•Equal length algorithm for the form-finding of cable-networks is proposed.•Compatible strategy between the cable-network and the supporting truss is proposed.•An iterative approach for the ...form-finding of cable-network antennas is proposed.•The advantages of the proposed approach are demonstrated by two case studies.
Cable-network structures are usually adopted as an ideal form of satellite antennas. The performance of cable-network antennas crucially depends on the surface accuracy and the tension distribution. In some cases, conventional algorithms, such as the equal tension algorithm and the equal force density algorithm, may lead to the decrease of the effective region. Thus the equal length algorithm based on the force density method is proposed in this paper. In this algorithm, the free nodes are restricted as close as possible to their desired positions, which ensures the area of the effective region and the high surface accuracy. The cable tensions are restricted by the maximum tension ratios, which ensures the uniform tension distribution. Furthermore, the elastic deformation of the supporting truss seriously affects the antenna’s performance. Therefore, a double-loop iterative form-finding approach for the cable-network antenna with flexible supporting truss is proposed to find a pre-tensioned configuration that meets the requirements of the surface accuracy and the tension distribution. Firstly, an inner loop based on the equal length algorithm is established for the form-finding of the cable-network. Through this inner loop, the high surface accuracy and the uniform tension distribution can be achieved. Secondly, a compatible strategy between the cable-network and the flexible supporting truss is proposed. Through this strategy, a nonlinear finite element (FE) model of the cable-network antenna is established to capture the compatible deformation. Thirdly, an outer loop combining the equal length algorithm and the compatible strategy is established, in which the node coordinates and the cable tensions are iteratively fed to the force density model and the FE model in steps 1 and 2. Through this outer loop, the compatible deformation is fully considered. The whole loop will stop and converge to a reasonable solution of the surface accuracy and the tension distribution within given criterions. Numerical examples of an offset cable-network antenna are provided, and the results are compared with previous literature.
The problem of determining those multiplets of forces, or sets of force multiplets, acting at a set of points, such that there exists a truss structure, or wire web, that can support these force ...multiplets with all the elements of the truss or wire web being under tension, is considered. The two-dimensional problem where the points are at the vertices of a convex polygon is essentially solved: each multiplet of forces must be such that the net anticlockwise torque around any vertex of the forces summed over any number of consecutive points clockwise past the vertex must be non-negative; and one can find a truss structure that supports under tension, and only supports, those force multiplets in a convex polyhedron of force multiplets that is generated by a finite number of force multiplets each satisfying the torque condition. Progress is also made on the problem where only a subset of the points are at the vertices of a convex polygon, and the other points are inside. In particular, in the case where only one point is inside, an explicit procedure is described for constructing a suitable truss, if one exists. An alternative recipe to that provided by Guevara Vasquez et al. (2011), based on earlier work of Camar-Eddine and Seppecher (2003), is given for constructing a truss structure, with elements under either compression or tension, that supports an arbitrary collection of balanced forces at the vertices of a convex polygon. Finally some constraints are given on the forces that a three-dimension truss, or wire web, under tension must satisfy.
The use of cross-tie is one of the effective countermeasures to suppress the undesired cable vibration in the cable-stayed bridges. The major benefits offered by the cross-tie solution are the ...increase in the in-plane stiffness and the flow of energy toward the higher order nodes. However, the formation of closely spaced local modes is one of the major disadvantages of the Cross-tied cable networks. There are only few studies available to understand the formation of local modes. In the current study, an energy-based approach is developed to differentiate between the global and the local modes. In the proposed approach, the kinetic energy equations are formulated to compute the energy stored in arbitrary cable segments. In the current study, the advantages of the proposed energy-based approach over the existing amplitude-based approach have been discussed. The suggested approach has been applied to multiple cable networks, and a comparison has been drawn between the amplitude-based approach and the proposed energy-based approach.
A large grid-connected private industrial and residential 11 kV network in northern Australia has its own 11 kV diesel generators to supply essential loads during grid supply outages. The generators ...each have a neutral earthing resistor (NER). When islanded from the grid, one NER provides the system reference. Significant circulating current was causing overheating of the NER. This paper describes the investigation undertaken, the options considered for rectification and the results from commissioning of the implemented solution.
The mechanisms underlying mammalian neural tube closure remain poorly understood. We report a unique cellular process involving multicellular rosette formation, convergent cellular protrusions, and ...F-actin cable network of the non-neural surface ectodermal cells encircling the closure site of the posterior neuropore, which are demonstrated by scanning electron microscopy and genetic fate mapping analyses during mouse spinal neurulation. These unique cellular structures are severely disrupted in the surface ectodermal transcription factor Grhl3 mutants that exhibit fully penetrant spina bifida. We propose a novel model of mammalian neural tube closure driven by surface ectodermal dynamics, which is computationally visualized.
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•Non-neural ectodermal cells form multicellular rosettes during mouse PNP closure.•Rosette-forming cells generate convergent F-actin protrusions and cable network.•Rosettes and protrusions are disrupted in the surface ectodermal Grhl3-KO mutants.•Computational modeling visualizes the stepwise closure of mouse PNP.
Various uncertainties existing in the manufacturing process, such as imperfect cable lengths and uncertain boundary node locations, will unavoidably deteriorate the shape precision of cable-network ...antennas. In this paper, an adaptive Kriging-based method is developed to investigate the global sensitivity of uncertain parameters and discover the influential factors. Existing strategies in literature usually use relative error of function values to measure the metamodel accuracy and then to determine when the sequential sampling process should be stopped. However, these indicators are mostly developed based on function values, not the sensitivity indices. Therefore, it is difficult to determine how small the indicators should be for efficiently defining an accurate metamodel for sensitivity analysis. In this paper, a straightforward sensitivity-based indicator is developed to measure the metamodel accuracy, which is defined as the weighted average of absolute errors of sensitivity values between two successive iterations. A use-controlled threshold, combined with the new indicator, can provide an automatic stopping criterion for the adaptive metamodel building process. The proposed method can provide a uniform framework to detect the convergence status effectively for problems with different uncertainties and dimensions. A numerical example and two cable-network antenna examples considering different manufacturing uncertainties are illustrated to validate the new method.
As a kind of large-scale connectivity infrastructure, submarine cables play a vital role in international telecommunication, socio-economic development and national defense security. However, the ...current understanding about the spatial pattern of global submarine cable network is relatively limited. In this article, we analyze the spatial distribution and connectivity pattern of global submarine cables, and identify their strategic pivots and strategic channels. The main conclusions are as follows: (1) The spatial distribution of global submarine cables is significantly unbalanced, which is characterized by the facts that the distribution of submarine cable lines is similar to that of sea lanes, and the agglomerations of landing stations are distributed unevenly along the coastline. (2) The connectivity pattern of global submarine cable network has a significant scale effect. At the micro, meso and macro scales, the connectivity structure presents chain model, cluster model and hub-and-spoke model, respectively. (3) The distribution of strategic pivots and strategic channels shows a pyramidal hierarchical feature. Singapore ranks highest among all the strategic pivots, while the Gulf of Aden and the Strait of Malacca rank highest among the strategic channels. Based on the identification of strategic pivots and channels, six strategic regions have been divided, which face various network security risks and need special attention and vigilance.
Generally, cables in cable-stayed bridges are modeled and designed as taut strings. This assumption simplifies the analytical formulation in a cross-tied cable network, which offers a cost-effective ...solution for mitigation of cable vibrations. However, such a solution is strongly influenced by the physical properties of the main cables and the cross-tie. The modal parameters of stay cables are also known to be affected by their bending stiffness. This study presents an analytical formulation for determining the modal parameters of such cable networks in which cable bending stiffness is included. The resulting 4th-order partial differential equation for the flexible cable network was numerically solved, and the analytically obtained modal frequencies of the example cable networks were compared with the values obtained from FEM numerical model and an excellent match between the two sets of values was obtained. The deviation between modal frequencies of taut and flexible cable networks was found to have a maximum value of 10.7% and 3.08% for cables with high and average bending stiffness parameter (
μ
), respectively. However, the inclusion of bending stiffness had negligible influence on the mode shapes regardless of the
μ
value. After validation of the method, a parametric study was conducted that explored the impact of length ratio, frequency ratio, and bending stiffness ratio on the fundamental frequency of a flexible two-cable network. Bending stiffness ratio parameter of the main cables (
ξ
)
played a significant role in increasing the fundamental frequency when the main cables had the same frequency ratio (
η
=
1
), while its effect diminished with decreasing value of
η
and the length ratio parameter (
ρ
) was more influential in increasing the fundamental frequency in such cases.
•Little academic attention is paid to the subsea fiber cable network in its entirety.•Public cable data and network analysis tools allow modeling the internet backbone.•Submarine communication cable ...links are unevenly distributed at global scale.•On average, developing economies have lower levels of backbone redundancy.•Internet outage risk due to subsea cable failure is higher in least developed areas.
The backbone network of submarine communication cables (SCC) carries 98% of international internet traffic. Coastal and island states strongly depend on this physical internet infrastructure to provide internet connectivity. Although about 100 SCC breakdowns of human or natural origin occur at yearly average, a literature review reveals that there is no approach to assess individual state vulnerability to SCC failure in global comparison. In this article, the global SCC network is modeled based on publicly available data. Besides the analysis of the global network properties, a focus is put on remaining bandwidth capacities in three different failure scenario simulations of SCC breakdowns. As a result, this study identifies 15 highly vulnerable states and overseas territories, and another 28 territories that are classified as partially vulnerable to SCC failures. Since economic market decisions shape the structure of the SCC network, an uneven distribution of redundancies and the resulting vulnerability of disadvantaged economies can be confirmed. Therefore, the study's findings may contribute to a better assessment of the necessity of preventive protection measures of critical telecommunication infrastructures in states and territories characterized by high and medium vulnerability.
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