Mesh Objects Research Articles

A Comprehensive Study of Watermarking Schemes for 3-D Polygon Mesh Objects

A Comprehensive Study of Watermarking Schemes for 3-D Polygon Mesh Objects

Simulation Informed CAD for 3D Nanoprinting

A promising 3D nanoprinting method, used to deposit nanoscale mesh style objects, is prone to non-linear distortions which limits the complexity and variety of deposit geometries. The method, focused electron beam-induced deposition (FEBID), uses a nanoscale electron probe for continuous dissociation of surface adsorbed precursor molecules which drives highly localized deposition. Three dimensional objects are deposited using a 2D digital scanning pattern—the digital beam speed controls deposition into the third, or out-of-plane dimension. Multiple computer-aided design (CAD) programs exist for FEBID mesh object definition but rely on the definition of nodes and interconnecting linear nanowires. Thus, a method is needed to prevent non-linear/bending nanowires for accurate geometric synthesis. An analytical model is derived based on simulation results, calibrated using real experiments, to ensure linear nanowire deposition to compensate for implicit beam heating that takes place during FEBID. The model subsequently compensates and informs the exposure file containing the pixel-by-pixel scanning instructions, ensuring nanowire linearity by appropriately adjusting the patterning beam speeds. The derivation of the model is presented, based on a critical mass balance revealed by simulations and the strategy used to integrate the physics-based analytical model into an existing 3D nanoprinting CAD program is overviewed.

Accelerated X-Ray Diffraction (Tensor) Tomography Simulation Using OptiX GPU Ray-Tracing Engine

X-ray diffraction tomography (XDT) is used to probe the material composition of objects providing improved contrast between materials compared with conventional transmission-based computed tomography (CT). Current challenges presented with XDT include long image acquisition and simulation time. To accelerate the simulation speed, our approach is to adopt NVIDIA’s OptiX ray-tracing engine, a parallelized pipeline for graphics processing units (GPUs), to perform XDT simulations on objects by making use of the innovative transformation from conventional 3-D physical space into a 2-D quasi-reciprocal space. The advantage is that ray tracing in this domain requires only 3-D mesh objects, yielding calculations without the need for voxels. The simulated XDT projections demonstrate high consistency with voxel models, with a normalized mean square difference less than 0.66%, and the ray-tracing time is two orders of magnitude less than the previously reported voxel-based GPU ray-tracing results. Due to an accelerated simulation time, XDT projections of objects with three spatial dimensions (4-D tensor) have also been reported, demonstrating the feasibility for large-scale high-dimensional tensor tomography simulations.

Observing Geomorphological Change on an Evolving Coastal Sand Dune Using SLAM-Based UAV LiDAR

Following over 20 years of manned airborne LiDAR in the remote sensing of geomorphological change in coastal environments, rapid advancements in unmanned aerial vehicle (UAV) technologies have expanded the possibilities of acquiring very high-resolution data efficiently over spatial-temporal scales not previously feasible. This study employed a new Simultaneous Localisation and Mapping (SLAM)–based LiDAR system (“Hovermap”) across a segment of coastal sand dune of Bribie Island, Queensland, Australia. The study area was identified by the local council as an area of interest over concern that continued erosion at an existing blowout could result in cutting off northern Bribie Island and adversely affect hydrodynamic processes of Pumicestone Passage, its shoreline, and its associated infrastructure. Here, we employed the Hovermap within a multi-temporal design in which four, quarterly, surveys undertaken over a 9-month period from July 2017 to April 2018. On the first survey, a Leica P40 (P40) terrestrial laser scanner (TLS) was also deployed across the study area to facilitate a performance comparison. Hovermap reported a mean point cloud density of 2532 ± 170 pts.·m-2, ground sample distance (GSD) of 0.02 ± 0.001 m, and RMSE of 0.050 ± 0.31 m relative to ground control points (GCPs). Three-dimensional mesh objects were derived from all point clouds obtained and evaluated in terms of elevation and slope with mesh-to-mesh deviations and volumetric change (cubature) analysis examined over consecutive surveys. The Hovermap closely matched results of the P40 with measures of elevation and slope differing by approximately 2% and 7%, respectively. Mean vertical deviation (0.01 ± 0.03 m) and cubature (~ 2.5 m3 net difference) results also showed close agreement. Due to stable wave conditions between the first three surveys, minimal changes in beach topography were observed, whilst pronounced erosion and scarping of the foredune were measured during the final survey. This erosion was evidenced from changes in mean elevation (− 16%), slope (+ 25%), and deviation (+ 86%) relative to the mean measurements over the first three survey dates. In addition, a net loss of approximately -1295 m3 of sand was measured between the final two survey dates (January–April 2018). This is supported by local marine weather data in which a significant increase in local wind speeds (ANOVA, F(1,180) = 6.257, p = 0.013) and wave heights (ANOVA F(1,180) = 41.769, p ≤ 0.001) were recorded over the same interval. The results presented here are first to demonstrate that UAV LiDAR performance was robust in a typical, moderate-energy, sandy beach and is suited for the detection and evaluation of coastal morphologic change at microspatial and temporal scales.

A micromorphic approach for gradient-enhanced anisotropic ductile damage

This paper deals with the numerically effective modeling of anisotropic material degradation caused by ductile damage. Although standard local anisotropic damage models are relatively well-developed nowadays, their regularization which is required in order to eliminate their mathematical ill-posedness is far from being straightforward. It bears emphasis that this regularization is not only required from a mathematical point of view, since the aforementioned ill-posedness is known to be the source for the pathological mesh dependence as far as the finite element method is concerned. Within this paper, a general local framework for capturing anisotropic material degradation caused by ductile damage is extended to a non-local model by means of a gradient-enhancement. However, in order to achieve a numerically effective implementation, the gradient-enhancement is not implemented in a direct manner, but by means of a micromorphic approximation. By doing so, the implementation of the underlying local model is almost unaffected. Particularly the inequalities resulting from the yield function can be restricted to the local integration point level. Since a naive micromorphic implementation turns out to be unsuitable for regularizing the underlying local model, a novel adaption of the yield function is proposed. It is shown that the resulting single-surface-model is indeed able to capture anisotropic material degradation caused by ductile damage and, furthermore, that the finite element implementation is mesh objective.

IMMERSIVE VISUALISATION OF CONSTRUCTION SITE POINT CLOUD DATA, MESHES AND BIM MODELS IN A VR ENVIRONMENT USING A GAMING ENGINE

Abstract. By adopting Building Information Modelling (BIM) software, the architecture, engineering and construction (AEC) industry shifted from a two-dimensional approach to a three-dimensional one in the design phase of a building. However, a similar three-dimensional approach for the visualisation of the current state of the construction works is lacking. Currently, progress reports typically include numerous pictures of the construction site or elements, alongside the appropriate parts of the 3D as-design BIM model. If a proper transition to a 3D design versus 3D current state were achieved, the evolved type of reports would become more comprehensible, resulting in more well-informed decision-making. This requires a single, unique software platform that is able to import, process, analyse and visualise both the as-design BIM model as well as the recorded data of the current construction state. At present however, the visualisation and interpretation of the different datasets alone requires already multiple software packages.As a partial solution this work presents a platform to easily visualise and interpret various data sources such as point clouds, meshes and BIM models and analysis results. Recent advances of gaming engines focus on and allow for an excellent visualisation of mesh data. Therefore all of the aforementioned data sources are converted into mesh objects upon importing. Moreover, gaming engines provide the necessary tools to traverse the scene intuitively allowing construction site managers and other stakeholders to gain a more complete and better oversight of the construction project. Furthermore, these engines also provide the possibility to take the immersion to the next level: incorporating the 3D entities into a Virtual Reality (VR) environment makes the visualised data and the executed analyses even more comprehensible.By means of a case study, the potential of the presented approach is showcased. The real-world construction site recordings, models and analyses are visualised and implemented in VR using the Unity gaming engine.

Laparoscopic sacral colpopexy with polyester fiber suture: Ozerkan modification.

Mesh-related problems are significant complications of laparoscopic sacral colpopexy. The conventional technique precludes performing laparoscopic sacral colpopexy without using a mesh. We describe the Ozerkan modification for laparoscopic sacral colpopexy using a polyester fiber suture instead of a standard mesh and report 1-year objective and subjective outcomes. Women diagnosed with stage ≥ 2 vaginal vault prolapse were prospectively recruited for the Ozerkan modification between 2015 and 2017. The primary outcome was the anatomic success of the repair, defined by objective parameters using the pelvic organ prolapse quantification system (stage 0 or 1). Secondary outcomes were subjective outcomes assessed with the quality of life scores. Twenty-two women underwent the Ozerkan modified laparoscopic sacrocolpopexy. Mean operation time was 85.6min. Mean estimated blood loss was 71ml. One patient was lost during the clinical follow-up in the outpatient clinic up to 1 year. Nineteen of 21 patients had stage 0 or 1 prolapse at the end of 1 year. Two patients were not satisfied with their pelvic floor after 1 year. Both the objective and subjective cure rates were 90.4%. There were no bladder or bowel complications during the peri- or postoperative period. The new modification of laparoscopic sacral colpopexy seems a feasible and safe option to avoid mesh complications in the treatment of vaginal vault prolapse.

An improved simple flexible cryptosystem for 3D objects with texture maps and 2D images

With the continued evolution of three dimensional (3D) object presentation and usage, the security of such objects has become an increasingly desirable research area. Previous efforts mostly concentrated on the encryption of point clouds, solid models, meshes, and 3D textured models. The (texture map) part of meshed 3D objects was overlooked by previous encryption techniques of 3D meshed objects in spite of its importance because they require preprocessing to be extracted. Therefore, this paper provides a system for the full encryption of 3D textured objects with their texture maps. It provides an improved system based on an existing flexible cryptosystem named Flexible cryptosystem based on Cellular Automata (FcCA). The FcCA system has two drawbacks. One drawback is shuffling plain data without changing their values, which yields the same histogram and nonstandard encryption ratios. The other drawback is the need for many generations to make the keyspace very large, which is unsuitable for the large size of textured object data. This work overcomes these drawbacks of FcCA and fully encrypts 3D textured objects with their texture maps. The improvements to FcCA include making intersect start points change with every generation and encrypting the values of plain data while shuffling them using cellular automata. At first, the plain 3D object is extracted to vertices, faces, and texture, in addition to its texture map. After that, extracted data are encrypted using the proposed improved FcCA (iFcCA) cryptosystem. Implementation and analysis of this new system showed its preponderance as it can encrypt and decrypt 3D textured objects better than FcCA and other existing methods. Moreover, it reduces the need for many generations of cellular automata, and consequently, reduces execution time. In addition, iFcCA has a very robust key, and it can resist different types of attacks.

Impact of Electron-Beam Heating during 3D Nanoprinting.

An artifact limiting the reproduction of three-dimensional (3D) designs using nanoprinting has been quantified. Beam-induced heating was determined through complementary experiments, models, and simulations to affect the deposition rate during the 3D nanoprinting of mesh objects using focused electron beam induced deposition (FEBID). The mesh objects are constructed using interconnected nanowires. During nanowire growth, the beam interaction driving deposition also causes local heating. The temperature at the beam impact region progressively rises as thermal resistance increases with nanowire growth. Heat dissipation resembles the classical mode of heat transfer from extended surfaces; heat must flow through the mesh object to reach the substrate sink. Simulations reveal that beam heating causes an increase in the rate of precursor desorption at the BIR, causing a concomitant decrease in the deposition rate, overwhelming an increase in the deposition rate driven by thermally enhanced precursor surface diffusion. Temperature changes as small as 10 K produce noticeable changes in deposit geometry; nanowires appear to deflect and curve toward the substrate because the vertical growth rate decreases. The 3D FEBID naturally ensues from the substrate surface upward, inducing a vertical temperature gradient along the deposit. Simulations, experiments, temperature-controlled studies, and process current monitoring all confirm the cause of nanowire distortion as beam-induced heating while also revealing the rate-determining physics governing the final deposit shape.

A mesh objective continuum damage model for quasi-brittle crack modelling and finite element implementation

In the framework of continuum damage mechanics, a computational model for quasi-brittle crack modelling is proposed. The proposed model has significant mesh-objectivity and accuracy advantages over existing methods for modeling quasi-brittle crack. These stem from the combination of the local crack tracking algorithm, the new calculation of crack bandwidth and the non-local treatment regarding strain field. Resorting to the implementation of local crack tracking algorithm, it is desirable that the spurious dependence of conventional continuum damage mechanics-based model on mesh bias can be effectively addressed. The new estimation of the real-time crack bandwidth can be not only depending on the element size and pattern, but also on the physical crack path within each consolidate cracked element. Thus, the energy dissipation during crack propagation can be characterized in a more accurate, physically based manner. The non-local averaging regarding the strain field in the course of failure evolution is carried out within an elliptical domain, the configuration of which is related to finite element and crack trajectory obtained by the local crack track algorithm. With this combined technique, it is expected that a more accurate crack evolution course can be achieved numerically, which allows engineers to adopt relatively coarse unstructured discretizations without sacrificing solution accuracy. By numerical examples, the proposed model, empowered by the combined techniques, demonstrates significant improvements in the prediction of crack propagating of quasi-brittle materials. This model may provide engineers a more reliable tool in practical application of computational material failure.

Versatile Solver of Nonconformal Volume Integral Equation Based on SWG Basis Function

In this paper, a versatile solver of a nonconformal volume integral equation based on the Schaubert-Wilton-Glisson (SWG) basis function is presented. Instead of using a piecewise constant function, the robust conventional SWG basis function is chosen and used directly for discontinuous boundaries. A new map method technique is proposed for constructing SWG pairs, which reduces the complexity from ON2 to ONlogN compared with a brute-force method. The integral equation is solved by the method of moments (MoM) and further accelerated by the multilevel fast multipole algorithm (MLFMA). What’s more, the hybrid scheme of MLFMA and adaptive cross approximation (ACA) is developed to resolve the low-frequency (LF) breakdown when dealing with over-dense mesh objects. Numerical results show that when in analysis of radiation or scattering problems from inhomogeneous dielectric objects or in LF conditions, the proposed solver shows high efficiency without loss of accuracy, which demonstrates the versatile performance of the proposed method.

Objective modeling of multixial softening of concrete

AbstractConcrete in tension and low confined compression is characterized by strain‐softening, which leads to highly localized cracks or shear bands. Attempting to incorporate this response in standard continuum descriptions causes numerical instabilities and mesh sensitive results. This work presents a regularized plasticity‐damage model, which ensures mesh objectivity for general multixial strain softening. Combining plasticity and damage is necessary to describe the cyclic response of concrete. The damage part contains a split to consider the transition between compression and tension. Regularization of the model is achieved by an over‐nonlocal implicit gradient formulation. The model is implemented into a 3D finite element code and its capabilities are illustrated by numerical examples.

The Adobe delta damage model: A locally regularized rate-dependent model for the static assessment of soil masonry bricks and mortar

A local damage model is proposed for the numerical assessment of the static performance of Adobe masonry components. The model was applied to simulate the experimental behaviour of sundried soil bricks and mud mortar tested in uniaxial compression and bending. Numerical simulations of the model are made mesh objective by means of a rate dependent regularization algorithm in statics. This is achieved using a generalization of the damage delay concept based on a decomposition of the Dirichlet boundary condition. It allows non-dimensionality of model parameters mathematically needed to prevent loss of ellipticity of the equilibrium equations of the model. The entire regularization algorithm is integrated within an implicit Newton-Raphson solver.

A mesh objective method for modeling crack propagation using the smeared crack approach

SummaryThis paper presents a mesh objective method for modeling crack propagation in brittle materials using a conventional finite element formulation. The primary shortcoming of the smeared crack approach is its pathological sensitivity to the mesh orientation, which is manifested by shear locking and stress field misalignment around the crack tip. Such undesirable characteristics preclude the ability to model arbitrary crack propagation at an angle through the mesh. Several techniques are developed to address these shortcomings. First, to preclude shear locking, a modified failure constitutive model is developed, which projects out the spurious stress increments as the crack opens. If a crack exists in an element, a crack tracking algorithm is used to identify the neighboring elements most likely to show crack continuation. This algorithm also identifies a crossover element when a crack passes through adjacent sides of an element. Then, the characteristic element length used in the constitutive equation is changed with the objective of providing the correct failure energy per unit crack length, a procedure called crossover scaling. The examples provided demonstrate that the developed methods work collectively to provide a simple and efficient method for modeling failure in brittle materials without mesh bias.

Improvement and validation of a physically based model for the shear and transverse crushing of orthotropic composites

This paper details a complete crush model for composite materials with focus on shear dominated crushing under a three-dimensional stress state. The damage evolution laws and final failure strain conditions are based on data extracted from shear experiments. The main advantages of the current model include the following: no need to measure the fracture toughness in shear and transverse compression, mesh objectivity without the need for a regular mesh and finite element characteristic length, a pressure dependency of the nonlinear shear response, accounting for load reversal and some orthotropic effects (making the model suitable for noncrimp fabric composites). The model is validated against a range of relevant experiments, namely a through-the-thickness compression specimen and a flat crush coupon with the fibres oriented at 45° and 90° to the load. Damage growth mechanisms, orientation of the fracture plane, nonlinear evolution of Poisson's ratio and energy absorption are accurately predicted.

On the constitutive modelling of fatigue damage in rubber-like materials

A finite-strain hyperelastic phenomenological constitutive damage model is proposed to model the rate-independent failure behavior of rubber-like materials under isothermal conditions. At large strain, non-local gradient-enhanced damage model has been formulated and numerically implemented to predict the initiation and propagation of damage in rubber-like materials. The theoretical framework is based on the Internal State Variables (ISV) approach and has been implemented in the commercial finite element code Abaqus via User Element subroutine (UEL). Robustness of the model was systematically investigated by undertaking the parametric study on the influence of damage parameters, both local and non-local, on the overall constitutive behavior of the material. The veracity of the theoretical framework was tested by quantitatively comparing the capability of the model to predict the onset of damage, its propagation and the corresponding load-displacement response of nitrile butadiene rubber material under quasi-static condition. Finally, the mesh objectivity simulations from the non-local model are presented for rubber under fatigue loading.

Nonlocal formulation of the modified K&C model to resolve mesh-size dependency of concrete structures subjected to intense dynamic loadings

With the aid of commercial concrete material models, numerical simulation plays an increasingly important role in the analyses of dynamic responses of concrete structures subjected to intense dynamic loadings. Mesh-size dependency is a known problem of local material models used to simulate concrete due to strain softening, which is observed in numerous simulations. In this paper, the widely used regularization technique for quasi-static problems, smeared crack approach, is evaluated and proven to be ineffective for dynamic situations. To resolve the mesh-size dependency of concrete under dynamic loadings, the nonlocal formulation of the modified K&C (MKC) model proposed in our recent work is presented. The nonlocal MKC model is validated against four experiments, covering a wide range of stress/loading conditions, namely: Modified Split-Hopkinson Bar (spalling) test, Split-Hopkinson Tension test, Split-Hopkinson Pressure Bar test, and reinforce concrete beam subjected to blast loading. The numerical predictions are mesh objective and in good agreement with the corresponding experimental data.

Reproducing two-dimensional mammograms with three-dimensional printed phantoms.

Mammography is currently the standard imaging modality used to screen women for breast abnormalities, and, as a result, it is a tool of great importance for the early detection of breast cancer. Physical phantoms are commonly used as surrogates of breast tissue to evaluate some aspects of the performance of mammography systems. However, most phantoms do not reproduce the anatomic heterogeneity of real breasts. New fabrication technologies, such as three-dimensional (3-D) printing, have created the opportunity to build more complex, anatomically realistic breast phantoms that could potentially assist in the evaluation of mammography systems. The reproducibility and relative low cost of 3-D printed objects might also enable the development of collections of representative patient models that could be used to assess the effect of anatomical variability on system performance, hence making bench testing studies a step closer to clinical trials. The primary objective of this work is to present a simple, easily reproducible methodology to design and print 3-D objects that replicate the attenuation profile observed in real two-dimensional mammograms. The secondary objective is to evaluate the capabilities and limitations of the competing 3-D printing technologies and characterize the x-ray properties of the different materials they use. Printable phantoms can be created using the open-source code introduced, which processes a raw mammography image to estimate the amount of x-ray attenuation at each pixel, and outputs a triangle mesh object that encodes the observed attenuation map. The conversion from the observed pixel gray value to a column of printed material with equivalent attenuation requires certain assumptions and knowledge of multiple imaging system parameters, such as x-ray energy spectrum, source-to-object distance, compressed breast thickness, and average breast material attenuation. To validate the proposed methodology, x-ray projections of printed phantoms were acquired with a clinical mammography system. The quality of the printing process was evaluated by comparing the mammograms of the printed phantoms and the original mammograms used to create the phantoms. The structural similarity index and the root-mean-square error were used as objective metrics to compare the two images. A detailed description of the software, a characterization of the printed materials using x-ray spectroscopy, and an evaluation of the realism of the sample printed phantoms are presented.

A Watermarking Mechanism With High Capacity for Three-Dimensional Mesh Objects Using Integer Planning

In this paper, a new mechanism for digital watermarking is proposed. Three processes are involved: First, the watermarks are encapsulated into a carrier image; second, a sparsity analysis process is conducted on one component; finally, a flexible selection process is eventually executed to embed the watermarks. Experimental results demonstrate high-capacity information and strong robustness.

Thickness‐aware voxelization

AbstractVoxelization is a crucial process for many computer graphics applications such as collision detection, rendering of translucent objects, and global illumination. However, in some situations, although the mesh looks good, the voxelization result may be undesirable. In this paper, we describe a novel voxelization method that uses the graphics processing unit for surface voxelization. Our improvements on the voxelization algorithm can address a problem of state‐of‐the‐art voxelization, which cannot deal with thin parts of the mesh object. We improve the quality of voxelization on both normal mediation and surface correction. Furthermore, we investigate our voxelization methods on indirect illumination, showing the improvement on the quality of real‐time rendering.