Exam 2 Flashcards
DTS sensor
Distributed temperature sensor
Raman and Brillouin
What are Distributed FOS
A class of FOSs that provide measurement along the entire cable
Based on different scattering processes (Rayleigh, Raman, Brillouin)
DSS sensor
Distributed strain sensor
Raman and Brillouin
OTDR
Optical time domain reflectometer
A type of Rayleigh analysis
OFDR
Optical frequency domain reflectometer
A type of Rayleigh analysis
Phase Modulated Sensors
measures phase difference between two rays of light that get separated by a coupler and read at the detector
Mach-Zehnder
Michelson
Fabry-Perot
Intensity Modulated Sensors
Encode information about the environment through changes in the intensity of the light travelling in the fiber
Techniques to create intensity modulated FOSs
Reflective
Micro/Macro Bend
Wavelength Modulated
Frequency/wavelength is changed and measured
Fiber Bragg Gratings
Long Period Gratings
Two types of Rayleigh sensors
Can be optical time domain reflectometer (OTDR) or optical frequency domain reflectometer (OFDR)
What type of sensor is Raman scattering used for?
distributed temperature sensor (DTS)
What type of sensor is Brillouin scattering used for?
Distributed temperature sensors (DTS)
Distributed strain sensors (DSS)
Two mechanisms/properties of SMAs used for damping capacity
Martensite reorientation
Stress-induced martensite transformation (superelasticity)
Which has larger damping capacity for single loop? Martensite or austenite
Martensite
What two modes can SMAs be used for structural control
Active and passive mode
Is the principle of active structural control using SMAs based on shape memory effect or superelasticity?
shape memory effect - must apply external heat source to change
Is vibration damping of civil structures mostly based on passive or active control?
Passive
How are SMAs used for passive vibration control of civil structures?
vibration isolation and energy dissipation
Is superelastic SMA or martensite SMA preferred for energy dissipation devices?
Superelastic is preferred although martensite has higher damping capacity
What are the two functional SMA wire groups?
Re-centering and dissipation groups
What property of SMA is the re-centering SMA wire group based on?
austenite superelastic wires
Why is pre-tension applied in the re-centering device for seismic isolation of civil structures?
To avoid the linear elastic region that does not dissipate energy
What are the two properties SMA springs posses in the case of base isolation?
Energy dissipation due to hysteresis and self-centering due to superelasticity
True or false: with inherent damping property, superelastic SMA wires also provide energy dissipation?
True
Strain of ECC concrete?
5%
What are superelastic SMA wires used for in ECC?
to reinforce the ECC to provide energy dissipation and self-repair
Highly non-linear phenomenon that requires feedback control for accurate actuation?
Hysteresis
Is hysteresis good for energy dissipation?
Yes
Is hysteresis good for actuation?
No
Two control methods for SMA actuators?
Position regulation and position tracking using sliding-mode based robust controller
Control method for controlling with uncertainty or variations
Robust control
Controllers used for convergence onto the sliding surface/sliding mode?
Bang-Bang controller, Saturation controller, Smooth controller
Difference in position regulation and position tracking controller design?
Position tracking is time-dependent and includes a “feed-forward” term whereas position regulation is point A to B
What is the feed-forward term?
Used in position tracking controller design and is used to provide the approximate amount of current required for the SMA actuator to follow the desired path
Power requirements for MR and ER fluids
MR requires low power12-24V, ER requires 2000-5000V
Max yield stress for MR and ER fluids
MR: 50-100 kPa
ER: 2-5 kPa
Key difference in ferrofluids compared to MR/ER fluids?
Particle size
Ferrofluids particle size is very small and is subjected to significant Brownian motion which is the random motion of particles suspended in fluid resulting from their collision with fast moving molecules in the fluid
Working principle of MR valve damper
electromagnetic coil surrounds fluid valve orifice, fluid flows through the valve and when the device is on the electrical charge is sent to the coil which induces a magnetic field as the fluid passes through
Advantages of MR valve type damper
no moving parts, continuously viable, low voltage controls, strong force
Does a larger loop mean larger or smaller energy dissipation?
Larger
True or false: increased voltage - > max damping force increases (MR damper)
True
What type of damper design (30 ton) is used for large buildings?
Bypass design where the electromagnet is incorporated into the bypass portion
What are FDI filters used for?
Detecting and isolating unknown faults in actuators, sensors, system components
Working principle of MR fluid when magnetic field is applied?
MR response results from polarization induced in suspended particles by application of external magnetic field
What is the bingham model used for?
to describe the flow behavior of certain types of fluids that behave like solids at low stress but flow like a viscous fluid when the applied stress exceeds a certain threshold
What does tau represent in the bingham model equations?
field dependent yield stress
Three operational modes of MR fluids
Pressure driven flow mode (valve mode), direct shear mode, squeeze film mode
Servo-valves, dampers, shock absorbers are examples of what MR fluid operational mode? (pressure driven, direct shear, squeeze)
Pressure driven
Clutches, brakes, chucking and locking devices are examples of what MR fluid operational mode? (pressure driven, direct shear, squeeze)
Direct shear
What is active fluid volume?
Fluid exposed to the magnetic field and responsible for providing the desired MR effect
Is resonance control using MR damper engine mount pressure driven or direct shear driven mode?
pressure driven
What operational mode are the equations of pressure drop of MR fluids used for?
Pressure driven mode
What are the two key parts of the pressure driven equations for MR fluids?
viscous component and field dependent induced yield stress
Equations for direct shear mode of MR fluids include components of what?
Force (viscous and applied)
Minimum active fluid volume is proportional to the product of what three terms?
MR fluid material properties, desired control ratio or dynamic range lambda, controlled mechanical power dissipation Wm
Why are bypass designs used for large MR dampers?
To provide adequate space for the large number of coils used in the electromagnet. Small dampers need less coils
Key points of “power-on” MR valve
Utilizes permanent magnet to reduce energy
Higher damping and lower energy
Provides a minimum damping force when powered off - no energy consumption
when powered on can increase or decrease damping by controlling the electromagnetic coil
what is a B-H curve?
characteristic curve of the magnetic property of a metal or material that tells us how the material responds to an external magnetic field
It is a critical piece of information when designing magnetic circuits
What is magnetic saturation?
The state reached when an increase in applied external magnetic field H, cannot increase the magnetization of the material further
Purpose of using steel or metal in MR damper/devices?
to provide a low-reluctance flux conduit to guide and focus magnetic flux into region of active magnetic fluid (fluid gap in the MR valve)
Four step process for magnetic circuit design
- select operating point (Hf, Bf) in MR fluid to give desired yield stress tau
- Use principle of continuity of magnetic flux to determine flux density Bs throughout flux conduit
- Determine operating point in steel
- Use Kirchoff’s law for magnetic circuits to determine necessary amp-turns
What is considered “active control” for MR damper modeling?
The force or torque inputs from the actuators are usually used to suppress vibration amplitudes based on on-line measurements from sensors
More effective than a passive system but requires system power supply
What is considered “passive control” for MR damper modeling?
Do not require external energy - more reliable but less effective
Examples of semi-active MR devices
variable orifice damper, friction controllable braces, friction controllable isolators, variable stiffness devices, controllable fluid devices
Passive damper types for civil engineering applications?
viscous damper, oil damper, viscoelastic damper, steel damper
Three models for MR damper modeling
Bingham, Bouc-Wen, Modified Bouc-Wen
MR damper model that is adequate for response analysis but not for control analysis?
Bingham model
What MR damper model is used to model hysteresis?
Bouc-Wen
Attempts to eliminate the tradeoff between resonance control and high frequency isolation common to passive suspensions?
Skyhook
What principle do fiber optics work off?
Total reflection of light rays within the core of the fiber optic cable
The three common types of fiber optic construction?
Single mode, multi-mode, plastic
Four basic components of a FOS system?
Light source, Transducer, Measurand, Detector
Three types of fiber optic sensors
Phase modulated, intensity modulated, wavelength modulated
Phase modulated FOSs
Detect changes in the phase of the light
Intensity modulated FOSs
Detect changes in the intensity of the light travelling through the fiber
Wavelength modulated FOSs
Detect changes in the wavelength of the light in the fiber
Used in measurement of temperature or strain
Distributed temperature sensing (DTS)
Operation principle of phase modulated FOS
Encode particular parameters of the environment by measuring the phase difference or a reference and measuring light rays
Also referred to as interferometric fiber optic sensors and use a coupler to split the light and compare the two
Five types of phase modulated sensors
Sagnac, Mach-Zehnder, Michelson, Fabry-Perot, Ring Resonator
Extrinsic vs Intrinsic FOSs
Extrinsic - sensing takes place in a region outside of the fiber and the fiber serves as a conduit
Intrinsic - one or more of the physical properties of the fiber undergo a change (fiber bragg)
Operation principle of intensity modulated sensors
Encode information about the environment through changes in the intensity of the light travelling within the fiber
Operation principle of wavelength modulated sensors
Frequency/wavelength of the light is changed by factors in the environment (intrinsic)
Fiber Bragg/ Long Period
Difference between distributed fiber optic sensors and other common FOSs?
DFOS are capable of providing measurements along the entire cable and not specific points like other sensors
Three different scattering processes
Rayleigh, Raman, Brillouin
Two categories of Rayleigh analysis techniques
Optical Time Domain Reflectometer (OTDR)
Optical Frequency Domain Reflectometer (OFDR)
Which scattering (Rayleigh, Raman, Brillouin) is based on the principle of density fluctuations
Rayleigh
Which FOS example is capable of determining (from scattered light) a component which indicates changes in the local axial strain along the fiber?
iDAS
