Applications of the Virtual Element Method to Discrete Fracture Networks

We put forward in this work several novel applications of the Virtual Element Method in the context of Discrete Fracture Networks. A family of methods is presented here for solving Darcy flow, time dependent-problems and the complete transport equation in both diffusion-dominated and convection-dominated problems. We present as well an implementation of mixed Virtual Elements in the context of Discrete Fracture Networks

Efficient combustion parameter prediction and performance optimization for a diesel engine with a low throughput combustion model

In this work, an efficient implementation of a zero-dimensional model is described for the estimation of key engine parameters for combustion control in compression-ignition engines. The direct problems of the estimation of the angle of 50% of fuel mass fraction burnt (MFB50) and of the mean effective pressure (IMEP) are addressed as well as the inverse problems of determining optimal start of injection (SOI) timing for target values of MFB50 and IMEP. The main focus is on the computational cost of the algorithms proposed, designed in order to keep the number of operations as low as possible without compromising the applicability of the methods to different engine configurations and operation points. Execution time of the order of few milliseconds are achieved for parameters prediction and of the order of one tenth of a second for the optimization problems, such that an implementation in engine ECU for model-based control purposes can be envisaged

The virtual element method for Discrete Fracture Network flow and transport simulations

We discuss several issues concerning the application of the Virtual Element Method (VEM) to the flow in fractured media modeled by the Discrete Fracture Network (DFN) model. Due to the stochastic nature of the computational domains, several geometrical complexities make the computations very challenging. The geometrical flexibility provided by the Virtual Element Method can be exploited to mutually couple local problems, either by resorting to a Mortar approach, or by allowing for the global conformity of the local meshes, while keeping the computational cost under control. We describe these two approaches in detail and we test them on a realistic test case, showing the viability of the two approaches

The Virtual Element Method for large scale Discrete Fracture Network simulations: fracture-independent mesh generation

We consider the problem of underground flow simulations in fractured media. This is a large scale, heterogeneous multi-scale phenomenon involving very complex geological configurations. Within the Discrete Fracture Network (DFN) model, we focus on the resolution of the steady-state flow in large fracture networks. Exploiting the peculiarity of the Virtual Element Method (VEM), which allows the use of rather general polygonal mesh elements, we propose an approach for building a suitable mesh for representing the solution on DFNs

The Virtual Element Method for large scale Discrete Fracture Network simulations: fracture-independent mesh generation

We consider the problem of underground flow simulations in fractured media. This is a large scale, heterogeneous multi-scale phenomenon involving very complex geological configurations. Within the Discrete Fracture Network (DFN) model, we focus on the resolution of the steady-state flow in large fracture networks. Exploiting the peculiarity of the Virtual Element Method (VEM), which allows the use of rather general polygonal mesh elements, we propose an approach for building a suitable mesh for representing the solution on DFNs

A family of methods with arbitrary meshes for DFN flow simulations

A new approach for the simulation of the steady-state flow in discrete fracture networks is presented, along with new numerical results on complex configurations. The networks considered may have an arbitrary number of planar polygonal fractures with random spatial orientation, size and hydrological properties. The method is based on the minimization of a proper functional to enforce matching conditions at fracture intersections; the solution of the flow equations on each fracture of the network is carried on independently from the solution on the other fractures. Non-conforming Finite Element meshes on the fractures are allowed. Different discretization strategies can be used and mixed in order to improve approximation properties and provide high levels of accuracy. Extended Finite Elements and Virtual Elements have been successfully explored, thus a great flexibility is ensured when dealing with complex DFN configurations. The process for generating a suitable mesh is independently performed for each fracture, without requiring conformity at intersections, thus being extremely reliable and computationally inexpensive. The overall method is parallel oriented, thus providing an efficient handling of problem size and complexity. This is of paramount importance for massive simulations for uncertainty quantification in stochastically generated networks, or in the resolution of networks at very large scale and/or composed of even millions of fractures. The modular structure of the algorithm can easily embody other physical models for the description of flow regimes of increasing complexit

Development of the CMS detector for the CERN LHC Run 3

International audienceSince the initial data taking of the CERN LHC, the CMS experiment has undergone substantial upgrades and improvements. This paper discusses the CMS detector as it is configured for the third data-taking period of the CERN LHC, Run 3, which started in 2022. The entire silicon pixel tracking detector was replaced. A new powering system for the superconducting solenoid was installed. The electronics of the hadron calorimeter was upgraded. All the muon electronic systems were upgraded, and new muon detector stations were added, including a gas electron multiplier detector. The precision proton spectrometer was upgraded. The dedicated luminosity detectors and the beam loss monitor were refurbished. Substantial improvements to the trigger, data acquisition, software, and computing systems were also implemented, including a new hybrid CPU/GPU farm for the high-level trigger

Search for high-mass exclusive diphoton production with tagged protons in proton-proton collisions at s= \sqrt{s} = 13 TeV

A search is presented for high-mass exclusive diphoton production via photon-photon fusion in proton-proton collisions at $\sqrt{s} =$ 13 TeV in events where both protons survive the interaction. The analysis utilizes data corresponding to an integrated luminosity of 103 fb$^{-1}$ collected in 2016--2018 with the central CMS detector and the CMS and TOTEM precision proton spectrometer (PPS). Events that have two photons with high transverse momenta ($p_{\mathrm{T}}^{\gamma} >$ 100 GeV), back-to-back in azimuth, and with a large diphoton invariant mass ($m_{\gamma\gamma} >$ 350 GeV) are selected. To remove the dominant inclusive diphoton backgrounds, the kinematic properties of the protons detected in PPS are required to match those of the central diphoton system. Only events having opposite-side forward protons detected with a fractional momentum loss between 0.035 and 0.15 (0.18) for the detectors on the negative (positive) side of CMS are considered. One exclusive diphoton candidate is observed for an expected background of 1.1 events. Limits at 95% confidence level are derived for the four-photon anomalous coupling parameters $|\zeta_1|$ 100 GeV), back-to-back in azimuth, and with a large diphoton invariant mass ($m_{\gamma\gamma} \gt$ 350 GeV) are selected. To remove the dominant inclusive diphoton backgrounds, the kinematic properties of the protons detected in PPS are required to match those of the central diphoton system. Only events having opposite-side forward protons detected with a fractional momentum loss between 0.035 and 0.15 (0.18) for the detectors on the negative (positive) side of CMS are considered. One exclusive diphoton candidate is observed for an expected background of 1.1 events. Limits at 95% confidence level are derived for the four-photon anomalous coupling parameters $\lvert\zeta_1\rvert \lt$ 0.073 TeV$^{-4}$ and $\lvert\zeta_2\rvert \lt$ 0.15 TeV$^{-4}$, using an effective field theory. Additionally, upper limits are placed on the production of axion-like particles with coupling strength to photons $f^{-1}$ that varies from 0.03 TeV$^{-1}$ to 1 TeV$^{-1}$ over the mass range from 500 to 2000 GeV

Search for high-mass exclusive diphoton production with tagged protons in proton-proton collisions at s\sqrt{s} = 13 TeV

International audienceA search is presented for high-mass exclusive diphoton production via photon-photon fusion in proton-proton collisions at $\sqrt{s}$ = 13 TeV in events where both protons survive the interaction. The analysis utilizes data corresponding to an integrated luminosity of 103 fb$^{-1}$ collected in 2016-2018 with the central CMS detector and the CMS and TOTEM precision proton spectrometer (PPS). Events that have two photons with high transverse momenta ($p_\mathrm{T}^\gamma >$ 100 GeV), back-to-back in azimuth, and with a large diphoton invariant mass ($m_{\gamma\gamma} \gt$ 350 GeV) are selected. To remove the dominant inclusive diphoton backgrounds, the kinematic properties of the protons detected in PPS are required to match those of the central diphoton system. Only events having opposite-side forward protons detected with a fractional momentum loss between 0.035 and 0.15 (0.18) for the detectors on the negative (positive) side of CMS are considered. One exclusive diphoton candidate is observed for an expected background of 1.1 events. Limits at 95% confidence level are derived for the four-photon anomalous coupling parameters $\lvert\zeta_1\rvert \lt$ 0.073 TeV$^{-4}$ and $\lvert\zeta_2\rvert \lt$ 0.15 TeV$^{-4}$, using an effective field theory. Additionally, upper limits are placed on the production of axion-like particles with coupling strength to photons $f^{-1}$ that varies from 0.03 TeV$^{-1}$ to 1 TeV$^{-1}$ over the mass range from 500 to 2000 GeV