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1、RAM Modelling using OptimiseModule 5 Conditional Logic,October 28 2009R Briggs,Module Roadmap,OverviewLogic Condition DefinitionTrigger Behaviour DefinitionReferences,RAM Modelling using OptimiseModule 5 Conditional Logic,Overview,1.Overview,Representation of an operational condition or restrictionR
2、ules constructed to defined condition using Boolean LogicOften used to model:subsea/plant restarts,following failures;interconnected/common equipment eg Heat Recovery Steam Generator with Steam Turbine;equipment/system bypasses;andvoting,2oo3 not equal to 3 x 100%,3 x 50%or 2 x 100%,1.Overview,A Dep
3、endent failure distribution specifies:A Logic Condition,which is an operational condition that must be met;andA Trigger Condition,which specifies how and when to trigger based on the Logic Condition,RAM Modelling using OptimiseModule 5 Conditional Logic,Logic Condition Definition,2.Logic Condition D
4、efinition Operators,Conditional Logic=Boolean Logic,evaluating TRUE or FALSE conditionConditional Logic uses a number of comparison operators:AB or A=B).(AB)|(A=B)(A greater than or equal to B),2.Logic Condition Definition Variables,Conditional Logic in Optimise is used to represent specific operati
5、ng conditions/scenarios based on the conditional state of equipment/system/linepackConditional Logic evaluates:element status;value and capacity;buffer level/condition;inflow/outflow;andcombination of any of the above.,2.Logic Condition Definition Element Status,Evaluates the state of an element An
6、element can be any of these:failed;under repair;andfunctional,2.Logic Condition Definition Element Status,Example Gas Turbine Waste Heat Recovery System2 x 70%LNG Liquefaction Compressor GTs,each with WHRUEach WHRU supplies supplementary heat to a hot oil systemGT provides heat to WHRU,GT fails,no h
7、eat provided,2.Logic Condition Definition Value and Capacity,Evaluates a capacity of a branch/group The Value and Capacity can be compared to another:current capacity(Branch or Group);maximum capacity(Branch or Group);orvalue(a fixed number,compared to current capacity or maximum capacity).,2.Logic
8、Condition Definition Value and Capacity,Example Distillation Column Maximum TurndownA distillation column has a minimum production rate of 70%Fed by 6 x 20%pumpsFailure of 3 pumps causes a total shut down,2.Logic Condition Definition Buffer Level/Condition,Evaluates a branch buffer level/statusBuffe
9、r Level(a numerical value)Buffer Status(can be either Full/Empty/in between)Some examples are:Buffer Volume a ValueBuffer Status!=Empty,Example Pipeline linepack between Upstream and LNG PlantLinepack provides a buffer to allow LNG production to continue.Linepack is normally full(maintain near max o
10、perating pressure)Buffer provides 12 hours of full production:24 hours at 50%LNG production,2.Logic Condition Definition Buffer Level/Condition,2.Logic Condition Definition Inflow/Outflow,Evaluates a branch current throughput capacity and compares it with a valueThe Inflow of a BranchThe outflow of
11、a BranchValue(a fixed number)An example:Inflow Branch A Outflow Branch B,2.Logic Condition Definition Inflow/Outflow,Example Management of Pipeline linepack between Upstream and LNG PlantLinepack provides a buffer to allow LNG production to continue.Linepack is normally full(maintain near max operat
12、ing pressure)Linepack usage is dependant on inflow into linepackLinepack drawdown is reduced to 40%when the inflow is less than 50%,2.Logic Condition Definition-Combinations of Logic,A combination of the basic logical expressionExample:If a downstream element X is failed,and the upstream linepack vo
13、lume is greater than 50%,and the level is rising,shut down the inflow to a branchThe logical expression:(X!=Functional)&(Linepack vol(50%*capacity)&(Linepack in Linepack out),RAM Modelling using OptimiseModule 5 Conditional Logic,Trigger Behaviour Definition,Defines when an effect should trigger and
14、 how long it should last for based on a Logic ConditionThe Logic Condition is used to evaluate the operational state,and at any time any given Logic Condition will be either TRUE or FALSEThree types of trigger behaviours are:common;independent;andsequential.,3.Trigger Behaviour Definition Overview,C
15、ommon behaviour is to mirror another condition in the modelElements governed by Common Logic change to the failed state when the condition defined by the logic string evaluates to true.It stays in the failed state until the logic condition becomes false.which means,The element fails when logic becom
16、es true;andThe element becomes functional when logic ceases to be true.,3.Trigger Behaviour Definition Common,3.Trigger Behaviour Definition Common,False,Functional,True,False,Failed,Functional,Time,Logic Condition State,The Element State,Time,Independent behaviour is to trigger off another conditio
17、n in the model,and then ignore that condition from there onElements governed by Independent Logic change to the failed state when the condition defined by the logic string evaluates to true.It stays in the failed state until the user defined repair length is completed,which means,The element fails w
18、hen logic becomes true;andThe element becomes functional based on the MTTR distribution.,3.Trigger Behaviour Definition Independent,3.Trigger Behaviour Definition Independent,False,Functional,True,False,Failed,Functional,Time,Logic Condition State,The Element State,Time,Under Repair,Sequential behav
19、iour is to wait until another condition elapses,before the element failure is triggeredElements governed by Sequential Logic monitors the model to detect when the condition defined by the logic string is true.It then waits till the condition evaluates to false,at which point it changes to a failed s
20、tatewhich means,The element fails when logic becomes false,having just been true;andThe element becomes functional based on the MTTR distribution.,3.Trigger Behaviour Definition Sequential,3.Trigger Behaviour Definition Sequential,False,Functional,True,False,Failed,Functional,Time,Logic Condition St
21、ate,The Element State,Time,Under Repair,Condition evaluates true,Condition evaluates false,RAM Modelling using OptimiseModule 5 Conditional Logic,Examples,4.Conditional Logic Examples,Counters Repair windows Restarts after outagesCommon equipment sparingVotingRestarts after linepack emptyTurndownsDe
22、ferred maintenance mobilisations,4.Examples Counters,Used to monitor equipmentCount how often a state occursExample:Frequency and Duration of BOG gas compressors frequency and duration of flaring.,4.Examples Repair Windows,It is used to simulate a production buffer ie,a storage tank.This allows the
23、downstream system to operate unaffected by a failure in the upstream system during the repair windowExample:a 48 hours repair window for a production buffer of a chemical injection system,4.Examples Restarts After Outages,It is used to simulate gradual ramp up of a process post shutdown.Linear ramp
24、up is often assumed.An example:An LNG plant requires a 24 hours gradual restart following an equipment failure in the liquefaction circuit.It has been assumed that the gradual restart for 24 hours is only required if the LNG plant is down for more than 10 hours.,4.Examples Common Equipment Sparing,C
25、ertain critical equipment may share spares.Conditional logic can be used to link these spares to the equipment that will use it.When the spare fails the equipment linked to it will be affected.Example:Loading arms and umbilical LP/HP cores,Reliability Data,In use?,4.Examples Voting,Equipment may be
26、voted 2oo3Not 2 x 100%,3 x 50%,3 x 100%Conditional logic can be used represent this.Example:Pressure Detection,4.Examples Restarts After Linepack Empty,Linepack is the ability to fill the export pipeline with additional gas.Linepack can be modelled in optimise.Linepack can be used to buffer upstream
27、 outages or to store production during downstream outage.Conditional logic is used to limit the linepack usage according to the clients needs.For example:linepack may only allow for a certain period of uninterrupted production until reduced production takes over.,4.Examples Turndowns,Some plants can
28、 not operate when the feed is less than 50%for example.Conditional logic can be used to shut the plant down when the capacity falls under a determined value.,4.Examples Deferred Maintenance Mobilisations,When an element(that has a maintenance utility assigned to it)fails in Optimise,the maintenance
29、utility will immediately mobilise to repair.Conditional logic can be used to defer the mobilisation until the logic is satisfied.When mobilisation times are high,mobilisations are deferred until a group of non critical elements fail.,4.Examples Deferred Maintenance Mobilisations,RAM Modelling using OptimiseModule 5 Conditional Logic,References,7.References,Optimise Software 3.00.2,
