Geometry Of Discontinuities Research Articles

Effects of 2-D and 3-D helical inserts on the turbulent flow in pipes

A constant search for more efficient heat exchangers motivates the use of innovative turbulators. Original flow-field measurements were performed with S-PIV to gain a better understanding of the role of 3-D wall obstacles in pipe flows. Such effects are compared with those of 2-D helically corrugated tubes, which are already provided in the literature. This work further investigates the impact of both continuous (2-D corrugation) and discontinuous (3-D corrugation) obstructions on the surrounding velocity field. The analysis of the flow structures is made by comparing two types of helicoidal turbulators. The continuous geometry has a pitch-to-diameter-ratio of p/D = 11 and an inclination angle of 80°. An obstacle height-to-diameter-ratio of e/D = 3.6% is used, which is constant throughout the helix-wise direction. The discontinuous geometry is equivalent to the continuous one except that it has a varying obstacle height throughout the helix. The reattachment and redevelopment of the flow are determined by time-averaged velocity analysis, at Re = 20,000. Notably, the aim of this study is to examine the effects of the discontinuity in the tube corrugation on the flow separation/reattachment, turbulence statistics, vorticity (ω) and strain-rate (Sxy) of the flow particles, and compare them with a previously studied continuous turbulator. As a result, the discontinuous rib has a lower impact on the pressure losses, on the azimuthal swirl, and on the turbulent kinetic energy generation. In the field close to the wall, the changing height of the discontinuous rib generates a turbulent kinetic energy and an azimuthal velocity, respectively, 50% and 35% lower than the continuous configuration. The irregularity of the discontinuous obstacles provides a reduced skin friction coefficient (Cf) which is 0.57 times the one given by the continuous 2-D helical turbulator. On the other hand, the observed less intense wall-bounded turbulence levels associated with the 3-D helical turbulator suggest a lower local heat transfer enhancement.

Application of 3D-DDA integrated with unmanned aerial vehicle–laser scanner (UAV-LS) photogrammetry for stability analysis of a blocky rock mass slope

In stability analysis of discontinuity-controlled slopes, the rationality of results is related to the accuracy of three-dimensional (3D) slope morphology and the reliability of the discontinuity survey. With the advent of remote sensing technologies for engineering geological surveys and slope stability analyses, step-change increases have been made in the quality of data available and geometrical characterization of rock slopes. Although these techniques are frequently employed in the characterization of slope geometry and joint surfaces at present, limited research has been undertaken to effectively process the derived data and improve the quality in the reconstruction of slope geometry imported into 3D discontinuous numerical models. In this paper, an integrated system coupling 3D-DDA and UAV-LS photogrammetry is presented as a tool to evaluate the stability of a blocky rock mass slope. The system includes a UAV-LS module, a modeling module, a block-generation module, and a 3D-DDA calculation module. In the UAV-LS module, the use of UAV-LS system integrated with field mapping and site observations allows the acquisition of detailed outputs (point clouds) on both the slope and discontinuity geometry. An effective combination of commercial software Geomagic and Hyperworks is used in the modeling module to process oceans of 3D point cloud data and construct complex 3D geometrical models based on reverse engineering. In the block-generation module, the three-dimensional discontinuous deformation analysis (3D-DDA) method is then carried out in order to simulate the movement of potentially unstable blocks, within which an independent block-cutting algorithm is used to generate the blocks with arbitrary shapes and the finite structural planes similar to the real cases. The 3D-DDA calculation module uses 3D-DDA calculation algorithm to derive the simulation results. The capability of the proposed system for stability analysis of a jointed slope is demonstrated by a practical example.

Development and implementation of an effective constitutive model for architected cellular iron-based shape memory alloys: Pressure dependency and transformation-plasticity interaction

Using architected cellular iron-based shape memory alloys (AC Fe-SMAs) can help compensate the relatively higher density of the base material compared to NiTi-based and Cu-based shape memory alloys, while providing good shape recovery, lower production cost, and greater energy dissipation. This article is dedicated to the development of an effective and pressure-dependent constitutive model that predicts the thermomechanical response of AC Fe-SMAs. We first simulate the behavior of the cellular material using the dense model that was previously developed by the authors, along with different unit cells (UCs) subject to periodic boundary. The shape memory effect is simulated by compressing the UCs by 2% of their height, followed by mechanical unloading, and heating above the austenite finish temperature. The results highlight stress concentration, maximum phase transformation, and maximum plastic deformation at the geometry discontinuities or strands necks. Post-processing the ABAQUS ODB files with Python scripts shows that the bending-dominated unit cell with the highest maximum local values of state variables exhibits the lowest volume-averaged outputs. Comparison of the unit cell to cubic multi-cell structures points out an asymptotic vanishing of the effects of the free boundaries as the number of cells in the multi-cell structure increases. The results of the unit cells are used to calibrate the parameters of the pressure-dependent effective model. The ratios of the inelastic hydrostatic strains to the equivalent total inelastic strains indicate higher pressure effects in the bending-dominated cellular lattice than in the stretch-dominated structures. The force-displacement and “dissipated energy”-temperature curves of the cellular beam and its equivalent bulk structure obtained by simulations of 4-point bending tests are found to be close enough that the effective model can be considered as an efficient design tool for architected cellular iron-based shape memory alloy structures.

Insight into the tension stiffening behavior of reinforced concrete tension members revealed by finite element modeling

The disasters happened in recent past pointed out the need of design criteria, ensuring adequate safety levels against progressive collapse. The attention was focused on the behavior of composite beam-to-column joint components in the field of large displacements. This article presents the experimental and numerical study enabling the simulation of the RC elements under tension. This has helped in understanding the non-negligible contribution of concrete in tension stiffening response up to failure especially in the case of discontinuous geometry marked in composite structures. The finite element model proposed may be considered a mid-way between smeared and discrete crack modeling approaches.

Modeling the Structure of Type IV Pili from Shewanella Oneidensis

The metal-reducing bacterium Shewanella oneidensis produces conductive nanowires, which are described as extensions of the outer membrane or type IV pili (T4P), of which the structural details remain unknown. To better understand the structure of S. oneidensis T4P as a nanowire candidate, and the potential mechanism for electron transport along them, theoretical energy-minimized models of these pili were constructed. The models showed a discontinuous geometry consisting of aromatic rings, with large gaps of ∼10 Å, providing a potential pathway for electron hopping, which may account for previously reported conductivity. Moreover, mutations of the pilin subunit based on the models were proposed, which might fill the gaps and possibly increase the conductivity. These models will facilitate further investigation of the nanowires and their applications in bioenergy and bioelectronics.

Stochastic geometry model of rock mass fracture network in tunnels

Geometric distributions of fractures or discontinuities control the behaviour, and limit the strength and the stability of rock masses where the best stabilization and improvement method for that rock mass could be achieved based on favourable discontinuity geometry. This study introduces an algorithm named ‘Stochastic Geometry Model of Fractures Network in Tunnels (SGMFNT)’, which was developed with the MATHEMATICA software. The SGMFNT method provides a fractures geometric distribution database to aid discontinuous rock mass stability analysis by block modelling codes. This algorithm increased the accuracy of the discontinuity model based on the Heliot and Baecher models in a 2D space. The SGMFNT that was used in two of the sectors of the Kani-Sib water conveyance tunnel in the west Azerbaijan province, Iran has successfully provided the rock mass geometrical discontinuity model for this case study.

Optical Metrology of Freeforms and Complex Lenses

AbstractOptical surfaces are becoming more and more complex and custom designs increasingly involve freeform surfaces and discontinuous geometries. This article discusses requirements and limitations of optical form measurements as part of the manufacturing process of such extreme optics.

Validation of 3D discrete fracture network model focusing on areal sampling methods-a case study on the powerhouse cavern of Rudbar Lorestan pumped storage power plant, Iran

. Discontinuities considerably affect the mechanical and hydraulic properties of rock mass. These properties of the rock mass are influenced by the geometry of the discontinuities to a great extent. This paper aims to render an account of the geometrical parameters of several discontinuity sets related to the surrounding rock mass of Rudbar Lorestan Pumped Storage Power Plant powerhouse cavern making use of the linear and areal (circular and rectangular) sampling methods. Taking into consideration quite a large quantity of scanline and the window samplings used in this research, it was realized that the areal sampling methods are more time consuming and cost-effective than the linear methods. Having corrected the biases of the geometrical properties of the discontinuities, density (areal and volumetric) as well as the linear, areal and volumetric intensity accompanied by the other properties related to four sets of discontinuities were computed. There is an acceptable difference among the mean trace lengths measured using two linear and areal methods for the two joint sets. A 3D discrete fracture network generation code (3DFAM) has been developed to model the fracture network based on the mapped data. The code has been validated on the basis of numerous geometrical characteristics computed by use of the linear, areal sampling methods and volumetric method. Results of the linear sampling method have significant variations. So, the areal and volumetric methods are more efficient than the linear method and they are more appropriate for validation of 3D DFN (Discrete Fracture Network) codes.

A Spatial Target Function for Metropolis Photon Tracing

The human visual system is sensitive to relative differences in luminance, but light transport simulation algorithms based on Metropolis sampling often result in a highly nonuniform relative error distribution over the rendered image. Although this issue has previously been addressed in the context of the Metropolis light transport algorithm, our work focuses on Metropolis photon tracing. We present a new target function (TF) for Metropolis photon tracing that ensures good stratification of photons leading to pixel estimates with equalized relative error. We develop a hierarchical scheme for progressive construction of the TF from paths sampled during rendering. In addition to the approach taken in previous work, where the TF is defined in the image plane, ours can be associated with compact spatial regions. This allows us to take advantage of illumination coherence to more robustly estimate the TF while adapting to geometry discontinuities. To sample from this TF, we design a new replica exchange Metropolis scheme. We apply our algorithm in progressive photon mapping and show that it often outperforms alternative approaches in terms of image quality by a large margin.

A spatial target function for metropolis photon tracing

The human visual system is sensitive to relative differences in luminance, but light transport simulation algorithms based on Metropolis sampling often result in a highly nonuniform relative error distribution over the rendered image. Although this issue has previously been addressed in the context of the Metropolis light transport algorithm, our work focuses on Metropolis photon tracing. We present a new target function (TF) for Metropolis photon tracing that ensures good stratification of photons leading to pixel estimates with equalized relative error. We develop a hierarchical scheme for progressive construction of the TF from paths sampled during rendering. In addition to the approach taken in previous work, where the TF is defined in the image plane, ours can be associated with compact spatial regions. This allows us to take advantage of illumination coherence to more robustly estimate the TF while adapting to geometry discontinuities. To sample from this TF, we design a new replica exchange Metropolis scheme. We apply our algorithm in progressive photon mapping and show that it often outperforms alternative approaches in terms of image quality by a large margin.

Beyond debuttressing: Mechanics of paraglacial rock slope damage during repeat glacial cycles

AbstractCycles of glaciation impose mechanical stresses on underlying bedrock as glaciers advance, erode, and retreat. Fracture initiation and propagation constitute rock mass damage and act as preparatory factors for slope failures; however, the mechanics of paraglacial rock slope damage remain poorly characterized. Using conceptual numerical models closely based on the Aletsch Glacier region of Switzerland, we explore how in situ stress changes associated with fluctuating ice thickness can drive progressive rock mass failure preparing future slope instabilities. Our simulations reveal that glacial cycles as purely mechanical loading and unloading phenomena produce relatively limited new damage. However, ice fluctuations can increase the criticality of fractures in adjacent slopes, which may in turn increase the efficacy of fatigue processes. Bedrock erosion during glaciation promotes significant new damage during first deglaciation. An already weakened rock slope is more susceptible to damage from glacier loading and unloading and may fail completely. We find that damage kinematics are controlled by discontinuity geometry and the relative position of the glacier; ice advance and retreat both generate damage. We correlate model results with mapped landslides around the Great Aletsch Glacier. Our result that most damage occurs during first deglaciation agrees with the relative age of the majority of identified landslides. The kinematics and dimensions of a slope failure produced in our models are also in good agreement with characteristics of instabilities observed in the field. Our results extend simplified assumptions of glacial debuttressing, demonstrating in detail how cycles of ice loading, erosion, and unloading drive paraglacial rock slope damage.

A symplectic analytical wave propagation model for damping and steady state forced vibration of orthotropic composite plate structure

• A symplectic analytical wave model is proposed for damping of orthotropic composites. • The vibration of composites is solved by a hybrid wave and finite element model. • The relationship between the wave damping and the modal damping is revealed. An analytical wave propagation model is proposed in this paper for damping and steady state forced vibration of orthotropic composite plate structure by using the symplectic method. By solving an eigen-problem derived in the symplectic dual system of free bending vibration of orthotropic rectangular thin plates, the wave shape of plate is obtained in symplectic analytical form for any combination of simple boundary conditions along the plate edges. And then the specific damping capacity of wave mode is obtained symplectic analytically by using the strain energy theory. The steady state forced vibration of built-up plates structure is calculated by combining the wave propagation model and the finite element method. The vibration of the uniform plate domain of the built-up plates structure is described using symplectic analytical waves and the connector with discontinuous geometry or material is modeled using finite elements. In the numerical examples, the specific damping capacity of orthotropic rectangular thin plate with three different combinations of boundary condition is first calculated and analyzed. Comparisons of the present method results with respect to the results from the finite element method and from the Rayleigh–Ritz method validate the effectiveness of the present method. The relationship between the specific damping capacity of wave mode and that of modal mode is expounded. At last, the damped steady state forced vibration of a two plates system with a connector is calculated using the hybrid solution technique. The availability of the symplectic analytical wave propagation model is further validated by comparing the forced response from the present method with the results obtained using the finite element method.

A Guided Wave Sensor Enabling Simultaneous Wavenumber-Frequency Analysis for Both Lamb and Shear-Horizontal Waves.

Guided waves in plate-like structures have been widely investigated for structural health monitoring. Lamb waves and shear horizontal (SH) waves, two commonly used types of waves in plates, provide different benefits for the detection of various types of defects and material degradation. However, there are few sensors that can detect both Lamb and SH waves and also resolve their modal content, namely the wavenumber-frequency spectrum. A sensor that can detect both waves is desirable to take full advantage of both types of waves in order to improve sensitivity to different discontinuity geometries. We demonstrate that polyvinylidene difluoride (PVDF) film provides the basis for a multi-element array sensor that detects both Lamb and SH waves and also measures their modal content, i.e., the wavenumber-frequency spectrum.

Taking a Sharp Turn: Modeling of Diffraction Coupling in Radio Propagation Inside Tunnels

The overall performance of a communication-based train control (CBTC) system largely depends on the performance of its data communications subsystem (DCS). The DCS network in almost all CBTC commercial system products marketed in the last decade uses radio communications in the open industrial, scientific, and medical (ISM) bands (2.4 or 5.8 GHz) to establish the bidirectional data link between central/wayside and onboard segments. Key factors in ensuring stable and sound radio communication are the number of wayside access points and locations of their antennas. Radio propagation modeling aims to provide optimal and reasonably reliable assurance of stable communication. However, the diffraction impact of sharp corners and edges in tunnels on the radio propagation process has been unaccounted for in the majority of models. The purpose of the present research is to incorporate the effect of diffraction coupling due to sharp edges in tunnel sections, including geometrical discontinuities such as cross junctions and L bends, through ray-mode conversion. The proposed modeling approach offers sufficient versatility to assimilate a variety of discontinuous geometries involving sharp edges in a tunnel environment. Numerical and empirical results suggest that the model provides an accurate tool for analyzing diffraction effects of tunnel discontinuities with sharp edges on the process of radio propagation.

A Spatial Target Function for Metropolis Photon Tracing

The human visual system is sensitive to relative differences in luminance, but light transport simulation algorithms based on Metropolis sampling often result in a highly nonuniform relative error distribution over the rendered image. Although this issue has previously been addressed in the context of the Metropolis light transport algorithm, our work focuses on Metropolis photon tracing. We present a new target function (TF) for Metropolis photon tracing that ensures good stratification of photons leading to pixel estimates with equalized relative error. We develop a hierarchical scheme for progressive construction of the TF from paths sampled during rendering. In addition to the approach taken in previous work, where the TF is defined in the image plane, ours can be associated with compact spatial regions. This allows us to take advantage of illumination coherence to more robustly estimate the TF while adapting to geometry discontinuities. To sample from this TF, we design a new replica exchange Metropolis scheme. We apply our algorithm in progressive photon mapping and show that it often outperforms alternative approaches in terms of image quality by a large margin.

Multiresolution eXtended Free-Form Deformations (XFFD) for non-rigid registration with discontinuous transforms.

Image registration is an essential technique to obtain point correspondences between anatomical structures from different images. Conventional non-rigid registration methods assume a continuous and smooth deformation field throughout the image. However, the deformation field at the interface of different organs is not necessarily continuous, since the organs may slide over or separate from each other. Therefore, imposing continuity and smoothness ubiquitously would lead to artifacts and increased errors near the discontinuity interface. In computational mechanics, the eXtended Finite Element Method (XFEM) was introduced to handle discontinuities without using computational meshes that conform to the discontinuity geometry. Instead, the interpolation bases themselves were enriched with discontinuous functional terms. Borrowing this concept, we propose a multiresolution eXtented Free-Form Deformation (XFFD) framework that seamlessly integrates within and extends the standard Free-Form Deformation (FFD) approach. Discontinuities are incorporated by enriching the B-spline basis functions coupled with extra degrees of freedom, which are only introduced near the discontinuity interface. In contrast with most previous methods, restricted to sliding motion, no ad hoc penalties or constraints are introduced to reduce gaps and overlaps. This allows XFFD to describe more general discontinuous motions. In addition, we integrate XFFD into a rigorously formulated multiresolution framework by introducing an exact parameter upsampling method. The proposed method has been evaluated in two publicly available datasets: 4D pulmonary CT images from the DIR-Lab dataset and 4D CT liver datasets. The XFFD achieved a Target Registration Error (TRE) of 1.17 ± 0.85mm in the DIR-lab dataset and 1.94 ± 1.01mm in the liver dataset, which significantly improves on the performance of the state-of-the-art methods handling discontinuities.

On the cubic law and variably saturated flow through discrete open rough-walled discontinuities

Fracture flow is fairly well documented with the widespread application of, for instance, the cubic law and assumed smooth parallel plate model. Geometrical intricacies such as aperture, roughness and infill do however significantly influence the validity of the cubic law with even its application to smooth parallel systems being contestable. Rock mechanical discontinuity surveys provide valuable information regarding the discontinuity geometry that can likely contribute to the evaluation of flow through individual fractures with variable properties. The hydraulic aperture is available for the transmission of flow, while normal and shear stresses alter discontinuity properties over time. In this, numerous advances have been made to better accommodate deviations of natural discontinuity geometry to that of smooth parallel plates and at partial saturation. The paper addresses these advances and details conditions under which the cubic law, even in local form, fails to adequately estimate the hydraulic properties. The role of roughness in open discontinuities is addressed in particular, as contact areas and high amplitude roughness cause most extensive deviation from the cubic law. Aperture of open fractures still governs hydraulic properties, but inertial forces control flow in very rough fractures, in which instances the applicability of the cubic law should be revisited. Open questions are finally posed, assessment of which will contribute significantly to the understanding of flow through individual discontinuities as well as fracture networks.

Numerical modeling of discontinuous rock slopes utilizing the 3DDGM (three-dimensional discontinuity geometrical modeling) method

The geometry of discontinuities in a rock mass is one of the most important influences on the behavior and characteristics of that rock mass. The geometry of discontinuities largely determines the stability of the rock mass, as well as appropriate methods for reinforcing and stabilizing that mass. This study introduces the 3DDGM (three-dimensional discontinuity geometrical modeling) method, which is based on the 3DGM (three-dimensional geometrical modeling) algorithm that was developed using the Mathematica software package. The 3DDGM method provides essential input data for the stability analysis of a discontinuous rock mass using block stability assessment techniques or block modeling codes. The 3DDGM method developed in the present work was designed to model discontinuities in rock masses and to provide accurate values for discontinuity parameters (i.e., location, spacing, separation, system, orientation, etc.). This algorithm was developed to increase the accuracy of the discontinuity model based on the Heliot algorithm. The 3DDGM algorithm was tested by applying it to a real case, the sloping discontinuous rock mass at the phase 7 gas flare site in the South Pars Gas Complex in Assalouyeh, Iran, and the algorithm was successful in providing a three-dimensional model of the discontinuities in the rock mass at the site.

Novel Fibonacci spiral antenna and its miniaturization using fractals

This paper reports the investigation on a new spiral antenna constructed using well-known Fibonacci sequence. Its performance has been compared first with a universal logarithmic spiral antenna (LSA) of nearly the same dimension. Next the discontinuous geometry of the proposed Fibonacci spiral antenna (FSA) has been exploited to fractalize it using Koch curve. The fractalized Koch-FSA has nearly two-third of physical size miniaturization while retaining antenna radiation characteristics.However like other spiral antennas, the multiband behavior of FSA is evident because of conducting ground plane just below it. The geometries of the antenna have been simulated using CST Microwave studio and fabricated over lossy FR-4 substrate with dielectric constant er = 4.33, loss tangent tanδ = 0.0025 and thickness, ts = 1.5 mm. The measured results are in well agreement with simulations. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1315–1319, 2016

Electromagnetic Embossing of Optical Microstructures

Electromagnetic forming (EMF) is a high-speed forming process that is already established in the macroworld. Due to its advantages like high deformation rate and cheaper tools, it is introduced to microforming. In this research, the replication of prismatic optical microstructures is investigated. EN AW-1050A (Al99.5) micrometal sheets with a thickness of 50 μm and 300 μm are electromagnetically micro-embossed. With this technique, it is possible to successfully replicate triangular cross section micro V-grooves of 86.6 μm in width and 24.1 μm in depth with an average surface roughness of Sa = 44 nm. The microstructures of the embossing tool are generated by diamond micro chiseling (DMC), a novel machining process to produce microstructures with discontinuous geometry, like miniature cube corner retro reflectors and V-grooves with well-defined endings.