Abstract: In this study, noise characteristics of structure were analyzed in an effort to reduce noise passing through an opening of an
enclosure surrounding the structure that generates noise. Enclosures
are essential measure to protect noise propagation from operating machinery. Access openings of the enclosures are important path of noise leakage. First, noise characteristics of structure were analyzed
and feed-forward noise control was performed using simulation in
order to reduce noise passing through the opening of enclosure, which
surrounds a structure generating noise. We then implemented a
feed-forward controller to actively control the acoustic power through
the opening. Finally, we conducted optimization of placement of the
reference sensors for several cases of the number of sensors. Good
control performances were achieved using the minimum number of microphones arranged an optimal placement.
Abstract: In this paper after reviewing some previous studies, in
order to optimize the above knee prosthesis, beside the inertial
properties a new controlling parameter is informed. This controlling
parameter makes the prosthesis able to act as a multi behavior system
when the amputee is opposing to different environments. This active
prosthesis with the new controlling parameter can simplify the
control of prosthesis and reduce the rate of energy consumption in
comparison to recently presented similar prosthesis “Agonistantagonist
active knee prosthesis".
In this paper three models are generated, a passive, an active, and
an optimized active prosthesis. Second order Taylor series is the
numerical method in solution of the models equations and the
optimization procedure is genetic algorithm.
Modeling the prosthesis which comprises this new controlling
parameter (SEP) during the swing phase represents acceptable results
in comparison to natural behavior of shank. Reported results in this
paper represent 3.3 degrees as the maximum deviation of models
shank angle from the natural pattern. The natural gait pattern belongs
to walking at the speed of 81 m/min.
Abstract: This paper presents the design, fabrication and
evaluation of magneto-rheological damper. Semi-active control
devices have received significant attention in recent years because
they offer the adaptability of active control devices without requiring
the associated large power sources. Magneto-Rheological (MR)
dampers are semi- active control devices that use MR fluids to
produce controllable dampers. They potentially offer highly reliable
operation and can be viewed as fail-safe in that they become passive
dampers if the control hardware malfunction. The advantage of MR
dampers over conventional dampers are that they are simple in
construction, compromise between high frequency isolation and
natural frequency isolation, they offer semi-active control, use very
little power, have very quick response, has few moving parts, have a
relax tolerances and direct interfacing with electronics. Magneto-
Rheological (MR) fluids are Controllable fluids belonging to the
class of active materials that have the unique ability to change
dynamic yield stress when acted upon by an electric or magnetic
field, while maintaining viscosity relatively constant. This property
can be utilized in MR damper where the damping force is changed by
changing the rheological properties of the fluid magnetically. MR
fluids have a dynamic yield stress over Electro-Rheological fluids
(ER) and a broader operational temperature range. The objective of
this papert was to study the application of an MR damper to vibration
control, design the vibration damper using MR fluids, test and
evaluate its performance. In this paper the Rheology and the theory
behind MR fluids and their use on vibration control were studied.
Then a MR vibration damper suitable for vehicle suspension was
designed and fabricated using the MR fluid. The MR damper was
tested using a dynamic test rig and the results were obtained in the
form of force vs velocity and the force vs displacement plots. The
results were encouraging and greatly inspire further research on the
topic.
Abstract: This paper presents anti-synchronization of chaos
between two different chaotic systems using active control method.
The proposed technique is applied to achieve chaos antisynchronization
for the Lü and Rössler dynamical systems.
Numerical simulations are implemented to verify the results.
Abstract: Experiments have been carried out at sub-critical
Reynolds number to investigate free-to-roll motions induced by
forebody and/or wings complex flow on a 30° swept back nonslender
wings-slender body-model for static and dynamic (pitch-up)
cases. For the dynamic (pitch-up) case it has been observed that roll
amplitude decreases and lag increases with increase in pitching
speed. Decrease in roll amplitude with increase in pitch rate is
attributed to low disturbing rolling moment due to weaker interaction
between forebody and wing flow components. Asymmetric forebody
vortices dominate and control the roll motion of the model in
dynamic case when non-dimensional pitch rate ≥ 1x10-2.
Effectiveness of the active control scheme utilizing rotating nose with
artificial tip perturbation is observed to be low in the angle of attack
region where the complex flow over the wings has contributions from
both forebody and wings.
Abstract: In the present paper, active control system is used in
different heights of the building and the most effective part was
studied where the active control system is applied. The mathematical
model of the building is established in MATLAB and in order to
active control the system FLC method was used. Three different
locations of the building are chosen to apply active control system,
namely at the lowest story, the middle height of the building, and at
the highest point of the building with TMD system. The equation of
motion was written for high rise building and it was solved by statespace
method. Also passive control was used with Tuned Mass
Damper (TMD) at the top floor of the building to show the robustness
of FLC method when compared with passive control system.
Abstract: The three-dimensional incompressible flow past a
rectangular open cavity is investigated, where the aspect ratio of the
cavity is considered as 4. The principle objective is to use large-eddy
simulation to resolve and control the large-scale structures, which are
largely responsible for flow oscillations in a cavity. The flow past an
open cavity is very common in aerospace applications and can be a
cause of acoustic source due to hydrodynamic instability of the shear
layer and its interactions with the downstream edge. The unsteady
Navier-stokes equations have been solved on a staggered mesh using
a symmetry-preserving central difference scheme. Synthetic jet has
been used as an active control to suppress the cavity oscillations in
wake mode for a Reynolds number of ReD = 3360. The effect of
synthetic jet has been studied by varying the jet amplitude and
frequency, which is placed at the upstream wall of the cavity. The
study indicates that there exits a frequency band, which is larger than
a critical value, is effective in attenuating cavity oscillations when
blowing ratio is more than 1.0.
Abstract: In this study, control performance of a smart base
isolation system consisting of a friction pendulum system (FPS) and a
magnetorheological (MR) damper has been investigated. A fuzzy
logic controller (FLC) is used to modulate the MR damper so as to
minimize structural acceleration while maintaining acceptable base
displacement levels. To this end, a multi-objective optimization
scheme is used to optimize parameters of membership functions and
find appropriate fuzzy rules. To demonstrate effectiveness of the
proposed multi-objective genetic algorithm for FLC, a numerical
study of a smart base isolation system is conducted using several
historical earthquakes. It is shown that the proposed method can find
optimal fuzzy rules and that the optimized FLC outperforms not only a
passive control strategy but also a human-designed FLC and a
conventional semi-active control algorithm.
Abstract: In the LFC problem, the interconnections among some areas are the input of disturbances, and therefore, it is important to suppress the disturbances by the coordination of governor systems. In contrast, tie-line power flow control by TCPS located between two areas makes it possible to stabilize the system frequency oscillations positively through interconnection, which is also expected to provide a new ancillary service for the further power systems. Thus, a control strategy using controlling the phase angle of TCPS is proposed for provide active control facility of system frequency in this paper. Also, the optimum adjustment of PID controller's parameters in a robust way under bilateral contracted scenario following the large step load demands and disturbances with and without TCPS are investigated by Particle Swarm Optimization (PSO), that has a strong ability to find the most optimistic results. This newly developed control strategy combines the advantage of PSO and TCPS and has simple stricture that is easy to implement and tune. To demonstrate the effectiveness of the proposed control strategy a three-area restructured power system is considered as a test system under different operating conditions and system nonlinearities. Analysis reveals that the TCPS is quite capable of suppressing the frequency and tie-line power oscillations effectively as compared to that obtained without TCPS for a wide range of plant parameter changes, area load demands and disturbances even in the presence of system nonlinearities.
Abstract: A semi-active control strategy for suspension
systems of passenger cars is presented employing
Magnetorheological (MR) dampers. The vehicle is modeled with
seven DOFs including the, roll pitch and bounce of car body, and
the vertical motion of the four tires. In order to design an optimal
controller based on the actuator constraints, a Linear-Quadratic
Regulator (LQR) is designed. The design procedure of the LQR
consists of selecting two weighting matrices to minimize the energy
of the control system. This paper presents a hybrid optimization
procedure which is a combination of gradient-based and
evolutionary algorithms to choose the weighting matrices with
regards to the actuator constraint. The optimization algorithm is
defined based on maximum comfort and actuator constraints. It is
noted that utilizing the present control algorithm may significantly
reduce the vibration response of the passenger car, thus, providing
a comfortable ride.
Abstract: In this paper, a generalized synchronization scheme, which is called function synchronization, for chaotic systems is studied. Based on Lyapunov method and active control method, we design the synchronization controller for the system such that the error dynamics between master and slave chaotic systems is asymptotically stable. For verification of our theory, computer and circuit simulations for a specific chaotic system is conducted.
Abstract: In the real application of active control systems to
mitigate the response of structures subjected to sever external
excitations such as earthquake and wind induced vibrations, since the
capacity of actuators is limited then the actuators saturate. Hence, in
designing controllers for linear and nonlinear structures under sever
earthquakes, the actuator saturation should be considered as a
constraint. In this paper optimal design of active controllers for
nonlinear structures by considering the actuator saturation has been
studied. To this end a method has been proposed based on defining
an optimization problem which considers the minimizing of the
maximum displacement of the structure as objective when a limited
capacity for actuator has been used as a constraint in optimization
problem. To evaluate the effectiveness of the proposed method, a
single degree of freedom (SDF) structure with a bilinear hysteretic
behavior has been simulated under a white noise ground acceleration
of different amplitudes. Active tendon control mechanism, comprised
of pre-stressed tendons and an actuator, and extended nonlinear
Newmark method based instantaneous optimal control algorithm
have been used as active control mechanism and algorithm. To
enhance the efficiency of the controllers, the weights corresponding
to displacement, velocity, acceleration and control force in the
performance index have been found by using the Distributed Genetic
Algorithm (DGA). According to the results it has been concluded
that the proposed method has been effective in considering the
actuator saturation in designing optimal controllers for nonlinear
frames. Also it has been shown that the actuator capacity and the
average value of required control force are two important factors in
designing nonlinear controllers for considering the actuator
saturation.
Abstract: Since the actuator capacity is limited, in the real
application of active control systems under sever earthquakes it is
conceivable that the actuators saturate, hence the actuator saturation
should be considered as a constraint in design of optimal controllers.
In this paper optimal design of active controllers for nonlinear
structures by considering actuator saturation, has been studied. The
proposed method for designing optimal controllers is based on
defining an optimization problem which the objective has been to
minimize the maximum displacement of structure when a limited
capacity for actuator has been used. To this end a single degree of
freedom (SDF) structure with a bilinear hysteretic behavior has been
simulated under a white noise ground acceleration of different
amplitudes. Active tendon control mechanism, comprised of prestressed
tendons and an actuator, and extended nonlinear Newmark
method based instantaneous optimal control algorithm have been
used. To achieve the best results, the weights corresponding to
displacement, velocity, acceleration and control force in the
performance index have been optimized by the Distributed Genetic
Algorithm (DGA). Results show the effectiveness of the proposed
method in considering actuator saturation. Also based on the
numerical simulations it can be concluded that the actuator capacity
and the average value of required control force are two important
factors in designing nonlinear controllers which consider the actuator
saturation.