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Kelvin Wedge

21 posts

Notes on Kelvin wakes and related water-wave problems across fluid mechanics and mathematics, including literature reading, derivations, work in progress, and documented negative results.

[Kelvin Wedge Reading Notes] What does $x^{\prime}$ mean in a Green’s function? — a linear algebra and operator view

In a Green's function \(G(x,x')\), the primed variable \(x'\) marks the source point — the location of a unit impulse — while \(x\) is the field point where the response is…

Fluid Mechanics

[Kelvin Wedge Reading Notes] From the Spectral Dirichlet-Neumann Symbol to the Physical-Space Operator Identity

We show how the spectral relation ∑ Formula implies the physical-space operator identity ∑ Formula, by inverse Fourier transform and the commutation of \(\partial_z\) with the hori…

Fluid Mechanics

[Kelvin Wedge Negative Results] Hankel Diagonalization of the Radial Bessel Operator

The math is sound. The method is not. We show that the order- \(n\) Hankel transform in \(r\) diagonalizes the Bessel-type radial operator \(\mathscr{L}_n\), mapping the PDE…

Mathematics

[Kelvin Wedge Negative Results] Fourier Coefficients of Quadratic Forms in $\cos \gamma$ for Steady Capillary-Gravity Waves

The math is sound. The method is not. We factor the quadratic denominator \(a+b \cos \gamma+c \cos ^2 \gamma\) and reduce the computation of its Fourier coefficients to those of ∑ Formula.…

Fluid Mechanics

[Kelvin Wedge Negative Results] Diagonalizing Azimuthal Mode Coupling via a Discrete Fourier Transform

The math is sound. The method is not. We recast the azimuthal mode-coupled surface equations as a block-Toeplitz convolution in the mode index and diagonalize this coupling via…

Fluid Mechanics

[Kelvin Wedge Negative Results] Cartesian Derivatives in Azimuthal Fourier–Hankel Space

The math is sound. The method is not. claim: ∑ Formula

Fluid Mechanics

[Kelvin Wedge Negative Results] DFT Method Main

The math is sound. The method is not. We consider the governing equations for water waves in the context of an inviscid fluid of infinite depth. The fundamental system of…

Fluid Mechanics

[Kelvin Wedge Negative Results] Axisymmetric Angular Fourier Modes and Hankel Transform of a Radial Heaviside Pressure Field

The math is sound. The method is not. We consider an axisymmetric pressure distribution \(p(r, \theta)=\bar{p} H(r-l)\) (radial dependence only) and show that its angular Fourier…

Mathematics

[Kelvin Wedge Negative Results] Self Adjoint Operators

The math is sound. The method is not. We consider the radial differential operator for a fixed angular mode \(n\), ∑ Formula

Mathematics

[Kelvin Wedge Negative Results] Azimuthal Fourier Analysis

The math is sound. The method is not. We introduce azimuthal Fourier expansion for functions with circular symmetry: we write \(f(r, \phi)\) as a sum of angular modes ∑ Formula, whe…

Fluid Mechanics

[Kelvin Wedge Negative Results] Operator Ladder Relations for Hankel Transforms of Bessel Type

The math is sound. The method is not. Hankel–Bessel Ladder Identities Claim. For suitable \(f_m(r)\) and \(k>0\), ∑ Formula Here ∑ Formula.

Fluid Mechanics

[Kelvin Wedge Reading Notes] Surface Waves Generated by A Travelling Pressure Point

We study the free-surface response to a moving pressure point over finite depth using 2D Fourier transforms, contour deformation, and a radiation condition. By analysing poles…

Fluid Mechanics

[Kelvin Wedge Reading Notes] Ray Geometry, and Wave Action in Uniform Currents

We summarize the ray-theoretic description of Kelvin ship waves in deep and finite depth, deriving the relationship between wavevector and wake angle, the Kelvin wedge, and the…

Fluid Mechanics

[Kelvin Wedge Reading Notes] Phase Geometry of Ship Waves: Deriving $p=a \cos ^2 \theta$

We derive the ship-wave crest relation \(p=a \cos ^2 \theta\) in deep water from the Doppler-shifted dispersion relation and stationary-phase arguments, interpret \(a\) as an inte…

Fluid Mechanics

[Kelvin Wedge Reading Notes] One Dimension Ship Wave With Surface Tension

The article develops a mathematical model for one-dimensional gravity-capillary ship waves, using residue theory to analyze wave components and show how surface tension and wave…

Fluid Mechanics

[Kelvin Wedge Reading Notes] Relations among Rays, Group Velocity, Phase Velocity, and the Wave Number Vector in Water Waves

In dispersive water waves (e.g., surface gravity waves on deep or shallow water), several concepts describe how waves travel, how energy moves, and how the wave patterns evolve.…

Fluid Mechanics

[Kelvin Wedge Reading Notes] Pressure Forcing on a Free Surface and Far-Field Waves in Lamb’s Hydrodynamics

We summarise Lamb’s treatment of a pressure disturbance on a free surface in a uniform stream, emphasising the contour‐integral evaluation of the far-field wavetrain, the…

Fluid Mechanics

[Kelvin Wedge Reading Notes] Wave Patterns from Ray Theory: Centered Waves, Wake Angles, and Phase Geometry

We collect the ray-theoretic relations for wave patterns generated by a point source, derive the slope of characteristics and their connection to the group-velocity symbol…

Fluid Mechanics

[Kelvin Wedge Reading Notes] Hankel Transform of the Bi-Laplacian and an Axisymmetric Free-Surface Problem

We show how the zeroth-order Hankel transform diagonalises the radial bi-Laplacian, clarify the sign convention \(\nabla^4 \leftrightarrow k^4\), and then apply the same transform…

Fluid Mechanics

[Kelvin Wedge Reading Notes] Eulerian and Lagrangian Forms of the Continuity and Momentum Equations

We recall the continuity and Euler momentum equations in Eulerian form, derive the material derivative ∑ Formula, and explain how Eulerian field descriptions relate to…

Fluid Mechanics

[Kelvin Wedge Reading Notes] The Equations for Water Waves (Linear and Nonlinear Waves)

This note primarily delves into incompressible flow momentum equation and Surface of water waves and boundary condition and Variational Formulation.

Fluid Mechanics