2,788,213 research outputs found
Modeling dynamics of parallel milling processes in time-domain
The use of parallel milling processes is increasing in various industries due to
several advantages of these machine tools. Parallel milling processes are the processes where more than one milling tool simultaneously cut a workpiece. Due to the increased number of cutting tools, they have the potential for considerable increase in productivity as a result of higher material removal rate (MRR). However, dynamic interactions between milling tools may reduce stability limits. Generally, direct dynamic coupling between two milling tools on such a machine is weak since they are located on different spindles. However, there can be a strong dynamic coupling in case of milling a flexible workpiece. In this case, the vibrations caused by one of the tools may have regenerative
effects on the other one. In order to address this problem, a stability model that works in time domain has been developed. The model is capable of simulating cases where two flexible milling tools are cutting a flexible workpiece. Several example cases are simulated with the model and results are presented
Parallel on-line parsing in constant time per word
An on-line parser processes each word as soon as it is typed by the user, without waiting for the end of the sentence. Thus, in an interactive system, a sentence will be parsed almost immediately after the last word has been presented.\ud
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The complexity of an on-line parser is determined by the resources needed for the analysis of a single word, as it is assumed that previous words have been processed already. Sequential parsing algorithms like CYK or Earley need O(n2) time for the nth word. A parallel implementation in O(n) time on O(n) processors is straightforward. In this paper a novel parallel on-line parser is presented that needs O(1) time on O(n2) processors
Static Analysis of Run-Time Errors in Embedded Real-Time Parallel C Programs
We present a static analysis by Abstract Interpretation to check for run-time
errors in parallel and multi-threaded C programs. Following our work on
Astr\'ee, we focus on embedded critical programs without recursion nor dynamic
memory allocation, but extend the analysis to a static set of threads
communicating implicitly through a shared memory and explicitly using a finite
set of mutual exclusion locks, and scheduled according to a real-time
scheduling policy and fixed priorities. Our method is thread-modular. It is
based on a slightly modified non-parallel analysis that, when analyzing a
thread, applies and enriches an abstract set of thread interferences. An
iterator then re-analyzes each thread in turn until interferences stabilize. We
prove the soundness of our method with respect to the sequential consistency
semantics, but also with respect to a reasonable weakly consistent memory
semantics. We also show how to take into account mutual exclusion and thread
priorities through a partitioning over an abstraction of the scheduler state.
We present preliminary experimental results analyzing an industrial program
with our prototype, Th\'es\'ee, and demonstrate the scalability of our
approach
Parallel-In-Time Simulation of Eddy Current Problems Using Parareal
In this contribution the usage of the Parareal method is proposed for the
time-parallel solution of the eddy current problem. The method is adapted to
the particular challenges of the problem that are related to the differential
algebraic character due to non-conducting regions. It is shown how the
necessary modification can be automatically incorporated by using a suitable
time stepping method. The paper closes with a first demonstration of a
simulation of a realistic four-pole induction machine model using Parareal
An efficient steady-state analysis of the eddy current problem using a parallel-in-time algorithm
This paper introduces a parallel-in-time algorithm for efficient steady-state
solution of the eddy current problem. Its main idea is based on the application
of the well-known multi-harmonic (or harmonic balance) approach as the coarse
solver within the periodic parallel-in-time framework. A frequency domain
representation allows for the separate calculation of each harmonic component
in parallel and therefore accelerates the solution of the time-periodic system.
The presented approach is verified for a nonlinear coaxial cable model
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