On the Importance of Displacement History in Soft-Body Contact Models

Two approaches are commonly used for handling frictional contact within the framework of the discrete element method (DEM). One relies on the complementarity method (CM) to enforce a nonpenetration condition and the Coulomb dry-friction model at the interface between two bodies in mutual contact. The second approach, called the penalty method (PM), invokes an elasticity argument to produce a frictional contact force that factors in the local deformation and relative motion of the bodies in contact. We give a brief presentation of a DEM-PM contact model that includes multi-time-step tangential contact displacement history. We show that its implementation in an open-source simulation capability called Chrono is capable of accurately reproducing results from physical tests typical of the field of geomechanics, i.e., direct shear tests on a monodisperse material. Keeping track of the tangential contact displacement history emerges as a key element of the model. We show that identical simulations using contact models that include either no tangential contact displacement history or only single-time-step tangential contact displacement history are unable to accurately model the direct shear test

Analysis of A Splitting Approach for the Parallel Solution of Linear Systems on GPU Cards

We discuss an approach for solving sparse or dense banded linear systems ${\bf A} {\bf x} = {\bf b}$ on a Graphics Processing Unit (GPU) card. The matrix ${\bf A} \in {\mathbb{R}}^{N \times N}$ is possibly nonsymmetric and moderately large; i.e., $10000 \leq N \leq 500000$. The ${\it split\ and\ parallelize}$(${\tt SaP}$) approach seeks to partition the matrix${\bf A}$into diagonal sub-blocks${\bf A}_i$,$i=1,\ldots,P$, which are independently factored in parallel. The solution may choose to consider or to ignore the matrices that couple the diagonal sub-blocks${\bf A}_i$. This approach, along with the Krylov subspace-based iterative method that it preconditions, are implemented in a solver called${\tt SaP::GPU}$, which is compared in terms of efficiency with three commonly used sparse direct solvers:${\tt PARDISO}$,${\tt SuperLU}$, and${\tt MUMPS}$.${\tt SaP::GPU}$, which runs entirely on the GPU except several stages involved in preliminary row-column permutations, is robust and compares well in terms of efficiency with the aforementioned direct solvers. In a comparison against Intel's${\tt MKL}$,${\tt SaP::GPU}$also fares well when used to solve dense banded systems that are close to being diagonally dominant.${\tt SaP::GPU}$ is publicly available and distributed as open source under a permissive BSD3 license.Comment: 38 page

High-Performance Modeling and Simulation of Anchoring in Granular Media for NEO Applications

NASA is interested in designing a spacecraft capable of visiting a near-Earth object (NEO), performing experiments, and then returning safely. Certain periods of this mission would require the spacecraft to remain stationary relative to the NEO, in an environment characterized by very low gravity levels; such situations require an anchoring mechanism that is compact, easy to deploy, and upon mission completion, easy to remove. The design philosophy used in this task relies on the simulation capability of a high-performance multibody dynamics physics engine. On Earth, it is difficult to create low-gravity conditions, and testing in low-gravity environments, whether artificial or in space, can be costly and very difficult to achieve. Through simulation, the effect of gravity can be controlled with great accuracy, making it ideally suited to analyze the problem at hand. Using Chrono::Engine, a simulation pack age capable of utilizing massively parallel Graphic Processing Unit (GPU) hardware, several validation experiments were performed. Modeling of the regolith interaction has been carried out, after which the anchor penetration tests were performed and analyzed. The regolith was modeled by a granular medium composed of very large numbers of convex three-dimensional rigid bodies, subject to microgravity levels and interacting with each other with contact, friction, and cohesional forces. The multibody dynamics simulation approach used for simulating anchors penetrating a soil uses a differential variational inequality (DVI) methodology to solve the contact problem posed as a linear complementarity method (LCP). Implemented within a GPU processing environment, collision detection is greatly accelerated compared to traditional CPU (central processing unit)- based collision detection. Hence, systems of millions of particles interacting with complex dynamic systems can be efficiently analyzed, and design recommendations can be made in a much shorter time. The figure shows an example of this capability where the Brazil Nut problem is simulated: as the container full of granular material is vibrated, the large ball slowly moves upwards. This capability was expanded to account for anchors of different shapes and penetration velocities, interacting with granular soils

Contracting Out Public Property Assets

Public property assets are subject exclusively to the legal regime of public law, which are inalienable, imprescriptible and imperceptible. According to the law, publicly owned property can be contracted out or given into use and can be leased or rented. In this study we aimed at identifying, based on content analysis and a descriptive research, the owners of administration right, its way of being established, its content and the legal nature of the right to administrate the public property assets

The Control of the Administrative Tutelage Exercised by the Prefect

This study aims at highlighting the important aspects of administrative tutelage control achieved by the prefect: notion; evolution; comparative law; administrative acts submitted to control; the limit for introducing the action in administrative contentious. In order to achieve the objectives of the paper we have performed an analysis of the specific legislation, of the specialized literature and jurisprudence. The traditional institution for administrative law, along with the administrative contentious, it can be said that since 1990, the administrative tutelage is constantly expanding. The tutelage control conducted by the prefect regards exclusively the legality of the administrative acts issued by the local government authorities. After the empirical analysis and research, the paper summarizes and specifies the general conclusions on the legality control exercised by the prefect on administrative acts of the local authorities, as defined by the Law of administrative contentious no. 554/2004

The Legal Procedure for Solving Complaints Filed under the Depositions of Law No. 101/2016

In the August issue (2016) of the Acta Universitatis Danubius. Juridica journal we have published the article in which we have analyzed issues related to administrative-jurisdictional settlement of complaints made in accordance with the Law on remedies and appeals concerning the award of public procurement and concession contracts (Law no. 101/2016). Within the current article we have analyzed some procedure issues regarding solving the requests addressed to the administrative contentious, in accordance with this law, using logical interpretation, case-study, and comparative analysis

Subjective Right and the Legitimate Interest in the Romanian Administrative Law

Regulating the administrative contentious represents the expression of the particular concern of the society to strengthen the legal protection of all individuals when it is in the position to “confront” a public authority. This paper examines, briefly, one of the special conditions of direct action in the administrative contentious, that is the condition referring to invoking by the claimant of its harm in a subjective right or in a legitimate interest. In this respect, the research of the two concepts - subjective right and legitimate interest - will have a starting point the presentation of various opinions from specialists in other branches of law, such as general theory of law and civil law. Based on analysis, observation and case study, benefiting from a rich and diverse literature, we highlighted the changes that have intervened in the Romanian law, which determined that the legitimate interests would be placed on equal footing with individual rights, especially since the jurisprudence tends to focus on the harm of the person and less on whether the damage was brought to its subjective right or legitimate interest