A penalisation approach to simulate root compressors

The simulation of the unsteady flow field in root compressors requires to deal with several challenges related to the presence of moving parts and complex geometries. In the present work a penalisation approach applied to the compressible Navier- Stokes equations is investigated as a possible technique to perform this kind of simulations. In particular, the compressible Navier- Stokes equations are augmented by source terms which represent the effects of the body on the fluid and then they are integrated in both the fluid and solid domains. The presence of moving bodies is taken into account by a level set function. A validation based on a grid convergence study is performed on the flow around an impulsively started cylinder. A preliminary simulation of the flow field inside a root compressor is performed in order to predict the unsteady mass flow rate through the machine

Quality of Transmission Estimation for Planning of Disaggregated Optical Networks

Modern optical networks depend upon advanced software-defined networking (SDN) technologies, which in turn rely on a network abstraction to infer the quality of transmission (QoT). In general, the QoT estimation is based upon the generalized signal-to-noise ratio (GSNR), which takes into account the ASE noise, cross-phase modulation (XPM) and self-phase modulation (SPM) components of the nonlinear interference (NLI). Uniquely, the SPM accumulates coherently, causing the total amount of SNR degradation to depend upon the physical lightpath (LP) history, preventing a fully disaggregated GSNR degradation evaluation. As the current signal symbol rate are increasing, the SPM will provide a progressively more significant contribution to the SNR degradation. We propose a method to evaluate the equivalent SPM component of the NLI that is generated in each fiber span within an optical line system (OLS), independent of the history or configuration of the optical network

Modelling non-linear interference in non-periodic and disaggregated optical network segments

We investigate the generation of nonlinear interference (NLI) within two disaggregated transmission scenarios, each considering a chain of three distinct optical line systems that contain fibers with different dispersion values, with 400G-ZR+ 64 GBd transmission simulated using the split-step Fourier method. Firstly, by separating the NLI into its main constituents: the self- and cross-phase modulations, we investigate the impact of accumulated dispersion upon NLI generation and compensate for the coherent accumulation of the former to produce a model that is fully spectrally and spatially separable, including for alien wavelengths. Considering ideal and optimized in-line amplification, we calculate the amplified spontaneous emission noise and combine this value with the recovered NLI to obtain the generalized signal-to-noise ratio. We show that this disaggregated model provides accurate and conservative results for both transmission scenarios, showing that abstracting these signals with a Gaussian noise approximation always results in a conservative prediction, even for non-uniform fiber dispersion scenarios

Simulative assessment of non-linear interference generation within disaggregated optical line systems

Lightpaths within optical line systems (OLS)s that deploy coherent optical technologies are mainly impaired by two additive Gaussian disturbances: the amplified spontaneous emission (ASE) noise from the optical amplifiers and the non-linear interference (NLI) from fiber propagation, together with some amount of phase noise, typically compensated for bythe carrier phase estimator module within the digital signal processing (DSP) unit. The main obstacle in accurately modelling the physical layer of a disaggregated optical network arises from the spatially-coherent and spectrally-aggregated general behavior of the NLI generation.Within this paper, we perform an accurate split-step Fourier method (SSFM) physical layer simulation campaign over a wide range of fiber chromatic dispersion values that range from 2to 16.7 ps / (nm·km) and channel symbol rates from 32 GBd to 85 GBd. For all the explored scenarios, we first show that the NLI generation in an OLS can be spectrally disaggregated in a practical manner by considering a superposition of self-channel (SC) and cross-channel (XC) NLI components only. Secondly, by considering the span-by-span generalized signal-to-noise ratio (GSNR) deterioration, we show that the XC-NLI accumulation components can also be considered as spatially disaggregated, leaving the SC-NLI as the only spatial coherency contribution. Consequently, by appropriately managing these coherent NLI contributions, we find that it is possible to produce a conservative physical layer model that is both spectrally and spatially disaggregated

Inter-Band GSNR Degradations and Leading Impairments in C+L Band 400G Transmission

Wideband optical transmission presents an appealing solution to network throughput and capacity requirements, improving existing network architectures with minimally invasive upgrades. This framework provides new perspectives into quality of transmission (QoT) management as a result of inter-band effects; the QoT is commonly given by the generalized signal-to-noise ratio (GSNR). In this study we address the leading impairments in multi-band nonlinear transmission in a C+L scenario from an operational point of view, supported by mathematical models and simulations. From this approach we identify that stimulated Raman scattering (SRS) is the main contributor to inter-band effects and causes the main variation in the GSNR degradation; correspondingly, we show that the inter-band nonlinear interference (NLI) can be neglected in a C+L scenario

Observing cross-channel NLI generation in disaggregated optical line systems

We investigate spatially separated XPM generation in a wide variety of 400G-ZR$+$ 64GBd pump-and-probe simulations, demonstrating the existence of a per-span upper bound that depends solely upon accumulated dispersion

C+L-band Network Upgrade: Capacity and Energy Analyses with Different Transceivers

We investigate the trade-off between network capacity and energy consumption in optical transport networks with three different transceiver implementations. Also, we provide evidence that C+L-band systems have similar energy consumption while attaining comparable network capacity as adding a second optical fiber and using C-band only

Networking Performance of Power Optimized C+L+S Multiband Transmission

Both spatial-division multiplexing (SDM) and band-division multiplexing (BDM) emerge as possible solutions to increase the optical network capacity to support the traffic demand which has been rising over time. In this work, two different ROADM (Re-configurable Optical Add Drop Multiplexer) switching techniques, namely SDM-InS (Independent switching) and SDM-CCC (Core Continue Constant) are investigated and the resulting network capacity is compared with the BDM approach. In the BDM case, both L- and S-bands have been used in addition to C-band to increase the network capacity. The launch power is optimized to control the QoT (Quality of Transmission) summarized by the generalized SNR (GSNR) per channel. Due to: stimulated Raman scattering, frequency variation of loss, frequency variation of dispersion coefficient and noise figures, an optimum power tilt and offset are calculated for each band. We show that the total network capacity increased by ∼2× and ∼3×, when using the L-band and L+S-bands in addition to the C-band, respectively, in both a reference German and a reference US network. Additionally, it was also shown that using additional bands, the increase in network capacity is close to the result of using additional optical fibers in the SDM case