scholarly journals THE INCREASE OP BED SHEAR IN A CURRENT DUE TO WAVE MOTION

1966 ◽  
Vol 1 (10) ◽  
pp. 42 ◽  
Author(s):  
E.W. Bijker
Keyword(s):  
Wave Propagation ◽  
Velocity Profile ◽  
Wave Motion ◽  
Indirect Method ◽  
Uniform Flow ◽  
Hydraulics Laboratory ◽  
A Current ◽  
Complicated Nature

As early as 1948 Exnstein [lj suggested that the approach to the calculation of the sand transportation by waves could be similar to that for uniform flow. Tests conducted by author proved that for a current, with waves being propagated m a direction perpendicular or almost perpendicular to this current, the sand transportation is a function of the intensity of bed shear in the direction of the current. Therefore, an attempt has been made to study the increase of the bed shear of a current due to wave motion. The results of this study are presented in this paper. This problem has also been studied by Jonsson and Lundgren !?l >L5] t>ut they have assumed that current and wave-propagation occurs m the same direction. As for normal beach conditions, the angle between current and wave crests is between 0° and 20°, tests have been executed in the Delft Hydraulics Laboratory for angles of 0° and 15°. For an angle of 0° between the wave crests and the direction of the current, results have been presented by Bijker in the proceedings of the seminars at the I.A.H.R. conference which was held m Leningrad in 1965. Because it is not feasible to measure the bed shear directly an indirect method had to be chosen. Determination of the bed shear by means of the velocity profile m the vicinity of the bed is not feasible m this case as the combined velocity profile is of a rather complicated nature. The bed shear is therefore determined by means of the energy slope.

scholarly journals TURBULENT CURRENTS IN THE PRESENCE OF WAVES

1970 ◽  
Vol 1 (12) ◽  
pp. 141
Author(s):  
Helge Lundgren
Keyword(s):  
Boundary Layer ◽  
Wave Propagation ◽  
Velocity Profile ◽  
Current Velocity ◽  
Friction Velocity ◽  
Approximate Theory ◽  
Current Direction ◽  
Constant Depth ◽  
Wave Boundary ◽  
A Current

This paper presents an approximate theory for the reduction of the velocity of a current due to the presence of sinusoidal waves. For a given slope, S, in water of constant depth, d, the current velocity profile is U(z) = U^ (2.5'ln — - A) (1) t zo as a function of the height, z, above the bed. Eq. 1 is valid only above the thin wave boundary layer near the bed, the roughness of which is k = 30 z . Uf is the current friction velocity defined by p Ul = y d S = T (2) f ' cw CW Values of A can be found from: Fig. 2 where Aj applies when the direction of wave propagation is parallel to the current direction, and Fig. 3 where A2 applies when the direction of wave propagation is perpendicular to the current direction, cf. Notation in Sec. 2. The theory is based upon a number of assumptions (see Sec. 4).

scholarly journals III. On the atomic weight of manganese

1883 ◽  
Vol 35 (224-226) ◽  
pp. 44-48
Keyword(s):  
Carbon Dioxide ◽  
Silver Chloride ◽  
Atomic Weight ◽  
Special Method ◽  
Its Analysis ◽  
A Current ◽  
Sulphuretted Hydrogen

Our attention has been directed for some time to a new determination of the atomic weight of manganese. This communication gives a succinct account of the results of the preliminary stages of such an inquiry, and although the further progress of the investigation may reveal some errors, still we feel convinced the final numbers can in no way differ materially from the present values, and therefore further delay in publication is unnecessary. The atomic weight of manganese has been determined by many chemists, but the resulting values vary considerably according to the special method selected. The results of the different investigators may be divided into two classes—those giving approximately 55 as the number, and those making it about 54. To the former class belong Turner, Berzelius, and Dumas, all of whom use the same method, viz., the determination of the silver chloride yielded by a weighed amount of chloride of manganese. Turner also made determinations from the analysis of the carbonate, and from the conversion of the monoxide into sulphate. Von Hauer used the same method as that employed by him in the determination of the atomic weight of cadmium, viz., the reduction of manganous sulphate to sulphide by ignition in a current of sulphuretted hydrogen. It is probable that this method is not very trustworthy, as, according to Schneider, the sulphide may be contaminated by oxysulphide. Schneider and Rawack belong to the second class of observers, the former employing the oxalate, and from its analysis calculating the atomic weight by deducting the weight of water and carbon dioxide obtained. Rawack, whose experiments were conducted in Schneider’s laboratory, weighed the water obtained by reducing manganoso-manganic oxide to manganous oxide.

Do centers of origin have a center?

Paleobiology ◽  
1981 ◽  
Vol 7 (3) ◽  
pp. 305-307 ◽  
Author(s):  
John C. Briggs
Keyword(s):  
United States ◽  
North America ◽  
Southeastern United States ◽  
Important Criterion ◽  
Centers Of Origin ◽  
Single Region ◽  
Evolutionary Radiation ◽  
A Current ◽  
Considerable Intensity

A current question being debated with considerable intensity is whether or not certain geographic areas act as centers of evolutionary radiation and supply species to other areas that are less active or less effective in an evolutionary sense. Darwin (1859) was the first to write about centers of origin which he called “single centers of creation.” He argued that each species was first produced within a single region and that it subsequently migrated from that area as far as its powers of migration and subsistence under past and present conditions permitted. Adams (1902), in discussing the influence of the southeastern United States as a center of distribution for the flora and fauna of North America, provided a series of criteria for the determination of “centers of dispersal.” His first, and evidently most important criterion was the location of “the greatest differentiation of a type.”

Study of the residual imperfections using methods of probability theory

2021 ◽  
Vol 87 (9) ◽  
pp. 44-49
Author(s):  
D. A. Kuzmin
Keyword(s):  
Probability Theory ◽  
Generalized Equation ◽  
Structural Elements ◽  
Non Destructive Testing ◽  
Operational Control ◽  
Destructive Testing ◽  
Control Procedures ◽  
Non Destructive ◽  
A Current

Discontinuities in the products that occur during manufacture, mounting or upon operation can be missed during non-destructive testing which do not provide their complete detectability at a current level of the technology. Therefore, it is necessary to take into account that certain structural elements may have discontinuities of significant dimensions. We present the results of using the methods of probability theory in studying the residual imperfections that remains in the structure after non-destructive control and repair of the previously identified defects. We used the results of operational control of units carried out by ultrasonic and radiographic methods. We present a method for determining a multifactorial coefficient that takes into account the detectability of defects, the number of control procedures and the errors in the instrumentation and methodological support, as well as a generalized equation for the probability distribution of detecting discontinuities. The developed approach provides assessing of the level of damage to the studied objects, their classification proceeding from the quantitative data and determination of the values of postulated discontinuities for deterministic calculations. The results obtained can be used to improve the methods of monitoring NPP facilities.

Robotic grasping with obstacle avoidance using octrees

2020 ◽  
Vol 25 (3) ◽  
pp. 7-12
Author(s):  
Rud V.V. ◽  
Keyword(s):  
Control Systems ◽  
Current Problem ◽  
Robot Manipulator ◽  
General Purpose ◽  
Advantages And Disadvantages ◽  
Specific Position ◽  
Recognition Of Objects ◽  
Manipulator Control ◽  
A Current

This paper considers the problems of the integration of independent manipulator control systems. Areas of control of the manipulator are: recognition of objects and obstacles, identification of objects to be grasped, determination of reliable positions by the grasping device, planning of movement of the manipulator to certain positions with avoidance of obstacles, and recognition of slipping or determination of reliable grasping. This issue is a current problem primarily in industry, general-purpose robots, and experimental robots. This paper considers current publications that address these issues. Existing algorithms and approaches have been found in the management of both parts of the robot manipulator and solutions that combine several areas, or the integration of several existing approaches. There is a brief review of current literature and publications on the above algorithms and approaches. The advantages and disadvantages of the considered methods and approaches are determined. There are solutions that cover either some areas or only one of them, which does not meet the requirements of the problem. Using existing approaches, integration points of existing implementations are identified to get the best results. In the process, a system was developed that analyzes the environment, finds obstacles, objects for interaction, poses for grasping, plans the movement of the manipulator to a specific position, and ensures reliable grasping of the object. The next step was to test the system, test the performance, and adjust the parameters for the best results. The resulting system was developed by the research team of RT-Lions, Technik University, Reutlingen. The hardware research robot includes an Intel Realsense camera, a Sawyer Arm manipulator from Rethink Robotics, and an internally grabbing device.

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