DiffPD: Differentiable Projective Dynamics

We present a novel, fast differentiable simulator for soft-body learning and control applications. Existing differentiable soft-body simulators can be classified into two categories based on their time integration methods: Simulators using explicit timestepping schemes require tiny timesteps to avoid numerical instabilities in gradient computation, and simulators using implicit time integration typically compute gradients by employing the adjoint method and solving the expensive linearized dynamics. Inspired by Projective Dynamics ( PD ), we present Differentiable Projective Dynamics ( DiffPD ), an efficient differentiable soft-body simulator based on PD with implicit time integration. The key idea in DiffPD is to speed up backpropagation by exploiting the prefactorized Cholesky decomposition in forward PD simulation. In terms of contact handling, DiffPD supports two types of contacts: a penalty-based model describing contact and friction forces and a complementarity-based model enforcing non-penetration conditions and static friction. We evaluate the performance of DiffPD and observe it is 4–19 times faster compared with the standard Newton’s method in various applications including system identification, inverse design problems, trajectory optimization, and closed-loop control. We also apply DiffPD in a reality-to-simulation ( real-to-sim ) example with contact and collisions and show its capability of reconstructing a digital twin of real-world scenes.

Air drag coefficient of textile-covered elastic cylinders – preliminary aerodynamic studies

This paper presents preliminary experimental results on the influence on the aerodynamic drag of a cylinder from the cylinder type (i.e., rigid or soft) and its textile surface. Both a rigid cylinder and a soft-body cylinder, with a gelatin layer, each with five different textile surfaces were measured in the wind tunnel using force measurement technology. The drag coefficient was determined for several Reynolds numbers. The study shows that the elasticity of a cylinder has a significant influence on the drag force and the airflow type. However, the influence of the soft-body cylinder depends on the respective fabric. With the given measurements, no exact statements can yet be made to quantify the influence. This influence must be studied independently and in conjunction with the textile surface in order to gain understanding of the overall system of airflow, textile and elastic body.

Correlative tomography of an exceptionally preserved Jurassic ammonite implies hyponome-propelled swimming

The extreme rarity of soft-tissue preservation in ammonoids has meant there are open questions regarding fundamental aspects of their biology. We report an exceptionally preserved Middle Jurassic ammonite with unrivaled information on soft-body organization interpreted through correlative neutron and X-ray tomography. Three-dimensional imaging of muscles and organs of the body mass for the first time in this iconic fossil group provides key insights into functional morphology. We show that paired dorsal muscles withdrew the body into the shell, rather than acting with the funnel controlling propulsion as in Nautilus. This suggests a mobile, retractable body as a defense strategy and necessitates a distinct swimming mechanism of hyponome propulsion, a trait that we infer evolved early in the ammonoid-coleoid lineage.

Worn Out or Worn In?

<p>Worn out or worn in started with the creation of a building. For an industrial designer, this was unfamiliar territory. Through working with a specific site came the recognition of the potential of weathering to add a unique quality to the design that goes beyond its initial concept. The inclusion of this potential in the design required a projection into the future and an acceptance of the inevitability of influences that could not be fully controlled. Rain, sun, footprints and cobwebs would all add or subtract to the initially simplistic design concept. It was another realm of design: a 4 dimensional one. Where does the equivalent of weathering exist within the familiar scale of mass produced products? It is in the interaction between the body and the products through use. The potential of this interaction to add another dimension to a design forms the core of this research. The body is a complex site: fluid, directed, precarious, yet nurturing. While it may at first seem unreasonable that the soft body could erode hard, seemingly durable materials, the evidence is all around us. Though it works at a time scale that is almost invisible to our everyday perception, over time the evidence is recorded in our products. Through research by reading, observing, designing, making and unmaking products, the concept of designs embedded within products has emerged. Like a box of chocolates with a series of layers, this research addresses how the wearing away of one layer can reveal the existence of another.</p>

Worn Out or Worn In?

<p>Worn out or worn in started with the creation of a building. For an industrial designer, this was unfamiliar territory. Through working with a specific site came the recognition of the potential of weathering to add a unique quality to the design that goes beyond its initial concept. The inclusion of this potential in the design required a projection into the future and an acceptance of the inevitability of influences that could not be fully controlled. Rain, sun, footprints and cobwebs would all add or subtract to the initially simplistic design concept. It was another realm of design: a 4 dimensional one. Where does the equivalent of weathering exist within the familiar scale of mass produced products? It is in the interaction between the body and the products through use. The potential of this interaction to add another dimension to a design forms the core of this research. The body is a complex site: fluid, directed, precarious, yet nurturing. While it may at first seem unreasonable that the soft body could erode hard, seemingly durable materials, the evidence is all around us. Though it works at a time scale that is almost invisible to our everyday perception, over time the evidence is recorded in our products. Through research by reading, observing, designing, making and unmaking products, the concept of designs embedded within products has emerged. Like a box of chocolates with a series of layers, this research addresses how the wearing away of one layer can reveal the existence of another.</p>