Multiple Wave Trains Research Articles

Enigmatic Tsunami Waves Amplified by Repetitive Source Events Near Sofugan Volcano, Japan

AbstractOn 8 October 2023, mysterious tsunamis with a maximum wave height of 60 cm were observed in Izu Islands and southwestern Japan, although only seismic events with body‐wave magnitudes mb 4–5 have been documented to the west of Sofugan volcano. To investigate the source process, we analyze tsunami waveforms recorded by an array network of ocean bottom pressure gauges. Stacked waveforms of pressure gauge records suggest recurrent arrivals of multiple wave trains. Deconvolution of the stacked waveforms by tsunami waveforms from an earlier event revealed over 10 source events that intermittently generated tsunamis for ∼1.5 hr. The temporal history of this sequence corresponds to the origin times of T‐phases estimated by an ocean bottom seismometer and of the seismic swarm, implying a common origin. Larger events later in the sequence occurred at intervals comparable to the tsunami wave period, causing amplification of later phases of the tsunami waves.

Modeling of Thermally Driven Resonance at Multiscales

Abstract Understanding the mechanisms of thermally driven resonance is a key for designing many engineering and physical systems especially at small scales. This paper focuses on the modeling aspects of such phenomena using the classical Fourier diffusion theory. Critical analysis revealed that the thermally induced resonant excitation is characterized by the generation of multiple wave trains with a constant phase shift as opposed to the single standing wave generated in a mechanically driven resonant response. The hypothesis proposed herein, underpin a broad range of scientific and technological developments and the analytical treatment enables design of thermally driven resonant systems with improved performance.

Shoaling and Decay of Two Wave Trains on Beach

Shoaling and decay of irregular wave trains with two distinct frequency peaks are simulated in a wave flume. The relative energy in each wave train, the closeness of the frequency peaks, and the total wave energy were varied over 12 cases. Wave-gauge measurements across the 1:30 plane slope in the flume show that linear superposition of single-peaked wave trains or lumping all energy into the dominant wave train are not satisfactory representations of multiple wave trains. The measurements also show that the wave train with the low-frequency peak dominates in the surf zone. Waves with the low-frequency peak appear unaffected by the second wave train, but the high-frequency wave train decays faster in the presence of the low-frequency waves. The variation of wave height through shoaling and breaking depends on the relative amount of energy in each of the wave trains and the closeness of the peak frequencies.

Chemically driven nonlinear waves and oscillations at an oil-water interface

An experimental investigation is presented of chemically driven dynamic instability of an oil-water interface in a cylindrical and annular glass container. The immiscible liquids are water containing a surfactant (TSAC) and nitrobenzene containing iodine. The reaction at the interface leads to complex deformation patterns including rotating solitary waves, multiple wave trains, periodic and nonperiodic oscillations, source-to-sink propagation, and intermittent behavior. A phase diagram is established for the two solute concentrations ranging from 10 -4 to 10 -1 M. It shows five distinct regions of different dynamic regimes, determined by interaction of at least three mechanisms: dynamic wetting of the container wall, capillary effect, and Marangoni instability of the liquid-liquid interface. The influences of aspect ratio, concentration product, and temperature are investigated and local time traces are derived from electropotential differences. Their spectral analysis reveals details of periodic or irregular motion. Transitions between the dynamic modes of the system during its temporal evolution are recorded. Quantitatively determined profiles of regular waves are analyzed by exponential functions and a simple model for this is proposed.

Field intercomparison of nearshore directional wave sensors

Five measurement strategies (four in situ, one remote) for estimating directional wave spectra were intercompared in a 1980 experiment at the Coastal Engineering Research Center's Field Research Facility in Duck, NC. The systems included two pressure sensor/biaxial current meter combinations (different manufacturers), a triaxial acoustic current meter, an SXY gauge (square array of four pressure sensors), and a shore-based imaging radar. A detailed error analysis suggests sources for differences in estimated wave spectra from the different instruments; in general, they intercompare favorably. The major deviation among in situ gauges was associated with the triaxial acoustic current meter. Reliance on a vertical velocity measurement (instead of a direct pressure or sea-surface elevation measurement) can contribute additional uncertainty in directional spectral estimates. The imaging radar was successful in distinguishing multiple wave trains at the same frequency, which was not possible with the simple spectral estimation analysis applied to in situ data. However, the radar is not useful in providing accurate estimates of spectral density, nor in distinguishing multiple wave trains of different frequencies coming from the same direction. Selection of a measurement strategy for a particular need depends on the precise data requirements for that application. Although the five tested intercompared well, in practice not all are equally suitable for every application.

Wave direction measured by four different systems

During a March 1977 experiment, four systems were used to provide wave-direction information offshore of Mission Beach, CA: a synthetic aperature radar (SAR) carried aboard a NASA CV990 aircraft, a coastal imaging radar, a pressure-gauge array offshore, and aerial photography aboard two aircraft. The coastal radar, aerial photographs, and SAR provided wave images. From the coastal radar images and the aerial photographs, the direction and length of the principal wavetrains were measured by a manual analysis. The SAR images were also processed using an FFT to give two-dimensional wave spectra. The array at the Naval Ocean Systems Center (NOSC) tower was used to provide directional wave spectra. Scatter diagrams are presented, which intercompare the measurements from these four systems. In addition, radar image spectral information is compared with the array spectra. The intercomparison of the data from these four systems shows good agreement among the imaging systems. Between the imaging systems and the pressure array there is agreement for the most prominent wavetrains and disagreement for several cases where multiple wavetrains from different directions but with similar periods are present.

Power Imbedding at the Carrier Frequency of Multiple Wave Trains Used in Radar Systems†

ABSTRACT This paper discusses methods of improving the power spectrum of two or multiple wave trains used in radar systems 30 that increased power clusters at their carrier frequency. The purpose of concentrating power close to the carrier frequency is to transmit maximal r.f. energy of delayed signals for interception and detection by the party originating the signal. The constructive and destructive interference phenomena in the frequency spectra of two sinusoidal wave trains with favourable and unfavourable phase relationships between each other are analysed. Methods of predicting those interference phenomena are given. Several theorems on the Fourier transforms of time-function signals having phase shift, time delay and frequency multiplication or division are included. Brief discussions are made on the synthesis of a given spectrum or the determination of required signals to yield a prescribed spectrum. The following methods of power imbedding are considered : (1) Wave trains of unequal amplitudes, (...