10,171 research outputs found
Model Based Mission Assurance: NASA's Assurance Future
Model Based Systems Engineering (MBSE) is seeing increased application in planning and design of NASAs missions. This suggests the question: what will be the corresponding practice of Model Based Mission Assurance (MBMA)? Contemporaneously, NASAs Office of Safety and Mission Assurance (OSMA) is evaluating a new objectives based approach to standards to ensure that the Safety and Mission Assurance disciplines and programs are addressing the challenges of NASAs changing missions, acquisition and engineering practices, and technology. MBSE is a prominent example of a changing engineering practice. We use NASAs objectives-based strategy for Reliability and Maintainability as a means to examine how MBSE will affect assurance. We surveyed MBSE literature to look specifically for these affects, and find a variety of them discussed (some are anticipated, some are reported from applications to date). Predominantly these apply to the early stages of design, although there are also extrapolations of how MBSE practices will have benefits for testing phases. As the effort to develop MBMA continues, it will need to clearly and unambiguously establish the roles of uncertainty and risk in the system model. This will enable a variety of uncertainty-based analyses to be performed much more rapidly than ever before and has the promise to increase the integration of CRM (Continuous Risk Management) and PRA (Probabilistic Risk Analyses) even more fully into the project development life cycle. Various views and viewpoints will be required for assurance disciplines, and an over-arching viewpoint will then be able to more completely characterize the state of the project/program as well as (possibly) enabling the safety case approach for overall risk awareness and communication
A layered fuzzy logic controller for nonholonomic car-like robot
A system for real time navigation of a nonholonomic car-like robot in a dynamic environment consists of two layers is described: a Sugeno-type fuzzy motion planner; and a modified proportional navigation based fuzzy controller. The system philosophy is inspired by human routing when moving between obstacles based on visual information including right and left views to identify the next step to the goal. A Sugeno-type fuzzy motion planner of four inputs one output is introduced to give a clear direction to the robot controller. The second stage is a modified proportional navigation based fuzzy controller based on the proportional navigation guidance law and able to optimize the robot's behavior in real time, i.e. to avoid stationary and moving obstacles in its local environment obeying kinematics constraints. The system has an intelligent combination of two behaviors to cope with obstacle avoidance as well as approaching a target using a proportional navigation path. The system was simulated and tested on different environments with various obstacle distributions. The simulation reveals that the system gives good results for various simple environments
A comprehensive fractal approach in determination of the effective thermal conductivity of gas diffusion layers in polymer electrolyte membrane fuel cells
The challenges in the fuel cell industry is to produce the efficient thermal and water
management for accurate determination of the effectiveness thermal conductivity of
gas diffusion layers (GDL) used in polymer electrolyte membrane fuel cells
(PEMFC‟s). This is one of the factors affecting the durability of a fuel cell and need
to get a solution to minimize costs and optimize the use of electrodes and cells. The
main objectives of this research focus on the capability of the fractal approach for
estimation the effectiveness of thermal conductivity of gas diffusion layer. Moreover,
on this research also to propose modified fractal equations in determination of the
effective thermal conductivity of GDL in PEMFCs based on previous study. Other
objectives in this study are demonstrated the thermal conductivity of GDL treated
with PTFE contents by using through-plane thermal conductivity experiment
method. The through-plane measurement (experiment method) has been used in
estimating through-plane thermal conductivity of the GDL. Thermal resistance for
GDL also has been investigated under compression pressure 0.1 MPa until 1.0 MPa.
In fractal equation, the determination of tortuous and pore fractal dimension can be
done by using Scanning Electron Microscopy (SEM) method. Determination of
effectiveness thermal conductivity using of fractal equation with slightly modified.
In findings, it was found that fractal equation have been modified and measured on
the GDL parameter characteristics. It was shown that the value of the effectiveness
thermal conductivity of the sample using fractal approach is in good agreement with
the experimental value. Finally, all the effective thermal conductivity measured by
experimental and fractal approach have been determined with the variant temperature
and compression pressure to show the validation result between of this two methods
Motion planning and assembly for microassembly workstation
In general, mechatronics systems have no standard
operating system that could be used for planning and
control when these complex devices are running. The
goal of this paper is to formulate a work platform that can
be used as a method for obtaining precision in the
manipulation of micro-entities using micro-scale
manipulation tools for microsystem applications. This
paper provide groundwork for motion planning and
assembly of the Micro-Assembly Workstation (MAW)
manipulation system. To demonstrate the feasibility of the
idea, the paper implements some of the motion planning
algorithms; it investigates the performance of the
conventional Euclidean distance algorithm (EDA),
artificial potential fields’ algorithm, and A* algorithm
when implemented on a virtual space
Modeling the power consumption of a Wifibot and studying the role of communication cost in operation time
Mobile robots are becoming part of our every day living at home, work or
entertainment. Due to their limited power capabilities, the development of new
energy consumption models can lead to energy conservation and energy efficient
designs. In this paper, we carry out a number of experiments and we focus on
the motors power consumption of a specific robot called Wifibot. Based on the
experimentation results, we build models for different speed and acceleration
levels. We compare the motors power consumption to other robot running modes.
We, also, create a simple robot network scenario and we investigate whether
forwarding data through a closer node could lead to longer operation times. We
assess the effect energy capacity, traveling distance and data rate on the
operation time
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