Abstract: The performance of a permanent magnet brushless direct current (BLDC) motor controlled by the Kalman filter based position-sensorless drive is studied in terms of its dependence from the system’s parameters variations. The effects of the system’s parameters changes on the dynamic behavior of state variables are verified. Simulated is the closed loop control scheme with Kalman filter in the feedback line. Distinguished are two separate data sampling modes in analyzing feedback output from the BLDC motor: (1) equal angular separation and (2) equal time intervals. In case (1), the data are collected via equal intervals of rotor’s angular position i, i.e. keeping = const. In case (2), the data collection time points ti are separated by equal sampling time intervals t = const. Demonstrated are the effects of the parameters changes on the sensorless control flow, in particular, reduction of the instability torque ripples, switching spikes, and torque load balancing. It is specifically shown that an efficient suppression of commutation induced instability torque ripples is an achievable selection of the sampling rate in the Kalman filter settings above a certain critical value. The computational cost of such suppression is shown to be higher for the motors with lower induction values of the windings.
Abstract: Significant legislative changes are set to revolutionise the commercial shipping industry. Upcoming emissions restrictions will force operators to look at technologies that can improve the efficiency of their vessels -reducing fuel consumption and emissions. A device which may help in this challenge is the Ship Wind-Assisted Propulsion system (SWAP), an actively controlled aerofoil mounted vertically on the deck of a ship. The device functions in a similar manner to a sail on a yacht, whereby the aerodynamic forces generated by the sail reach an equilibrium with the hydrodynamic forces on the hull and a forward velocity results. Numerical and experimental testing of the SWAP device is presented in this study. Circulation control takes the form of a co-flow jet aerofoil, utilising both blowing from the leading edge and suction from the trailing edge. A jet at the leading edge uses the Coanda effect to energise the boundary layer in order to delay flow separation and create high lift with low drag. The SWAP concept has been originated by the research and development team at SMAR Azure Ltd. The device will be retrofitted to existing ships so that a component of the aerodynamic forces acts forward and partially reduces the reliance on existing propulsion systems. Wind tunnel tests have been carried out at the de Havilland wind tunnel at the University of Glasgow on a 1:20 scale model of this system. The tests aim to understand the airflow characteristics around the aerofoil and investigate the approximate lift and drag coefficients that an early iteration of the SWAP device may produce. The data exhibits clear trends of increasing lift as injection momentum increases, with critical flow attachment points being identified at specific combinations of jet momentum coefficient, Cµ, and angle of attack, AOA. Various combinations of flow conditions were tested, with the jet momentum coefficient ranging from 0 to 0.7 and the AOA ranging from 0° to 35°. The Reynolds number across the tested conditions ranged from 80,000 to 240,000. Comparisons between 2D computational fluid dynamics (CFD) simulations and the experimental data are presented for multiple Reynolds-Averaged Navier-Stokes (RANS) turbulence models in the form of normalised surface pressure comparisons. These show good agreement for most of the tested cases. However, certain simulation conditions exhibited a well-documented shortcoming of RANS-based turbulence models for circulation control flows and over-predicted surface pressures and lift coefficient for fully attached flow cases. Work must be continued in finding an all-encompassing modelling approach which predicts surface pressures well for all combinations of jet injection momentum and AOA.
Abstract: Software development for complex systems requires
efficient and automatic tools that can be used to verify the
satisfiability of some critical properties such as security ones. With
the emergence of Aspect-Oriented Programming (AOP), considerable
work has been done in order to better modularize the separation of
concerns in the software design and implementation. The goal is to
prevent the cross-cutting concerns to be scattered across the multiple
modules of the program and tangled with other modules. One of the
key challenges in the aspect-oriented programs is to be sure that all
the pieces put together at the weaving time ensure the satisfiability
of the overall system requirements. Our paper focuses on this problem and proposes a formal property
verification approach for a given property from the woven program.
The approach is based on the control flow graph (CFG) of the
woven program, and the use of a satisfiability modulo theories (SMT)
solver to check whether each property (represented par one aspect)
is satisfied or not once the weaving is done.
Abstract: Control Flow Integrity (CFI) is one of the most
promising technique to defend Code-Reuse Attacks (CRAs).
Traditional CFI Systems and recent Context-Sensitive CFI use coarse
control flow graphs (CFGs) to analyze whether the control flow
hijack occurs, left vast space for attackers at indirect call-sites. Coarse
CFGs make it difficult to decide which target to execute at indirect
control-flow transfers, and weaken the existing CFI systems actually.
It is an unsolved problem to extract CFGs precisely and perfectly
from binaries now. In this paper, we present an algorithm to get a
more precise CFG from binaries. Parameters are analyzed at indirect
call-sites and functions firstly. By comparing counts of parameters
prepared before call-sites and consumed by functions, targets of
indirect calls are reduced. Then the control flow would be more
constrained at indirect call-sites in runtime. Combined with CCFI,
we implement our policy. Experimental results on some popular
programs show that our approach is efficient. Further analysis show
that it can mitigate COOP and other advanced attacks.
Abstract: Control flow graphs are a well-known representation of
the sequential control flow structure of programs with a multitude
of applications. Not only single functions but also sets of functions
or complete programs can be modeled by control flow graphs. In
this case the size of the graphs can grow considerably and thus
makes it difficult for software engineers to analyze the control flow.
Graph reductions are helpful in this situation. In this paper we define
reductions to subsets of nodes. Since executions of programs are
represented by paths through the control flow graphs, paths should
be preserved. Furthermore, the composition of reductions makes a
stepwise analysis approach possible.
Abstract: Formal Specification languages are being widely used
for system specification and testing. Highly critical systems such as
real time systems, avionics, and medical systems are represented
using Formal specification languages. Formal specifications based
testing is mostly performed using black box testing approaches thus
testing only the set of inputs and outputs of the system. The formal
specification language such as VDMµ can be used for white box
testing as they provide enough constructs as any other high level
programming language. In this work, we perform data and control
flow analysis of VDMµ class specifications. The proposed work is
discussed with an example of SavingAccount.
Abstract: Aircraft propulsion systems often use Y-shaped
subsonic diffusing ducts as twin air-intakes to supply the ambient air
into the engine compressor for thrust generation. Due to space
constraint, the diffusers need to be curved, which causes severe flow
non-uniformity at the engine face. The present study attempt to
control flow in a mild-curved Y-duct diffuser using trapezoidalshaped
vortex generators (VG) attached on either both the sidewalls
or top and bottom walls of the diffuser at the inflexion plane. A
commercial computational fluid dynamics (CFD) code is modified
and is used to simulate the effects of SVG in flow of a Y-duct
diffuser. A few experiments are conducted for CFD code validation,
while the rest are done computationally. The best combination of Yduct
diffuser is found with VG-2 arranged in co-rotating sequence
and attached to both the sidewalls, which ensures highest static
pressure recovery, lowest total pressure loss, minimum flow
distortion and less flow separation in Y-duct diffuser. The decrease in
VG height while attached to top and bottom walls further improves
axial flow uniformity at the diffuser outlet by a great margin as
compared to the bare duct.
Abstract: Graph rewriting-based visual model processing is a
widely used technique for model transformation. Visual model
transformations often need to follow an algorithm that requires a
strict control over the execution sequence of the transformation steps.
Therefore, in Visual Model Processors (VMPs) the execution order
of the transformation steps is crucial. This paper presents the visual
control flow support of Visual Modeling and Transformation System
(VMTS), which facilitates composing complex model
transformations of simple transformation steps and executing them.
The VMTS Visual Control Flow Language (VCFL) uses stereotyped
activity diagrams to specify control flow structures and OCL
constraints to choose between different control flow branches. This
paper introduces VCFL, discusses its termination properties and
provides an algorithm to support the termination analysis of VCFL
transformations.
Abstract: In this paper test generation methods and appropriate fault models for testing and analysis of embedded systems described as (extended) finite state machines ((E)FSMs) are presented. Compared to simple FSMs, EFSMs specify not only the control flow but also the data flow. Thus, we define a two-level fault model to cover both aspects. The goal of this paper is to reuse well-known FSM-based test generation methods for automation of embedded system testing. These methods have been widely used in testing and validation of protocols and communicating systems. In particular, (E)FSMs-based specification and testing is more advantageous because (E)FSMs support the formal semantic of already standardised formal description techniques (FDTs) despite of their popularity in the design of hardware and software systems.
Abstract: Software maintenance and mainly software
comprehension pose the largest costs in the software lifecycle. In
order to assess the cost of software comprehension, various
complexity measures have been proposed in the literature. This paper
proposes new cognitive-spatial complexity measures, which combine
the impact of spatial as well as architectural aspect of the software to
compute the software complexity. The spatial aspect of the software
complexity is taken into account using the lexical distances (in
number of lines of code) between different program elements and the
architectural aspect of the software complexity is taken into
consideration using the cognitive weights of control structures
present in control flow of the program. The proposed measures are
evaluated using standard axiomatic frameworks and then, the
proposed measures are compared with the corresponding existing
cognitive complexity measures as well as the spatial complexity
measures for object-oriented software. This study establishes that the
proposed measures are better indicators of the cognitive effort
required for software comprehension than the other existing
complexity measures for object-oriented software.
Abstract: This paper presents the visual control flow support of Visual Modeling and Transformation System (VMTS), which facilitates composing complex model transformations out of simple transformation steps and executing them. The VMTS Visual Control Flow Language (VCFL) uses stereotyped activity diagrams to specify control flow structures and OCL constraints to choose between different control flow branches. This work discusses the termination properties of VCFL and provides an algorithm to support the termination analysis of VCFL transformations.
Abstract: The ever-growing usage of aspect-oriented
development methodology in the field of software engineering
requires tool support for both research environments and industry. So
far, tool support for many activities in aspect-oriented software
development has been proposed, to automate and facilitate their
development. For instance, the AJaTS provides a transformation
system to support aspect-oriented development and refactoring. In
particular, it is well established that the abstract interpretation of
programs, in any paradigm, pursued in static analysis is best served
by a high-level programs representation, such as Control Flow Graph
(CFG). This is why such analysis can more easily locate common
programmatic idioms for which helpful transformation are already
known as well as, association between the input program and
intermediate representation can be more closely maintained.
However, although the current researches define the good concepts
and foundations, to some extent, for control flow analysis of aspectoriented
programs but they do not provide a concrete tool that can
solely construct the CFG of these programs. Furthermore, most of
these works focus on addressing the other issues regarding Aspect-
Oriented Software Development (AOSD) such as testing or data flow
analysis rather than CFG itself. Therefore, this study is dedicated to
build an aspect-oriented control flow graph construction tool called
AJcFgraph Builder. The given tool can be applied in many software
engineering tasks in the context of AOSD such as, software testing,
software metrics, and so forth.