標(biāo)題: CFD analysis from scanned models help [打印本頁(yè)] 作者: cowrie 時(shí)間: 2010-5-19 19:40 標(biāo)題: CFD analysis from scanned models help by Erin Hatfield
作者：Erin Hatfield
Tenths of a second can mean the difference between a gold medal and fourth place in Olympic track cycling.
在零點(diǎn)幾秒可以決定一個(gè)金牌，在奧運(yùn)會(huì)場(chǎng)地自行車第四位的分別。
Before the 2004 Olympics in Athens, the British Cycling Team found a unique way to help save those precious fractions of a second: The team commissioned computational fluid dynamics (CFD) studies from the Sports Engineering Research Group (SERG) at the University of Sheffield to improve the overall aerodynamics of their equipment. A combination of 3D scanning technology, Geomagic Studio reverse-engineering software, CFD programs from Fluent, and EnSight visualization software produced results that helped the team earn four medals.
之前在2004年雅典奧運(yùn)會(huì)上，英國(guó)自行車隊(duì)發(fā)現(xiàn)了一個(gè)獨(dú)特的方式幫助拯救這些珍貴的第二個(gè)分?jǐn)?shù)：車隊(duì)委托計(jì)算（CFD）的在英國(guó)謝菲爾德大學(xué)的研究從體育工程研究集團(tuán)（塞格），以流體動(dòng)力學(xué)提高其設(shè)備的整體空氣動(dòng)力學(xué)。一種掃描技術(shù)，Geomagic Studio中的逆向工程軟件，從良好的CFD方案，EnSight三維可視化軟件結(jié)合產(chǎn)生的結(jié)果，幫助球隊(duì)獲得4枚獎(jiǎng)牌。
Last-minute CFD analysis
In June 2004, just weeks before the Summer Olympics, the cycling governing body enacted a rule change stating that only helmets passing a formal safety test in an accredited laboratory could be used in Olympic track competition. The British Cycling Team had four helmet designs that fit the specifications, each with different aerodynamic stylings.
最后一分鐘的CFD分析
2004年6月，前幾個(gè)星期的夏季奧運(yùn)會(huì)，單車管理機(jī)構(gòu)制定的規(guī)則的變化說(shuō)明，只有在一個(gè)頭盔通過(guò)正式認(rèn)可的實(shí)驗(yàn)室安全測(cè)試可在奧運(yùn)田徑比賽使用。英國(guó)自行車隊(duì)有4個(gè)頭盔設(shè)計(jì)適合的規(guī)格，與每一個(gè)不同的空氣動(dòng)力學(xué)造型。
To help determine which helmet was best for competition, the team turned to SERG for a quick CFD analysis. The British Cycling Team had worked with SERG months before to optimize the aerodynamics of the handlebar and wheel/fork designs on the team bikes in preparation for the Olympics.
為了幫助確定哪些是競(jìng)爭(zhēng)最好的頭盔，車隊(duì)轉(zhuǎn)向塞格的快速CFD分析。英國(guó)自行車隊(duì)曾與塞格個(gè)月前，以優(yōu)化的把手和車輪在為奧運(yùn)會(huì)準(zhǔn)備的球隊(duì)自行車/前叉設(shè)計(jì)的空氣動(dòng)力學(xué)。
SERG’s Dr. John Hart ruled out CAD as an option for creating the digital models needed for CFD analysis: There was not enough time to model from scratch, and CAD is not well-suited to create the organic shapes required for accurate modeling and CFD analysis of the helmets and athletes. Hart decided that the best solution was to capture the geometry of the athletes and helmets with 3D Scanners’ ModelMaker X70 non-contact 3D laser fitted on a Faro Gold arm, then merge the scans and create a NURBS model of the data in Geomagic Studio.
塞格的博士約恩哈特排除作為建立所需的CFD分析的CAD數(shù)字模型：有沒(méi)有足夠的時(shí)間從頭到模型，以及CAD不是很適合創(chuàng)造的精確建模和計(jì)算流體力學(xué)分析所需的有機(jī)形狀該頭盔和運(yùn)動(dòng)員。赫德決定，最好的解決辦法是捕捉到的運(yùn)動(dòng)員和三維掃描儀'ModelMaker X70鋼的非接觸式三維激光法魯黃金手臂上安裝，然后頭盔幾何合并掃描并創(chuàng)建一個(gè)在Geomagic Studio中的數(shù)據(jù)的NURBS模型。
“CAD engineers work at different tolerances than those required for CFD analysis,” Hart says. “Even if we had the CAD files for the helmets, we would have had to spend a great deal of time cleaning up the model to make it watertight. Reverse engineering the helmets and surfacing them in Geomagic Studio guaranteed a highly detailed, watertight model in less time.”
“CAD工程師在比計(jì)算流體力學(xué)分析所需的各種公差的工作，”赫德說(shuō)。 “即使我們?cè)?jīng)為頭盔的CAD文件，我們將不得不花費(fèi)大量的時(shí)間清理模型，以使其水密。逆向工程的頭盔及堆焊在Geomagic Studio中他們保證了非常詳細(xì)的，在較短的時(shí)間水密模式?！?
Scanning the helmets was relatively straightforward. Each helmet took approximately 25 minutes to scan depending on the complexity of the design. The Faro arm moved around the object, capturing point-cloud data and depth information.
掃描是相對(duì)簡(jiǎn)單的頭盔。每個(gè)頭盔花了大約25分鐘，掃描根據(jù)設(shè)計(jì)的復(fù)雜性。在法魯手臂到處移動(dòng)的對(duì)象，捕捉點(diǎn)云數(shù)據(jù)和深入的信息。
SERG planned to capture data from the athletes by scanning them in different racing positions; one aerodynamic posture and one where the cyclist has his or her head down to test more fully the effect of the helmet shapes.
塞格計(jì)劃掃描捕獲他們從不同的賽車運(yùn)動(dòng)員的位置數(shù)據(jù)，一個(gè)姿勢(shì)，一個(gè)地方的空氣動(dòng)力學(xué)的車手都有他低著頭，測(cè)試更充分的頭盔形狀的影響。
Because of the time crunch, however, Hart did not have access to a cyclist; he had to scan a colleague for the human geometry. The subject was scanned over the course of two hours, allowing for rest breaks during the scan session. Completed scans were broken into sections that followed closely in succession – upper arm, lower arm, hand – to help eliminate issues from sudden movement during the process.
由于時(shí)間緊絀，不過(guò)，赫德沒(méi)有獲得一個(gè)騎單車，他不得不為人類掃描幾何同事。掃描的主題是兩小時(shí)以上的課程，讓休息期間掃描會(huì)議。完成掃描被分成區(qū)段，隨后相繼密切 - 上臂，下臂，手 - 幫助消除突然移動(dòng)過(guò)程中的問(wèn)題。
Refining complex scan data
Point-cloud data collected from the scans of the four different helmets was imported into Geomagic Studio, reverse-engineering software used to generate models for accurate CFD analysis, and to custom manufacture devices fit to an individual’s body parts.
煉油復(fù)雜的掃描數(shù)據(jù)
點(diǎn)云數(shù)據(jù)，從四個(gè)不同的頭盔收集到的掃描到Geomagic Studio中，逆向工程軟件用于生成精確的計(jì)算流體力學(xué)分析模型，并定制生產(chǎn)設(shè)備進(jìn)口的適合個(gè)人的身體部位。
Geomagic Studio automatically aligned the scan data and a polygon mesh was applied. The model was cleaned to remove holes and defects in the data. Then patches were created over the polygons, outlining the positions of the NURBS surfaces.
Geomagic Studio自動(dòng)對(duì)齊掃描數(shù)據(jù)和采用的多邊形網(wǎng)格。該模型是清洗，以消除漏洞和缺陷的數(shù)據(jù)。然后是創(chuàng)造了補(bǔ)丁的多邊形，概述了NURBS曲面的立場(chǎng)。
Scan data from the human subject was handled in much the same way, except additional work had to be done to reduce noise and align the data due to subtle movement from Hart’s colleague as he was being scanned.
從人類主體掃描數(shù)據(jù)的處理方式大致相同，除了額外的工作，都必須進(jìn)行，以減少噪音和調(diào)整資料，因?yàn)閺墓氐耐挛⒚畹倪\(yùn)動(dòng)，他被掃描。
Hart used Geomagic Studio’s noise-reduction feature, as well as editing and filter tools, to refine the human model. He then used the software’s polygon geometric reconstruction functions to fill in missing data such as body hair and eyebrows that weren’t captured due to laser scatter.
哈特利用Geomagic Studio的降噪功能，以及編輯和過(guò)濾工具，以完善人的模型。然后，他使用的軟件的多邊形幾何重建功能，以填補(bǔ)如體毛和眉毛在不丟失數(shù)據(jù)捕獲由于激光散射。
“Geomagic Studio’s editing tools and ability to handle large, complex data sets made it a great match for this project,” says Hart. “We used the tools to refine scan data around the ears and in tight gaps, which enabled us to maintain a high degree of geometric realism on such a challenging human scan with nearly six million raw data points.”
“Geomagic Studio的編輯工具，有能力處理大型，復(fù)雜的數(shù)據(jù)集使它成為該工程的偉大的比賽，”赫德說(shuō)。 “我們使用的工具，以改進(jìn)在耳朵周圍掃描數(shù)據(jù)和嚴(yán)密的差距，使我們能夠保持這樣的幾何現(xiàn)實(shí)挑戰(zhàn)人類掃描近600萬(wàn)點(diǎn)的原始數(shù)據(jù)的高度?！?
Polygons and NURBS patches were applied to the human model and output by Geomagic Studio as a STEP file.
“The STEP file format provides a robust geometric file that’s not too large,” Hart says. “We can end up with a model with a large number of NURBS patches in order to capture the detail we need. The accuracy of the CFD study was highly dependent upon the geometrical accuracy of the assembled model.”
Visualization that proves results
The STEP file containing each helmet design and the human geometry was imported into Fluent’s Gambit software, where it was meshed for CFD analysis and a flow domain was generated around each model. The meshes ranged from two to seven million cells, depending on the geometry that was modeled. Wherever possible, prism cells were generated over the surface geometry to capture boundary-layer flow features in detail.
Fluent software was used for CFD analysis, which incorporated data on boundary and physical conditions that SERG had acquired from a previous British Cycling project.
CFD results were imported into CEI’s EnSight software, which produced highly detailed flow visualizations showing the aerodynamic properties of the helmets. SERG chose to concentrate on the drag and lift forces in the simulations, using isosurfaces to show wake structures and particle streamlines to visualize swirling, recirculating flow paths.
Based on the wake structures and recirculating flows in the visualizations, SERG was able to quickly identify how different geometric components of the models – such as the helmet and cyclist – interacted and influenced each other. They were also able to pinpoint large wakes that resulted in high drag forces.
Hart colored different aspects of the model within EnSight, and applied properties such as reflective surfaces for the bike and helmet and matte surfaces for fabric and skin. Lighting effects applied to the model helped complete the life-like look, according to Hart, making the results more believable.
“The flow visualizations and images were vital in presenting the physics-based simulation results in an understandable manner to the cycling team,” Hart says. “Being able to clearly show a client what is happening is essential to their understanding of the results.”
Hart and his colleagues used the EnSight images and animations to reinforce the hard data output from the Fluent simulations and help the engineers understand the flow physics that created the lift and drag forces. Based on the results, SERG was able to recommend an optimal helmet style that reduced aerodynamic drag and lift.
“The quality of the model geometry from Geomagic Studio and realistic color renderings and surfaces we applied in EnSight enabled us to incorporate a great deal of realism in the visualization,” says Hart.
The optimized bike design and helmet recommendations SERG made contributed to the team’s medal haul in the Olympic cycling events. SERG is working with the team again through UK Sport for the 2008 Beijing Summer Olympics.