Altomare, Corrado (Ghent University) | Tagliafierro, Bonaventura (University of Salerno) | Suzuki, Tomohiro (Flanders Hydraulics Research) | Dominguez, Jose M. (Vigo University) | Crespo, Alejandro J. C. (Vigo University) | Briganti, Riccardo (University of Nottingham)
The Relaxation Zone method (RZ) has been implemented in the meshless SPH-based DualSPHysics code. RZ acts as an internal wave maker and allows coupling DualSPHysics with any other model or analytical solution to generate sea waves. In this work, the coupling with the SWASH model is performed to simulate multi-scale and long-duration phenomena in coastal engineering, which represent a challenge for researcher and practitioners. In fact, despite the fact that SPH-based models are getting more and more popular in coastal and civil engineering, they still present a huge computational cost. In the present work, RZ is validated for phenomena of overtopping flow impacts on vertical walls. The results proved that the RZ is efficient and reliable alternative for wave generation in SPH-based models for coastal engineering applications.
Smoothed Particle Hydrodynamics method (SPH) is a promising meshless technique for modelling fluid flows and fluid-structure interaction (FSI) as it is capable to deal with large deformations, complex geometries, violent free-surface flows inducing large abrupt hydrodynamic loads and highly nonlinear phenomena (Violeau, 2012).
In general, SPH methods can be categorized into two groups: weakly compressible and incompressible. The Weakly Compressible SPH (WCSPH) methods solve an appropriate equation of state (Tait's equation) in a fully explicit form. The DualSPHysics model used in the present work is based on WCSPH. The incompressible SPH (ISPH) methods (e.g. Shao & Lo, 2003) solve a Poisson pressure equation (PPE) by applying project-based methods. Latest advancements have been made during the last decade in the context of SPH methods in terms of model stability, accuracy, energy conservation, boundary conditions and improved simulations of multiphase flows and fluid-structure interactions. A comprehensive review of it is presented in Gotoh & Khayyer (2016, 2018).
SPH methods have been widely applied to coastal engineering problems, such as wave breaking (e.g. Khayyer et al., 2008), wave overtopping (e.g. Gómez-Gesteira et al., 2005), wave run-up (e.g. Zhang et al., 2018), wave impacts (e.g. Altomare et al., 2015), tsunamilike wave processes (e.g. St-germain et al., 2014), wave energy applications (e.g. Crespo et al., 2017). Notwithstanding, further research is still needed to enhance the reliability of SPH methods and to widen their applicability for coastal engineering problems. Lately Rota Roselli et al. (2018) presented an automatic optimization framework to find the set of SPH parameters in DualSPHysics for an accurate wave propagation modelling. Yet, there are still limitations to be solved, one of which consisting in the unphysical oscillations in the pressure field due to high-frequency acoustic noise. Meringolo et al. (2017) proposed a procedure to filter out this noise, however the work is dedicated to post-processing analysis rather than solve the problem a priori. For WCSPH, besides the most classical diffusion schemes such as artificial viscosity (Monaghan, 1992), the so-called δ-SPH scheme has been proposed (e.g. Molteni & Colagrossi, 2009) to increase accuracy of the pressure field. To improve both accuracy and stability in SPH, particle regularization schemes have been proposed in order to regularize the anisotropic distributions of particles prone to be formed due to Lagrangian characteristics of particle methods (Lind et al., 2012).
Hydrogen (H) presence in metals is detrimental as unpredictable failure might occur. Though decades of research have been done, the underlying mechanism is still not fully understood. During state-of-the-art developments in material's design, precipitates play an essential role since they can both enhance the resistance against H induced failure and strengthen the material. Well-designed H trapping sites may be a relevant strategy to enhance the H embrittlement (HE) resistance. This work studies five types of carbides in three Fe-C-X alloys with increasing carbon content: Ti, Cr, Mo, V and W-based precipitates. To evaluate the effect of these precipitates, two conditions were compared for each composition: as quenched and quenched and tempered. Carbides were introduced during tempering. The material/H interaction was fully characterized: in-situ tensile testing was performed to assess the HE sensitivity, hot/melt extraction was done to determine the H content, thermal desorption spectroscopy was performed to evaluate the H trapping capacity of the carbides and permeation experiments were executed to evaluate the H diffusivity. The HE degree was correlated with the amount of H. Three different types of H, determined by the strength by which they were trapped, were considered by combining the different H characterization techniques. It was established that H trapped at dislocations played a determinant factor. This confirmed the crucial role of an enhanced dislocation mobility in the presence of H, which is a solid experimental proof of the HELP mechanism. In contrast, H trapped by the carbides did not show a significant effect on the H induced mechanical degradation. Since all precipitates were able to deeply trap a significant amount of H, their addition was beneficial to enhance the HE resistance.
Since hydrogen (H) can generate an energy revolution as a clean energy carrier for renewable energy, the awareness of a possible H economy has recently regained more attention (Brandon, 2017). The increased H production and use can help to circumvent the climate change we are currently facing. Though, due to the required infrastructural investments (Ball, 2009), together with the challenges regarding production, transportation, distribution and storage (Amid, 2016), the development of a H based economy has proven to be challenging. Still, H can play a role in the future energy system, while H fuel cells for instance are already used to replace batteries. Furthermore, the offshore industry faces issues concerning H as well since corrosion is there avoided by cathodic protection. However, often cathodic overprotection occurs and H absorbs into the material leading to an increase in H concentration. The ductility will consequently be deteriorated to a certain extent and H induced failure issues arise (Olden, 2009). Moreover, in the automotive industry, advanced high strength steels are progressively more used since they guarantee an improved safety together with weight reduction, which is required to meet the CO2 emission regulations. Unfortunately, these steels are also assumed to be prone to H embrittlement (HE). The harmful H effect on mechanical properties of steels has recently even been described to hinder further development of advanced high strength steels (Loidl, 2011).
In this study, an effective method is developed to couple the multi-directional pore-network (MDPN) model, called PoreFlow, with the chemistry simulator PHREEQC in order to simulate the reactive flow of chelating agents into carbonate media. A novel method based on solving a 1D chemical reactions and projecting the chemistry in the 3D pore scale flow field is developed, which significantly increased the computational efficiency. Results from several simulations are presented to demonstrate the capability of PoreFlow and the developed method to mimic reactive transport of chelating agents in porous media. It is also shown that the interactions between chelating agents and carbonate rocks can be accurately modeled by implementing the proper multi-step protonation kinetic of chelating agents versus pH. The developed model is capable of computing the change in porosity and the 3D flow field due to calcite dissolution by the progress of chemical reactions. In addition, the evolving flow model provides the corresponding relationship between porosity and permeability for a specific porous media. The model successfully reproduced the experimentally observed permeability changes due to the creation of wormholes at various acid flow rates. The results are validated by comparing the simulation outputs to the micro-CT images taken from the samples after the chelating experiments. Moreover, it is shown that the average dissolution rate for heterogeneous carbonate rocks is not only governed by the pore-scale physical heterogeneities but also by the local chemical equilibrium and speciation of chelating agents at various pH values.
An accurate knowledge of the fatigue limit plays an important role in the fatigue structural design. Traditional experimental methods to estimate this stress level are highly time consuming. In recent years the application of Infrared (IR) technology for accelerated fatigue damage evaluation has increased. However, this technology is not always deployable, e.g. due to lack of space or accessibility, in aqueous environments. Under such circumstances, the Potential Drop (PD) technique has shown to be applicable for crack initiation and crack growth assessment. This paper focuses on the description and comparison of the established IR and a novel PD method to find the fatigue limit of an HSLA steel in an efficient manner. Based on preliminary tests, the results of both methods show good correlation.
The definition of the fatigue limit (σfl) is an important step during the design stage of a component subjected to cyclic loads. For some materials (steel e.g.), and constant amplitude cyclic loads, it is accepted that a steady fatigue limit is achieved after approximately 5*10⁶ (Nfl). The stresses below this limit (see Fig. 1) are defined as not damaging and it might therefore be taken as a stress reference for “safe life” structural design.
Traditionally, the fatigue limit is estimated from a series of (constant amplitude) fatigue tests conducted to determine the entire S-N curve of the material. For design purposes, the fatigue limit is generally taken equal to the endurance level at 5*10⁶ cycles. In any case, the S-N curve has to be partially or totally determined in order to establish this parameter. Such experimental analysis is highly time consuming.
In the last two decades the use of infrared thermography for the rapid determination of the fatigue limit has increased. Several authors have published (slightly) different methodologies to quickly estimate it in an accurate manner (Luong MP, 1998; La Rosa G, 2000; Crupi, 2008). Notwithstanding this technique is a powerful tool to estimate the fatigue limit, its application might be hindered by different factors such as accessibility of the interesting region, composition of the surrounding environment and its temperature, among others.
This work presents a numerical model of the coupled interactions between temperature profile, electrolytic potential drop, and steady-state oxygen concentration gradient in soils surrounding buried pipelines. Three different soil types are considered (sand, clay, and peat), with porosity ratios varying between 0.4 and 0.8. Two volumetric wetness ratios are simulated for each soil type, representing moisture changes during successive soil drying-wetting cycles. The motivation behind this study is to model the interdependencies of heat transfer, cathodic protection, and oxygen diffusion on pipeline steel corrosion in various soil environments. A key benefit of the developed model is its rapid scalability, allowing the simulation of these interrelated phenomena for different geometries, dimensions, and boundary/initial conditions. The results of a select number of cases are presented in this paper.
Based on the oxygen diffusion, cathodic protection, and iron oxidation behavior of an exposed 90°° arc on the pipeline’s external surface facing a magnesium cathodic protection anode, it is found that drier sand and clay soil structures cause the most corrosion. The geometric location of the coating holiday relative to the ground surface and the cathodic protection anode has a particular influence on oxygen concentration and iron oxidation. Temperature fluctuations during seasonal weather cycles have observable effects on iron oxidation rates due to influences on heat transfer and oxygen diffusivity. An overall trend of decreased oxygen concentration and iron oxidation in wetter and warmer soils is detected and quantified.
External corrosion of buried transmission pipelines is a common problem encountered in the oil and gas industry. To mitigate this corrosion, a combination of cathodic protection (CP) and protective coatings are applied to the structure’s outer surface.1 The CP protects the pipeline steel from corrosion where coating defects and/or damage are present. CP performance is strongly dependent on properties of the soil (electrolyte) between the anode and the pipeline (cathode). Governing soil properties such as electrical resistivity, gas diffusivity, or heat transfer coefficients are themselves dependent on parameters such as soil particle distribution, organic content, structure, air-filled void porosity, moisture, and temperature. 2 As such, corrosion of exposed steel where a coating fails will depend on numerous physicochemical soil parameters, in addition to reaction kinetics at the steel-soil boundary. Numerical models and simulations of CP under the influence of these parameters can help determine unfavorable environmental conditions of the surrounding soil and identify the most critical corrosion locations on exposed surfaces. Also, simulations may highlight the fundamental processes occurring in field conditions, helping to increase the effectiveness of system operation through less reliance on empirical conventions. This study aims to model interactions between temperature, oxygen diffusion, and charge transport in soil and their effect on external corrosion of buried steel pipelines.
The application of spiral welded pipes in strain based design related projects has gained (economic) interest. A potential weak link is the helical seam weld region. This paper investigates the structural response of a pipe with a flawed spiral weld under remote plastic tensile deformation, resulting in a mixed mode flaw tip loading. A combined numerical-experimental framework is proposed to determine the tensile strain capacity. Based on a set of experimental and numerical data it is concluded that higher pipe forming angles are beneficial with respect to tensile strain capacity.
Van Minnebruggen, Koen (Ghent University) | Hertelé, Stijn (Ghent University) | Verstraete, Matthias (Ghent University) | Denys, Rudi (Ghent University) | De Waele, Wim (Ghent University) | Thibaux, Philippe (ArcelorMittal Global R&D) | Van Wittenberghe, Jeroen (ArcelorMittal Global R&D)
The structural response of spiral welded pipes in strain based design related projects has gained interest. The spiral weld is a potential weak link, whose structural response is influenced by directional material anisotropy introduced during the production of skelp and pipe. In this paper, Hill’s 1948 yield criterion is used to investigate the response of curved wide plate sections taken from a spiral pipe under plastic tensile deformation by means of numerical analysis. It is concluded that conducting finite element calculations of spiral welded pipes sections can yield unconservative designs, when neglecting anisotropic plastic material response.
Neubauer, Wolfgang (Boltzmann Institute for Archaeological Prospection and Virtual Archaeology) | Hinterleitner, Alois (Boltzmann Institute for Archaeological Prospection and Virtual Archaeology) | Doneus, Michael (Boltzmann Institute for Archaeological Prospection and Virtual Archaeology) | Löcker, Klaus (Boltzmann Institute for Archaeological Prospection and Virtual Archaeology) | Trinks, Immo (Boltzmann Institute for Archaeological Prospection and Virtual Archaeology) | Nau, Eric (Boltzmann Institute for Archaeological Prospection and Virtual Archaeology) | Pregesbauer, Michael (Boltzmann Institute for Archaeological Prospection and Virtual Archaeology) | Kucera, Matthias (Boltzmann Institute for Archaeological Prospection and Virtual Archaeology) | Verhoeven, Geert (Boltzmann Institute for Archaeological Prospection and Virtual Archaeology) | Seren, Sirri (Archeo Prospections) | Saey, Timothy (Ghent University) | De Smedt, Philippe (Ghent University) | Van Meirvenne, Marc (Ghent University)
Versteeg, Willem (Ghent University) | el Allouche, Nihed (Delft University of Technology) | Thorbecke, Jan W. (Delft University of Technology) | Ghose, Ranajit (Delft University of Technology) | Drijkoningen, Guy G. (Delft University of Technology)
Point absorbers are wave energy converters (WECs) consisting of small (floating) bodies oscillating with either one or more degrees of freedom. They can either move with respect to a fixed reference, or with respect to a floating reference. Different buoy geometries are evaluated to obtain the ideal values of size, shape and draft with regard to power absorption for a given moderate wave climate. In this paper, the performance of a heaving point absorber in a floating platform is analysed in a linear way. INTRODUCTION More and more the current energy problem is spotlighted nowadays. The oil prices are increasing steadily, the energy demand increases by 1 to 2 % a year and the Kyoto targets are not being reached. Moreover the EU imports 50 % of its energy and this number will rise to 70 % in 2030, which makes the EU dependent and consequently economically vulnerable. Most of the energy imports concern fossil fuels which contribute to global warming. Ocean waves contain huge amounts of -almost- unexploited energy. This energy can be absorbed by wave energy converters. Ocean energy is a renewable energy type that is becoming more and more important. Several systems have been invented, among them point absorber systems which are wave energy converters consisting of small (floating) bodies oscillating with one or more degrees of freedom. They can either operate with respect to a fixed reference, or with respect to a floating reference. The latter principle has been adopted in a novel way in the wave energy converter that is studied in the SEEWEC project, where multiple point absorbers are combined in a floating, moored platform. The impact of variations in point absorber geometry and stroke limitation on system performance is treated. A boundary element method (BEM) package is used to determine the hydrodynamic behaviour of both the platform and the oscillating point absorbers.