International Benchmark Exercise Research Articles

Large-eddy simulation on two-liquid mixing in the horizontal leg and downcomer (the TAMU-CFD Benchmark), with respect to fluctuation behavior of liquid concentration

Pressurized Thermal Shock (PTS) is induced potentially by the rapid cooling of the cold-leg and downcomer wall in the primary system of a Pressurized Water Reactor (PWR) due to the initiation of Emergency Core Cooling System (ECCS). Thus, fluids mixing in a horizontal cold-leg and downcomer should be predicted accurately. However, turbulence production and damping often hinders this prediction due to the presence of the density gradients. Hence, the Fifth International Benchmark Exercise, “the cold-leg mixing Computational Fluid Dynamics (CFD) Benchmark,” was conducted under the support of OECD/NEA. The experiment was designed for visualization of the mixing phenomena of two liquids with different densities. The heavy liquid was a simulant of cold water from ECCS, in a horizontal leg and downcomer. We used the Large-eddy Simulation (LES) to investigate the time fluctuation behaviors of velocity and liquid concentration. The CFD simulation was performed with two turbulence models and three different numerical meshes. We investigated the characteristics of the appearance frequency of the heavy liquid concentration with the statistical method. Based on our findings, we propose further experiments and numerical investigations to understand the fluid mixing phenomena related to PTS.

Novel test-rig for compaction behaviour analysis of textile reinforcements for improved RTM-process replication

This paper presents a novel testing method for evaluating the compaction behaviour of textile reinforcements in the context of liquid composite moulding processes. The existing testing approach utilizing pre-saturated samples (ex-ante) fails to accurately represent the unsaturated state of samples during vacuum infusion or resin transfer moulding (RTM) processes, leading to unreliable results and potential discrepancies with simulation. To address this limitation, a newly designed test-rig is introduced in this study, enabling compressibility testing based on real process specifications. The proposed method allows for the measurement of both dry and wet compression characteristics using a single specimen through in-situ impregnation of the materials under compressive load. Moreover, the test-rig enables tests according to ex-ante specifications, facilitating direct comparison with the proposed in-situ method. Finally, the test-rig allows for compressibility tests at elevated temperatures up to 200 °C. This is of particular relevance for studying the compaction behaviour of bindered technical fabrics. Preliminary comparative tests demonstrate excellent agreement between the results obtained using the ex-ante method under the 2020 international benchmark exercise and the novel in-situ impregnation method. This confirms the validity and reliability of the results obtained through the proposed testing method. By providing a more realistic representation of the compaction behaviour of textile reinforcements, the novel approach presented in this study offers valuable insights for optimizing liquid composite moulding processes and improving the accuracy of simulation models.

Experimental characterisation of textile compaction response: A benchmark exercise

This paper reports the results of an international benchmark exercise on the measurement of fibre bed compaction behaviour. The aim was to identify aspects of the test method critical to obtain reliable results and to arrive at a recommended test procedure for fibre bed compaction measurements. A glass fibre 2/2 twill weave and a biaxial (±45°) glass fibre non-crimp fabric (NCF) were tested in dry and wet conditions. All participants used the same testing procedure but were allowed to use the testing frame, the fixture and sample geometry of their choice. The results showed a large scatter in the maximum compaction stress between participants at the given target thickness, with coefficients of variation ranging from 38% to 58%. Statistical analysis of data indicated that wetting of the specimen significantly affected the scatter in results for the woven fabric, but not for the NCF. This is related to the fibre mobility in the architectures in both fabrics. As isolating the effect of other test parameters on the results was not possible, no statistically significant effect of other test parameters could be proven. The high sensitivity of the recorded compaction pressure near the minimum specimen thickness to changes in specimen thickness suggests that small uncertainties in thickness can result in large variations in the maximum value of the compaction stress. Hence, it is suspected that the thickness measurement technique used may have an effect on the scatter.

Methodology of dry and wet compressibility measurement

This paper describes a methodology to obtain and analyse data in composite reinforcement fabric compaction tests in dry and saturated conditions using a standard electromechanical test machine and an indirect thickness measurement method.The main goal is the identification of machine compliance sources and the understanding of its effects in typical compression tests and compression with relaxation stage tests. This methodology was used in the first international compressibility benchmark exercise promoted by NPL (National Physics Laboratory, UK) in the years 2017 and 2018. The methodology accounts for the test setup compliance and evaluates errors in fabric thickness measurements in the range of tens of microns especially during the relaxation phase. Overall, the setup compliance and data analysis strategy proved to have a significant effect on the data if not properly accounted for.

Evaluation of RANS k – ε calculations for turbulent stably stratified layers based on GEMIX experiments using the CUPID code

In the present study, the prediction capability of RANS k − ε turbulence models implemented in the CUPID code which has been developed by KAERI for nuclear safety assessment was evaluated based on GEMIX (GEneric MIxing eXperiment) experiments.The present study is a part of the work participating in the International Benchmark Exercise based on the GEMIX experiment done by OECD/NEA and PSI. The GEMIX experiment performed by PSI is focused on the basic turbulent mixing mechanisms in unstratified and stably stratified conditions.For both the unstratified and stably stratified conditions considered, the RANS k − ε turbulence model calculations show reasonably good agreement with experimental data for time-averaged axial velocity. However, the turbulent kinetic energy measured in the GEMIX experiment was not well predicted by RANS k − ε model, which becomes worse in the stably stratified conditions.The influence of grid resolution and the inclusion of buoyancy terms in k − ε model were not significant. Also, the different RANS models such as SST and RST showed similar results to k − ε model, which indicates the fact that the drawbacks of k − ε model such as the isotropic feature do not play significant role of underestimation of turbulent kinetic energy in the present GEMIX benchmark problems. On the other hand, with the tuning of the model constant Cμ based on the experimental data of k and uv¯, the prediction capability of RANS turbulence models is shown to improve the estimation of the turbulent kinetic energy in stably stratified conditions, which is consistent with the turbulence modeling theory reported in the literature. The present sensitivity approach for Cμ could be elaborated by a calibration approach in order to improve the prediction capability of the current RANS k − ε calculations. As has been seen by the RANS society, such a pragmatic modeling could be a successful means.

INVESTIGATION INTO THE POTENTIAL OF SINGLE PHOTON AIRBORNE LASER SCANNING TECHNOLOGY

Abstract. Following several years of incremental technological developments in airborne laser scanning, the field is currently witnessing potentially revolutionary change through the introduction of new technologies, namely Single Photon (SP) and Geiger-Mode (GM) lidar. These new sensors potentially provide more efficient approaches to perform high-resolution 3D mapping, but seemingly to the detriment of accuracy and noise. Despite concerns, the technology is perceived to offer higher efficiency with respect to conventional airborne laser scanning and additional 3D mapping capability in terms of swath width, spatial resolution, acquisition time and density of range returns. These developments have led to some European National Mapping and Cadastral Agencies (NMCAs) to consider a potential change in their production pipelines, while some mapping companies are contemplating upgrading their existing airborne sensor systems. However, few open datasets and experiences are available to inform such decisions, and the community is keen to learn more about the technology and its deployment for 3D territorial mapping. These facts and considerations motivated EuroSDR Commission 1 to launch a new initiative in 2018 to better understand, explore and report to its NMCA membership the developments in SP and GM technologies. This paper describes the activities that have thus far been conducted as part of this EuroSDR initiative, comprising: a global on-line questionnaire into awareness of the technology; a preliminary investigation into a Leica SPL100 dataset of Easton, USA; and a community workshop at which a proposal to run an international benchmarking exercise was discussed.

Seismic fragility analysis of pressurized piping systems considering ratcheting: A case study

In the present paper, a methodology is presented for seismic fragility analysis of pressurized piping systems considering ratcheting. The methodology is applied for a typical piping system, which was considered for an international benchmark exercise on seismic margin assessment. A numerical tool, which was earlier validated with experimental results on ratcheting in pressurized piping components and systems, is used for evaluation of strains in piping system. Variations in damping and natural frequency of the piping system are considered for the fragility assessment in addition to ground motion variability. Twenty intra-plate earthquake records are considered for ground motion variability. Three performance levels are considered for the assessment: first one is the present design stress limit, remaining two are strain limits based on codal guidance and experiments. Response surface techniques in conjunction with Monte Carlo simulations are used for fragility evaluation.

Inelastic soil amplification in three sites during the Tokachi-oki MJMA 8.0 earthquake

Earthquake case histories of soil response in the last half century have revealed the nonlinear behavior of soils under strong shaking. Over the years numerous efforts have been made to represent realistically soil behavior in the nonlinear range. In the aftermath of an international benchmark exercise (PRENOLIN) aimed at verifying 23 nonlinear codes and then validating them against the recorded seismic responses of two soil sites, this paper investigates the response of 3 soil sites in Hokkaido, Japan, shaken by the Tokachi-oki 2003 earthquake. Surface and deep (“in-borehole”) accelerographs recorded the event at each site. The objective of our study is to see if available nonlinear codes, without any after-the-event calibration and with imperfect knowledge of the soil layer properties, can lead to practically acceptable results. Before embarking into the nonlinear analyses, the linear response to an aftershock is first simulated with reasonable success. Then, using three different nonlinear 1D soil-amplification codes, which incorporate different constitutive relations, numerical wave propagation analyses are performed for each site, excited with the motion recorded in each borehole (at the depth of the presumed bedrock). Computed results in the form of acceleration time histories and response spectra for the ground surface are systematically compared with the respective recorded motions. It is found that the numerical codes perform generally quite satisfactorily. Exceptions are discussed in the light of the other research findings.

Playing the game: explaining how Luxembourg has responded to the Networked Readiness Index

PurposeOver the past decade or so, successive Luxembourgish governments have sought to develop the country’s information and communication technologies (ICT) sector. In this paper, the authors will aim to examine how Luxembourg’s relative position in the “Networked Readiness Index” (NRI), a key international benchmarking exercise published by the World Economic Forum, has evolved over time as these ambitions have been achieved. The paper also explores what policy initiatives could be implemented to further improve Luxembourg’s ranking in the NRI.Design/methodology/approachA longitudinal case study-based approach, drawing on secondary data and the annual publication of the NRI between 2003 and 2016, was adopted.FindingsLuxembourg’s position in the NRI has improved from 27th in 2003, so that it now ranks among the top ten countries in the world. In particular, Luxembourg has substantially improved its position with regards to “infrastructure” and “international connectivity”. However, there are also areas, mainly linked to education, the provision of human resources and policies that allow for and stimulate entrepreneurship where further improvements appear possible.Social implicationsThe paper highlights the need for an overall, holistic, ICT development strategy. Such a strategy would cover not only cover infrastructural and technical aspects but also educational, social, regulatory and economic issues as well.Originality/valueThe paper charts the evolution over time of Luxembourg’s position in an important international ICT index and identifies its current strengths and weaknesses in terms of the different elements that constitute the NRI. This paper represents the first attempt to investigate the position of a small country, which are often overlooked in the literature, in terms of its changing position and the policies developed and enacted by a national government.

Nozzle Geometry Effect on Stratified Layer Erosion by Vertical Turbulent Jet

Knowledge of the nuclear power plants (NPPs) containment atmosphere composition in the course of a severe accident is crucial for the effective design and positioning of the hydrogen explosion countermeasures. This composition strongly depends on containment flows which may include turbulent jet mixing in the presence of buoyancy, jet impingement onto the stratified layer, stable stratification layer erosion, steam condensation on the walls of the containment, condensation by emergency spray systems and other processes. Thus, in modeling of containment flows, it is essential to correctly predict these effects. In particular, a proper prediction of the turbulent jet behavior before it reaches the stably stratified layer is critical for the correct prediction of its mixing and impingement. Accordingly, validation study is presented for free neutral and buoyancy-affected turbulent jets, based on well-known experimental results from the literature. This study allows for the choice of a proper turbulence model to be applied for containment flow simulations. Furthermore, the jet behavior strongly depends on the issuing geometry. A comparative study of erosion process for the conditions similar to the ones of international benchmark exercise (IBE-3) is presented for different jet nozzle shapes.

Synthesis of the OECD/NEA-PSI CFD benchmark exercise

The third International Benchmark Exercise (IBE-3) conducted under the auspices of OECD/NEA is based on the comparison of blind CFD simulations with experimental data addressing the erosion of a stratified layer by an off-axis buoyant jet in a large vessel. The numerical benchmark exercise is based on a dedicated experiment in the PANDA facility conducted at the Paul Scherrer Institut (PSI) in Switzerland, using only one vessel. The use of non-prototypical fluids (i.e. helium as simulant for hydrogen, and air as simulant for steam), and the consequent absence of the complex physical effects produced by steam condensation enhanced the suitability of the data for CFD validation purposes. The test started with a helium–air layer at the top of the vessel and air in the lower part. The helium-rich layer was gradually eroded by a low-momentum air/helium jet emerging at a lower elevation. Blind calculation results were submitted by nineteen participants, and the calculation results have been compared with the PANDA data. This report, adopting the format of the reports for the two previous exercises, includes a ranking of the contributions, where the largest weight is given to the time progression of the erosion of the helium-rich layer. In accordance with the limited scope of the benchmark exercise, this report is more a collection of comparisons between calculated results and data than a synthesis. Therefore, the few conclusions are based on the mere observation of the agreement of the various submissions with the test result, and do not entail any interpretation of the discrepancies, which is left to the individual participants.

Analysis of a gas stratification break-up by a vertical jet using the GOTHIC code

During a severe accident in light water reactor (LWR), hydrogen concentration can overpass the flammability limits locally, so the correct simulation of its behavior during a release is critical. The capability assessment of computational fluid dynamics tools to calculate the hydrogen distribution under different conditions has been the focus of intense research worldwide. In this context, the OECD/NEA conducted an international benchmark exercise (IBE-3), which was focused on the break-up of a stratified layer of a light gas by a vertical jet. The participants performed their simulations before the experiment data was released. When the data was released, it was noticed that a combination of several parameters like the mesh, turbulence model or solver controls were responsible for the broad differences between the participants’ results. To obtain information about how each parameter affects the simulation, a post-test sensitivity analysis has been done by the UPM. In this paper, the IBE-3 experiment simulation with GOTHIC 8.0 is presented along with extensive sensitivity analyses of the relevant parameters. The first objective of the work is to test the capability of GOTHIC 8.0 to simulate properly a gas stratification break-up by a vertical jet with a relatively coarse mesh. The second objective of the paper is to relate each sensitivity parameter with each other and with the experiment through the Parameter Influence Chart, a helpful tool specially designed for this purpose.

Transformation of water resource management: a case study of the South-to-North Water Diversion project

Water transformation plays a crucial role in the rational allocation and avoiding over-exploitation of natural resources. Mega water transformation project will not only bring opportunities for ecological and economical use of water resources, but also contribute towards regional industrial and societal transformations. The scarcity of water is a serious issue for north China, accordingly the Chinese government decided to implement the South-to-North Water Diversion project in order to transfer water from the water rich south China to China's northern region. The South-to-North Water Diversion project is the largest water diversion project in the world involving significant long distance and inter-basin water transfer features. The management of this mega project faced a number of significant challenges as it had to contend with a variety of issues including politics, the economy, society, local culture, the environment and the local ecology. This project has also drawn global attention to the question of how to coordinate, manage and implement the world's largest water resource project. This study focuses on management practices of the South-to-North Water Diversion project by investigating the project's eastern and central routes. The three project management approaches that were used in this project, i.e. project owner direct management, project consignment management, and agent construction management (Daijianzhi) were investigated. Management regulations, control measures and common issues associated with the South-to-North Water Diversion project were also examined. These included: land acquisition and resettlement, bidding and tendering, construction supervision, quality management, cost management and schedule management. A questionnaire survey was conducted with key project participants in order to identify the key factors that contribute towards cost overruns and delays in the project. This is one of very limited number of studies which have in-depth investigation of mega water transformation projects in a systematic manner. The findings are expected to assist both academics and industry practitioners gain a better understanding of management practices in this mega water transformation project. This is particularly useful as the project team has to deal with a variety of sustainability related issues apart from traditional project management duties. Similarly, the lessons learnt from this case study will provide a valuable reference for the management of mega engineering projects and act as useful inputs for an international benchmarking exercise.

RANS analyses on erosion behavior of density stratification consisted of helium–air mixture gas by a low momentum vertical buoyant jet in the PANDA test facility, the third international benchmark exercise (IBE-3)

Density stratification in the reactor containment vessel is an important phenomenon on an issue of hydrogen safety. The Japan Atomic Energy Agency (JAEA) has started the ROSA-SA project on containment thermal hydraulics. As a part of the activity, we participated in the third international CFD benchmark exercise (IBE-3) focused on density stratification erosion by a vertical buoyant jet in containment vessel. This paper shows our approach for the IBE-3, focusing on the turbulence transport phenomena in eroding the density stratification and introducing modified turbulence models for improvement of the CFD analyses. For this analysis, we modified the CFD code OpenFOAM by using two turbulence models; the Kato and Launder modification to estimate turbulent kinetic energy production around a stagnation point, and the Katsuki model to consider turbulence damping in density stratification. As a result, the modified code predicted well the experimental data. The importance of turbulence transport modeling is also discussed using the calculation results.

Turbulent mixing in a rod bundle with vaned spacer grids: OECD/NEA–KAERI CFD benchmark exercise test

An experimental study titled the 2nd International Benchmark Exercise (IBE-2) has been conducted to provide high-precision data of detailed turbulent flow mixing in a rod bundle for validating the CFD codes being used widely in the nuclear power industry. A 5×5 rod bundle having mixing spacer grids was adopted as a test rig, and was contained in a square flow housing with a 170mm side length and 4670mm length. The 25 rods in a bundle have dimensions of 25.4mm in outer diameter and a 3863mm length. The benchmark experiments have been performed at the MATiS-H water loop facility in KAERI. The axial bulk velocity in a rod bundle was maintained at about 1.50m/s (equivalent to Re ∼50,000) with loop conditions of 35°C and 1.57bar measured upstream of the spacer during the experiments. Detailed measurements of the turbulent flow in the subchannels were accomplished using 2-D LDA at four different distances (0.5, 1, 4 and 10DH) from the downstream of the mixing spacer grid. The upstream flow profiles also have been measured at the inlet of the mixing spacer grid for the inlet boundary condition. Precise measurements of the lateral and axial velocities in the subchannels are presented at four downstream distances, as well as the inlet from the mixing spacer grid of two types. Turbulence intensities and vorticities in the subchannels are also evaluated from the velocity measurements.

Synthesis of the turbulent mixing in a rod bundle with vaned spacer grids based on the OECD-KAERI CFD benchmark exercise

The second international CFD benchmark exercise on turbulent mixing in a rod bundle has been launched by OECD/NEA, to validate relevant CFD (Computational Fluid Dynamics) codes and develop problem-specific Best Practice Guidelines (BPG) based on the KAERI (Korea Atomic Energy Research Institute) MATiS-H experiments on the turbulent mixing in a 5×5 rod array having two different types of vaned spacer grids: split and swirl types. For this 2nd international benchmark exercise (IBE-2), the MATiS-H testing provided a unique set of experimental data such as axial and lateral velocity components, turbulent intensity, and vorticity information. Blind CFD calculation results were submitted by twenty-five (25) participants to KAERI, who is the host organization of the IBE-2, and then analyzed and synthesized by comparing them with the MATiS-H data. Based on the synthesis of the results from both the experiments and blind CFD calculations for the IBE-2, and also by comparing with the IBE-1 benchmark exercise on the mixing in a T-junction, useful information for simulating this kind of complicated physical problem in a rod bundle was obtained. And some additional Best Practice Guidelines (BPG) are newly proposed. A summary of the synthesis results obtained in the IBE-2 is presented in this paper.

A CFD benchmarking exercise based on flow mixing in a T-junction

The paper describes an international benchmarking exercise, sponsored by the OECD Nuclear Energy Agency (NEA), aimed at testing the ability of state-of-the-art computational fluid dynamics (CFD) codes to predict the important fluid flow parameters affecting high-cycle thermal fatigue induced by turbulent mixing in T-junctions. The results from numerical simulations are compared to measured data from an experiment performed at 1:2 scale by Vattenfall Research and Development, Älvkarleby, Sweden. The test data were released only at the end of the exercise making this a truly blind CFD-validation benchmark. Details of the organizational procedures, the experimental set-up and instrumentation, the different modeling approaches adopted, synthesis of results, and overall conclusions and perspectives are presented.

Computation of the Couplex-Gaz Exercise with TOUGH2-MP: Hydrogen Flow and Transport in the Pore Water of a Low-Permeability Clay Rock Hosting a Nuclear Waste Repository

Significant quantities of hydrogen can be produced by the corrosion of metal components. It is necessary to forecast gas migration and pressure buildup in the context of deep geological radioactive waste disposal. One of the major problems in representing gas migration in a radioactive waste repository is that of simultaneously modeling all gas sources and complex transfer pathways constituted by the network of underground drifts and the surrounding low-permeability rock. In 2006, the French National Agency for Radioactive Waste Management launched an international multiphase flow simulation benchmark exercise for modeling such a two-phase (gas and liquid) flow system. The exercise was designed to compare the performance of the numerical methods being used to resolve the designed problems. This paper presents the results of test case 2 of the exercise completed by the authors. The three-dimensional model represents a fraction of a repository for long-lived radioactive waste in a clay rock. The model simulates ambient pressure and flow conditions (considering influence of site evacuation on the flow system) after placement of wastes, with full consideration of two-phase initial and boundary conditions. Isothermal conditions are assumed. Time-dependent gas sources are applied to the model. Since the natural environment is unable to evacuate the entire amount of hydrogen in a dissolved state, a free gas phase is formed within the disposal structures. The model is used to study the dissipation of those gases to determine their influence on the transient phases throughout the lifetime of the repository, and to investigate possible pressure buildup, which may introduce a risk of damage to the host rock. We use the model to investigate how the presence of gas in the repository influences the nature of water flow around the disposal structures and the resaturation (process of saturation increasing) transient processes after closure of the repository. The TOUGH2-MP code, a parallel multiphase flow simulator, has been adopted for this study.

Experimental determination of the permeability of textiles: A benchmark exercise

In this international permeability benchmark exercise, in-plane permeability data for two reinforcement fabrics, obtained using a total of 16 different experimental procedures, were compared. Although, for each procedure, the results appear consistent, different procedures result in a scatter of up to one order of magnitude in principal permeability values for each fabric at any given fibre volume fraction. The ratio of the principal permeability values varies by factors of up to 2. While experimental uncertainties and variability of the specimens affect the scatter in results for any single series of experiments, it is suspected that the main source of scatter in results from different procedures is related to human factors. Aiming at standardisation of measurement methods and interchangeability of results, “good practice” guidelines will be formulated in order to eliminate sources of scatter.

Home Parenteral Nutrition (HPN): An international benchmarking exercise

An abstract is not available for this content. As you have access to this content, full HTML content is provided on this page. A PDF of this content is also available in through the ‘Save PDF’ action button.