Survivability using traffic balancing and backup resource reservation in multi‐domain optical networks

Survivability in the geographically distributed backbone multi‐domain optical networks (MDONs) is critical because of issues related to its size, usage of resources, and domain management policies of the comprising domains. In MDONs, the emerging scheduled traffic is increasingly multivendor, multimedia, and periodic. It is high during the office (working) hours and low during the non‐office (non‐working) hours in a day. A connection failure during the office hours may result in huge amount of information being lost. Towards providing an acceptable level of service even when a connection fails, we first provide traffic balancing (TB) based solutions where the intra/inter‐domain traffic is slided (S1‐TB), shifted (S2‐TB), or slided as well as shifted (S3‐TB) based on the service level agreement between the client and domain service provider. Of the above solutions, the solution based on sliding as well as shifting (S3‐TB) performs best, and hence for further improvement in S3‐TB, we incorporate backup multiplexing with advance backup resource reservation (BRR) and evaluate the performance of the strategy and report results. The performance evaluation of the above strategies is compared with the existing extended path shared protection (EPSP) by a simulator developed in MATLAB and tested on three‐domain and five‐domain standard network topologies, on the metrics of blocking probability, network resource utilization ratio, network capacity utilized by backup route, wavelength link used per backup lightpath, and a newly introduced metric, network resource utilization index. As compared with the existing strategy EPSP, the S3‐TB and S3‐TB with BRR showed improved performance on all the metrics.     

Wind tunnel tests on scale models of a large power station chimney

This work is aimed at providing a better understanding of the parameters required for the wind-tunnel simulation of the wind loads on large power station chimneys. Measurements of mean and fluctuating pressure distributions have been made on scale models of Fawley power station chimney, for comparison with the full-scale measurements of Tunstall. The measurements have been made in a simulated atmospheric boundary layer of height 1.2 m (nominal scale 1:500), using the method developed by Counihan.Initial measurements of mean pressure distribution were made on a 1:250 scale model chimney in the 1:500 scale boundary layer, in order to obtain as high a Reynolds number as possible in the wind tunnel available. No fluctuating pressure measurements were made owing to the limited tunnel time available. Following the good agreement between mean pressure distributions obtained on the 1:250 model and full-scale measurements, a 1:500 scale model chimney was tested in the same simulated atmospheric boundary layer. Mean pressure measurements gave good agreement with full-scale measurements at a Reynolds number of 2.3 × 10⁷, for model Reynolds numbers above 1.5 × 10⁵, and with a smooth or slightly rough model surface. Good agreement was obtained between model and full scale for the distribution of fluctuating pressure coefficients, when the difference in turbulence intensity between the simulated and full-scale flow was considered. No coherent vortex shedding was found on the model, in agreement with full-scale measurements.