Exam 2 - Study guide questions Flashcards
Principles of using martensite SMA and superelastic SMA for passive vibration damping
Both have potential for passive vibration control through vibration isolation and energy dissipation
Superelastic is preferred because it is passive (requires no external source) but martensite has greater capacity for damping
Two mechanisms for passive vibration control using SMAs
Vibration isolation and Energy dissipation
Why pre-tension is often required when the superelastic SMA is used for passive vibration damping?
Pre-tension is applied to avoid the linear elastic region that does not dissipate energy
What is the function of superelastic SMA in the friction damper subject to seismic load?
To provide re-centering capacity while the integrated friction device provides the most energy dissipation (superelastic SMAs provide an inherent damping property also)
Effect of nitinol SMA wires in the case of ECC reinforcement
To provide energy dissipation and self-repair cracks
Principle of using martensite SMA and superelastic SMA in concrete structure self-rehab
Self-rehab property through heating martensite SMA
increased damping
self-sensing ability through monitoring the electrical resistance value of the SMA wire strands
What does monitoring the electrical resistance values of SMA cables tell us in concrete structure?
elongation of SMA wires increases electrical resistance thereby monitoring the electrical resistance we can monitor the elongation
MANSIDE project - how the SMA device provides self-centering and energy dissipation
re-centering group is based on superelastic SMA wires to re-center the device/building
pre-tension superelastic wires wound around studs dissipate energy by acting as two counteracting springs
Basic principle of using SMA wires for base isolation
Two superelastic SMA springs used for passive base isolation provide energy dissipation due to hysteresis and self-centering due to superelastic effect
Why are feedback controllers needed in the operation of SMA wire actuators?
Challenges posed by the nonlinear response (hysteresis) feedback controllers help manage this nonlinearity by continuously monitoring the actuators position and adjusting inputs accordingly
Difference in position regulation and position tracking controllers
Position regulation: moving from point A to point B - focuses on reaching and maintaining a fixed target position
Position tracking: time dependent - suitable for applications requiring dynamic movement and accurate following of a changing path and also incorporates a feed-forward term which is used to anticipate the desired trajectory and provide initial control input that guides the actuator along its path
The feed-forward term is designed to provide the approximate amount of current required for the SMA actuator to follow the desired path
Liquid vehicle of MR fluids
mineral oil, synthetic hydrocarbon oil, silicone oil, water
Polarizable particles of MR fluids
Carbonyl iron, powdered iron, iron/cobalt alloys
Size of polarizable MR fluid particles
1-10 microns
Yield stress of MR fluids
50 - 100 kPa
Power requirements of MR damper/fluid
50 watts, 12-24 volts, 1-2 amps
Power requirements of ER damper/fluid
50 watts, 2,000-5,000 volts, 1-10 amps
What is a bingham model used for?
rheological model used to describe the flow behavior of certain non-newtonian fluids and characterizes materials that behave as a rigid body at low stresses but flow as a viscous fluid at high stress
Slope of stress vs. strain
Key features of the bingham model
Yield stress and viscosity
When applied stress exceeds yield stress the fluid will flow
Three common operational modes of MR fluids
Pressure driven (valve mode) - fixed poles (servo-valves, dampers and shock absorbers)
Direct shear driven - relatively moveable poles (clutches, brakes, locking devices)
Squeeze film
Which operational mode of MR fluids uses disks?
Direct shear driven - clutches/brakes
Pressure driven flow mode is a result of the sum of what two components?
Viscous component and field dependent induced yield stress
What is the volume of MR fluid exposed to the magnetic field and thus is responsible in providing the desired MR effect
Active fluid volume
geometric constraints and necessary aspect ratios for MR devices can be determined from manipulating what equations?
Equation for active fluid volume V (eq. 5)
The force or torque inputs from actuators are usually used to suppress vibration amplitudes based on on-line measurements from sensors
Active vibration control (MR damper)
System that combines the best features of active+passive control offering the reliability of passive devices, yet maintaining the versatility and adaptability of active systems
Semi-active control (MR dampers)
Viscous damper, oil damper, viscoelastic damper, steel damper are all what types of dampers?
Passive Damper
variable orifice damper, friction controllable braces, friction controllable isolators, variable stiffness devices are all what types of dampers?
Semi-Active damper
Three models of MR dampers
Bingham Viscoplastic, Bouc-Wen, Modified Bouc-Wen
What is Bingham Viscoplastic model good for? Bouc-Wen?
Bingham for response analysis, but not for control analysis
Bouc-Wen for hysteresis modeling
Proper selection of a control algorithm for MR damper may be dependent on what three things?
The type of non-linearity present, available feedback measurements, number of devices to be implemented in the structure
Simplest and cheapest way to implement a control law and useful for vibration isolation of rotating machines ?
Open-loop (on-off) control (sponge damper for washing machine)
Working principle of FOSs
Total reflection of light rays within the core of the fiber optic cable
Main components of a FOS system?
Light source, transducer, measurand, detector
Four common types of sensors by modulation process
Intensity (amplitude), phase, frequency/wavelength, polarization
Extrinsic vs Intrinsic FOS
Extrinsic - sensing takes place outside of the fiber
Intrinsic - one or more of the physical properties of the fiber undergo a change
Modulation of point FOS
One point of fiber is a sensor
Distributed FOS
Whole cable is sensor
Quasi-Distributed FOS
Periodic portions of fiber act as sensor
Mach-Zehnder, Michelson, Fabry-Perot, EFPI skin friction sensor, EFPI acoustic emission sensor are all what type of FOS?
Phase modulated
Reflective, Fiber displacement, transmission loss, micro/macro bend, evanescent are all techniques to create what type of FOS?
Intensity modulated
Fiber Bragg and Long Period Grating FOSs are what types of FOSs?
Wavelength modulated
Guided modes and cladding modes that propagate in the same direction - the results are attenuation bands in the transmission spectrum
Long period grating sensors
Made by inscribing periodic gratings into the core of the fiber. The gratings are of a different refractive index and will reflect portions of a certain wavelength backwards in phase
Fiber Bragg grating sensor
Capable of providing measurements along the entire FOC
Distributed FOSs
Three scattering processes used in DFOS
Rayleigh, Raman, Brillouin
Brillouin scattering is used to implement what two types of FOSs?
Distributed temperature sensor (DTS) and distributed strain sensor (DSS)
Two categories of Rayleigh analysis techniques
Optical time domain reflectometer (OTDR) and optical frequency domain reflectometer (OFDR)
And is often used for Distributed Acoustic Sensor (DAS)
