The technology of large-scale CFD simulations

The paper presents the technology of large-scale CFD simulations on supercomputers using finite-volume or finite-difference methods. The study covers various aspects of the numerical experiment and its implementation. The considered problems include the optimal choice of computational domain, minimization of disk space usage, choice of an optimum configuration for a multilevel parallel model, and a method for loading supercomputer nodes. Special attention is paid to the performance problems of multiple access systems taking into account the waiting time in the system queues, the problem of computing reliability, prevention of emergency shutdowns leading to timeconsuming repeated waiting, automatic correction, and optimization of the calculation parameters, etc. Methods are presented for improving the quality of the averaging of the flow fields and the spectral characteristics.     

A mesh adaptivity procedure for CFD and fluid-structure interactions

We present a procedure to adapt and repair meshes in the general solution of Navier–Stokes incompressible and compressible fluid flows, including structural interactions. For fluid-structure interactions, FSI, the fluid is described by an arbitrary-Lagrangian–Eulerian formulation fully coupled to general solids and structures described by Lagrangian formulations. The solids and structures can undergo highly nonlinear response due to large deformations, nonlinear material behavior, contact and temperature. We focus on the need to adapt the fluid mesh in pure CFD solutions when high gradients are present or boundary layer effects are important, and FSI solutions when large structural deformations take place. The procedure is a practical scheme to solve complex problems. We illustrate the proposed scheme in various example solutions.     

Nonlinear modelling and control of the flow over aerofoils using CFD simulations

A simulation based approach for nonlinear dynamical modelling and feedback control of the drag to lift ratio for aerofoils is investigated through case studies involving NACA 23012, ag13 and b737a aerofoils. The flow around the aerofoils is studied via numerical solutions of the 2D Navier–Stokes (NS) equations. A standard computational fluid dynamics (CFD) solver is extended to be able to measure desired feedback values and to apply a control input to the flow field. The proposed modelling and control approach is based on first determining the measurement points and injection points on the aerofoil for the control input. Then, to estimate the dynamical model, some input–output data are collected by injecting a chirp input flow to the field and saving the measurement data. Next a Hammerstein–Wiener (HW) type nonlinear dynamical model of the flow field is estimated using system identification. For control design, the nonlinear part of the model is eliminated by means of inverse functions, followed by the application of automated tuning methods to the linear part to obtain the closed-loop system. The results show that the designed feedback control system can reduce the drag to lift ratio considerably as compared to the unactuated case.     

Parallel CFD simulations of an original and redesigned hydraulic turbine draft tube

The design of hydraulic turbine draft tubes has traditionally been based on simplified analytic methods, model and full-scale experiments. In the recent years the use of numerical methods such as computational fluid dynamics (CFD) has increased in the design process, due to the rapid escalation in computer performance. Today with parallel computer architectures, new aspects of flow can be considered. However, several problems have still to be solved before CFD can routinely be applied in product development. This paper aims to investigate the parallel performance of commercial CFD software on homogeneous computer networks, as common solutions encountered in the industry today. In addition, the efficiency improvements obtained in earlier experiments by modifying the shape of the draft tube will be considered, to deduce if the improvements can be captured with aid of CFD. Results from both the steady and the unsteady CFD simulations show that almost full scalability is obtained with the commercial CFD software CFX-5.7.1. Furthermore, no noticeable improvement in the pressure recovery factor or the flow field is noticed in the CFD simulations as compared to experiments. The discrepancy may be to the applied inlet boundary conditions and/or the turbulence model.     

Long-range interactions and parallel scalability in molecular simulations

Typical biomolecular systems such as cellular membranes, DNA, and protein complexes are highly charged. Thus, efficient and accurate treatment of electrostatic interactions is of great importance in computational modeling of such systems. We have employed the GROMACS simulation package to perform extensive benchmarking of different commonly used electrostatic schemes on a range of computer architectures (Pentium-4, IBM Power 4, and Apple/IBM G5) for single processor and parallel performance up to 8 nodes—we have also tested the scalability on four different networks, namely Infiniband, GigaBit Ethernet, Fast Ethernet, and nearly uniform memory architecture, i.e. communication between CPUs is possible by directly reading from or writing to other CPUs' local memory. It turns out that the particle-mesh Ewald method (PME) performs surprisingly well and offers competitive performance unless parallel runs on PC hardware with older network infrastructure are needed. Lipid bilayers of sizes 128, 512 and 2048 lipid molecules were used as the test systems representing typical cases encountered in biomolecular simulations. Our results enable an accurate prediction of computational speed on most current computing systems, both for serial and parallel runs. These results should be helpful in, for example, choosing the most suitable configuration for a small departmental computer cluster.     

气象条件对苯泄漏扩散影响的CFD模拟

化工企业即使在不发生事故的情况下,也会通过无组织排放等方式泄露少量的有害物质.它们会在气象环境等条件下扩散,影响周边地区,因此受到人们的关注.本文针对某大型化工企苯污染物低度泄露的情况,采用CFD模拟方法考察了当地气象条件对低浓度苯污染物扩散规律的影响.模拟过程中以Fluent软件为工具,采用标准K-ε模型建模,用风速廓线曲线确定风速,大气稳定度分别取的是非常稳定、中度稳定和极度不稳定等级3种情况,湿度分别取92%、75%、64%.模拟结果表明,随着风速的增加,远处的苯浓度值逐渐大于近处的苯浓度值;随着大气稳定度等级的增加,苯的浓度值增大:随着大气相对湿度的增加,苯的浓度值呈现出先增加后减少的趋势.     

Modeling of redox electrochemical MHD and three-dimensional CFD simulations of transient phenomena in microfluidic cells

Computational fluid dynamics simulations of redox electrochemical magneto-hydrodynamics (MHD) covering a large parameter space have been done to establish the effects of redox species concentration, electrode area, and magnetic field strength and orientation on the limiting current. Simulations of milli-electrode and microelectrode systems show similarities and differences between the two. Potential sweep and potential step simulations using time-accurate solution algorithms enabled accurate capture of transient phenomena which is crucial to the development of lab-on-a-chip flow control applications. Power-law correlations reported in previous experimental investigations of milli-electrodes are found to be less accurate for microelectrodes and nano-electrodes suggesting possible effects of multidimensional diffusion. Further, the orientation of the magnetic field in relation to the electrode surface has a strong influence on the flow field. Interesting and complex flow features are observed in the post-processed still images and animations. This work advances redox MHD simulations by incorporating important aspects in the models that were not considered in previous models. Our simulations based on these new models provide new insight into redox electrochemical MHD.     

Visual scan patterns reflect to human-computer interactions on processing different types of messages in the flight deck

The flight deck of commercial aircraft is sophisticated and searching for the necessary information at the right time is sometimes challenging. This research investigates pilot's visual parameters while interacted with two different designs of crew alerting system by eye tracking technology. There are 24 aviation professionals that participated in this experiment including commercial pilots, private pilots and avionic engineers. Compared with traditional design, the new integrated design applied proximity compatibility principles to assist pilots in searching necessary information to deal with urgent situations. The results demonstrated that the integrated design is superior to traditional design in providing accurate instructions as determined by visual behaviors. However, the integrated design increases pilot's situation awareness by redirecting attention from current task to the most critical task with the cost of a longer total fixation duration time. Pilot's visual parameters demonstrated significant differences while interacting with PFD mainly numeric, ND mostly by symbols and EICAS with presented text messages. Therefore, flight deck design has to adopt a holistic approach as pilot's visual attentions is shifting among all types of different displays to gain situation awareness rather than focus on only one display. The design of integrated EICAS can provide detailed instructions to deal with urgent situations which induced higher cognitive loads as pilot's pupil dilation is significant bigger than interacted with traditional design. By eye tracking technology, it is applicable to design human-centred flight decks to improve safety and human performance in aviation.     

Molecular mechanics and molecular orbital simulations on specific interactions between peroxisome proliferator-activated receptor PPARalpha and plasticizer

Peroxisome proliferator-activated receptor α (PPARα) has various physiological functions such as lipid and glucose metabolism, inflammation and fibrosis in living organisms. Many types of ligand molecules such as phthalate and adipate esters control these physiological functions. In the present study, to elucidate the dependence of PPARα properties on ligand binding, we investigated stable structures and electronic properties for the complexes of PPARα and phthalate as well as adipate esters, which are used as a plasticizer, by molecular simulations based on molecular mechanics and molecular orbital methods. Furthermore, to elucidate the influence of these esters in vivo, we injected them into male mice and observed the change in the expression of PPARα-related enzymes. The comparison between the calculated and observed results indicates that the change in the expression has a correlation with the size of energy gaps between highest occupied and lowest unoccupied molecular orbitals of the complexes with mouse PPARα and esters.     

Binding and discerning interactions of PTP1B allosteric inhibitors: Novel insights from molecular dynamics simulations

The α7 helix is either disordered or missing in the three co-crystal structures of allosteric inhibitors with protein tyrosine phosphatase 1B (PTP1B). It was modeled in each complex using the open form of PTP1B structure and studied using molecular dynamics (MD) simulations for 25 ns. B-factor analysis of the residues sheds light on its disordered nature in the co-crystal structures. Further, the ability of inhibitors to act as allosteric inhibitor was studied and established using novel hydrogen bond criteria. The MD simulations were utilized to determine the relative importance of electrostatic and hydrophobic component in to the binding of inhibitors. It was revealed that the hydrophobic interactions predominantly drive the molecular recognition of these inhibitors. Per residue energy decomposition analysis attributed dissimilar affinities of three inhibitors to the several hydrogen bonds and non-bonded interactions. Among the secondary structure elements that surround the allosteric site, helices α6, α7 and loop α6–α7 were notorious in providing variable affinities to the inhibitors. A novel hydrophobic pocket lined by the α7 helix residues Val287, Asn289 and Trp291 was identified in the allosteric site. This study provides useful insights for the rational design of high affinity PTP1B allosteric inhibitors.     

Application and experience of colour CRT flight deck displays

Colour CRT displays have the potential both to enhance the presentation of primary flight information and also to improve the interface between complex avionic systems and the flight deck crew. This paper describes research to explore this potential, and reports the opinions of a wide range of pilots who experienced such displays in the working environment.     

Investigating detailed interactions between novel PAR1 antagonist F16357 and the receptor using docking and molecular dynamic simulations

Currently, Vorapaxar is the only recently FDA-approved antiplatelet drug targeting Protease-activated receptor 1 (PAR1). However, a novel antagonist, F16357, has been shown to prevent painful bladder syndrome, also known as interstitial cystitis (IC). Unfortunately, there is no high resolution structure of the F16357-receptor complex, hindering its optimization as a therapeutic agent. In this study, we used docking and molecular dynamic (MD) simulations to investigate the detailed interactions between F16357 and PAR1 at a molecular level. The recently solved crystal structure of human PAR1 complexed with Vorapaxar was used in our docking of F16357 into the binding pocket of the receptor. To enhance binding pose selection, F16357 was docked first without constraints and then with a positional constraint to invert its orientation to become similar to that of Vorapaxar. The three systems, with crystal Vorapaxar, F16357 and an inverted F16357, were subjected to 3.0 μs MD simulations. The MM-GBSA binding energy analysis showed that F16357 binds more strongly in a pose obtained from an unrestrained docking than in the inverted pose from a restrained docking; and Vorapaxar binds more strongly than F17357. This ordering is consistent with the experimental pIC₅₀ values. Our structural data showed subtle changes in the binding pose between Vorapaxar and F16357. Transmembrane helices 1, 2, 5, and 7 were most significantly affected; most notably a large kink at F279^5.47 in TM helix 5 of the Vorapaxar complex was completely absent in the F16357 complex. The results of this study facilitate the future development of other therapeutic PAR1 antagonists.     

Design and analysis of anti-vibration system for the stylish dvd deck

Up to recently, the ODD(Optical Disk Drive) decks for CD and DVD have been mostly manufactured to be operated horizontally. Anti-vibration problems for this type of ODD deck have been concentrated on making focusing and tracking servo safe, when the deck is laid horizontally and is affected by disturbance, shock, vertical deviation or planner vibration of the disk, eccentricity, or radial run-out of the disk, tilt, etc. But consumers‘ various tastes have led to a demand for the deck like the stylish DVD player that can be laid in any directions, such as horizontal, vertical, upward, hanging on the wall and even being arbitrary position like a picture frame. Therefore, it is essential that we observe carefully this kind of deck mechanism and cope with the vibration problems of the deck in various positions. The purpose of this paper is to design the slot-in type deck mechanism that can be placed in all directions, to design and analyze the anti-vibration system for this type of deck, and to prove its propriety through transmissibility experiments and external vibration tests.     

Flight deck environment and pilot workload: biological measures of workload

The object of this paper is to examine some of the techniques that are being used to study the demands of the work situation upon the individual. While the emphasis throughout the paper is on studies of aircrew workload, the findings have a general applicability to applied ergonomics.     

Evaluation of the seating of Qantas flight deck crew

In 1985 Qantas Airways (Australia) requested an ergonomics assessment of three pilots' seats so that one could be selected for fitting in all new aircraft as well replacement in existing aircraft. The Ipeco seat was chosen. In 1991, after all aircraft were fitted with the Ipeco seats, the company then requested a further evaluation of the seat to see if it was acceptable to the pilots and if there were any outstanding problems. A seat feature checklist plus a body chart discomfort rating scale was given to the total crew of 1030 pilots. The results from the 202 respondents indicated that although the pilots found the Ipeco seat an improvement on the Weber seat there were some modifications required. The main problems included insufficient adjustment range of the lumbar support area and the thigh supports, and infrequent replacement of the seat cushion. The body charts supported the checklist results in that the main areas of discomfort indicated were the buttocks and low back. Recommendations for improvements in design of the Ipeco seat, training in use and maintenance are presented. The method used in this study has application for field assessment of seating in a wide range of occupations, particularly bus drivers, truck drivers and train drivers, who spend long hours seated without being able to take breaks.     

Preparation and assembly of discrete adjoint CFD codes

A methodology for constructing the sensitivity of the incompressible Navier–Stokes equations is presented as the context for differentiating high-level Fortran source code using source-transformation automatic differentiation tools. The methodology aims to be scalable and to retain all the compile-time and run-time safety the language offers. The incompressible solver is presented as it is the standard kernel in industrial CFD software. To complement this paper, the software used for this work has been made available on www.gpde.net.     

On the contribution of volume scattering to the microwave backscattered signal from wet snow and wet soil

Abstract

The contribution of volume scattering from the subsurface stratum of soil or snow to the backscattered radar signal decreases rapidly with increasing moisture content as compared to the contribution by rough-surface scattering. In order to obtain an evaluation of the relative importance of volume scattering of moist strata, a heterogeneous two-component mixture of water inclusions in a dry background medium is assumed and the formulation of the distorted Born approximation according to Tsang et al. is applied. Computed permittivities and backscatter cross-sections are compared with experimental data of situations with modest moisture content. From there, conclusions on the relative portion of volume scattering and on shape and size of the effectively-scattering water inclusions can be drawn.     

斜拉桥中拉索对桥面动力特性的影响

将斜拉桥的拉索和桥面抽象为带弹性支承的压弯弹性梁模型,并根据轴向受力梁的弯曲振动方程和哈密尔顿原理,建立了考虑拉索索力影响的单梁多索索梁结构-梁的动力学控制方程,应用传递矩阵法进行求解,并编制了求解程序.通过算例对影响桥面动力学特性的索的刚度、张拉力和桥面裂纹等因素进行了数值分析.分析结果表明,在斜拉桥的施工阶段,随着梁的长度的改变,梁的刚度讯速下降,由于索对梁的支承作用使结构的刚度有一定的提高,而索的拉力对桥面作用的压力越来越大,轴向压力使结构的刚度降低越来越明显,另一方面轴向压力对桥面裂纹引起的刚度降低有一定的抑制作用.由此,在桥梁的建设中应重视索力对桥面动力特性的影响.     

CFD差分格式及限制器计算对比分析

差分格式是计算流体力学中最为核心的因素,一直是CFD发展的主线.为了分析比较各种差分格式和限制器,以激波管Biemann问题为算例,应用八种差分格式和五种限制器进行了计算分析,对比了各种格式对于膨胀波、激波及接触间断的分辨率,讨论了中心型和迎风型格式的粘性机理和优劣,比较了各类限制器的压缩性和耗散性.研究表明,各类差分格式对间断和粘性的处理,是提高格式精度和判别格式优劣的关键.采用MUSCL方法插值时,应权衡压缩性和耗散性,合理选择限制器.各类格式通过与MUSCL高阶插值方法相结合,可以有效提高的计算效率和计算精度.