Grid Deformation Research Articles

Facial cues to physical strength are not always associated with facial masculinity: Comparative study of Europeans and Southern Siberians.

The aim of our study was to compare morphometric patterns of facial sexual dimorphism with strength-face relationship in members of two distinct populations of European and Central Asian origin: Russians and Tuvans. Handgrip strength (HGS) measures and facial photographs were collected from Russian (n = 233) and Tuvan (n = 187) men and women. We digitized 70 landmarks and semilandmarks on full-face and 54 landmarks and semilandmarks on profile photos. This was done to capture variation in facial morphology. After that, we performed the shape regressions of landmarks' coordinates upon sex and HGS. Results were visualized in forms of thin-plate deformation grids and geometric morphometric morphs. In both populations, HGS was associated significantly with male facial shape only. In Russian men, strength-related changes of facial shape were almost completely in direction of increase in male-typicality. This was especially evident for the relative lower facial width, which was higher in men compared to women, as well as in stronger men compared to weaker ones. On the contrary, in Tuvans the lower face was relatively narrower in men than in women. However, the facial shape of strong Tuvan men was also associated with relatively wider lower face. Our results indicate that the effect of strength on facial shape is relatively independent of facial sexual dimorphism. Our findings clearly demonstrate that physical strength is associated with the shape of the lower part of male faces even in populations with a mismatched direction of lower face sexual dimorphism.

Adaptive grid deformation method for CFD application to hull optimization

This work introduces a new grid deformation method for an efficient CFD-based optimization of ship hull forms. The method uses a two-level point transformation technique to manipulate grid points with a small number of design points. At the first level, generic B-spline is employed to transfer grid points based on movements of control points sampled inside a control box, ensuring accuracy and smoothness of surface modification. At the second level, Radial Basis Function with Wendland’s C2 continuity is adopted to interpolate movements of control points based on relatively few design points. It is shown to be effective in preserving good mesh quality and efficiency. The method is applied to the deformation of hull surfaces for ship models KVLCC2 and KCS, and to investigate the effects of bulbous bow on calm-water resistance with fixed Lpp. A regression model is proposed for ship length, location of buoyancy, wet surface area, and displacement. Numerical results show that the present method is well-suited for CFD-based hull form optimization with better efficiency.

Unsteady Low-Reynolds Number Aerodynamic Analysis For Flapping Wing Mav Executing a 3D Motion

There is an emerging interest in the field of Nano Aerial Vehicles (NAV) especially of smaller size. These types of vehicles originally developed from the concept of insects, hummingbirds, flying beetles and bats fights. The main objective of this research work is trying to execute a 3D motion (figure of eight) to estimate lift and drag for 3D flapping wing and analysed with the help of computational fluid dynamics, which is related to grid deformation, finite volume method, dynamic mesh and User Defined Function (UDF) for the geometric model with 200mm wing span and 70mm chord. The numerical simulation was carried out at a free stream velocity of 5 m/s. A comprehensive research was carried out to estimate the lift and drag under this condition. The 3D motion helps in better prediction of aerodynamic lift as close to nature and this study is a pointer towards the swarm operations

A kinetic grid for fabric draping simulation

In allusion to the hot issue of fabric simulation, this paper proposes a kinetic grid for reproducing the drape profile of fabric in three-dimensional space. In our model, the interaction inside fabric is built up through a constraint factor as well as an attenuation factor, and the contact between the flexible body of the fabric and the rigid plane is emulated with a touch-counteract mechanism. The forces on the particles in the grid, which are calculated with grid deformation, are then used to generate the additional displacement of the grid. Evolution of the grid is led by step-by-step iteration so that the draping kinetics of the virtual fabric can be achieved. When the draping process meets its steady state, the drape coefficient is worked out through identifying and quantifying the projection area of the grid. The unevenness of the ripples along the drape surface is characterized and manifested by emulating the mechanical anisotropy of the fabric through differentiated constraint factors. The evolution algorithm is improved and an optimized version that reduces calculation error using the third-order Taylor theorem is presented, by which a smoother curved surface for the drape can be produced. The convergence of the grid under different fineness values is explored to reveal the capacity of the model, and a reasonable grid scale has been identified. The computed drape is then compared to a real drape featuring different strengths in the warp and weft, and adjusted to meet the target drape coefficient, as well as drape unevenness considering the anisotropy index. The result shows they are properly matched. The virtual drape is also tested in additional scenes including square support with sharp corners, one-way overhanging and mixed. It has turned out to be a simple, rapid and precise model for fabric drape simulation and assessment.

Dynamic Structural Scaling Concept for a Delta Wing Wind Tunnel Configuration Using Additive Manufacturing

Considering aeroelastic effects plays a vital role in the aircraft design process. The construction of elastic wind tunnel models is a critical element in the investigation of occurring aeroelastic phenomena. However, the structural scaling between full-scale and reduced-scale configurations is a complex design and manufacturing task and is usually avoided in wind tunnel testing. This work proposes a numerical approach for a dynamic aeroelastic scaling technique, which is applied to a fictive delta wing configuration. This scaling methodology is designed to optimise the structural layout of wind tunnel models with an integrated rib and spar structure to meet the behaviour of a realistic full-scale equivalent. For the modelling approach of the wing structure, a beam and shell structure is utilised. The applied scaling laws for the relevant quantities and the applied procedures are described. Computational fluid dynamics (CFD) calculations are performed by solving the Reynolds-averaged Navier–Stokes (RANS) equations for the assumption of a rigid full-scale and down-scaled wing. These calculations are used to verify the aerodynamic scaling assumptions, which are applied to the scaling procedure of the wind tunnel model. Global aerodynamic coefficients are evaluated for a variety of angles of attack. The local flow phenomena of the full-scale and the scaled model are compared in more detail for a medium and a high angle of attack. The pressure coefficient distribution shows a proper accordance for the full-scale and the scaled model. To verify the results of the structural scaling optimisation, a high-fidelity structural full-scale model is compared with the scaled model using the ELFINI FEM solver. Therefore, all structural components are modelled by 2D elements. The results for the reduced eigenfrequencies and according modes of the full-scale and the scaled model show a high level of similarity. A static deformation of the structural grids is performed by applying the aerodynamic loads from the CFD simulations. The results show that the deviation of the nondimensional deformation between the scaled and the full-scale model is negligible. Consequently, the applied scaling methodology proves to be a valuable tool for the conceptual approach of designing aeroelastically scaled wind tunnel models considering 3D-printed material.

Numerical simulation and investigation of ultra-short pulse laser ablation on Ti6Al4V and stainless steel

In ultra-short pulse laser machining and micro/surface processing, accurate simulation of laser ablation is important for understanding laser-target interaction and improving ablation performance, but it remains challenging. This work aims to develop a numerical model to improve the accuracy of the ablation depth calculation. A grid deformation scheme is proposed based on energy conservation and considering contributions to instant material removal from both the electron and lattice subsystems. By incorporating this scheme with the two-temperature model (TTM), a reasonable prediction of the instant target surface profile during laser ablation has been achieved. In the case of single-pulse femtosecond laser ablation of Ti6Al4V, the calculated ablation depth ranges from 0.06 to 0.56 μm for laser energy from 1.0 to 10.0 μJ. For single-pulse picosecond laser ablation of stainless steel, as laser energy increases from 6.0 to 18.5 μJ, the predicted ablation crater deepens accordingly from 40 to 87 nm. In addition, for multi-pulse picosecond laser ablation of stainless steel, a linear dependence of the ablation depth on the pulse number is observed up to a depth of about 803 nm at 6.0 μJ and 20 pulses. In all the above-mentioned cases, the calculation results are in better agreement with experimental measurements than conventional TTM or other material removal schemes, validating the accuracy of the proposed model.

Influence of incoming wave conditions on the hysteretic behavior of an oscillating water column system for wave energy conversion

The performance difference of a Wells turbine in an oscillating water column (OWC) system in the acceleration and deceleration phases of the incoming waves is known as its hysteresis characteristic. In the present work, a laboratory OWC system is simulated numerically with deformable grids to simulate the air–water interface, and a lumped-parameter model is used to reproduce the interaction between the air flow and the Wells turbine in the OWC system. The model results are compared with experimental and numerical results, with excellent agreement, then the model is used to quantify the hysteresis intensity of the hysteresis loop under different incoming wave conditions and turbine rotation speeds. After separating the hysteresis of the OWC system from that of its Wells turbine, the lumped-parameter model shows that the former is due largely to the compressibility of the air in the chamber. When the compression ratio of the OWC system decreases from 4.40 to 2.00, the hysteresis intensity of the hysteresis loop decreases by 64.13%, and when the rotation speed of the Wells turbine increases from 3600 rpm to 4800 rpm, the hysteresis intensity increases by 34.53%. The present work contributes to predicting the performance of Wells turbines and quantifying the hysteresis intensity for maximum extraction of sea-wave energy.

Research on Airspace Conflict Detection Method Based on Spherical Discrete Grid Representation

With the continuous development of general aviation, the contradiction between the air demand of general aviation low-altitude airspace and civil aviation routes is sharp. The difficulty of airspace planning is complex and changeable, and the existing working mode of simply using computer mapping and manually finding airspace conflict contradictions can no longer meet the large-scale air use demand. In response to the existing spatial representation model of longitude and latitude grid, which has large grid deformation in high latitude areas, and the problem of slow computation speed of the conflict detection (CD) algorithm that determines whether the airspace boundary coordinates overlap, we propose a grid model that represents airspace with a spherical rhombic discrete grid of positive icosahedron and design a matrix-based digital representation method of airspace, which uses matrix product operation. The matrix product operation is used to quickly determine whether there is a conflict between airspace and airspace and between airspace and routes.

Fourth order compact scheme for the Navier–Stokes equations on time deformable domains

In this work, we report the development of a spatially fourth order temporally second order compact scheme for incompressible Navier–Stokes (N–S) equations in time-varying domain. Sen (2013) put forward an implicit compact finite difference scheme for the unsteady convection–diffusion equation. It is now further extended to simulate fluid flow problems on deformable surfaces using curvilinear moving grids. The formulation is conceptualized in conjunction with recent advances in numerical grid deformations techniques such as inverse distance weighting (IDW) interpolation and its hybrid implementation. Adequate emphasis is provided to approximate grid metrics up to the desired level of accuracy and freestream preserving property has been numerically examined. As we discretize the non-conservative form of the N–S equation, the importance of accurate satisfaction of geometric conservation law (GCL) is investigated. To the best of our knowledge, this is the first higher order compact method that can directly tackle the non-conservative form of the N–S equation in single and multi-block time dependent complex regions. Several numerical verification and validation studies are carried out to illustrate the flexibility of the approach to handle high-order approximations on evolving geometries. The method presented here is found to be effective in modeling incompressible flow on deformable domains, including situations of fluid–structure interaction (FSI). Additionally, the necessity of GCL preserving metric computation is eased as a result of the scheme’s adaptation for non-conservative formulation.

Neural-network-based fluid–structure interaction applied to vortex-induced vibration

In this paper, a fluid–structure interaction (FSI) solver with neural-network-based fluid-flow prediction is proposed. This concept is applied to the problem of vortex-induced vibration of a cylinder. The majority of studies that are concerned with fluid-flow prediction using neural networks solve problems with fixed boundary. In this paper, a convolutional neural network (CNN) is used to predict unsteady incompressible laminar flow with moving boundary. A deformable non-Cartesian grid, which traces the boundary of the fluid domain, is used in this paper. The CNN is trained for oscillating cylinder with various frequencies and amplitudes. The dynamics of the elastically-mounted cylinder is modelled using a linear spring–mass–damper model and solved by an implicit differential scheme. The results show that the CNN-based FSI solver is capable of capturing the so-called lock-in phenomenon for the problem of vortex-induced vibration of a cylinder and the quantitative behaviour is similar to the results of the CFD-based FSI solver. Moreover, the CNN-based FSI solver is two orders of magnitude faster than the CFD-based FSI solver and the speedup is expected to be even greater on larger problems.

Investigation of a Realistic Flap Modeling Using a Combination of Chimera Method and Grid Deformation on a Wing Fuselage Configuration

AbstractFlap deflections of an aircraft wing for active load alleviation within CFD simulations are realized using pure grid deformation due to time saving and low modeling complexity. In this case, spanwise gaps are neglected, which are present in reality during a flap deflection. Another possibility to realize the deflections is the combination of pure grid deformation and Chimera method, which allows the modeling of the gap between flap and wing or consecutive flaps. The overall aim of this work is the analysis of the aerodynamic effects caused by the different modeling approaches realizing leading and trailing edge flap deflections. The comparison of the modeling methods is investigated on the DLR LEISA configuration, which is a generic wing‐fuselage configuration. For active gust load alleviation, the leading edge flaps are deflected downward and the trailing edge flaps are deflected upward. Due to the downward deflection of the leading edge flaps, vortices are formed using the combined Chimera method as a result of the gap consideration. These vortices lead to a local drag increase resulting in a difference between both modeling methods in the spanwise as well as global drag coefficient. With the pure grid deformation these vortices do not occur. Due to the upward trailing edge deflection, the combined Chimera method leads to a pressure compensation via the effective gap enlargement, which is not present in the pure grid deformation. Overall, the combined Chimera method offers a good possibility to model the induced drag as well as the pressure compensation at a large flap deflection.

Ontogenetic Variation and Sexual Dimorphism of Beaks among Four Cephalopod Species Based on Geometric Morphometrics.

Investigating the ontogenetic variation of biological individuals helps us to fully understand the characteristics of evolution. In order to explore the ontogenetic variation and sexual dimorphism of the beak shape in Octopus minor, Uroteuthis edulis, Sepia esculenta and Sthenoteuthis oualaniensis of the China's coastal waters, the differences between immature and mature stages and the sex-linked differences in the beak shape and size were analyzed with geometric morphometrics methods in this study. The results of Procrustes analysis of variance, principal component analysis and multivariate regression showed that the shapes of the upper beaks of O. minor, U. edulis and S. esculenta differed significantly among various ontogenetic stages (p < 0.05). The shapes of the lower beaks of U. edulis, S. esculenta and Sthenoteuthis oualaniensis were also significantly different among various ontogenetic stages (p < 0.05). The results of thin-plate spline deformation grids showed that the beaks of the four cephalopod species presented different variation patterns. This study gives us basic beak geometry morphology information for Octopus minor, Uroteuthis edulis, Sepia esculenta and Sthenoteuthis oualaniensis present in China's coastal waters. The ontogenetic differences in beak shape might be related to extrinsic factors (diet difference and intra and interspecific competition) in habitat.

Investigation of Aeroelasticity Effect on Missile Separation from the Internal Bay

There is a strong aerodynamic interference when launching the missile in the embedded mode. During the separation process, the carrier aircraft safety may be threatened due to large slenderness ratio, low structural stiffness, and aeroelasticity effects of the missile. The present study simulates missile separation in the presence of the aeroelasticity effects based on the computational fluid dynamics (CFD), rigid body dynamics (RBD), and computational structure dynamics (CSD) coupling method. A hybrid dynamic grid method consisting of the mixed overset unstructured grid and deformation grid is utilized. In order to verify the accuracy of the coupled numerical method, store separation from a wing and AGARD 445.6 wing flutter are first simulated as two standard test cases. The verification results imply that the present coupled numerical method is reliable and capable in simulation of the aeroelastic effect in missile separation. The influence of aeroelasticity on the separation trajectory of a missile from the internal bay is systematically studied at different states. Numerical results show that aeroelasticity substantially affects the missile angular displacement, while it has a slight impact on the linear displacement of the center of mass. Mach number and flight altitude are two important flight parameters that characterize the aeroelasticity effect on missile separation from the internal bay.

Modeling seismic wave propagation in the Loess Plateau using a viscoacoustic wave equation with explicitly expressed quality factor

The thick Quaternary loess on the Loess Plateau of China produces strong seismic attenuation, resulting in weak reflections from subsurface exploration targets. Accurately simulating seismic wavefield in the Loess Plateau is important for guiding subsequent data processing and interpretation. We present a 2D/3D wavefield simulation method for the Loess Plateau using a viscoacoustic wave equation with explicitly expressed quality factor. To take into account the effect of irregular surface, we utilize a vertically deformed grid to represent the topography, and solve the viscoacoustic wave equation in a regular computational domain that conforms to topographic surface. Grid deformation introduces the partial derivatives such as ∂vx/∂z and ∂vy/∂z in the wave equation, which is difficult to be accurately computed using traditional staggered-grid finite-difference method. To mitigate this issue, a finite-difference scheme based on a fully staggered-grid is adopted to solve the viscoacoustic wave equation. Numerical experiments for a simple layer model and 2D/3D realistic Loess Plateau models demonstrate the feasibility and adaptability of the proposed method. The 3D modeling results show comparable amplitude and waveform characteristics to the field data acquired from the Chinese Loess Plateau, suggesting a good performance of the proposed modeling method.

Research on Aerodynamic Characteristics of Trans-Media Vehicles Entering and Exiting the Water in Still Water and Wave Environments

The problem of aircraft entering and exiting water is a complex, nonlinear, strongly disturbed, and multi-coupled multiphase flow problem, which involves the precise capture of the air/water interface and the multi-coupling interaction between aircraft, water, and air. Moreover, due to the large difference in medium properties during the crossing, the load on the body will suddenly change. In this paper, the VOF (volume of fluid) algorithm is used to capture the liquid surface at the air/water interface, and since body movement is involved in this process, the overset grid technology is used to avoid the traditional dynamic grid deformation problem. In the process of this numerical simulation prediction, the effects of different water-entry angles and different water-entry heights on the body load and attitude of the trans-medium aircraft, as well as the cavitation evolution law of the body water entry are analyzed. On this basis, to simulate the authenticity and complexity of the water-entry environment, numerical wave-making technology was introduced to analyze the water-entry load, posture, and cavitation evolution law of the body under different wave environments. The numerical parameters under the condition of wave and no wave are compared, and the difference in water-entry performance under the condition of wave and no wave is analyzed.

Modeling of rock multiple fractures system with a new contact algorithm and a novel approach for complex topology construction

Multiple fractures intersection induced by crack propagation and coalescence is extremely significant for revealing the fracturing essence and establishing mechanical models of natural rock with complex fracture network. A complex discrete interface dynamically adding algorithm (CDIDA) and a potential function-based fracture contact calculation method (PBFCC) are proposed for multiple fractures propagation with complex topology in rocks. Through combining fracture representation with dynamic cyclic “nodal splitting” and nodal assignment with local topological structure identification, CDIDA is proposed to dynamically construct the complex fracture network for the discrete interface approach. CDIDA is able to efficiently establish reasonable local interface topology as the premise of accurately calculating the interaction of multiple fracture systems. Noting that the line attributable to any fracture interfaces can be defined as a set of discrete points, PBFCC transforms the complex contact calculation into the equilibrium problem of these points connecting with hypothetical bonds. The constitutive relation of these bonds is based on a modified potential function, and it is changeable and movable according to the current fracture interface configuration. PBFCC avoids the computing problems such as setting prior contact pairs and contact detecting at each iteration, and is suitable for complex interface contact scenarios with large grid deformations. Moreover, PBFCC ensures that the complex interacting mechanical field calculation of the multiple fracture system is reduced to individual discrete point level, leading to the advantages of high efficiency and wide applicability. Based on the numerical implementation in Cellular Automata Software for engineering Rockmass fracturing process (CASRock), single edge fracture, collinear tensile fracture system, multiple fracture system and complex multiple fracture system simulations are provided to validate the efficiency and accuracy of the proposed methods.

Virtual calculations for analyzing the operation of air spring

The 3D-model of an air spring for road vehicles is presented. A virtual calculation of the air spring has been carried out. Calculation results have been analyzed for adequacy by investigating grid deformation and checking pressure inside the rubber part of the air spring. The most dangerous places of the air spring are shown. Possibilities of LS-Dyna software package for engineering analysis are demonstrated. The influence of computer-aided design systems on modern engineering solutions is considered.

Geometric morphometrics and ecological niche modelling for delimitation of Triatoma pallidipennis (Hemiptera: Reduviidae: Triatominae) haplogroups

A recent phylogenetic analysis of Triatoma pallidipennis, an important Chagas disease vector in Mexico, based on molecular markers, revealed five monophyletic haplogroups with validity as cryptic species. Here, we compare T. pallidipennis haplogroups using head and pronotum features, environmental characteristics of their habitats, and ecological niche modeling. To analyze variation in shape, images of the head and pronotum of the specimens were obtained and analyzed using methods based on landmarks and semi-landmarks. Ecological niche models were obtained from occurrence data, as well as a set of bioclimatic variables that characterized the environmental niche of each analyzed haplogroup. Deformation grids for head showed a slight displacement towards posterior region of pre-ocular landmarks. Greatest change in head shape was observed with strong displacement towards anterior region of antenniferous tubercle. Procrustes ANOVA and pairwise comparisons showed differences in mean head shape in almost all haplogroups. However, pairwise comparisons of mean pronotum shape only showed differences among three haplogroups. Correct classification of all haplogroups was not possible using discriminant analysis. Important differences were found among the environmental niches of the analyzed haplogroups. Ecological niche models of each haplogroup did not predict the climatic suitability areas of the other haplogroups, revealing differences in environmental conditions. Significant differences were found between at least two haplogroups, demonstrating distinct environmental preferences among them. Our results show how the analysis of morphometric variation and the characterization of the environmental conditions that define the climatic niche can be used to improve the delimitation of T. pallidipennis haplogroups that constitute cryptic species.

Numerical modelling of porosity with combined gas and shrinkage effects in HPDC

High-pressure die casting is a manufacturing process in which near-net-shape components are produced rapidly under a pressurized environment. However, due to the relatively higher cooling rate prevailing during the process, isolated liquid pockets form at certain locations, leading to increased porosity formation. A one-dimensional deformable grid numerical model has been developed for predicting the evolution of a single pore in an elementary volume, which combines the diffusion model with the shrinkage affected growth. The model accounts for the change in pore size due to shrinkage and inter-granular growth. This model can provide predictions in representative volumes and be used for component level predictions by combining with a macroscopic model.

Deformable Pyramid R-CNN for 3D object detection (ChinaMM2022)

3D object detector performance has gradually improved, but it still faces huge challenges for accurate detection from point clouds due to incomplete shapes and sparse point clouds. To solve this problem, recent two-stage approaches usually divide the region of interest (RoI) into regular grids and aggregate the internal features of the RoI within a certain radius for refinement proposals. However, for objects with sparse points, only the features inside the RoI cannot satisfy the need for accurate detection. In view of this objective fact, we present a new two-stage 3D object detection framework from point clouds to 3D voxels inside and outside RoI, named Deformable Pyramid R-CNN. Specially, we firstly propose the Voxel Feature Pyramid, which dynamically selects multi-layers of 3D features based on the sparsity of non-empty voxels within the RoI for proposal refinement. Secondly, a new Deformable Voxel RoI Pooling is introduced to abstract rich context information from the voxels of interest outside RoI, to better align semantic information by deformation grid points set with multiple receptive fields for accurate detection. Our method achieves progressive performance in both KITTI Dataset and Waymo Open Dataset. Especially on KITTI Dataset, our method outperforms PV-RCNN by 0.47%, 1.63%, 1.34% on val set easy, moderate and hard levels for car detection, respectively. Code will be available at https://github.com/june2678/DP-RCNN.