Nicolas Rivière

Bubble-induced agitation and microstructure in uniform bubbly flows at small to moderate particle Reynolds numbers

The bubble-induced agitation has been quantified in dilute and homogeneous bubbly flows. To characterize the microstructure, experimental techniques have been developed that provide the average perturbed liquid velocity and the pair density. For particulate Reynolds numbers Rep about unity and contaminated bubbles, the liquid agitation is shown to increase as α/Rep where α is the local void fraction. Although in partial agreement with the scaling proposed by Koch (Phys. Fluids, 1993), the pair-density distribution does not exhibit any deficit. On the opposite, experiments at Rep=O(10) and clean bubbles reveal a strong deficit in the rear of test bubbles as well as a moderate accumulation both in a horizontal plane and all along the deficit zone. The extent of the deficit slowly decreases with the void fraction, roughly as α−0.3±0.1. It is shown that the agitation originates from this near wake region, the structure of which strongly differs from the one due to a single inclusion both in terms of its later...

Reachability and temporal conflicts in t-time Petri nets

The first aim of this paper is to characterize marking reachability within scenarios defined on t-time Petri nets. This reachability can be structural (does not depend on the enabling durations), necessary (for all the possible values of the enabling durations within some given enabling intervals) or possible (for some values of the enabling durations). This approach is based on the computation of sojourn times of tokens in places by means of the construction of proof trees in linear logic. The second aim is to illustrate the fact that these sojourn times can also be used to analyze the conflicts between two scenarios, taking into account all the temporal constraints. In some cases, one of the scenarios will invalidate the other one: the temporal constraints are such that this scenario will never occur.

Mobile Systems from a Validation Perspective: a Case Study

Advances in wireless networking have yielded the development of mobile applications. However, sound technology to specify, design and validate such applications is still to be investigated. In order to exemplify some of the challenges that are raised, this paper reports on a case study: a group membership protocol for ad hoc networks. The protocol has been analyzed by reviewing the specification and the code, and then by testing the implementation. The outcomes provides us with hints for research direction.

Testing mobile computing applications: toward a scenario language and tools

Advances in wireless networking have yielded the development of mobile computing applications. Their unique characteristics (dynamicity of the system structure, communication with unknown partners in local vicinity, context dependency) provide new challenges for verification. This paper elaborates on the testing technology. As a first step, a review of the state-of-the-art is performed together with a case study (a group membership protocol in mobile ad hoc settings), which allowed us to gain insights into testing problems. Work is then directed toward: (1) the definition of a scenario language with extensions to better account for mobile settings (spatial relationships, broadcast communication with neighbors), and (2) an automated support for the off-line analysis of execution traces to identify occurrences of described scenarios.

RELATIONSHIPS BETWEEN PETRI NETS AND CONSTRAINT GRAPHS: APPLICATION TO MANUFACTURING

The purpose of the paper is to compare timed and time Petri nets with constraint satisfaction problems and activity-on-arc graphs in the context of manufacturing. It is shown that constraints are not defined in the same way but that timed and time Petri nets could be translated into a set of activity-on-arc graphs. This translation is only straightforward for p-timed and p-time Petri nets.

GraphSeq: A Graph Matching Tool for the Extraction of Mobility Patterns

Mobile computing systems provide new challenges for verification. One of them is the dynamicity of the system structure, with mobility-induced connections and disconnections, dynamic creation and shutdown of nodes. Interaction scenarios have then to consider the spatial configuration of the nodes as a first class concept. This paper presents GraphSeq, a graph matching tool for sequences of configurations developed in the framework of testing research. It aims to analyze test traces to identify occurrences of the successive spatial configurations described in an abstract scenario. We present the GraphSeq algorithm, as well as first experiments using randomly generated graphs, outputs from a mobility simulator, and test traces from a case study in ad hoc networks.

TERMOS: A Formal Language for Scenarios in Mobile Computing Systems

This paper presents TERMOS, a UML-based formal language for specifying scenarios in mobile computing systems. TERMOS scenarios are used for the verification of test traces. They capture key properties to be checked on the traces, considering both the spatial configuration of nodes and their communication. We give an overview of the TERMOS design and semantics. As part of the semantics, we present the principle of an algorithm that computes the orders of events from a scenario. Two proof-of-concept prototypes have been developed to study the realization of the algorithm.

SYMBOLIC TEMPORAL CONSTRAINT ANALYSIS, AN APPROACH FOR VERIFYING HYBRID SYSTEMS

Abstract The purpose of the paper is to illustrate a method, based on theorem proving, allowing the determination of a set of constraints such that some property of an hybrid system is verified. The approach is based on the generation of scenarios by proving some linear logic sequents and on the analysis of symbolic temporal constraints in a Simple Temporal Network. In the presented example, the property is the reachability of a given state within some temporal constraint.

A UML-based environment for test scenarios in mobile settings

TERMOS is an UML-based formal language for specifying scenarios in mobile computing systems. TERMOS scenarios are used for the verification of test traces: they represent mandatory or forbidden interactions that are searched for in the trace. Building upon previous work on the semantics of TERMOS, this paper presents the complete integration of the language into UML support technology. A TERMOS profile has been developed for the editing of scenarios, as well as an Eclipse plugin for the automated checking of traces. We demonstrate the approach on a case study, a group membership protocol in ad hoc networks.

GraphSeq Revisited: More Efficient Search for Patterns in Mobility Traces

GraphSeq is a graph matching tool previously developed in the framework of a scenario-based test approach. It targets mobile computing systems, for which interaction scenarios must consider the evolution of the spatial configuration of nodes. GraphSeq allows the analysis of test traces to identify occurrences of the successive configurations of a scenario. This paper presents a recent improvement made to the tool, to allow for better performance in the average cases. It consists in re-arranging the configuration patterns extracted from the scenario, so that the most discriminating nodes are matched first. The improvement is assessed using randomly generated graphs and a test trace from a case study in ad hoc networks.