TY - JOUR

T1 - Generation of higher harmonic internal waves by oscillating spheroids

AU - Shmakova, Natalia

AU - Ermanyuk, Evgeny

AU - Flór, Jan Bert

PY - 2017/11/7

Y1 - 2017/11/7

N2 - Oscillating bodies in stratified fluids may emit higher harmonics in addition to fundamental waves. In the present experimental study, we consider higher harmonics of an internal wave field generated by a horizontally oscillating spheroid in a linearly stratified fluid for moderate to high oscillation amplitudes, i.e., scaled oscillation amplitude A/a≥0.5, with a the minor radius of the spheroid. Three different spheroid shapes are tested. The results are discussed in the context of the different theories on the generation of higher harmonics. Higher harmonics are observed at the intersections of fundamental wave beams, and at the critical points of the topography where the topographic slope equals the wave slope. The velocity amplitudes of the fundamental, second, and third harmonic waves grow respectively linearly, quadratically, and with the third power of the scaled oscillation amplitude A/a. Though these amplitudes are generally higher when the object's slope is larger, the increase in amplitude above and below the axisymmetric oscillating objects is found to be due to the effect of focusing. In order to discern the relative importance of the harmonics to the fundamental wave, the horizontal structure of the wave amplitude is measured. The results suggest that the nth harmonic of the internal wave field is associated with a radiation diagram corresponding to a multipole of order 2n, with 2n directions of propagation.

AB - Oscillating bodies in stratified fluids may emit higher harmonics in addition to fundamental waves. In the present experimental study, we consider higher harmonics of an internal wave field generated by a horizontally oscillating spheroid in a linearly stratified fluid for moderate to high oscillation amplitudes, i.e., scaled oscillation amplitude A/a≥0.5, with a the minor radius of the spheroid. Three different spheroid shapes are tested. The results are discussed in the context of the different theories on the generation of higher harmonics. Higher harmonics are observed at the intersections of fundamental wave beams, and at the critical points of the topography where the topographic slope equals the wave slope. The velocity amplitudes of the fundamental, second, and third harmonic waves grow respectively linearly, quadratically, and with the third power of the scaled oscillation amplitude A/a. Though these amplitudes are generally higher when the object's slope is larger, the increase in amplitude above and below the axisymmetric oscillating objects is found to be due to the effect of focusing. In order to discern the relative importance of the harmonics to the fundamental wave, the horizontal structure of the wave amplitude is measured. The results suggest that the nth harmonic of the internal wave field is associated with a radiation diagram corresponding to a multipole of order 2n, with 2n directions of propagation.

KW - VIBRATING ELLIPTIC CYLINDERS

KW - STRATIFIED FLUID

KW - PART 1

KW - VISUALIZATION

KW - TOPOGRAPHY

KW - BEAMS

KW - FIELD

UR - http://www.scopus.com/inward/record.url?scp=85038422938&partnerID=8YFLogxK

U2 - 10.1103/PhysRevFluids.2.114801

DO - 10.1103/PhysRevFluids.2.114801

M3 - Article

AN - SCOPUS:85038422938

VL - 2

JO - Physical Review Fluids

JF - Physical Review Fluids

SN - 2469-990X

IS - 11

M1 - 114801

ER -