Measurements of Form and Frictional Drags over a Rough Topographic Bank

Pressure differences across topography generate a form drag that opposes the flow in the water column, and viscous and pressure forces acting on roughness elements of the topographic surface generate a frictional drag on the bottom. Form drag and bottom roughness lengths were estimated over the East Flower Garden Bank (EFGB) in the Gulf of Mexico by combining an array of bottom pressure measurements and profiles of velocity and turbulent kinetic dissipation rates. The EFGB is a coral bank about 6 km wide and 10 km long located at the shelf edge that rises from 100-m water depth to about 18 m below the sea surface. The average frictional drag coefficient over the entire bank was estimated as 0.006 using roughness lengths that ranged from 0.001 cm for relatively smooth portions of the bank to 1–10 cm for very rough portions over the corals. The measured form drag over the bank showed multiple time-scale variability. Diurnal tides and low-frequency motions with periods ranging from 4 to 17 days generated form drags of about 2000 N m−1 with average drag coefficients ranging between 0.03 and 0.22, which are a factor of 5–35 times larger than the average frictional drag coefficient. Both linear wave and quadratic drag laws have similarities with the observed form drag. The form drag is an important flow retardation mechanism even in the presence of the large frictional drag associated with coral reefs and requires parameterization.

Rapid Design of Injection Molding of Plastic Buckle

In order to achieve higher speed and better efficiency of the plastic buckle molding, Imageware, the reverse design software, was adopted in this paper to process the point cloud data of the plastic buckle, mesh feature lines and reconstruct the surface,and then the reconstructed plastic buckle model was imported into UG and saved in STL format with the powerful surface repair function of UG to suture discontinuous surfaces. Mold Wizards of UG, the mold design module, was used to create mold assembly model, design parting surface, generate three-dimensional solid model of molding parts according to STL format saved previously and eventually the injection-molded plastic buckle was analyzed with Moldflow / MPI. As was indicated, the optimized design parameters tally with the experimental results basically.

Influence of Surface Topography on the Tribo-Characteristics of an Eccentric-Tappet Pair

The cam-tappet pair is one of the most important components in an engine and determines the overall performance of the motor. Compared with modern car engines using rolling-sliding tappets for the transmission of the rapid up-down lifting motion of the cam to open and close the engine’s inlet and exhaust valves, the flat-tappets are often subject to fatigue failure. Upon stripping down a damaged motor, the tappets are invariably found to be heavily pitted. This study performs a theoretical simulation of the surface topography influence on the tribo-characteristics of an eccentric-tappet pair. The asperities on the flat-tappet surface generate fluctuations of the pressure, film thickness and temperature distributions. The pressure fluctuations result in alternative stresses in the metal. The periodical variations of pressure, minimum film thickness and thermal rise are investigated by changing the eccentricity and roughness wavelength. The results suggest an explanation for the rapid occurrence of cracks or even complete fracture in the cam and flat-tappet pair.

Machining Trajectory Generation and Simulation of Miniature Integral Impeller

This paper describes machining trajectory generation and simulation of miniature integral impeller. Taking into account the closed and miniature of integral impeller, and low stiffness of the micro-milling tool, in order to avoid interference in the processing, through reasonably division of the impeller blade surface, generate the miniature integral impeller machining trajectory. Then impeller machining NC code is generated, and is simulated in Vericut software. Simulation result shows that the machining programs generated in this paper are effective, and the simulation machined workpiece surface is relatively smooth.

WIND WAVES AND SWELL

Winds blowing over the water surface generate waves. In general the higher the wind velocity, the larger the fetch over which it blows, and the longer it blows the higher and longer will be the average waves . Waves still under the action of the winds that created them are called wind waves, or a sea. They are forced waves rather than free waves. They are variable in their direction of advance (Arthur, 1949). They are irregular in the direction of propagation. The flow is rotational due to the shear stress of the wind on the water surface and it is quite turbulent as observations of dye in the water indicates. After the waves leave the generating area their characteristics become somewhat different, principally they are smoother, losing the rough appearance due to the disappearance of the multitude of smaller waves on top of the bigger ones and the whitecaps and spray. When running free of the storm the waves are known as swell. In Fig. 1 are shown some photographs taken in the laboratory of waves still rising under the action of wind and this same wave system after it has left the windy section of the wind-wave tunnel. It can be seen thati-the freely running swell has a smoother appearance than the waves in the windy section. The motion of the swell is nearly irrotational and nonturbulent, unless the swell runs into other regions where the water is in turbulent motion. Turbulence is a property of the fluid rather than of the wave motion. After the waves have travelled a distance from the generating area they have lost some energy due to air resistance, internal friction, and by large scale turbulent scattering if they run into other storm areas, and the rest of the energy has become spread over a larger area due to the dispersive and angular spreading characteristics of water gravity waves. All of these mechanisms lead to a decrease in energy density. Thus, the waves become lower in height. In addition, due to their dispersive characteristic the component wave periods tend to segregate in such a way that the longest waves lead the main body of waves and the shortest waves form the tail of the main body of waves. Finally, the swell may travel through areas where winds are present, adding new wind waves to old swell, and perhaps directly increasing or decreasing the size of the old swell.

Field tests of electroseismic hydrocarbon detection

Geophysicists, looking for new exploration tools, have studied the coupling between seismic and electromagnetic waves in the near-surface since the 1930s. Our research explores the possibility that electromagnetic-to-seismic (ES) conversion is useful at greater depths. Field tests of ES conversion over gas sands and carbonate oil reservoirs succeeded in delineating known hydrocarbon accumulations from depths up to [Formula: see text]. This is the first observation of electromagnetic-to-seismic coupling from surface electrodes and geophones. Electrodes at the earth’s surface generate electric fields at the target and digital accelerometers detect the returning seismic wave. Conversion at depth is confirmed with hydrophones placed in wells. The gas sands yielded a linear ES response, as expected for electrokinetic energy conversion, and in qualitative agreement with numerical simulations. The carbonate oil reservoirs generate nonlinear conversions; a qualitatively new observation and a new probe of rock properties. The hard-rock results suggest applications in lithologies where seismic hydrocarbon indicators are weak. With greater effort, deeper penetration should be possible.

A Permeable Coating Model for Predicting the Environment at the Pipe Surface Under CP-Compatible Coatings

Some underground pipeline coatings, such as asphalt, coal tar enamel and fusion-bonded epoxy, are said to be CP-compatible. When these coatings degrade and groundwater contacts the pipe, the surface is still protected from corrosion and stress corrosion cracking (SCC) as the CP current can pass through the permeable coating. The electrochemical reactions on the pipe surface generate a local environment under the coating that is quite different from that in the surrounding soil. In general, the pH of the trapped water increases due to the cathodic reduction of water and oxygen by the CP current. A mathematical model has been developed to predict the generation and evolution of the environment under a disbonded permeable coating as a consequence of the action of CP. The model couples the electrochemical reactions on the surface of the pipe to the transport of species to and from the pipe surface through the permeable coating and the surrounding soil. The model is structured to use available field data (such as soil and ground water data and information from CP surveys) to predict conditions on the pipe surface. The model can be used to predict CP and environmental conditions under which the pipe may be susceptible to corrosion or SCC.

GONIHEDRIC STRING AND ASYMPTOTIC FREEDOM

Very few natural basic principles allow to extend Feynman integral over the paths to an integral over the surfaces so that they coincide at long time scale, that is when the surface degenerates into a single particle world line. In the classical approximation the loop Green functions have perimeter behavior. That corresponds to the free quarks. Quantum fluctuations of the surface generate nonzero string tension, that is the area law and we have quark confinement. In this string theory confinement and asymptotic freedom can coexist.

Activation currents, sperm entry and surface contractions in ascidian eggs

SummarySpermatozoa from the mollusc Ostrea edulis are capable of fusing to and entering de-chorionated ascidian eggs. During interaction they generate activation currents, comparable to the fertilisation currents induced by homologous spermatozoa. Activation currents are inward at − 80 mV, with a mean initial slope of 111 ± 124 pA/s for Ciona intestinalis eggs and 47 ± 25 pA/s for Phallusia mammillata eggs, while the mean peak currents are 2782 ± 1132 pA and 1523 ± 1668 pA, respectively. The fertilisation and activation currents reverse at a holding potential of 0 mV to + 20 mV, suggesting that oyster sperm and ascidian sperm gate the same channel precursor, a non-specific, large conductance channel described previously (Dale & DeFelice, 1984). In contrast to homologous fertilisation, the activation current is not followed by a polarised contraction of the egg surface, nor other signs of egg activation. Staining eggs with Hoechst 33342 after insemination shows the female nucleus and a single oyster sperm nucleus at the antipode. This suggests a specialised predetermined site at the vegetal pole for sperm entry. Homologous and heterologous spermatozoa delivered, in a large pipette, to localised areas of the egg surface generate fast inward currents of 200–2000 pA, but do not induce contraction of the egg surface. This shows that although channel precursors are located globally over the egg surface, channel activation does not necessarily trigger the contraction wave. Subsequent induction of both a fertilisation current and a contraction by homologous sperm added to the bath, implies a regionalised activation site with an accumulation of channel precursors and a ‘pacemaker’ for the initiation of the contraction wave.