Mesh Deformation Research Articles

Three-Dimensional Wheat Modelling Based on Leaf Morphological Features and Mesh Deformation

The three-dimensional (3D) morphological structure of wheat directly reflects the interrelationship among genetics, environments, and cropping systems. However, the morphological complexity of wheat limits its rapid and accurate 3D modelling. We have developed a 3D wheat modelling method that is based on the progression from skeletons to mesh models. Firstly, we identified five morphological parameters that describe the 3D leaf features of wheat from amounts of 3D leaf digitizing data at the grain filling stage. The template samples were selected based on the similarity between the input leaf skeleton and leaf templates in the constructed wheat leaf database. The leaf modelling was then performed using the as-rigid-as-possible (ARAP) mesh deformation method. We found that 3D wheat modelling at the individual leaf level, leaf group, and individual plant scales can be achieved. Compared with directly acquiring 3D digitizing data for 3D modelling, it saves 79.9% of the time. The minimum correlation R2 of the extracted morphological leaf parameters between using the measured data and 3D model by this method was 0.91 and the maximum RMSE was 0.03, implying that this method preserves the morphological leaf features. The proposed method provides a strong foundation for further morphological phenotype extraction, functional–structural analysis, and virtual reality applications in wheat plants. Overall, we provide a new 3D modelling method for complex plants.

Effect of the Computational Model and Mesh Strategy on the Springback Prediction of the Sandwich Material

The effect of the computational model and mesh strategy on the springback prediction of the thin sandwich material made of micro-alloyed steel was investigated in this paper. To verify the chosen computational strategy, a comparison of the experimentally obtained specimen (U-bending) with the FEA result was performed. The Vegter yield criterion combined both with the isotropic and kinematic hardening law was used for the calculation. In addition, the effect of the deformation mesh element (surface and volume) on the accuracy of the springback prediction was investigated. It was concluded that the choice of the volume deformation mesh does not significantly improve the accuracy of the results. Moreover, it is quite a time-consuming approach. The much greater influence was monitored by concerning the selection of hardening law, where the anisotropic one was more suitable to be used on the springback prediction of a given sandwich material.

Parametric Geometric Metamodel of Nonlinear Magnetostatic Problem Based on POD and RBF Approaches

A parametric geometric metamodel is built for a nonlinear magnetostatic problem, using proper orthogonal decomposition (POD) approach combined with radial basis functions (RBFs) interpolation. Furthermore, the geometrical variation of the problem is modeled using an RBF interpolation for smooth mesh deformation. The metamodel is applied for a single-phase EI inductance, and the aim is to create precise flux cartographies based on few solutions of the original finite element (FE) model. The results show that the POD-RBF approach can reduce efficiently the evaluation time of a parametric nonlinear magnetostatic problem.

The Effect of Inflow Distortion on the Rotordynamic Characteristics of a 1400-MW Reactor Coolant Pump Annular Seal

The annular seal between stator and rotor substantively acts as a bearing that affects the rotordynamic characteristic of the turbomachinery rotor system. The rotor wake turbulence in a canned motor Reactor Coolant Pump (RCP) will lead to inflow pressure distortion at the annular seal entrance, thus further affecting the seal rotordynamic characteristics and threatening the stable operation of RCP. In order to obtain the seal rotordynamic coefficients, a transient numerical method applies the mesh deformation technique to simulate the multiple-frequency elliptical rotor whirling orbit model. The transient solutions were proposed to solve the unsteady reaction forces of annular seals at five excitation frequencies for each case. The inflow pressure distortion patterns were simplified as harmonic functions, including two important influence parameters that are impeller blades number m and pressure fluctuation ratio λ. The numerical results showed that with nonuniform time-averaged pressure distribution at the entrance of the annular seal in Case 2, the inflow distortion significantly affects the seal rotordynamic coefficients, while the rotational spinning speed in Case 3 can weaken the time-averaged nonuniformity and accordingly make a dent in the influence. Increasing impeller blades number m and pressure fluctuation λ both result in a sharp diminution of the negative stiffness Keff, as well as an obvious increase in the effective damping Ceff, which will strengthen rotor misalignment and system stability. In addition, the larger impeller blades number m and higher pressure fluctuation λ will make the effective damping Ceff more independent of the whirling frequency. These results provide theoretical guidance for the operation safety of RCP.

Numerical modeling of extreme wave interaction with point-absorber using OpenFOAM

Extreme waves are critical for the WEC’s development. CFD toolboxes have been widely used in the simulation of extreme waves–structure interaction. However, the quality of the mesh is a sensitive issue; the WEC’s large response can lead to mesh deformation and subsequent numerical instability. In this paper, 100-year extreme waves are chosen from the environmental contour of the Humboldt Bay site in California, and their interaction with the WEC is modeled using the open-source CFD software OpenFOAM. The overset mesh technique is an advanced method recently available in OpenFOAM, able to handle great body motions. Here, the overset method is utilized and compared with the commonly used morphing method. The two methods provide equivalent results, but the latter is prone to the mesh deformation and fails to complete the simulations. Regarding the impact of extreme waves on WECs, the results further show that the combination of wave height and steepness is critical; i.e., the 100-year wave height does not necessarily result in the maximum forces, but rather steeper sea states tend to contribute in higher wave loadings. Additionally, the WEC is studied for 40% higher generator’s damping, as it is a common control strategy during the harsh environmental conditions.

Modeling Horizontal Salt Cavern Leaching in Bedded Salt Formations

Summary The leaching of a salt cavern will trigger a series of rock-fluid interactions, including salt rock dissolution, cavity expansion, and brine transport caused by convection, turbulence, and diffusion effects. These interactions have influences on one another. The primary objectives of this study include developing a 3D multiphysical coupled model for horizontal salt cavern leaching and quantifying these interactions. The species transport equation and standard κ-ε equation were combined to describe the brine transport dynamics within the cavity. Based on the velocity and concentration distribution characteristics predicted, the interface movement equation implemented with mesh deformation techniques was applied to describe the cavity expansion. Next, the Volgograd cavern monitored data were collected for model validation. The predicted results are consistent with the field data. The average relative errors are 11.0% for brine displacing concentration and 4.5% for cavity volume. The results suggest that the cavity can be divided into three regions, including the main flow region, circulation region, and reflux region. The results also suggest that the brine concentration distribution is relatively uniform. With the dissolution threshold angle and anisotropic dissolution rates considered, the resultant cavity cross section is crown top and cone bottom. The results also show that the cavity can be divided into dissolution and erosion sections according to its position relative to the injection point.

Shape optimization of composite porous vapor chamber with radial grooves: A study on the minimization of maximum pressure drop

Composite porous vapor chamber (CPVC) with uniform radial grooves is a recently developed vapor chamber, exhibiting good temperature uniformity and excellent stability under high heat flux of 280 W/cm2 with the thermal resistance less than 0.15 °C/W. However, the maximum pressure drop in CPVC due to liquid flow is prone to exceed the limits of capillary pressure, and the shape design of the wicks lacks scientific and objective enough criteria. This paper proposes a shape optimization method to optimize the shape of the evaporator wick in CPVC, based on the study on the minimization of the maximum pressure drop. In this method, the discrete adjoint method is utilized to efficiently analyze the sensitivities and find the most rapid descendant directions for the minima problem. The shape of the evaporator wick is updated by the polynomial-based approach based on the sensitivity information. Results indicate that the bottom contours of the wick blocks’ surfaces surrounding the circular cavity contribute the highest sensitivities. Consequently, the mesh deformations near the contours change the shape of the lateral surfaces of wick blocks from rectangular to concave trapezoidal in both Cylindrical and Cartesian coordinate systems. This reduces the maximum velocities and flow resistance in CPVC, due to the smoother structural transition from the condenser wick to the evaporator wick, thus reducing the maximum pressure drop by about 18.5% and 23.3% in Cartesian and Cylindrical coordinate systems, respectively. The proposed method may pave a more objective and scientific alternative to design the shape of the wicks in CPVC.

Computational investigation of drop behavior and breakup in peristaltic flow

The behavior of liquid drops in the retropulsive jet produced by a peristaltic wave is investigated computationally. The computational geometry consists of a tube which is closed at one end, with the peristaltic wave that deforms the boundary moving toward it. A modified solver with the capability to couple mesh deformation and adaptive mesh refinement around moving drops was developed and validated with experimental data, and good agreement was found. A parametric study was then performed to determine the effect of interfacial tension, viscosity ratio, relative occlusion, and initial drop position on the drop's behavior and breakup characteristics. In particular, breakup regimes on graphs of capillary number vs viscosity ratio were determined for each initial drop position and relative occlusion. It was found that these breakup regimes were bounded above and below, and an optimal capillary number for breakup was determined. The volume of the parent drop after breakup decreased linearly with capillary number for low capillary numbers and was independent of the viscosity ratio. For higher capillary numbers, this volume generally increased with the viscosity ratio. It was also found that a drop with lower interfacial tension reached the apex plane sooner than a drop with higher interfacial tension, but once there, took longer to pass through this plane and longer to breakup. The viscosity ratio had negligible influence on the drop transit times for viscosity ratios less than one, while the breakup time generally increased with the viscosity ratio.

Lightweight design method and application of MEWP bracket based on multi-level optimization

<abstract> <p>Mobile elevating work platform (MEWP) is a large-scale engineering machinery equipment that transports workers and tools to the designated height for operation. As the key supporting component of MEWP, the bracket simultaneously needs to meet the performances of high stiffness and strength. Furthermore, the mechanical performance of the bracket can be significantly influenced by its cross-sectional shape. However, the optimal cross-sectional shape of bracket is not easily to obtain owing to the lacking of lightweight design method. Thus, a lightweight design method of MEWP bracket based on multi-level optimization is proposed in this paper. Firstly, the multi-case topology optimization model of MEWP bracket is constructed by using the compromise programming method, and the optimal section configuration of MEWP bracket is obtained based on Solid Isotropic Material with Penalization (SIMP). Secondly, the parameterization of the cross-sectional shape of bracket is realized using the mesh deformation technology, and the multi-case optimization mathematical model of the MEWP bracket is established. Then, the cross-sectional shape and gauge of the bracket are optimized using multi-level optimization method. The optimized results show that weight reduction mass is 11.66 kg and the ratio is 52.4% under the premise that the stiffness of the bracket does not decrease. Furthermore, the weight of MEWP bracket optimized by the multi-level optimization method reduced by 1.27 kg compared with single gauge optimization method. Finally, a physical prototype is developed according to the optimization results.</p> </abstract>

Efficient and Accurate Stitching for 360° Dual-Fisheye Images and Videos.

Back-to-back dual-fisheye cameras are the most cost-effective devices to capture 360° visual content. However, image and video stitching for such cameras often suffer from the effect of fisheye distortion, photometric inconsistency between the two views, and non-collocated optical centers. In this paper, we present algorithms for geometric calibration, photometric compensation, and seamless stitching to address these issues for back-to-back dual-fisheye cameras. Specifically, we develop a co-centric trajectory model for geometric calibration to characterize both intrinsic and extrinsic parameters of the fisheye camera to fifth-order precision, a photometric correction model for intensity and color compensation to provide efficient and accurate local color transfer, and a mesh deformation model along with an adaptive seam carving method for image stitching to reduce geometric distortion and ensure optimal spatiotemporal alignment. The stitching algorithm and the compensation algorithm can run efficiently for 1920×960 images. Quantitative evaluation of geometric distortion, color discontinuity, jitter, and ghost artifact of the resulting image and video shows that our solution outperforms the state-of-the-art techniques.

The Extreme Mesh Deformation Approach (X-Mesh) for the Stefan Phase Change Model

The eXtreme Mesh deformation approach (X-MESH) is a new paradigm to follow sharp interfaces without remeshing and without changing the mesh topology. Even though the mesh does not change its topology, it can follow interfaces that do change their topology (nucleation, coalescence, splitting). To make this possible, the key X-MESH idea is to allow elements to reach zero measure. This permits interface relaying between nodes as well as interface annihilation and seeding in a time continuous manner. The paper targets the Stefan phase change model in which the interface (front) is at a given temperature. Several examples demonstrate the capability of the approach.

Fluid–structural coupling of an impinging shock–turbulent boundary layer interaction at Mach 3 over a flexible panel

We present high-fidelity numerical simulations of the interaction of an oblique shock impinging on the turbulent boundary layer developed over a rectangular flexible panel, replicating wind tunnel experiments by Daub et al. (AIAA Journal, vol. 54, 2016, pp. 670–678). The incoming free-stream Mach and unit Reynolds numbers are $M_{\infty } = 3$ and $Re_{\infty }=49.4\times 10^6 {\rm m}^{-1}$ , respectively. The reference boundary layer thickness upstream of the interaction with the shock is $\delta _0 = 4$ mm. The oblique shock is generated with a rotating wedge initially parallel to the flow that increases the deflection angle up to $\theta _{{max}} = 17.5^{\circ }$ within approximately $15$ ms. A loosely coupled partitioned flow–structure interaction simulation methodology is used, combining a finite-volume flow solver of the compressible wall-modelled large-eddy simulation equations, an isoparametric finite-element solid mechanics solver and a spring-system-based mesh deformation solver. Simulations are conducted with rigid and flexible panels, and the results compared to elucidate the effects of panel flexibility on the interaction. Three-dimensional effects are evaluated by conducting simulations with both full ( $50 \delta _0$ ) and reduced ( $5\delta _0$ ) spanwise panel width, the latter enforcing spanwise periodicity. Panel flexibility is found to increase the separation bubble size and modify its spectral dynamics. Time- and spanwise-averaged streamwise profiles of the wall pressure exhibit a drop over the flexible panel prior to the interaction and a reduced peak pressure in comparison with the rigid case. Spectral analyses of wall pressure data indicate that the low-frequency motions have a similar spectral distribution for the rigid and flexible cases, but the flexible case shows a wider region dominated by low-frequency motions and traces of the panel vibration on the wall pressure signal. The sensitivity of the interaction to small variations in the wedge extent and incoming boundary layer thickness is evaluated. Predictions obtained from lower-fidelity modelling simplifications are also assessed.

A new many-objective aerodynamic optimization method for symmetrical elliptic airfoils by PSO and direct-manipulation-based parametric mesh deformation

A new many-objective aerodynamic optimization method is proposed to design the distinctive symmetrical elliptic airfoil applied on the canard rotor wing aircraft with special requirements on both low drag in different Mach numbers and large drag divergence Mach number. A parameterized direct manipulation of free form deformation (DFFD) method is proposed to realize the one-step process on geometry parameterization and mesh deformation. Then an efficient multi and many-objective particle swarm optimization algorithm (LMPSO) is built to optimize the symmetrical elliptic airfoil to comprehensively improve its aerodynamics. The biobjective optimization of drag reductions at hover stage and at cruise flight shows that the new method can significantly reduce the drag of the elliptic airfoil but at the cost of drag increases at high angles of attack. The four-objective optimization results indicate that the consideration of the high angle of attack flight conditions can improve the aerodynamic performance of the airfoil over a large lift range, which is more practical in engineering application. The five-objective optimization presents that the maximization of the drag divergence Mach number of the elliptic airfoil can be significantly promoted when adding three more design conditions at high Mach number. In general, the optimization results demonstrate that the developed new method can effectively improve the aerodynamic performance of symmetrical elliptic airfoils and provide support on the development of the canard rotor wing aircraft.

Exploring the mechanics of fish escape attempts through mesh

Predictive selectivity modelling is used to study fishing gear selectivity. These models rely on fish morphology parameters and fall-through experiments. Here, we developed a model of the mechanical interaction between a fish and a netting mesh during an escape attempt. In this model, the fish is described with three parameters: the first parameter measures its mechanical ability to penetrate a mesh and the others are body stiffness coefficients accounting for fish body deformation under mesh twine pressure. These parameters were identified from the results of a bench test simulating a fall-through experiment through a single 60-mm Polyethylene (PE) mesh. A rigid circular cone, a rigid elliptical cone and a small number of horse mackerel and haddock, offering a limited length range, were tested. Results were generalised and compared with those obtained on a piece of netting. Within the model's assumptions, it is possible to predict the success of an escape attempt if one knows the three fish parameters and the mesh load in normal and transverse directions. The study showed that escape potential is greater through an actual deformable mesh than through a non-deformable mesh. The potential size of this difference depends on the mesh load and orientation.

Active yarn meshes for segmentation on X-ray computed tomography of textile composite materials at the mesoscopic scale

For the past decade, the composite material community has been struggling to bridge the gap between the X-ray tomography of fiber composites and the realistic modelling of their internal structure at the mesoscopic scale. This paper proposes a new yarn segmentation method relying on a variational approach with deformable 3D surfacic meshes representing the yarn envelopes. It requires the previous localisation of yarn centroids. We apply five forces directly applied on the mesh vertices to drive the mesh fitting towards the visible yarn edges on the tomographic volume. The five forces enable a compromise between the intrinsic aspect of the envelope and the attachment to the yarn contours and regions, while limiting inter-yarn overlap. Results are presented on a X-ray tomography of a non-crimp fabric composite with unidimensional fiber bundles and on a woven composite tomography.

A Hybrid Model Method for Accurate Surface Deformation and Incision Based on FEM and PBD

In some simulations like virtual surgery, an accurate surface deformation method is needed. Many deformation methods focus on the whole model swing and twist. Few methods focus on surface deformation. For the surface deformation method, two necessary characteristics are needed: the accuracy and real-time performance. Some traditional methods, such as position-based dynamics (PBD) and mass-spring method (MSM), focus more on the real-time performance. Others like the finite element method (FEM) focus more on the accuracy. To balance these two characteristics, we propose a hybrid mesh deformation method for accurate surface deformation based on FEM and PBD. Firstly, we construct a hybrid mesh, which is composed of a coarse volume mesh and a fine surface mesh. Secondly, we implement FEM on coarse volume mesh and PBD on fine surface mesh, and the deformation of fine surface mesh is constrained by the displacement of the coarse volume mesh. Thirdly, we introduced a small incision process for our proposed method. Finally, we implemented our method on a simple deformation simulation and a small incision simulation. The result shows an accurate surface deformation performance by implementing our method. The incision effect shows the compatibility of our proposed method. In conclusion, our proposed method acquires a better trade-off between accuracy and real-time performance.

A mass conserving arbitrary Lagrangian–Eulerian formulation for three‐dimensional multiphase fluid flows

AbstractThe arbitrary Lagrangian–Eulerian (ALE) framework presented in [Sahin and Guventurk, An arbitrary Lagrangian–Eulerian framework with exact mass conservation for the numerical simulation of 2D rising bubble problem.Int J Numer Methods Eng. 2017;112:2110–2134] has been extended to simulate three‐dimensional immiscible incompressible multiphase fluid flows. The div‐stable side centered unstructured finite volume formulation is used for the discretization of the incompressible Navier–Stokes equations. A novel kinematic boundary condition that satisfies the local discrete geometric conservation law (DGCL) is implemented to ensure the mass conservation of each species at the machine precision. The pressure field is treated to be discontinuous across the interface with the discontinuous treatment of density and viscosity. Surface tension force is treated as a tangent force and discretized in a semi‐implicit form. Two different approaches for the computation of unit normal vector have been implemented: the least squares biquadratic surface fitting (LSBSF) and the mean weighted by sine and edge length reciprocals (MWSELR). The resulting large system of algebraic equations is solved in a fully coupled manner in order to improve the time step restrictions. As a preconditioner, an approximate matrix factorization similar to that of the projection method is employed and the parallel algebraic multigrid solver BoomerAMG provided by the HYPRE library, which is accessed through the PETSc library, has been utilized for the scaled discrete Laplacian of pressure and the diagonal blocks of mesh deformation equations. The accuracy of the proposed method is initially validated on the static bubble problem, since the surface tension force is highly sensitive to the accurate evaluation of the unit normal vector and the inaccuracies significantly contribute to unphysical velocities, called parasitic currents. The calculations indicate that the parasitic currents can be reduced to machine precision for the MWSELR method. Then, the proposed approach is applied to the single bubble rising in a viscous quiescent liquid for both low and high density ratios. The calculations produce accurate predictions of the bubble shape, center of mass, rise velocity, and so forth. Furthermore, the mass of each species is conserved at machine precision and discontinuous pressure field is obtained in order to avoid errors due to the incompressibility restriction in the vicinity of liquid‐liquid interfaces at large density and viscosity ratios.

Dynamic failure behavior of steel wire mesh subjected to medium velocity impact: Experiments and simulations

Considerable property damage is caused by windborne debris during extreme weather. The object of interest in this study, steel wire mesh, is an effective means of providing protection against windborne debris. However, the design and manufacture of security screens made of wire mesh typically depend on a laborious and imprecise trial-and-error process. Additionally, this anisotropic, inhomogeneous, and porous material comprising in-contact wires has rarely been examined in a comprehensive manner. Considering these issues, the current research experimentally tested the impact response of plain-weave steel wire mesh by firing a spherical projectile in a velocity regime ranging from 112 m/s to 152 m/s. The deformation and failure mechanisms of the wire mesh during the impact process were investigated via high-speed photography. The results showed that the wire mesh behaved as a membrane and failed mainly in tension over the impact velocity range of interest. Further, with a detailed finite element model consisting of interlaced warp and weft wires, additional virtual tests were carried out at a broader velocity range of 20–200 m/s. The findings indicated a linear relationship between residual velocity and impact velocity under a velocity range that exceeded the ballistic limit. The energy absorbed by the wire mesh increased with impact velocity (or impact energy) before the material reached peak absorption at the ballistic limit. Beyond this threshold, the energy absorption gradually declined to an asymptotic level. Such energy absorption was well correlated with the extent of transverse deformation in the wire mesh. Internal energy due to the deformation of wires and frictional energy associated with the interactions between sliding wires at their crossovers were two primary energy absorbing mechanisms. Moreover, the effects of impact location, clamped wire direction and projectile size were analyzed.

Fast Optimization Design of the Flexure for a Space Mirror Based on Mesh Deformation

According to the requirements of high force-thermal stability and high performance of a space telescope, a space mirror assembly must not be influenced by environmental factors. In this study, a space mirror assembly under load conditions, such as gravity, thermal, and assembly error, is considered. After the mirror is optimized, the surface shape error is reduced by 22%, and the mass is increased by 0.113 kg. In order to improve the efficiency of integration optimization, we present a fast optimization method using mesh deformation to be applied to the flexure. The size parameters of flexure and axial mount position are obtained by optimization. With our method, the single optimization time reduces from 10 min to 40 s, which can improve the efficiency of multi-objective optimization. The mirror assembly is fabricated and assembled based on optimization results. Finite element analysis (FEA) and test results for the space mirror assembly confirm the validity and feasibility of the fast optimization method, and we believe that the flexure based on fast optimization meets the requirements of a space mirror assembly for space applications.

Prediction of Vertical Tail Buffet Using CFD/CSD Coupling Method

The vertical tail buffet induced by the vortex breakdown flow is numerically investigated. The unsteady flow is calculated by solving the RANS equations. The structural dynamic equations are decoupled in the modal coordinates. The radial basis functions (RBFs) are employed to generate the deformation mesh. The buffet response of the flexible tail is predicted by coupling the three sets of equations. The results show that the presence of asymmetry flow on the inner and outer surface of the tail forced the structural deflection offsetting the outboard. The frequency of the 2nd bending mode of the tail structure meets the peak frequency of the pressure fluctuation upon the tail surface, and the resonance phenomenon was observed. Therefore, the 2nd bending responses govern the flow field surrounding the vertical tail. Finally, the displacement of the vertical tail is small, while the acceleration with a large quantitation forces the vertical tail undergoing severe addition inertial loads.