Numerical simulations of hydrodynamic loads and structural responses of a Pre-Swirl Stator

Reproduction of Monopile Ringing Events in Reduced-Duration Model Tests

Volume 7B: Ocean Engineering ◽

10.1115/omae2017-61034 ◽

2017 ◽

Author(s):

Erin E. Bachynski ◽

Trygve Kristiansen

Keyword(s):

Time Windows ◽

Full Scale ◽

Offshore Wind ◽

Maximum Deviation ◽

Wave Loads ◽

Traditional Practice ◽

Hydrodynamic Loads ◽

Offshore Wind Turbines ◽

Irregular Wave ◽

Structural Responses

Monopile support structures for offshore wind turbines may experience ringing-type responses in steep wave conditions. In order to experimentally capture the statistical distribution of the hydrodynamic loads and structural responses, traditional practice is to generate many 3-hour (full scale) realizations of the relevant sea states. An experimental campaign at 1:48 scale was carried out in the Lilletanken wave tank at NTNU/MARINTEK in order to examine the possibility of using shorter time windows to recreate irregular wave ringing events. Wave elevations and hydrodynamic loads on a rigid vertical circular cylinder in 27 m water depth were measured for a variety of 3-hour, 450 s (7.5-minute), 800 s (13.3-minute), 1150 s (19.2-minute), and 1500 s (25-minute) wave realizations, where all durations are listed in full scale. Wavelet transformations and a single degree-of-freedom oscillator were used to investigate the magnitude and repeatability of the high-frequency content of the wave loads. Large variations in the repeatability were seen among events. On average, the repeatability in the ringing response was 4.2 % for 3-hour tests, while 13.3-minute tests reproduced the same events within 9.1 %. The maximum deviation was, nonetheless, much higher when only 13.3 minutes were used.

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Horizontal and Torsional Modes of an Ultra Large Container Ship (ULCS)

Volume 6B: Ocean Engineering ◽

10.1115/omae2020-18659 ◽

2020 ◽

Author(s):

P. P. Vijith ◽

Suresh Rajendran

Keyword(s):

Numerical Model ◽

Numerical Method ◽

Natural Frequency ◽

Flexible Structures ◽

Complex Problem ◽

Mode Shapes ◽

Beam Model ◽

Torsional Vibrations ◽

Hydrodynamic Loads ◽

Structural Responses

Abstract The hydro elastic responses of flexible structures under fluid loading is an important concern during the design of large ocean structures. The two-way coupling between the structural responses and the hydrodynamic loads is a complex problem in large flexible floating structures since the structures can vibrate in longitudinal, vertical, horizontal, or torsional modes. The antisymmetric distortion modes may be coupled depending on the location of the centroid and the shear centre. In the case of thin walled open structures, horizontal and torsional vibrations are usually coupled due to the asymmetry of cross section as well as eccentricity between centroid of the section and shear deformation centres. The acurate estimation of dry natural frequency and modes shapes of structure is indispensable since it helps to validate the accuracy of the structural modelling. A numerical method available from one of the existing literatures is used for the estimation of dry and wet natural frequencies, and mode shapes of horizontal and torsional vibrations of an ULCS. The natural frequency and modes are essential parameters for the analysis of interaction between structural responses and hydrodynamic loads. The numerical method is based on a 1D FEM beam model. Distortion due to warping is included in the numerical model since it is well known that containerships with large hatch opening are susceptible to warping. The numerical model is subdivided into 50 stations and the mass distribution and the sectional properties are calculated in order to match the bending, shear, torsion and warping moduli of the experimental model. The dry and wet natural frequency and mode shapes for the horizontal and torsional vibrations of the ULCS is numerically calculated and compared with the experimental results.

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Heave Plate Design With Computational Fluid Dynamics

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.1337096 ◽

2000 ◽

Vol 123 (1) ◽

pp. 22-28 ◽

Cited By ~ 13

Author(s):

Samuel Holmes ◽

Shankar Bhat ◽

Pierre Beynet ◽

Anil Sablok ◽

Igor Prislin

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Numerical Simulations ◽

Floating Platform ◽

Hydrodynamic Loads ◽

Least Mean Squares ◽

Harmonic Motion ◽

Plate Design ◽

Computational Fluid Dynamics Cfd ◽

Heave Plate

Computational fluid dynamics (CFD) methods are used to predict the hydrodynamic loads on heave plates. A series of numerical simulations for plates undergoing simple harmonic motion is used to determine the force and moment resultant histories. Then a least mean squares method is used to obtain the appropriate Morison coefficients for the plates under a variety of sea conditions. Finally, force and moment histories are predicted for a plate on a floating platform excited by a random sea motion.

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An analytical method to assess the structural responses of ship side structures by raked bow under oblique collision scenarios

Proceedings of the Institution of Mechanical Engineers Part M Journal of Engineering for the Maritime Environment ◽

10.1177/1475090220980277 ◽

2020 ◽

pp. 147509022098027

Author(s):

Zeping Wang ◽

Kun Liu ◽

Gang Chen ◽

Zhiqiang Hu

Keyword(s):

Numerical Simulations ◽

Analytical Method ◽

Structural Damage ◽

Structural Response ◽

Design Stage ◽

Shipping Industry ◽

Oblique Collision ◽

Finite Element Software ◽

Hull Structure ◽

Structural Responses

With the development of the shipping industry, the number of ships at sea has increased significantly. According to the statistical data, oblique ship collisions are much more frequently happened than that of head-on ship collisions. However, there are less researches on oblique ship collisions than those of head-on ship collisions. The responses of hull structure during oblique collision scenarios are different from those in head-on collision scenarios, and might have wider structural damages, which demonstrate the significance of research on oblique collision scenarios and structural damage. In this paper, the oblique collision scenarios are firstly investigated through numerical simulations. Finite element software LS_DYNA is used for the numerical simulations. Six typical oblique collision scenarios are defined, on purpose of finding the main deformation characteristics of the struck ship. Two basic assumptions were made accordingly. Then, a simplified analytical method is proposed to predict the structural response of ship side structures by raked bow under oblique collision scenarios. The new analytical method includes the deformation mechanism of the side plating, the web girder and the transverse frame. The resistance and energy dissipation of these components are used in an integrated way to evaluate the overall crashworthiness of the side structure of the struck ship. The numerical simulation results match well with the results of analytical calculations, which validates the accuracy of the proposed analytical method. The proposed analytical method can provide an effective way to evaluate the structural crashworthiness of ship side structures in oblique collision scenarios during the structural design stage.

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Direct Numerical Simulations of Gas–Liquid Multiphase Flows

10.1017/cbo9780511975264 ◽

2001 ◽

Cited By ~ 151

Author(s):

Grétar Tryggvason ◽

Ruben Scardovelli ◽

Stéphane Zaleski

Keyword(s):

Numerical Simulations ◽

Multiphase Flows ◽

Direct Numerical Simulations

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Saturation mechanism and generated viscosity in gravito-turbulent accretion disks

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038023 ◽

2020 ◽

Vol 640 ◽

pp. A53

Author(s):

L. Löhnert ◽

S. Krätschmer ◽

A. G. Peeters

Keyword(s):

Growth Rate ◽

Numerical Simulations ◽

Accretion Disks ◽

Gravitational Instability ◽

Turbulent Viscosity ◽

Radial Distance ◽

Maximum Growth ◽

Wave Number ◽

Radiative Cooling ◽

Mixing Length

Here, we address the turbulent dynamics of the gravitational instability in accretion disks, retaining both radiative cooling and irradiation. Due to radiative cooling, the disk is unstable for all values of the Toomre parameter, and an accurate estimate of the maximum growth rate is derived analytically. A detailed study of the turbulent spectra shows a rapid decay with an azimuthal wave number stronger than ky−3, whereas the spectrum is more broad in the radial direction and shows a scaling in the range kx−3 to kx−2. The radial component of the radial velocity profile consists of a superposition of shocks of different heights, and is similar to that found in Burgers’ turbulence. Assuming saturation occurs through nonlinear wave steepening leading to shock formation, we developed a mixing-length model in which the typical length scale is related to the average radial distance between shocks. Furthermore, since the numerical simulations show that linear drive is necessary in order to sustain turbulence, we used the growth rate of the most unstable mode to estimate the typical timescale. The mixing-length model that was obtained agrees well with numerical simulations. The model gives an analytic expression for the turbulent viscosity as a function of the Toomre parameter and cooling time. It predicts that relevant values of α = 10−3 can be obtained in disks that have a Toomre parameter as high as Q ≈ 10.

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