Selected Mathematical Models Describing Flow in Gas Pipelines

The main aim of simulation programs is to study the behavior of gas pipe networks in certain conditions. Solving a specified set of differential equations describing transient (unsteady) flow in a gas pipeline for the adopted parameters of load and supply will help us find out the value of pressure or flow rate at selected points or along selected sections of the network. Transient gas flow may be described by a set of simple or partial differential equations classified as hyperbolic or parabolic. Derivation of the mathematical model of transient gas flow involves certain simplifications, of which one-dimensional flow is most important. It is very important to determine the conditions of pipeline/transmission network operation in which the hyperbolic model and the parabolic model, respectively, should be used. Parabolic models can be solved numerically in a much simpler way and can be used to design simulation programs which allow us to calculate the network of any structure and any number of non-pipe elements. In some conditions, however, they describe the changes occurring in the network less accurately than hyperbolic models do. The need for analysis, control, and optimization of gas flows in high-pressure gas pipelines with complex structure increases significantly. Very often, the time allowed for analysis and making operational decisions is limited. Therefore, efficient models of unsteady gas flows and high-speed algorithms are essential.

Modeling in the OMNET ++ environment of connection processes in Wi-Fi networks

Предложен подход к разработке в среде OMNeT++ INET простейшей имитационной модели инфраструктурного режима функционирования Wi-Fi сети, который позволяет проводить подробный анализ функционирования таких сетей, а также строить и анализировать временные диаграммы взаимодействия всех элементов сети. Разработанную модель можно использовать как базовую для формирования более сложных моделей с произвольным числом мобильных клиентов, позволяя определять необходимое количество точек доступа и мест их размещения для обеспечения полноценного покрытия зоны мониторинга лесной территории. An approach to the development in the OMNeT ++ INET environment of the simplest simulation model of the infrastructure mode of Wi-Fi network operation is proposed, which allows a detailed analysis of the functioning of such networks, as well as to build and analyze the time diagram of the interaction of all network elements. The developed model can be used as a base for the formation of more complex models with an arbitrary number of mobile clients, allowing you to determine the required number of access points and their locations to ensure full coverage of the monitoring area of the forest area.

An Optimization-Based Orchestrator for Resource Access and Operation Management in Sliced 5G Core Networks

Network slicing is a promising technology that network operators can deploy the services by slices with heterogeneous quality of service (QoS) requirements. However, an orchestrator for network operation with efficient slice resource provisioning algorithms is essential. This work stands on Internet service provider (ISP) to design an orchestrator analyzing the critical influencing factors, namely access control, scheduling, and resource migration, to systematically evolve a sustainable network. The scalability and flexibility of resources are jointly considered. The resource management problem is formulated as a mixed-integer programming (MIP) problem. A solution approach based on Lagrangian relaxation (LR) is proposed for the orchestrator to make decisions to satisfy the high QoS applications. It can investigate the resources required for access control within a cost-efficient resource pool and consider allocating or migrating resources efficiently in each network slice. For high system utilization, the proposed mechanisms are modeled in a pay-as-you-go manner. Furthermore, the experiment results show that the proposed strategies perform the near-optimal system revenue to meet the QoS requirement by making decisions.

OSNR Prediction Based on Federal Learning in Multi-Domain Optical Networks

With the continuous expansion of the scale of optical communication network and the rapid increase of network traffic demand, the management form of multi-domain optical network has widely existed. OSNR is an important indicator to judge the quality of communication. It is very important to predict OSNR more accurately in a low-cost and energy-saving way in multi-domain optical networks. In this paper, a scheme of federal learning in multi-domain optical networks is proposed to improve the accuracy of the OSNR prediction. The main idea is to train hybrid machine learning model in each single domain, then the strategy of federal learning is used for optimization it in multi-domains. The performance of the proposed scheme is verified by simulation experiments. The strategy can alleviate the problems of data silos and model training set caused by multi-domain optical network. According to simulation result, when the amount of data reaches 5×103, adding this strategy will reduce the mean square error of the prediction model by about 18%. It can improve the performance of machine learning model, the ability of OSNR prediction and the reliability of network operation.

Multiscenario-Based Train Headway Analysis under Virtual Coupling System

Chinese high-speed railway has implemented large-scale network operation with an urgent need for capacity improvement. The concept of virtual coupling seems to be a promising solution that provides a new operational scenario for high-speed railway, where trains are formed into a cooperative convoy and run synchronously with small train headways. The train-following principles under the virtual coupling signalling are quite different from those under conventional train control systems. Therefore, train headway analysis for different operational scenarios should be carried out to ensure railway safety and evaluate capacity benefits brought by virtual coupling. This paper proposes a potential virtual coupling architecture with reference to ETCS/ERTMS specifications. We compare blocking time models under different train control systems, and eight typical train-following scenarios are investigated for virtual coupling, including train arrival and departure cases. A detailed multiscenario-based train headway analysis is provided based on the microscopic infrastructure of the station and technological characteristics of virtual coupling. All computational outcomes are based on the train dynamic motion model. A comparative analysis of train headways under virtual coupling and CTCS-3 is provided in the case study. Results show that train headways can be substantially reduced under virtual coupling and are related to the station infrastructure layout.

Assessment of a Broadband Differential Absorption Lidar (DIAL) for use in a ground-based measurement network

<p>Convective-scale forecasts require more detailed and continuous observational data of thermodynamic profiles and wind profiles in the atmospheric boundary layer (ABL) than currently provided. In order to meet these data requirements in the future, DWD evaluates various surface remote sensing systems targeted on ABL-profiling for routine network operation.</p> <p>One of the candidate systems in operation at the Observatory Lindenberg is a new pre-production broadband DIAL from Vaisala. DIAL instruments are well-established in research activities, but this instrument is developed for operationally providing water vapor profile observations in the ABL during all weather conditions. We present evaluation results of the DIAL’s operational performance regarding the quality of the water vapor profiles and report on its ability to monitor sub-grid scale processes, such as convection and associated weather phenomena. This includes comparisons with radiosounding observations (4 per day) over at least one year of continuous observations and additional comparisons with Raman lidar for a three-month period during summer 2021. Furthermore, we provide observation-minus-background statistics between the DIAL and the ICON limited area model (ICON-LAM) to evaluate the model performance, e.g. under convection, and to identify observational error sources.</p> <p>This contribution provides knowledge regarding the operational viability of the new pre-production broadband DIAL, its value for monitoring water vapour profiles 24/7 and ABL processes for future model applications.</p>

Rules of incidental operation risk propagation in metro networks under fully automatic operations mode

The frequent interruptions of network operation due to any incident suggest the necessity to study the rules of operational risk propagation in metro networks, especially under fully automatic operations mode. In this study, risk indicator computation models were developed by analyzing risk propagation processes within transfer stations and metro networks. Moreover, indicator variance rules for a transfer station and different structural networks were discussed and verified through simulation. After reviewing the simulation results, it was concluded that under the impacts of both sudden incident and peak passenger flow, the more the passengers coming from platform inlets, the longer the non-incidental line platform total train operation delay and the higher the crowding degree. However, train headway has little influence on non-incidental line platform risk development. With respect to incident risk propagation in a metro network, the propagation speed varies with network structure, wherein an annular-radial network is the fastest, a radial is moderately fast, and a grid-type network is the slowest. The conclusions are supposed to be supports for metro operation safety planning and network design.