@article{9208, abstract = {Bending-active structures are able to efficiently produce complex curved shapes from flat panels. The desired deformation of the panels derives from the proper selection of their elastic properties. Optimized panels, called FlexMaps, are designed such that, once they are bent and assembled, the resulting static equilibrium configuration matches a desired input 3D shape. The FlexMaps elastic properties are controlled by locally varying spiraling geometric mesostructures, which are optimized in size and shape to match specific bending requests, namely the global curvature of the target shape. The design pipeline starts from a quad mesh representing the input 3D shape, which defines the edge size and the total amount of spirals: every quad will embed one spiral. Then, an optimization algorithm tunes the geometry of the spirals by using a simplified pre-computed rod model. This rod model is derived from a non-linear regression algorithm which approximates the non-linear behavior of solid FEM spiral models subject to hundreds of load combinations. This innovative pipeline has been applied to the project of a lightweight plywood pavilion named FlexMaps Pavilion, which is a single-layer piecewise twisted arch that fits a bounding box of 3.90x3.96x3.25 meters. This case study serves to test the applicability of this methodology at the architectural scale. The structure is validated via FE analyses and the fabrication of the full scale prototype.}, author = {Laccone, Francesco and Malomo, Luigi and Perez Rodriguez, Jesus and Pietroni, Nico and Ponchio, Federico and Bickel, Bernd and Cignoni, Paolo}, issn = {25233971}, journal = {SN Applied Sciences}, number = {9}, publisher = {Springer Nature}, title = {{A bending-active twisted-arch plywood structure: Computational design and fabrication of the FlexMaps Pavilion}}, doi = {10.1007/s42452-020-03305-w}, volume = {2}, year = {2020}, } @article{6650, abstract = {We propose a novel technique for the automatic design of molds to cast highly complex shapes. The technique generates composite, two-piece molds. Each mold piece is made up of a hard plastic shell and a flexible silicone part. Thanks to the thin, soft, and smartly shaped silicone part, which is kept in place by a hard plastic shell, we can cast objects of unprecedented complexity. An innovative algorithm based on a volumetric analysis defines the layout of the internal cuts in the silicone mold part. Our approach can robustly handle thin protruding features and intertwined topologies that have caused previous methods to fail. We compare our results with state of the art techniques, and we demonstrate the casting of shapes with extremely complex geometry.}, author = {Alderighi, Thomas and Malomo, Luigi and Giorgi, Daniela and Bickel, Bernd and Cignoni, Paolo and Pietroni, Nico}, issn = {0730-0301}, journal = {ACM Transactions on Graphics}, number = {4}, publisher = {ACM}, title = {{Volume-aware design of composite molds}}, doi = {10.1145/3306346.3322981}, volume = {38}, year = {2019}, } @article{6660, abstract = {Commercially available full-color 3D printing allows for detailed control of material deposition in a volume, but an exact reproduction of a target surface appearance is hampered by the strong subsurface scattering that causes nontrivial volumetric cross-talk at the print surface. Previous work showed how an iterative optimization scheme based on accumulating absorptive materials at the surface can be used to find a volumetric distribution of print materials that closely approximates a given target appearance. In this work, we first revisit the assumption that pushing the absorptive materials to the surface results in minimal volumetric cross-talk. We design a full-fledged optimization on a small domain for this task and confirm this previously reported heuristic. Then, we extend the above approach that is critically limited to color reproduction on planar surfaces, to arbitrary 3D shapes. Our method enables high-fidelity color texture reproduction on 3D prints by effectively compensating for internal light scattering within arbitrarily shaped objects. In addition, we propose a content-aware gamut mapping that significantly improves color reproduction for the pathological case of thin geometric features. Using a wide range of sample objects with complex textures and geometries, we demonstrate color reproduction whose fidelity is superior to state-of-the-art drivers for color 3D printers.}, author = {Sumin, Denis and Weyrich, Tim and Rittig, Tobias and Babaei, Vahid and Nindel, Thomas and Wilkie, Alexander and Didyk, Piotr and Bickel, Bernd and Křivánek, Jaroslav and Myszkowski, Karol}, issn = {0730-0301}, journal = {ACM Transactions on Graphics}, number = {4}, publisher = {ACM}, title = {{Geometry-aware scattering compensation for 3D printing}}, doi = {10.1145/3306346.3322992}, volume = {38}, year = {2019}, } @article{7117, abstract = {We propose a novel generic shape optimization method for CAD models based on the eXtended Finite Element Method (XFEM). Our method works directly on the intersection between the model and a regular simulation grid, without the need to mesh or remesh, thus removing a bottleneck of classical shape optimization strategies. This is made possible by a novel hierarchical integration scheme that accurately integrates finite element quantities with sub-element precision. For optimization, we efficiently compute analytical shape derivatives of the entire framework, from model intersection to integration rule generation and XFEM simulation. Moreover, we describe a differentiable projection of shape parameters onto a constraint manifold spanned by user-specified shape preservation, consistency, and manufacturability constraints. We demonstrate the utility of our approach by optimizing mass distribution, strength-to-weight ratio, and inverse elastic shape design objectives directly on parameterized 3D CAD models.}, author = {Hafner, Christian and Schumacher, Christian and Knoop, Espen and Auzinger, Thomas and Bickel, Bernd and Bächer, Moritz}, issn = {0730-0301}, journal = {ACM Transactions on Graphics}, number = {6}, publisher = {ACM}, title = {{X-CAD: Optimizing CAD Models with Extended Finite Elements}}, doi = {10.1145/3355089.3356576}, volume = {38}, year = {2019}, } @misc{7154, author = {Guseinov, Ruslan}, publisher = {Institute of Science and Technology Austria}, title = {{Supplementary data for "Programming temporal morphing of self-actuated shells"}}, doi = {10.15479/AT:ISTA:7154}, year = {2019}, } @inproceedings{9261, abstract = {Bending-active structures are able to efficiently produce complex curved shapes starting from flat panels. The desired deformation of the panels derives from the proper selection of their elastic properties. Optimized panels, called FlexMaps, are designed such that, once they are bent and assembled, the resulting static equilibrium configuration matches a desired input 3D shape. The FlexMaps elastic properties are controlled by locally varying spiraling geometric mesostructures, which are optimized in size and shape to match the global curvature (i.e., bending requests) of the target shape. The design pipeline starts from a quad mesh representing the input 3D shape, which defines the edge size and the total amount of spirals: every quad will embed one spiral. Then, an optimization algorithm tunes the geometry of the spirals by using a simplified pre-computed rod model. This rod model is derived from a non-linear regression algorithm which approximates the non-linear behavior of solid FEM spiral models subject to hundreds of load combinations. This innovative pipeline has been applied to the project of a lightweight plywood pavilion named FlexMaps Pavilion, which is a single-layer piecewise twisted arc that fits a bounding box of 3.90x3.96x3.25 meters.}, author = {Laccone, Francesco and Malomo, Luigi and Perez Rodriguez, Jesus and Pietroni, Nico and Ponchio, Federico and Bickel, Bernd and Cignoni, Paolo}, booktitle = {IASS Symposium 2019 - 60th Anniversary Symposium of the International Association for Shell and Spatial Structures; Structural Membranes 2019 - 9th International Conference on Textile Composites and Inflatable Structures, FORM and FORCE}, isbn = {9788412110104}, issn = {2518-6582}, location = {Barcelona, Spain}, pages = {509--515}, publisher = {International Center for Numerical Methods in Engineering}, title = {{FlexMaps Pavilion: A twisted arc made of mesostructured flat flexible panels}}, year = {2019}, } @article{304, abstract = {Additive manufacturing has recently seen drastic improvements in resolution, making it now possible to fabricate features at scales of hundreds or even dozens of nanometers, which previously required very expensive lithographic methods. As a result, additive manufacturing now seems poised for optical applications, including those relevant to computer graphics, such as material design, as well as display and imaging applications. In this work, we explore the use of additive manufacturing for generating structural colors, where the structures are designed using a fabrication-aware optimization process. This requires a combination of full-wave simulation, a feasible parameterization of the design space, and a tailored optimization procedure. Many of these components should be re-usable for the design of other optical structures at this scale. We show initial results of material samples fabricated based on our designs. While these suffer from the prototype character of state-of-the-art fabrication hardware, we believe they clearly demonstrate the potential of additive nanofabrication for structural colors and other graphics applications.}, author = {Auzinger, Thomas and Heidrich, Wolfgang and Bickel, Bernd}, journal = {ACM Transactions on Graphics}, number = {4}, publisher = {ACM}, title = {{Computational design of nanostructural color for additive manufacturing}}, doi = {10.1145/3197517.3201376}, volume = {37}, year = {2018}, } @article{5976, abstract = {We propose FlexMaps, a novel framework for fabricating smooth shapes out of flat, flexible panels with tailored mechanical properties. We start by mapping the 3D surface onto a 2D domain as in traditional UV mapping to design a set of deformable flat panels called FlexMaps. For these panels, we design and obtain specific mechanical properties such that, once they are assembled, the static equilibrium configuration matches the desired 3D shape. FlexMaps can be fabricated from an almost rigid material, such as wood or plastic, and are made flexible in a controlled way by using computationally designed spiraling microstructures.}, author = {Malomo, Luigi and Perez Rodriguez, Jesus and Iarussi, Emmanuel and Pietroni, Nico and Miguel, Eder and Cignoni, Paolo and Bickel, Bernd}, issn = {0730-0301}, journal = {ACM Transactions on Graphics}, number = {6}, publisher = {Association for Computing Machinery (ACM)}, title = {{FlexMaps: Computational design of flat flexible shells for shaping 3D objects}}, doi = {10.1145/3272127.3275076}, volume = {37}, year = {2018}, } @article{6003, abstract = {Digital fabrication devices are powerful tools for creating tangible reproductions of 3D digital models. Most available printing technologies aim at producing an accurate copy of a tridimensional shape. However, fabrication technologies can also be used to create a stylistic representation of a digital shape. We refer to this class of methods as ‘stylized fabrication methods’. These methods abstract geometric and physical features of a given shape to create an unconventional representation, to produce an optical illusion or to devise a particular interaction with the fabricated model. In this state‐of‐the‐art report, we classify and overview this broad and emerging class of approaches and also propose possible directions for future research.}, author = {Bickel, Bernd and Cignoni, Paolo and Malomo, Luigi and Pietroni, Nico}, issn = {0167-7055}, journal = {Computer Graphics Forum}, number = {6}, pages = {325--342}, publisher = {Wiley}, title = {{State of the art on stylized fabrication}}, doi = {10.1111/cgf.13327}, volume = {37}, year = {2018}, } @inproceedings{6195, abstract = {In the context of robotic manipulation and grasping, the shift from a view that is static (force closure of a single posture) and contact-deprived (only contact for force closure is allowed, everything else is obstacle) towards a view that is dynamic and contact-rich (soft manipulation) has led to an increased interest in soft hands. These hands can easily exploit environmental constraints and object surfaces without risk, and safely interact with humans, but present also some challenges. Designing them is difficult, as well as predicting, modelling, and “programming” their interactions with the objects and the environment. This paper tackles the problem of simulating them in a fast and effective way, leveraging on novel and existing simulation technologies. We present a triple-layered simulation framework where dynamic properties such as stiffness are determined from slow but accurate FEM simulation data once, and then condensed into a lumped parameter model that can be used to fast simulate soft fingers and soft hands. We apply our approach to the simulation of soft pneumatic fingers.}, author = {Pozzi, Maria and Miguel Villalba, Eder and Deimel, Raphael and Malvezzi, Monica and Bickel, Bernd and Brock, Oliver and Prattichizzo, Domenico}, isbn = {9781538630815}, location = {Brisbane, Australia}, publisher = {IEEE}, title = {{Efficient FEM-based simulation of soft robots modeled as kinematic chains}}, doi = {10.1109/icra.2018.8461106}, year = {2018}, } @article{12, abstract = {Molding is a popular mass production method, in which the initial expenses for the mold are offset by the low per-unit production cost. However, the physical fabrication constraints of the molding technique commonly restrict the shape of moldable objects. For a complex shape, a decomposition of the object into moldable parts is a common strategy to address these constraints, with plastic model kits being a popular and illustrative example. However, conducting such a decomposition requires considerable expertise, and it depends on the technical aspects of the fabrication technique, as well as aesthetic considerations. We present an interactive technique to create such decompositions for two-piece molding, in which each part of the object is cast between two rigid mold pieces. Given the surface description of an object, we decompose its thin-shell equivalent into moldable parts by first performing a coarse decomposition and then utilizing an active contour model for the boundaries between individual parts. Formulated as an optimization problem, the movement of the contours is guided by an energy reflecting fabrication constraints to ensure the moldability of each part. Simultaneously, the user is provided with editing capabilities to enforce aesthetic guidelines. Our interactive interface provides control of the contour positions by allowing, for example, the alignment of part boundaries with object features. Our technique enables a novel workflow, as it empowers novice users to explore the design space, and it generates fabrication-ready two-piece molds that can be used either for casting or industrial injection molding of free-form objects.}, author = {Nakashima, Kazutaka and Auzinger, Thomas and Iarussi, Emmanuel and Zhang, Ran and Igarashi, Takeo and Bickel, Bernd}, journal = {ACM Transaction on Graphics}, number = {4}, publisher = {ACM}, title = {{CoreCavity: Interactive shell decomposition for fabrication with two-piece rigid molds}}, doi = {10.1145/3197517.3201341}, volume = {37}, year = {2018}, } @article{13, abstract = {We propose a new method for fabricating digital objects through reusable silicone molds. Molds are generated by casting liquid silicone into custom 3D printed containers called metamolds. Metamolds automatically define the cuts that are needed to extract the cast object from the silicone mold. The shape of metamolds is designed through a novel segmentation technique, which takes into account both geometric and topological constraints involved in the process of mold casting. Our technique is simple, does not require changing the shape or topology of the input objects, and only requires off-the- shelf materials and technologies. We successfully tested our method on a set of challenging examples with complex shapes and rich geometric detail. © 2018 Association for Computing Machinery.}, author = {Alderighi, Thomas and Malomo, Luigi and Giorgi, Daniela and Pietroni, Nico and Bickel, Bernd and Cignoni, Paolo}, journal = {ACM Trans. Graph.}, number = {4}, publisher = {ACM}, title = {{Metamolds: Computational design of silicone molds}}, doi = {10.1145/3197517.3201381}, volume = {37}, year = {2018}, } @article{398, abstract = {Objective: To report long-term results after Pipeline Embolization Device (PED) implantation, characterize complex and standard aneurysms comprehensively, and introduce a modified flow disruption scale. Methods: We retrospectively reviewed a consecutive series of 40 patients harboring 59 aneurysms treated with 54 PEDs. Aneurysm complexity was assessed using our proposed classification. Immediate angiographic results were analyzed using previously published grading scales and our novel flow disruption scale. Results: According to our new definition, 46 (78%) aneurysms were classified as complex. Most PED interventions were performed in the paraophthalmic and cavernous internal carotid artery segments. Excellent neurologic outcome (modified Rankin Scale 0 and 1) was observed in 94% of patients. Our data showed low permanent procedure-related mortality (0%) and morbidity (3%) rates. Long-term angiographic follow-up showed complete occlusion in 81% and near-total obliteration in a further 14%. Complete obliteration after deployment of a single PED was achieved in all standard aneurysms with 1-year follow-up. Our new scale was an independent predictor of aneurysm occlusion in a multivariable analysis. All aneurysms with a high flow disruption grade showed complete occlusion at follow-up regardless of PED number or aneurysm complexity. Conclusions: Treatment with the PED should be recognized as a primary management strategy for a highly selected cohort with predominantly complex intracranial aneurysms. We further show that a priori assessment of aneurysm complexity and our new postinterventional angiographic flow disruption scale predict occlusion probability and may help to determine the adequate number of per-aneurysm devices.}, author = {Dodier, Philippe and Frischer, Josa and Wang, Wei and Auzinger, Thomas and Mallouhi, Ammar and Serles, Wolfgang and Gruber, Andreas and Knosp, Engelbert and Bavinzski, Gerhard}, journal = {World Neurosurgery}, pages = {e568--e578}, publisher = {Elsevier}, title = {{Immediate flow disruption as a prognostic factor after flow diverter treatment long term experience with the pipeline embolization device}}, doi = {10.1016/j.wneu.2018.02.096}, volume = {13}, year = {2018}, } @article{4, abstract = {We present a data-driven technique to instantly predict how fluid flows around various three-dimensional objects. Such simulation is useful for computational fabrication and engineering, but is usually computationally expensive since it requires solving the Navier-Stokes equation for many time steps. To accelerate the process, we propose a machine learning framework which predicts aerodynamic forces and velocity and pressure fields given a threedimensional shape input. Handling detailed free-form three-dimensional shapes in a data-driven framework is challenging because machine learning approaches usually require a consistent parametrization of input and output. We present a novel PolyCube maps-based parametrization that can be computed for three-dimensional shapes at interactive rates. This allows us to efficiently learn the nonlinear response of the flow using a Gaussian process regression. We demonstrate the effectiveness of our approach for the interactive design and optimization of a car body.}, author = {Umetani, Nobuyuki and Bickel, Bernd}, journal = {ACM Trans. Graph.}, number = {4}, publisher = {ACM}, title = {{Learning three-dimensional flow for interactive aerodynamic design}}, doi = {10.1145/3197517.3201325}, volume = {37}, year = {2018}, } @article{486, abstract = {Color texture reproduction in 3D printing commonly ignores volumetric light transport (cross-talk) between surface points on a 3D print. Such light diffusion leads to significant blur of details and color bleeding, and is particularly severe for highly translucent resin-based print materials. Given their widely varying scattering properties, this cross-talk between surface points strongly depends on the internal structure of the volume surrounding each surface point. Existing scattering-aware methods use simplified models for light diffusion, and often accept the visual blur as an immutable property of the print medium. In contrast, our work counteracts heterogeneous scattering to obtain the impression of a crisp albedo texture on top of the 3D print, by optimizing for a fully volumetric material distribution that preserves the target appearance. Our method employs an efficient numerical optimizer on top of a general Monte-Carlo simulation of heterogeneous scattering, supported by a practical calibration procedure to obtain scattering parameters from a given set of printer materials. Despite the inherent translucency of the medium, we reproduce detailed surface textures on 3D prints. We evaluate our system using a commercial, five-tone 3D print process and compare against the printer’s native color texturing mode, demonstrating that our method preserves high-frequency features well without having to compromise on color gamut.}, author = {Elek, Oskar and Sumin, Denis and Zhang, Ran and Weyrich, Tim and Myszkowski, Karol and Bickel, Bernd and Wilkie, Alexander and Krivanek, Jaroslav}, issn = {07300301}, journal = {ACM Transactions on Graphics}, number = {6}, publisher = {ACM}, title = {{Scattering-aware texture reproduction for 3D printing}}, doi = {10.1145/3130800.3130890}, volume = {36}, year = {2017}, } @inproceedings{1001, abstract = {We present a computational approach for designing CurveUps, curvy shells that form from an initially flat state. They consist of small rigid tiles that are tightly held together by two pre-stretched elastic sheets attached to them. Our method allows the realization of smooth, doubly curved surfaces that can be fabricated as a flat piece. Once released, the restoring forces of the pre-stretched sheets support the object to take shape in 3D. CurveUps are structurally stable in their target configuration. The design process starts with a target surface. Our method generates a tile layout in 2D and optimizes the distribution, shape, and attachment areas of the tiles to obtain a configuration that is fabricable and in which the curved up state closely matches the target. Our approach is based on an efficient approximate model and a local optimization strategy for an otherwise intractable nonlinear optimization problem. We demonstrate the effectiveness of our approach for a wide range of shapes, all realized as physical prototypes.}, author = {Guseinov, Ruslan and Miguel, Eder and Bickel, Bernd}, location = {Los Angeles, CA, United States}, number = {4}, publisher = {ACM}, title = {{CurveUps: Shaping objects from flat plates with tension-actuated curvature}}, doi = {10.1145/3072959.3073709}, volume = {36}, year = {2017}, } @inproceedings{1002, abstract = { We present an interactive design system to create functional mechanical objects. Our computational approach allows novice users to retarget an existing mechanical template to a user-specified input shape. Our proposed representation for a mechanical template encodes a parameterized mechanism, mechanical constraints that ensure a physically valid configuration, spatial relationships of mechanical parts to the user-provided shape, and functional constraints that specify an intended functionality. We provide an intuitive interface and optimization-in-the-loop approach for finding a valid configuration of the mechanism and the shape to ensure that higher-level functional goals are met. Our algorithm interactively optimizes the mechanism while the user manipulates the placement of mechanical components and the shape. Our system allows users to efficiently explore various design choices and to synthesize customized mechanical objects that can be fabricated with rapid prototyping technologies. We demonstrate the efficacy of our approach by retargeting various mechanical templates to different shapes and fabricating the resulting functional mechanical objects. }, author = {Zhang, Ran and Auzinger, Thomas and Ceylan, Duygu and Li, Wilmot and Bickel, Bernd}, issn = {07300301}, location = {Los Angeles, CA, United States }, number = {4}, publisher = {ACM}, title = {{Functionality-aware retargeting of mechanisms to 3D shapes}}, doi = {10.1145/3072959.3073710}, volume = {36}, year = {2017}, } @inproceedings{1097, abstract = {We present an interactive system for computational design, optimization, and fabrication of multicopters. Our computational approach allows non-experts to design, explore, and evaluate a wide range of different multicopters. We provide users with an intuitive interface for assembling a multicopter from a collection of components (e.g., propellers, motors, and carbon fiber rods). Our algorithm interactively optimizes shape and controller parameters of the current design to ensure its proper operation. In addition, we allow incorporating a variety of other metrics (such as payload, battery usage, size, and cost) into the design process and exploring tradeoffs between them. We show the efficacy of our method and system by designing, optimizing, fabricating, and operating multicopters with complex geometries and propeller configurations. We also demonstrate the ability of our optimization algorithm to improve the multicopter performance under different metrics.}, author = {Du, Tao and Schulz, Adriana and Zhu, Bo and Bickel, Bernd and Matusik, Wojciech}, location = {Macao, China}, number = {6}, publisher = {ACM}, title = {{Computational multicopter design}}, doi = {10.1145/2980179.2982427}, volume = {35}, year = {2016}, } @inproceedings{1099, abstract = {We present FlexMolds, a novel computational approach to automatically design flexible, reusable molds that, once 3D printed, allow us to physically fabricate, by means of liquid casting, multiple copies of complex shapes with rich surface details and complex topology. The approach to design such flexible molds is based on a greedy bottom-up search of possible cuts over an object, evaluating for each possible cut the feasibility of the resulting mold. We use a dynamic simulation approach to evaluate candidate molds, providing a heuristic to generate forces that are able to open, detach, and remove a complex mold from the object it surrounds. We have tested the approach with a number of objects with nontrivial shapes and topologies.}, author = {Malomo, Luigi and Pietroni, Nico and Bickel, Bernd and Cignoni, Paolo}, location = {Macao, China}, number = {6}, publisher = {ACM}, title = {{FlexMolds: Automatic design of flexible shells for molding}}, doi = {10.1145/2980179.2982397}, volume = {35}, year = {2016}, } @article{1446, abstract = {The accuracy of interdisciplinarity measurements is directly related to the quality of the underlying bibliographic data. Existing indicators of interdisciplinarity are not capable of reflecting the inaccuracies introduced by incorrect and incomplete records because correct and complete bibliographic data can rarely be obtained. This is the case for the Rao–Stirling index, which cannot handle references that are not categorized into disciplinary fields. We introduce a method that addresses this problem. It extends the Rao–Stirling index to acknowledge missing data by calculating its interval of uncertainty using computational optimization. The evaluation of our method indicates that the uncertainty interval is not only useful for estimating the inaccuracy of interdisciplinarity measurements, but it also delivers slightly more accurate aggregated interdisciplinarity measurements than the Rao–Stirling index.}, author = {Calatrava Moreno, Maria and Auzinger, Thomas and Werthner, Hannes}, journal = {Scientometrics}, number = {1}, pages = {213 -- 232}, publisher = {Springer}, title = {{On the uncertainty of interdisciplinarity measurements due to incomplete bibliographic data}}, doi = {10.1007/s11192-016-1842-4}, volume = {107}, year = {2016}, }