Numerical formulation based on ocean wave mechanics for offshore structure analysis – a review

Tensegrity systems have been used in several disciplines such as architecture, biology, aerospace, mechanics, and robotics during the last 50 years. However, just a few references in literature have stated the possibility of using such systems in ocean or energy-related applications. This work addresses the kinematic and dynamic analyses of a planar tensegrity mechanism for ocean wave energy harvesting. Ocean wave mechanics and the most important concepts related to fluid–structure interaction are presented. Then, a planar 3 degrees of freedom (3-dof) tensegrity mechanism, based on a morphology defined by Kenneth Snelson in 1960 which is known as “X-frame,” is proposed as connecting linkage to transmit wave-generated forces. A geometric approach is used to solve the forward and reverse displacement problems. The theory of screws is used to perform the forward and reverse velocity analyses of the device. The Lagrangian approach is used to deduce the equations of motion considering the interaction between the mechanism and ocean waves. The tensegrity-based mechanism is analyzed using a linear model of ocean waves and its energy harvesting capabilities are compared to a purely heaving device. Results show that the proposed tensegrity configuration allows to harvest 10% more energy than the traditional heaving mechanism used in several wave energy harvesting applications. Therefore, tensegrity systems could play an important role in the expansion of clean energy technologies that help the world's sustainable development.

Download Full-text

Ocean Wave Mechanics

Advanced Series on Ocean Engineering - Ocean Wave Dynamics for Coastal and Marine Structures ◽

10.1142/9789811236679_0003 ◽

2021 ◽

pp. 49-90

Keyword(s):

Ocean Wave ◽

Wave Mechanics

Download Full-text

Cylinder loading in transient motion representing flow under a wave group

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2008.0345 ◽

2009 ◽

Vol 465 (2105) ◽

pp. 1467-1488 ◽

Cited By ~ 3

Author(s):

T. Stallard ◽

P.H. Taylor ◽

C.H.K. Williamson ◽

A.G.L. Borthwick

Keyword(s):

Orbital Motion ◽

Fluid Motion ◽

Horizontal Cylinder ◽

Ocean Wave ◽

Good Representation ◽

Wave Group ◽

Fluid Loading ◽

Offshore Structure ◽

Force Fluctuations ◽

Force Magnitude

There are a great many studies that investigate the force on bodies in periodic oscillatory motions, but almost no studies that focus on the kinds of fluid loading that are of great relevance to offshore structure designers; namely, the problem of a cylinder subjected to the forces from ocean wave groups, especially those of large amplitude. In this study, we move a vertical circular cylinder in non-periodic horizontal orbital motion through stationary fluid, in a towing tank at Re ≲1.15×10 4 . The motion is chosen to represent the relative fluid motion incident upon a horizontal cylinder with its axis aligned parallel to the crest of a large ocean wave group, as defined by the ‘NewWave’ formulation. The vector form of the well-known Morison equation provides a good representation of the measured forces. By measuring the force components in the radial and azimuthal directions, we clearly demonstrate that the presence of vigorous force fluctuations at a higher frequency than the orbital motion are associated with vortex shedding that is otherwise masked by the choice of coordinates. We find vortex frequencies comparable with those for flow past fixed bodies and a ‘transverse’ force magnitude similar to the fixed flow case at the same average speed. Finally, we show that by retaining only an azimuthal (constant) drag coefficient term to represent the fluid loading throughout the wave group orbits, the resolved X - and Y -force fluctuations agree well with measured forces. This demonstrates that we can obtain a reasonable estimate of time-varying forces using a single term. It is expected that such a simple force representation will become less effective in shallower fluids and for smaller wave amplitudes relative to body size.

Download Full-text

A NEW THEORY ON OCEAN WAVE MECHANICS AND ITS APLICATION IN ENERGY POWER GENERATION

DYNA INGENIERIA E INDUSTRIA ◽

10.6036/9931 ◽

2021 ◽

Vol 96 (3) ◽

pp. 276-280

Author(s):

JOSE JAVIER DORIA IRIARTE ◽

IÑIGO DORIA ELEJOSTE

Keyword(s):

Power Generation ◽

Wave Energy ◽

Ocean Wave ◽

Wave Power ◽

Wave Mechanics ◽

Propagation Process ◽

Sand Waves ◽

Numerical Result ◽

New Type ◽

Power And Energy

We provide here a theoretical solution to the calculation of wave power generation possibilities, showing that the energy and other parameters of each wave are a function exclusively of its height. The numerical result obtained is compatible with the most used formulations. All authors cited, offer oversimplified formulas for complicated wave power and energy calculations in contrast with our very simple, coherent and innovative formulas, treating each wave individually and assuming the same sinusoidal profile, without wind and ocean currents. The sand waves, or ripple marks, generation is described. This proposed wave generation and propagation process lead us to use turbines directly driven by waves, device capable of extracting energy from both waves and rivers or tides with this new type of turbines. The exposed theory has been supported by tests in the laboratory, at sea, and in breakers Key Words: Ocean wave mechanics. Wave energy. Energy generation

Download Full-text

200kv superconducting cryo electron microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100127645 ◽

1987 ◽

Vol 45 ◽

pp. 642-643

Author(s):

M. Iwatsuki ◽

Y. Kokubo ◽

Y. Harada ◽

J. Lehman

Keyword(s):

Electron Microscope ◽

Structure Analysis ◽

Organic Materials ◽

Strong Interactions ◽

Specimen Preparation ◽

Great Effort ◽

Electron Microscopic ◽

Crystal Fields ◽

Special Skill ◽

Long Time

In recent years, the electron microscope has been significantly improved in resolution and we can obtain routinely atomic-level high resolution images without any special skill. With this improvement, the structure analysis of organic materials has become one of the interesting targets in the biological and polymer crystal fields.Up to now, X-ray structure analysis has been mainly used for such materials. With this method, however, great effort and a long time are required for specimen preparation because of the need for larger crystals. This method can analyze average crystal structure but is insufficient for interpreting it on the atomic or molecular level. The electron microscopic method for organic materials has not only the advantage of specimen preparation but also the capability of providing various information from extremely small specimen regions, using strong interactions between electrons and the substance. On the other hand, however, this strong interaction has a big disadvantage in high radiation damage.

Download Full-text