Mesh Method Research Articles

Investigation on high contact ratio harmonic two-dimensional tooth profile design based on mid-point meshing method

Investigation on high contact ratio harmonic two-dimensional tooth profile design based on mid-point meshing method

Suppression of Leidenfrost instability using multiple rods and rectangular mesh elements

Large Leidenfrost drops may be unstable when their diameters exceed a critical value. Through theoretical and experimental investigations, this study explored the feasibility of suppressing Leidenfrost instability in a large container, by meshing the container or its central portion into rectangular elements. Thin rods were used to construct these rectangular elements. Leidenfrost instability was considered in four rectangular configurations. They were also the rectangular mesh elements that might be used. There were two findings. First, the diameter of the largest inscribed cylinder in a rectangular configuration was the critical dimension for determining Leidenfrost instability. Second, the threshold value of this diameter in a rectangular configuration with rod(s) was 8.9λ ± 0.7λ, where λ is the capillary length of water. It was larger than its counterparts in both a rectangular container (without the presence of a rod) and a circular container (with or without the presence of a rod), due to the strong effect of the rod in a rectangular configuration. Based on these two findings, a large rectangular container was meshed into rectangular elements using thin rods, with the diameter of the largest inscribed cylinder in each element below the threshold value. This mesh method suppressed the Leidenfrost instability in the large container.

Numerical study of transient indoor airflow and virus-laden droplet dispersion: Impact of interactive human movement

Human movement affects indoor airflow and the airborne transmission of respiratory infectious diseases, which has attracted scholars. However, the interactive airflow between moving and stationary people has yet to be studied in detail. This study used the numerical method validated by experimental data to explore the transient indoor airflow and virus-laden droplet dispersion in scenes with interactive human movement. Human-shaped numerical models and the dynamic mesh method were adopted to realize human movement in scenes with different lateral distances (0.2–1.2 m) between a moving person and stationary (standing/sitting) persons. The interactive human movement obviously impacts other persons' respiratory airflow, and the lateral fusion ranged about 0.6 m. The interactive human movement strengthens the indoor airflow convection, and some exhaled virus-laden droplets were carried into wake flow and enhanced long-range airborne transmission. The impact of interactive human movement on sitting patients' exhalation airflow seems more evident than on standing patients. The impact might last over 2 min after movement stopped, and people in the affected area might be at a higher exposure. The results can provide a reference for epidemic control in indoor environments.

An arbitrary Lagrangian–Eulerian discontinuous Galerkin method for two‐dimensional compressible flows on adaptive quadrilateral meshes

AbstractIn this article, a discontinuous Galerkin (DG) scheme on the adaptive quadrilateral meshes is proposed to simulate two‐dimensional compressible flows in the direct arbitrary Lagrangian–Eulerian (ALE) framework. In our scheme, the Euler equations are discretized in the reference element with the help of a bilinear map. A kind of Taylor expansion basis functions in the reference element is used to construct the interpolation polynomials of variables. We describe the property that the material derivatives of the basis functions used in the DG discretization are equal to zero, with which the scheme is simplified. Furthermore, the mesh velocity in our ALE framework is obtained by implementing the approach of mesh movement based on the variational principle from [Adaptive mesh methods for one‐ and two‐dimensional hyperbolic conservation laws. SIAM J Numer Anal. 2003;41:487–515]. This approach of mesh movement automatically concentrates the mesh nodes near the regions with large gradient values of the variables and can greatly improve the resolution of the solution near these regions. In addition, a WENO (weighted essentially non‐oscillatory) reconstruction helps our scheme remove the numerical oscillations. Some numerical examples are presented to demonstrate the accuracy, high resolution, and robustness of our scheme.

NEW AND RAPID METHODS FOR GRIDDING OF POINT CLOUDS

Abstract. Point clouds are among the most important photogrammetry and remote sensing data that provide three-dimensional information about objects and features. These points have unorganized, irregular structures and do not have uniform spacing. In this paper, two innovative methods for converting the point cloud into a grid are presented. The first method is called the mesh method. It generates all possible 3D grid points covering the point cloud. Then, the distances between the generated grid points and the original points are measured. Based on these distances, the required grid points are determined. The second method is the resampling method. It uses three equations to resample the original point so that the points are moved to new coordinates to create the grid points. The methods are tested on three different point clouds. The results show that the two methods are very fast. However, the resampling method is much faster, especially for very large areas.

Flight simulation from takeoff to yawing of eVTOL airplane with coaxial propellers by fluid-rigid body interaction

In this study, we adopt a coupled fluid-rigid body simulation using the moving computational domain method and multi-axis sliding mesh method for the takeoff, hovering, and yawing flight of an electric vertical takeoff and landing aircraft (eVTOL). The aircraft model has four pairs of coaxial propellers, and the computational domain is divided into three domains to move the aircraft and eight propeller domains to rotate the propellers. As a result, we clarify the behavior and aerodynamic force of the aircraft when the input values are determined by the automatic control. The results in the flow field also show that the downwash spreads in a crisscross pattern on the ground, the wind reaches different ranges on the ground depending on the flight altitude, and that the coaxial propeller causes an asymmetry in the velocity field during yawing. Consequently, we conclude that this method is effective for the flight simulation of an eVTOL.

Abundance of Procamallanus (Spirocamallanus) inopinatus (Nematoda: Camallanidae) in Characiformes fish and associated factors in Midwest Brazil.

The success of Procamallanus (Spirocamallanus) inopinatus infection in fish involves a complexity of variables. This study aims to evaluate the relationship between abundance of P. (S.) inopinatus with biometric and somatic parameters, sex, relative condition factor (Kn) and hosts diet, as well as to evaluate length relationship of the parasites and the hosts. The fishes were collected by the mesh method and data, length, weight, sex, gonad and liver weight, Gonadosomatic index (GSI) and hepatosomatic index (HSI), Kn and stomach content were recorded. Twenty-seven specimens of P. (S.) inopinatus were collected in the intestine from Serrasalmus rhombeus and 52 from Leporinus friderici. In general, the prevalence, mean intensity and mean abundance of infection was higher in L. friderici. The total abundance was explained by the variables GSI, HSI total length, gonad and liver weight. Fish relative condition factor (kn) and sex were not influenced by the infection, being that the parasite infection did not impair the body condition of the hosts. There is no relationship between host length and parasite length in any of the evaluated fish species. On average, S. rhombeus parasites are 0.69 cm larger than L. friderici parasites.

Modelling of Hydraulic Dynamics in Sludge Treatment Reed Beds with Moving Boundary Condition

The conventional method of simulation using fixed mesh method (FMM) of discretization is a well-known and trusted procedure in modelling hydraulic dynamics. However, new ideas of innovation in modelling should be advanced. The moving mesh method (MMM) has been considered as a novel approach in modelling hydraulic dynamics after depending on the existing simulation model for decades. The MMM is capable of describing the moving boundary condition of an actual wetland system due to water ponding. An idealized model should be able to simulate the actual hydraulic flows through the system with the corresponding porosity. Hence, a combination of MMM and FMM (MM-FMM) of discretization for hydraulic dynamics is studied in this project to model the flux with respect to water ponding scenario in a sludge treatment reed bed and unsaturated transient flow within the bed. Such method has evidently proved to simulate the actual hydraulic flows in contrast to conventional method. The application of MMM limits the maximum flux to keep within its saturated conductivity, thus reduces the effect of flow overprediction. Subsequently, the simulated results for hydraulic head and moisture content can be predicted for actual condition of different cases according to their respective fluxes.

A vectorized spherical convolutional network for recognizing 3D mesh models with unknown rotation

目的3维目标分类是视觉领域的一个基本问题，3维目标的旋转变化给分类带来极大挑战。同时不规则3维网格模型难以运用传统2维卷积网络提取特征。针对这两个问题，提出一种基于矢量型球面卷积网络的分类方法，用于识别未知旋转的3维网格模型。方法 使用矢量型神经元作为网络的基础神经元，并提出一种新型矢量层间的卷积方式。首先，将3维模型规范化并映射到单位球上，获取球面的信号表示；然后，使用矢量型分类网络和重建网络学习等变的3维模型特征；最后，使用分类网络完成3维模型分类。结果 经过消融实验对比，使用本文提出的球面卷积模块和矢量卷积层，并在训练时加入重建模块。对原本未旋转（no rotation，NR）数据集进行任意旋转（arbitrary rotation，AR），并设定NR/AR，AR/AR，NR/NR共3种训练/测试策略的分类任务，其中NR/AR任务衡量模型识别未知旋转的能力。在刚性数据集ModelNet40上，相比基于球面卷积网络（spherical convolutional neural network，SCNN）的分类方法，在3种任务上分别提高了7.7%，1.8%，3.1%。为验证本文方法在识别非刚性3维网格目标的优越性，在非刚性数据集SHREC15（shape retrieval contest 2015）上，相比SCNN，本文方法在3种任务上分别提高了8.8%，4.5%，5.0%。结论 本文提出一种将矢量型网络运用在3维目标分类的思路，使用光线投射法获得分布在球面空间的特征，便于使用统一的球面卷积算子进行处理；设计一种球面残差模块避免梯度消失；使用矢量型神经元并设计矢量层之间的卷积方式以保证网络的等变性，使得识别任意旋转的3维模型时更加准确。;Objective The 3D meshes are concerned of spatial information-demonstrated surface triangles，which can optimize surface information than other related representations like voxel or point cloud. The 3D shape analysis is still to be resolved in relevant to mesh representation on two aspects：1）the irregular data structure of the mesh model is challenged for feature extraction using traditional 2D convolutional networks，and 2）the 3D rotation transformation is challenged for object recognition as well. The emerging convolutional neural networks（CNNs）have been developing dramatically in the context of 2D vision like classification，segmentation，detection，as well as 3D objects-oriented applications. Current CNNbased 3D mesh classification is developed from two aspects：1）the 3D object is transferred to 2D images and the following 2D-based CNN methods are used，and 2）convolution methods are designed on 3D mesh data. However，it is still challenged to recognize rotated objects due to traditional CNN-equivariant-lacked pooling operation. The lack of rotation equivariance can be improved on the basis of two networks which are vectorized and equivariant networks. The vectorized network，known as capsule network，has shown its potentials in learning spatial transformation on 2D images，but convolutionconstrained method is required to be applied on 3D mesh further. To apply the vectorized neural network to 3D mesh data and preserve rotation equivariance，we develop a vectorized spherical neural network-derived method for 3D mesh classification. Method Our method can be segmented into three categories as mentioned below：First，the 3D mesh model is preprocessed to signals on the sphere. We normalize the 3D mesh into a unit sphere and get the spherical signals on the unit sphere using the ray casting scheme. The obtained spherical signals are nearly equivalent 3D shape representations and can be further processed by spherical convolution methods. The aims of processing 3D mesh to spherical signals are 1）to utilize the spherical signals-defined equivariant spherical convolution operators，and 2）to design vectorized neurons in a coordinated manner. Second，the autoencoder-structured model is used to learn the feature of the spherical signal. The model is composed of two sub-networks：i）a vectorized spherical convolutional neural network（VSCNN）to encode the equivariant feature and classify the 3D object，and ii）a multilayer perceptron decoder to decode the extracted feature back to sphere signal. The VSCNN is based on two kinds of spherical residual convolution block and the vector convolution layer. To train deeper networks and resist overfitting，we develop two spherical convolution modules which are S2 convolution block and SO(3) convolution block，and the primary vectorized neurons are obtained after that. The vector convolution layer is used to learn high-level vectorized features derived from the lower layer. The vector convolutional layer can be used to transfer the primary vectorized neurons to get high-level ones. A deep vectorized network can be constructed through the vector convolutional layer-based stacking. To guarantee the rotation-equivariant spherical vector neurons can be learned well during convolution，we use the SO(3) convolution operator to predict the high-level neurons. The VSCNN and the network-reconstructed are trained simultaneously. Third，the VSCNN-based 3D object classification is demonstrated. For validation，we use VSCNN to clarify the category information of the 3D model only. Result The ModelNet40 and SHREC15 of two 3D datasets are verified for the effectiveness of the proposed method. Our model is trained on the non-rotated（NR） and arbitrarily rotated（AR）training set，and it is tested on the non-rotated and rotated test set as well. The robustness of the model is demonstrated to rotation. For the rigid data set ModelNet40，the accuracy of rotation-unidentified targets can be reached to 85. 2%，surpassing the baseline method by 7. 7%. The comparative analysis shows that our method proposed can surpass most of multi-view and point cloud methods compared to other related 3D data representations. The NR/NR result can show its optimization ability in comparison with the benchmarks. At the same time，to identify non-rigid threedimensional grid targets，we carry out a rotation classification experiment on the non-rigid data set SHREC15，and the accuracy rate can be reached to 90. 4%，surpassing the baseline method by 8. 8%. Conclusion We develop a 3D object classification method for rotated mesh. The robustness to 3D rotation can be optimized in terms of vectorized neurons and the equivariant vector convolution layer. The 3D models-rotated recognition is facilitated excluding rotation augmentation， and it shows the learning ability for vectorized networks-based transformation.

Investigation of deposition characteristics on tube-bundle heat exchanger with an improved ash particle model

The deposition of fly ash in the tube-bundle heat exchanger has become an urgent problem that must be resolved. During the deposition process, the fly ash particles will alter the physical properties and geometry of the heat exchange surface. A random function model combined with the dynamic mesh method is proposed to improve the existing particle deposition model. The effects of various flow velocities and particle sizes on particle deposition are analyzed. The results indicated that the total deposition mass of large particles decreases and the small particles increases as the flow velocity increases. With increasing particle size at the same flow velocity, the total particle deposition mass increases first and then decreases for in-line tube bundles. Local analysis indicates that the initial deposition occurs primarily on the windward side of the tube, with a greater number of particles deposited on the upstream tube bundles than on the downstream tube bundles.

A new designed slit mesh method with the least recurrence and complication rate in laparoscopic hernia surgery

Background: The aim of our study is to determine the method with the least recurrence and complication rate in laparoscopic hernia surgery. For this reason, the purpose of cutting the graft is to give it a closer and appropriate shape to the anatomy and thus to minimize the recurrence rate. Methods: A total of 142 patients with hernias, 135 men and 7 women, were included in the study. The cases were divided into two groups; the conventional shape of the graft was applied to the first group without slit, in the second group; the graft was cut in the middle to spread around the pampiniform plexus, and the hernia sac and pampiniform plexus were dissected, and then spread around the pampiniform plexus with slit. The methods of spreading around the inguinal cord by cutting versus spreading on the inguinal cord without cutting were compared. Results: While the slit mesh status of those with postoperative testicular edema was 100% present and 0% absent, and a statistically significant difference was determined between the groups (p=0.027). The patients' time to return home after surgery was statistically significantly higher in the slit mesh present group compared to the absent group (p=0.001). A statistically significant difference was found when those who did not have reoperation and those who had reoperation status were compared (p=0.044). Conclusion: It was concluded that this new approach minimizes early and late recurrences with faster recovery after repair of laparoscopic extraperitoneal inguinal hernia. We suggest a slit mesh method by changing the shape and spreading the mesh without using any fixation material can also be used as a fixation method such as self-adhesive mesh and fibrin glue.

Numerical investigations on roof ventilator turbine performance characteristics using ANSYS

Rooftop wind turbine ventilators are natural air circulation systems that employ a rotating blade to remove stale air from a building, improving the indoor air quality and saving money in the process. The effectiveness of a roof ventilator turbine depends heavily on its construction. By varying the diameter of the turbine blades (500, 670, and 690 mm), this CFD study modeled and examined three distinct designs for wind-driven ventilation devices. This numerical analysis was further developed to compute the presentation of a rotating ventilator by analyzing the pressure, turbulence kinetic energy, and velocity of the airflow related with the ventilator at variant designs. To investigate the viability of a numerical approach to modeling the many aspects of a ventilator flow, a computational fluid dynamics (CFD) analysis was conducted utilizing the conventional k- turbulence model with the multiple reference frame meshing method. The proposed design of a 690 mm ventilator blade for a rooftop turbine was found to perform better than two alternative designs using computational fluid dynamics (500 and 670 mm turbine blade diameter). The trend lines appear to be in virtuous contract with formerly available data, signifying that mathematical modelling could be a useful and cost-efficient tool for the design, growth, and performance evaluation of a wind-driven rotational ventilation system in the future.

Fitted mesh method for singularly perturbed fourth order differential equation of convection diffusion type with integral boundary condition

<abstract><p>This article focuses on a class of fourth-order singularly perturbed convection diffusion equations (SPCDE) with integral boundary conditions (IBC). A numerical method based on a finite difference scheme using Shishkin mesh is presented. The proposed method is close to the first-order convergent. The discrete norm yields an error estimate and theoretical estimations are tested by numerical experiments.</p></abstract>

Numerical analysis of wave processes under high-speed impact on an object from CFRP

Numerical simulation of the impact of an aluminum particle on a composite medium was carried out. Carbon fiber reinforced plastic (CFRP) laminates T300/69 were used as a research object. The behavior of CFRP was analyzed at an impact velocity of 11 km/s and an aluminum particle mass of 1 g. The composite layers were located in planes oriented perpendicular to the direction of reinforcement. The Smoothed-particle hydrodynamics (SPH) method in conjunction with Ansys Autodyn was used for numerical modeling. Since large deformations and fracture of the objects were observed at such high impact velocities, which indicated a violation of the continuity of the material, that makes it incorrect to use of traditional mesh methods. The dependence of the shock wave propagation velocities in CFRP on time was obtained. The minimum thickness of the protective screen made of CFRP was estimated.

Mesh Division Method of Large Span Spatial Structure based on Free-Form Surface

All Free-form architecture has novel and unique shapes, complex and diverse changes, and has become the trend of modern architectural development with its rich shape changes and soft lines. The traditional grid layout method is not applicable to the grid division of free-form surfaces, and how to divide a smooth and beautiful grid is a hot research problem for large-span spatial structures. In response to the above problems, after investigating the current scientific research results at home and abroad, our team proposes a meshing method using the 3D software Rhino platform to solve the problems of uneven meshing of free-form surfaces and low intelligence, and to divide a smooth and beautiful mesh.

Numerical Simulation of Aerodynamic Interaction Effects in Coaxial Compound Helicopters

The so-called coaxial compound helicopter features two rigid coaxial rotors, and possesses high-speed capabilities. Nevertheless, the small separation of the coaxial rotors causes severe aerodynamic interactions, which require careful analysis. In the present work, the aerodynamic interaction between the various helicopter components is investigated by means of a numerical method considering both hover and forward flight conditions. While a sliding mesh method is used to deal with the rotating coaxial rotors, the Reynolds-Averaged Navier-Stokes (RANS) equations are solved for the flow field. The Caradonna & Tung (CT) rotor and Harrington-2 coaxial rotor are considered to validate the numerical method. The results show that the aerodynamic interaction of the two rigid coaxial rotors significantly influences hover’s induced velocity and pressure distribution. In addition, the average thrust of an isolated coaxial rotor is smaller than that of the corresponding isolated single rotor. Compared with the isolated coaxial rotor, the existence of the fuselage results in an increment in the thrust of the rotors. Furthermore, these interactions between the components of the considered coaxial compound helicopter decay with an increase in the advance ratio.

EFFECT OF MESH COUNT AND PERCENTAGE OPEN AREA ON THROUGHPUT CAPACITY IN DEVELOPING CASSAVA CAKE SCREENING MEDIUM

The screen is a medium for breaking cassava cake lump into fine particles before the heating process that turns the fine particles into garri. The objective of this research is ascertain the effect of mesh count and percentage open area on throughput capacity of cassava cake screening medium, with respect to two methods of development. To this end, six screens each of diameters 1.5, 3, 4.5, 6, 7.5 and 9mm were developed using perforated and the traditional woven wire mesh method respectively. Measurement was made of the mesh count and open area of the screens and screening was done with 2kg of cassava cake across each screening medium. Data was obtained from the mesh count and open area of the screens as well as the throughput capacities. The data obtained were analyzed using t test and regression analysis. Result showed that the mesh count for 3mm screen for the woven wire mesh was approximately 3 while the mesh count for a smaller diameter of 1.5mm for the perforated screen was 10.6. This resulted to percentage open area of 11 and 28.3 respectively. Also screening time was 4.1min for 3mm against 3.4min for 1.5mm, given throughput capacity of 24kg/hr and 35.6kh/hr, for the woven wire and perforated mesh respectively. The t-test showed that there is a statistical significant difference in the throughput capacity of the two methods. The perforated method has advantage of higher throughput capacity, lower time and energy input and hence is recommended for manual and motorized screening process.

Breakup process modeling and production of FeSiAl magnetic powders by close-coupled gas atomization

Close-coupled gas atomization is extensively used in the industrial production of alloy powders due to the advantages of high efficiency, low cost and excellent powder properties. In order to investigate the complex gas-liquid interaction during atomization, primary atomization was simulated through the VOF (Volume of Fluid) model and the dynamic adaptive mesh method, and a two-way coupling DPM (Discrete Particle Model) was used to simulate secondary atomization. The results showed that under the low melt mass flow rate of 0.0050 kg s−1, the flow separation and droplet backflow occurred at the atomization pressure of 1 MPa, while gas-liquid interfaces deformed and rotated drastically when the atomization pressure is above 3 MPa, which led to the formation of hollow powders. When the melt mass flow rate was 0.0150 kg s−1, the d50 decreased from 40.7 to 38.4 μm as the atomization pressure increased from 2 to 3 MPa. However, the chance of collision between particles increased due to the decrease in the spray cone angle, and both the standard deviation of particle size and atomization efficiency deteriorated, which indicated that 2 MPa was the optimum atomization pressure. As the mass flow rate increased from 0.0050 to 0.0150 kg s−1, the gas to melt ratio decreased, but the d50 only increased from 32.3 to 40.7 μm, indicating that the mass flow rate of 0.0150 kg s−1 did not significantly affect the particle size distribution, but also contributed to improve the production efficiency and avoided the risk of the nozzle freeze-off. The d50 of the spherical FeSiAl powders produced by the industrial tests at 2 MPa and 0.0150 kg s−1 was 44.7 ± 2.1 μm, which was basically consistent with the simulation results, indicating that the parameter optimization by the coupling model developed in this study could provide theoretical and practical guidance for the preparation of high-performance alloy powders by gas atomization.

가상경계법과 중첩격자법을 활용한 스윙 체크 밸브의 동수력학적 특성 비교

Nuclear Power Plant operators regularly check the performance of pumps and valves to verify the safety functions, and to monitor the degree of vulnerability over time through In-Service Test(IST). The swing check valve is one of the representative IST-related valve type. This valve functions to flow the fluid in only one direction, and automatically closes when the backflow occurs. In this study, the swing check valve performance test is conducted, and the result is compared with the computational fluid dynamics analysis using the immersed boundary method(ANSYS CFX R19) and overset mesh method(ANSYS Fluent R19). Overall, the inlet pressure depending on the disc angle predicted by the Fluent(overset mesh method) showed less error than the measured data compared to the CFX(immersed boundary method).The difference in the flow pattern passing through the gap between the valve entrance and top of the valve disc predicted by both methods was estimated to be the cause of the error in the simulation result compared to the measurement.

CFD Model of a Mechanical Oscillator Flowmeter

Most of the studies on mechanical oscillator flowmeters were conducted in the '80s and '90s when computational fluid dynamics (CFD) was not a viable scientific tool in flow metrology. Still, many topics related to the application of mechanical oscillator flowmeters require further investigation. In the article, a numerical model of a mechanical oscillator flowmeter is developed with the commercial software ANSYS Fluent. The model is validated against experimental data obtained at a water calibration stand. The influence of the selected turbulence model, dynamic mesh method, as well as grid and time step size is studied. The model's qualitative behavior is correct, allowing investigation into the flowmeter operation in detail. It can provide a base for the improvement of the flowmeter's performance. Relative differences in the frequency of oscillations did not exceed 4% for a DN50 flowmeter in the flow rate range (2-40) m3/h.