Two phenomena: Honji instability, and ringing of offshore structures

AbstractHonji instability and ringing of offshore structrures are two different phenomena. Honji instability occurs at a circular cylinder in transverse periodic finite motion in a water tank. It is superposed on the streaming flow induced by the cylinder's boundary layer. Its oscillation period is half of the period of the cylinder oscillation. Finite volume calculations of the filtered Navier-Stokes equations visualize the three-dimensional instability, where fluid particles transported by the circumferencial roll pairs exhibit a periodic mushroom-like pattern. Force is the same with and without the Honji instability. The large eddy simulation calculations for high Reynolds number support a drag coefficient in accordance with the Stokes-Wang solution below separation and conform with experimental measurements of the damping force on a harmonically oscillating cylinder. Ringing of offshore structures are vibrations which appear at natural frequencies and concern fatigue. It is generated by a higher harmonic force oscillating with frequency being 3–4 times the fundamental wave frequency. Together with a strong inertia load in phase with the incoming wave's acceleration, a secondary load cycle appears in strong seas when the wave crest leaves the structure; this occurs about 1/4 wave period after the main force peak, it starts when the wave crest is about one cylinder radius behind the cylinder, lasts for about 15–20 percent of the wave period and has a magnitude up to 11 % of the peak-to-peak total force. It is a gravity effect and appears in strong irregular seas when kA > 0.18 and um/gD>0.4 (k wavenumber, A amplitude, um maximal wave induced velocity, g acceleration of gravity, D cylinder diameter)

Shear induced breaking of large internal solitary waves

The stability properties of 24 experimentally generated internal solitary waves (ISWs) of extremely large amplitude, all with minimum Richardson number less than 1/4, are investigated. The study is supplemented by fully nonlinear calculations in a three-layer fluid. The waves move along a linearly stratified pycnocline (depth h2) sandwiched between a thin upper layer (depth h1) and a deep lower layer (depth h3), both homogeneous. In particular, the wave-induced velocity profile through the pycnocline is measured by particle image velocimetry (PIV) and obtained in computation. Breaking ISWs were found to have amplitudes (a1) in the range a1>2.24 √h1h2(1+h2/h1), while stable waves were on or below this limit. Breaking ISWs were investigated for 0.27 0.86 and stable waves for Lx/λ < 0.86. The results show a sort of threshold-like behaviour in terms of Lx/λ. The results demonstrate that the breaking threshold of Lx/λ = 0.86 was sharper than one based on a minimum Richardson number and reveal that the Richardson number was found to become almost antisymmetric across relatively thick pycnoclines, with the minimum occurring towards the top part of the pycnoclinePostprintPeer reviewe

An investigation into and recommendations for appropriate technology education

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 32-33).The purpose of this paper is to present an example of appropriate technology (AT) education in a university setting, and make recommendations for using open source technology to aid AT education (OSAT). This paper presents a brief overview of the AT movement, and defines critical criteria for creating and implementation solutions for the developing world using this approach. The International Development Initiative (IDI) at the Massachusetts Institute of Technology is described in detail as a model example of efforts to promote the study of AT in higher education. OSAT is investigated in further detail to prove validity as a new aspect of the AT movement and a course of study incorporating the use of OSAT is developed to aid educators.by Amanda J. Grue.S.B

Infinitary Combinatory Reduction Systems

We define infinitary Combinatory Reduction Systems (iCRSs), thus providing the first notion of infinitary higher-order rewriting. The systems defined are sufficiently general that ordinary infinitary term rewriting and infinitary $\lambda$-calculus are special cases. Furthermore, we generalise a number of known results from first-order infinitary rewriting and infinitary $\lambda$-calculus to iCRSs. In particular, for fully-extended, left-linear iCRSs we prove the well-known compression property, and for orthogonal iCRSs we prove that (1) if a set of redexes $\mathcal{U}$ has a complete development, then all complete developments of $\mathcal{U}$ end in the same term and that (2) any tiling diagram involving strongly convergent reductions $S$ and $T$ can be completed iff at least one of $S/T$ and $T/S$ is strongly convergent. We also prove an ancillary result of independent interest: A set of redexes in an orthogonal iCRS has a complete development iff the set has the so-called finite jumps property

Mechanical and Chemical Control of Smooth Cordgrass in Waillapa Bay, Washington

We evaluated four methods to control smooth cordgrass (Spartina alterniflora Loisel), hereafter spartina, in Willapa Bay, Washington: mowing, mowing plus herbicide combination, herbicide only for clones, and aerial application of herbicide for meadows. (PDF has 7 pages.

Transformation of internal solitary waves at the "deep" and "shallow" shelf: satellite observations and laboratory experiment

An interaction of internal solitary waves with the shelf edge in the time periods related to the presence of a pronounced seasonal pycnocline in the Red Sea and in the Alboran Sea is analysed via satellite photos and SAR images. Laboratory data on transformation of a solitary wave of depression while passing along the transverse bottom step were obtained in a tank with a two-layer stratified fluid. The certain difference between two characteristic types of hydrophysical phenomena was revealed both in the field observations and in experiments. The hydrological conditions for these two processes were named the "deep" and the "shallow" shelf respectively. The first one provides the generation of the secondary periodic short internal waves – "runaway" edge waves – due to change in the polarity of a part of a soliton approaching the shelf normally. Another one causes a periodic shear flow in the upper quasi-homogeneous water layer with the period of incident solitary wave. The strength of the revealed mechanisms depends on the thickness of the water layer between the pycnocline and the shelf bottom as well as on the amplitude of the incident solitary wave

Rewriting Transfinite Terms

We define rewriting over terms with positions of transfinite length

Habitat Requirements of Breeding Scaled Quail in Texas

Habitat variables were correlated with scaled quail (Callipep/,a squamata) whistle counts on 133 (24-km) random transects in Texas. Whether or not a particular habitat variable was correlated with whistle counts appeared to depend upon abundance and distribution of other habitat types and structural features. If \u3e= 1 requisite for quail survival and reproduction (food, water, cover, nest sites) was limited, habitat types and structural features were usually positively correlated with whistle counts (P \u3c 0.10). Conversely, abundant habitat types which did not provide all of these requisites were usually negatively correlated with whistle counts (P\u3c 0.10). Correlations indicated breeding scaled quail selected the more dense, shorter shrub habitats. Mesquite (Prosopsis spp.) habitats were especially important to scaled quail in the Trans-Pecos region