bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Analysis of a Heaving Point Absorber in Frequency Domain via Statistical Linearization
Authors: S. P. da Silva Leandro , Morishita Helio M. , Pesce Celso P. , Gonçalves Rodolfo T.
Published: November 2019

The majority of wave energy devices operate close to resonant conditions to enhance energy conversion resulting in large displacements. As a result, nonlinearities significantly contribute to the dynamics of the system. A typical approach to predict the behavior of the system and power output relies on the derivation of a mathematical model in the time domain to simulate the dynamics through some numerical codes. However, a relatively high computational demand is required for those simulations. In this regard, the present work deals with the nonlinearities in the frequency domain via Statistical Linearization. Two different power-take-off systems are investigated, a linear and a hydraulic one, and their mean power calculations are derived based on the Statistical Linearization. The reliability of the method is verified against the Power Spectrum Density (PSD) of nonlinear time domain simulations. Only the heave motion is analyzed, and several nonlinearities commonly reported for Point Absorbers (PA) were considered, such as cubic stiffness, geometric nonlinearities, drag forces, and Coulomb forces. The approach employed in this work offers a reliable estimation of body dynamics for all nonlinearities considered. In addition, the present method produced a fast estimation, which can be valuable for the assessment of several designs and sea load conditions.
Evaluation of Uncertainty of Damage Results in Experimental Modelling of Monopile Foundation Scour Protection
Authors: Wu Minghao , Arnout Jonas , Molina Ruiz Josep , Arboleda Chavez Carlos , Stratigaki Vasiliki , Troch Peter
Published: November 2019

The waves and currents acting near a monopile foundation will potentially lead to scour, which may affect the stability of the wind turbine. The design of scour protection against the seabed lowering around a wind turbine monopile foundation is an important issue for wind energy industries. Many laboratory tests have been carried out to investigate the relationship between the hydrodynamic conditions and the monopile foundation scour protection layer damage, and various design criteria have been proposed. However, the experimental uncertainty of the underlying test results has not been discussed in detail.

In the present research, small scale wave flume experiments of a 5m diameter monopile foundation scour protection under waves combined with currents in shallow water are described. Two groups of repetitive experiments are completed under the same wave and current conditions. The erosion development of the scour protection armor layer is measured by using a laser profiler and is evaluated based on three dimensional damage numbers. Together with visualization of the damage pattern, the damage analysis discusses the erosion in different subareas and the variances of the subarea damage number.

The analysis of the uncertainty of the erosion results based on two sets of repetitive tests has been carried out. Using the uncertainty analysis methodology stated in ISO GUM standard: JCGM 100-2008, the Type A uncertainty, calibration uncertainty and combined uncertainty of the experiment are evaluated separately. The Type A uncertainty gives an overall uncertainty level and it shows that higher uncertainty occurs in the regions where stronger vortices exist. The combined uncertainty is analyzed based on scour protection dynamic stability design formula. Analysis result shows that the uncertainty due to modelling is a major source of the total uncertainty. The study gives a preliminary result of uncertainty level in wave flume test of monopile scour protection and provides a reference for future experimental research.
Multi-Phase Simulation of Droplet Trajectories of Wave-Impact Sea Spray Over a Vessel
Authors: Mintu Shafiul A. , Molyneux David , Colbourne Bruce
Published: November 2019

Sea spray, generated by ship-wave collisions, is the main source of marine icing. In certain, but not all, circumstances a cloud of spray forms after a wave impacts a ship. The spray cloud comprises numerous water droplets of various sizes. These droplets are dispersed and transported over the vessel deck by the surrounding wind and fall onto the deck or into the ocean under the effect of gravity. The motion of these droplets is important since they determine the extent of the spray cloud and its duration over the deck, which consequently affects the distribution of icing accumulation on a ship in freezing weather. In this paper, a multi-phase air-water simulation of droplet trajectory is used to predict the cloud motion of various size droplets. A smooth particle hydrodynamics (SPH) computational fluid dynamics (CFD) model is implemented and the simulation is accelerated using GPU computing.

The field observation data is used to simulate the trajectory. The results of the simulations are compared with an available theoretical model and reasonable agreement is found. The inverse dependence of size and velocity for droplets after the breakup process is examined. The simulation results are consistent with the theoretical model in that neither the largest nor the smallest droplets reach the maximum height of the spray cloud, but the mid-size droplets do. The spray cloud spreads faster and crosses the front of the vessel quicker than predicted by the theoretical model. It is also found that the trajectory of a single droplet is significantly affected by surrounding droplets in a multi-droplet trajectory model. A mono-droplet theoretical trajectory model, therefore, is not as accurate as the multi-droplet CFD model.
Introducing a Novel MEG/EtOH Mixture to Improve Gas Hydrate Blockages Removal During Offshore Oil and Gas Production
Authors: Paz Paulo , Netto Theodoro Antoun
Published: November 2019

Offshore oil and gas production may present gas hydrate formation problems. Using thermodynamic hydrate inhibitors as methanol, mono ethylene glycol, (MEG), and ethanol among others to deal with these issues is frequent. The inhibition process initially consists of pumping thousands of barrels from topside to seabed in order to be injected into the reservoir or into the flowlines where the hydrates may form. Research has shown the difference between injecting MEG or Methanol. Methanol has a better performance dissolving hydrates and MEG can be cleaned and used again. A disadvantage for methanol is that part of it goes to the gas phase where is not useful for hydrate inhibition. Recently there has been proposed the possibility to mix them in order to increase their individual performance, which has been proved as satisfactory to both hydrate dissolving, and injection operation. In this study, the characteristics of current inhibition treatments and a new mixture of Ethanol and MEG were used to simulate the efficiency of the process to pump them from topside to seabed. To compare the mixture performance as a new hydrate inhibitor with the other THI treatments, data from real scenarios were used. The results can be used on the selection process for the THI pumping system, in order to optimize the needs of the gas hydrate inhibition system, in terms of power and storage on the platform.
A Hybrid Data-Driven Deep Learning Technique for Fluid-Structure Interaction
Authors: Miyanawala T. P. , Jaiman Rajeev K.
Published: November 2019

This paper is concerned with the development of a hybrid data-driven technique for unsteady fluid-structure interaction systems. The proposed data-driven technique combines the deep learning framework with a projection-based low-order modeling. While the deep learning provides low-dimensional approximations from datasets arising from black-box solvers, the projection-based model constructs the low-dimensional approximations by projecting the original high-dimensional model onto a low-dimensional subspace. Of particular interest of this paper is to predict the long time series of unsteady flow fields of a freely vibrating bluff-body subjected to wake-body synchronization. We consider convolutional neural networks (CNN) for the learning dynamics of wake-body interaction, which assemble layers of linear convolutions with nonlinear activations to automatically extract the low-dimensional flow features. Using the high-fidelity time series data from the stabilized finite element Navier-Stokes solver, we first project the dataset to a low-dimensional subspace by proper orthogonal decomposition (POD) technique. The time-dependent coefficients of the POD subspace are mapped to the flow field via a CNN with nonlinear rectification, and the CNN is iteratively trained using the stochastic gradient descent method to predict the POD time coefficient when a new flow field is fed to it. The time-averaged flow field, the POD basis vectors, and the trained CNN are used to predict the long time series of the flow fields and the flow predictions are quantitatively assessed with the full-order (high-dimensional) simulation data. The proposed POD-CNN model based on the data-driven approximation has a remarkable accuracy in the entire fluid domain including the highly nonlinear near wake region behind a freely vibrating bluff body.
Numerical Simulation of Submarine Self-Propulsion Based on Different Turbulent Simulation Models
Authors: Bai Tiechao , Wu Yongfeng , Wei Peng , Wang Shuang , Liu Liwei
Published: November 2019

Design requirements for submarines regarding resistance, maneuverability, stability and stealth tighten with each new generation. Fully understanding the hydrodynamics of the vessels is key if performance requirements need to be met. In this paper, the numerical simulation with three different turbulent models, Reynolds averaged Navier-Stokes (RANS) Realizable k-ε model, RANS SST (Menter’s Shear Stress Transport) k-ω model and the large eddy simulation (LES) are used to simulate the self-propulsion of DARPA SUBOFF submarine under V = 2.755m/s, and the simulation results are compared and analyzed. The comparisons show that the RANS method can be used to simulate the drag and pressure of submarine self-propulsion accurately. The surface pressure of LES is more accurate for fine flow field, the simulation of self-propelled parameters is less as accurate might because the mesh is not refine enough.
REEF3D Wave Generation Interface for Commercial CFD Codes
Authors: Pakozdi Csaba , Bihs Hans , Kamath Arun , Hermundstad Elin Marita
Published: November 2019

In recent years CFD developments have shown a trend to combine RANS CFD simulation with other methods such as wave theories or velocity potential based numerical wave tanks, in order to reduce to computation costs. This is however not a new approach, and there exists a large amount of literature about domain decomposition techniques describing a two way coupling between the RANS CFD models and other methods. One can also observe an increasing popularity in the use of a less sophisticated technique where different fluid solvers are combined with one-way coupling. In these methods a predefined solution is provided in the far-field (ignoring the structure), while a three-dimensional (3D) CFD simulation is applied in a limited zone near the structure. The predefined solution is used to specify the background far-field solution. The governing equations are extended by the addition of a source term. The published solutions use wave theory or a numerical wave tank where the predefined solution is calculated parallel to the RANS solver. In this way it is possible to reduce the interpolation inaccuracy and the amount of transferred data to the CFD simulation. The disadvantage of this technique is that the far field solver has to be prepared in order to run in parallel with the CFD solver. Due to the one way coupling it is possible to predefine this information in tables before the CFD simulation. This technique makes it possible to define a general interface between difference solvers without modifying existing codes. This paper presents such a technique where the predefined solution is stored into files. An interpolation function delivers all data to the far-field solution for the CFD simulation. The paper analyses the necessary accuracy of the interpolation and the costs of the input/output operation of the CFD simulation through several verification cases.
Effect of Tensile Pre-Strain on Collapse Pressure of Coated Linepipe
Authors: Sakimoto Takahiro , Handa Tsunehisa , Tajika Hisakazu , Murakami Yoshiaki , Kondo Joe
Published: November 2019

As offshore pipeline projects have expanded to deeper water regions with depths of more than 2,000 m, linepipes are required to have higher resistance against collapse by external pressure. Collapse resistance is mainly controlled by the pipe geometry and compressive yield strength. In UOE pipe, the compressive yield strength along the circumferential direction changes dramatically due to tensile pre-strain that occurs in pipe forming processes such as the expansion process. In order to improve the compressive yield strength of pipes, it is important to consider the Bauschinger effect caused by pipe expansion. As the mechanism of this effect, it is understood that internal stress is generated by the accumulation of dislocations, and this reduces reverse flow stress. Compressive yield strength is also changed by the thermal cycle associated with application of fusion-bond epoxy in pipe anti-corrosion coating by the induction heating process. In the typical thermal heat cycle of this coating process, the maximum heat temperature is from 200 °C to 250 °C. In this case, compressive yield strength increases as an effect of the thermal cycle, resulting in increased collapse resistance. Thus, for deep water application of UEO linepipe, it is important to clarify the conflicting effects of the Bauschinger effect and the thermal heat cycle on compressive yield strength. Based on this background, in this study, the combined effect of the Bauschinger effect and the thermal heat cycle on compressive stress is investigated by conducting tensile pre-strain tests and simulation of the thermal cycle associated with coating. Compressive yield strength was obtained for several pre-strain and thermal cycle conditions, and the collapse pressure was calculated by an FE analysis based on the obtained compressive yield strength. This study discusses the effect of tensile pre-strain on the collapse pressure of linepipes with these simulated thermal heat cycles.
Design Methodology for a Floating Offshore Wind Turbine Large-Scale Outdoor Prototype
Authors: Fontanella Alessandro , Taruffi Federico , Muggiasca Sara , Belloli Marco
Published: November 2019

This paper discusses the methodology introduced by the authors to design a large-scale wind turbine model starting from the DTU 10MW RWT. The wind turbine will be coupled with the model of a multi-purpose floating structure, designed within the EU H2020 Blue Growth Farm project, and it will be deployed at the Natural Ocean Engineering Laboratory (NOEL). In this paper the different strategies used to design the wind turbine model rotor, tower and nacelle are discussed, focusing on how it has been possible to reproduce the full-scale system aero-elastic response while ensuring the same functionalities of a real wind turbine.
The Vortex and Wall Fluctuating Pressure Around Submarine Sail Based on DDES Method
Authors: Luo Rui , Sun Yue , Zhang Hang , Zhan Jin , Cai Xiao
Published: November 2019

Vortex around ships is easy to cause noise, vibration and fatigue of propellers. In addition, the complexity and variability of vortex will also have a greater impact on sensors and detection equipment installed on the surface of the vehicle. It is necessary to carry out corresponding research. In this paper, the fluctuating pressure was numerically analyzed using improved DDES model. And applying overset grids to better capture vortices around submarine sail. The numerical study of a three-dimensional unsteady vortex structure was performed for calculation. There were two vortex tubes and some broken small vortices behind the sail. The simulation results showed that trailing vortices behind sail slightly swept up and the distance between two vortex tubes became larger.
Development of Elemental Technologies for Seafloor Mineral Processing of Seafloor Massive Sulfides
Authors: Nakajima Yasuharu , Yamamoto Joji , Takahashi Tomoko , Thornton Blair , Yamabe Yuta , Dodbiba Gjergj , Fujita Toyohisa
Published: November 2019

Seafloor Massive Sulfides have been expected to be future mineral resources. The grade of valuable metallic elements in ores of Seafloor Massive Sulfides is usually small percentage. If valuable minerals can be extracted from the ores on deep seafloor, the total mining cost can be reduced significantly. The authors proposed Seafloor Mineral Processing, where ores are to be ground into fine particles and separated into concentrates and tailings on seafloor. The Seafloor Mineral Processing system consists of processing units for unit operations such as grinding and separation. To investigate the applicability of flotation, which is a method to separate ore particles by using the difference in wettability of minerals, to the separation unit, measurements of contact angles of sulfide minerals at high pressures were carried out. The results suggested that the contact angles of the minerals would have relationships with pressure in depending on the kind of minerals and solutions. In addition, applying Laser-Induced breakdown Spectroscopy (LIBS), an optical method for elemental analysis, to measurement of metal grade of ore particles handled as slurry in the processing units was also investigated. Signals assigned to copper, zinc, and lead were successfully detected in the spectra obtained from ore particles in slurry flow.
Experimental Study on Ultimate Strength of Thin-Walled Square Tube Under Axial Compression
Authors: Zhou Hanwei , Zhu Ling , Zhang Shengming , Yu T. X.
Published: November 2019

There are many welded thin-walled square tube structures in ship structures. At present, researchers are mainly involved in axial compressive ultimate strength of square tubes with large aspect ratios. However, the study of square tubes with small aspect ratios on ultimate strength capacity have seldom been conducted. In order to study the ultimate strength capacity of thin-walled square tubes with small aspect ratio under axial compression, three welded thin-walled square tubes with different slenderness ratios were manufactured and studied in this paper. The ultimate strength of those models under axial compression were obtained experimentally. The experimental results were compared with numerical results performed by ABAQUS. The influence of slenderness ratios on the axial compressive ultimate strength of thin-walled square tubes is analyzed, and a feasible modelling of finite element method is proposed.
REDWIN Foundation Models for Integrated Dynamic Analyses of Offshore Wind Turbines
Authors: Page Ana M. , Norén-Cosgriff Karin , Skau Kristoffer S. , Kaynia Amir M.
Published: November 2019

Due to the complex nature of the loads on Offshore Wind Turbines (OWTs), accurate and optimized design of these structures require integrated simulation tools that can properly capture the various structural interactions governing the response. Considerable progress has been made in recent years on developing proper models for coupled aerodynamic and hydrodynamic loads together with advanced control systems for turbines. These efforts have resulted in a suite of aero-servo-hydro-elastic numerical simulation codes available to the industry. However, proper foundation models have been lagging behind in these tools despite availability of various advanced nonlinear models for foundations in general. This has led to uneconomical design of OWTs that have consistently failed to reproduce the measured natural frequencies and can negatively affect the design and structural performance of OWTs.

This paper presents a library of recently developed foundation models based on the theory of plasticity together with their verification against large-scale field test data. These models are cast in the framework of macro-elements that represent the nonlinear response of the soil-foundation system due to arbitrary coupled loads at the seabed. The paper also presents results of the numerical simulations of the dynamic response of a monopile-based OWT in the North Sea using an aero-servo-hydro-elastic code and comparison with the data collected from one of the instrumented OWTs in the field. It is further presented how the characteristics of the measured dynamic response change with loading over a long period and the way the response characteristics relate to the basic features of the developed models.
Study of the Relationship Between Oriented Downhole Dynamic Weight on Bit and Drilling Parameters in Coring Isotropic Natural and Synthetic Rocks
Authors: Abugharara Abdelsalam N. , Molgaard John , Hurich Charles A. , Butt Stephen D.
Published: November 2019

Coring natural rocks (granite) and synthetic rocks (rock like material, RLM) using diamond impregnated coring bit was performed by A rigid coring system. RLM and granite were previously tested to be isotropic rocks by the author [1, 2, 3, 4] A baseline procedure was developed for isotropic rock characterization [2] and this work is to contribute to the developed baseline procedure by considering downhole dynamic weight on bit (DDWOB). The drilling parameters involved in the analysis included rate of penetration (ROP) depth of cut (DOC), rpm, and torque. All parameters were studied as a function of DDWOB at 300 and 600 input rpm. A fully instrumented laboratory scale rotary drilling rig was used with 5 liter/minute water flow rate. Samples were first cored in 47.6 mm diameter in the desired orientations. Samples of granite were cored in two perpendicular directions (vertical and horizontal) and samples of RLM were cored in three directions including vertical, oblique, and horizontal. The coring experiments were performed using 25.4 mm diamond impregnated coring bit. At each input rpm and at each applied static weight, multiple coring runs were repeated and then averaged; therefore, each point of the displayed data was averaged of at least three repeated experiments at the same inputs. DDWOB was recorded by a load cell fixed beneath the sample holder and connected to a Data Acquisition System that records at 1000 HZ sampling rate. Several sensors were used to record the required data, including operational rotary speed, advancement of drill bit for ROP calculation, and motor current for torque measurement. Results showed similar trends in different orientations at the same inputs demonstrating RLM and granite isotropy. The results also showed the influence of DDWOB on ROP, DOC, rpm, and torque (TRQ) expanding the baseline procedure through considering DDWOB for isotropic rock characterization.
Ship As a Wave Buoy: Using Simulated Data to Train Neural Networks for Real Time Estimation of Relative Wave Direction
Authors: Mak Bart , Düz Bülent
Published: November 2019

Being able to give real time on-board advice, without depending on extensive sets of measured data, is the ultimate goal of the digital twin concept. Ideally, the models used in a digital twin only rely on current in-service data, although they have been built using simulated and possibly some measured data. Working with just the 6-DOF motions of a ship, can the local sea state reliably be estimated using the digital twin concept? Does a general model exist to do so, without the need to measure or simulate the particular ship?

In this paper, we discuss how simulations of an advancing ship, subjected to various sea states, can be used to estimate the relative wave direction from in-service motion measurements of the corresponding ship. Various types of neural networks are used and evaluated with simulated data and measured data. In order to study the generalization power of the neural networks, a range of ships has been simulated, with varying lengths, drafts and geometries. Neural networks have been trained on selections of the ships in this extended training set and evaluated on the remaining ships.

Results show that the developed neural networks give a remarkable performance in simulation data. Furthermore, generalization over geometry is very good, opening the door to train a general model for estimating sea state characteristics. Using the same model for in-service measurements does not perform well enough yet and further research is required. The paper will include discussion on possible causes for this performance gap and some promising ideas for future work.
Force Dynamics and Stationkeeping Costs for Multiline Anchor Systems in Floating Wind Farms With Different Spatial Parameters
Authors: Fontana Casey , Arwade Sanjay , DeGroot Don , Hallowell Spencer , Aubeny Charles , Diaz Brian , Landon Melissa , Ozmutlu Senol , Myers Andrew
Published: November 2019

While the offshore wind industry has shown a steady trend towards floating turbines, costs of these systems remain high. A multiline anchor concept may significantly reduce the high cost of floating wind, in which floating turbines share anchors. This work investigates the potential cost benefit of implementing a multiline anchor system relative to the conventional single-line anchor system over a range of spatial parameters. The OC4 DeepCwind semisubmersible platform is used to design catenary mooring systems for different water depths and turbine spacings. In all cases, the maximum anchor force in the 3-line anchor system is less than or equal to that of the single-line anchor system. Cost models for the mooring lines, anchors, installation and geotechnical site investigation are presented and discussed. In a 100-turbine farm, the multiline anchor system results in a 9–19% reduction in stationkeeping costs, with high and low estimates for the cost models additionally included. Larger reductions in the combined line and anchor cost result from mooring system configurations with smaller ratios of water depth to turbine spacing. Due to perimeter effects in the multiline configuration, larger cost reductions can be achieved for larger farm sizes.
Extreme Load Computational Fluid Dynamics Analysis and Verification for a Multibody Wave Energy Converter
Authors: van Rij Jennifer , Yu Yi-Hsiang , McCall Alan , Coe Ryan G.
Published: November 2019

A wave energy converter (WEC) must be designed to survive the extreme sea states that it will be subject to throughout its lifetime. Although there are many analysis methods and codes available to accomplish this, there are currently several engineering challenges to WEC survival design. Foremost, the computational design approach will typically involve a trade-off between accuracy and computational efficiency. Additionally, most computational fluid dynamics (CFD) codes are not ideally suited to modeling extreme events for WECs with multibody dynamics, power-take-off systems, and mooring systems. Finally, although WEC design standards and CFD guidelines are emerging, with the current immaturity of the WEC industry, they are not yet well established. In this study, loads on a 1:35-scale, moored, multibody WEC are evaluated with CFD. The CFD results are compared with results obtained from a computationally efficient, midfidelity model based on linearized potential flow hydrodynamics. For these model verification comparisons, both operational and survival configurations are considered. The extreme load results obtained, using both codes, indicate that the survival configuration successfully sheds loads during extreme sea states. It is also found that WEC-Sim, when appropriately applied, can provide reasonable load results, at a fraction of the computational expense of CFD. However, for the more extreme sea states, and for higher-order effects not included in the WEC-Sim model, the linear-based results have significant errors in comparison to the CFD-based results, and should be used judiciously.
Use of Tracer Particles for Tracking Fluid Interfaces in Primary Cementing
Authors: Taheri Amir , Ytrehus Jan David , Taghipour Ali , Lund Bjørnar , Lavrov Alexandre , Torsæter Malin
Published: November 2019

In this study, a new approach for detailed tracking of the interface between well fluid and cement by using particles is investigated. This can improve the quality of annular cementing of CO2 wells and thus the storage safety. For this purpose, the displacement mechanisms of Newtonian and non-Newtonian fluids in the annulus of vertical and inclined wells is investigated by using an experimental set-up with an eccentric annular geometry and by finite element analysis of an equivalent model with COMSOL Multiphysics solver. For more efficient displacement, the displacing fluid has a higher density than the displaced fluid, and the intermediate-buoyancy particles that reside at the interface between successive fluids are introduced into the models. Such particles must overcome strong secondary flows in order to travel with the interface.

Particle motions are investigated in different experimental and numerical models, and their effectiveness is investigated. The experimental results confirm that while the particles with a size of 425–500 um are unable to overcome the secondary flows in eccentric vertical models and track the interface, they can be useful for tracking the interface between two fluids in an eccentric model with a small inclination to the narrow side. CFD analysis investigates this behavior with more details and shows the effects of some parameters on the particle motions.
Application of Machine Learning Techniques As a Means of Mooring Integrity Monitoring
Authors: Gumley Jonathan M. , Marcollo Hayden , Wales Stuart , Potts Andrew E. , Carra Christopher J.
Published: November 2019

There is growing importance in the offshore floating production sector to develop reliable and robust means of continuously monitoring the integrity of mooring systems for FPSOs and FPUs, particularly in light of the upcoming introduction of API-RP-2MIM. Here, the limitations of the current range of monitoring techniques are discussed, including well established technologies such as load cells, sonar, or visual inspection, within the context of the growing mainstream acceptance of data science and machine learning. Due to the large fleet of floating production platforms currently in service, there is a need for a readily deployable solution that can be retrofitted to existing platforms to passively monitor the performance of floating assets on their moorings, for which machine learning based systems have particular advantages.

An earlier investigation conducted in 2016 on a shallow water, single point moored FPSO employed host facility data from in-service field measurements before and after a single mooring line failure event. This paper presents how the same machine learning techniques were applied to a deep water, semi taut, spread moored system where there was no host facility data available, therefore requiring a calibrated hydrodynamic numerical model to be used as the basis for the training data set.

The machine learning techniques applied to both real and synthetically generated data were successful in replicating the response of the original system, even with the latter subjected to different variations of artificial noise. Furthermore, utilizing a probability-based approach, it was demonstrated that replicating the response of the underlying system was a powerful technique for predicting changes in the mooring system.
Crack Growth due to Flow Mixing
Authors: Hannink M. H. C. , Blom F. J.
Published: November 2019

Turbulent mixing of hot and cold flows can lead to thermal fatigue of piping systems. Especially in primary pipework of nuclear power plants this is an important, safety related issue. Because the frequencies of the involved temperature fluctuations are generally too high to be detected well by common plant instrumentation, accurate numerical simulations are indispensable for a proper fatigue assessment. In this paper, fatigue crack growth analyses are presented for turbulent mixing in a T-junction. The temperatures in the fluid and the pipe were calculated by large eddy simulations with conjugate heat transfer, and the resulting stresses in the pipe by the finite element method. The stresses in the pipe wall have subsequently been used as input for crack growth analyses, which were performed according to ASME Boiler and Pressure Vessel Code, Section XI (2017). The time to a through-wall crack has been calculated for different temperature differences between the hot and cold flows. The analyses presented in this paper have been performed in preparation for the analyses of the EU project ATLAS+. In that project similar analyses will be performed on a different configuration.
Leakage of a High Temperature and High Pressure Flange Metal Gasket due to its Ratcheting in Alternating Pours of Rain
Authors: Chen Yanan , Wang Jianbo , Yu Chulin , Gao Bingjun
Published: November 2019

In the high pressure ethylene polymerization process, pipes transmitting reaction product are often bolt-flange connected with metal gaskets which demands high tightness. However ethylene and polyethylene was found leaking from a flange connection in the pipe out of a polymerization kettle after several pours of rain, which leads to an emergency shutdown. A finite element model was worked out to simulate the ratcheting of the metal gasket during the on and off rains by keeping the temperature of the pipe, flange, and gasket as 270°C, but changing the temperature of bolts from higher temperature 270°C to a lower temperature cyclically. Elastic and perfect plastic model was conservatively employed in the ratcheting analysis. It is found that gasket plastic strains accumulate with the bolt temperature drop cycles. The higher the bolt temperature drop, the more plastic strain accumulation. Consequently, the contact pressure between the flange and the gasket reduces with the bolt temperature cycles. The higher the temperature drop, the less the flange connection tightness. It reveals that bolt temperature drop below 155°C does not destroy the flange connection tightness with a gasket parameter 3.0. When temperature drops are above 155°C, temperature cycles to destroy the flange connection tightness decrease with temperature drops, namely the higher the temperature drop, the less temperature cycles needed to destroy the flange connection tightness. A margin line has been worked out to correlate the bolt temperature drops and cycles to the gasket leakage.
The Optimization Design of Storage Efficiency and Structural Analysis for the 3 Cubic Meter Radioactive Waste Container
Authors: Shen Yu-Yu , Lin Hsien-Chou , Chou Hsoung-Wei
Published: November 2019

Because the Taiwan domestic boiling water reactor nuclear power plant is under shutdown and going to be decommissioned, the development of radioactive waste container used for containing the radioactive waste from nuclear facility decommissioning and dismantling is a critical issue in recent years. The main purpose of this study is to design a metal container which can provide the highest storage efficiency for the low level radioactive waste, and ensure the structure meeting the safety requirements of related regulations. This paper first introduces the related regulations for the container in Taiwan. To determine the optimal storage efficiency of the container, the shielding analyses were performed by varying dimensions of 3 cubic meter containers to select the best one, and conduct the structural analyses. Then, a series of structural analyses for operational conditions such as static standstill analysis, lifting test and stacking test with full load were performed, as well as the drop impact analysis, to ensure the container structure meeting the safety requirements of regulations. Present work can provide design information of the development of radioactive waste container for decommissioned nuclear facility in Taiwan.
Proposed Modifications to API 579 Part 3 Brittle Fracture Screening Procedures
Authors: Macejko Brian R. , Kummari Seetha Ramudu , Prueter Phillip E.
Published: November 2019

Significant inconsistencies and inadequacies exist in the current brittle fracture screening procedures in the 2016 edition of API 579-1/ASME FFS-1, Fitness-For-Service (API 579). Results from an evaluation completed using the current published guidance could prove unsafe in some instances. The ASME/API Joint Committee on Fitness-For-Service (FFS) recently initiated a project to rewrite API 579 Part 3, Assessment of Existing Equipment for Brittle Fracture. The intent of the project is to establish new Level 1 and Level 2 evaluation procedures and acceptance criteria developed using state-of-the-art fracture mechanics consistent with the Part 9 Failure Assessment Diagram (FAD) approach, currently employed in Level 3 FFS evaluations. This paper will provide a comprehensive summary of deficiencies and concerns with current published methods for evaluating susceptibility of pressure equipment to potential brittle fracture failures. Additionally, the paper will provide an overview of the methodology employed in the recently proposed procedure modifications for Part 3 of API 579 to mitigate the current deficiencies.
A New Design Method for Axially Loaded Thin-Walled Cylindrical Shells Based on Elasto-Plastic Buckling Analysis
Authors: Jiao Peng , Chen Zhiping , Ma He
Published: November 2019

In engineering, thin-walled cylindrical shells subjected to axial compression load are very sensitive to geometric imperfections and are prone to buckling. However, how to reasonably take into account the influence of geometric imperfections on the load carrying capacity of thin-walled cylindrical shells is always the bottleneck of light-weight design of these structures. In this paper, four perturbation load approach (4PLA) is adopted to consider the influence of geometric imperfections. By judging the potential buckling status of cylindrical shells, a new improved design method based on 4PLA for thin-walled cylindrical shells is proposed, in which the influence of radius-to-thickness ratio, length-to-radius ratio, Young’s modulus and material yield strength are systematically considered. Correspondingly, the buckling tests for two steel cylindrical shells with the same geometric and material parameters are conducted. Compared with the experimental results and other test results in open literatures, the superiority and safety of proposed method for the preliminary design of thin-walled cylindrical shells are validated.
Fracture Toughness Testing of an Overmatched Pipe Girth Weld Using Clamped SE(T) Specimens
Authors: Ferreira Claudinei , Burgos Diego F. S. , Ruggieri Claudio
Published: November 2019

This work presents an investigation of the ductile tearing properties for a girth weld made of an ASTM A106 Gr C steel using the SMAW welding process with a low hydrogen E7018 electrode thereby resulting in a weld with high strength overmatching with respect to the base material. Testing of the pipe girth welds employed side-grooved, clamped SE(T) specimens with a weld centerline notch to determine the crack growth resistance curves based upon the unloading compliance (UC) method using a single specimen technique. Recently developed compliance functions and η-factors applicable to weld centerline notched SE(T) specimens are introduced to determine crack growth resistance data from laboratory measurements of load-displacement records. While the UC procedure resulted in measured crack extensions for the tested specimens with weld centerline notch that underestimated the 9-point average crack extension, our preliminary results demonstrate the capability of the methodology in describing crack growth resistance behavior which serves as a basis for ductile tearing assessments in ECA procedures applicable to overmatched girth welds and similar structural components.
Strain-Controlled Low Cycle Fatigue of Stainless Steel in PWR Water
Authors: Seppänen Tommi , Alhainen Jouni , Arilahti Esko , Solin Jussi
Published: November 2019

Fatigue is a major degradation mechanism and life-limiting factor for primary circuit piping. High temperature, pressurized reactor coolant aggravates fatigue damage with a suitable combination of loading parameters. Nonstandard test methods, incompatible with design codes and the peculiar material behaviour of austenitic stainless steel have been widely used. This complicates quantification of the effect of water environment, commonly referred to as the Fen factor.

Four test series in simulated PWR coolant were completed over four years with stainless steel alloys 347 and 304L, hypothesizing that Fen=f⁡ε.pl. Linear strain waveforms were used with non-constant strain rate to represent simplified plant transients and non-realistic mirrored strain waveforms for comparison purposes. Applying multiple strain rates allows identifying potentially non-damaging effects of effectively elastic strain near the valley of a strain cycle and on the other hand the damaging effect of effectively plastic strain.

Results generated within this project were used to draft a replacement to the Fen methodology presented in NRC report NUREG/CR-6909. Initially, this model remains based on total strain rate and is presently limited to the narrow parameter window in which valid experiments were performed. It does however reduce the scatter and unnecessarily high conservatism associated with the NUREG Fen by a factor of approximately two. This paper presents new results for 304L and an outline of the draft model proposal for Fen evaluation in PWR water.
Influence of the Pitch-to-Diameter Ratio on Two-Phase Flow-Induced Forces Across a Tube Bundle
Authors: Deri Enrico
Published: November 2019

Flow-induced vibrations of Steam Generator tube bundles are a major concern for the operators and designers of nuclear power plants. In order to predict damages due to such vibrations, predictive calculations are performed, both by designers and by operators, which allow one to evaluate safety margins and thereafter to optimize the SG maintenance policy.

In cases when semi analytical models of fluid-dynamic forces are used, together with corresponding dimensionless fluid force coefficients, closures are assessed by experiment. The database of dimensionless coefficients should then cover relevant tube bundle configurations.

Within this framework, a test rig which was available at EDF was modified in order to arrange different pitch-to-diameter ratio bundles and different tube diameters. This paper discusses the fluid-induced forces measured on a set of flexible tubes placed in a triangular pitch bundle both in the lift and drag directions. Two-phase flow excitation spectra are presented as well.
Simulation of Sloshing Wave Crest Impact Acting on a Fixed Roof Cylindrical Tank Subjected to a Sinusoidal Excitation
Authors: Toyoda Yukihiro , Ohtori Yasuki
Published: November 2019

This paper describes the applicability of an open source code “OpenFOAM” on estimating of sloshing wave crest impact pressure acting on a fixed roof of cylindrical tank. Based on the computed results, slosh-induced pressure loads and distribution on the tank roof is presented. A series of large scale tests, which are conducted on the “E-defence” shaking table, has been analyzed. In the shaking table tests, partially water-filled cylindrical tank (diameter/height:3m, water depth:2.3m/1.9m) with the flat fixed roof was subjected to a sinusoidal excitation at the first sloshing resonant frequency. The computer code well simulated the observed waveform with a sharp pressure peak at the time of liquid impact on the tank roof, including appearance of negative pressures in the post impact period, with sufficient accuracy. As for the liquid impact zone of the tank roof, the numerical results indicated good agreement with the observed ones. Consequently, the computer code was capable of predicting the complex nonlinear sloshing behavior with the collision of the liquid surface against the tank roof with an acceptable level of accuracy.
Piping Vibration of Multi-Treater System in OCU Process Plant
Authors: Park Jae-Yeol , Kim Manjin , Han Minkyu
Published: November 2019

Acoustic-Mechanical coupling effect on piping dynamics is examined on site with measurement and analytical development. In this article, a multi-treater piping system in OCU (Olefin Conversion Unit) plant is subjected to investigation since significant piping vibration prevents the normal operation when some specific combinations of two treaters are operated. There is severe piping and structure vibration problem especially with increased capacity. Measurement in frequency domain shows two peaks so close each other to result in high amplitude in the piping system vibration by beating phenomenon. In search of solution, extra safety valve is manually opened to increase the acoustic volume which changes the acoustic natural frequency in the subjected piping system and decrease the vibration. Analytical study with acoustic analysis software is also conducted and it shows the same results as the actual piping dynamics. Based on the acoustic study, piping modification is designed and applied to the piping system and vibration improvement is achieved as expected.
Study on the Predictive Evaluation Method of Nonlinear Sloshing Wave Crest Impact Load on the Roof of Cylindrical Tanks
Authors: Morita Hideyuki , Takata Tomoshige , Madokoro Hideki , Sago Hiromi , Yokoi Shinobu , Yamamoto Tomohiko
Published: November 2019

When cylindrical tanks installed on the ground, such as oil tanks and liquid storage tanks, receive strong seismic waves, including the long-period component, motion of the free liquid surface inside the tank called sloshing may occur. If high-amplitude sloshing occurs and the waves collide with the tank roof, it may lead to accidents such as damage of the tank roof or outflow of internal liquid of the tank. Therefore, it is important to predict the wave height of sloshing generated by earthquake motion.

Sloshing is a type of vibration of free liquid surface, and if the sloshing wave height is small, it can be approximated with a linear vibration model. In this case, the velocity-response-spectrum method using velocity potential can estimate the sloshing wave height under earthquake motion. However, if the sloshing wave height increases, the sloshing becomes nonlinear, and necessary to evaluate the wave height using other methods such as numerical analysis.

Design earthquake magnitude levels in Japan tend to increase in recent years, long-period components of earthquake wave which act on the sloshing wave height also increase instead of introducing seismic isolation mechanisms. To evaluate sloshing wave crest impact load acting on the roof of a tank, there are few applications which quantitatively evaluated the crest impact load of nonlinear sloshing.

To construct a simple technique to evaluate the sloshing impact load considering the nonlinear sloshing wave height which acts on a flat roof of cylindrical tanks, it is proposed that flow diagram of evaluating the sloshing impact load which newly took into consideration the nonlinearity of sloshing and the dynamic amplification factor. The applicability of the technique was verified with the shaking table tests results for cylindrical tank and flow-analysis results.