@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{452, abstract = {Spinning tops and yo-yos have long fascinated cultures around the world with their unexpected, graceful motions that seemingly elude gravity. Yet, due to the exceeding difficulty of creating stably spinning objects of asymmetric shape in a manual trial-and-error process, there has been little departure from rotationally symmetric designs. With modern 3D printing technologies, however, we can manufacture shapes of almost unbounded complexity at the press of a button, shifting this design complexity toward computation. In this article, we describe an algorithm to generate designs for spinning objects by optimizing their mass distribution: as input, the user provides a solid 3D model and a desired axis of rotation. Our approach then modifies the interior mass distribution such that the principal directions of the moment of inertia align with the target rotation frame. To create voids inside the model, we represent its volume with an adaptive multiresolution voxelization and optimize the discrete voxel fill values using a continuous, nonlinear formulation. We further optimize for rotational stability by maximizing the dominant principal moment. Our method is well-suited for a variety of 3D printed models, ranging from characters to abstract shapes. We demonstrate tops and yo-yos that spin surprisingly stably despite their asymmetric appearance.}, author = {Bächer, Moritz and Bickel, Bernd and Whiting, Emily and Sorkine Hornung, Olga}, journal = {Communications of the ACM}, number = {8}, pages = {92 -- 99}, publisher = {ACM}, title = {{Spin it: Optimizing moment of inertia for spinnable objects}}, doi = {10.1145/3068766}, volume = {60}, 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}, } @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 = {0730-0301}, 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{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 = {0730-0301}, 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{1364, abstract = {We present a computational method for designing wire sculptures consisting of interlocking wires. Our method allows the computation of aesthetically pleasing structures that are structurally stable, efficiently fabricatable with a 2D wire bending machine, and assemblable without the need of additional connectors. Starting from a set of planar contours provided by the user, our method automatically tests for the feasibility of a design, determines a discrete ordering of wires at intersection points, and optimizes for the rest shape of the individual wires to maximize structural stability under frictional contact. In addition to their application to art, wire sculptures present an extremely efficient and fast alternative for low-fidelity rapid prototyping because manufacturing time and required material linearly scales with the physical size of objects. We demonstrate the effectiveness of our approach on a varied set of examples, all of which we fabricated.}, author = {Miguel Villalba, Eder and Lepoutre, Mathias and Bickel, Bernd}, location = {Anaheim, CA, USA}, number = {4}, publisher = {ACM}, title = {{Computational design of stable planar-rod structures}}, doi = {10.1145/2897824.2925978}, volume = {35}, year = {2016}, } @article{1414, abstract = {In this paper, we present a method to model hyperelasticity that is well suited for representing the nonlinearity of real-world objects, as well as for estimating it from deformation examples. Previous approaches suffer several limitations, such as lack of integrability of elastic forces, failure to enforce energy convexity, lack of robustness of parameter estimation, or difficulty to model cross-modal effects. Our method avoids these problems by relying on a general energy-based definition of elastic properties. The accuracy of the resulting elastic model is maximized by defining an additive model of separable energy terms, which allow progressive parameter estimation. In addition, our method supports efficient modeling of extreme nonlinearities thanks to energy-limiting constraints. We combine our energy-based model with an optimization method to estimate model parameters from force-deformation examples, and we show successful modeling of diverse deformable objects, including cloth, human finger skin, and internal human anatomy in a medical imaging application.}, author = {Miguel Villalba, Eder and Miraut, David and Otaduy, Miguel}, journal = {Computer Graphics Forum}, number = {2}, pages = {385 -- 396}, publisher = {Wiley-Blackwell}, title = {{Modeling and estimation of energy-based hyperelastic objects}}, doi = {10.1111/cgf.12840}, 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}, } @inproceedings{1319, abstract = {We present a novel optimization-based algorithm for the design and fabrication of customized, deformable input devices, capable of continuously sensing their deformation. We propose to embed piezoresistive sensing elements into flexible 3D printed objects. These sensing elements are then utilized to recover rich and natural user interactions at runtime. Designing such objects is a challenging and hard problem if attempted manually for all but the simplest geometries and deformations. Our method simultaneously optimizes the internal routing of the sensing elements and computes a mapping from low-level sensor readings to user-specified outputs in order to minimize reconstruction error. We demonstrate the power and flexibility of the approach by designing and fabricating a set of flexible input devices. Our results indicate that the optimization-based design greatly outperforms manual routings in terms of reconstruction accuracy and thus interaction fidelity.}, author = {Bächer, Moritz and Hepp, Benjamin and Pece, Fabrizio and Kry, Paul and Bickel, Bernd and Thomaszewski, Bernhard and Hilliges, Otmar}, location = {San Jose, California, USA}, pages = {3806 -- 3816}, publisher = {ACM}, title = {{DefSense: computational design of customized deformable input devices}}, doi = {10.1145/2858036.2858354}, year = {2016}, } @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}, } @inproceedings{1520, abstract = {Creating mechanical automata that can walk in stable and pleasing manners is a challenging task that requires both skill and expertise. We propose to use computational design to offset the technical difficulties of this process. A simple drag-and-drop interface allows casual users to create personalized walking toys from a library of pre-defined template mechanisms. Provided with this input, our method leverages physical simulation and evolutionary optimization to refine the mechanical designs such that the resulting toys are able to walk. The optimization process is guided by an intuitive set of objectives that measure the quality of the walking motions. We demonstrate our approach on a set of simulated mechanical toys with different numbers of legs and various distinct gaits. Two fabricated prototypes showcase the feasibility of our designs.}, author = {Bharaj, Gaurav and Coros, Stelian and Thomaszewski, Bernhard and Tompkin, James and Bickel, Bernd and Pfister, Hanspeter}, isbn = {978-1-4503-3496-9}, location = {Los Angeles, CA, United States}, pages = {93 -- 100}, publisher = {ACM}, title = {{Computational design of walking automata}}, doi = {10.1145/2786784.2786803}, year = {2015}, } @inproceedings{1625, abstract = {In recent years we have seen numerous improvements on 3D scanning and tracking of human faces, greatly advancing the creation of digital doubles for film and video games. However, despite the high-resolution quality of the reconstruction approaches available, current methods are unable to capture one of the most important regions of the face - the eye region. In this work we present the first method for detailed spatio-temporal reconstruction of eyelids. Tracking and reconstructing eyelids is extremely challenging, as this region exhibits very complex and unique skin deformation where skin is folded under while opening the eye. Furthermore, eyelids are often only partially visible and obstructed due to selfocclusion and eyelashes. Our approach is to combine a geometric deformation model with image data, leveraging multi-view stereo, optical flow, contour tracking and wrinkle detection from local skin appearance. Our deformation model serves as a prior that enables reconstruction of eyelids even under strong self-occlusions caused by rolling and folding skin as the eye opens and closes. The output is a person-specific, time-varying eyelid reconstruction with anatomically plausible deformations. Our high-resolution detailed eyelids couple naturally with current facial performance capture approaches. As a result, our method can largely increase the fidelity of facial capture and the creation of digital doubles.}, author = {Bermano, Amit and Beeler, Thabo and Kozlov, Yeara and Bradley, Derek and Bickel, Bernd and Gross, Markus}, location = {Los Angeles, CA, United States}, number = {4}, publisher = {ACM}, title = {{Detailed spatio-temporal reconstruction of eyelids}}, doi = {10.1145/2766924}, volume = {34}, year = {2015}, } @inproceedings{1626, abstract = {This paper introduces "OmniAD," a novel data-driven pipeline to model and acquire the aerodynamics of three-dimensional rigid objects. Traditionally, aerodynamics are examined through elaborate wind tunnel experiments or expensive fluid dynamics computations, and are only measured for a small number of discrete wind directions. OmniAD allows the evaluation of aerodynamic forces, such as drag and lift, for any incoming wind direction using a novel representation based on spherical harmonics. Our datadriven technique acquires the aerodynamic properties of an object simply by capturing its falling motion using a single camera. Once model parameters are estimated, OmniAD enables realistic realtime simulation of rigid bodies, such as the tumbling and gliding of leaves, without simulating the surrounding air. In addition, we propose an intuitive user interface based on OmniAD to interactively design three-dimensional kites that actually fly. Various nontraditional kites were designed to demonstrate the physical validity of our model.}, author = {Martin, Tobias and Umetani, Nobuyuki and Bickel, Bernd}, location = {Los Angeles, CA, United States}, number = {4}, publisher = {ACM}, title = {{OmniAD: Data-driven omni-directional aerodynamics}}, doi = {10.1145/2766919}, volume = {34}, year = {2015}, } @inproceedings{1627, abstract = {We present a computational tool for fabrication-oriented design of flexible rod meshes. Given a deformable surface and a set of deformed poses as input, our method automatically computes a printable rod mesh that, once manufactured, closely matches the input poses under the same boundary conditions. The core of our method is formed by an optimization scheme that adjusts the cross-sectional profiles of the rods and their rest centerline in order to best approximate the target deformations. This approach allows us to locally control the bending and stretching resistance of the surface with a single material, yielding high design flexibility and low fabrication cost.}, author = {Pérez, Jesús and Thomaszewski, Bernhard and Coros, Stelian and Bickel, Bernd and Canabal, José and Sumner, Robert and Otaduy, Miguel}, location = {Los Angeles, CA, United States}, number = {4}, publisher = {ACM}, title = {{Design and fabrication of flexible rod meshes}}, doi = {10.1145/2766998}, volume = {34}, year = {2015}, } @inproceedings{1628, abstract = {We propose a method for fabricating deformable objects with spatially varying elasticity using 3D printing. Using a single, relatively stiff printer material, our method designs an assembly of smallscale microstructures that have the effect of a softer material at the object scale, with properties depending on the microstructure used in each part of the object. We build on work in the area of metamaterials, using numerical optimization to design tiled microstructures with desired properties, but with the key difference that our method designs families of related structures that can be interpolated to smoothly vary the material properties over a wide range. To create an object with spatially varying elastic properties, we tile the object's interior with microstructures drawn from these families, generating a different microstructure for each cell using an efficient algorithm to select compatible structures for neighboring cells. We show results computed for both 2D and 3D objects, validating several 2D and 3D printed structures using standard material tests as well as demonstrating various example applications.}, author = {Schumacher, Christian and Bickel, Bernd and Rys, Jan and Marschner, Steve and Daraio, Chiara and Gross, Markus}, location = {Los Angeles, CA, USA}, number = {4}, publisher = {ACM}, title = {{Microstructures to control elasticity in 3D printing}}, doi = {10.1145/2766926}, volume = {34}, year = {2015}, } @article{1734, abstract = {Facial appearance capture is now firmly established within academic research and used extensively across various application domains, perhaps most prominently in the entertainment industry through the design of virtual characters in video games and films. While significant progress has occurred over the last two decades, no single survey currently exists that discusses the similarities, differences, and practical considerations of the available appearance capture techniques as applied to human faces. A central difficulty of facial appearance capture is the way light interacts with skin-which has a complex multi-layered structure-and the interactions that occur below the skin surface can, by definition, only be observed indirectly. In this report, we distinguish between two broad strategies for dealing with this complexity. "Image-based methods" try to exhaustively capture the exact face appearance under different lighting and viewing conditions, and then render the face through weighted image combinations. "Parametric methods" instead fit the captured reflectance data to some parametric appearance model used during rendering, allowing for a more lightweight and flexible representation but at the cost of potentially increased rendering complexity or inexact reproduction. The goal of this report is to provide an overview that can guide practitioners and researchers in assessing the tradeoffs between current approaches and identifying directions for future advances in facial appearance capture.}, author = {Klehm, Oliver and Rousselle, Fabrice and Papas, Marios and Bradley, Derek and Hery, Christophe and Bickel, Bernd and Jarosz, Wojciech and Beeler, Thabo}, journal = {Computer Graphics Forum}, number = {2}, pages = {709 -- 733}, publisher = {Wiley-Blackwell}, title = {{Recent advances in facial appearance capture}}, doi = {10.1111/cgf.12594}, volume = {34}, year = {2015}, }