Simulation of hyperelastic materials in real-time using Deep Learning

The finite element method (FEM) is among the most commonly used numerical methods for solving engineering problems. Due to its computational cost, various ideas have been introduced to reduce computation times, such as domain decomposition, parallel computing, adaptive meshing, and model order reduction. In this paper we present U-Mesh: a data-driven method based on a U-Net architecture that approximates the non-linear relation between a contact force and the displacement field computed by a FEM algorithm. We show that deep learning, one of the latest machine learning methods based on artificial neural networks, can enhance computational mechanics through its ability to encode highly non-linear models in a compact form. Our method is applied to two benchmark examples: a cantilever beam and an L-shape subject to moving punctual loads. A comparison between our method and proper orthogonal decomposition (POD) is done through the paper. The results show that U-Mesh can perform very fast simulations on various geometries, mesh resolutions and number of input forces with very small errors

Haptic rendering of complex deformations through handle-space force linearization

The force-update-rate requirements of transparent rendering of vir-tual environments are in conflict with the computational cost re-quired for computing complex interactions between deforming ob-jects. In this paper we introduce a novel method for satisfying high force update rates with deformable objects, yet retaining the visual quality of complex deformations and interactions. The objects that are haptically manipulated may have many de-grees of freedom, but haptic interaction is often implemented in practice through low-dimensional force-feedback devices. We ex-ploit the low-dimensional domain of the interaction for devising a novel linear approximation of interaction forces that can be ef-ficiently evaluated at force-update rates. Moreover, our linearized force model is time-implicit, which implies that it accounts for con-tact constraints and the internal dynamics of deforming objects. In this paper we show examples of haptic interaction in complex sit-uations such as large deformations, collision between deformable objects (with friction), or even self-collision

Passive set-position modulation approach for haptics with slow, variable, and asynchronous update

We consider the following problem in haptics: information update from the virtual world is slow w.r.t. the local servo-loop rate of the haptic device, and the information transmission/update between the haptic device and the virtual world is of variable rate and/or asyn-chronous. For this, we propose a novel control framework, that, by relying on our recently proposed passive set-position modulation (PSPM) and discrete-time passive non-iterative integrators, enables us to enforce two-port hybrid (i.e. continuous-discrete) passivity for such slow and variable/asynchronous haptics as well as to separate the virtual world simulation design from the device’s servo-loop tuning. Relevant experimental results are also presented.

Efficient Collision Detection for Brittle Fracture

International audienceIn complex scenes with many objects, collision detection plays a key role in the simulation performance. This is particularly true for fracture simulation, where multiple new objects are dynamically created. In this paper, we present novel algorithms and data structures for collision detection in real-time brittle fracture simulations. We build on a combination of well-known efficient data structures, namely distance fields and sphere trees, making our algorithm easy to integrate on existing simulation engines. We propose novel methods to construct these data structures, such that they can be efficiently updated upon fracture events and integrated in a simple yet effective self-adapting contact selection algorithm. Altogether, we drastically reduce the cost of both collision detection and collision response. We have evaluated our global solution for collision detection on challenging scenarios, achieving high frame rates suited for hard real-time applications such as video games or haptics. Our solution opens promising perspectives for complex brittle fracture simulations involving many dynamically created objects

Real‐time interaction of virtual and physical objects in mixed reality applications

We present a real-time method for computing the mechanical interaction between real and virtual objects in an augmented reality environment. Using model order reduction methods we are able to estimate the physical behavior of deformable objects in real time, with the precision of a high-fidelity solver but working at the speed of a video sequence. We merge tools of machine learning, computer vision, and computer graphics in a single application to describe the behavior of deformable virtual objects allowing the user to interact with them in a natural way. Three examples are provided to test the performance of the method.Ministerio de Ciencia e Innovación, Grant/Award Number: CICYT-DPI2017-85139-C2-1-

Data-driven simulation for augmented surgery

International audienceTo build an augmented view of an organ during surgery, it is essential to have a biomechanical model with appropriate material parameters and boundary conditions , able to match patient specific properties. Adaptation to the patient's anatomy is obtained by exploiting the image-rich context specific to our application domain. While information about the organ shape, for instance, can be obtained preoper-atively, other patient-specific parameters can only be determined intraoperatively. To this end, we are developing data-driven simulations, which exploit information extracted from a stream of medical images. Such simulations need to run in real-time. To this end we have developed dedicated numerical methods, which allow for real-time computation of finite element simulations. The general principle consists in combining finite element approaches with Bayesian methods or deep learning techniques, that allow to keep control over the underlying computational model while allowing for inputs from the real world. Based on a priori knowledge of the mechanical behavior of the considered organ, we select a constitutive law to model its deformations. The predictive power of such constitutive law highly depends on the knowledge of the material parameters and A. Mendizaba

Sanal heykeltraşlıkta optimize edilmiş hash-temelli octree veri yapısının kullanılması

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Sanal heykeltıraşlık, kullanıcılara sanat, tasarım ve hızlı prototipleme alanlarında sanal gerçeklik donanım ve yazılımları tarafından sağlanan bir sanal dünya içerisinde yeni 3B katı nesne oluşturma veya mevcut nesneleri değiştirebilme imkânı sağlayan 3B bir modelleme işlemidir. Bu tez çalışmasında haptic kuvvet geri-beslemesi ile voksel-temelli bir sanal heykeltıraşlık uygulaması için optimize edilmiş hash-temelli bir octree veri yapısı kullanımı önerilmektedir. Amaç, hacim voksel veri kümesini saklamak için gerekli hafızayı ve hesaplama maliyetini düşürmek, aynı zamanda da gerçek-zamanda etkileşim esnasında gerçekleşen octree kullanımından doğan ağaç dolanım süresini azaltarak model yüzeyinin lokal olarak yeniden oluşturulma süresini kısaltmaktır. İlk önce, üzerinde çalışılan sanal ham maddeye ait hacim verisi daha az hafıza kullanarak saklayabilmek ve gerçek-zamanda yontabilmek amacıyla vokselleştirilerek optimize-edilmiş hash-temelli bir octree veri yapısına dönüştürülmektedir. Daha sonra, küre olarak tasarlanan sanal araç tarafından heykelin hangi voksellerine dokunulduğu belirlenerek bu vokseller veri yapısından çıkarılmaktadır. Sonuç verisine gerçekçi bir görüntü verebilmek amacıyla üçgen kafes modelini yeniden oluşturmak için Marching Cubes algoritması kullanılmaktadır. Tüm hacim için hesaplama maliyeti yüksek olduğundan dolayı bu çalışmada sadece yontma işleminden sonra modifiye edilen vokseller tarafından etkilenen eş yüzey yeniden hesaplanarak lokal güncelleme gerçekleştirildi. İkinci olarak, önerilen sanal heykeltıraşlık sistemine, sanal yontma aracının üç-boyutlu kontrolünü sağlamak ve kullanıcıların yontma işlemi sırasında heykel üzerinde uyguladıkları kuvvete karşı meydana gelen direnci hissedebilmelerine imkan sağlamak amacıyla bir haptic cihazı yolu ile haptic kuvvet-geri beslemesi entegre edilmiştir. Sanal heykeltıraşlıkta hafıza optimizasyonu ve gerçek-zaman etkileşimi üzerine odaklanılan bu çalışmada, önerilen optimize edilmiş hash-temelli octree veri yapısının performansını test etmek amacıyla hafıza maliyetleri ve çalışma süreleri, işaretçi-temelli ve hash temelli veri yapıları ile karşılaştırılmıştır. Sonuç olarak, bu yeni optimize edilmiş hash-temelli octree veri yapısının hem ön-işleme zamanında hem de gerçek zamanda hafıza maliyetleri ve çalışma sürelerindeki düşüşler gösterilmiştir. Anahtar kelimeler: Sanal Heykeltaşlık, Haptics, Vokselleştirme, Octree, HashingVirtual sculpting is a 3D modelling process which allows users to create new 3D solid models or modify existing objects provided by virtual reality software and hardware in art, design and rapid prototyping areas. In this thesis, an optimized hash-based octree data structure in a voxel-based virtual sculpting application with haptic force feedback is proposed. The goal is to reduce the memory and computation costs to store volumetric voxel dataset and also to reduce the local surface reconstruction times of the model by decreasing tree traversal time caused by octree during real-time interaction. First, in order to store with less memory and carve in real-time, volumetric data of virtual workpiece is converted into an optimized hash-based octree data structure by voxelizing them. Then, voxels collided with the carving tool that is designed as a sphere are removed from this data structure. Marching Cubes algorithm is used to reconstruct the triangular mesh model in order to give a realistic display of the voxel data. Since the computational cost is very high for the whole volume, in this study, local update is performed by reconstructing the isosurface affected from the modified voxels after carving process. Afterwards, by the way of a haptic device, a haptic force feedback is integrated in the proposed virtual sculpting application in order to provide 3D control of the virtual tool and allow to feel the resistance against the applied force on the sculpture object. This study focused on memory optimization and real-time interaction, memory costs and runtimes of the proposed optimized hash-based octree data structure are compared with the pointer-based and hash-based ones in order to test the performance. Consequently, memory cost and working time decreases on both pre-processing and runtime of this new optimized hash-based octree data structure are shown. Keywords: Virtual Sculpting, Haptics, Voxelization, Octree, Hashin