Right-angled Junction Research Articles

Water surface topology of supercritical junction flow

Abstract The complexity of flow conditions at junctions amplifies significantly with supercritical flow. It is a pronounced three-dimensional two-phased flow phenomenon, where standing waves with non-stationary water surface are formed. To analyse the hydrodynamic conditions at an asymmetric right-angled junction with incoming supercritical flows at Froude numbers between 2 and 12, an experimental approach was used. For a phenomenological determination of the relations between the integral parameters of incoming flows and the characteristics of standing waves at the junction area, water surface topographies for 168 scenarios at the junction were measured using non-intrusive measurement techniques. The new, phenomenologically derived equations allow for determination of location, height and extent of the main standing waves at the junction. Research results give important information on the processes and their magnitude for engineering applications.

Flow at 90° Equal-Width Open-Channel Junction

This paper describes a one-dimensional approach to solving water depth upstream of a subcritical open-channel right-angled junction and to solving the contraction coefficient at the maximum flow constriction. The energy and momentum correction coefficients at the maximum flow constriction were found to be related to the inverse of the upstream-to-downstream discharge ratio of the main channel. The cross-sectional mean flow angle at the branch channel entrance was determined through detailed measurement of velocity vectors and was found to decrease as the discharge ratio increases. The shape index of the separation zone was also checked through observations of surface-dye trajectory and was found to agree with that obtained in previous studies. With known Froude numbers and the energy and momentum correction coefficients at the maximum flow constriction, the one-dimensional prediction and experimental results of this study correlate well to the data of other studies.

Diffusion-controlled current densities close to a right-angled electrode edge

The current density close to the edge of an electrode may be either enhanced or diminished compared with current densities remote from the edge. This effect is quantified here for the case of diffusion-controlled currents at a planar electrode which abuts either a second electrode face or an insulating plane. Concentrations in the vicinity of the electrodes are also investigated. The cases of right-angled junctions receive special attention.

A numerical study of division of flow in open channels

A two-dimensional numerical model which employs the depth-averaged forms of continuity and momentum equations along with k-e turbulence closure scheme is used to simulate the flow at the open channel divisions. The model is generalised to flows of arbitrary geometries and MacCormack finite volume method is used for solving governing equations. Application of cartesian version of the model to analyse the flow at right-angled junction is presented. The numerical predictions are compared with experimental data of earlier investigators and measurements made as part of the present study. Performance of the model in predicting discharge distribution, surface profiles, separation zone parameters and energy losses is evaluated and discussed in detail. To illustrate the application of the numerical model to analyse the flow in acute angled offtakes and streamlined branch entries, a few computational results are presented.

Increased hydraulic resistance in combining open channel flows

In combining open channel flows, blockage at the junction is manifested by the rise in the stage due to the effect of lateral inflow from the branch channel. Blockage results in pockets of flow where the flow velocity is very small and the depth of flow is large. The entry of the lateral flow into the main channel also throttles the main channel flow and results in an increase in the hydraulic resistance to flow which in turn leads to considerable energy losses. In the design of open channel networks, the expected increase in the flow depth near the channel junction permits one to estimate the height of the channel walls in the vicinity of the junction. A relationship between blockage and the ratio of the discharges is proposed on the basis of the energy principle. Using this relationship, one can predict blockage for a right-angled junction in combining flow. Using experimental results, the proposed relationship is verified.

Field approximations at thin-wire junctions for the finite-difference time-domain method

Approximations for the circumferential magnetic fields at right-angled junctions are derived and validated by computing the radiation patterns of a square-loop antenna by means of the finite-difference time-domain (FD-TD) method. The radiated time-domain fields are transformed to the frequency domain and then compared to the frequency domain results obtained from the method of moments.

How does the cytoskeleton read the laws of geometry in aligning the division plane of plant cells?

Abstract Since Robert Hooke observed the froth-like texture of sectioned plant tissue, there have been numerous attempts to describe the geometrical properties of cells and to account for the patterns they form. Some aspects of biological patterning can be mimicked by compressed spheres and by liquid foams, implying that compression or surface tension are physical bases of patterning. The 14-sided semi-regular tetrakaidecahedron encloses a given volume most efficiently and packs to fill space. However, observations of real plant tissue (and of soap bubbles) in the first half of this century established that plant cells only rarely form this mathematically ideal figure composed predominantly of 6-sided polygons. Instead, they tend to form a topologically transformed variant having mainly pentagonal faces although there is variability in the number of sides and the angles formed. But the one irreducible component of normal cell and tissue geometry is that only three edges meet at a point in a plane. In solid space, this gives rise to tetrahedral junctions and it is from this that certain limitations on sidedness flow. For three edges to meet at a point means that there must be an avoidance mechanism which prevents a new cell plate from aligning with an existing 3-way junction. Sinnott and Bloch (1940) saw that the cytoplasmic strands which precede the cell plate, predicted its alignment and also avoided 3-way junctions in unwounded tissues. Recently, F-actin and microtubules have been detected in these pre-mitotic, transvacuolar strands. The question considered here is why those cytoskeletal elements avoid aligning with the vertex where a neighbouring cross wall has already joined the mother wall. An hypothesis is discussed in which tensile strands - against a background of cortical re-organization during pre-mitosis - tend to seek the minimal path between nucleus and cortex. In this way, it is suggested that unstable strands are gradually drawn into a transvacuolar baffle (the phragmosome) within which cell division occurs. Vertices are avoided by the strands because they constitute unfavoured longer paths. The demonstrable tendency of tensile strands to contact mother walls perpendicularly would seem to account for Hofmeister’s and Sachs’ rules involving right-angled junctions. As others have discussed, such right-angled junctions give way to co-equal 120°angles between the three walls during subsequent cell growth. It is this asynchrony of cell division - where attachment of a cell plate causes the neighbouring wall to buckle - that forms a vertex to be avoided by subsequent pre-mitotic strands in that neighbouring cell. In this way, successive division planes would not co-align. It is therefore suggested that the exceptional formation of 4-way junctions in wounded tissue results from the fact that adjacent cells divide simultaneously; the lack of prebuckling of a common wall under these circumstances means that there is no vertex to be avoided by the minimal path mechanism.

Dividing Flow in Open Channels

Junctions are of considerable importance in the study of openchannel flows. For dividing flow at rightangled junctions of rectangular open channels, an estimate of the discharge ratio is obtained i...

The theory and experimental behaviour of right-angled junctions in rectangular-section wave guides

The paper opens with a general theoretical analysis of a wave-guide junction of n members in terms of an equivalent transmission line system. This is then applied to the particular case of a right-angled junction in a guide of rectangular section excited in the H01 mode. The behaviour is expressed in terms of six parameters, the values of which have been calculated over a range of wavelengths around 10 cm and determined experimentally at four points within this range. A description of the experimental technique employed is given, and an assessment made of the order of accuracy attained in the measurements.

The theory and experimental behaviour of right-angled junctions in rectangular-section wave guides

The paper opens with a general theoretical analysis of a wave-guide junction of n members in terms of an equivalent transmission line system. This is then applied to the particular case of a right-angled junction in a guide of rectangular section excited in the H01 mode. The behaviour is expressed in terms of six parameters, the values of which have been calculated over a range of wavelengths around 10 cm and determined experimentally at four points within this range. A description of the experimental technique employed is given, and an assessment made of the order of accuracy attained in the measurements.

The distribution of atheroma in the aorta

Atheroma in the aorta is most marked around the origins of the intercostal and lumbar arteries. These differ from the larger branches in forming right-angled junctions with the main trunk and their origins are therefore sites of increased strain due to (1) weakness of structure and (2) increased internal stress.

DANGERS ATTENDANT ON ATTEMPTS AT GAINING THE INTERVAL IN OPERATIONS FOR APPENDICITIS.

It is strange that medical men in general and anatomists and physiologists in particular claim that the appendix vermiformis has no function, that it is a useless appendage, playing the part of catching any old thing, or furnishing the surgeon opportunity to rake in illgotten gain. Ridiculous as it is to compare inanimate things to parts of the human body, it may be well to do so here, in order to state that at such a right-angled junction as is formed by the ileocecal connection, an oil cup would be furnished in mechanics, while in hydraulics, as in a sewerage system, for instance, a manhole would be placed. This appendage apparently has secretory functions by which, it is fair to assume, the natural tendency to pastiness of the residue of digestion, after it comes to the cecum, is so modified that it is rendered less