Name 4 of the 7 propulsion Modes Flashcards
Name the main 5 of the 7 Propulsion modes?
Turbo reduction Turbo Electric Battery Diesel electric AIP
Diesel reduction and Diesel direct not used
What are the Advantages and disadvantages of Nuclear and Diesel
Define Sound
A periodic variation of pressure, particle displacement, or particle velocity in an elastic medium
Describe/ draw the 3 layer ocean model
Define a choke point
Choke points are a geographical feature above or below the surface that restrict the freedom of movement of a submarine
Give example of a choke point
Strait of Malacca
Straits of Gibraltar
English Channel
What are the three main requirements of a successful underwater detection system?
Good penetration/ sensitivity
High resolution
High data rate
Name the following components on turbo reduction system
What are three factors that effect speed of sound in water and what figures are attributed to them?
Temperature - 1oC increase = 3m/s increase
Pressure - 100m depth increase = 2m/s increase
Salinity 1pp thousand = 1.1m/s increase
Which of these factors has the greatest effect on speed of sound on water?
Temperature
Define the doppler phenomenon
Doppler is the apparent change in frequency due to relative motion between a source and a stationary receiver.
A submarine is detected at 405hz and drops 4hz before fading out. Assuming AV of 1500 work out the speed of the submarine?
1500 x (405-401)
———————— = 14.8kts
403
What does DIFAR stand for?
Directional Frequency Analysis & Recording (passive)
What are the variable depths and operating life associate with DIFAR?
90, 200, 400, 1000ft
0.5, 1, 2, 4 or 8 hrs
What does DICASS stand for?
Directional Command Activated Sonobouy System (active)
What is DICASS operating life and what are the associated depths
60 minutes / 50 ping seconds
D1: 50,150,300ft
D2: 90,400,1500ft
What 6 information can be gained from CPA? (Closest point of approach)
f0 Depth Speed Range Track Bearing
What is HALT?
High Away Low Towards
In relation to SNELLS LAW - Sound is lazy and will bend away from areas of high velocity towards areas of low velocity
Draw the basic topography of the north Atlantic ocean
What are the NATO designators for Submarines and what is DSRV?
Deep sea rescue vehicle
SS on his own because he’s a nazi
BAG for nuclear
NCP for others
National Car Parks
What are the 2 types of seamounts?
guyots
pinnacle
Define ambient noise and what are the two types?
Ambient noise is defined as any noise within the ocean that is not target related.
- Man made
- Natural
State the man-made and natural sources of ambient noise
- Drilling (oil and gas)
- Shipping (merchant traffic/fishing)
- Active transmission (military/civilian)
- Seismic Surveys
- Biological
- Ice
- Seismic (volcanic activity /tectonic plates)
- Weather
What are 3 main types of bottom composition?
sand, rock, mud and silt
What are the 4 dimensions from a lofar gram?
colour
frequency
time
intensity
What are the 4 bottom types in order of reflectivity
Sand, Rock, mud/silt and ooze
To double in sound is an increase of how many dB?
3dB
To increase 5X in sound is how many dB?
7db
To increase 100 times in sound is how many dB?
20db
What is the difference between Active and passive?
Active is 2 way
Passive is 1 way
Spherical spreading decreases by how much when doubled?
6db
Cylindrical spreading decreases by how much each double?
3db
What is the Sonic Layer Depth? (SLD)
The MAXIMUM acoustic velocity (AV) over the first 1000ft of water
Normally SLD is the depth at the bottom of the mixed layer
Define the critical angle?
The steepest angle at which there is a 100% reflection from the bottom or surface
At what temperature is water most dense?
4oC
What percentage of the convergence zone is the annulus?
10%
Describe basic Ocean topography? And what are the two other names for seamounts/ridges
Guyots/pinnacles
Describe the snorting system
What are the 2 forms of propagation loss?
Spreading and Attenuation
What are the two types of spreading and how do they differ?
Spherical Spreading dissipates in all directions. Decrease of 6dB when the distance is doubled
Cylindrical spreading is concentrated so sound decreases by 3dB when the distance is doubled
What are the 4 types of attenuation?
Absorption
Scattering
Duct leakage
Deep scattering layer
What are the convergence zone ranges in the North Atlantic and Mediterranean?
North Atlantic = 28 - 32nms
Mediterranean = 14 to 18nms
What is the average velocity of sound in water?
1500m/s average
What are the 4 reasons a submarine would surface?
- Snort/charge batteries
- Emergencies
- Attack solutions
- Communications
What is wavelength?
One cycle of compression and rarefaction
What is frequency?
The number of complete cycle waves passing a fixed point in one second.
How is water depth measured and what are the figures associated?
Fathom = 6ft/2m
Define reflection
sound energy up to 99% of which is reflected from the sea bed or surface
Describe what’s happening and why?
Describe what’s happening and why?
Describe what’s happening and why?
Describe what’s happening and why?
What are the 5 sound propagation paths .
Surface ducting Bottom Bounce Convergence zone Sound channels Direct Path
What temperature reduction is needed for iso conditions to occur when the depth increases
Decrease of 0.6oC
Define ambient noise
Any background noise which is non target related
What are the 5 sources of noise from a submarine?
Broad band - when received energy is spread over a wide spectrum and individual frequencies are not distinguishable
Broadband effect - caused by multiple paths of BB energy reflecting off the sea bed
Lloyds mirror - multiple paths of BB energy reflect off the surface allowing depth to be calculated
Narrow band - when revived energy is concentrate in one discrete spectrum
Transients - noise that occurs over a short or long term over irregular intervals
What are the different types of propellor?
Fixed pitch (tankers/cargo) Controllable/Variable pitch Azipod (cruise liners/fast ferries) Skewed (submarines) Propulsor drive (military surface)
What is the general blade and shaft fit of military vessels
Multi-shaft (up to 4) and usually 4-7 blades. 2 shaft / 5 blade most common
What is the general blade and shaft fit of merchant vessels?
Single shaft, large vessels 4-7 blades, small & medium 3-4 blades
What is the predominant frequency spectrum for blade and shaft?
0-70hZ
Define blade rate
The number of times a blade passes a given point in 1 second (given in Hz)
Define shaft rate
The number of times the shaft passes a given point in 1 second (given in hZ)
What is a fundamental frequency?
It is the base or origin frequency measured in cycles per second and expressed in Hz
What is a harmonic frequency?
It is an echo of the fundamental frequency (can be numerous echoes)
What is the definition of CPA? (closest point of approach)
The point at which the vessel passes from high to low (F0) and the track of the vessel is at 90 degrees to the buoy.
What is the frequency range of 4 stroke engines ?
Predominately 150Hz and above
What is the frequency range of blade and shaft?
Predominately 0-70Hz
What is the frequency range of 2 stroke engines?
Predominately 70-150Hz
Define an ocean front
The boundary between to water masses of different thermal and velocity characteristics.
What are ocean fronts divided into and how do they differ?
Semi-permanent - remain more or less static for long periods.
Temporary - temporary changes in ocean structure brought about by significant meteorological changes or tidal activity
What are the effects of ocean fronts on sound propagation?
Propagation is poor, varies by as much as 25db
Causes significant errors in sonar bearings
What are the size of ocean waves determined by?
Wind strength
Wind duration
Fetch (size of area)
What are the sonobuoy sizes?
A, G, F
What are the components of a sonobuoy?
Housing Flip plate and parachute Aerial and flotation bag Surface unit Cable drunk/compliant cable Strum net and damper Hydrophone
What are the two types of beam forming?
Cardioid (Bum)
Limacon (turtle head)
What pilot frequency does a DIFAR transmit?
7.5khz
What is the channel separation of a DIFAR and what channels are/aren’t available?
375khz separation
1-99 except 57,58 and 93)
What are the characteristics of a bathy buoy?
Measure temp vs depth
12 mins life
2624ft depth
5ft/sec sink rate
DIFAR can be programmed to what modes of operation?
Omni-directional Pseudo-Omni or POM (default) Null Automatic noise cancel Look
What are the 3 types of Gram Displays?
Full band
Main band
Vernier
How can a DIFAR be affected?
1) Bouy wash over
2) The speed at which a contact passes the buoy
3) Poor signal to noise ratio
4) Biasing
What are the two mediums on which DIFAR is displayed?
BCP (bearing coherent processing)
Gram
What are noise sources associated with Fishing vessels?
Exhaust flutter Trawl Noise In/out Shaft rub Blade Flutter Diesel roar
What are noises associated with Merchant vessels?
In/out Shaft rub Flutter Slap Cav Constant RPM
What is absorption?
Loss by molecular action
What is aliasing?
A term used to describe the mirror imaging of a frequency. To combat aliasing the sampling rate needs to be double the bandwidth.
What are factors affecting detection by a sonobuoy?
DCT - Data Collection Time Resolution IT - Integration Time Frequency History Normalisation
What is the relationship between Data Collection Time (DCT) and resolution?
Res = 1 / DCT or DCR = 1 / Res
What is the Passive Sonar Equation?
Signal Excess = Source Level - Prop Loss - Ambient Noise - Recognition Differential - Directivity Index
SE = SL - PL - AN - RD - DI
What is the median detection range (MDR)?
The range at which there is a 50% probability of detection on a single sonobuoy.
What are the characteristic of mimic and wader?
Mimic = Low Freq 50, 60, 120Hz
Wader = High Freq 180, 300, 500Hz
Define Signal Excess
The amount of signal in dBs available for detection
Diesels engine diagram
Primary coolant loop
What are the three types of AIP?
Mesma, fuel cell, Stirling
