2,054 research outputs found
Advanced Mathematics and Computational Applications in Control Systems Engineering
Control system engineering is a multidisciplinary discipline that applies automatic control theory to design systems with desired behaviors in control environments. Automatic control theory has played a vital role in the advancement of engineering and science. It has become an essential and integral part of modern industrial and manufacturing processes. Today, the requirements for control precision have increased, and real systems have become more complex. In control engineering and all other engineering disciplines, the impact of advanced mathematical and computational methods is rapidly increasing. Advanced mathematical methods are needed because real-world control systems need to comply with several conditions related to product quality and safety constraints that have to be taken into account in the problem formulation. Conversely, the increment in mathematical complexity has an impact on the computational aspects related to numerical simulation and practical implementation of the algorithms, where a balance must also be maintained between implementation costs and the performance of the control system. This book is a comprehensive set of articles reflecting recent advances in developing and applying advanced mathematics and computational applications in control system engineering
An efficient numerical method for computation of the number of complex zeros of real polynomials inside the open unit disk
AbstractIn this paper, a simple and efficient numerical method is proposed for computing the number of complex zeros of a real polynomial lying inside the unit disk. The proposed protocol uses the Boubaker polynomial expansion scheme (BPES) to build sequence of polynomials based on the concept of Sturm sequences. The method is used in a direct way without using any restrictions in reference to other existing methods. The protocol is applied to some example polynomials of different orders and utility of the algorithm is noticed
Analytical Algorithm Expressions in Simulation of the Temperature Field in Electric Resistance Spot Welding
The paper presents the method of obtaining mathematical equations named "Analytical algorithm expressions" which enable simple creation of computer programs for simulation of the temperature field in the weld zone in electric resistance spot welding. Knowledge of these equations and the manner of their formulation make creation of program packages easier but they do not change anything with respect to the structure and scope of necessary input data which determine concrete initial and boundary conditions. In addition to providing algorithm description of the temperature field, the considered approach is applied for mathematical description of the field of any other physical value relevant for the welding process (specific current, electric potential, density, etc.). In this paper they are realized in temperature fields, as hierarchically superior to the fields of stress and current density, i.e. fields of physical properties of materials of the sheet and the electrode (superiority refers to the algorithm domain). Results of simulation for the non-stationary period of the welding process at two extreme discreet moments are presented at the end
A mesoscale approach to simulate residual deformations in complex laser welding processes
Laser welding can be characterized by very small radii of beam, in the order of tenths of a millimeter, and very short high
power inputs (more kW in few ms), and thus, it can be certainly classified as a microscale process with a high level of
physical complexity. This is clearly incompatible, due to the high computational costs, with the analysis of macroscale
processes related to large geometries and non-uniform welding patterns. In order to overcome this issue, a simplified
finite element method (FEM)–based thermo-elastoplastic model is presented to simulate heat transfer and residual
deformations due to thermal expansion and material plasticity. The idea is to substitute the microscale analysis with a
mesoscale approach that renounces to describe in detail all the physical phenomena occurring in the heated zone and
focuses attention on the correct prediction of the keyhole depth and weld pool size, that are the most important para meters to describe the mechanical characteristics of the welded joint. The concept of passive element, based on the
numerical adjustment of the material properties in order to take into account the orthotropic behavior during the key hole formation, is introduced. In particular, the new approach has been tested on the pulsed laser welding process of
two overlapping DC04 steel plates with thickness of 0.5 mm (so-called sandwich) and validated through experimental
tests involving different input parameters, such as power, pulse duration and frequency, speed, and geometrical pattern
Improved micro-contact resistance model that considers material deformation, electron transport and thin film characteristics
This paper reports on an improved analytic model forpredicting micro-contact resistance needed for designing microelectro-mechanical systems (MEMS) switches. The originalmodel had two primary considerations: 1) contact materialdeformation (i.e. elastic, plastic, or elastic-plastic) and 2) effectivecontact area radius. The model also assumed that individual aspotswere close together and that their interactions weredependent on each other which led to using the single effective aspotcontact area model. This single effective area model wasused to determine specific electron transport regions (i.e. ballistic,quasi-ballistic, or diffusive) by comparing the effective radius andthe mean free path of an electron. Using this model required thatmicro-switch contact materials be deposited, during devicefabrication, with processes ensuring low surface roughness values(i.e. sputtered films). Sputtered thin film electric contacts,however, do not behave like bulk materials and the effects of thinfilm contacts and spreading resistance must be considered. Theimproved micro-contact resistance model accounts for the twoprimary considerations above, as well as, using thin film,sputtered, electric contact
Modeling and control of a DC upset resistance butt welding process
This paper presents the analysis and synthesis of modeling and control of the DC upset resistance butt welding process used in rim production lines. A new control strategy is developed, enabling active control of the welding seam temperature and the upset size. As a result, set-up times and energy consumption are reduced significantly
Life Cycle Impact of Different Joining Decisions on Vehicle Recycling
Stricter vehicle emission legislation has driven significant
reduction in environmental impact of the vehicle use phase
through increasing use of lightweight materials and
multi-material concepts to reduce the vehicle mass. The joining
techniques used for joining multi-material designs has led to
reduction in efficiency of the current shredder-based recycling
practices. This thesis quantifies this reduction in efficiency
using data captured from industrial recycling trials.
Life Cycle Assessment has been widely used to assess the
environmental impact throughout the vehicle life cycle stages.
Although there is significant research on material selection or
substitution to improve the vehicle’s carbon footprint, the
correlation between multi-material vehicle designs and the
material separation through commonly used shredding process is
not well captured in the current analysis. This thesis addresses
this gap using data captured from industrial trials to measure
the influence of different joining techniques on material
recycling efficiencies. The effects of material degradation due
to joining choices are examined using the life cycle analysis
including exergy losses to account for a closed-loop system. The
System Dynamics approach is then performed to demonstrate the
dynamic life cycle impact of joining choices used for new
multi-material vehicle designs.
Observations from the case studies conducted in Australia and
Europe showed that mechanical fasteners, particularly machine
screws, are increasingly used to join different material types
and are less likely to be perfectly liberated during the
shredding process. The characteristics of joints, such as joint
strength, material type, size, diameter, location, temperature
resistance, protrusion level, and surface smoothness, have an
influence on the material liberation in the current sorting
practices. Additionally, the liberation of joints is also
affected by the density and thickness of materials being joined.
The life cycle analysis including exergy losses shows a
significant environmental burden caused by the amount of
impurities and valuable material losses due to unliberated
joints. By measuring the influence of joints quantitatively, this
work has looked at the potential of improving the quality of
materials recycled from ELV to be reused in a closed-loop system.
The dynamic behaviours between the joining choices and their
delayed influence on material recycling efficiencies from the
life cycle perspective are performed using the data from case
studies. It shows that the short-term reduction in environmental
impact through multi-material structures is offset over the
long-term by the increasing impurities and valuable material
losses due to unliberated joints. The different vehicle recycling
systems can then be resembled using two widely known system
archetypes: “Fixes that Fail” and “Shifting the Burden”.
Despite the adoption of more rigorous recycling approaches, the
life cycle impact of different joining techniques on vehicle
recycling continue to exist. The enactment of strict regulations
in current ELV recycling systems is unable to solve the
underlying ELV waste problem, and only prolongs the delay in
material degradation due to joining choices. This work shows that
the choice of joining techniques used for multi-material vehicle
designs has a significant impact on the environmental performance
during the ELV recycling phase
Aeronautical Engineering: A continuing bibliography, supplement 120
This bibliography contains abstracts for 297 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1980
Impact Assessment of Hypothesized Cyberattacks on Interconnected Bulk Power Systems
The first-ever Ukraine cyberattack on power grid has proven its devastation
by hacking into their critical cyber assets. With administrative privileges
accessing substation networks/local control centers, one intelligent way of
coordinated cyberattacks is to execute a series of disruptive switching
executions on multiple substations using compromised supervisory control and
data acquisition (SCADA) systems. These actions can cause significant impacts
to an interconnected power grid. Unlike the previous power blackouts, such
high-impact initiating events can aggravate operating conditions, initiating
instability that may lead to system-wide cascading failure. A systemic
evaluation of "nightmare" scenarios is highly desirable for asset owners to
manage and prioritize the maintenance and investment in protecting their
cyberinfrastructure. This survey paper is a conceptual expansion of real-time
monitoring, anomaly detection, impact analyses, and mitigation (RAIM) framework
that emphasizes on the resulting impacts, both on steady-state and dynamic
aspects of power system stability. Hypothetically, we associate the
combinatorial analyses of steady state on substations/components outages and
dynamics of the sequential switching orders as part of the permutation. The
expanded framework includes (1) critical/noncritical combination verification,
(2) cascade confirmation, and (3) combination re-evaluation. This paper ends
with a discussion of the open issues for metrics and future design pertaining
the impact quantification of cyber-related contingencies
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