Grid Deformation Research Articles

Static and moving solid/gas interface modeling in a hybrid rocket engine

A numerical model was developed with CFD-ACE software to study the working condition of an oxygen-nitrogen/polyethylene hybrid rocket combustor. As a first approach, a simplified numerical model is presented. It includes a compressible transient gas phase in which a two-step combustion mechanism is implemented coupled to a radiative model. The solid phase from the fuel grain is a semi-opaque material with its degradation process modeled by an Arrhenius type law. Two versions of the model were tested. The first considers the solid/gas interface with a static grid while the second uses grid deformation during the computation to follow the asymmetrical regression. The numerical results are obtained with two different regression kinetics originating from ThermoGravimetry Analysis and test bench results. In each case, the fuel surface temperature is retrieved within a range of 5% error. However, good results are only found using kinetics from the test bench. The regression rate is found within 0.03 mm s−1 and average combustor pressure and its variation over time have the same intensity than the measurements conducted on the test bench. The simulation that uses grid deformation to follow the regression shows a good stability over a 10 s simulated time simulation.

ATMAD: robust image analysis for Automatic Tissue MicroArray De-arraying

BackgroundOver the last two decades, an innovative technology called Tissue Microarray (TMA), which combines multi-tissue and DNA microarray concepts, has been widely used in the field of histology. It consists of a collection of several (up to 1000 or more) tissue samples that are assembled onto a single support – typically a glass slide – according to a design grid (array) layout, in order to allow multiplex analysis by treating numerous samples under identical and standardized conditions. However, during the TMA manufacturing process, the sample positions can be highly distorted from the design grid due to the imprecision when assembling tissue samples and the deformation of the embedding waxes. Consequently, these distortions may lead to severe errors of (histological) assay results when the sample identities are mismatched between the design and its manufactured output. The development of a robust method for de-arraying TMA, which localizes and matches TMA samples with their design grid, is therefore crucial to overcome the bottleneck of this prominent technology.ResultsIn this paper, we propose an Automatic, fast and robust TMA De-arraying (ATMAD) approach dedicated to images acquired with brightfield and fluorescence microscopes (or scanners). First, tissue samples are localized in the large image by applying a locally adaptive thresholding on the isotropic wavelet transform of the input TMA image. To reduce false detections, a parametric shape model is considered for segmenting ellipse-shaped objects at each detected position. Segmented objects that do not meet the size and the roundness criteria are discarded from the list of tissue samples before being matched with the design grid. Sample matching is performed by estimating the TMA grid deformation under the thin-plate model. Finally, thanks to the estimated deformation, the true tissue samples that were preliminary rejected in the early image processing step are recognized by running a second segmentation step.ConclusionsWe developed a novel de-arraying approach for TMA analysis. By combining wavelet-based detection, active contour segmentation, and thin-plate spline interpolation, our approach is able to handle TMA images with high dynamic, poor signal-to-noise ratio, complex background and non-linear deformation of TMA grid. In addition, the deformation estimation produces quantitative information to asset the manufacturing quality of TMAs.

Study of the key factors affecting the triple grid lifetime of the LIPS-300 ion thruster

In order to ascertain the key factors affecting the lifetime of the triple grids in the LIPS-300 ion thruster, the thermal deformation, upstream ion density and component lifetime of the grids are simulated with finite element analysis, fluid simulation and charged-particle tracing simulation methods on the basis of a 1500 h short lifetime test. The key factor affecting the lifetime of the triple grids in the LIPS-300 ion thruster is obtained and analyzed through the test results. The results show that ion sputtering erosion of the grids in 5 kW operation mode is greater than in the case of 3 kW. In 5 kW mode, the decelerator grid shows the most serious corrosion, the accelerator grid shows moderate corrosion, and the screen grid shows the least amount of corrosion. With the serious corrosion of the grids in 5 kW operation mode, the intercept current of the acceleration and deceleration grids increases substantially. Meanwhile, the cold gap between the accelerator grid and the screen grid decreases from 1 mm to 0.7 mm, while the cold gap between the accelerator grid and the decelerator grid increases from 1 mm to 1.25 mm after 1500 h of thruster operation. At equilibrium temperature with 5 kW power, the finite element method (FEM) simulation results show that the hot gap between the screen grid and the accelerator grid reduces to 0.2 mm. Accordingly, the hot gap between the accelerator grid and the decelerator grid increases to 1.5 mm. According to the fluid method, the plasma density simulated in most regions of the discharge chamber is 1 × 1018−8 × 1018 m−3. The upstream plasma density of the screen grid is in the range 6 × 1017−6 × 1018 m−3 and displays a parabolic characteristic. The charged particle tracing simulation method results show that the ion beam current without the thermal deformation of triple grids has optimal perveance status. The ion sputtering rates of the accelerator grid hole and the decelerator hole are 5.5 × 10−14 kg s−1 and 4.28 × 10−14 kg s−1, respectively, while after the thermal deformation of the triple grids, the ion beam current has over-perveance status. The ion sputtering rates of the accelerator grid hole and the decelerator hole are 1.41 × 10−13 kg s−1 and 4.1 × 10−13 kg s−1, respectively. The anode current is a key factor for the triple grid lifetime in situations where the structural strength of the grids does not change with temperature variation. The average sputtering rates of the accelerator grid and the decelerator grid, which were measured during the 1500 h lifetime test in 5 kW operating conditions, are 2.2 × 10−13 kg s−1 and 7.3 × 10−13 kg s−1, respectively. These results are in accordance with the simulation, and the error comes mainly from the calculation distribution of the upstream plasma density of the grids.

Coupled heat transfer and thermo-mechanical behavior of hypersonic cylindrical leading edges

The analysis of heat transfer and thermo-mechanical behavior is crucial to the leading edge of hypersonic vehicles under high thermal and mechanical loads due to severe aeroheating. The present paper proposes a time-adaptive loosely coupled strategy for the modeling and analysis of hypersonic intrinsic fluid-thermal-structural characteristics. A framework of hypersonic computational coupling dynamics (HyCCD) is developed for integrating an independently developed program solving hypersonic aerothermodynamics and a finite element analysis professional software. The embedded adaptive time-step approach, hybrid interpolation strategy, and grid deformation method have taken into consideration coupling variables and their properties. A typical cylindrical leading edge is considered as the simulation model to study the effects of chemical nonequilibrium, aeroheating duration, flight trajectory, and shock interference. The time-adaptive loosely coupled analysis of aerothermostructural response provides a reliable, applicable and efficient prediction for the fluid thermal-structural coupling of hypersonic vehicles.

Numerical simulation of the composite foundation of cement soil mixing piles using FLAC3D

In the road construction process often encountered in the construction of the phenomenon in the soft soil area, due to the physical properties of soft soil often can not meet the design requirements, it is often on the soft ground to add additives to achieve a more solid foundation. In order to compare the settlement of two different piles to determine a more suitable engineering method.The silty soft soil foundation of Xinxicheng Road was numerically simulated by the software of FLAC$$^\mathrm{3D}$$, and a single-pile model was established to simulate the load test of single pile by loading load step by step. The resulting deformation grid diagrams of the cement soil mixing pile and cement sand soil mixing pile under loads of 300 kPa indicate that deformation gradually decreases from the center to the surrounding, and the maximum settlements of the two deformation maps were 19.36 and 13.60 mm, respectively. The relationships between maximum settlement and load show that the settlement values of the cement soil pile and cement sand soil pile were similar (within 1–2 mm of each other). The settlement value of the cement sand soil mixing pile was smaller than that of the cement soil mixing pile under large loads. Therefore, the use of cement sand soil piles can reduce the maximum settlement to meet engineering requirements. This paper provides a theoretical basis and guidance for the future treatment of soft ground deformation.

The Motion of An Inv Nodal Cilium: a Realistic Model Revealing Dynein-Driven Ciliary Motion with Microtubule Mislocalization

Background/Aims: Nodal cilia that rotate in the ventral node play an important role in establishing left-right asymmetry during embryogenesis; however, inv mutant cilia present abnormal movement and induce laterality defects. The mechanism of their motility, which is regulated by dynein activation and microtubule arrangement, has not been fully understood. This study analyzed the dynein-triggered ciliary motion in the abnormal ultrastructure of the inv mutant, aiming to quantitatively evaluate the influence of microtubule mislocalization on the movement of the cilium. Methods: We established a realistic 3-D model of an inv mutant cilium with an ultrastructure based on tomographic datasets generated by ultra-high voltage electron microscopy. The time-variant activation of the axonemal dynein force was simulated by pairs of point loads and embedded at dynein-mounted positions between adjacent microtubule doublets in this mathematical model. Utilizing the finite element method and deformable grid, the motility of the mutant cilium that is induced by various dynein activation hypotheses was investigated and compared to experimental observation. Results: The results indicate that for the inv mutant, simulations of the ciliary movement with the engagement of dyneins based on the distance-controlled pattern in the partially activation scenario are broadly consistent with the observation; the shortening of the microtubules induces smaller movement amplitudes, while the angles of the mislocalized microtubules affect the pattern of the ciliary movement, and during the ciliary movement, the microtubules swing and twist in the mutant ciliary body. Conclusion: More generally, this study implies that dynein engagement is sensitive to subtle geometric changes in the axoneme, and thus, this geometry greatly influences the integrity of a well-formed ciliary rotation.

Freely Deformable Liquid Metal Grids as Stretchable and Transparent Electrodes

A new structure of stretchable and transparent metal-grid electrodes is described, where a liquid metal alloy, eutectic gallium–indium (EGaIn) is employed as a stretchable conducting material. By a “roll-painting and lift-off” technique based on photolithography, stretchable EGaIn-grids with the linewidth of 20 $\mu \text{m}$ and the line pitch of 400–1000 $\mu \text{m}$ are produced, providing the transmittance of 75%–88% with the sheet resistance less than 2.3 $\Omega $ /square. Powered by the freely deformable nature of the liquid phase conductor, the EGaIn-grid provides stable conductivity under highly stretched condition up to 40%, as well as high reliability against cyclic deformation. By combining the EGaIn-grid with a homogeneous and transparent poly(3,4-thylenedioxythiophene):poly(styrensulfonate) (PEDOT:PSS) layer in a hybrid manner, we can construct highly stretchable and uniformly conducting transparent electrodes. The hybrid PEDOT:PSS/EGaIn-grid electrodes can be utilized as electrodes for a stretchable inorganic electroluminescence device with a ZnS phosphor-elastomer composite as the emission layer, which maintains uniform and stable emission under highly and repeatedly stretched conditions.

A kinetic energy preserving DG scheme applied to mechanical FSI

AbstractIn the context of mechanical fluid‐structure interaction (FSI) comprising moving or deforming structures, fluid discretizations need to cope with time‐dependent fluid domains and resulting grid deformations in addition to the general challenges regarding e.g. boundary layers and turbulent phenomena. Recent approaches in the simulation of compressible turbulent flow are based on so‐called split forms of conservation laws to guarantee the preservation of secondary physical quantities such as kinetic energy. For the simulation of turbulent flows, this often leads to a better representation of the kinetic energy spectrum. Initially, kinetic energy preserving(KEP) DG schemes have been constructed on Gauss‐Legendre‐Lobatto(GLL) nodes containing the interval end points, however, KEP DG schemes based on the classical Gauss‐Legendre(GL) nodes are potentially more accurate and may be also more efficient than its GLL variant for certain applications. In this work, the KEP‐DG schemes both on GL and GLL nodes are applied to the classical moving piston test case via an ALE formulation on moving fluid grids showing a more accurate frequency representation of the structure displacement in case of GLL nodes. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Numerical analysis of aerodynamic damping for a centrifugal impeller

ABSTRACTIn order to realize the numerical analysis of aerodynamic damping for the centrifugal impellers, a numerical code integrating the flow-structure data transfer, grid deformation and flow simulation under the moving grid system is first developed. To decrease the huge consumptions of CPU time and memory space, the compactly supported radial basis function is adopted to carry out the data transfer and grid deformation, and the alternating digital tree technique is utilized to calculate the wall distances. By the test cases of an oscillating cascade and a centrifugal impeller, the correctness of the code for the flow simulations with moving boundaries and the flow fields in centrifugal impellers is validated. Then taking a centrifugal impeller as the research object, the calculations of aerodynamic damping characteristics were carried out. The results show that, the modal aerodynamic damping ratio has no relationship with the vibrating amplitude under small vibrations. For the disk-dominant vibration mode, the modal aerodynamic damping ratio decreases as the operating point shifts toward the stall point. The aerodynamic damping caused by the backward traveling wave vibration is larger than that by the forward traveling wave vibration.

Experimental and numerical investigation of the effect of entrapped air on the mechanical response of Nomex honeycomb under flatwise compression

Nomex honeycomb has very low relative density, thus there is a lot of the air entrapped within the cells of Nomex honeycomb sandwich structures. The air has a significant effect on the mechanical response under flatwise compression, and it was investigated herein. Firstly, experiments of the honeycomb with and without facesheets were performed to study the entrapped air effect. Secondly, the unit cell model and multi-cell model of the honeycomb were proposed, in which, two methods of modeling the entrapped air using commercial software LS-DYNA were developed. In the first method, six cell walls and two facesheets as well as the air entrapped by them are simulated as an air-filled cavity using Airbag tools. In the second method, the entrapped air is simulated by ALE (Arbitrary Lagrangian Eulerian) elements, which realize the grid deformation and material flow. Interaction between the entrapped air and cell walls under compression is analyzed using fluid-structure coupling algorithm. It is found in this paper that energy absorption capacity of Nomex honeycomb sandwich can be enhanced through the effect of the entrapped air on the cell walls folding process. The ALE method is superior to the airbag method in the unit cell models as regard to the energy absorption capacity and the energy absorbing process.

<b>Morphometric analysis of three normal facial types in mixed dentition using posteroanterior cephalometric radiographs: preliminary results

The aim of the present investigation was to evaluate the craniofacial features of subjects with normal occlusion with different vertical patterns in the mixed dentition using morphometric analysis (Thin-Plate Spline analysis - TPS) applied to posteroanterior (PA) films. The sample comprised 39 individuals (18 females and 21 males), all in mixed dentition, aged from 8.4 to 10 years with satisfactory occlusion and balanced profile and with no history of orthodontic or facial orthopedic treatment. The sample was divided into three groups (mesofacial, brachyfacial and dolichofacial) according to the facial types proposed by Ricketts (1989). The average craniofacial configurations of each study group were obtained by orthogonal superimposition of Procrustes, thereby eliminating size differences and allowing only shape differences between groups to be analyzed by viewing the TPS deformation grid. Significant differences were found among the three facial types but were more remarkable between mesofacials and dolichofacials than between mesofacials and brachyfacials. TPS morphometric analysis proved efficient for accurate visualization of transverse and vertical differences among facial types even before pubertal growth spurt. These differences cannot be easily detected by traditional posteroanterior cephalometry.

Estimation of Large Motion in Lung CT by Integrating Regularized Keypoint Correspondences into Dense Deformable Registration.

We present a novel algorithm for the registration of pulmonary CT scans. Our method is designed for large respiratory motion by integrating sparse keypoint correspondences into a dense continuous optimization framework. The detection of keypoint correspondences enables robustness against large deformations by jointly optimizing over a large number of potential discrete displacements, whereas the dense continuous registration achieves subvoxel alignment with smooth transformations. Both steps are driven by the same normalized gradient fields data term. We employ curvature regularization and a volume change control mechanism to prevent foldings of the deformation grid and restrict the determinant of the Jacobian to physiologically meaningful values. Keypoint correspondences are integrated into the dense registration by a quadratic penalty with adaptively determined weight. Using a parallel matrix-free derivative calculation scheme, a runtime of about 5 min was realized on a standard PC. The proposed algorithm ranks first in the EMPIRE10 challenge on pulmonary image registration. Moreover, it achieves an average landmark distance of 0.82 mm on the DIR-Lab COPD database, thereby improving upon the state of the art in accuracy by 15%. Our algorithm is the first to reach the inter-observer variability in landmark annotation on this dataset.

Deforming grid generation for numerical simulations of fluid dynamics in sliding vane rotary machines

The limiting factor for the employment of advanced 3D CFD tools in the analysis and design of rotary vane machines is the unavailability of methods for generation of a computational grid suitable for fast and reliable numerical analysis. The paper addresses this issue through an analytical grid generation based on the user defined nodal displacement which discretizes the moving and deforming fluid domain of the sliding vane machine and ensures conservation of intrinsic quantities by maintaining the cell connectivity and structure. Mesh boundaries are defined as parametric curves generated using trigonometrical modelling of the axial cross section of the machine while the distribution of computational nodes is performed using algebraic algorithms with transfinite interpolation, post orthogonalisation and smoothing. Algebraic control functions are introduced for distribution of nodes on the rotor and casing boundaries in order to achieve good grid quality in terms of cell size and expansion. For testing of generated grids, single phase simulations of an industrial air rotary vane compressor are solved by use of commercial CFD solvers FLUENT and CFX. This paper presents implementation of the mesh motion algorithm, stability and robustness experienced with the solvers when working with highly deforming grids and the obtained flow results.

Reactive Liquid‐Flow Simulation of Micromixers Based on Grid Deformation Techniques

AbstractProcess intensification of engineering applications in the framework of reacting flows in micromixer devices attracts the attention of engineers and scientists from various fields. With the steadily increasing available computational resources, the traditional experimentally supported investigations may be extended by computational ones. For this purpose, a simulation framework based on state‐of‐the‐art numerical techniques extended with special grid deformation techniques has been developed. Its validation in terms of comparison with computational and experimental results in reacting as well as in non‐reacting frameworks has been performed on the basis of the T‐mixer and SuperFocus mixer, respectively. The computational efficiency of the developed tool is shown to be applicable for optimization tasks, such as reverse engineering purposes.

An enhanced obstacle avoidance method for the visually impaired using deformable grid

Various obstacle avoidance (OA) methods with the monocular vision have been studied to assist visually impaired people. Recently, a method that effectively locates obstacles at a risk of collision using the shape variation of a grid, called deformable grid (DG), was introduced [11]. To further improve the detection performance of the previous work, a vertex deformation function representing the displacement of each vertex in the DG is firstly defined employing the perspective projection geometry. Then, the collision risk is accurately estimated based on the shape variation of the DG that is measured using the vertex deformation function. Experimental results show that the proposed method outperforms other conventional methods as well as the previous work in terms of both the accuracy and processing time, and clearly detects obstacles that present a risk of collision in a variety of scenarios. This method is suitable for application to electronic travel aid (ETA) systems using consumer devices, such as smart-phones, tablets, and wearable devices.

A structure-aware axis-aligned grid deformation approach for robust image retargeting

Content-based image retargeting is a technique that resizes an input image to a given target resolution while minimizing distortions of important objects caused by aspect ratio variations. Conventional approaches have shared a similar methodology which aims to preserve salient regions as much as possible while allowing distortions of less important regions. Those methods have shown satisfactory results for input images whose objects are distinct and backgrounds are monotonous. However, their performance is not always guaranteed for images containing structural components such as straight lines, which are prone to be distorted after resizing and sensitive to human visual perception. In this paper, we propose a structure-aware axis-aligned grid deformation approach for robust image retargeting. Based on axis-aligned grid, our method finds the optimal grid for target image by quadratic optimization represented by two objective functions. The first one is the As-similar-as-possible (ASAP) energy function, which aims to preserve important regions while allowing distortions of trivial regions. The second one is the Adaptive Laplacian regularization (ALR) energy function, which aims to relieve structural distortions. Those two energy functions are combined into single quadratic optimization model ensuring the global convexity and solved by a quadratic programming solver for finding the optimal grid. Experimental results show that our method is robust to structural distortions while achieving the basic purpose of content-based image retargeting. For objective comparisons with other methods, we have provided objective evaluation scores by using a recent state-of-the-art image retargeting quality assessment scheme.

Outdoor Markerless Motion Capture with Sparse Handheld Video Cameras.

We present a method for outdoor markerless motion capture with sparse handheld video cameras. In the simplest setting, it only involves two mobile phone cameras following the character. This setup can maximize the flexibilities of data capture and broaden the applications of motion capture. To solve the character pose under such challenge settings, we exploit the generative motion capture methods and propose a novel model-view consistency that considers both foreground and background in the tracking stage. The background is modeled as a deformable 2D grid, which allows us to compute the background-view consistency for sparse moving cameras. The 3D character pose is tracked with a global-local optimization through minimizing our consistency cost. A novel motion regularizer is also proposed in the optimization to constrain the solution pose space. The whole process of the proposed method is simple as frame by frame video segmentation is not required. Our method outperforms several alternative methods on various examples demonstrated in the paper.

CFD-based aeroelastic reduced-order modeling robust to structural parameter variations

This article deals with the development of two efficient computational-fluid-dynamics (CFD) based models for the computation of unsteady aerodynamic motion-induced forces. In contrast to established reduced-order modeling (ROM) approaches, which are generally fixed to a given set of structural eigenmodes, the proposed methods can be applied for variable mode shapes. Hence, the generated aerodynamic models remain valid to some extent even if mass and stiffness variations within the underlying finite-element (FE) model are considered. In this way, additional computationally demanding CFD computations are avoided once the model has been obtained. Under this premise, two modeling frameworks robust to structural parameter variations are developed, while so-called basis modes are employed to approximate arbitrary mode shapes. Firstly, a time-domain ROM originating from linear system identification principles (SI-ROM) is presented and, secondly, a frequency-domain approach based on a small disturbance CFD solver (SD-ROM) is proposed. Moreover, two different strategies for the basis mode generation are evaluated. The first method is based on a local approximation using radial basis functions, whereas the second method uses two-dimensional Chebyshev polynomials in order to yield a global approximation of the structural grid deformations. Both novel ROM approaches combined with the two basis mode construction techniques are demonstrated and assessed regarding their efficiency and accuracy. The results in terms of the well-known AGARD 445.6 wing configuration demonstrate that the proposed methods can reproduce the unsteady aerodynamic forces accurately, while the computational effort is significantly reduced. Moreover, generic modifications with respect to the FE model are considered to indicate the potential of the new methods regarding aircraft aeroelastic design and optimization.

A finite volume scheme for solving anisotropic diffusion on ALE‐AMR grids

SummaryIn the context of High Energy Density Physics and more precisely in the field of laser plasma interaction, Lagrangian schemes are commonly used. The lack of robustness due to strong grid deformations requires the regularization of the mesh through the use of Arbitrary Lagrangian Eulerian methods. Theses methods usually add some diffusion and a loss of precision is observed. We propose to use Adaptive Mesh Refinement (AMR) techniques to reduce this loss of accuracy. This work focuses on the resolution of the anisotropic diffusion operator on Arbitrary Lagrangian Eulerian‐AMR grids.In this paper, we describe a second‐order accurate cell‐centered finite volume method for solving anisotropic diffusion on AMR type grids. The scheme described here is based on local flux approximation which can be derived through the use of a finite difference approximation, leading to the CCLADNS scheme. We present here the 2D and 3D extension of the CCLADNS scheme to AMR meshes. Copyright © 2017 John Wiley & Sons, Ltd.

An agglomeration strategy for accelerating RBF-based mesh deformation

RBF-based mesh deformation methods have been recognized during the past years as an essential tool for numerical simulations involving mesh deformation. Nevertheless, they call for excessive memory and computation time requirements, especially for large-scale problems. A remedy to this shortcoming appears to be the selection of a reduced number of surface mesh nodes, to be used as RBF-centers, resulting in decreased dimensions of the system of equations. In this study a methodology for the reduction of the RBF-centers is developed, based on the agglomeration of boundary nodes' control areas. This technique has been adopted from the multigrid methods frequently employed in numerical simulation of fluid flow, heat transfer, etc. The fusion strategy is performed on a topology-preserving framework, while it resembles the advancing front technique, as it begins from regions with surface discontinuities extending successively to the interior. The proposed algorithm was evaluated against benchmark test cases, concerning deformation of the wing of a transonic commercial aircraft and the blade of a wind turbine, revealing its potential for radically improved computational performance of the grid deformation procedure. Moreover, the obtained results confirm its capability to preserve grid quality, despite the notable reduction of RBF-centers.