Basics of System Reliability Analysis - Revision history

Richard House: /* BlockSim's Computation Modes */

2016-01-05T20:28:36Z

BlockSim's Computation Modes

← Older revision		Revision as of 20:28, 5 January 2016
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	As shown in the figure below, BlockSim includes two independent computation modes: analytical and simulation. The analytical mode uses the exact reliability solutions for the system, employing the system's reliability function or cumulative density function (''cdf''). BlockSim can resolve even the most complex systems analytically and this method should be used when one is performing reliability analysis. In the context of BlockSim and this reference, we use the term ''reliability analysis'' to refer to all analyses that do not include repairs or restorations of the component. In contrast to the analytical mode, the simulation mode takes into account repair and restoration actions, including behaviors of crews, spare part pools, throughput, etc. Both of these methods will be explored in the chapters that follow. <br>		As shown in the figure below, BlockSim includes two independent computation modes: analytical and simulation. The analytical mode uses the exact reliability solutions for the system, employing the system's reliability function or cumulative density function (''cdf''). BlockSim can resolve even the most complex systems analytically and this method should be used when one is performing reliability analysis. In the context of BlockSim and this reference, we use the term ''reliability analysis'' to refer to all analyses that do not include repairs or restorations of the component. In contrast to the analytical mode, the simulation mode takes into account repair and restoration actions, including behaviors of crews, spare part pools, throughput, etc. Both of these methods will be explored in the chapters that follow. <br>

	[[Image:Chp2fig10.png\|center\|162px\|BlockSim's two independent computation modes.]]		[[Image:Chp2fig10.png\|center\|162px\|BlockSim's two independent computation modes.\|link=]]

	<br>		<br>

Richard House: /* Reliability Block Diagrams (RBDs) */

2016-01-05T20:27:27Z

Reliability Block Diagrams (RBDs)

← Older revision		Revision as of 20:27, 5 January 2016
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	A block is usually represented in the diagram by a rectangle. In a reliability block diagram, such blocks represent the component, subsystem or assembly at its chosen black box level. The following figure shows two blocks, one representing a resistor and one representing a computer.		A block is usually represented in the diagram by a rectangle. In a reliability block diagram, such blocks represent the component, subsystem or assembly at its chosen black box level. The following figure shows two blocks, one representing a resistor and one representing a computer.

	[[Image:Chp2fig4.png\|center\|~~400px~~\|Blocks representing a resistor and a computer.\|link=]]		[[Image:Chp2fig4.png\|center\|300px\|Blocks representing a resistor and a computer.\|link=]]

	It is possible for each block in a particular RBD to be represented by its own reliability block diagram, depending on the level of detail in question. For example, in an RBD of a car, the top level blocks could represent the major systems of the car, as illustrated in the figure below. Each of these systems could have their own RBDs in which the blocks represent the subsystems of that particular system. This could continue down through many levels of detail, all the way down to the level of the most basic components (e.g., fasteners), if so desired.		It is possible for each block in a particular RBD to be represented by its own reliability block diagram, depending on the level of detail in question. For example, in an RBD of a car, the top level blocks could represent the major systems of the car, as illustrated in the figure below. Each of these systems could have their own RBDs in which the blocks represent the subsystems of that particular system. This could continue down through many levels of detail, all the way down to the level of the most basic components (e.g., fasteners), if so desired.

Richard House: /* Reliability Block Diagrams (RBDs) */

2016-01-05T20:26:56Z

Reliability Block Diagrams (RBDs)

← Older revision		Revision as of 20:26, 5 January 2016
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	A block is usually represented in the diagram by a rectangle. In a reliability block diagram, such blocks represent the component, subsystem or assembly at its chosen black box level. The following figure shows two blocks, one representing a resistor and one representing a computer.		A block is usually represented in the diagram by a rectangle. In a reliability block diagram, such blocks represent the component, subsystem or assembly at its chosen black box level. The following figure shows two blocks, one representing a resistor and one representing a computer.

	[[Image:Chp2fig4.png\|center\|~~500px~~\|Blocks representing a resistor and a computer.\|link=]]		[[Image:Chp2fig4.png\|center\|400px\|Blocks representing a resistor and a computer.\|link=]]

	It is possible for each block in a particular RBD to be represented by its own reliability block diagram, depending on the level of detail in question. For example, in an RBD of a car, the top level blocks could represent the major systems of the car, as illustrated in the figure below. Each of these systems could have their own RBDs in which the blocks represent the subsystems of that particular system. This could continue down through many levels of detail, all the way down to the level of the most basic components (e.g., fasteners), if so desired.		It is possible for each block in a particular RBD to be represented by its own reliability block diagram, depending on the level of detail in question. For example, in an RBD of a car, the top level blocks could represent the major systems of the car, as illustrated in the figure below. Each of these systems could have their own RBDs in which the blocks represent the subsystems of that particular system. This could continue down through many levels of detail, all the way down to the level of the most basic components (e.g., fasteners), if so desired.

Richard House: /* Block Failure Models */

2015-12-11T18:38:58Z

Block Failure Models

← Older revision		Revision as of 18:38, 11 December 2015
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	[[Image:FailureDistributionBlockProperties.png\|center\|550px\|Failure distribution assigned in the Block Properties window.]]		[[Image:FailureDistributionBlockProperties.png\|center\|550px\|Failure distribution assigned in the Block Properties window.\|link=]]


	[[Image:RepairDistributionBlockProperties.png\|center\|550px\|Repair distribution assigned in the Block Properties window.]]		[[Image:RepairDistributionBlockProperties.png\|center\|550px\|Repair distribution assigned in the Block Properties window.\|link=]]

	== System Reliability Function ==		== System Reliability Function ==

Richard House: /* Time-Dependent */

2015-12-11T18:11:33Z

Time-Dependent

← Older revision		Revision as of 18:11, 11 December 2015
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	Time-dependent analysis looks at reliability as a function of time. That is, a known failure distribution is assigned to each component. The time scale in BlockSim can assume any quantifiable time measure, such as years, months, hours, minutes or seconds, and also units that are not directly related to time, such as cycles or miles of use. In many of the discussions and examples that follow, and to maintain generality, time units may be omitted or a general time unit ( <math>tu\,\!</math> ) may be utilized. It is very important to remember that even though any time unit may be used, the time units used throughout an analysis must be consistent in order to avoid incorrect results. The primary objective in system reliability analysis is to obtain a failure distribution of the entire system based on the failure distributions of its components, as illustrated below. <br>		Time-dependent analysis looks at reliability as a function of time. That is, a known failure distribution is assigned to each component. The time scale in BlockSim can assume any quantifiable time measure, such as years, months, hours, minutes or seconds, and also units that are not directly related to time, such as cycles or miles of use. In many of the discussions and examples that follow, and to maintain generality, time units may be omitted or a general time unit ( <math>tu\,\!</math> ) may be utilized. It is very important to remember that even though any time unit may be used, the time units used throughout an analysis must be consistent in order to avoid incorrect results. The primary objective in system reliability analysis is to obtain a failure distribution of the entire system based on the failure distributions of its components, as illustrated below. <br>

	[[Image:SystemtoComponentpdf.png\|center\|~~550px~~\|Obtaining the system's ''pdf'' from the ''pdfs'' of the components.\|link=]]		[[Image:SystemtoComponentpdf.png\|center\|700px\|Obtaining the system's ''pdf'' from the ''pdfs'' of the components.\|link=]]

	<br>		<br>

Richard House: /* Static */

2015-12-11T18:11:10Z

Static

← Older revision		Revision as of 18:11, 11 December 2015
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	Static analytical calculations are performed on RBDs that contain static blocks. A static block can be interpreted either as a block with a reliability value that is known only at a given time (but the block's entire distribution is unknown) or as a block with a probability of success that is constant with time. Static calculations can be performed both in the analytical mode and the simulation mode. The following figure illustrates a static RBD. <br>		Static analytical calculations are performed on RBDs that contain static blocks. A static block can be interpreted either as a block with a reliability value that is known only at a given time (but the block's entire distribution is unknown) or as a block with a probability of success that is constant with time. Static calculations can be performed both in the analytical mode and the simulation mode. The following figure illustrates a static RBD. <br>

	[[Image:SystemFrozeninTime.png\|center\|~~250~~\|Reliability block diagram (RBD) of a static system.\|link=]]		[[Image:SystemFrozeninTime.png\|center\|500\|Reliability block diagram (RBD) of a static system.\|link=]]

	<br>		<br>

Richard House: /* BlockSim's Computation Modes */

2015-12-11T18:09:48Z

BlockSim's Computation Modes

← Older revision		Revision as of 18:09, 11 December 2015
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	As shown in the figure below, BlockSim includes two independent computation modes: analytical and simulation. The analytical mode uses the exact reliability solutions for the system, employing the system's reliability function or cumulative density function (''cdf''). BlockSim can resolve even the most complex systems analytically and this method should be used when one is performing reliability analysis. In the context of BlockSim and this reference, we use the term ''reliability analysis'' to refer to all analyses that do not include repairs or restorations of the component. In contrast to the analytical mode, the simulation mode takes into account repair and restoration actions, including behaviors of crews, spare part pools, throughput, etc. Both of these methods will be explored in the chapters that follow. <br>		As shown in the figure below, BlockSim includes two independent computation modes: analytical and simulation. The analytical mode uses the exact reliability solutions for the system, employing the system's reliability function or cumulative density function (''cdf''). BlockSim can resolve even the most complex systems analytically and this method should be used when one is performing reliability analysis. In the context of BlockSim and this reference, we use the term ''reliability analysis'' to refer to all analyses that do not include repairs or restorations of the component. In contrast to the analytical mode, the simulation mode takes into account repair and restoration actions, including behaviors of crews, spare part pools, throughput, etc. Both of these methods will be explored in the chapters that follow. <br>

	[[Image:Chp2fig10.png\|center\|~~150px~~\|BlockSim's two independent computation modes.]]		[[Image:Chp2fig10.png\|center\|162px\|BlockSim's two independent computation modes.]]

	<br>		<br>

Richard House: /* Reliability Block Diagrams (RBDs) */

2015-12-11T18:07:55Z

Reliability Block Diagrams (RBDs)

← Older revision		Revision as of 18:07, 11 December 2015
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	It is possible for each block in a particular RBD to be represented by its own reliability block diagram, depending on the level of detail in question. For example, in an RBD of a car, the top level blocks could represent the major systems of the car, as illustrated in the figure below. Each of these systems could have their own RBDs in which the blocks represent the subsystems of that particular system. This could continue down through many levels of detail, all the way down to the level of the most basic components (e.g., fasteners), if so desired.		It is possible for each block in a particular RBD to be represented by its own reliability block diagram, depending on the level of detail in question. For example, in an RBD of a car, the top level blocks could represent the major systems of the car, as illustrated in the figure below. Each of these systems could have their own RBDs in which the blocks represent the subsystems of that particular system. This could continue down through many levels of detail, all the way down to the level of the most basic components (e.g., fasteners), if so desired.

	[[Image:corvettesubsystem.png\|center\|~~600px~~\|Example of a system containing a number of different subsystems.\|link=]]		[[Image:corvettesubsystem.png\|center\|500px\|Example of a system containing a number of different subsystems.\|link=]]

	The level of granularity or detail that one chooses should be based on both the availability of data and on the lowest actionable item concept. To illustrate this concept, consider the aforementioned computer system shown earlier. When the computer manufacturer finds out that the hard drive is not as reliable as it should be and decides not to try to improve the reliability of the current hard drive but rather to get a new hard drive supplier, then the lowest actionable item is the hard drive. The hard drive supplier will then have actionable items inside the hard drive, and so forth.		The level of granularity or detail that one chooses should be based on both the availability of data and on the lowest actionable item concept. To illustrate this concept, consider the aforementioned computer system shown earlier. When the computer manufacturer finds out that the hard drive is not as reliable as it should be and decides not to try to improve the reliability of the current hard drive but rather to get a new hard drive supplier, then the lowest actionable item is the hard drive. The hard drive supplier will then have actionable items inside the hard drive, and so forth.

Richard House: /* Block Failure Models */

2015-12-11T18:07:40Z

Block Failure Models

← Older revision		Revision as of 18:07, 11 December 2015
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	Additionally, component life data may also be provided by the manufacturer or supplier of the component/subsystem. Once the data set has been obtained, the life distribution of a component/subsystem can be estimated using ReliaSoft's Weibull++ or ALTA software. For example, consider a resistor that is part of a larger system to be analyzed. Failure data for this resistor can be obtained by performing in-house reliability tests and by observing the behavior of that type of resistor in the field. As shown below, a life distribution is then fitted to the data and the parameters are obtained. The parameters of that distribution represent the life distribution of that resistor block in the overall system RBD.		Additionally, component life data may also be provided by the manufacturer or supplier of the component/subsystem. Once the data set has been obtained, the life distribution of a component/subsystem can be estimated using ReliaSoft's Weibull++ or ALTA software. For example, consider a resistor that is part of a larger system to be analyzed. Failure data for this resistor can be obtained by performing in-house reliability tests and by observing the behavior of that type of resistor in the field. As shown below, a life distribution is then fitted to the data and the parameters are obtained. The parameters of that distribution represent the life distribution of that resistor block in the overall system RBD.

	[[Image:BS2.5.png\|center\|~~400px~~\|Obtaining the failure distribution parameters for a component.\|link=]]		[[Image:BS2.5.png\|center\|500px\|Obtaining the failure distribution parameters for a component.\|link=]]


	[[Image:BS2.6.png\|center\|~~400px~~\|Other block properties\|link=]]		[[Image:BS2.6.png\|center\|500px\|Other block properties\|link=]]

Richard House: /* Reliability Block Diagrams (RBDs) */

2015-12-11T18:06:43Z

Reliability Block Diagrams (RBDs)

← Older revision		Revision as of 18:06, 11 December 2015
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	A reliability block diagram is a graphical representation of the components of the system and how they are reliability-wise related (connected). It should be noted that this may differ from how the components are physically connected. An RBD of a simplified computer system with a redundant fan configuration is shown below.		A reliability block diagram is a graphical representation of the components of the system and how they are reliability-wise related (connected). It should be noted that this may differ from how the components are physically connected. An RBD of a simplified computer system with a redundant fan configuration is shown below.

	[[Image:Chp2fig3.png\|center\|~~350px~~\|A simple reliability block diagram.\|link=]]		[[Image:Chp2fig3.png\|center\|500px\|A simple reliability block diagram.\|link=]]

	RBDs are constructed out of blocks. The blocks are connected with direction lines that represent the reliability relationship between the blocks.		RBDs are constructed out of blocks. The blocks are connected with direction lines that represent the reliability relationship between the blocks.
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	A block is usually represented in the diagram by a rectangle. In a reliability block diagram, such blocks represent the component, subsystem or assembly at its chosen black box level. The following figure shows two blocks, one representing a resistor and one representing a computer.		A block is usually represented in the diagram by a rectangle. In a reliability block diagram, such blocks represent the component, subsystem or assembly at its chosen black box level. The following figure shows two blocks, one representing a resistor and one representing a computer.

	[[Image:Chp2fig4.png\|center\|~~250px~~\|Blocks representing a resistor and a computer.\|link=]]		[[Image:Chp2fig4.png\|center\|500px\|Blocks representing a resistor and a computer.\|link=]]

	It is possible for each block in a particular RBD to be represented by its own reliability block diagram, depending on the level of detail in question. For example, in an RBD of a car, the top level blocks could represent the major systems of the car, as illustrated in the figure below. Each of these systems could have their own RBDs in which the blocks represent the subsystems of that particular system. This could continue down through many levels of detail, all the way down to the level of the most basic components (e.g., fasteners), if so desired.		It is possible for each block in a particular RBD to be represented by its own reliability block diagram, depending on the level of detail in question. For example, in an RBD of a car, the top level blocks could represent the major systems of the car, as illustrated in the figure below. Each of these systems could have their own RBDs in which the blocks represent the subsystems of that particular system. This could continue down through many levels of detail, all the way down to the level of the most basic components (e.g., fasteners), if so desired.

	[[Image:corvettesubsystem.png\|center\|~~350px~~\|Example of a system containing a number of different subsystems.\|link=]]		[[Image:corvettesubsystem.png\|center\|600px\|Example of a system containing a number of different subsystems.\|link=]]

	The level of granularity or detail that one chooses should be based on both the availability of data and on the lowest actionable item concept. To illustrate this concept, consider the aforementioned computer system shown earlier. When the computer manufacturer finds out that the hard drive is not as reliable as it should be and decides not to try to improve the reliability of the current hard drive but rather to get a new hard drive supplier, then the lowest actionable item is the hard drive. The hard drive supplier will then have actionable items inside the hard drive, and so forth.		The level of granularity or detail that one chooses should be based on both the availability of data and on the lowest actionable item concept. To illustrate this concept, consider the aforementioned computer system shown earlier. When the computer manufacturer finds out that the hard drive is not as reliable as it should be and decides not to try to improve the reliability of the current hard drive but rather to get a new hard drive supplier, then the lowest actionable item is the hard drive. The hard drive supplier will then have actionable items inside the hard drive, and so forth.