Abstract: This paper considers the problem of scheduling maintenance actions for identical aircraft gas turbine engines. Each one of the turbines consists of parts which frequently require replacement. A finite inventory of spare parts is available and all parts are ready for replacement at any time. The inventory consists of both new and refurbished parts. Hence, these parts have different field lives. The goal is to find a replacement part sequencing that maximizes the time that the aircraft will keep functioning before the inventory is replenished. The problem is formulated as an identical parallel machine scheduling problem where the minimum completion time has to be maximized. Two models have been developed. The first one is an optimization model which is based on a 0-1 linear programming formulation, while the second one is an approximate procedure which consists in decomposing the problem into several two-machine subproblems. Each subproblem is optimally solved using the first model. Both models have been implemented using Lingo and have been tested on two sets of randomly generated data with up to 150 parts and 10 turbines. Experimental results show that the optimization model is able to solve only instances with no more than 4 turbines, while the decomposition procedure often provides near-optimal solutions within a maximum CPU time of 3 seconds.
Abstract: Wind turbine should be controlled to capture maximum
wind energy and to prevent the turbine from being stalled. To achieve
those two goals, wind turbine controller controls torque on generator
and limits input torque from wind by pitching blade. Usually, torque
on generator is controlled using inverter torque set point. However,
verifying a control algorithm in actual wind turbine needs a lot of
efforts to test and the actual wind turbine could be broken while testing
a control algorithm. So, several software have developed and
commercialized by Garrad Hassan, GH Bladed, and NREL, FAST.
Even though, those programs can simulate control system modeling
with subroutines or DLLs. However, those simulation programs are
not able to emulate detailed generator or PMSG. In this paper, a small
size wind turbine simulator is developed with induction motor and
small size drive train. The developed system can simulate wind turbine
control algorithm in the region before rated power.
Abstract: A CFD study on heat flux reduction in hypersonic flow with opposing jet has been conducted. Flowfield parameters, reattachment point position, surface pressure distributions and heat flux distributions are obtained and validated with experiments. The physical mechanism of heat reduction has been analyzed. When the opposing jet blows, the freestream is blocked off, flows to the edges and not interacts with the surface to form aerodynamic heating. At the same time, the jet flows back to form cool recirculation region, which reduces the difference in temperature between the surface and the nearby gas, and then reduces the heat flux. As the pressure ratio increases, the interface between jet and freestream is gradually pushed away from the surface. Larger the total pressure ratio is, lower the heat flux is. To study the effect of the intensity of opposing jet more reasonably, a new parameter RPA has been introduced by combining the flux and the total pressure ratio. The study shows that the same shock wave position and total heat load can be obtained with the same RPA with different fluxes and the total pressures, which means the new parameter could stand for the intensity of opposing jet and could be used to analyze the influence of opposing jet on flow field and aerodynamic heating.
Abstract: In this paper, the bond strength of thermal spray
coatings in high speed shafts has been studied. The metallurgical and
mechanical studies has been made on the coated samples and shaft
using optical microscopy, scanning electron microscopy (SEM).
Abstract: In the normal operation conditions of a pico satellite,
conventional Unscented Kalman Filter (UKF) gives sufficiently good
estimation results. However, if the measurements are not reliable
because of any kind of malfunction in the estimation system, UKF
gives inaccurate results and diverges by time. This study, introduces
Robust Unscented Kalman Filter (RUKF) algorithms with the filter
gain correction for the case of measurement malfunctions. By the use
of defined variables named as measurement noise scale factor, the
faulty measurements are taken into the consideration with a small
weight and the estimations are corrected without affecting the
characteristic of the accurate ones. Two different RUKF algorithms,
one with single scale factor and one with multiple scale factors, are
proposed and applied for the attitude estimation process of a pico
satellite. The results of these algorithms are compared for different
types of measurement faults in different estimation scenarios and
recommendations about their applications are given.
Abstract: In aerospace applications, interactions of airflow with
aircraft structures can result in undesirable structural deformations.
This structural deformation in turn, can be predicted if the natural
modes of the structure are known. This can be achieved through
conventional modal testing that requires a known excitation force in
order to extract these dynamic properties. This technique can be
experimentally complex because of the need for artificial excitation
and it is also does not represent actual operational condition. The
current work presents part of research work that address the practical
implementation of operational modal analysis (OMA) applied to a
cantilevered hybrid composite plate employing single contactless
sensing system via laser vibrometer. OMA technique extracts the
modal parameters based only on the measurements of the dynamic
response. The OMA results were verified with impact hammer modal
testing and good agreement was obtained.
Abstract: Heavy rainfall greatly affects the aerodynamic performance of the aircraft. There are many accidents of aircraft caused by aerodynamic efficiency degradation by heavy rain.
In this Paper we have studied the heavy rain effects on the aerodynamic efficiency of cambered NACA 64-210 and symmetric
NACA 0012 airfoils. Our results show significant increase in drag and decrease in lift. We used preprocessing software gridgen for creation of geometry and mesh, used fluent as solver and techplot as postprocessor. Discrete phase modeling called DPM is used to model the rain particles using two phase flow approach. The rain particles are assumed to be inert.
Both airfoils showed significant decrease in lift and increase in drag in simulated rain environment. The most significant difference between these two airfoils was the NACA 64-210 more sensitivity than NACA 0012 to liquid water content (LWC). We believe that the results showed in this paper will be useful for the designer of the commercial aircrafts and UAVs, and will be helpful for training of the pilots to control the airplanes in heavy rain.
Abstract: Pollution emission levels of aircraft engines are a
nowadays high concern. Any technological advance that could reduce
emission levels is always welcome. In what concerns aircraft engines,
a possible solution for this problem could be the use of regenerators
and intercoolers. These components might reduce the specific fuel
consumption, increase efficiency and specific thrust and consequently
reduce the pollution levels of the engine. This is not a novel solution.
These heat exchangers are already is use in stationary engines. For
aircraft engines, the extra weight of the needed hardware could
overcome the fuel saved. This work compares a conventional engine
with configurations that use intercoolers and regenerators.
Abstract: The Prediction of aerodynamic characteristics and
shape optimization of airfoil under the ground effect have been carried
out by integration of computational fluid dynamics and the multiobjective
Pareto-based genetic algorithm. The main flow
characteristics around an airfoil of WIG craft are lift force, lift-to-drag
ratio and static height stability (H.S). However, they show a strong
trade-off phenomenon so that it is not easy to satisfy the design
requirements simultaneously. This difficulty can be resolved by the
optimal design. The above mentioned three characteristics are chosen
as the objective functions and NACA0015 airfoil is considered as a
baseline model in the present study. The profile of airfoil is
constructed by Bezier curves with fourteen control points and these
control points are adopted as the design variables. For multi-objective
optimization problems, the optimal solutions are not unique but a set
of non-dominated optima and they are called Pareto frontiers or Pareto
sets. As the results of optimization, forty numbers of non- dominated
Pareto optima can be obtained at thirty evolutions.
Abstract: Multifunctional structures are a potentially disruptive
technology that allows for significant mass savings on spacecraft.
The specific concept addressed herein is that of a multifunctional
power structure. In this paper, a parametric optimisation of the
design of such a structure that uses commercially available battery
cells is presented. Using numerical modelling, it was found that there
exists several trade-offs aboutthe conflict between the capacity of the
panel and its mechanical properties. It was found that there is no
universal optimal location for the cells. Placing them close to the
mechanical interfaces increases loading in the mechanically weak
cells whereas placing them at the centre of the panel increases the
stress inthe panel and reduces the stiffness of the structure.
Abstract: Numerical simulations are performed for laminar
continuous and pulsed jets impinging on a surface in order to
investigate the effects of pulsing frequency on the heat transfer
characteristics. The time-averaged Nusselt number of pulsed jets is
larger in the impinging jet region as compared to the continuous jet,
while it is smaller in the outer wall jet region. At the stagnation point,
the mean and RMS Nusselt numbers become larger and smaller,
respectively, as the pulsing frequency increases. Unsteady behaviors
of vortical fluid motions and temperature field are also investigated to
understand the underlying mechanisms of heat transfer enhancement.
Abstract: Applicability of tuning the controller gains for Stewart manipulator using genetic algorithm as an efficient search technique is investigated. Kinematics and dynamics models were introduced in detail for simulation purpose. A PD task space control scheme was used. For demonstrating technique feasibility, a Stewart manipulator numerical-model was built. A genetic algorithm was then employed to search for optimal controller gains. The controller was tested onsite a generic circular mission. The simulation results show that the technique is highly convergent with superior performance operating for different payloads.
Abstract: In the competitive environment of aircraft industries it becomes absolutely necessary to improve the efficiency, performance of the aircrafts to reduce the development and operating costs considerably, in order to capitalize the market. An important contribution to improve the efficiency and performance can be
achieved by decreasing the aircraft weight through considerable
usage of composite materials in primary aircraft structures. In this study, a type of composite material called Carbon Fiber Reinforced
Plastic (CFRP) is explored for the usage is aircraft skin panels. Even
though there were plenty of studies and research has been already
carried out, here a practical example of an aircraft skin panel is taken
and substantiated the benefits of composites material usage over the
metallic skin panel. A crown skin panel of a commercial aircraft is
designed using both metal and composite materials. Stress analysis
has been carried out for both and margin of safety is estimated for the
critical load cases. The skin panels are compared for manufacturing,
tooling, assembly and cost parameters. Detail step by step comparison between metal and composite constructions are studied
and results are tabulated for better understanding.
Abstract: A 3D simulation study for an incompressible
slip flow around a spherical aerosol particle was performed.
The full Navier-Stokes equations were solved and the velocity
jump at the gas-particle interface was treated numerically by
imposition of the slip boundary condition. Analytical solution
to the Stokesian slip flow past a spherical particle was used as
a benchmark for code verification, and excellent agreement
was achieved. The Simulation results showed that in addition
to the Knudsen number, the Reynolds number affects the slip
correction factor. Thus, the Cunningham-based slip corrections
must be augmented by the inclusion of the effect of
Reynolds number for application to Lagrangian tracking of
fine particles. A new expression for the slip correction factor
as a function of both Knudsen number and Reynolds number
was developed.
Abstract: This paper presents a numerical investigation of the
unsteady flow around an American 19th century vertical-axis
windmill: the Stevens & Jolly rotor, patented on April 16, 1895. The
computational approach used is based on solving the complete
transient Reynolds-Averaged Navier-Stokes (t-RANS) equations: a
full campaign of numerical simulation has been performed using the
k-ω SST turbulence model. Flow field characteristics have been
investigated for several values of tip speed ratio and for a constant
unperturbed free-stream wind velocity of 6 m/s, enabling the study of
some unsteady flow phenomena in the rotor wake. Finally, the global
power generated from the windmill has been determined for each
simulated angular velocity, allowing the calculation of the rotor
power-curve.
Abstract: A stiffened laminated composite panel (1 m length ×
0.5m width) was optimized for minimum weight and deflection under
several constraints using genetic algorithm. Here, a significant study
on the performance of a penalty function with two kinds of static and
dynamic penalty factors was conducted. The results have shown that
linear dynamic penalty factors are more effective than the static ones.
Also, a specially combined linear-exponential function has shown to
perform more effective than the previously mentioned penalty
functions. This was then resulted in the less sensitivity of the GA to
the amount of penalty factor.
Abstract: The aerodynamics characteristics of a blended-wing body (BWB) aircraft were obtained in Universiti Teknologi MARA low speed wind tunnel. The scaled-down of BWB model consisted of a canard as its horizontal stabilizer. There were four canards with different aspect ratio used in the experiments. Canard setting angles were varied from -20q to 20q. All tests were conducted at velocity of 35 m/s, with Mach number 0.1. At low angles of attacks, the increment of lift slope for various canards aspect ratio is small and almost constant. Higher canard aspect ratio will cause higher drag. However, canard has a high effect to the moment at zero lift, CM,0.The visualization using mini tuff was performed to observe the airflow at the upper surface of canard. KeywordsAerodynamics,blended-wing body, canard, wind tunnel.
Abstract: This paper presents a model for the evaluation of
energy performance and aerodynamic forces acting on a small
straight-bladed Darrieus-type vertical axis wind turbine depending on
blade geometrical section. It consists of an analytical code coupled to
a solid modeling software, capable of generating the desired blade
geometry based on the desired blade design geometric parameters.
Such module is then linked to a finite volume commercial CFD code
for the calculation of rotor performance by integration of the
aerodynamic forces along the perimeter of each blade for a full period
of revolution.After describing and validating the computational
model with experimental data, the results of numerical simulations
are proposed on the bases of two candidate airfoil sections, that is a
classical symmetrical NACA 0021 blade profile and the recently
developed DU 06-W-200 non-symmetric and laminar blade
profile.Through a full CFD campaign of analysis, the effects of blade
geometrical section on angle of attack are first investigated and then
the overall rotor torque and power are analyzed as a function of blade
azimuthal position, achieving a numerical quantification of the
influence of airfoil geometry on overall rotor performance.
Abstract: In order to improve the simulation effects of space cold
black environment, this paper described a rectangular channel plate
heat sink. By using fluid mechanics theory and finite element method,
the internal fluid flow and heat transfer in heat sink was numerically
simulated to analyze the impact of channel structural on fluid flow and
heat transfer. The result showed that heat sink temperature uniformity
is well, and the impact of channel structural on the heat sink
temperature uniformity is not significant. The channel depth and
spacing are important factors which affect the fluid flow and heat
transfer in the heat sink. The two factors of heat transfer and resistance
need to be considered comprehensively to determine the optimal flow
structure parameters.
Abstract: Numerical study of a plane jet occurring in a vertical
heated channel is carried out. The aim is to explore the influence of
the forced flow, issued from a flat nozzle located in the entry section
of a channel, on the up-going fluid along the channel walls. The
Reynolds number based on the nozzle width and the jet velocity
ranges between 3 103 and 2.104; whereas, the Grashof number based
on the channel length and the wall temperature difference is 2.57
1010. Computations are established for a symmetrically heated
channel and various nozzle positions. The system of governing
equations is solved with a finite volumes method. The obtained
results show that the jet-wall interactions activate the heat transfer,
the position variation modifies the heat transfer especially for low
Reynolds numbers: the heat transfer is enhanced for the adjacent
wall; however it is decreased for the opposite one. The numerical
velocity and temperature fields are post-processed to compute the
quantities of engineering interest such as the induced mass flow rate,
and the Nusselt number along the plates.