Discontinuity Surfaces Research Articles

Effect of engineering geological properties on dam type selection of the Qadis Khordak Dam, Afghanistan

This paper deals with engineering geological properties of Qadis Khordak dam site in Northwest Afghanistan. This study is based on on-site and laboratory tests, surface discontinuity surveying, drilled borehole and permeability test of dam foundation. The engineering geological properties at the dam site were studied in order to evaluate geotechnical characteristics of rock masses at dam foundation, geotechnical properties of alluvium at dam axis, reservoir and borrow materials. The structural geological studies also carried out due to stability and safety of dam on their abutments reservoir and seismicity. Existence of a fault, high permeable zone at dam foundation and the thickness of alluvium at dam axis, are the most engineering geological issues that cause change on dam type selection. In the feasibility phase, the dam type was chosen as the concrete face rock-fill dam, because of state of engineering geological properties of dam site. However, in the design phase dam type has been changed as a rock-fill with a clay core.

Universal Guide for Skull Extraction and Custom-Fitting of Implants to Continuous and Discontinuous Skulls.

Intracranial neurophysiological recordings require chronic implants to provide transcranial access to the brain. Especially in larger animals, which participate in experiments over extended periods of time, implants should match the skull curvature to promote osseointegration and avoid tissue and bacterial ingress over time. Proposed CAD methods for designing implants to date have focused on naive animals with continuous and even skull surfaces and calculate Boolean differences between implant and skull surface to fit the implant to the skull curvature. However, custom-fitting by calculating the difference fails, if a discontinuous skull surface needs to be matched. Also, the difference method does not allow designs with constant material thickness along the skull curvature, e.g., to allow fixed screw lengths. We present a universal step-by-step guide for custom-fitting implants which overcomes these limitations. It is suited for unusual skull conditions, like surface discontinuities or irregularities and includes virtual bending as a process to match skull surfaces while maintaining implant thickness. We demonstrate its applicability for a wide spectrum of scenarios, ranging from complex-shaped single-pieced implants to detailed multicomponent implant systems built on even or discontinuous skull. The guide uses only a few software tools and the final virtual product can be manufactured using CNC milling or 3D printing. A detailed description of this process is available on GitHub including step-by-step video instructions suitable for users without any prior knowledge in CAD programming. We report the experience with these implants over several years in 11 rhesus monkeys.

Generalized Riemann Problem on the Decay of a Discontinuity with Additional Conditions at the Boundary and Its Application for Constructing Computational Algorithms

We construct an approximation of the fundamental solution of a problem for a hyperbolic system of first-order linear differential equations with constant coefficients. We propose an algorithm for an approximate solution of the generalized Riemann problem on the decay of a discontinuity under additional conditions at the boundaries, which allows one to reduce the problem of finding the values of variables on both sides of the discontinuity surface of the initial data to the solution of a system of algebraic equations. We construct a computational algorithm for an approximate solution of the initial-boundary-value problem for a hyperbolic system of first-order linear differential equations. The algorithm is implemented for a system of equations of elastic dynamics; it is used for solving some applied problems associated with oil production.

Coaxial laser directed energy deposition with wire of thin-walled duplex stainless steel parts: Process discontinuities and their impact on the mechanical properties

The topic of this paper is the process stability and its influence on the tensile material properties of duplex stainless steel manufactured via coaxial laser directed energy deposition with wire. The influence of slight changes in the prescribed offset per layer and laser power on the process stability, occurrence of discontinuities, and mechanical properties of duplex stainless steel 2209 parts was investigated. If the prescribed offset or laser power was too high, overheating of the melt-pool was observed. Otherwise, plunging of the wire through the melt-pool occurred. Stable processing was achieved by the adaptation of prescribed offset and laser power according to limited exponential growth laws. The overheating of the melt-pool leads to unsalvageable instabilities, whereas plunging of the wire through the melt-pool leads to self-stabilization by lowering the effective deposition rate and layer height. The discontinuities at sites, where wire plunged through the melt-pool are limited to the surface of the parts. The microstructure and tensile mechanical properties are unaffected by the presence of the surface discontinuities when they are removed by a machining step. The yield strength, ultimate tensile strength, and fracture strain exhibit a strong directionality, which can be explained by the anisotropy and inhomogeneity of the microstructure consisting of austenite-rich layers and ferrite-rich layer bands.

Effect of the initial resin distribution in partially impregnated thermoplastic prepregs on consolidation

The relation between the initial resin distribution in partially-impregnated thermoplastic UD prepregs and the gas evacuation mechanism as they are consolidated under oven vacuum bagging (OVB) process is explored. To conduct the investigation, carbon fiber (CF) tows were partially impregnated using poly (ether ketone) (PEEK) powders to fabricate three specific prepreg architectures with different surface and through-thickness resin distributions. The initial through-thickness resin distributions, porosity, surface impregnation and surface roughness of the prepregs were measured. Next, OVB consolidation experiments were performed. The effectiveness of gas evacuation and void reduction were quantified based on the initial and the final porosity state of their consolidated laminates. The results show that dry prepreg surfaces provide the most effective gas evacuation through interlayer air pathways, whereas, uniform impregnation in the midzone likely reduces the interconnectedness of voids potentially reducing the ability to evacuate voids both in the through-thickness and the in-plane directions. To achieve void-free consolidation, extra attention must be attributed to design features of prepregs to create more discontinuous through-thickness and surface resin distributions to reduce the distance between dry fiber zones on the surface while maintaining interconnectedness of interlayer and intralayer voids. A preliminary 1D single-ply consolidation model was developed, and a numerical study was carried out. The model predictions were assessed by comparison with single-ply (prepreg) consolidation experiments. It was found that the model gives plausible predictions however the model can be improved by coupling it with other simultaneous phenomena occurring during the consolidation process.

High-Precision Printing of Complex Glass Imaging Optics with Precondensed Liquid Silica Resin.

3D printing of optics has gained significant attention in optical industry, but most of the research has been focused on organic polymers. In spite of recent progress in 3D printing glass, 3D printing of precision glass optics for imaging applications still faces challenges from shrinkage during printing and thermal processing, and from inadequate surface shape and quality to meet the requirements for imaging applications. This paper reports a new liquid silica resin (LSR) with higher curing speed, better mechanical properties, lower sintering temperature, and reduced shrinkage, as well as the printing process for high‐precision glass optics for imaging applications. It is demonstrated that the proposed material and printing process can print almost all types of optical surfaces, including flat, spherical, aspherical, freeform, and discontinuous surfaces, with accurate surface shape and high surface quality for imaging applications. It is also demonstrated that the proposed method can print complex optical systems with multiple optical elements, completely removing the time‐consuming and error‐prone alignment process. Most importantly, the proposed printing method is able to print optical systems with active moving elements, significantly improving system flexibility and functionality. The printing method will enable the much‐needed transformational manufacturing of complex freeform glass optics that are currently inaccessible with conventional processes.

Addressing a novel problem on the basis of the generalized vectorial laws of reflection and refraction along with offering novel treatments of derivation of some results in geometrical optics

The generalized vectorial laws of reflection and refraction have been applied in this paper to develop novel determinantal equations involving the coordinates of the object point, image point, and point of incidence in cases of reflection and refraction of light when reflection (refraction) takes place from a plane reflecting surface (plane surface of discontinuity) or from a concave (convex) spherical reflecting surface (spherical surface of discontinuity). Establishment of the theoretical proof of the validity of the principle of reversibility of light has also been accomplished by making use of the novel determinantal equations developed in an earlier work by the author. Furthermore, looking at the interest of the readership, novel treatments for the derivation of the relationship between object distance and image distance in case of reflection of light at a plane reflecting surface as well as for the derivation of the relationships between real depth (height) and apparent depth (height) when refraction of light takes place at a plane surface of discontinuity are also offered in this paper.

Stress-strain curve determined from a non-uniformly deformed specimen: An application of autonomous finite element analysis

Stress-strain curve cannot be directly converted from force-displacement curve if the deformation is not uniform in test specimen. An automated inverse analysis is developed to select the candidate stress-strain curve whose force-displacement result in simulation has the best goodness of fit (GOF) to the test measurement. The candidate stress-strain curves are randomly generated by a Random Stress Strain Curve Generator (RSSCG) under several physical constrains without using test data or analytical formula. The process of finite element analysis (FEA) is packed into a white box function with stress-strain curve as input and its corresponding GOF as output. A Leveled Random Search (LRS) algorithm optimizes the shape of stress-strain curve for a better GOF value. LRS preforms several random probes at each search level. At next level, the size of search zone is reduced while the center of the search zone is repositioned to the best solution found so far. This process continues until a satisfactory result is found. LRS is designed to work with discontinuous response surface and overcome local minimal problem. As an optional feature, Human in the Loop (HITL) can be used to adjust the search zone for fast convergence. Examples in tension and compression test are provided to demonstrate the process. The concept of the automated inverse analysis is summarized as Autonomous Finite Element Analysis (AFEA). The fully automated computer program has been successfully used in material modeling of automobile crashworthiness, producing 40 beyond-necking point stress-strain curves in two weeks.

Development of a free surface flow solver using the Ghost Fluid Method on OpenFOAM

This study is devoted to the development of a VoF/GFM solver using the open source CFD library OpenFOAM. An industrial point of view is adopted in this paper, meaning that simulations are run with large CFL conditions. Weaknesses of the standard OpenFOAM VoF solver interFoam are identified (free surface wiggles and light phase accelerations). Using available literature, MULES algorithm has been abandoned to the profits of algebraic schemes (HRIC, MHRIC, MCICSAM) and the Ghost Fluid Method (GFM, Fedkiw et al. (1999)) has been adopted for dealing with free surface discontinuity. The resulting solver called marineFoam is tested and compared to interFoam on the following test cases : 3D wave impact on a tall structure (dam break) (Gomez-Gesteira, 2013), periodic wave propagation simulation (Larsen et al., 2019), model and full-scale ship resistance simulations (Larsson et al., 2014; Tokyo Workshop, 2015; Lloyd’s Register, 2016). marineFoam can allow large CFL numbers while avoiding free surface wiggles and most of spurious currents. interFoam achieves reliable results but requires additional VoF sub-cycle iterations or a shorter time step.

Seismic Stratigraphy Of The Makassar Basin

Seismic reflection profiles from the Makassar basin have been analysed in terms of seismic stratigraphy. Systematic patterns of reflection terminations indicate the existence of at least three surfaces of discontinuity across the profiles-designated in order of superposition as C1, C2 and C3 - which define the boundaries of four seismic sequences, ie. :- seismic sequence I : topped by C1- seismic sequence II : the interval between C1 and C2- seismic sequence III : the interval between C2 and C3- seismic sequence IV : the interval between Cz and the sea floor Seismic sequence II is dominated by basin slope and basin floor seismic facies whereas seismic sequences II and IV consist of mainly shelf and shelf margin seismic facies. Correlation of seismic sequences with well data facilitates the exposition of basin development, The Late Cretaceous-early Tertiary regional uplift and erosion produced a major unconformity C1, upon which the transgressive facies of seismic sequence II was deposited. A lowstand of sea level due to the so-called intra-Mio- cene orogeny occurred in the upper Early Miocene and produced the C2. Deposition of seismic sequence III is marked by a relative rise of sea level, probably followed by another lowstand of sea level during Mio-Pliocene which formed the C3. The final event is an overall transgression and deposition of seismic sequence IV, with a possible minor lowstand of sea level in Pliocene-Recent, The occurrence of basin slope and basin floor seismic facies within seismic sequence II suggests that in the pre-Lower Miocene, basin subsidence was slightly greater than the rate of depositions. Since Lower Miocene both subsidence and sedimentation rates were equal and the deposition of shelf and shelf margin seismic facies of seismic sequences III and IV was prevailed in the basin.

Developing diagnostic skills from preclinical dental education: Caries detection and assessment using e-learning assisted practice.

To evaluate the feasibility of developing visual diagnostic skills for detecting and assessing dental caries using e-learning assisted practice in preclinical dental education. A one-group before and after the study was conducted. After a theoretical lesson on cariology, 53 inexperienced second-year preclinical students assessed 78 clinical photographs using the Nyvad criteria; they received automated feedback upon completion of the test. After a week, all students reassessed the same set of photographs, which were randomly reordered. Differential diagnostic accuracy was analyzed category-pairwise, and overall accuracy measures were based on the receiver operator curve. Diagnostic accuracy in both attempts was evaluated and compared through estimation and pooling of individual student accuracies. Pooled category-pairwise accuracy was lower for discriminating Sound surface from Non-cavitated-active caries, and for discriminating inactive caries (surface discontinuity) from intact surface inactive caries and Cavitated-active caries. Pooled overall accuracy, after the theoretical lesson, was 0.79 (95% confidence interval [CI] 0.77-0.81), and it increased to 0.99 (95% CI 0.98-0.99) after feedback. Between-student variability in accuracy was reduced from I2 =0.66 to 0.55. E-learning assisted practice is a feasible alternative to start developing visual diagnostic skills for detecting and assessing dental caries using the Nyvad criteria from preclinical dental education in cariology. However, further studies are required to evaluate its effectiveness in improving real-world practice knowledge and skills.

AERODYNAMIC ANALYSIS OF MORPHING WING.

This thesis presents a modelling and design exploration study of a novel twisting wing whose motion is enabled by a tensegrity mechanism. First, the aerodynamic characteristics of the twisting wing, which does not require control surfaces to modulate its shape, are compared with those of a conventional wing having a control surface. It is shown via computational fluid dynamics analyses that the twisting wing displays higher lift-to-drag ratio than the conventional wing and hence the twisting wing is more aerodynamically efficient. In addition, due to the reduction of discontinuous rudder surfaces, morphing wings can further improve the stealth performance. A finite element model with geometrical nonlinear effects is then proposed to correct the errors of the linear analysis and verify the effectiveness of the optimization method. This design is shown to be able to reduce the overall weight of the structure and achieve control of the macro mechanical performance of the wing. The work provides a general optimization design method for similar modular structures, allowing independent programmable adjustment of the parameters of each single structural cell.

Bedding parallel fractures in fine-grained sedimentary rocks: Recognition, formation mechanisms, and prediction using well log

Core, thin section, conventional and image logs are used to provide insights into distribution of fractures in fine grained sedimentary rocks of Permian Lucaogou Formation in Jimusar Sag. Bedding parallel fractures are common in fine grained sedimentary rocks which are characterized by layered structures. Core and thin section analysis reveal that fractures in Lucaogou Formation include tectonic inclined fracture, bedding parallel fracture, and abnormal high pressure fracture. Bedding parallel fractures are abundant, but only minor amounts of them remain open, and most of them are partly to fully sealed by carbonate minerals (calcite) and bitumen. Bedding parallel fractures result in a rapid decrease in resistivity, and they are recognized on image logs to extend along bedding planes and have discontinuous surfaces due to partly-fully filled resistive carbonate minerals as well as late stage dissolution. A comprehensive interpretation of distribution of bedding parallel fractures is performed with green line, red line, yellow line and blue line representing bedding planes, induced fractures, resistive fractures, and open (bedding and inclined) fractures, respectively. The strike of bedding parallel fractures is coinciding with bedding planes. Bedding parallel fractures are closely associated with the amounts of bedding planes, and high density of bedding planes favor the formation of bedding parallel fractures. Alternating dark and bright layers have the most abundant bedding parallel fractures on the image logs, and the bedding parallel fractures are always associated with low resistivity zones. The results above may help optimize sweet spots in fine grained sedimentary rocks, and improve future fracturing design and optimize well spacing.

Numerical event location techniques in discontinuous differential algebraic equations

In this paper, we consider numerical methods for the location of events of differential algebraic equations of index one. These events correspond to cross a discontinuity surface, beyond which another differential algebraic equation holds. Convergence theorems of the numerical event time and event point to the true event time and event point are given. It is proved that, for integrations by semi-implicit methods or Rosenbrock methods, the order of convergence of the numerical event location is the order of convergence of the continuous extension and, for integration by implicit Runge-Kutta methods, the order of convergence is the order of convergence of the implicit RK method.

Capturing rockfall kinematic and fragmentation parameters using high-speed camera system

This paper presents a procedure for tracking rockfall trajectories and extracting kinematic parameters from both the impacts and the resultant fragments. A set of full scale rockfall experiments was performed in a quarry located in Vallirana, Barcelona (Spain). The study site was chosen due to the presence of a rigid discontinuity surface, inclined at 42° in the middle of the slope, whose configuration was expected to favor the breakage of the blocks. The trajectories of the blocks released and of the resultant fragments were recorded with three video cameras. A C++ program was specifically developed to track the 3D trajectory of blocks and fragments, and measure velocities before and after the impact. Two different modules were implemented, one for the blocks that break and one for those that do not. The trajectory of a non-fragmented block is obtained by comparing it to its 3D model. In this way, both the center of mass position and the orientation of the block are tracked. For fragmented blocks, the local coordinates of the fragments determined from the images are converted to terrain coordinates using the program we developed. A total of 16 blocks and 36 rock fragments after impact were tracked. The parameters obtained were georeferenced and linked to a common system of 3D terrestrial coordinates.The captured parameters allow obtaining the velocity distribution of fragments, the coefficient of restitution, and energy balance for the blocks that break. To our knowledge, this is the first attempt to capture kinematic parameters of rock fragments that result from the impact and breakage of rock blocks in full-scale tests. Although the analysis of the rockfall fragmentation phenomenon is beyond of this work, we have compared the performance of the fragmented and unbroken blocks. To this purpose, we have built 3D models of the rock fragments generated using images captured with a drone.The results indicate that blocks that fragment show higher rebound velocities and coefficients of restitution than the blocks that do not although there exists a certain overlap between the two groups. Despite the experiment is carried out on the same discontinuity surface and with small variations in the impact velocities, impact kinetic energies and impact angles, the coefficients of restitution obtained present a wide range of values, both for the blocks that break and for those who do not. The number of tested blocks is too small to draw generalizable conclusions, but they highlight the stochastic nature of the rebound process and the necessity to consider additional parameters for its understanding. Finally, the results confirm the relation between the dissipated energy and, especially the impact energy and the new area created by fragmentation. Furthermore, the blocks that hit the ground with the face are those that generate the most new area while those that hit the vertex generate less.

A new framework based on XFEM to study the role of electrostatic tractions in semipermeable piezoelectric material

In this work, a crack opening model is proposed to study the role of electrostatic tractions in a cracked semipermeable piezoelectric material. The extended finite element method (XFEM) is used in conjunction with six-fold electro-mechanical enrichment functions to capture the singularity and the discontinuous surface independent of the background mesh. The electric displacement intensity factor (EDIF) is evaluated using an electromechanical interaction integral approach in the presence of a dielectric medium inside the crack cavity. The accuracy of the proposed XFEM based approach is verified by comparing the numerical results with available analytical solutions. Further, a systematic numerical study is done to study the influence of electrostatic tractions on the EDIF using different crack configurations under far-field loading.

Self-Motion of Water Droplets along a Spacing Gradient of Micropillar Arrays on Copper.

Self-driven droplet transport along an open gradient surface is increasingly becoming popular for various microfluidics applications. In this work, a gradient copper oxide layer is formed on a copper sheet (as a bipolar electrode, BPE) in a KOH solution by bipolar electrochemistry. The deposits at different positions present a rich variety of colors, compositions, and microstructures along the longitudinal axis of the BPE. More than half the length of the anodic pole is covered by a Cu(OH)2/CuO composite layer of several micrometers thick, which is composed of dense micropillars with a decreasing spacing gradient to the anodic direction. The micropillar arrays are superhydrophilic, and after modified with 1-dodecanethiol, the tops of the dense micropillars constitute a hydrophobic and microscopically discontinuous surface with a wettability gradient. On such a gradient surface water droplets can move spontaneously to more hydrophilic direction at a velocity of about 16 mm s-1. The superhydrophobicity of the modified micropillar arrays is discussed through a comparison with the wax tubules on a lotus leaf. Theoretical analysis of the driving force reveals that the concave surface effect of water at the spacings between the micropillars is the critical factor for driving the rolling motion of the droplets along the gradient micropillar arrays.

Boosting the Model Discovery of Hybrid Dynamical Systems in an Informed Sparse Regression Approach

Abstract We present an efficient data-driven sparse identification of dynamical systems. The work aims at reconstructing the different sets of governing equations and identifying discontinuity surfaces in hybrid systems when the number of discontinuities is known a priori. In a two-stage approach, we first locate the switches between separate vector fields. Then, the dynamics among the manifolds are regressed, in this case by making use of the existing algorithm of Brunton et al. (2016, “Discovering Governing Equations From Data by Sparse Identification of Nonlinear Dynamical Systems,” Proc. Natl. Acad. Sci., 113(15), pp. 3932–3937). The reconstruction of the discontinuity surfaces comes as the outcome of a statistical analysis implemented via symbolic regression with small clusters (microclusters) and a rigid library of models. These allow to classify all the feasible discontinuities that are clustered and to reduce them into the actual discontinuity surfaces. The performances of the sparse regression hybrid model discovery are tested on two numerical examples, namely, a canonical spring-mass hopper and a free/impact electromagnetic energy harvester (FIEH), engineering archetypes characterized by the presence of a single and double discontinuity, respectively. Results show that a supervised approach, i.e., where the number of discontinuities is pre-assigned, is computationally efficient and it determines accurately both discontinuities and set of governing equations. A large improvement in the time of computation is found with the maximum achievable reliability. Informed regression-based identification offers the prospect to outperform existing data-driven identification approaches for hybrid systems at the expense of instructing the algorithm for expected discontinuities.

UPPER-BOUND SOLUTIONS FOR BEARING CAPACITY OF STRIP FOOTINGS OVER ANISOTROPIC NONHOMOGENEOUS CLAYS

All available solutions for the problem of bearing capacity on clays of anisotropic and nonhomogeneous strength are based on the assumption of either circular or Prandtl-type failure mechanisms. Although these solutions are rigorous within the concept of limit analysis or limit equilibrium methods, the formulations are too mathematical and exceedingly cumbersome and the bearing capacity value can only be determined through numerical optimization for each given combination of soil and failure mechanism parameters. By means of the upper bound approach of limit analysis, and adopting translational failure mechanisms, this paper presents analytical solutions for the bearing capacity of surface strip footings on clays of strength anisotropic and linearly increasing with depth. Closed-form expressions for bearing capacity factors in the case of smooth and rough footings, have been derived by considering two newly introduced kinematically admissible translational failure mechanisms with varying wedge angles. It was remarkable to find that the two mechanisms would render closed-form expressions for the bearing capacity factor if and only if the deformed region underneath the footing is set to be bounded by two vertical discontinuity surfaces. The derived formulas are expressed in terms of degree of strength anisotropy and a nondimensional parameter that reflects strength nonhomogeneity. Besides being the only closed-form solutions yet available for the bearing capacity of strip footings on clays with anisotropic and nonhomogeneous strength, the derived expressions have been found to not only provide upper bound values for the bearing capacity factor that compared favorably with available solutions, but also yield the best upper bound values when strength increase with depth becomes predominant.

A novel phase-shifting profilometry to realize temporal phase unwrapping simultaneously with the least fringe patterns

A novel phase-shifting profilometry (PSP) to realize temporal phase unwrapping (TPU) simultaneously with the least fringe patterns is proposed. By combining a unit-frequency ramp pattern with the least three phase-shifting sinusoidal fringe patterns at a shifted-phase of π/2 respectively, three composite patterns are formed. While these three composite patterns are projected onto the measured object successively, three corresponding deformed patterns can be captured by a CCD camera. After demodulation, both the unit-frequency component and the high-frequency components characterized by phase-shifting deformed patterns can be extracted efficiently. So the wrapped phase caused by the measured object can be calculated from the high-frequency components of the deformed patterns with PSP and the fringe orders can be derived from the unit-frequency components to pixel-wise auxiliary phase unwrapping. It employs no other additional structure pattern to achieve full-field phase unwrapping. The accuracy of the measurement is guaranteed by using three phase-shifting fringe patterns, and the combination of the TPU can measure the discontinuous surfaces or multiple isolated objects simultaneously. PSP and TPU are integrated skillfully with least fringe patterns in the proposed method. The experimental results demonstrated the feasibility and validity of the proposed method.