Loose rock scour protections are widely applied as countermeasure for scour development at offshore foundations. This study presents a deformation model that predicts the deformation depth in loose ...rock scour protections around monopiles using two relatively simple parameters. The first parameter is the relative mobility, which is the ratio between the Shields number and the critical Shields number. The relative mobility is a measure of the hydraulic loading relative to the resistance of the material. The second parameter is the total Keulegan–Carpenter (KC) number, which is the ratio between the length of the orbital motion at the pile and the diameter of the pile. The total KC number accounts for the contribution of both a steady current and a wave-induced current. It is a measure of the wave stroke asymmetry (leading to a larger net displacement) and the differences in bed shear stress amplification around the pile (thus increasing the effect of the relative mobility). The deformation model is based on an experimental database consisting of roughly 380 individual tests spanning a wide range of parameters representative for typical North Sea conditions. The derived model can directly be applied in the design of loose rock scour protections in engineering practice.
•Easy-to-use loose rock scour protection deformation depth formula.•Experimental database consisting of roughly 380 individual test results.•Directly applicable in scour protection design practice.
Morocco imports about 96% of its required energy needs. Solar energy, as one of the most abundant and valuable renewable energy alternatives in the country, offers interesting opportunities for ...Morocco. In order to minimize its strong foreign energy dependence, Morocco hosts actually the largest Concentrated Solar Power (CSP) using parabolic trough collectors (PTC) as a technology for converting solar irradiation into thermal energy for electricity generation. The purpose of this paper is to assess the thermal performance of this technology and the potential projects concerned by Moroccan Solar Plan. A physical model is developed to determine flow parameters and heat transfer applied to PTC technology. Annual simulations in six climatic regions in Morocco were carried out. Several suggestions were drawn with regards to the design and parametric studies effectuated under Ouarzazate CSP project. It is found that the location and the climate are determinant parameters on the global performance of the parabolic trough solar collectors.
Field examples of subsidence from sequential extraction of overlapping coal longwall panels have shown that complex and unexpected subsidence effects can occur. Physical models, comprising sand and ...plaster obeying relevant similarity rules, were used to investigate the subsidence mechanisms. Displacements within the models were measured using a combination of optical transducers, photogrammetry and laser scanning. The observed results were compared with finite element models. The models demonstrate that the incremental subsidence and substrata movement profiles after lower seam extraction can be separated into three different zones. These zones undergo different horizontal and vertical movement characteristics. The zone of overlap of the two longwall panels undergoes greater total subsidence compared to a single seam of equivalent thickness. The limit angle of the subsidence also differs at the two ends of the lower extraction as a result of the effects of the previously mined-out area above.
•We investigated the mechanism of ground surface subsidence due to multiple-seam longwall coal mining.•We used physical and numerical modelling techniques to simulate a multiple-seam mining case study.•The simulated mining configuration resulted in three different substrata movement zones•Ground surface subsidence after multiple-seam mining is different from single-seam mining.•Results can be utilized for developing a prediction method for multiple-seam subsidence.
Multi-seam mining-induced subsidence profile is observed to be different from that of single-seam mining. Understanding the characteristics of multi-seam subsidence is the first step in achieving ...reliable subsidence predictions. Characteristics of multi-seam subsidence are investigated by means of several sand-plaster physical models. Geological and site specific parameters are kept constant in all the models in order to compare the multi-seam subsidence parameters for different mining configurations. Based on observations from the physical models, it is concluded that the panel configurations of the two seams have significant impact on the multi-seam subsidence development. Based on the relative location of the panels the multi-seam mine area can be divided into different zones, to which suitable subsidence characteristics can be assigned. Dividing the mine area into different zones enables characterisation of the strata movement and multi-seam subsidence for various multi-seam configurations. The proposed characterisation of the multi-seam subsidence can also be utilised in subsidence prediction methods in order to achieve reliable prediction results.
•Physical modelling is used to investigate multi-seam subsidence characteristics.•Effects of different mining configurations on subsidence profile are investigated.•The multi-seam subsidence is characterised based on the physical modelling results.•The proposed characterisation can be employed in subsidence prediction methods.
Effects of slag layer thickness on the fluid dynamics of liquid steel in gas-stirred ladles by bottom injection of argon was studied through water modeling experiments and numerical simulations. ...Mixing times increase considerably with thicker slag layers and decrease of gas flow rates. The physical properties of the system have a smaller influence on mixing time. Slag Eye Opening (SEO) area is increased under thin slag layers, increase of gas flow rates, and denser and less viscous slags. The planes close to the metal-slag interface, under the presence of thick slag layers for a given gas flow rate, are split in subregions of small velocities with different orientations making the lower fluid to come close to a stagnant condition. The presence of, either, thick or thin slag layers does not influence the axial velocity along the plume height for a fixed flow rate of gas. The SEO area follows a linear relationship with the square root of the densiometric Froude number based on the slag layer thickness.
The study provides a comprehensive examination of single row Rectangular Pile Head Breakwaters (RPHB), encompassing both non-perforated and perforated variations. In the non-perforated RPHB category, ...the investigation delves into the effects of pile head height and width, and wave climate. For perforated RPHB structures, the study analyses the influence of percentage of perforations, perforation size, and depth of water. Further, the research includes a comparative assessment between non-perforated and perforated RPHB structures. Additionally, the research conducts a comparative analysis with similar structures. In the case of non-perforated RPHB, the configuration with relative pile head diameter (D/d) of 2.4 and relative pile head height (Y/Hmax) of 1.5 stood out as the most effective model. Similarly, the perforated RPHB demonstrated its maximum wave attenuation potential with percentage of perforations (P) of 24% with relative size of perforations (S/D) of 0.25. This optimal configuration achieved a minimal wave transmission coefficient (Kt) of 0.53, reflection coefficient (Kr) of 0.33, and energy dissipation coefficient (Kd) of 0.79 at a relative water depth (h/H) 0.865. Notably, the introduction of perforations on the RPHB structure led to an improvement in wave attenuation performance by 4–8%, resulting in lower reflection and higher energy dissipation. Comparatively, the RPHB structure outperformed the Enlarged (cylindrical) Pile Head Breakwater (EPHB) and Conical Pile Head Breakwater (CPHB) structures in terms of wave attenuation, exhibiting higher reflection and superior energy dissipation characteristics. The consistent outcome of these investigations reveals that the RPHB exhibits superior hydrodynamic performance characteristics and design suitability, making it a promising choice for breakwater applications.
•The perforated RPHB is found to perform better in wave attenuation than the non-perforated counterpart.•The RPHB demonstrated superiority in wave attenuation compared to other similar structures, with higher energy dissipation.
The application of the electromagnetic stirring from an oscillating magnetic field can improve the metal mixing in wire feed laser beam welding. However, the extra parameters introduced in this ...technique make the selection of an optimal combination of process parameters more difficult. In the current study, besides the commonly concerned magnetic flux density and frequency, the influence of the magnetic field orientation (magnetic field angle) on the transport of filler metal is studied numerically and experimentally. Ex-situ X-ray fluorescence spectrometer measurements are used to map the metal mixing in the final weld. A three-dimensional transient multi-physical model is developed to reveal the deeper physical essence, considering the coupling between heat transfer, fluid flow, keyhole dynamics, element transport and magnetohydrodynamics. The spatial distribution of the laser energy on the keyhole wall is calculated by a ray tracing algorithm. The results show that the magnetic field with smaller angle with respect to the transverse direction provides better penetration capacity, and its stirring effect can reach the lower part of the molten pool. Therefore, the smaller magnetic field angle produces better metal mixing. A constant downward flow is formed at the lower part of the molten pool when magnetic field of 10° angle is applied, which brings the filler metal to the root region. As the magnetic field angle increases to 40°, the beneficial downward flow changes into a constant upward flow, resulting in a concentration of the filler metal in the upper region. This study provides further insight of the underlying physics in the electromagnetically enhanced laser beam welding, which may guide the optimization of parameters to achieve property homogeneity or to avoid potential defects.
We compare waves generated by subaerial solid-block and granular landslides and propose equations for predicting their maximum initial wave amplitudes. The recent Anak Krakatau subaerial landslide ...tsunami in December 2018, which resulted in more than 450 deaths, demonstrated the knowledge gap on this subject and motivated this study. Here, we make numerical models using the numerical package FLOW3D-Hydro for solid-block and granular landslides and validate them using physical experiments. Results indicate that the maximum initial wave amplitudes generated by solid-block landslides are 107% larger than those generated by granular landslides in our experiments. The relationship between maximum initial wave amplitude and slope angle is inverse for solid-block slides whereas, it is direct for granular slides. However, a critical angle of 60° is achieved for granular slides, and for slope angles more than this critical value, the maximum wave amplitudes start to decrease. Regarding wave period, our results show that it remains nearly unchanged for both types of landslides as water depth and slide volume vary. The period generated by solid-block slides increases as the slope angle decreases; however, it remains unchanged for granular slides. The predictive equations are applied to real landslide tsunamis and resulted in satisfactory performances.
•Maximum amplitudes of subaerial solid-block slides were 107% larger than granular.•A critical slope angle of 60° was obtained for granular slides.•Wave periods remain unchanged as water depth and slide volume vary for both slides.•Wave period increases as the slope angle decreases for solid-block slides.•Water particle speed for solid-block slides was nearly twice that of granular.
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