--- _id: '12358' abstract: - lang: eng text: "The complex yarn structure of knitted and woven fabrics gives rise to both a mechanical and\r\nvisual complexity. The small-scale interactions of yarns colliding with and pulling on each\r\nother result in drastically different large-scale stretching and bending behavior, introducing\r\nanisotropy, curling, and more. While simulating cloth as individual yarns can reproduce this\r\ncomplexity and match the quality of real fabric, it may be too computationally expensive for\r\nlarge fabrics. On the other hand, continuum-based approaches do not need to discretize the\r\ncloth at a stitch-level, but it is non-trivial to find a material model that would replicate the\r\nlarge-scale behavior of yarn fabrics, and they discard the intricate visual detail. In this thesis,\r\nwe discuss three methods to try and bridge the gap between small-scale and large-scale yarn\r\nmechanics using numerical homogenization: fitting a continuum model to periodic yarn simulations, adding mechanics-aware yarn detail onto thin-shell simulations, and quantitatively\r\nfitting yarn parameters to physical measurements of real fabric.\r\nTo start, we present a method for animating yarn-level cloth effects using a thin-shell solver.\r\nWe first use a large number of periodic yarn-level simulations to build a model of the potential\r\nenergy density of the cloth, and then use it to compute forces in a thin-shell simulator. The\r\nresulting simulations faithfully reproduce expected effects like the stiffening of woven fabrics\r\nand the highly deformable nature and anisotropy of knitted fabrics at a fraction of the cost of\r\nfull yarn-level simulation.\r\nWhile our thin-shell simulations are able to capture large-scale yarn mechanics, they lack\r\nthe rich visual detail of yarn-level simulations. Therefore, we propose a method to animate\r\nyarn-level cloth geometry on top of an underlying deforming mesh in a mechanics-aware\r\nfashion in real time. Using triangle strains to interpolate precomputed yarn geometry, we are\r\nable to reproduce effects such as knit loops tightening under stretching at negligible cost.\r\nFinally, we introduce a methodology for inverse-modeling of yarn-level mechanics of cloth,\r\nbased on the mechanical response of fabrics in the real world. We compile a database from\r\nphysical tests of several knitted fabrics used in the textile industry spanning diverse physical\r\nproperties like stiffness, nonlinearity, and anisotropy. We then develop a system for approximating these mechanical responses with yarn-level cloth simulation, using homogenized\r\nshell models to speed up computation and adding some small-but-necessary extensions to\r\nyarn-level models used in computer graphics.\r\n" acknowledged_ssus: - _id: SSU alternative_title: - ISTA Thesis article_processing_charge: No author: - first_name: Georg full_name: Sperl, Georg id: 4DD40360-F248-11E8-B48F-1D18A9856A87 last_name: Sperl citation: ama: 'Sperl G. Homogenizing yarn simulations: Large-scale mechanics, small-scale detail, and quantitative fitting. 2022. doi:10.15479/at:ista:12103' apa: 'Sperl, G. (2022). Homogenizing yarn simulations: Large-scale mechanics, small-scale detail, and quantitative fitting. Institute of Science and Technology Austria. https://doi.org/10.15479/at:ista:12103' chicago: 'Sperl, Georg. “Homogenizing Yarn Simulations: Large-Scale Mechanics, Small-Scale Detail, and Quantitative Fitting.” Institute of Science and Technology Austria, 2022. https://doi.org/10.15479/at:ista:12103.' ieee: 'G. Sperl, “Homogenizing yarn simulations: Large-scale mechanics, small-scale detail, and quantitative fitting,” Institute of Science and Technology Austria, 2022.' ista: 'Sperl G. 2022. Homogenizing yarn simulations: Large-scale mechanics, small-scale detail, and quantitative fitting. Institute of Science and Technology Austria.' mla: 'Sperl, Georg. Homogenizing Yarn Simulations: Large-Scale Mechanics, Small-Scale Detail, and Quantitative Fitting. Institute of Science and Technology Austria, 2022, doi:10.15479/at:ista:12103.' short: 'G. Sperl, Homogenizing Yarn Simulations: Large-Scale Mechanics, Small-Scale Detail, and Quantitative Fitting, Institute of Science and Technology Austria, 2022.' date_created: 2023-01-24T10:49:46Z date_published: 2022-09-22T00:00:00Z date_updated: 2024-02-28T12:57:46Z day: '22' ddc: - '000' - '620' degree_awarded: PhD department: - _id: GradSch - _id: ChWo doi: 10.15479/at:ista:12103 ec_funded: 1 file: - access_level: open_access checksum: 083722acbb8115e52e3b0fdec6226769 content_type: application/pdf creator: cchlebak date_created: 2023-01-25T12:04:41Z date_updated: 2023-02-02T09:29:57Z description: 'This is the main PDF file of the thesis. File size: 105 MB' file_id: '12371' file_name: thesis_gsperl.pdf file_size: 104497530 relation: main_file title: Thesis - access_level: open_access checksum: 511f82025e5fcb70bff4731d6896ca07 content_type: application/pdf creator: cchlebak date_created: 2023-02-02T09:33:37Z date_updated: 2023-02-02T09:33:37Z description: This version of the thesis uses stronger image compression for a smaller file size of 23MB. file_id: '12483' file_name: thesis_gsperl_compressed.pdf file_size: 23183710 relation: main_file title: Thesis (compressed 23MB) - access_level: open_access checksum: ed4cb85225eedff761c25bddfc37a2ed content_type: application/x-zip-compressed creator: cchlebak date_created: 2023-02-02T09:39:25Z date_updated: 2023-02-02T09:39:25Z file_id: '12484' file_name: thesis-source.zip file_size: 98382247 relation: source_file file_date_updated: 2023-02-02T09:39:25Z has_accepted_license: '1' language: - iso: eng month: '09' oa: 1 oa_version: Published Version page: '138' project: - _id: 2533E772-B435-11E9-9278-68D0E5697425 call_identifier: H2020 grant_number: '638176' name: Efficient Simulation of Natural Phenomena at Extremely Large Scales publication_identifier: isbn: - 978-3-99078-020-6 issn: - 2663-337X publication_status: published publisher: Institute of Science and Technology Austria related_material: record: - id: '11736' relation: part_of_dissertation status: public - id: '9818' relation: part_of_dissertation status: public - id: '8385' relation: part_of_dissertation status: public status: public supervisor: - first_name: Christopher J full_name: Wojtan, Christopher J id: 3C61F1D2-F248-11E8-B48F-1D18A9856A87 last_name: Wojtan orcid: 0000-0001-6646-5546 title: 'Homogenizing yarn simulations: Large-scale mechanics, small-scale detail, and quantitative fitting' type: dissertation user_id: 8b945eb4-e2f2-11eb-945a-df72226e66a9 year: '2022' ... --- _id: '839' abstract: - lang: eng text: 'This thesis describes a brittle fracture simulation method for visual effects applications. Building upon a symmetric Galerkin boundary element method, we first compute stress intensity factors following the theory of linear elastic fracture mechanics. We then use these stress intensities to simulate the motion of a propagating crack front at a significantly higher resolution than the overall deformation of the breaking object. Allowing for spatial variations of the material''s toughness during crack propagation produces visually realistic, highly-detailed fracture surfaces. Furthermore, we introduce approximations for stress intensities and crack opening displacements, resulting in both practical speed-up and theoretically superior runtime complexity compared to previous methods. While we choose a quasi-static approach to fracture mechanics, ignoring dynamic deformations, we also couple our fracture simulation framework to a standard rigid-body dynamics solver, enabling visual effects artists to simulate both large scale motion, as well as fracturing due to collision forces in a combined system. As fractures inside of an object grow, their geometry must be represented both in the coarse boundary element mesh, as well as at the desired fine output resolution. Using a boundary element method, we avoid complicated volumetric meshing operations. Instead we describe a simple set of surface meshing operations that allow us to progressively add cracks to the mesh of an object and still re-use all previously computed entries of the linear boundary element system matrix. On the high resolution level, we opt for an implicit surface representation. We then describe how to capture fracture surfaces during crack propagation, as well as separate the individual fragments resulting from the fracture process, based on this implicit representation. We show results obtained with our method, either solving the full boundary element system in every time step, or alternatively using our fast approximations. These results demonstrate that both of these methods perform well in basic test cases and produce realistic fracture surfaces. Furthermore we show that our fast approximations substantially out-perform the standard approach in more demanding scenarios. Finally, these two methods naturally combine, using the full solution while the problem size is manageably small and switching to the fast approximations later on. The resulting hybrid method gives the user a direct way to choose between speed and accuracy of the simulation. ' acknowledgement: "ERC H2020 programme (grant agreement no. 638176)\r\nFirst of all, let me thank my committee members, especially my supervisor, Chris\r\nWojtan, for supporting me throughout my PhD. Obviously, none of this work would\r\nhave been possible without you.\r\nFurthermore, Thank You to all the people who have contributed to this work in various\r\nways, in particular Martin Schanz and his group for providing and supporting the\r\nHyENA boundary element library, as well as Eder Miguel and Morten Bojsen-Hansen\r\nfor (repeatedly) proof reading and providing valuable suggestions during the writing\r\nof this thesis.\r\nI would also like to thank Bernd Bickel, and all the members – past and present – of his\r\nand Chris’ research groups at IST Austria for always providing honest and insightful\r\nfeedback throughout many joint group meetings, as well as Christopher Batty, Eitan\r\nGrinspun, and Fang Da for many insights into boundary element methods during our\r\ncollaboration.\r\nAs only virtual objects have been harmed in the process of creating this work, I would\r\nlike to acknowledge the Stanford scanning repository for providing the “Bunny” and\r\n“Armadillo” models, the AIM@SHAPE repository for “Pierre’s hand, watertight”, and\r\nS. Gainsbourg for the “Column” via Archive3D.net. Sorry for breaking these models\r\nin many different ways.\r\n" alternative_title: - ISTA Thesis article_processing_charge: No author: - first_name: David full_name: Hahn, David id: 357A6A66-F248-11E8-B48F-1D18A9856A87 last_name: Hahn citation: ama: Hahn D. Brittle fracture simulation with boundary elements for computer graphics. 2017. doi:10.15479/AT:ISTA:th_855 apa: Hahn, D. (2017). Brittle fracture simulation with boundary elements for computer graphics. Institute of Science and Technology Austria. https://doi.org/10.15479/AT:ISTA:th_855 chicago: Hahn, David. “Brittle Fracture Simulation with Boundary Elements for Computer Graphics.” Institute of Science and Technology Austria, 2017. https://doi.org/10.15479/AT:ISTA:th_855. ieee: D. Hahn, “Brittle fracture simulation with boundary elements for computer graphics,” Institute of Science and Technology Austria, 2017. ista: Hahn D. 2017. Brittle fracture simulation with boundary elements for computer graphics. Institute of Science and Technology Austria. mla: Hahn, David. Brittle Fracture Simulation with Boundary Elements for Computer Graphics. Institute of Science and Technology Austria, 2017, doi:10.15479/AT:ISTA:th_855. short: D. Hahn, Brittle Fracture Simulation with Boundary Elements for Computer Graphics, Institute of Science and Technology Austria, 2017. date_created: 2018-12-11T11:48:47Z date_published: 2017-08-14T00:00:00Z date_updated: 2024-02-21T13:48:02Z day: '14' ddc: - '004' - '005' - '006' - '531' - '621' degree_awarded: PhD department: - _id: ChWo doi: 10.15479/AT:ISTA:th_855 ec_funded: 1 file: - access_level: open_access checksum: 6c1ae8c90bfaba5e089417fefbc4a272 content_type: application/pdf creator: system date_created: 2018-12-12T10:14:46Z date_updated: 2020-07-14T12:48:13Z file_id: '5100' file_name: IST-2017-855-v1+1_thesis_online_pdfA.pdf file_size: 14596191 relation: main_file - access_level: closed checksum: 421672f68d563b029869c5cf1713f919 content_type: application/zip creator: dernst date_created: 2019-04-05T08:40:30Z date_updated: 2020-07-14T12:48:13Z file_id: '6207' file_name: 2017_thesis_Hahn_source.zip file_size: 15060566 relation: source_file file_date_updated: 2020-07-14T12:48:13Z has_accepted_license: '1' language: - iso: eng license: https://creativecommons.org/licenses/by-sa/4.0/ month: '08' oa: 1 oa_version: Published Version page: '124' project: - _id: 2533E772-B435-11E9-9278-68D0E5697425 call_identifier: H2020 grant_number: '638176' name: Efficient Simulation of Natural Phenomena at Extremely Large Scales publication_identifier: issn: - 2663-337X publication_status: published publisher: Institute of Science and Technology Austria publist_id: '6809' pubrep_id: '855' related_material: record: - id: '1362' relation: part_of_dissertation status: public - id: '1633' relation: part_of_dissertation status: public - id: '5568' relation: popular_science status: public status: public supervisor: - first_name: Christopher J full_name: Wojtan, Christopher J id: 3C61F1D2-F248-11E8-B48F-1D18A9856A87 last_name: Wojtan orcid: 0000-0001-6646-5546 title: Brittle fracture simulation with boundary elements for computer graphics tmp: image: /images/cc_by_sa.png legal_code_url: https://creativecommons.org/licenses/by-sa/4.0/legalcode name: Creative Commons Attribution-ShareAlike 4.0 International Public License (CC BY-SA 4.0) short: CC BY-SA (4.0) type: dissertation user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1 year: '2017' ... --- _id: '1122' abstract: - lang: eng text: "Computer graphics is an extremely exciting field for two reasons. On the one hand,\r\nthere is a healthy injection of pragmatism coming from the visual effects industry\r\nthat want robust algorithms that work so they can produce results at an increasingly\r\nfrantic pace. On the other hand, they must always try to push the envelope and\r\nachieve the impossible to wow their audiences in the next blockbuster, which means\r\nthat the industry has not succumb to conservatism, and there is plenty of room to\r\ntry out new and crazy ideas if there is a chance that it will pan into something\r\nuseful.\r\nWater simulation has been in visual effects for decades, however it still remains\r\nextremely challenging because of its high computational cost and difficult artdirectability.\r\nThe work in this thesis tries to address some of these difficulties.\r\nSpecifically, we make the following three novel contributions to the state-of-the-art\r\nin water simulation for visual effects.\r\nFirst, we develop the first algorithm that can convert any sequence of closed\r\nsurfaces in time into a moving triangle mesh. State-of-the-art methods at the time\r\ncould only handle surfaces with fixed connectivity, but we are the first to be able to\r\nhandle surfaces that merge and split apart. This is important for water simulation\r\npractitioners, because it allows them to convert splashy water surfaces extracted\r\nfrom particles or simulated using grid-based level sets into triangle meshes that can\r\nbe either textured and enhanced with extra surface dynamics as a post-process.\r\nWe also apply our algorithm to other phenomena that merge and split apart, such\r\nas morphs and noisy reconstructions of human performances.\r\nSecond, we formulate a surface-based energy that measures the deviation of a\r\nwater surface froma physically valid state. Such discrepancies arise when there is a\r\nmismatch in the degrees of freedom between the water surface and the underlying\r\nphysics solver. This commonly happens when practitioners use a moving triangle\r\nmesh with a grid-based physics solver, or when high-resolution grid-based surfaces\r\nare combined with low-resolution physics. Following the direction of steepest\r\ndescent on our surface-based energy, we can either smooth these artifacts or turn\r\nthem into high-resolution waves by interpreting the energy as a physical potential.\r\nThird, we extend state-of-the-art techniques in non-reflecting boundaries to handle spatially and time-varying background flows. This allows a novel new\r\nworkflow where practitioners can re-simulate part of an existing simulation, such\r\nas removing a solid obstacle, adding a new splash or locally changing the resolution.\r\nSuch changes can easily lead to new waves in the re-simulated region that would\r\nreflect off of the new simulation boundary, effectively ruining the illusion of a\r\nseamless simulation boundary between the existing and new simulations. Our\r\nnon-reflecting boundaries makes sure that such waves are absorbed." acknowledgement: "First and foremost I would like to thank Chris. I have been incredibly lucky to have\r\nyou as my advisor. Your integrity and aspiration to do the right thing in all walks of\r\nlife is something I admire and aspire to. I also really appreciate the fact that when\r\nworking with you it felt like we were equals. I think we had a very synergetic work\r\nrelationship: I learned immensely from you, but I dare say that you learned a few\r\nthings from me as well. ;)\r\nNext, I would like to thank my amazing committee. Hao, it was a fantastic\r\nexperience working with you. You showed me how to persevere and keep morale\r\nhigh when things were looking the most bleak before the deadline. You are an\r\nincredible motivator and super fun to be around! Vladimir, thanks for the shared\r\nlunches and the poker games. Sorry for not bringing them back when I got busy.\r\nAlso, sorry for embarrassing you by asking about your guitar playing that one\r\ntime. You really are quite awesome! Nils, one of the friendliest and most humble\r\npeople you will meet and a top notch researcher to boot! Thank you for joining\r\nmy committee late!\r\nI would also like to acknowledge the Visual Computing group at IST Austria\r\nfrom whom I have learned so much. The excellent discussions we had in reading\r\ngroups and research meetings really helped me become a better researcher!\r\nNext, I would like to thank all the amazing people that I met during my PhD\r\nstudies, both at IST Austria, in Vienna and elsewhere. " alternative_title: - ISTA Thesis article_processing_charge: No author: - first_name: Morten full_name: Bojsen-Hansen, Morten id: 439F0C8C-F248-11E8-B48F-1D18A9856A87 last_name: Bojsen-Hansen orcid: 0000-0002-4417-3224 citation: ama: Bojsen-Hansen M. Tracking, correcting and absorbing water surface waves. 2016. doi:10.15479/AT:ISTA:th_640 apa: Bojsen-Hansen, M. (2016). Tracking, correcting and absorbing water surface waves. Institute of Science and Technology Austria. https://doi.org/10.15479/AT:ISTA:th_640 chicago: Bojsen-Hansen, Morten. “Tracking, Correcting and Absorbing Water Surface Waves.” Institute of Science and Technology Austria, 2016. https://doi.org/10.15479/AT:ISTA:th_640. ieee: M. Bojsen-Hansen, “Tracking, correcting and absorbing water surface waves,” Institute of Science and Technology Austria, 2016. ista: Bojsen-Hansen M. 2016. Tracking, correcting and absorbing water surface waves. Institute of Science and Technology Austria. mla: Bojsen-Hansen, Morten. Tracking, Correcting and Absorbing Water Surface Waves. Institute of Science and Technology Austria, 2016, doi:10.15479/AT:ISTA:th_640. short: M. Bojsen-Hansen, Tracking, Correcting and Absorbing Water Surface Waves, Institute of Science and Technology Austria, 2016. date_created: 2018-12-11T11:50:16Z date_published: 2016-07-15T00:00:00Z date_updated: 2024-02-21T13:50:48Z day: '15' ddc: - '004' - '005' - '006' - '532' - '621' degree_awarded: PhD department: - _id: ChWo doi: 10.15479/AT:ISTA:th_640 file: - access_level: open_access content_type: application/pdf creator: system date_created: 2018-12-12T10:13:02Z date_updated: 2018-12-12T10:13:02Z file_id: '4982' file_name: IST-2016-640-v1+1_2016_Bojsen-Hansen_TCaAWSW.pdf file_size: 13869345 relation: main_file file_date_updated: 2018-12-12T10:13:02Z has_accepted_license: '1' language: - iso: eng month: '07' oa: 1 oa_version: Published Version page: '114' publication_identifier: issn: - 2663-337X publication_status: published publisher: Institute of Science and Technology Austria publist_id: '6238' related_material: record: - id: '5558' relation: other status: public status: public supervisor: - first_name: Christopher J full_name: Wojtan, Christopher J id: 3C61F1D2-F248-11E8-B48F-1D18A9856A87 last_name: Wojtan orcid: 0000-0001-6646-5546 title: Tracking, correcting and absorbing water surface waves tmp: image: /images/cc_by.png legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0) short: CC BY (4.0) type: dissertation user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1 year: '2016' ...