Redesign of a conformal boundary recovery algorithm for 3D Delaunay triangulation

Boundary recovery is one of the main obstacles in applying the Delaunay criterion to mesh generation. A stan- dard resolution is to add Steiner points directly at the intersection positions between missing boundaries and triangulations. We redesign the algorithm with the aid of some new concepts, data structures and operations, which make its implementation routine. Furthermore, all possible intersection cases and their solutions are presented, some of which are seldom discussed in the litera- ture. Finally, numerical results are presented to evaluate the performance of the new algorithm.

A flexible architecture for job management in a grid environment

Job management is a key issue in computational grids, and normally involves job definition, scheduling, executing and monitoring. However, job management in the existing grid middleware needs to be improved in terms of efficiency and flexibility. This paper addresses a flexible architecture for job management with detailed design and implementation. Frameworks for job scheduling and monitoring, as two important aspects, are also presented. The proposed job management has the advantages of reusability of job definition, flexible and automatic file operation, visual steering of file transfer and job execution, and adaptive application job scheduler. A job management wizard is designed to implement each step. Therefore, what the grid user needs to do is only to define the job by constructing necessary information at runtime. In addition, the job space is adopted to ensure the security of the job management. Experimental results showed that this approach is user-friendly and system efficient.

Application-adaptive resource scheduling in a computational grid

Selecting appropriate resources for running a job efficiently is one of the common objectives in a computational grid. Resource scheduling should consider the specific characteristics of the application, and decide the metrics to be used accordingly. This paper presents a distributed resource scheduling framework mainly consisting of a job scheduler and a local scheduler. In order to meet the requirements of different applications, we adopt HGSA, a Heuristic-based Greedy Scheduling Algorithm, to schedule jobs in the grid, where the heuristic knowledge is the metric weights of the computing resources and the metric workload impact factors. The metric weight is used to control the effect of the metric on the application. For different applications, only metric weights and the metric workload impact factors need to be changed, while the scheduling algorithm remains the same. Experimental results are presented to demonstrate the adaptability of the HGSA.

A meshfree method and its applications to elasto-plastic problems

Standard finite element approaches are still ineffective in handling extreme material deformation, such as cases of large deformations and moving discontinuities due to severe mesh distortion. Among meshfree methods developed to overcome the ineffectiveness, Reproducing Kernel Particle Method (RKPM) has demonstrated its great suitability for structural analysis.This paper presents applications of RKPM in elasto-plastic problems after a review of meshfree methods and an introduction to RKPM. A slope stability problem in geotechnical engineering is analyzed as an illustrative case. The corresponding numerical simulations are carried out on an SGI Onyx3900 supercomputer. Comparison of the RKPM and the FEM under identical conditions showed that the RKPM is more suitable for problems where there exists extremely large strain such as in the case of slope sliding.

SimWall:a practical user-friendly stereo tiled display wall system

SimWall is a user-friendly, stereo tiled display wall system composed of 18 commodity projectors operated by a Linux graphics cluster. Collaborating together, these projectors work as a single logical display capable of giving a high-resolution show, large-scale, and passive stereo scene. In order to avoid tedious system setup and maintenance, software-based automatic geometry and photometric calibration are used. The software calibration is integrated to the system seamlessly by an on-card transform method and is transparent to users. To end-users, SimWall works just as a common PC, but provides super computing, rendering and displaying ability. In addition, SimWall has stereoscopic function that gives users a semi-immersive experience in polarized passive way. This paper presents system architecture, implementation, and other technical issues such as hardware constraints, projectors alignment, geometry and photometric calibration, implementation of passive stereo, and development of overall soft- ware environment.

Fast advancing layer method for viscous mesh generation

An efficient Advancing Layer Method(ALM)is presented to create semi-structured prisms on viscous walls,in which a procedure that checks possible front intersections is essential to its efficiency.This paper develops various novel schemes to improve the algorithm’s efficiency precisely while not sacrificing its robustness and the resulting mesh quality.First,it employs a set of new techniques,and data structures are developed to improve the efficiency of the frontcheck procedure.Then,within each octant,a new filter is developed to reduce the intersection computations in the searching process.In addition,data structures are well designed to store the contiguously accessed data in each computing-intensive loop in a contiguous space for a potentially better cache hit ratio.We built a geometry model library formed by examples of industrial complexity to demonstrate the practicability of the algorithm.All the efforts mentioned above enable us to reduce the percentage of computing time taken by intersection check to an acceptable level(approximately 26%),which make it no longer be the most time-consuming part.

Hybrid grid generation for viscous flow simulations in complex geometries

In this paper,we present a hybrid grid generation approach for viscous flow simulations by marching a surface triangulation on viscous walls along certain directions.Focuses are on the computing strategies used to determine the marching directions and distances since these strategies determine the quality of the resulting elements and the reliability of the meshing procedure to a large extent.With respect to marching directions,three strategies featured with different levels of efficiencies and robustness performance are combined to compute the initial normals at front nodes to balance the trade-off between efficiency and robustness.A novel weighted strategy is used in the normal smoothing scheme,which evidently reduces the possibility of early stop of front generation at complex corners.With respect to marching distances,the distance settings at concave and/or convex corners are locally adjusted to smooth the front shape at first;a further adjustment is then conducted for front nodes in the neighbourhood of gaps between opposite viscous boundaries.These efforts,plus other special treatments such as multi-normal generation and fast detection of local/global intersection,as a whole enable the setup of a hybrid mesher that could generate qualitied viscous grids for geometries with industry-level complexities.

A 4 W K-band GaAs MMIC power amplifier with 22 dB gain

A 4 W K-band AIGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor （PHEMT） monolithic microwave integrated circuit （MMIC） high power amplifier （PA） is reported. This amplifier is designed to fully match for a 50 f2 input and output impedance based on the 0.15μm power PHEMT process. Under the condition of 5.6 V and 2.6 A DC bias, the amplifier has achieved a 22 dB small-signal gain, better than a 13 dB input return loss, and 36 dBm saturation power with 25% PAE from 19 to 22 GHz.

An incentive model for voting based on information-hiding in P2P networks

We propose an incentive model based on information-hiding to encourage peers to vote for resources in peer-to-peer (P2P) networks. The following are key motives for our model: (1) Some trust and reputation systems have been deployed in modern P2P systems, but a lot of blank rating resources exist in these P2P systems; (2) E-commerce consumer-to-consumer (C2C) websites that adopt simple rating strategies are receiving accusations that false and useless ratings are flooded. We establish an information-hiding based RRR/RIR (resource reputation rating/reputation incentive rating) voting model, which awards or punishes voters according to their behaviors. The RRR generating algorithm and the RIR generating algorithm are presented in detail, and the information-hiding mechanism is given. Experimental results showed that the incentive RRR/RIR model can effectively encourage valid voting and prevent malicious or arbitrary voting in the P2P reputation system.

An ultralight geometry processing library for parallel mesh refinement

In applications such as parallel mesh refinement,it remains a challenging issue to ensure the refined surface respects the original Computer-Aided Design(CAD)model accurately.In this paper,an ultralight geometry processing library is developed to resolve this issue effectively and efficiently.Here,we say the kernel is ultralight because it has a very small set of data-structures and algorithms by comparison with industrial-level geometry kernels.Within the library,a simplified surface boundary representation(B-rep)and a radial edge structure are developed respectively to depict the geometry model and the surface mesh,plus hash tables that record the connections between the geometry model and the surface mesh.Based on these data structures,a set of efficient algorithms are developed,which initializes the connection tables,projects a point back to the original geometry,etc.With these data-structure and algorithmic infrastructures set up,the callings of eight well-designed Application Programming Interfaces(APIs)are powerful enough to enable the parallel mesh refinement algorithm outputs a mesh respecting the input CAD model accurately.Numerical experiments will be finally presented to evaluate the performance of the overall parallel mesh refinement algorithm and the algorithms in relation with the developed library.

Enabling Technologies in the Problem Solving Environment HEDP

Enabling technologies are those technologies preparing input data,analyzing output data and facilitating the whole processes for numerical simulations.This paper outlines current enabling technologies for large-scale multidisciplinary simulations used in the High End Digital Prototyping(HEDP)system,a problem solving environment equipped with capability of mesh generation and large-scale visualization.A problem solving environment is a computer system that provides all the computational facilities necessary to solve a target class of problems.Mesh generation continues to be the pacing technology for a practical numerical analysis,which is essential to yielding an accurate and efficient solution.Large-scale visualization maps the massive data to some kinds of scenes interactively,which can be realized through a tiled display wall system with distributed visualization capability.HEDP is designed for large-scale andmultidisciplinary simulations,and there are four categories of modules involved,namely pre-processing module,computing module,post-processing module,and platform control module.All these modules are coupled through a software bus,which makes the modules integrated seamlessly.Detailed design principles and applications of the HEDP environment are addressed in this paper.

An efficient projection defocus algorithm based on multi-scale convolution kernel templates

The focal problems of projection include out-of-focus projection images from the projector caused by incomplete mechanical focus and screen-door effects produced by projection pixilation. To eliminate these defects and enhance the imaging quality and clarity of projectors, a novel adaptive projection defocus algorithm is proposed based on multi-scale convolution kernel templates. This algorithm applies the improved Sobel-Tenengrad focus evaluation function to calculate the sharpness degree of intensity equalization and then constructs multi-scale defocus convolution kernels to remap and render the defocus projection image. The resulting projection defocus corrected images can eliminate out-of-focus effects and improve the sharpness of uncorrected images. Experiments show that the algorithm works quickly and robustly and that it not only effectively eliminates visual artifacts and can run on a self-designed smart projection system in real time but also significantly improves the resolution and clarity of the observer's visual perception.

Effects of temperature on drag reduction in a subsonic turbulent boundary layer via micro-blowing array

A comparative study of two micro-blowing temperature cases has been performed to investigate the characteristics of drag reduction in a subsonic flat-plate flow(where the freestream Mach number is 0.7) by means of Direct Numerical Simulation(DNS). With minute amount of blowing gas injected from a 32 × 32 array of micro-holes arranged in a staggered pattern, the porosity of micro-holes is 23% and the blowing coefficient is 0.125%. The simulation results show that a drag reduction is achieved by micro-blowing, and a lower wall-friction drag can be obtained at a higher blowing temperature. The role of micro-blowing is to redistribute the total kinetic energy in the boundary layer, and the proportion of stream-wise kinetic energy decreases, resulting in the thickened boundary layer. Increasing micro-blowing temperature can accelerate this process and obtain an enhanced drag reduction. Moreover, an explanation of drag reduction by microblowing related to the micro-jet vortex clusters is proposed that these micro-jet vortex clusters firmly attached to the wall constitute a stable barrier, which is to prevent the direct contact between the stream-wise vortex and the wall. By Dynamic Mode Decomposition(DMD) from temporal/spatial aspects, it is revealed that small structures in the near-wall region play vital role in the change of turbulent scales. The high-frequency patterns are clearly strengthened, and the lowfrequency patterns just maintain but are lifted up.

Numerical analysis of turbulence characteristics in a flat-plate flow with riblets control

A comparative study about riblets-controlled turbulent boundary layers has been performed to investigate the turbulence characteristics associated with drag reduction in a compressive flat-plate flow(where the free-stream Mach number is 0.7)by means of direct numerical simulations(DNSs).With a setting of the triangular riblets(s+≈30.82,h+≈15.41)settled on the Reτ≈500 turbulent boundary layer,an effective global drag reduction was achieved.By comparing velocity and its fluctuation distribution,vorticity fluctuation and streaks structures between the smooth and riblets flat-plate cases,two roles of lifting and rectification in terms of riblets drag control are revealed that the micro-scale riblets can lift up logarithmic-law region of the boundary layer,which leads to a smaller wall friction velocity and thus a drag reduction.The streamwise vortices and its fluctuation structures are shifted upward,thus the interactions between them and the wall surface are weakened,which causes the suppressed intensity of Reynolds normal stresses,streamwise vorticity and turbulent kinetic energy production inside the riblets.Moreover,the streaks associated with streamwise velocity or 3D vortices are ruled from the distorted to long and straight structures as they pass through the riblets,indicating an ability of riblets to turn turbulence into a more ordered state.