Dp Knowledge Transfer: Control System

Front 1

Name the six main DP Control Systems suppliers.

Back 1

Kongsberg, GE, L3, Marine Technologies, Rolls Royce, FL Beier(Navis).

Front 2

What mode is needed for pulling in a Steel Catenary Riser?

Back 2

External force compensation (EFC).

Front 3

What mode might be needed when landing a lift to prevent DP instability?

Back 3

Heavy Lift Mode.

Front 4

What two items need to be compared to check if heavy lift mode is needed?

Back 4

Restoring force of the load per meter offset and the DPCS proportional gain in tonnes per meter for the affected axis..

Front 5

When can track follow be used by a DP vessel working for Shell?

Back 5

Outside the 500m zone.

Front 6

"In simple terms how is Newton’s Second Law of Motion, force = mass x acceleration, used by the DP control system?"

Back 6

Using the mass of the vessel (plus added mass as the vessel drags a large volume of water with it) and the forces (thrusters) on the vessel the acceleration can be calculated and used to derive velocity and position.

Front 7

What names get used for the DP control system algorithm that calculates the required demand for each thruster to achieve the DP controller’s output of fore/aftforce, port/stbd force and turning moment?

Back 7

Thruster Allocation Logic or Thruster Transform.

Front 8

For the simple vessel shown what are the equations that have to be solved to meet the demands of X fore/aft, Y port/stbd and N turning moment. diagram

Back 8

"X1= X, Y1 + Y2 = Y, Y1R1 – Y2R2 = N diagram tba"

Front 9

What are the three common ways a DP control system might utilize multiple positionreference systems?

Back 9

A priority queue, operator set weighting and automaticweighting based on a systems noise.

Front 10

Whatare the three control actions the DP control system can be considered to take to control position and heading?

Back 10

Proportional,differential and integral.

Front 11

In simple terms how are Kalman Mathematics use by the DP Controller and associatedvessel mathematical model?

Back 11

To optimize the position measurements and the model’s estimates based on confidence in the model and the expected noise onthe position measurements.

Front 12

Whatis the definition of a Dynamic Positioning System?

Back 12

All the systems on a DP vessel necessary to hold position and heading just by using thrusters.

Front 13

In light environment what DP Control System feature can be used to prevent excessive demands on azimuth rotation mechanics?

Back 13

Thruster Bias

Front 14

What is the key advantage of having three of any measurement into the DP control system?

Back 14

Two out of three voting can reject an errant measurement.

Front 15

Whatis the most likely ‘systematic’ failures in a DP system?

Back 15

DP control system software is common to all DPCS and if an untested set of conditions arise then all DPCS's can fail. Similar for any systems with common software or firmware for examplegyros or networks.

Front 16

What check is included in the DP control system to prevent a supposed perfect position reference system from causing a loss of position?

Back 16

Median check

Front 17

What feature of the DP control system should warn the operator that the vessels isoperating outside its capability should the worst case failure occur?

Back 17

Consequence Analysis.

Front 18

What action might a DP control system take to avoid a black out?

Back 18

DPCS constantly checks if the next output the thrust allocation logic will overload the power plant and if it will it reduces the demand to stay within the available power.

Front 19

What can happen if the DP Control System has faulty information about the power available to it?

Back 19

It may power limit too early or too late depending on what signal is faulty.

Front 20

What is a ‘systematic’ error or failure?

Back 20

This is where all the DP controllers run the same software so if any untested set of conditions occur they may fail all the controllers. The main example of these would be the millennium bug. A good DP relatedexample the Bibby Topaz incident in 2012. This can apply to any systems that run the same software for example 3 gyros all from the .

Front 21

For triple redundant DP control systems how is the voting on the thruster commands carried out at the thruster outstation?

Back 21

It uses then middle (median) value of the three it receives.

Front 22

What are the six degrees of motion does a vessel have and which does a DP control system control?

Back 22

Roll, pitch, heave, surge (fore/aft), sway (port/stbd) andyaw (heading). The DPCS controls thelast three.

Front 23

What motion comes in as noise to the DP control system and has to be filtered out to avoid it getting onto the thrusters as noise?

Back 23

First order wave motion.

Front 24

What are the two types of wave motion on a vessel and how can they be described?

Back 24

First order is that the wave physically lifts the ship in a circular motion but puts it back down in nearly the same place. These forces are massive and the DP control system should not attempt torespond to them. Second order is where the vessel will slowly drift in the waves and this can be controlled by the DPControl system.

Front 25

What environmental forces cannot be measured directly by the DP control system but need to be figured out over time?

Back 25

Current and second order wave drift.

Front 26

What should a capability plot look like for worse case failure for that only has a bow thruster, one main prop and one rudder remaining after WCF?

Back 26

There is an environment below which the vessel can’t operate as the rudder is no where near 100% efficient so the plot should have a hole in it.

Front 27

Why can’t the DP control system’s estimate for current be relied upon to be very accurate?

Back 27

TheDPCS try to calculate current from the leant force in the Kalman Model – unfortunately this includes many unknowns other than current (wave drift, thruster errors, thruster interactions with hull andother thrusters, wind force errors etc.) and cannot therefore always be relied upon.

Front 28

Why does care have to be taken when using a Center of Rotation other than the vessel's center of gravity?

Back 28

Any heading changes will also make a positon change and much increased thrust levels that might exceed the worse case failure limits.

Front 29

Name three ‘external interfaces’ to the DP control system whose failure modes might adversely affect the DP control?

Back 29

Tension ,draft and fire monitors.

Front 30

What are two ways a DP vessel can utilize the DPCS to follow and ROV?

Back 30

Either just DP off an acoustic transponder or responder fitted to it so that when it moves vesselwill keep position relative to it. Or target follow mode where DP is no DGNSS and the DPCS uses DGNSS and only reactswhen the ROV moves outside a ‘reaction window’ as its set point is changed.

Front 31

What initial checks does a DP control system do on any measurement such as PRS, gyros, etc.?

Back 31

Rate of change

Front 32

What are the seven pillars that are essential to make a DP systems behavior predictable?

Back 32

Autonomy, segregation, diversity, independence, fault resistance, fault ride through, fault tolerance.

Front 33

Why does DP vessel have an independent joystick?

Back 33

In case of a total failure of all DP control systems or its networks.

Front 34

What does the DPCS do if it losses all position references or gyros?

Back 34

Uses the model alone in dead reckoning mode?

Front 35

What is the mode called where the DP control system adjusts the heading automatically to minimize the load on the thrusters?

Back 35

Minimum power or optimum heading.

Front 36

What DP control system mode can be provided for relaxed DP?

Back 36

Hold area mode.

Front 37

What modes could be provided by the DP control system to need a lot less thrust and use the environmental forces to its advantage?

Back 37

Bow only mode, position control by maneuvering and weather vaning for vessels with an aft super structure.

Front 38

Why should the use of ‘safety anchor(s)’ while on DP be discouraged?

Back 38

Too tight and it will destabilize the DP control. Too slack and they will not be effective.

Front 39

What special modes does a DP offtake shuttle tanker have different than regular DP?

Back 39

There is a reaction windows for position and heading. DP is normally based on DGNSS and stationaryrelative to the sea bed then if the FPSO changes position or heading outsidethe respective reaction window the DP will automatically move the DP position or heading set point to follow the move.

Front 40

What axis does the DP control system normally prioritize if there is insufficientpower to meet its thruster demands and why that axis?

Back 40

Heading because on a monohull once heading is lost and a vessel broaches beam to the weather and the vessel will rapidly lose position.

Front 41

What is the Reference Origin?

Back 41

The reference origin is determined by the first reference put into the system after a position dropout. It’s annotated by an asteriskon the ref system page.