A Sliding-Mode Control Algorithm to Enhance In-Hand Motion Capabilities

This paper reports a method for regulating the internal forces during in hand manipulation of an unknown shaped object with soft robotic fingers. The internal forces ensure that the object does not move between the robotic fingers, thus improving the grip. It is shown that if soft fingers show bounded conformity and the finger-object interface have bounded relative slip, then the relative angular velocity between the object and the fingertip coordinate frame in contact is bounded. Detailed derivation of the proof is presented. The proof is used to define a new metric of relative slip. The metric is used to design a sliding mode control algorithm that results in an efficient grip which is robust towards uncertainty in object shape. The robotic fingers are assumed to be under virtual rigidity constraint, that is, the distance between the fingertips do not change. The control algorithm is attractive as it skirts the requirement of information of the shape of the object or to solve optimization problems. The grip with the robust control algorithm is shown to be finite-time stable through Lyapunov's method. The methodology is demonstrated using simulations.

Bubbly Recessions

We develop a tractable bubbles model with financial friction and downward wage rigidity. Competitive speculation in risky bubbles can result in excessive investment booms that precede inefficient busts, where post-bubble aggregate economic activities collapse below the pre-bubble trend. Risky bubbles can reduce ex ante social welfare, and leaning-against-the-bubble policies that balance the boom-bust trade-off can be warranted. We further show that the collapse of a bubble can push the economy into a “secular stagnation” equilibrium, where the zero lower bound and the nominal wage rigidity constraint bind, leading to a persistent recession, such as the Japanese “lost decades.” (JEL E22, E24, E32, E44, L26)

A Sliding-Mode Control Algorithm to Enhance In-Hand Motion Capabilities

This paper reports a method for regulating the internal forces during in hand manipulation of an unknown shaped object with soft robotic fingers. It is known that for the case of multifingered manipulation, a part of the forces applied by the fingers result in the motion of the object, whereas the other part is considered to be an internal force. The internal forces do not result in the motion of the object but are used to improve the grip on the object. For an object with unknown shape, the internal forces are regulated to ensure that the object does not slip off during manipulation. It is shown that if soft fingers show bounded conformity and the finger-object interface does not have relative slip (or a bounded slip), then the relative angular velocity between the object and the fingertip frame in contact is bounded. The proof is used to define of a new metric of relative slip. The metric is used to design a sliding mode control algorithm. The robotic fingers are assumed to be under virtual rigidity constraint, that is, the distance between the fingers do not change. The control algorithm is attractive as it skirts requirement of information of the shape of the object or to solve optimization problems. The control algorithm developed controls the internal forces and does not require the knowledge of the shape of the object. The methodology is simulated for the case of one spherical object and one conical object.

Failure Mode and Stability of Excavation Face on Shield Tunnel Undercrossing Existing Tunnel

The supporting pressure value of excavation face directly determines the stable state of excavation face, and its value will directly lead to instability of excavation face if the value is too small. When the shield is underneath the existing tunnel, special attention should be paid to the support pressure setting of the shield working face. When setting support pressure, the rigidity constraint of existing tunnel on surrounding soil should be fully considered. In this paper, we used ABAQUS software to analyse the failure mode of the soil around the existing tunnel due to the instability of the excavation surface caused by the small pressure setting of the excavation face, which is caused by the small pressure setting of the excavation face. By using the method of theoretical analysis, we optimized the prism in the traditional wedge model to chamfer platform with different opening angles to make it closer to the actual situation, and calculated the critical support pressure of shield tunnel face when it passes through the built tunnel. The research results can provide a reference for the effective value of support force of shield excavation face when the shield tunnel passes under the existing tunnel at a short distance.

Relative Performance of Body-Fitted and Fictitious Domain Simulations of Flow Through Porous Media

The relative performance of (i) a body-fitted unstructured grid Navier-Stokes solver [Moin and Apte, AIAA J. 2006], and (ii) a fictitious domain based finite-volume approach [Apte et al. JCP 2009] is examined for simulating flow through packed beds of spheres at moderate flow rates, 50 ≲ Re ≲ 1300. The latter employs non-body conforming Cartesian grids and enforces the no-slip conditions on the pore boundaries implicitly through a rigidity constraint force. At these flow rates, fluid inertia can result in complex steady and unsteady pore scale flow features that influence macro-scale properties. We examine the requirements on both methods to properly capture these features in both simple and complex arrangements of spheres. First, two prototypical test cases of flow through packed beds are studied thoroughly at a range of Reynolds numbers in the inertial flow regime. Next flow through a random packing of 51 spheres at Re = 1322 is simulated using both methods. The suitability of both approaches to the complex configurations observed in large randomly packed beds is discussed.

Reduced-order modeling by POD-multiphase approach for fluid-structure interaction

This paper describes the Reduced Order Modeling (ROM) for fluid rigid body interaction problem and discusses Proper Orthogonal Decomposition (POD) utilisation. The principal difficulty for using POD being the moving domains, a referenced fixed domain has been introduced. The POD has been applied for the velocity field obtained on the fixed domain. Then a method to reduce dynamical system for rigid body fluid interaction has been developed. This method consists in treating the entire fluid-solid domain as a fluid. The rigid body has then been considered as a fluid, by using a high viscosity which can play the role of a penalisation factor of the rigidity constraint. The fluid flow problem is then formulated on the reference domain and POD modes have been used in the weak formulation.