The Research of Flow Resistance Property in the Tugging and Mooring of Tube Segment

The tube tugging and mooring is the key step in the process of the immersed tunnel, and the most important theoretical is the calculation of water flow force. According to the numerical simulation and physical model of the tube in the Pearl River, the difference value of the flow resistance coefficient can be calculated. The fluent software is used to simulate the process of the tube tugging and mooring. On the basis of the empirical data of the tube experiment in the Pearl River, the flow resistance coefficient is obtained in the process of the tube tugging.

Route Length, Curve Radius and Layout of Evacuated Tube Maglev Space Launch System

Current space launch is expensive and low-efficient because the invalid load----rocket and fuel in it occupies over 80% of the total launch weight. A solution to reduce the space launch cost and increase the launch efficiency is to construct the evacuated tube, pump air out from the tube and have the maglev vehicle loaded with the spacecraft run in it; the spacecraft fly out the tube when the maglev is accelerated to ultra-speed, e.g. 5km/s even 8km/s in the tube. By this way, the first class of the rocket could be saved, so that the launch cost would be low and lead the large scale space exploitation to become reality in the soon future. As for the tube construction, the route layout should be concerned on at first. Because of the engineering restriction, the height at the tube end wouldnt be very high, and the embedding depth wouldnt be very deep, practically about 8km. However, the tube length will be 700km at least, a completely straight tube or a completely curve tube (on a single circle) would lead a too small launch angle. Thus both of them are not feasible. Reasonable tube routes in vertical section will include two or more than two segments, for example, a straight tube segment and a curve tube segment, or two or more than two curve segments in different radius or different curve direction.

Analysis on Additional Pressure of Tube Sidewall of Immersed Tube Tunnel in Sinking Process of Tube Segment

The numerical simulation analysis on the whole process of the tube immersing is researched, which use computational fluid dynamics method, is based on RNG k~ε turbulence model. The analysis shows that: additional pressure of tube lateral wall depends on the changed flow field cause by tube immersing; through the analysis, it have explored the special position of additional pressure changes in the process of immersing; it also shows some problems should be paid attention, through analysis the stress of special position.

A new view of flow topology and conditional statistics in turbulence

By partitioning a turbulent flow field into relative simple units, the original complex system may be better understood from studying decomposed structures. In this paper, some general principles for identifying geometrical decomposition are discussed. Logically, to make analysis more objective and quantitative, the decomposed units need to be non-arbitrarily defined and space filling. Following this vein, we introduced two topological approaches satisfying these prerequisites and the relevant work is reviewed. For a given scalar variable, dissipation elements are defined as the spatial regions that the gradient trajectories of this scalar can share the same pair of scalar extremums (one maximum and one minimum), whereas for the general vector variables, vector tube segments are the part of vector tubes bounded by adjacent extremums of the magnitude of the given vector. Both structures can be characterized by representative shape parameters: the length scale and the extremum difference. On the basis of direct numerical simulation data, the statistics of the shape parameters have been studied. Physically, those structures reveal the ‘nature’ topology of turbulence, and thus their characteristic parameters reflect the flow properties. For instance, when the vector tube segment approach is applied to the velocity case, the negative skewness of the velocity derivative can be explained by the asymmetry of the joint probability density function of the shape parameters of streamtube segments. Conditional statistics based on these newly defined structures identify finer flow physics and are believed helpful for modelling improvement. Application examples illustrate that, in principle, these methods can generally be applied to different flow cases under different situations.

Boundary-integral model of permanent magnet of a tube segment as shape

Boundary-integral model of permanent magnet of a tube segment as shape The magnetic field due to a permanent magnet of a tube-side segment as shape and of radial-oriented magnetization is considered. Such a sheet modelling a single pole of the magnet is used to express the suitable contribution to magnetic quantities. A boundary-integral approach is applied that is based on a virtual scalar quantity attributed to the magnet pole. Such an approach leads to express analytically the scalar magnetic potential and the magnetic flux density by means of the elliptic integrals. Numerical examples of the computed fields are given. The general idea of the presented approach is mainly directed towards designing the magnetic field within the air gap of electric machines with permanent magnets as an excitation source. Other technical structures with permanent magnets may be a subject of this approach as well.

Analyses of the Failed Impulsion Lines of NPP Dukovany Steam Generator

Over the years the cracks have been detected on the impulsion lines of all steam generators of the NPP Dukovany. The tubing is made from the austenitic stainless steel. These lines are designed for purposes of measurement and also containment of possible leaks, e.g. between the primary and secondary steam generator seals. Their integrity is periodically tested during each outage and if the leak is detected the tube segment must be cut out and the new one is welded in place. Most of the time the tubes are “dry”, i.e. no medium is flowing inside. Due to confined space the movement of persons around the steam generator is difficult and often the relatively subtle impulsion lines have been subjected to stresses leading to their bending. This deformation has then led to evolution of the failure. To address the issue the original manufacturing, test and control procedures for the impulsion tubing have been studied. Several cracked tubes have been analyzed thoroughly to find the root cause and offer possible remedies.