發(fā)布時(shí)間：2018-07-07 23:32

  本文選題：流體仿真 + 表面張力　； 參考：《浙江大學(xué)》2016年博士論文

【摘要】：物理仿真是基于真實(shí)世界物理規(guī)律,在計(jì)算機(jī)中虛擬地重現(xiàn)流體運(yùn)動(dòng)、彈性體形變等各種物理現(xiàn)象的過程。由于物理仿真能夠達(dá)到很高的精度,而成本比物理實(shí)驗(yàn)要低,因此被廣泛應(yīng)用于航空航天、機(jī)械制造、生物醫(yī)藥等諸多領(lǐng)域的前期研究。影視制作中許多難以實(shí)際拍攝的場(chǎng)景,也是通過對(duì)流水、風(fēng)沙、火焰等現(xiàn)象進(jìn)行物理仿真,并結(jié)合高質(zhì)量的渲染器,制作出的視覺特效。近年來,隨著3D打印技術(shù)的發(fā)展和普及,數(shù)字化制造再次成為前沿的研究領(lǐng)域。將物理仿真應(yīng)用于3D打印,對(duì)模型進(jìn)行結(jié)構(gòu)力學(xué)分析,可以及時(shí)發(fā)現(xiàn)設(shè)計(jì)缺陷,保證制造出模型的結(jié)構(gòu)穩(wěn)定;通過運(yùn)動(dòng)學(xué)分析,可以制造出具有特殊運(yùn)動(dòng)規(guī)律的模型。物理仿真的應(yīng)用極大提高了數(shù)字化制造的水平。面網(wǎng)格在物理仿真中有著非常重要的作用。首先,薄層結(jié)構(gòu)的物體(如紙張、布料、板材、氣泡等)通常都是用面網(wǎng)格來直接表示。其次,面網(wǎng)格可以表示模型的表面形狀,因此被廣泛用于碰撞檢測(cè)以及場(chǎng)景的實(shí)時(shí)顯示。對(duì)于流體等無固定形狀的物質(zhì),還可以用動(dòng)態(tài)面網(wǎng)格追蹤其自由液面。盡管自然界中真實(shí)物體都具有一定的體積,但是體網(wǎng)格拓?fù)浣Y(jié)構(gòu)和計(jì)算往往都比較復(fù)雜。因此,如果能用面網(wǎng)格對(duì)計(jì)算模型進(jìn)行近似,就可以顯著減少運(yùn)算量,提高仿真速度。本文用面網(wǎng)格對(duì)水滴、粘性流體薄膜、塑性薄膜等三種物質(zhì)進(jìn)行了建模和仿真。水滴體積很小,其形狀主要受表面張力的影響,因此可以忽略水滴內(nèi)部的流體運(yùn)動(dòng),通過面網(wǎng)格的直接形變進(jìn)行仿真。水滴之間的融合與分裂,可以通過面網(wǎng)格的布爾運(yùn)算及網(wǎng)格優(yōu)化來實(shí)現(xiàn)。粘性流體薄膜和塑性薄膜都是薄層結(jié)構(gòu),因此用面網(wǎng)格可以很好地對(duì)其進(jìn)行仿真。我們將其仿真技術(shù)應(yīng)用于兩種傳統(tǒng)制造工藝的虛擬化:水轉(zhuǎn)印和熱塑成型,提出“可計(jì)算水轉(zhuǎn)印刷”和“可計(jì)算熱塑成型”的方法,使其能夠用于三維曲面全彩著色。我們研制了這些新型工藝的原型系統(tǒng),并通過實(shí)驗(yàn)證明了其實(shí)用性和可靠性。本文的主要貢獻(xiàn)如下:·提出了一種基于面網(wǎng)格的實(shí)時(shí)水滴仿真方法。通過對(duì)水滴表面網(wǎng)格直接形變,對(duì)水滴的運(yùn)動(dòng)、水滴與親水表面接觸,以及水滴在固體表面滑動(dòng)的現(xiàn)象進(jìn)行仿真。該方法把流體仿真從三維體素簡(jiǎn)化為面網(wǎng)格的形變,從而使計(jì)算量大幅減少,不僅能夠?qū)崟r(shí)仿真,還可以讓用戶與水滴進(jìn)行交互�！ねㄟ^面網(wǎng)格對(duì)粘稠流體薄膜漂浮在水面上的現(xiàn)象進(jìn)行仿真,模擬物體經(jīng)過薄膜浸入水中,薄膜被拉伸并貼在物體表面的過程。我們將該現(xiàn)象的仿真應(yīng)用于曲面著色工藝——水轉(zhuǎn)印的虛擬化流程,提出“可計(jì)算水轉(zhuǎn)印刷”的方法,解決了傳統(tǒng)水轉(zhuǎn)印工藝中對(duì)復(fù)雜曲面著色時(shí),圖案與模型難以精確對(duì)齊的問題。我們搭建了計(jì)算水轉(zhuǎn)印的原型系統(tǒng),實(shí)現(xiàn)了虛擬仿真、系統(tǒng)標(biāo)定、運(yùn)動(dòng)控制的集成。針對(duì)復(fù)雜模型水轉(zhuǎn)印過程中,水轉(zhuǎn)印膜拉伸過大導(dǎo)致顏色失真的缺陷,我們提出了多次轉(zhuǎn)印的方法。每次只在一個(gè)方向?qū)δＰ途植恐��?多次轉(zhuǎn)移之后圖案相疊加,在模型表面上共同形成目標(biāo)紋理。·通過面網(wǎng)格對(duì)塑性薄膜進(jìn)行建模,模擬軟化塑料片在大氣壓力下產(chǎn)生形變,并貼在物體表面的過程。我們將該現(xiàn)象的仿真應(yīng)用于塑料成型工藝——真空熱塑成型的虛擬化流程,提出“可計(jì)算熱塑成型”的方法,并結(jié)合3D打印,將帶紋理的虛擬數(shù)字化模型制作成為實(shí)物模型。首先,將數(shù)字化模型作為模具,對(duì)真空成型的過程進(jìn)行虛擬仿真。根據(jù)塑料片形變的仿真結(jié)果,計(jì)算出預(yù)形變圖案,將其打印在透明塑料片上。通過對(duì)抽真空過程的仿真,找出塑料片與模具之間可能出現(xiàn)的氣體空腔,據(jù)此在模型上設(shè)置排氣孔,并通過3D打印制作出帶有排氣孔的模具。我們對(duì)一臺(tái)小型真空成型機(jī)進(jìn)行了改造,使塑料片上的圖案能夠與物體精確對(duì)齊。經(jīng)過真空成型,打印的紋理就貼在了模具的表面,同時(shí)塑料片也為圖案覆蓋了一層透明保護(hù)殼,最終得到與數(shù)字化模型相同的實(shí)物模型。
[Abstract]:Physical simulation is a process based on real world physical laws to reproduce a variety of physical phenomena, such as fluid motion, elastic body shape, and so on in a computer. Physical simulation can achieve high precision, and the cost is lower than physical experiment. So it is widely used in the early stage of aerospace, mechanical manufacturing, biological medicine and many other fields. Research. Many scenes which are difficult to be photographed in film and television production are also physical simulation through the phenomena of water, wind sand, flame and so on. The visual effects are made with high quality renderers. In recent years, with the development and popularization of 3D printing technology, digital manufacturing has become the frontier of research again. The physical simulation is applied to the 3D The structural mechanics analysis of the model can detect the design defects in time and ensure the structure stability of the model. Through the kinematic analysis, a model with special motion laws can be produced. The application of physical simulation greatly improves the level of digital manufacturing. The surface grid has a very important role in the physical simulation. First, thin structure objects (such as paper, cloth, plate, bubble, etc.) are usually expressed directly by surface mesh. Second, the surface mesh can represent the surface shape of the model, so it is widely used for collision detection and real-time display of the scene. The free surface can be traced with a dynamic surface mesh for materials such as fluid and so on. Although the real objects in the natural world have a certain volume, the topology and calculation of the body mesh are often complicated. Therefore, if the surface mesh can be used to approximate the calculation model, the computation can be reduced and the speed of the simulation can be improved. In this paper, three materials, such as water droplets, viscous fluid film, plastic film and so on, are used in this paper. The volume of water droplets is very small and its shape is mainly influenced by the surface tension. Therefore, the fluid movement inside the water droplets can be ignored and the direct deformation of the surface mesh is simulated. The fusion and splitting of water droplets can be realized by the Boolean operation and the mesh optimization of the surface mesh. Both viscous fluid film and plastic film can be achieved. It is a thin layer structure, so the surface mesh can be well simulated. We apply its simulation technology to the virtualization of two traditional manufacturing processes: water transfer and thermoplastic molding, the method of "computable water transfer printing" and "computable thermoplastic molding", so that it can be used in full color coloring of 3D surfaces. We developed this method. Some new technology prototype systems have been proved to be practical and reliable. The main contributions of this paper are as follows:. A real-time water drop simulation method based on surface mesh is proposed. By direct deformation of the surface grid of water droplets, the movement of water droplets, the contact of water droplets with the surface of hydrophilic surface, and the sliding of water droplets on the solid surface. Simulation. This method simplifies the fluid simulation from the three-dimensional voxel to the deformation of the surface mesh, so that the calculation can be reduced greatly. It can not only simulate the real time, but also allow users to interact with the water droplets. The process of being stretched and attached to the surface of an object. We applied the simulation of the phenomenon to a surface coloring process, a virtual process of water transfer, and proposed a "computable water transfer printing" method to solve the problem of precise alignment between patterns and models in the process of coloring complex surfaces in the traditional water transfer process. The prototype system has realized the virtual simulation, the system calibration and the integration of motion control. In view of the defects of the color distortion caused by the overstretching of the water transfer film during the process of water transfer to the complex model, we put forward a multiple transfer method. Each time the model is localized in one direction only, the pattern is superimposed after multiple transfers, and the model surface is on the model surface. The plastic film is modeled by the surface mesh to simulate the deformation of the plastic film under atmospheric pressure and to be attached to the surface of the object. We apply the simulation to the plastic molding process, the virtual flow process of vacuum thermoplastic molding, and put forward the method of "calculable thermoplastic molding". Combined with 3D printing, the virtual digital model with texture is made into a physical model. First, the digital model is used as a mold to simulate the process of vacuum forming. According to the simulation results of the plastic sheet deformation, the preformed pattern is calculated and printed on the transparent plastic sheet. By simulation of the vacuum process, the plastic is found out. A gas cavity may appear between the die and the mold. According to this, the exhaust holes are set on the model, and the mold with the vent hole is produced by 3D printing. We have reformed a small vacuum forming machine to make the pattern on the plastic sheet aligned with the object accurately. After vacuum molding, the print texture is attached to the surface of the mold. At the same time, the plastic sheet also covered a transparent protective shell for the pattern, and finally got the same physical model as the digital model.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TP391.9

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