Wave Heights and Damping Coefficients for Half-Submerged Ellipsoids in Low-Frequency Sway and Yaw

1964 ◽  
Vol 31 (4) ◽  
pp. 597-604
Author(s):  
J. Lurye ◽  
O. Pinkus
Keyword(s):  
Radiation Pattern ◽  
Low Frequency ◽  
Ideal Incompressible Fluid ◽  
Damping Coefficient ◽  
Nonzero Term ◽  
Strip Theory ◽  
Higher Power ◽  
Dipole Term ◽  
Wave Heights ◽  
Quadrupole Term

The authors consider the problem of an ellipsoid performing simple-harmonic swaying or yawing oscillations of small amplitude in the free surface of an ideal incompressible fluid, with gravity. The problem is examined in the limit of low frequency. The first nonzero term in the radiation pattern, which is a dipole term, and the damping coefficient, are found for sway. In the case of yaw the first nonzero term in the radiation pattern is a quadrupole term, and involves a higher power of frequency. Hence, the damping coefficient for yaw is of smaller order than the damping coefficient for sway, at low frequency. The strip-theory prediction of the sway damping coefficient is compared with the exact value and is shown to be too large by a factor of order K.

Sensitivity of Wave Drift Damping Coefficient Predictions to the Hydrodynamic Analysis Models Used in the Added Resistance Gradient Method

1988 ◽  
Vol 110 (4) ◽  
pp. 337-347 ◽  
Author(s):  
G. E. Hearn ◽  
K. C. Tong ◽  
S. M. Lau
Keyword(s):  
Interaction Analysis ◽  
Low Frequency ◽  
Damping Coefficient ◽  
Published Data ◽  
Added Resistance ◽  
Hydrodynamic Models ◽  
Frequency Wave ◽  
Damping Coefficients ◽  
Strip Theory ◽  
Calculation Procedures

This paper is concerned with the formulation and simplifications of the general fluid structure interaction analysis for an advancing oscillating vessel in waves to provide alternative 3D hydrodynamic models to determine first and second-order wave-induced fluid loadings, and, hence, the prediction of low-frequency wave damping coefficients. Heuristic arguments which lead to the Added Resistance Gradient (ARG) method of calculating low-frequency damping coefficients together with two 3D-based calculation procedures are presented. Predictions of added resistance and motion responses are compared with other published data. The intermediate hydrodynamic coefficient predictions based on 2D and 3D hydrodynamic models are compared. Low-frequency damping coefficient predictions based on the two proposed 3D calculation procedures are compared with experimental measurements and earlier published generalized strip theory values. Assessment of the applicability of the procedures, the result of their application, and further possible generalizations of the methods are discussed.

On the Structure and Some Properties of LaCo Co-substituted NiZn Ferrites Prepared Using the Standard Ceramic Technique

2016 ◽  
Vol 35 (4) ◽  
pp. 417-423 ◽  
Author(s):  
Xiaofei Niu ◽  
Xiansong Liu ◽  
Xin Huang ◽  
Kai Huang ◽  
Yuqi Ma ◽  
...  
Keyword(s):  
Grain Size ◽  
Power Loss ◽  
Low Frequency ◽  
Secondary Phase ◽  
Lattice Parameter ◽  
Initial Permeability ◽  
High Resistivity ◽  
X Ray Diffraction ◽  
Ferrite Sample ◽  
Higher Power

AbstractZn0.5Ni0.5-xCoxFe2-yLayO4 ferrites (with x=0, 0.02 and y=0, 0.02) were prepared by an industrial method using the standard ceramic technique and sintered at 1,250°C in air. X-ray diffraction (XRD) was used to obtain the phase formation of the NiZn ferrites. The microstructure of ferrites was investigated by scanning electron microscopy (SEM). The XRD reveals that lattice parameter (a) is decreased and a secondary phase (LaFeO3) is formed in the La–Co co-substituted NiZn ferrite sample, meanwhile, the grain size (D) of this sample decreased obviously by observing SEM photographs. Vibrating sample magnetometry (VSM), B-H analyzer, impedance analyzer and electrometer were carried out in order to characterize some properties of the ferrites. This investigation indicates that, La–Co co-substituted NiZn ferrite sample has higher power loss (Pcv) than other samples at low frequency with an increase in coercive field (Hc) and magnetocrystalline anisotropy (K1), a decrease in initial permeability (μi) and saturation magnetization (Ms). However, at high frequency, the power loss of La–Co co-substituted sample is low, which is attributed to high resistivity (ρ), small grain size (D), less number of Fe2+ ions and low porosity (P).

Bending Moments and Shear Forces in Ships Sailing in Irregular Waves

1981 ◽  
Vol 25 (04) ◽  
pp. 243-251
Author(s):  
J. Juncher Jensen ◽  
P. Terndrup Pedersen
Keyword(s):  
Linear Part ◽  
Vertical Motion ◽  
Bending Moment ◽  
Irregular Waves ◽  
Bending Moments ◽  
Shear Forces ◽  
Strip Theory ◽  
Wave Heights ◽  
Exciting Forces ◽  
Wave Induced

This paper presents some results concerning the vertical response of two different ships sailing in regular and irregular waves. One ship is a containership with a relatively small block coefficient and with some bow flare while the other ship is a tanker with a large block coefficient. The wave-induced loads are calculated using a second-order strip theory, derived by a perturbational procedure in which the linear part is identical to the usual strip theory. The additional quadratic terms are determined by taking into account the nonlinearities of the exiting waves, the nonvertical sides of the ship, and, finally, the variations of the hydrodynamic forces during the vertical motion of the ship. The flexibility of the hull is also taken into account. The numerical results show that for the containership a substantial increase in bending moments and shear forces is caused by the quadratic terms. The results also show that for both ships the effect of the hull flexibility (springing) is a fair increase of the variance of the wave-induced midship bending moment. For the tanker the springing is due mainly to exciting forces which are linear with respect to wave heights whereas for the containership the nonlinear exciting forces are of importance.

Rough Sea Deghosting Using Wave Heights Derived from Low Frequency Pressure Recordings - A Case Study

2004 ◽  
Author(s):  
J.O.A. Robertsson ◽  
E. Kragh ◽  
R. Laws ◽  
L. Amundsen ◽  
T. Rösten ◽  
...  
Keyword(s):  
Low Frequency ◽  
Wave Heights ◽  
Rough Sea

Evaluation of an Extended Operational Boussinesq-Type Wave Model for Calculating Low-Frequency Waves in Intermediate Depths

2011 ◽  
Author(s):  
Martijn P. C. de Jong ◽  
Mart Borsboom ◽  
Jan A. M. de Bont ◽  
Bas van Vossen
Keyword(s):  
Low Frequency ◽  
Wave Model ◽  
Coastal Engineering ◽  
Extended Model ◽  
Depth Range ◽  
Frequency Range ◽  
Frequency Wave ◽  
Type Wave ◽  
Wave Heights ◽  
Low Frequency Waves

The motions of (LNG) vessels moored offshore at depths ranging from about 20 to 100 m may depend significantly on the presence of (bound) low-frequency waves with periods in the order of 100 s. This is because these moored vessels show a large motion response in this frequency range and because the energy contents of low-frequency waves at these ‘intermediate’ depths is relatively large. As part of the Joint Industry Project HawaI, the operational Boussinesq-type wave model of Deltares, TRITON, was used to investigate whether this type of wave models could predict bound low-frequency waves (setdown waves) at intermediate depths. Comparison to measured and theoretical data, however, showed an underestimation of the computed levels of bound low-frequency wave heights for this depth range by a factor 2 to 4. Recently, additional tests were made with TRITON in situations for which the model has been designed: coastal engineering applications in shallow water (depths up to at most 20 m). These also showed an underestimation of the bound low-frequency wave heights, albeit smaller, up to a factor 2. In view of the importance of the energy contained in the low-frequency range for certain nearshore and shoreline processes, such as morphological processes, this underestimation is also of concern in coastal engineering. This triggered the development of a higher-order extension of the TRITON model equations (Borsboom, 2008, Wellens, 2010), with the aim to improve the accuracy of the model for long waves while still keeping computational times within acceptable (operational) limits. This paper reports on the usefulness of the extended model for the field of application considered in JIP HawaI/II: providing wave data for calculating the motions of vessels moored in intermediate depths. The results show a significant improvement of the modeling of nonlinear wave dynamics, including the prediction of bound low-frequency waves. This means that the model extension is an important step towards an operational Boussinesq-type wave model with sufficient accuracy in both the wave-frequency (sea, swell) and the low-frequency range for applications in intermediate depths.

scholarly journals Effects of finite source rupture on landslide triggering: The 2016 <i>M<sub>W</sub></i> 7.1 Kumamoto earthquake

2018 ◽  
Author(s):  
Sebastian von Specht ◽  
Ugur Ozturk ◽  
Georg Veh ◽  
Fabrice Cotton ◽  
Oliver Korup
Keyword(s):  
Radiation Pattern ◽  
Ground Motion ◽  
Low Frequency ◽  
New Physics ◽  
Rupture Directivity ◽  
Ground Shaking ◽  
Kumamoto Earthquake ◽  
Directivity Effect ◽  
Seismic Rupture ◽  
Landslide Distribution

Abstract. The propagation of a seismic rupture on a fault introduces spatial variations in the seismic wavefield surrounding the fault during an earthquake. This directivity effect results in larger shaking amplitudes in the rupture propagation direction. Its seismic radiation pattern also causes amplitude variations between the strike-normal and strike-parallel components of horizontal ground motion. We investigated the landslide response to these effects during the 2016 Kumamoto earthquake (MW 7.1) in central Kyūshū (Japan). Although the distribution of some 1,500 earthquake-triggered landslides as function of rupture distance is consistent with the observed Arias intensity, the landslides are more concentrated to the northeast of the southwest-northeast striking rupture. We examined several landslide susceptibility factors: hillslope inclination, median amplification factor (MAF) of ground shaking, lithology, land cover, and topographic wetness. None of these factors can sufficiently explain the landslide distribution or orientation (aspect), although the landslide headscarps coincide with elevated hillslope inclination and MAF. We propose a new physics-based ground motion model that accounts for the seismic rupture effects, and demonstrate that the low-frequency seismic radiation pattern consistent with the overall landslide distribution. The spatial landslide distribution is primarily influenced by the rupture directivity effect, whereas landslide aspect is influenced by amplitude variations between the fault-normal and fault-parallel motion at frequencies

Evaluación preliminar de la Variabilidad de la Frecuencia Cardiaca de Pacientes con Fibrilación Auricular Paroxística y Apnea Obstructiva Barra lateral del artículo

2021 ◽  
Author(s):  
◽  
B. Becerra-Luna
Keyword(s):  
Frequency Band ◽  
Noise Suppression ◽  
Spectral Power ◽  
Low Frequency ◽  
Ecg Signals ◽  
Higher Power ◽  
Regular Sampling ◽  
Respiratory Polygraphy ◽  
Hypopnea Syndrome ◽  
Constant Period

This paper describes the processing of electrocardiographic (ECG) signals from 16 patients diagnosed with paroxysmal atrial fibrillation and sleep apnea-hypopnea syndrome (SAHS) classified as either moderate or severe by respiratory polygraphy. Processing goes from acquisition up to the analysis of their heart rate variability (HRV), where original computer scripts written in MATLAB R2020b are used within scripts adapted from other research groups. Computer processing included linear resampling, noise suppression, R-wave detection, misidentified peaks correction, tachogram resampling at a constant period and trend removal. Regular sampling is mandatory for Fourier analysis through Welch’s periodogram. Once the spectral power was estimated, the HRV was evaluated before, during and after an apnea episode. The behavior of the HRV was compared to the group of patients with moderate SAHS against those with severe SAHS. When comparing the groups at post-apnea stage, significant differences were found in the normalized low-frequency band (LF: 0.04–0.15Hz, p=0.0183), and also in the normalized high frequency band (HF: 0.15–0.4 Hz, p=0.0182), which suggests that in patients with severe SAHS the sympathetic activity is higher (power in LF band), which in turn presupposes that the autonomic nervous system is in frequent alertness, which has been associated with high cardiovascular risk.

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