Eldorado - Repository of the TU Dortmund
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AnaConDaR: anatomically-constrained data-adaptive facial retargeting
(2024-06-27) Wagner, Nicolas; Schwanecke, Ulrich; Botsch, Mario
Offline facial retargeting, i.e., transferring facial expressions from a source to a target character, is a common production task that still regularly leads to considerable algorithmic challenges. This task can be roughly dissected into the transfer of sequential facial animations and non-sequential blendshape personalization. Both problems are typically solved by data-driven methods that require an extensive corpus of costly target examples. Other than that, geometrically motivated approaches do not require intensive data collection but cannot account for character-specific deformations and are known to cause manifold visual artifacts.
We present AnaConDaR, a novel method for offline facial retargeting, as a hybrid of data-driven and geometry-driven methods that incorporates anatomical constraints through a physics-based simulation. As a result, our approach combines the advantages of both paradigms while balancing out the respective disadvantages. In contrast to other recent concepts, AnaConDaR achieves substantially individualized results even when only a handful of target examples are available. At the same time, we do not make the common assumption that for each target example a matching source expression must be known. Instead, AnaConDaR establishes correspondences between the source and the target character by a data-driven embedding of the target examples in the source domain. We evaluate our offline facial retargeting algorithm visually, quantitatively, and in two user studies.
Amtliche Mitteilungen der Technischen Universität Dortmund Nr. 32/2025
(Technische Universität Dortmund, 2025-11-13)
A generalized, computationally versatile plasticity model framework - part II: theory and verification focusing on shear anisotropy
(2024-10-28) Hou, Yong; Min, Junying; Lee, Hyung-Rim; Ha, Jinjin; Park, Namsu; Lee, Myoung-Gyu
Shear-dominated deformation (SHDD) is pivotal in sheet metal forming; however, comprehensive modeling of plastic anisotropy in SHDD, specifically shear anisotropy considering both yield stress and plastic flow, has been inadequately addressed in existing literature. In this work, a generalized constitutive framework is introduced on the basis of stress triaxiality-dependent state variable to accurately emulate plastic anisotropy and the physics-based shear constraint in SHDD. The framework is capable to seamlessly integrate with existing yield criteria, preserving computational efficiency and versatility. Notably, the yield function, anisotropic parameters, and their optimization or analytical determination for the non-shear deformation state remain unaltered. When integrated with the Hill48 yield function, featuring either one or two anisotropic parameters within the generalized constitutive framework, precise characterization of yield strength and plastic flow in SHDD is achieved. The applicability of the framework extends to various anisotropic yield functions such as the widely employed Yld2k-2d and the sixth-order polynomial (Poly6) function as a class of associated flow rule-based yield functions, and one non-quadratic yield function for non-associated flow rule scenarios. Experimental validation with two engineering sheet metals, high-strength dual-phase steel DP980 and high-strength aluminum alloy AA7075-T6, was conducted. Comparative analyses with several recently proposed yield criteria, especially Poly6–18p, highlighted the efficiency of the proposed constitutive framework. Furthermore, this study explores intrinsic shear constraints, particularly the absence of through-thickness strains under in-plane shear stress. Additionally, it offers an enhanced description of plastic anisotropy in shear yield stress within the general framework, providing valuable insights into the complexities of SHDD.
An ADP framework for flexibility and cost aggregation: guarantees and open problems
(2024-06-27) Beraldo Bandeira, Maísa; Faulwasser, Timm; Engelmann, Alexander
With the increasing amount of Distributed Energy Resources (DERs), coordination of Distribution Grid Operators (DSOs) and Transmission Grid Operators (TSOs) is of paramount importance. Managing a large number of DERs at the TSO level is, however, challenging. To address this problem, flexibility aggregation is a topic of frequent research activities. Aggregation means to describe the combined flexibility of the DERs at the vertical grid coupling between DSO and TSO. Existing works are often limited with respect to guaranteeing feasibility, with respect to efficient numerical implementation, and in terms of quantification of the cost of DER usage. In the present paper, we investigate aggregation based on Approximate Dynamic Programming (ADP). We propose efficient numerical aggregation schemes using tools from computational geometry thus avoiding the need to solve multiple OPF problems. We rely on different variants of the DistFlow model for radial grids, which are computationally efficient. This allows to model of current and voltage limits and enables the consideration of voltage dependencies in the aggregation. Furthermore, we propose a method for cost aggregation and identify open problems of flexibility aggregation.
Advancing the aqueous biphasic hydroformylation of oleochemicals in the loop: continuous reaction and separation using a jet-loop reactor concept
(2024-05-17) Roth, T. F. H.; Häusler, M.; Vogt, D.; Seidensticker, T.
The hydroformylation of renewable oleochemicals in aqueous liquid-liquid multiphase systems was operated continuously using a jet-loop reactor concept, demonstrated in two case studies. The main challenge on this path was to find an optimal compromise between activity and catalyst retention. In Case 1, methyl oleate was converted in an isopropanol/water system with stationary yields of up to 35 % in more than 55 hours of continuous operation at low catalyst loss of only 0.1 %/h and very high selectivity. In Case 2, a reaction system consisting of butanol/water was used to convert methyl 10-undecenoate. Fine-tuning of the substrate loading and separation temperature was required. Under optimised reaction conditions, steady-state yields of >80 % were achieved in a campaign of >55 hours of continuous operation. As little as 16.7 mg of rhodium was leached per kilogram of product formed at excellent selectivities to the linear product. This is the first time a miniplant concept has been presented that enables the hydroformylation of these two renewables in continuous operation.