуге с аналитическим решением. Для неустойчивой детонации продемонстрирована зависимость результатов расчета от порядка аппроксимации правых частей. An algorithm for numerical simulation of one-dimensional detonation using a one-stage irreversible model of chemical kinetics is proposed. The discretization of the convective parts of governing equations is made in accordance with the balance-characteristic CABARET (Compact Accurately Boundary Adjusting-REsolution Technique) approach. The approximation of source terms is performed implicitly without splitting into physical processes with a regulated order of approximation. It is shown that the numerically obtained Chapman-Jouget detonation parameters are in exact agreement with the analytical solution. It is also shown that, in the case of unstable detonation, the numerical results are dependent on the order of approximation chosen for the right-hand sides of the governing equations.

The Present State of Lubrication and Its Relation to Rheology

1968 ◽  
Vol 90 (3) ◽  
pp. 526-530 ◽  
Author(s):  
J. K. Appeldoorn
Keyword(s):  
Thin Film ◽  
Reynolds Equation ◽  
Mathematical Treatment ◽  
Load Carrying Capacity ◽  
Thin Film Lubrication ◽  
Load Carrying ◽  
Viscoelastic Effects ◽  
Viscoelastic Liquids ◽  
Film Lubrication ◽  
Made In

In thick-film lubrication, Reynolds’ equation is generally satisfactory. However, the assumptions made in deriving this equation cannot be justified for non-Newtonian, viscoelastic liquids. It is concluded that no satisfactory mathematical treatment is yet available for calculating the load-carrying capacity of such liquids. In thin-film lubrication, elastohydrodynamic calculations indicate that the lubricant film may be quite thick even under heavily loaded conditions, but discrepancies exist between calculation and experiment. These can be explained by assuming non-Newtonian behavior, or unusual viscoelastic effects, but the assumptions are largely unfounded. There is virtually a complete absence of data on the behavior of liquids under impact loading. Such data are needed to resolve whether thin-film lubrication is primarily chemical or primarily physical.

An intuitionistically plausible interpretation of intuitionistic logic

1977 ◽  
Vol 42 (4) ◽  
pp. 564-578 ◽  
Author(s):  
H. C. M. de Swart
Keyword(s):  
Intuitionistic Logic ◽  
Predicate Calculus ◽  
Mathematical Treatment ◽  
First Order ◽  
The Past ◽  
Definition Of ◽  
Image Position ◽  
Order Predicate Calculus ◽  
Made In

Let IPC be the intuitionistic first-order predicate calculus. From the definition of derivability in IPC the following is clear:(1) If A is derivable in IPC, denoted by “⊦IPCA”, then A is intuitively true, that means, true according to the intuitionistic interpretation of the logical symbols. To be able to settle the converse question: “if A is intuitively true, then ⊦IPCA”, one should make the notion of intuitionistic truth more easily amenable to mathematical treatment. So we have to look then for a definition of “A is valid”, denoted by “⊨A”, such that the following holds:(2) If A is intuitively true, then ⊨ A.Then one might hope to be able to prove(3) If ⊨ A, then ⊦IPCA.If one would succeed in finding a notion of “⊨ A”, such that all the conditions (1), (2) and (3) are satisfied, then the chain would be closed, i.e. all the arrows in the scheme below would hold.Several suggestions for ⊨ A have been made in the past: Topological and algebraic interpretations, see Rasiowa and Sikorski [1]; the intuitionistic models of Beth, see [2] and [3]; the interpretation of Grzegorczyk, see [4] and [5]; the models of Kripke, see [6] and [7]. In Thirty years of foundational studies, A. Mostowski [8] gives a review of the interpretations, proposed for intuitionistic logic, on pp. 90–98.

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