Free Surface Research Articles

Effects of Dip Angle on Rupture Propagation Along Branch Fault Systems

ABSTRACT An important consideration in assessing seismic hazards is determining what is likely to happen when an earthquake rupture encounters a geometric complexity such as a branch fault. Previous studies showed parameters such as branch angle, stress orientation, and stress heterogeneity as key factors in the self-determined rupture path on branch faults. However, most of these studies were conducted in 2D or 3D with perfectly vertical faults. Therefore, in this study, we investigate the effects of dipping angle on rupture propagation along a branch fault system. We construct 3D finite-element meshes where we vary the dip angles (nine geometries in total) of the main and secondary faults, the stressing angle (Ψ=20°, 40°, and 65°), and the hypocenter location with nucleation on both the main and secondary segments. We find that for Ψ=40°, a rupture on the main fault is most likely to propagate across the branch intersection when the secondary fault is dipping. In addition, for Ψ=65°, a rupture on the secondary fault is most likely to propagate to the main fault when the secondary fault is shallowly dipping. This is caused by a fast rupture speed on the secondary fault and the dynamic stress effect that develops with the interaction of the free surface and the dipping secondary fault. These results indicate that dip angle is an important parameter in the determination of rupture path on branch fault systems, with potentially significant impact for seismic hazard, and should be considered in future dynamic rupture modeling studies.

Free-surface-induced ground effect for flapping swimmers

Numerous flying and swimming creatures use the ground effect to boost their propulsive performance, with the ‘ground’ referring to either a solid boundary or a free surface. While our knowledge of how a solid boundary affects biolocomotion is relatively comprehensive, the ground effect of a free surface is not fully understood. To address this limitation, we conduct a numerical investigation on the propulsion performance of a flapping plate under a free surface, subject to a range of control parameters. When the Froude number ( $Fr$ ) is very low (i.e. little surface deformation), the effects of a free surface are similar to those of a solid boundary, with enhanced thrust and input power but little change in efficiency. However, as $Fr$ increases (i.e. more surface deformation), our results reveal an optimal $Fr$ of approximately 0.6, where the free surface induces a more streamlined flow around the flapping plate, effectively reducing the added mass. This results in a significant decrease in input power and greatly enhanced efficiency.

Exploring submergence impact on flow-induced motion energy-harvesting with circular-triangular prisms

AbstractRecent advancements in energy-harvesting have utilized Flow-Induced Motion (FIM) as a renewable source, diverging from past efforts aimed at minimizing FIM's adverse effects. This study introduces kinetic energy converters using alternating lift technology (ALT), employing a prism with a Circular-Triangular (Cir-Tria) shape, coupled with a spring and damper, to generate energy. Utilizing computational fluid dynamics in OpenFOAM for Reynolds numbers between 2 × 103 and 13 × 103 and varying submergence depth ratio from 0.98 to 5.91, this research employs a moving computational grid, two-dimensional incompressible Navier–Stokes equations, the k-omega Shear Stress Transport (SST) turbulence model, the Volume of Fluid, VOF, two-phase model, and the cylinder mass–spring–damper equation. Findings show that approaching the flow surface negatively impacts the FIM response due to the interaction of vortices from the flow surface and the prism’s upper shear layer. This interaction weakens and neutralizes the upper vortices, altering the flow structure around the prism and the governing FIM phenomena. Proximity to the free surface significantly affects FIM responses, with a notable decrease in vibration amplitude and energy conversion as the submergence depth ratio increases from 0.98 to 5.91. Maximum system efficiency of 1.4% is observed in the VIV initial branch at infinite submergence (single-phase flow). Beyond a submergence depth ratio of 5.91, FIM amplitude and energy conversion flatten, indicating negligible free surface effects.

A Review on the Effect of Wood Surface Modification on Paint Film Adhesion Properties

Wood surface treatment aims to improve or reduce the surface activity of wood by physical treatment, chemical treatment, biological activation treatment or other methods to achieve the purpose of surface modification. After wood surface modification, the paint film adhesion performance, gluing performance, surface wettability, surface free energy and surface visual properties would be affected. This article aims to explore the effects of different modification methods on the adhesion of wood coating films. Modification of the wood surface significantly improves the adhesion properties of the paint film, thereby extending the service life of the coating. Research showed that physical external force modification improved the hydrophilicity and wettability of wood by changing its surface structure and texture, thus enhancing the adhesion of the coating. Additionally, high-temperature heat treatment modification reduced the risk of coating cracking and peeling by eliminating stress and moisture within the wood. Chemical impregnation modification utilized the different properties of organic and inorganic substances to improve the stability and durability of wood. Organic impregnation effectively filled the wood cell wall and increased its density, while inorganic impregnation enhanced the adhesion of the coating by forming stable chemical bonds. Composite modification methods combined the advantages of the above technologies and significantly improved the comprehensive properties of wood through multiple modification treatments, showing superior adhesion and durability. Comprehensive analysis indicated that selecting the appropriate modification method was key for different wood types and application environments.

A Study of Free Surface Agitation in a Shipyard Using Numerical Modeling

In recent years, the Port of Topolobampo, Sinaloa, Mexico, has experienced unusual free sea surface elevations, particularly during the months of November and December, affecting the shipyard areas, service docks, and berthing locations. This study focuses on analyzing the oscillatory behavior of free surface elevations in shipyard regions. A hydrodynamic model was employed to simulate the circulation and sea surface agitation, aiming to quantify the elevation magnitudes based on oceanographic and meteorological data from November of the preceding year. A 30-day numerical simulation was conducted, revealing the velocity fields associated with coastal currents and tides during November, as well as the interaction between incident waves and wave transformations due to protective structures. The results demonstrated accurate behavior in 95% of the simulation period, while anomalous elevations exceeding those specified in the design and operational guidelines of the Port of Topolobampo were observed during the final five days of the simulation. An ANOVA test was performed between the surface elevation and vertically integrated velocity to assess whether the deviations in the last five days were statistically significant compared to the rest of the simulation period. With a P-value of less than 0.05, the null hypothesis of no difference was rejected, confirming a significant variation. These findings suggest that the extreme values recorded should be considered for the potential redesign of shipyard infrastructure.

Detection of MUC1+/MUC2 and MUC5AC− Membrane-Associated Mucins in the Intraepithelial Surface Mucous Cells of the Developing Rabbit Esophagus

Introduction: Mucins are polydisperse molecules created to perform a variety of functions at the mucosal surface of the adult gastrointestinal tract. Two main groups of mucins could be identified: the membrane-associated mucins (MUC1, MUC4, MUC13, and MUC16), those bound to the apical plasma membrane of epithelial cells, and the secreted mucins (MUC2, MUC5AC, MUC5B, and MUC6), those secreted from the goblet cells. Little is known about the types and distribution patterns of mucins in prenatal life. Methods: We detected mucin-secreting cells in the developing rabbit esophagus though these cells are absent in the adult one. In order to identify the content and possible functions of these cells, we investigated the histochemical and immunohistochemical characteristics of their mucins. Results: Starting at 16th day of pregnancy, periodic acid Schiff (PAS), alcian blue (AB) pH (2.5), and PAS-AB combination intensely stained the mucous content, demonstrating both acidic and neutral mucopolysaccharides. Some blebs could be recognized on the free surface of the esophageal epithelium. Also, the mucous cells and some basal cells strongly immunoreacted with MUC1, but not MUC2, nor MUC5AC antibodies. Conclusion: Collectively, these data suggest that surface mucous cells are modified epithelial cells, not goblet cells, and may originate from the basal layer of the epithelial cells. A possible regulatory role for these MUC1-positive mucins in esophageal epithelial and mesenchymal cell differentiation and late organogenesis is suggested. However, future functional studies are recommended.

Effective and environment-friendly oil removal with microbubble jet

Effective removal of oil contaminants from solid surfaces is crucial for various applications. However, traditional cleaning methods often involve the use of hazardous chemicals. Because of their stability and ability to adsorb pollutants, microbubbles are considered as a promising alternative for environmentally friendly cleaning. This study explores the enhancement of oil cleaning efficiency using a microbubble water jet. The properties of the microbubbles generated via ultrasonic agitation are examined under varying water temperatures, ultrasonic amplitudes, and surfactant concentrations. The microbubble jet demonstrates approximately 29 % enhanced cleaning efficiency compared with a single-phase water jet. Visualization techniques, including particle image velocimetry, reveal that this enhancement is driven by the behavior of microbubbles consistently adsorbing oil through hydrophobic interactions as well as the instability and increased turbulence intensity of the microbubble jet. Additionally, the higher (by 7 %) spreading velocity of the microbubble jet indicates the free surface of bubbles results in a drag reduction. Consequently, this enables the jet to cover wider regions to be cleaned effectively. The present findings demonstrate the potential of microbubble jets as an effective and eco-friendly alternative for oil removal and offer insights for their practical implementation in diverse fields utilizing microbubbles.

An adaptive internal mass source wave-maker for short wave generation

The mass source wave-maker is commonly employed for generating water waves in numerical simulations, during which a correct amount of mass is introduced or subtracted from the internal flow region to produce target waves. The method has proven to be effective in producing waves in shallow and intermediate water depths, while its efficiency is declined for short wave generation. The main reason for this efficiency declination is that the internal mass source in deeper water region is not effective to generate short waves with their motions primarily on water surface. In order to overcome this shortcoming, many of the previous numerical treatments have introduced various enhancement factors into the source functions, which are empirically obtained and also violate the law of mass conservation. In this study, we develop a new adaptive internal wave-maker model that can be self-adjusted to suit different wave conditions. The line source starts from the bottom and extends to the computational cell right beneath free surface at each time step. The depth dependent weighting coefficient is introduced to the source function based on the linear wave theory for each wave component. No empirical coefficients are necessary, and the mass conservation is strictly and explicitly enforced. In principle, the method can be applied to all types of linear waves in the entire range of kh. The numerical experiments show that the present method can produce very good results for linear waves with kh up to 16.11, adequate for most of wave conditions in coastal engineering. For generation of fifth-order Stokes waves, the method can be extended straightforwardly for each of five wave components. For irregular waves composed of many linear wave components, different weighting coefficients can be readily calculated for each of them, respectively. As a result, the new model can generate irregular waves with overall better performance of reproducing wave spectrum, whose high-frequency part has been underestimated by previous methods. The numerical experiments also show that the new model can produce better results for focused waves where many linear waves of different frequencies start from the same point with specific phase angles, due to its capability of generating shorter wave components.

Numerical simulation of open channel basaltic lava flow through topographical bends

In this study, we utilised computational fluid dynamics to investigate the behaviour of open-channel basaltic lava flows navigating bends on shield volcanoes. Our focus was on understanding the relationship between flow velocity, rheology, and bend geometry. Employing a simple Force Balance Model (FBM), which considers the equilibrium between hydrostatic pressure and centrifugal force, we accurately approximated the changes in the height of the lava’s free surface through various bend geometries. Our analysis includes examining the influence of channel depth, width, and bend radius on the flow, revealing that variations in these parameters significantly affect the flow’s vertical displacement. Additionally, the bend sector angle emerged as a critical factor, indicating a minimum angle necessary for the flow to fully develop before exiting the bend.Further, we assessed the applicability of the Shallow Water Equations (SWE) for modelling the inertial displacement of the lava flow in bends, finding a good fit. The study extended to comparing the FBM’s predictions of the tilt angle of the flow’s free surface with the SWE results, showing notable agreement under specific conditions, particularly at a bend angle of 90 degrees. The impact of fluid density was also considered, revealing that density is a contributing factor to the development of the wetted line in the bend, a factor that is not captured by the simple FBM model. Finally, we explored different rheologies akin to natural lava flows, such as viscoplastic flow, and determined that factors like yield stress, consistency index, and power law index have a small impact on the flow behaviour in a steady-state condition within a bend.

Dual modification of the aggregation behavior and in vitro digestion of oxidized pine kernel protein via a combination of homogenization and succinylation

Protein oxidation affects the high-value utilization of nuts as oxidative attack causes protein aggregation, thereby challenging their technological functionality. Herein, a strategy using homogenization-assisted octenyl succinic anhydride (OSA) modification was proposed to tailor the structure, aggregation behavior, and digestive characteristics of oxidized pine kernel proteins. Results indicated that the ratio of α-helices to β-turns ranged from as low as 0.43 up to 0.67 after homogenization, suggesting greater molecular flexibility. With increasing protein oxidation, the acylation degree exhibited an inverted V-shaped trend, peaking at 67.22 %. OSA treatment reduced the aggregation rate and prolonged the lag time of proteins by stabilizing the α-helices and β-turns, increasing hydrogen bonding, and decreasing hydrophobicity. This increased the solubility of oxidized pine kernel proteins by ~30 % and improved their fluidity and thermal stability. A lower degree of succinylation was associated with higher free sulfhydryl content and surface hydrophobicity, which facilitated the thermal aggregation and the formation of elastomeric gels. Furthermore, the in vitro dynamic digestion and morphological observations of hydrolysis products indicated that cotreated proteins exhibited higher digestibility and formed small spherical particles ranging from 405.50 to 676.50 nm. These findings provide a promising approach to mitigate the adverse effects of oxidation on nut proteins.

Study of the role of abyssal ocean stratification in the rearrangement of potential vorticity through the water column

Abstract. Observations of abyssal variability performed in the Ionian Sea (Mediterranean Sea) have revealed the presence of a dense, stable abyssal layer, whose thermohaline and dynamical properties changed drastically over a decade. Building upon these available observations, we aim to investigate the role that stratification can play in the transmission of vorticity throughout the water column to the abyss and, in turn, in the redistribution of energy stored in the deep sea, with a set of stationary states. A quasi-geostrophic level model equipped with four coupled layers, a free surface, and a mathematical artifice for parameterizing decadal time evolution has been considered, proving that the relative-thickness and relative-density differences among the layers are the two critical factors that determine the dynamical characteristics of this rearrangement. The variability in ocean stratification is a relevant aspect that can activate deep and intermediate dynamics, engaging in the propagation and stabilization of signals throughout the water column. This demonstrates the non-negligible active connection between the dynamics of the bottom layers and the surface. The theoretical framework and parameterization used are based on specific observations made in the Ionian Sea over the last decades but retain general applicability to all ocean basins that are characterized by the presence of a stratified, dense water mass in their deep and intermediate layers.

A Deep Learning-Driven Sampling Technique to Explore the Phase Space of an RNA Stem-Loop.

The folding and unfolding of RNA stem-loops are critical biological processes; however, their computational studies are often hampered by the ruggedness of their folding landscape, necessitating long simulation times at the atomistic scale. Here, we adapted DeepDriveMD (DDMD), an advanced deep learning-driven sampling technique originally developed for protein folding, to address the challenges of RNA stem-loop folding. Although tempering- and order parameter-based techniques are commonly used for similar rare-event problems, the computational costs or the need for a priori knowledge about the system often present a challenge in their effective use. DDMD overcomes these challenges by adaptively learning from an ensemble of running MD simulations using generic contact maps as the raw input. DeepDriveMD enables on-the-fly learning of a low-dimensional latent representation and guides the simulation toward the undersampled regions while optimizing the resources to explore the relevant parts of the phase space. We showed that DDMD estimates the free energy landscape of the RNA stem-loop reasonably well at room temperature. Our simulation framework runs at a constant temperature without external biasing potential, hence preserving the information on transition rates, with a computational cost much lower than that of the simulations performed with external biasing potentials. We also introduced a reweighting strategy for obtaining unbiased free energy surfaces and presented a qualitative analysis of the latent space. This analysis showed that the latent space captures the relevant slow degrees of freedom for the RNA folding problem of interest. Finally, throughout the manuscript, we outlined how different parameters are selected and optimized to adapt DDMD for this system. We believe this compendium of decision-making processes will help new users adapt this technique for the rare-event sampling problems of their interest.

FESTA: A Polygon-Based Approach for Extracting Relevant Structures from Free Energy Surfaces Obtained in Molecular Simulations.

An easy-to-use script named FESTA (Free Energy Surface Trajectory Analysis) is provided to streamline the extraction of equilibrium structures from free energy maps obtained with enhanced sampling simulation techniques and their associated trajectories. This approach efficiently identifies relevant structures by automatically selecting minima on the free energy surface using a connected-component labeling algorithm and extracts them utilizing a Shapely-polygon-based trajectory analysis process. The script is general and portable; it incorporates an automatic periodicity detection system; and multiprocessing is utilized to leverage all available computational resources for enhanced efficiency. The effectiveness of the proposed polygon-based approach is demonstrated through comparison with a naïve and largely inefficient loop-based script and its application across three distinct systems for benchmarking purposes.

Rock Fracturing Characteristics and Roadway Expansion Application of Static Crushing Agent under Multi-Row Drilling Condition

Static crushing agent (SCA) offers advantages such as good safety, no harmful gases, and minimal vibration, making SCA ideal for rock crushing in mines or underground engineering. To scientifically implement the section expansion of mine roadway, the rock mechanical parameters, SCA expansion properties, and cracking behavior of surrounding rock were investigated using laboratory tests, numerical simulations, and field experiments. Results indicate that the smaller hole spacing of SCA improves the fracturing effect on rock mass, reduces the required fracture initiation stress and penetration stress, and the presence of a free surface aids in fracture development in the rock mass. Optimal borehole design parameters and spacing distributions of the SCA were determined, and corresponding construction techniques of roadway expansion were proposed. Field tests demonstrate that static crushing technology, under multi-row drilling conditions, is highly effective for rock roadway expansion projects. These findings provide valuable guidance for non-explosive expansion and other roof breaking treatment projects.

Free surface simulation over broad crested weirs using VOF and SPH methods

Free surface simulation over broad crested weirs using VOF and SPH methods

Three-dimensional fracture modes decoupling by means of invariant integrals in wood under mixed mode loading

This paper addresses the determination of the energy release rate in an orthotropic elastic material such as wood with a three-dimensional view of the problem. The mixed mode loading associated with the anisotropy of the material required mode decoupling by isolating the energy release rates in mode I, mode II and in mode III. These energy release rates are calculated using the invariant integral M of Linear Elastic Fracture Mechanics (LEFM). This decoupling has necessitated the introduction of kinetically and statically admissible three-dimensional virtual displacement and stress fields in the vicinity of the crack front. The fracture mode decoupling strategy is presented and implemented through finite element modelling of a Mixed Mode Crack Growth (MMCG) specimen. Different thicknesses are investigated to highlight the 3D effects. The modelling highlighted the effect of Mode II at the edges of free surfaces for mixed loadings including mode III (mode III, mode (II+III) and mode (I+II+III)), while mode III was the predominant at the middle of the specimen. In cases of mixed mode (I+II), the energy release rate GI was highest at the middle of the specimen and lowest at the edges of the free surfaces, regardless of the degree of mixing for a given thickness. The correlation between the results obtained using the proposed approach and the non-dependence of the integration domain, as well as with the usual approaches employed in the literature, is demonstrated.

Characterization of the scattered pressure from a cylindrical shell close to a free surface and understanding of the depth-dependent phenomenon

The characterization of the scattered pressure field of a submerged cylindrical target is of interest for underwater acoustics applications. The aim of this work is to study the vibroacoustic behavior of an immersed cylindrical shell excited by a plane wave, particularly in close proximity to a free surface. To achieve this goad, finite element simulation and experimental investigation are carried out on a mock-up. The effect of the free surface is highlighted by comparing results to those obtained in a free field situation, in both time and frequency domains. Additional echoes are observed on the time signals due to the presence of the free surface. In fact, after being scattered by the target, these echoes reflect on the surface, implying a time shift between echoes directly from the target and those that have travelled a longer path. The spectrum is also impacted as the form function shows additional oscillations. These observations are depth-dependent. To determine wave trajectories, a study based on flight time and ray theory is conducted.

Calcium Carbonate Deposition Model Supporting Multiple Operating Conditions Based on the Phase-Field Method for Free-Surface Flows

The drainage systems of tunnels situated in limestone regions frequently encounter crystallization blockages. Numerous studies have addressed this issue, and their findings identified factors such as the flow velocity and temperature as influencing the crystallization process. However, these studies could not predict the occurrence of crystallization. Regarding theoretical approaches, most studies have focused on full-pipe operations or have solely considered flow-field dynamics without including simulations of the chemical reactions and mass transfers. This study introduces a mass-transfer model for drainage pipes based on a two-phase flow (water and air) with a free surface and non-full pipe flow that simulates the crystallization deposition process in drainage pipes. This model can predict the deposition conditions at varying flow velocities and intuitively visualize the crystallization process under the influence of various factors. The impact of flow velocity on the overall crystallization deposition process can be directly analyzed through simulations developed using this model. The results show that under conditions of incomplete pipe flow with no pressure at the outlet, the weight of the deposition first increases and then decreases within a certain velocity. This model can depict the variations within a 30 d period.

Acoustic pattern of a full scale simplified ship

Underwater radiated noise from ship propellers is one of the major contributors to the increase in overall noise levels in marine environments. The development of numerical tools for the computation of noise propagation is of paramount importance for the assessment of the noise impact on the environment. Hybrid approaches, based on the decoupling of the computation of the fluid flow and the successive evolution of the noise using an acoustic analogy, are typically conducted in open-water conditions, which do not correspond to a realistic environment. The Full Acoustic Analogy, which couples a propagation model based on the solution of the acoustic wave equation to the hybrid approach, enables the propagation of the noise generated by a marine propeller in a confined heterogeneous domain. The near-field scattering characteristics of a simplified hull positioned in front of a ship's propeller are analyzed in shallow and deep water, in the presence of the free surface, and compared to the open water case. The analysis determines the directivity of the propeller noise and how this may affect how the noise propagates in the marine environment.

CO2-Laser Irradiation Affects Positively Surface Energy of Rough Titanium Surfaces.

The purpose of this study was to investigate the free surface energy before and after CO2 irradiation on rough titanium surfaces. Sandblasted, large grit, acidetched (SLA) implant surfaces were used for this study. Contact angle evaluations were performed for saline, albumin, and artificial blood using a contact angle goniometer in 25°C and 37°C (20 droplets in each group, 120 in total). The titanium disks were then irradiated with a CO2 laser (10,600 nm) using a non-contact, defocused, 2W continuous wave for 30 seconds. Contact angle measurements for saline, albumin and artificial blood were evaluated immediately after irradiation (new 120 in total contact angle measurements) and compared with the measurements before laser irradiation. Paired t-test using SPSS was performed for 5% statistical significance level. Lower numbers of contact angle measurements were found and changes after CO2-laser irradiation were statistically significant (p < 0.05) for all groups except for albumin at 25°C, as follows: 25℃: (saline) (Pre) 111.97° ±13.67°, (Post) 79.29° ±10.83° / p<0.0001; (albumin) (Pre) 89.04° ±12.02°, (Post) 83.29° ±20.71° / p&#61;0.297; (blood) (Pre) 97.79° ±14.44°, (Post) 86.29° ±10.82° / p&#61;0.019; 37℃: (saline) (Pre) 104.12° ±13.138°, (Post) 92.66° ±4.777° / p&#61;0.001; (albumin) (Pre) 89.04° ±12.02°, (Post) 83.29° ±20.71° / p&#61;0.297 (blood) (Pre) 80.42° ±19.00°, (Post) 58.62° ±24.34° / p&#61;0.012. The CO2 laser irradiation in general positively affected the wettability and hydrophilicity of rough titanium (SLA) surfaces.