Abstract: The noise requirements for naval and research vessels
have seen an increasing demand for quieter ships in order to fulfil
current regulations and to reduce the effects on marine life. Hence,
new methods dedicated to the characterization of propeller noise,
which is the main source of noise in the far-field, are needed. The
study of cavitating propellers in closed-section is interesting for
analyzing hydrodynamic performance but could involve significant
difficulties for hydroacoustic study, especially due to reverberation
and boundary layer noise in the tunnel. The aim of this paper
is to present a numerical methodology for the identification of
hydroacoustic sources on marine propellers using hydrophone arrays
in a large hydrodynamic tunnel. The main difficulties are linked to the
reverberation of the tunnel and the boundary layer noise that strongly
reduce the signal-to-noise ratio. In this paper it is proposed to estimate
the reflection coefficients using an inverse method and some reference
transfer functions measured in the tunnel. This approach allows to
reduce the uncertainties of the propagation model used in the inverse
problem. In order to reduce the boundary layer noise, a cleaning
algorithm taking advantage of the low rank and sparse structure of the
cross-spectrum matrices of the acoustic and the boundary layer noise
is presented. This approach allows to recover the acoustic signal even
well under the boundary layer noise. The improvement brought by
this method is visible on acoustic maps resulting from beamforming
and DAMAS algorithms.
Abstract: A loading factor performance is necessary for the modeling of centrifugal compressor gas dynamic performance curve. Measured loading factors are linear function of a flow coefficient at an impeller exit. The performance does not depend on the compressibility criterion. To simulate loading factor performances, the authors present two parameters: a loading factor at zero flow rate and an angle between an ordinate and performance line. The calculated loading factor performances of non-viscous are linear too and close to experimental performances. Loading factor performances of several dozens of impellers with different blade exit angles, blade thickness and number, ratio of blade exit/inlet height, and two different type of blade mean line configuration. There are some trends of influence, which are evident – comparatively small blade thickness influence, and influence of geometry parameters is more for impellers with bigger blade exit angles, etc. Approximating equations for both parameters are suggested. The next phase of work will be simulating of experimental performances with the suggested approximation equations as a base.
Abstract: This paper presents a numerical analysis for the dynamic performance of a finite journal bearing lubricated with couple stress fluid taking into account the effect of the deformation of the bearing liner. The modified Reynolds equation has been solved by using finite difference technique. The dynamic characteristics in terms of stiffness coefficients, damping coefficients, critical mass and whirl ratio are evaluated for different values of eccentricity ratio and elastic coefficient for a journal bearing lubricated with a couple stress fluids and a Newtonian fluid. The results show that the dynamic characteristics of journal bearings lubricated with couple stress fluids are improved compared to journal bearings lubricated with Newtonian fluids.
Abstract: This paper demonstrates dynamic performance evaluation of load frequency control (LFC) with different intelligent techniques. All non-linearities and physical constraints have been considered in simulation studies such as governor dead band (GDB), generation rate constraint (GRC) and boiler dynamics. The conventional integral time absolute error has been considered as objective function. The design problem is formulated as an optimisation problem and particle swarm optimisation (PSO), bacterial foraging optimisation algorithm (BFOA) and differential evolution (DE) are employed to search optimal controller parameters. The superiority of the proposed approach has been shown by comparing the results with published fuzzy logic control (FLC) for the same interconnected power system. The comparison is done using various performance measures like overshoot, undershoot, settling time and standard error criteria of frequency and tie-line power deviation following a step load perturbation (SLP). It is noticed that, the dynamic performance of proposed controller is better than FLC. Further, robustness analysis is carried out by varying the time constants of speed governor, turbine, tie-line power in the range of +40% to -40% to demonstrate the robustness of the proposed DE optimized PID controller.
Abstract: In this paper, type-2 fuzzy logic control (T2FLC) and neuro-fuzzy control (NFC) for a doubly fed induction generator (DFIG) based on direct power control (DPC) with a fixed switching frequency is proposed for wind generation application. First, a mathematical model of the doubly-fed induction generator implemented in d-q reference frame is achieved. Then, a DPC algorithm approach for controlling active and reactive power of DFIG via fixed switching frequency is incorporated using PID. The performance of T2FLC and NFC, which is based on the DPC algorithm, are investigated and compared to those obtained from the PID controller. Finally, simulation results demonstrate that the NFC is more robust, superior dynamic performance for wind power generation system applications.
Abstract: More PV systems have been connected to the electrical network each year. As the number of PV systems increases, some issues affecting grid operations have been identified. This paper studied the impacts related to changes in solar irradiance on a distribution/sub-transmission network, considering variations due to moving clouds and daily cycles. Using MATLAB/Simulink software, a solar farm of 30 MWp was built and then implemented to a test network. From simulations, it has been determined that irradiance changes can have a significant impact on the grid by causing voltage fluctuations outside the allowable thresholds. This work discussed some local control strategies and grid reinforcements to mitigate the negative effects of the irradiance changes on the grid.
Abstract: This paper treats a design of combined control of a
single phase power factor correction (PFC). The strategy of the
proposed control is based on two parts, the first, for the outer loop
(DC output regulated voltage), and the second govern the input
current of the converter in order to achieve a sinusoidal form in phase
with the grid voltage. Two kinds of regulators are used, Fuzzy
controller for the outer loop and predictive controller for the inner
loop. The controllers are verified and discussed through simulation
under MATLAB/Simulink platform. Also an experimental
confirmation is applied. Results present a high dynamic performance
under various parameters changes.
Abstract: This article presents a numerical analysis of a turbulent flow past DTMB 4119 marine propeller by the means of RANS approach; the propeller designed at David Taylor Model Basin in USA. The purpose of this study is to predict the hydrodynamic performance of the marine propeller, it aims also to compare the results obtained with the experiment carried out in open water tests; a periodical computational domain was created to reduce the unstructured mesh size generated. The standard kw turbulence model for the simulation is selected; the results were in a good agreement. Therefore, the errors were estimated respectively to 1.3% and 5.9% for KT and KQ.
Abstract: This paper presents Differential Evolution Algorithm (DEA) based Variable Structure Position Control (VSPC) of Laboratory DC servomotor (LDCSM). DEA is employed for the optimal tuning of Variable Structure Control (VSC) parameters for position control of a DC servomotor. The VSC combines the techniques of Sliding Mode Control (SMC) that gives the advantages of small overshoot, improved step response characteristics, faster dynamic response and adaptability to plant parameter variations, suppressed influences of disturbances and uncertainties in system behavior. The results of the simulation responses of the VSC parameters adjustment by DEA were performed in Matlab Version 2010a platform and yield better dynamic performance compared with the untuned VSC designed.
Abstract: The effectiveness of microchannels in enhancing heat
transfer has been demonstrated in the semiconductor industry. In
order to tap the microscale heat transfer effects into macro
geometries, overcoming the cost and technological constraints,
microscale passages were created in macro geometries machined
using conventional fabrication methods. A cylindrical insert was
placed within a pipe, and geometrical profiles were created on the
outer surface of the insert to enhance heat transfer under steady-state
single-phase liquid flow conditions. However, while heat transfer
coefficient values of above 10 kW/m2·K were achieved, the heat
transfer enhancement was accompanied by undesirable pressure drop
increment. Therefore, this study aims to address the high pressure
drop issue using Constructal theory, a universal design law for both
animate and inanimate systems. Two designs based on Constructal theory were developed to study
the effectiveness of Constructal features in reducing the pressure drop
increment as compared to parallel channels, which are commonly
found in microchannel fabrication. The hydrodynamic and heat
transfer performance for the Tree insert and Constructal fin (Cfin)
insert were studied using experimental methods, and the underlying
mechanisms were substantiated by numerical results. In technical
terms, the objective is to achieve at least comparable increment in
both heat transfer coefficient and pressure drop, if not higher
increment in the former parameter. Results show that the Tree insert improved the heat transfer
performance by more than 16 percent at low flow rates, as compared
to the Tree-parallel insert. However, the heat transfer enhancement
reduced to less than 5 percent at high Reynolds numbers. On the
other hand, the pressure drop increment stayed almost constant at 20
percent. This suggests that the Tree insert has better heat transfer
performance in the low Reynolds number region. More importantly,
the Cfin insert displayed improved heat transfer performance along
with favourable hydrodynamic performance, as compared to Cfinparallel
insert, at all flow rates in this study. At 2 L/min, the
enhancement of heat transfer was more than 30 percent, with 20
percent pressure drop increment, as compared to Cfin-parallel insert.
Furthermore, comparable increment in both heat transfer coefficient
and pressure drop was observed at 8 L/min. In other words, the Cfin
insert successfully achieved the objective of this study. Analysis of the results suggests that bifurcation of flows is
effective in reducing the increment in pressure drop relative to heat
transfer enhancement. Optimising the geometries of the Constructal
fins is therefore the potential future study in achieving a bigger stride
in energy efficiency at much lower costs.
Abstract: This paper describes a simple way to control the speed
of PMBLDC motor using Fuzzy logic control method. In the
conventional PI controller the performance of the motor system is
simulated and the speed is regulated by using PI controller. These
methods used to improve the performance of PMSM drives, but in
some cases at different operating conditions when the dynamics of
the system also vary over time and it can change the reference speed,
parameter variations and the load disturbance. The simulation is
powered with the MATLAB program to get a reliable and flexible
simulation. In order to highlight the effectiveness of the speed control
method the FLC method is used. The proposed method targeted in
achieving the improved dynamic performance and avoids the
variations of the motor drive. This drive has high accuracy, robust
operation from near zero to high speed. The effectiveness and
flexibility of the individual techniques of the speed control method
will be thoroughly discussed for merits and demerits and finally
verified through simulation and experimental results for comparative
analysis.
Abstract: Motion response of floating structures is of great
concern in marine engineering. Nonlinearity is an inherent property
of any floating bodies subjected to irregular waves. These floating
structures are continuously subjected to environmental loadings from
wave, current, wind etc. This can result in undesirable motions of the
vessel which may challenge the operability. For a floating body to
remain in its position, it should be able to induce a restoring force
when displaced. Mooring is provided to enable this restoring force.
This paper discusses the hydrodynamic performance and motion
characteristics of an 8 point spread mooring system applied to a pipe
laying barge operating in the West African sea. The modelling of the
barge is done using a computer aided-design (CAD) software
RHINOCEROS. Irregular waves are generated using a suitable wave
spectrum. Both frequency domain and time domain analysis is done.
Numerical simulations based on potential theory are carried out to
find the responses and hydrodynamic performance of the barge in
both free floating as well as moored conditions. Initially, potential
flow frequency domain analysis is done to obtain the Response
Amplitude Operator (RAO) which gives an idea about the structural
motion in free floating state. RAOs for different wave headings are
analyzed. In the following step, a time domain analysis is carried out
to obtain the responses of the structure in the moored condition. In
this study, wave induced motions are only taken into consideration.
Wind and current loads are ruled out and shall be included in further
studies. For the current study, 2000 seconds simulation is taken. The
results represent wave induced motion responses, mooring line
tensions and identify critical mooring lines.
Abstract: Brushless DC motors (BLDC) are widely used in
industrial areas. The BLDC motors are driven either by indirect ACAC
converters or by direct AC-AC converters. Direct AC-AC
converters i.e. matrix converters are used in this paper to drive the
three phase BLDC motor and it eliminates the bulky DC link energy
storage element. A matrix converter converts the AC power supply to
an AC voltage of variable amplitude and variable frequency. A
control technique is designed to generate the switching pulses for the
three phase matrix converter. For the control of speed of the BLDC
motor a separate PI controller and Fuzzy Logic Controller (FLC) are
designed and a hysteresis current controller is also designed for the
control of motor torque. The control schemes are designed and tested
separately. The simulation results of both the schemes are compared
and contrasted in this paper. The results show that the fuzzy logic
control scheme outperforms the PI control scheme in terms of
dynamic performance of the BLDC motor. Simulation results are
validated with the experimental results.
Abstract: In addition to the advantages of light weight, resistant
corrosion and ease of processing, aluminum is also applied to the
long-span spatial structures. However, the elastic modulus of
aluminum is lower than that of the steel. This paper combines the
high performance aluminum honeycomb panel with the aluminum
latticed shell, forming a new panel-and-rod composite shell structure.
Through comparative analysis between the static and dynamic
performance, the conclusion that the structure of composite shell is
noticeably superior to the structure combined before.
Abstract: This study addresses a concept of the Sustainable Building Environmental Model (SBEM) developed to optimize energy consumption in air conditioning and ventilation (ACV) systems without any deterioration of indoor environmental quality (IEQ). The SBEM incorporates two main components: an adaptive comfort temperature control module (ACT) and a new carbon dioxide demand control module (nDCV). These two modules take an innovative approach to maintain satisfaction of the Indoor Environmental Quality (IEQ) with optimum energy consumption; they provide a rational basis of effective control. A total of 2133 sets of measurement data of indoor air temperature (Ta), relative humidity (Rh) and carbon dioxide concentration (CO2) were conducted in some Hong Kong offices to investigate the potential of integrating the SBEM. A simulation was used to evaluate the dynamic performance of the energy and air conditioning system with the integration of the SBEM in an air-conditioned building. It allows us make a clear picture of the control strategies and performed any pre-tuned of controllers before utilized in real systems. With the integration of SBEM, it was able to save up to 12.3% in simulation of overall electricity consumption, and maintain the average carbon dioxide concentration within 1000ppm and occupant dissatisfaction in 20%.
Abstract: Complex lifting entry was selected for precise landing
performance during the Mars Science Laboratory entry. This study
aims to develop the three-dimensional numerical method for precise
computation and the surface panel method for rapid engineering
prediction. Detailed flow field analysis for Mars exploration mission
was performed by carrying on a series of fully three-dimensional
Navier-Stokes computations. The static aerodynamic performance was
then discussed, including the surface pressure, lift and drag coefficient,
lift-to-drag ratio with the numerical and engineering method.
Computation results shown that the shock layer is thin because of
lower effective specific heat ratio, and that calculated results from both
methods agree well with each other, and is consistent with the
reference data. Aerodynamic performance analysis shows that CG
location determines trim characteristics and pitch stability, and certain
radially and axially shift of the CG location can alter the capsule lifting
entry performance, which is of vital significance for the aerodynamic
configuration design and inner instrument layout of the Mars entry
capsule.
Abstract: This study presented to reduce earthquake damage and
emergency rehabilitation of critical structures such as schools, hightech
factories, and hospitals due to strong ground motions associated
with climate changes. Regarding recent trend, a strong earthquake
causes serious damage to critical structures and then the critical
structure might be influenced by sequence aftershocks (or tsunami)
due to fault plane adjustments. Therefore, in order to improve seismic
performance of critical structures, retrofitted or strengthening study
of the structures under aftershocks sequence after emergency
rehabilitation of the structures subjected to strong earthquakes is
widely carried out. Consequently, this study used composite material
for emergency rehabilitation of the structure rather than concrete and
steel materials because of high strength and stiffness, lightweight,
rapid manufacturing, and dynamic performance. Also, this study was
to develop or improve the seismic performance or seismic retrofit of
critical structures subjected to strong ground motions and earthquake
aftershocks, by utilizing GFRP-Corrugated Infill Panels (GCIP).
Abstract: This paper presents dynamic models of distributed
generators (DG) and investigates dynamic behavior of the DG units
in the micro grid system. The DG units include photovoltaic and fuel
cell sources. The voltage source inverter is adopted since the
electronic interface which can be equipped with its controller to keep
stability of the micro grid during small signal dynamics. This paper
also introduces power management strategies and implements the DG
load sharing concept to keep the micro grid operation in gridconnected
and islanding modes of operation. The results demonstrate
the operation and performance of the photovoltaic and fuel cell as
distributed generators in a micro grid. The entire control system in
the micro grid is developed by combining the benefits of the power
control and the voltage control strategies. Simulation results are all
reported, confirming the validity of the proposed control technique.
Abstract: Fixed-geometry hydrodynamic journal bearings are
one of the best supporting systems for several applications of rotating
machinery. Cylindrical journal bearings present excellent loadcarrying
capacity and low manufacturing costs, but they are subjected
to the oil-film instability at high speeds. An attempt of overcoming
this instability problem has been the development of non-circular
journal bearings. This work deals with an analysis of oil-lubricated
elliptical journal bearings using the finite element method. Steadystate
and dynamic performance characteristics of elliptical bearings
are rendered by zeroth- and first-order lubrication equations obtained
through a linearized perturbation method applied on the classical
Reynolds equation. Four-node isoparametric rectangular finite
elements are employed to model the bearing thin film flow. Curves of
elliptical bearing load capacity and dynamic force coefficients are
rendered at several operating conditions. The results presented in this
work demonstrate the influence of the bearing ellipticity on its
performance at different loading conditions.
Abstract: In order to study the aerodynamic performance of a
semi-flexible membrane wing, Fluid-Structure Interaction simulations
have been performed. The fluid problem has been modeled using
two different approaches which are the vortex panel method and the
numerical solution of the Navier-Stokes equations. Nonlinear analysis
of the structural problem is performed using the Finite Element
Method. Comparison between the two fluid solvers has been made.
Aerodynamic performance of the wing is discussed regarding its
lift and drag coefficients and they are compared with those of the
equivalent rigid wing.