scholarly journals Measurement of Seafloor Acoustic Backscatter Angular Dependence at 150 kHz Using a Multibeam Echosounder

2021 ◽  
Vol 13 (23) ◽  
pp. 4771
Author(s):  
Karolina Trzcinska ◽  
Jaroslaw Tegowski ◽  
Pawel Pocwiardowski ◽  
Lukasz Janowski ◽  
Jakub Zdroik ◽  
...  
Keyword(s):  
Angular Dependence ◽  
Fine Sand ◽  
Frequency Range ◽  
Response Curves ◽  
Sandy Gravel ◽  
True Incidence ◽  
Angular Response ◽  
Backscattering Strength ◽  
Ground Truthing ◽  
Acoustic Classification

Acoustic seafloor measurements with multibeam echosounders (MBESs) are currently often used for submarine habitat mapping, but the MBESs are usually not acoustically calibrated for backscattering strength (BBS) and cannot be used to infer absolute seafloor angular dependence. We present a study outlining the calibration and showing absolute backscattering strength values measured at a frequency of 150 kHz at around 10–20 m water depth. After recording bathymetry, the co-registered backscattering strength was corrected for true incidence and footprint reverberation area on a rough and tilted seafloor. Finally, absolute backscattering strength angular response curves (ARCs) for several seafloor types were constructed after applying sonar backscattering strength calibration and specific water column absorption for 150 kHz correction. Thus, we inferred specific 150 kHz angular backscattering responses that can discriminate among very fine sand, sandy gravel, and gravelly sand, as well as between bare boulders and boulders partially overgrown by red algae, which was validated by video ground-truthing. In addition, we provide backscatter mosaics using our algorithm (BBS-Coder) to correct the angle varying gain (AVG). The results of the work are compared and discussed with the published results of BBS measurements in the 100–400 kHz frequency range. The presented results are valuable in extending the very sparse angular response curves gathered so far and could contribute to a better understanding of the dependence of backscattering on the type of bottom habitat and improve their acoustic classification.

Intrinsic Localized Modes of Harmonic Oscillations in Pendulum-Arrays Subjected to Horizontal Excitation

2013 ◽  
Author(s):  
Takashi Ikeda ◽  
Yuji Harata ◽  
Keisuke Nishimura
Keyword(s):  
Theoretical Analysis ◽  
Frequency Response ◽  
Excitation Frequency ◽  
System Response ◽  
Stable Steady State ◽  
Frequency Range ◽  
Localized Modes ◽  
Response Curves ◽  
Harmonic Oscillations ◽  
Intrinsic Localized Modes

The behavior of intrinsic localized modes (ILMs) is investigated for an array with N pendula which are connected with each other by weak, linear springs when the array is subjected to horizontal, sinusoidal excitation. In the theoretical analysis, van der Pol’s method is employed to determine the expressions for the frequency response curves for fundamental harmonic oscillations. In the numerical calculations, the frequency response curves are presented for N = 2 and 3 and compared with the results of the numerical simulations. Patterns of oscillations are classified according to the stable steady-state solutions of the response curves, and the patterns in which ILMs appear are discussed in detail. The influence of the connecting springs of the pendula on the appearance of ILMs is examined. Increasing the values of the connecting spring constants may affect the excitation frequency range of ILMs and cause Hopf bifurcation to occur, followed by amplitude modulated motions (AMMs) including chaotic vibrations. The influence of the imperfections of the pendula on the system response is also investigated. Bifurcation sets are calculated to examine the influence of the system parameters on the excitation frequency range of ILMs and determine the threshold value for the connecting spring constant after which ILMs do not appear. Experiments were conducted for N = 2, and the data were compared with the theoretical results in order to confirm the validity of the theoretical analysis.

Superharmonic Oscillations as Solutions to Duffing’s Equation as Solved by an Electronic Differential Analyzer

1957 ◽  
Vol 24 (4) ◽  
pp. 520-525
Author(s):  
C. P. Atkinson
Keyword(s):  
Free Vibration ◽  
Higher Order ◽  
Frequency Range ◽  
Response Curves ◽  
Maximum Displacement ◽  
Duffing's Equation ◽  
The Third ◽  
Duffing’S Equation ◽  
Forcing Function ◽  
Differential Analyzer

Abstract This paper presents the experimental response curves for the solutions of Duffing’s equation for that frequency range where higher-order harmonics (called superharmonics as opposed to lower order or subharmonics) of the fundamental are important components of the solution. The experimental results were obtained by solving Duffing’s equation on an electronic differential analyzer. The paper presents corroboration of analytical results for the third-order superharmonic component of solutions which were calculated by a two-term Ritz approximation. The results of this paper indicate that superharmonics of higher order than the third, that is, fifth and seventh order, and even-order harmonics such as second and fourth order can be found in the frequency range studied. This paper points out a definite relationship which exists between the superharmonic generated and the free-vibration curve (“backbone”) of the system. For example, if we compare the maximum displacement of the solution containing an nth order superharmonic with the same amplitude of the free-vibration curve, it is seen that the frequency of the fundamental (the forcing frequency) is 1/n times this natural frequency or, conversely, the frequency of the superharmonic component is n times that of the fundamental and has in fact the frequency of the free vibration for that amplitude. Thus a superharmonic of order n can be pictured as a sustained free vibration which is generated when the frequency of the forcing function is 1/n of the frequency of the free-vibration response curve. The phenomenon of superharmonic oscillations is pictured here as a nonlinear resonance. Experimental evidence of the superharmonic-jump phenomenon as discovered analytically by John Burgess (1) also is presented in this paper.

A Combined Steady-State/Transient Approach to Study Very Large Amplitude Ship Rolling

1995 ◽  
Author(s):  
J. Falzarano ◽  
R. Kota ◽  
I. Esparza
Keyword(s):  
Steady State ◽  
Large Amplitude ◽  
Wave Amplitude ◽  
Practical Importance ◽  
Rolling Motion ◽  
Frequency Range ◽  
Response Curves ◽  
Type Of Behavior ◽  
Steady State Solutions ◽  
Ship Rolling

Abstract For ships, rolling motion is the most critical due to the possibility of capsizing. In a regular (periodic) sea, if no bounded steady state solutions exist, then capsizing may be imminent. Determining for exactly which wave amplitude and frequency the steady-state solutions disappear or become unstable is of great practical importance. In previous works (Falzarano, Esparza, and Taz Ul Mulk, 1994) and abstracted presentations (Falzarano, 1993), the global transient dynamics of large amplitude ship rolling motion was studied. The effect on the steady-state solutions of changing wave frequency for a fixed wave amplitudes was studied. It was shown how the in-phase and out-of-phase solutions evolve as the frequency passes through the linear natural frequency. For small wave amplitudes (external forcing) there exists a single steady-state throughout the frequency range, for moderate wave amplitudes there exists a frequency range where multiple steady state harmonic solutions exists. As the wave amplitude was increased further there existed a frequency range where no steady-state harmonic solution existed. In the present work, the very large amplitude ship rolling motion in the region where no steady-state solutions exist will be studied in more detail. Moreover, the mechanisms (bifurcations) that cause this type of behavior to evolve from more simple behavior will be studied using a combination of both frequency response curves and Poincaré maps. It is expected that global chaotic bifurcations such as those previously described (e.g., Thompson and Stewart, 1989) will be identified.

Nonlinear Interaction of a Parametrically-Excited Coupled Column-Pendulum Oscillator

1993 ◽  
Author(s):  
G. Mustafa ◽  
A. Ertas
Keyword(s):  
Regular Solution ◽  
Reverse Flow ◽  
Flexible Structures ◽  
Zero Solution ◽  
Homoclinic Orbits ◽  
Frequency Range ◽  
Response Curves ◽  
Strong Indicator ◽  
Jump Phenomena ◽  
The Cost

Abstract A new vibration absorbing device is introduced for large flexible structures. The bifurcation diagrams obtained for the averaged system, indicate that the system loses stability via two distinct routes. One leading to a saddle-node bifurcation, normally associated with the jump phenomena. The second instability is due to the Hopf bifurcation, that results in amplitude modulated motion of the oscillator. A parameter range has been identified where these bifurcations coalesce. This phenomenon is a strong indicator of existence of homoclinic orbits. In addition to the regular solution branches, that bifurcate from the zero solution, the system also possesses isolated solutions (the so-called “isolas”) that form isolated loops bounded away from zero. As the forcing amplitude is varied, the isolas appear, disappear or coalesce with the regular solution branches. The response curves indicate that the column amplitude shows saturation. The pendulum acts as a vibration absorber over a range of frequency where the column response is saturated. However, there is also a frequency range over which a reverse flow of energy occurs, where the pendulum shows reduced amplitude at the cost of large amplitudes of the column.

scholarly journals Detrital carbonate sedimentation of the Rocas Atoll, South Atlantic

2013 ◽  
Vol 85 (1) ◽  
pp. 57-72 ◽  
Author(s):  
NATAN S. PEREIRA ◽  
VALDIR A.V. MANSO ◽  
RENÊ J.A. MACEDO ◽  
JOÃO M.A. DIAS ◽  
ADRIANA M.C. SILVA
Keyword(s):  
Sedimentary Environment ◽  
Fine Sand ◽  
High Energy ◽  
South Atlantic ◽  
Depositional Environments ◽  
Coralline Algae ◽  
Brazilian Coast ◽  
Sandy Gravel ◽  
Kurtosis Parameter ◽  
Mean Size

Located 266 km offshore Brazilian coast, Rocas Reef complex is the only atoll in the South Atlantic. Two scientific expeditions carried out detailed sedimentological studies of the complex. Sand texture was dominant in the sedimentary environment, although other textures such as gravel, sandy gravel and gravelly sand, were also observed. Mean size ranged from fine sand to coarse sand (-1.23 to 2.34ø), with an average value of 0.69ø (sand fraction), which from a geological perspective represents a high-energy environment. The values of mean size varied in the different geomorphologic compartments, a response to variable hydrodynamics on the reef. Sorting ranged from very well sorted to poorly sorted, with a mean value of 0.97ø (moderately sorted). The values of mean size and sorting are directly proportional (i.e. the larger the grain size, the better the sorting), a fact that might be controlled by the decreasing of organism diversity that contributes to the sedimentary environment as the mean size of the particles increase. Skewness parameter was used to correlate positive values to depositional environments. The Kurtosis parameter showed little relevance in this study. The sedimentary particles analyzed are exclusively composed of biogenic grains. In total eleven major groups were described, coralline algae being the most unusual.

scholarly journals On palaeomagnetic dating of fluvial deposits in the section of Neporotove gravel quarry on the Middle Dniester

2019 ◽  
Vol 28 (2) ◽  
pp. 241-249
Author(s):  
Kseniia Bondar ◽  
Bogdan Ridush ◽  
Mariia Baryshnikova ◽  
Yana Popiuk
Keyword(s):  
Fine Sand ◽  
Illuvial Horizon ◽  
Sandy Gravel ◽  
Lacustrine Deposits ◽  
Light Yellow ◽  
River Terraces ◽  
Geological Age ◽  
Sand Filler ◽  
Geomagnetic Polarity ◽  
The Right

The paper presents the results of palaeomagnetic studies of Quaternary noncemented deposits from the section of Neporotove on the VIIIth terrace of the Dniester River valley with abnormal thickness (more than 20 m) of the channel alluvium near the village of Neporotove, located on the right bank of the Dniester River. Alluvial facies of river terraces’ deposits are valuable palaeogeographic archives but not quite complete. They are affected by denudation and often do not contain fossils. The possible way for their dating is provided by a palaeomagnetic method performed on suitable for sampling underlying and overlying beds. The alluvial sequence consists of four units. Unit I is composed of inclined gravel-pebble layers with the sand filler with a visible thickness of about 8 m. Unit II has bedded over the denudated surface of Unit I; it consists of light-yellow laminated aleurit loam, 5-30 cm thick underlaid by 0.5-1.5 bed of fine sand. We consider Unit II to be lacustrine deposits accumulated in quiet water. Unit III is represented with inclined or sub-horizontally layered gravel-pebble-boulder deposits with up to 10 m of visible thickness. It includes boulders and blocks of sedimentary rocks up to 1.0 in diameter, considered as drop-stones. In the roof of the gravel-pebble Unit III, there is the white carbonate layer, probably, the illuvial horizon of the palaeosol (mr1), which transited up into the brownish-red horizon A (Unit IV). Unit IV – dark-red sandy-gravel horizon, pedosediment, probably partly the reworked material washed into ice wages in the roof of Unit III. As a result of alternating field stepwise demagnetisation of natural remanence of sediments, we determined that loamy Unit II, which separates members of gravel stratum, and sandy Unit IV, which overlays packs of gravel alluvium, bear characteristic remanent magnetisation (RM) with normal geomagnetic polarity. Taking into consideration lithology and two-fold structure of terrace gravel alluvium as well as palaeomagnetic results, we assume the lacustrine deposits of Unit II was formed during Jaramillo palaeomagnetic subchron corresponding to the end of Shyrokyne Stage, and a pedosediment of Unit IV was formed during Martonosha Stage. The upper alluvial suite of a terrace (Unit III) was generally deposited during a cold stage,directly prior to the onset of lacustrine loam sedimentation, while the lower alluvial member (Unit I) dates from the preceding warm stage. Thus, we defined the geological age of the whole channel alluvium strata of the VIIIth Dniester terrace as Shyrokyne-Pryazovya Stage.

Superharmonic Resonance of Order 2 for an Impacting Hertzian Contact Oscillator: Theory and Experiments

2006 ◽  
Vol 2 (2) ◽  
pp. 190-196 ◽  
Author(s):  
Joël Perret-Liaudet ◽  
Emmanuel Rigaud
Keyword(s):  
Threshold Level ◽  
Wide Frequency Range ◽  
Hertzian Contact ◽  
Frequency Range ◽  
Test Rig ◽  
Response Curves ◽  
Superharmonic Resonance ◽  
Moving Body ◽  
Oscillator Theory ◽  
Theory And Experiments

The purpose of this paper is to investigate experimental responses of a preloaded vibroimpact Hertzian contact to an order 2 superharmonic excitation. A test rig is used, corresponding to a double sphere–plane contact preloaded by the weight of a moving body. Typical response curves are obtained under the superharmonic excitation. The Hertzian nonlinearity constitutes the precursor of vibroimpacts established over a wide frequency range. This behavior can be related to the existence of a transcritical bifurcation. In conjuction with the experiments, numerical results lead to the same conclusion. In particular, the threshold level of the excitation necessary to induce vibroimpact is confirmed.

Superharmonic Resonance of Order 2 for an Impacting Hertzian Contact Oscillator: Theory and Experiments

2005 ◽  
Author(s):  
Joe¨l Perret-Liaudet ◽  
Emmanuel Rigaud
Keyword(s):  
Threshold Level ◽  
Wide Frequency Range ◽  
Hertzian Contact ◽  
Frequency Range ◽  
Test Rig ◽  
Response Curves ◽  
Superharmonic Resonance ◽  
Moving Body ◽  
Oscillator Theory ◽  
Theory And Experiments

The purpose of this paper is to investigate experimental responses of a preloaded vibroimpact Hertzian contact to an order 2 superharmonic excitation. A test rig is used, corresponding to a double sphere-plane contact preloaded by the weight of a moving body. Typical response curves are obtained kinder the superharmonic excitation. The Hertzian non linearity constitutes the precursor of vibroimpacts established over a wide frequency range. This behaviour can be related to the existence of a transcritical bifurcation. In conjuction with the experiments, numerical results lead to the same conclusion. In particular, the threshold level of the excitation necessary to induce vibroimpact is confirmed.

Nonlinear liquid sloshing in a square tank subjected to obliquely horizontal excitation

2012 ◽  
Vol 700 ◽  
pp. 304-328 ◽  
Author(s):  
Takashi Ikeda ◽  
Raouf A. Ibrahim ◽  
Yuji Harata ◽  
Tasuku Kuriyama
Keyword(s):  
Theoretical Analysis ◽  
Frequency Response ◽  
Natural Frequencies ◽  
Equations Of Motion ◽  
Excitation Frequency ◽  
Frequency Range ◽  
Response Curves ◽  
Chaotic Motions ◽  
Nonlinear Responses ◽  
Good Agreement

AbstractNonlinear responses of surface waves in rigid square and nearly square tanks partially filled with liquid subjected to obliquely horizontal, sinusoidal excitation are investigated theoretically and experimentally. Two predominant modes of sloshing are significantly coupled nonlinearly because their natural frequencies are nearly identical resulting in 1:1 internal resonance. Therefore, if only one of these modes is directly excited, the other mode is indirectly excited due to the nonlinear coupling. In the nonlinear theoretical analysis, the modal equations of motion are derived for the two predominant sloshing modes as well as five higher sloshing modes. The linear viscous terms are incorporated in order to consider the damping effect of sloshing. The expressions for the frequency response curves are determined using van der Pol’s method. The influences of the excitation direction and the aspect ratio of the tank cross-section on the frequency response curves are numerically examined. Planar and swirl motions of sloshing, and Hopf bifurcations followed by amplitude modulated motions including chaotic motions, are predicted when the excitation frequency is close to one of the natural frequencies of the two predominant sloshing modes. Lyapunov exponents are calculated and reveal the excitation frequency range over which liquid chaotic motions occur. In addition, bifurcation sets are shown to clarify the influences of the parameters on the change in the structural stability. The theoretically predicted results are in good agreement with the measured data, thus the theoretical analysis was experimentally validated.

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