Reliable Mesh Research Articles

Development of personalizable female and male pedestrian SAFER human body models

Objectives Vulnerable road users are globally overrepresented as victims of road traffic injuries. Developing biofidelic male and female pedestrian human body models (HBMs) that represent diverse anthropometries is essential to enhance road safety and propose intervention strategies. Methods In this study, 50th percentile male and female pedestrians of the SAFER HBM were developed via a newly developed image registration–based mesh morphing framework. The performance of the HBMs was evaluated by means of a set of cadaver experiments, involving subjects struck laterally by a generic sedan buck. Results In simulated whole-body pedestrian collisions, the personalized HBMs effectively replicate trajectories of the head and lower body regions, as well as head kinematics, in lateral impacts. The results also demonstrate the personalization framework’s capacity to generate personalized HBMs with reliable mesh quality, ensuring robust simulations. Conclusions The presented pedestrian HBMs and personalization framework provide robust means to reconstruct and evaluate head impacts in pedestrian-to-vehicle collisions thoroughly and accurately.

Design and Optimization of Wing Internal Structure to Study the Flutter Frequency of Aircraft Wing

The field of aviation has reached a lot of milestones in the 19th and early 20th century, but the supersonic commercial flights are still a nightmare in 21st century. The major obstacle to reach this milestone is the effect of flutter, which is an aeroelastic phenomenon. It is very important to understand the effect of flutter to reduce it. In this paper effect of flutter is studied by varying the wing internal structures. A scaled down model of the AGARD 445.6 wing having 65A004 aerofoil is designed using Catia V5, for which the experimental data is available for validation. Grid independence study is carried out to obtain more reliable mesh quality. Since flutter is a transient phenomenon time-step independence study is carried out for the time steps of, 0.005s, 0.0025s and 0.00125s. Since there is no difference between the flutter frequency readings for 0.0025 seconds and 0.00125 seconds, 0.0025 seconds is chosen to reduce the computation time. The baseline case is validated with an experimental data available and an error of 0.2-5.32% is observed. Aircraft wing is mainly made out of aluminium alloys. Hence a suitable aluminium alloy is selected by comparing the flutter frequencies. To choose a suitable material, three materials each from wood, alloys and composite are considered i.e., mahogany, aluminium alloy 7075 T6 and Aluminium Metal Matrix Composite (AMC) which are widely used in the Aviation industry. AMC is considered on the basis of frequency charts whose flutter frequency is 30Hz. In this paper in order to supress the flutter we have introduced optimization of ribs and spars in the wing. Variation in the number of ribs, flange width and rib thickness are considered individually. Wing configuration with 10 ribs, flange width of +10% and 10mm rib thickness respectively are having the best flutter frequencies. The wing with above features is further optimised by keeping weight as a constraint by introducing circular and triangular cut-outs section. Flutter frequency for without cut-out, circular cut-out and triangular cut-out are 77.84 Hz, 78.27Hz and 78.43Hz respectively. Hence it is concluded that ribs with triangular cut-outs can be able to reach maximum flutter frequency.

A non‐uniform rational B‐splines enhanced finite element formulation based on the scaled boundary parameterization for the analysis of heterogeneous solids

AbstractThe contribution is concerned with a finite element formulation for the nonlinear analysis of heterogeneous solids in boundary representation. It results in an element with an arbitrary number of curved boundary edges. The curved edges can be parametrized by, for example, non‐uniform rational B‐splines (NURBS). The presented element formulation is based on the scaling concept, which is adopted from the so‐called scaled boundary finite element method (SBFEM). In contrast to SBFEM, the proposed method uses a numerical approximation for the displacement response in scaling direction. This enables the analysis of geometrically and physically nonlinear problems in solid mechanics. The interpolation at the boundary in circumferential direction is independent of interpolation in scaling direction. Thus, different basis functions can be used for each direction, for example, NURBS basis functions in circumferential and Lagrange basis functions in radial direction. It allows the construction of polygonal elements with an arbitrary number of curved sides, which are described by either whole NURBS curves or NURBS curves' segments. The advantage of the presented element formulation is the flexibility in mesh generation. For example, using Quadtree algorithms, a fast and reliable mesh generation can be achieved. Furthermore, in connection with trimming algorithms, the element formulation allows a precise representation of the geometry even with coarse meshes. Some benchmark tests are presented to evaluate the accuracy of the proposed numerical method against analytical solutions, and a comparison to standard element formulations is given as well.

Cross-Layer MAC/Routing Protocol for Reliability Improvement of the Internet of Things

The IEEE 802.15.4 standard is recognized as one of the most successful for short-range low-rate wireless communications and is used in Internet of Things (IoT) applications. To improve the performance of wireless networks, interest in protocols that rely on interaction between different layers has increased. Cross-layer design has become an issue in wireless communication systems as it can improve the capacity of wireless networks by optimizing cooperation between multiple layers that constitute network systems. Power efficiency and network scalability must be addressed to spread IoT. In multi-hop networks, many devices share wireless media and are geographically distributed; consequently, efficient medium access control (MAC) and routing protocols are required to mitigate interference and improve reliability. Cross-layer design is a novel network design approach to support flexible layer techniques in IoT. We propose a cross-layer protocol for the MAC layer and routing layer to satisfy the requirements of various networks. The proposed scheme enables scalable and reliable mesh networking using the IEEE 802.15.4 standard and provides robust connectivity and efficient path discovery procedures. It also proposes a novel address-allocation technique to improve address-allocation methods that cannot support large sensor networks. Simulation results indicate that the proposed scheme could improve reliability and reduce end-to-end delay.

CFD simulation of shockwave-boundary layer interaction induced oscillation in NACA SC2-0714 transonic airfoil

Abstract To develop an advanced way of designing transonic airfoils for industry, a reliable and user-friendly mesh generator and a robust CFD solver are necessary. Especially, the prediction of unsteady shock buffet phenomenon is always a focus for the CFD simulation of transonic airfoils. In this study, BOXERmesh (an automatic mesh generator) and NEWT (a robust CFD solver), which are developed by CFS (Cambridge Flow Solutions) in collaboration with MHI (Mitsubishi Heavy Industries), are used to perform the CFD simulation of NACA SC2-0714 transonic airfoil. CFD simulation is conducted at two different attack angles with Mach number as 0.74 and Reynold number as 1.5×107 (non-buffet: α=2°; shock buffet: α=3°). A hexahedral dominant mesh is generated by BOXERmesh with the cell number as 5.52 million. Both unsteady RANS (URANS) and LES are performed using the CFD solver NEWT. Specifically, the governing equation is discretized by central differencing scheme with 2nd order accuracy in space by applying Swanson and Turkel type artificial viscosity, and the Adams-Bashford time integration with the dual-time stepping method is applied for temporal discretization in the density-based solver. Results show CFD simulation could reproduce the time averaged chordwise distribution of pressure coefficient at the two conditions. Both URANS and LES successfully capture the unsteady shock buffet phenomenon when increasing attack angle from 2° to 3°. However, the calculated peak oscillation location and the shock buffet frequency are different between URANS and LES. Applying the same mesh resolution, URANS performances better than LES, with the deviation of the shock buffet frequency less than 6% (Exp.: 69 Hz; URANS: 73 Hz). The reason is considered as the wall-normal mesh refinement near the airfoil surface (y+∼66) being not enough for LES to accurately resolve the turbulence scale and capture the boundary layer separation behavior. On the other hand, URANS is thought to be enough to reproduce the periodic moving of the onset of boundary separation and to predict the main characteristics of the shock buffet phenomenon.

A NURBS enhanced polygonal element formulation based on the scaled boundary method for the analysis of solids in boundary representation

AbstractThe contribution is concerned with a numerical element formulation for the nonlinear analysis of solid in boundary representation. Its results in a polygonal element with an arbitrary number of sides. Straight edges are possible as well as curved edges, which are described by e.g. Non‐Uniform Rational B‐Splines (NURBS). The element formulation is based on the so‐called scaled boundary finite element method (SBFEM). The basic idea is to scale the domain's boundary with respect to a scaling center in order to describe the interior domain. In contrast to SBFEM, the proposed method makes use of a numerical aproximation for the displacement response in scaling direction. This enables the analysis of geometrically and physically nonlinear problems in solid mechanics. The interpolation at the boundary in circumferential direction is independent of the interpolation in scaling direction. So, different basis functions can be used for each direction, e.g. NURBS basis functions in circumferential and Lagrange basis functions in radial direction. The advantage of the presented element formulation is the flexibility in mesh generation. The avoidance of so‐called hanging node problems as arbitrary element geometries are possible. For example, using Quadtree algorithms, a fast and reliable mesh generation can be achieved. Furthermore, in connection with trimming algorithms, the element formulation allows a precise representation of the geometry even with coarse meshes. Some benchmark tests are presented to evaluate the accuracy of the proposed numerical method against analytical solutions.

FAN: Fast and Active Network Formation in IEEE 802.15.4 TSCH Networks

The IEEE 802.15.4 TSCH standard is designed to improve the reliability, timeliness, and energy efficiency of short-range wireless communications in industrial applications. TSCH relies upon a network formation process to efficiently create and maintain a synchronized reliable mesh network. The standard adopts a purely passive scan mechanism enabling joining nodes to listen to periodic Enhanced Beacons (EBs) in order to locate a TSCH network and associate to it. Nevertheless, the standard defines neither the advertisement strategy nor the rate at which the EBs should be sent. Consequently, long (re)association times might be observed, which postpones the proper functioning of the network and might have devastating consequences on the industrial application. In this paper, we propose a Fast and Active Network formation scheme (FAN) that leans on active scan procedures and Trickled beacon advertising strategies to accelerate the (re)association process. To do so, FAN equips joiners with a collision avoidance mechanism and allows them to initiate EB requests, on free channels, to trigger EBs. FAN is implemented in Contiki and evaluated through extensive realistic simulations and public testbed experiments. Obtained results assert the robustness of FAN compared to state-of-the-art solutions in terms of association times and overhead.

An adaptive multigrid solver for DPG methods with applications in linear acoustics and electromagnetics

We propose an adaptive multigrid preconditioning technology for solving linear systems arising from Discontinuous Petrov–Galerkin (DPG) discretizations. Unlike standard multigrid techniques, this preconditioner involves only trace spaces defined on the mesh skeleton, and it is suitable for adaptive hp-meshes. The key point of the construction is the integration of the iterative solver with a fully automatic and reliable mesh refinement process provided by the DPG technology. The efficacy of the solution technique is showcased with numerous examples of linear acoustics and electromagnetic simulations, including simulations in the high-frequency regime, problems which otherwise would be intractable. Finally, we analyze the one-level preconditioner (smoother) for uniform meshes and we demonstrate that theoretical estimates of the condition number of the preconditioned linear system can be derived based on well established theory for self-adjoint positive definite operators.

A polyhedral element formulation based on the scaled boundary method for the analysis of nonlinear problems in solid mechanics

AbstractIn this contribution a numerical element formulation for the nonlinear analysis of solids is proposed. The element is defined by a polyhedron with an arbitrary number of polygonal faces. It is based on the scaling concept, which is adopted from the so‐called scaled boundary finite element method (SBFEM). The SBFEM is a semi‐analytical formulation to analyze problems in linear elasticity. Within this method the fundamental concept is to scale the domain's boundary with respect to a scaling center in order to describe the interior domain. The present element formulation employs the scaling concept twice and in contrast to SBFEM, uses a numerical approximation for the displacement response in both scaling directions. This makes it suitable for the analysis of geometrically and physically nonlinear problems. The advantages of the proposed element formulation is its high flexibility in mesh generation. It avoids the hanging node problems as arbitrary element geometries are possible. For example, using Octree algorithms, a fast and reliable mesh generation can be achieved. In case of curved boundaries the element formulation allows a precise representation of the geometry even with coarse meshes. Some numerical examples are presented to evaluate the accuracy of the proposed numerical method against analytical solutions, and a comparison to standard element formulations is given as well.

A simple fully nonlinear Kirchhoff-Love shell finite element

Abstract The current paper implementates a simple fully non-linear Kirchhoff-lovel shell penalty based finite element. The 6 nodes and 21 DoF triangular element developed in this work has a quadratic displacement field associated to it and the C1 continuity required by Kirchhoff-Love Hyphotesis is approximated by an internal penalty. The biggest novelty in this article is the simultaneous use of penalty and a Rodrigues incremental Rotation parameter (scalar DOF) between neighboring elements further explained in the text. The nonlinear finite element model developed in this article is compared to analytical results, commercial finite element code and another FEM model developed in bibliography. Simulations have demonstrated consistency when comparing results to other models and it is deemed that reliable mesh generation together with a powerfull triangular finite element is a good option for trustworthy thin shell simulations.

The Effectiveness of a Wireless Sensor Network System for Landslide Monitoring

In this paper, the application of a WSN (Wireless Sensor Network) for landslide monitoring was studied. The WSN system consists of a sensor node for collecting and transmitting data using the IEEE 802.14e standard and a gateway for processing and transmitting the data to the final server. The topology of the sensor network adopts a highly flexible and reliable mesh type, and a test bed was built in three locations in Seoul. An instrumentation is done for each sensor node composing of two soil moisture sensors, one tensiometer, and one inclinometer and one rain gauge per test bed. For the estimation of optimal network topology among the sensor nodes, a susceptibility assessment of landslides, the density of trees and a viewshed analysis of the terrain were analyzed. As a result, the network connection worked quite well, and the response of the soil from rainfall was similar to the soil water characteristic curve obtained from laboratory tests. Therefore, a WSN system can be applied to landslide monitoring by collecting reliable data. In addition, the appropriate design method of WSN system for landslide monitoring was proposed.

Cyanoacrylate for Safer Mesh Fixation During Laparoscopic Repair of Morgagni Hernia

The surgical repair of all Morgagni hernias is recommended to avoid the risk of strangulation of hernia contents. Mesh augmentation repair can reduce the risk of recurrence, but severe injuries have been reported when tacks are used for mesh fixation to the diaphragm. Cyanoacrylate can provide reliable mesh fixation, and in addition, its application is easy and quick by either the transthoracic or laparoscopic approach. This report describes the main steps of laparoscopic mesh augmentation repair of a Morgagni hernia with a focus on atraumatic mesh fixation with cyanoacrylate, which should prevent the potential complications associated with the use of tacks or sutures.

Laparoscopic totally extra-peritoneal groin hernia repair with self-gripping polyester mesh: a series of 780 repairs.

Laparoscopic groin hernia repair is an increasingly common procedure with benefits of reduced post-operative pain and infection. Post-operative chronic pain remains an ongoing concern in about 10% of patients. Parietex ProGrip™, a polyester self-gripping mesh, has a theoretical benefit of avoiding tacks for mesh-fixation. This case series reflects our long-term experience of this technique. We conducted a retrospective case series from November 2011 to December 2017. Patients were identified through an operative Medicare Benefits Schedule item number search. Clinical documentation was reviewed with length of stay, mesh infection, chronic pain, recurrence and re-operation as primary data points. A total of 514 patients underwent 780 laparoscopic inguinal hernia repairs with self-gripping polyester mesh during this period. There were 53 female (10.3%) and 461 male patients (89.7%). Unilateral hernia repair was performed in 248 patients (48.2%) and bilateral repair in 266 patients (51.8%). Almost all repairs (779, 99.8%) were primary hernias. There were no mesh infections. Four recurrences were noted (0.51%) and three of these subsequently underwent open redo-hernia repairs (0.38%). Post-operative follow-up was up to 4.4 years. Our series of laparoscopic groin hernia repair with self-gripping mesh demonstrate this is a safe and reliable mesh and effective technique with low recurrence rates.

HYBRID RSA based highly efficient, reliable and strong personal Full Mesh Networked messaging scheme

Efficient balancing of privacy and strong authentication in end-to-end (E2E) security constitutes a challenging task in the field of personal messaging. Since RSA is a ubiquitous approach, we here propose a hybrid RSA-based, highly efficient, reliable and strong personal full mesh networked messaging scheme. M-prime RSA and CRT-RSA with shared RSA makes our hybrid RSA decryption much more secure and efficient and protects our users with complete privacy. However, computational modular exponentiation complexity and partial key exposure vulnerability of RSA present two major obstacles. Low modular complexity and asymptotic very slow speed of decryption of RSA, with the ease and speed problem in encryption of RSA are also problems to be solved. Our hybrid RSA cipher resolves all of the above issues and provides protection against exploitation of multiplicative property and homomorphic property of RSA. Our full mesh networking scheme also ensures E2E encryption for all peers. So, our three-way authenticated hybrid RSA messaging scheme achieves a perfect balance of efficiency, security, authentication, reliability and privacy. Consequently, our scheme offers a smarter choice for private messaging in existing, as well as future, internet architectures.

Francis-99: Transient CFD simulation of load changes and turbine shutdown in a model sized high-head Francis turbine

With increasing requirements for hydropower plant operation due to intermittent renewable energy sources like wind and solar, numerical simulations of transient operations in hydraulic turbo machines become more important. As a continuation of the work performed for the first workshop which covered three steady operating conditions, in the present paper load changes and a shutdown procedure are investigated. The findings of previous studies are used to create a 360° model and compare measurements with simulation results for the operating points part load, high load and best efficiency. A mesh motion procedure is introduced, allowing to represent moving guide vanes for load changes from best efficiency to part load and high load. Additionally an automated re-mesh procedure is added for turbine shutdown to ensure reliable mesh quality during guide vane closing. All three transient operations are compared to PIV velocity measurements in the draft tube and pressure signals in the vaneless space. Simulation results of axial velocity distributions for all three steady operation points, during both load changes and for the shutdown correlated well with the measurement. An offset at vaneless space pressure is found to be a result of guide vane corrections for the simulation to ensure similar velocity fields. Short-time Fourier transformation indicating increasing amplitudes and frequencies at speed-no load conditions. Further studies will discuss the already measured start-up procedure and investigate the necessity to consider the hydraulic system dynamics upstream of the turbine by means of a 1D3D coupling between the 3D flow field and a 1D system model.

HexEx

State-of-the-art hex meshing algorithms consist of three steps: Frame-field design, parametrization generation, and mesh extraction. However, while the first two steps are usually discussed in detail, the last step is often not well studied. In this paper, we fully concentrate on reliable mesh extraction. Parametrization methods employ computationally expensive countermeasures to avoid mapping input tetrahedra to degenerate or flipped tetrahedra in the parameter domain because such a parametrization does not define a proper hexahedral mesh. Nevertheless, there is no known technique that can guarantee the complete absence of such artifacts. We tackle this problem from the other side by developing a mesh extraction algorithm which is extremely robust against typical imperfections in the parametrization. First, a sanitization process cleans up numerical inconsistencies of the parameter values caused by limited precision solvers and floating-point number representation. On the sanitized parametrization, we extract vertices and so-called darts based on intersections of the integer grid with the parametric image of the tetrahedral mesh. The darts are reliably interconnected by tracing within the parametrization and thus define the topology of the hexahedral mesh. In a postprocessing step, we let certain pairs of darts cancel each other, counteracting the effect of flipped regions of the parametrization. With this strategy, our algorithm is able to robustly extract hexahedral meshes from imperfect parametrizations which previously would have been considered defective. The algorithm will be published as an open source library [Lyon et al. 2016].

Reliable Communication Networks for Smart Grid Transmission Systems

In this paper, we discuss the communications reliability requirements posed by the smart power grid with a focus on communications in support of wide area situational awareness. Implementation of wide area situational awareness relies on both transmission substation networks and wide area optical networks. We study the reliability of a sample communications network of the California Power Grid and find that its reliability falls short of proposed requirements. To overcome this issue, we consider the problem of designing the substation network and the wide area network to meet the reliability requirements while minimizing the network cost. For the wide area network design problem, we propose two alternate design approaches, namely: (1) following the power lines and (2) a mesh based design interconnecting the nodes. For the first approach we develop two greedy iterative heuristics and a heuristic integer linear programming (H-ILP) model using minimum cut-sets for network reliability optimization. The greedy iterative algorithms outperform the H-ILP approach in terms of cost, but require a larger amount of computing resources. Both proposed models are in fact complementary and thus provide a framework to optimize the reliability of smart grid communications networks restricted to following the power lines. In the second approach a greenfield mesh network method is proposed based on starting with a minimum spanning tree which is then augmented through a greedy heuristic into a mesh. Comparative numerical results show that the reliable mesh design has advantages in terms of the number of links and total link distance needed.

Innovations in irregular meshing to improve the performance of 2D finite volume flood simulation

There are now many successful applications of 2D finite difference flood simulations on rectangular grids. However, finite volume algorithms are now starting to take over as the preferred choice for simulating flood inundation. The use of finite volume algorithms allows the simulation to be based on irregular meshes. Yet many users are not convinced of the benefits of irregular meshing. This is partly because meshing adds a rather unwelcome extra process to the modelling. But it is more likely because the process of generating irregular meshes has been problematic and time consuming. In the rush to develop excellent finite volume flow engines, meshing has been rather left behind. Yet the quality of the flow modelling depends on the quality of the meshing. The authors have been working on innovative mesh generation techniques. The aim has been to come up with a faster, more reliable mesh generation process. But also to improve the resulting mesh in order to speed up the hydraulic simulation and to generate better quality flood inundation results. This paper discusses and illustrates these advances in meshing. Results are presented to show how well the meshing techniques deal with problematic boundaries. The resulting meshes are applied to test cases to show the impact of either grids or different qualities of mesh on flood inundation results for a variety of circumstances.

An Improved Refinement Algorithm of Triangular Mesh Subdivision Based on Minimum Weight Theory

The triangular mesh subdivision to any planar field has been widely adopted in such applicable fields as configurable engineer, computer graphics, and scientific computation visualization and so on because of its well approach to the borderline. Thus, developing and researching on one certain effective and reliable triangular mesh subdivision algorithm has important theoretical and practical meanings. This paper firstly describes a refined algorithm about triangular mesh based on geometrical multi-grid method, and discusses its advantages and disadvantages. Secondly a new refined algorithm about triangular mesh subdivision is put forward by applying Fermat point and its properties as well as the minimum weight theory of triangular meshed subdivision. Finally, this paper proves that this refined algorithm can actually improve the efficiency of triangular mesh subdivision and generate grids amount and quality.

OpenWSN: a standards‐based low‐power wireless development environment

ABSTRACTThe OpenWSN project is an open‐source implementation of a fully standards‐based protocol stack for capillary networks, rooted in the new IEEE802.15.4e Time Synchronized Channel Hopping standard. IEEE802.15.4e, coupled with Internet of Things standards, such as 6LoWPAN, RPL and CoAP, enables ultra‐low‐power and highly reliable mesh networks, which are fully integrated into the Internet. The resulting protocol stack will be cornerstone to the upcoming machine‐to‐machine revolution.This article gives an overview of the protocol stack, as well as key integration details and the platforms and tools developed around it. The pure‐C OpenWSN stack was ported to four off‐the‐shelf platforms representative of hardware currently used, from older 16‐bit microcontroller to state‐of‐the‐art 32‐bit Cortex‐M architectures. The tools developed around the low‐power mesh networks include visualisation and debugging software, a simulator to mimic OpenWSN networks on a PC, and the environment needed to connect those networks to the Internet.Experimental results presented in this article include a network where motes operate at an average radio duty cycle well below 0.1% and an average current draw of 68 μA on off‐the‐shelf hardware. These ultra‐low‐power requirements enable a range of applications, with motes perpetually powered by micro‐scavenging devices. OpenWSN is, to the best of our knowledge, the first open‐source implementation of the IEEE802.15.4e standard. Copyright © 2012 John Wiley & Sons, Ltd.