Design redundancy

The objective is to estimate, numerically, the probability that a system composed of many components will fail. The obvious question is, "Why don t you just estimate the failure rate of the system from operating experience " There are three reasons IJ the system may not exist, so new data are not available, 2) the injuries and fatalities from the developmental learning experience are unacceptable - the risk must be known ahead of time, and 3) by designing redundancy, the probability of the system failing can be made acceptably remote in which case system failure data caimot be collected directly. The only practical way uses part failure statistics in a system model to estimate the system s reliability. 

One evolutionary strategy is to search for thermodynamic inefficiencies to attack, for example, through exergy analysis. Another strategy is to search for structural inefficiencies including design redundancies. In our first flowsheet, both flash columns have similar feed compositions, both overheads go to the same decanter, and both underflows go to wastewater treatment. Therefore, these... 

In Table 5.10, column 12 may be used to proactively prescribe compensating provisions (e.g. need check intervals or prescribed design features) or to reference existing provisions (e.g. existing design redundancy or existing check intervals) (Table 5.9). 

The SSCs which are required to perform the fundamental safety functions should be designed to withstand the loads induced by the design basis events and able to perform their functions during and after such events. This should be achieved through adequate stmctural design, redundancy and separation. 

Redundant devices using different technologies may also decrease common-cause susceptibility if the redundant units respond differently to a common stress. This can be accomplished by designing redundant subsystems using diverse technology. Many think that using "different manufacturers" provides diversity. This is not true if both devices respond similarly to the same stress. Diversity works only if the redundant devices respond differently to a common stress. 

Software fault tolerance For software, fault tolerant design redundancies are required to mask residual design faults. Some of the issues related to this shall include but are not limited to ... 

CCFs and CMFs are a form of dependent failures, created by dependencies built into the system design. In essence, CCF and CMF modes are SPFs that result in the elimination of intended design redundancy. Design diversity in redundant components can eliminate some CCF and CMF scenarios. 

Throughout the product life cycle, MTBF data will require validation and possible re-baselining, particularly if predictive methods were used. This is necessary because predicted MTBF data would have been used to determine initial design redundancies, verify requirements and architecture, and justify the accomplishment of safety objectives. Should the observed in-service MTBF be less than the predicted MTBF, the aircraft... 

The approach to heat exchanger network design discussed so far is based on the creation of an irreducible structure. No redundant features were included. Of course, when the network is optimized, some of the features might be removed by the optimization. The scope for the optimization to remove features results from the assumptions made during the creation of the initial structure. However, no attempt was made to deliberately include redundant features. 

Although the problem of compilation of training and test datasets is crucial, unfortunately no de-faao standard technique has been introduced. Nevertheless, we discuss here a method that was designed within our group, and that is used quite successfully in our studies. The method is mainly addressed to the task of finding and removing redundancy. 

System rehabihty is improved by providing alternative means for performing the same task. For example, automobiles were equipped with hand cranks even though they had electric starters. This back-up equipment was provided because at that time starters were unrehable. In contemporary system design, factors such as added cost, weight, and space may prohibit the use of redundant systems. 

Reactors are designed to be inherently safe based on physical principles, supplemented by redundant equipment and special procedures. Nuclear power benefits from the appHcation of the concept of defense in depth, ie, by using fuel form, reactor vessel, building containment, and emergency backup procedures to ensure safety. 

Special high rehabiUty systems have been developed for safety shutdowns, eg, triple modular redundant systems (TMRS), which are designed to be... 

Since the t distribution relies on the sample standard deviation. s, the resultant distribution will differ according to the sample size n. To designate this difference, the respec tive distributions are classified according to what are called the degrees of freedom and abbreviated as df. In simple problems, the df are just the sample size minus I. In more complicated applications the df can be different. In general, degrees of freedom are the number of quantities minus the number of constraints. For example, four numbers in a square which must have row and column sums equal to zero have only one df, i.e., four numbers minus three constraints (the fourth constraint is redundant). 

The difficulties of such operations on the research platform Nordsee are described in Ref. 9. The Murchison platform was provided with a combination of impressed current protection and galvanic anodes because there was a limit to the load to be transported [12]. The anodes for platforms are installed and provided with cables at the yard. They are installed with redundancy and excess capacity so that no repairs are necessary if there is a breakdown. The lower part of the platform up to the splash zone is usually placed in position in the designated location at least 1 year before the erection of the deck structure so that impressed current protection cannot initially be put in operation. This requires cathodic protection with galvanic anodes for this period. This also means that the impressed current protection is more expensive than the galvanic anodes. 

The proteetive system is independent of the eontrol system and provides proteetion from over-speed, over-temperature, vibration, loss of flame, and loss of lubrieation. The over-speed proteetion system generally has a trans-dueer mounted on the aeeessory gear or shaft, and trips the gas turbine at approximately 10% of maximum design speed. The over-temperature system has thermoeouples similar to the normal temperature eontrols with a similar redundant system. The flame deteetion system eonsists of at least two ultraviolet flame deteetors to sense a flame in the eombustion eans. 

The first requirement for threading is to have a database of all the known different protein folds. Eisenberg has used his own library of about 800 folds, which represents a minimally redundant set of the more than 6000 structures deposited at the Protein Data Bank. Other groups use databases available on the World Wide Web, where the folds are hierarchically ordered according to structural and functional similarities, such as SCOP, designed by Alexey Murzin and Cyrus Chothia in Cambridge, UK. 

Proteetion of the load and of the power supply from failures in the load should be an important eonsideration within all switehing power supply designs. It is important to know what failures are likely to oeeur within the switehing power supply and the load. An exereise that is frequently required in military designs is what is ealled a FMEA (failure modes and effeets analysis), where eaeh eom-ponent is hypothetieally assumed to fail open-eireuited and then short-eireuited. With sueh failures, how does eaeh failure affeet the other seetions of the eireuit This antieipation of failures ean make a power supply design robust. It is the responsibility of the power supply designer to provide proteetion to the load eireuitry from anomalies eneountered from the input line and failures within the supply and the load eireuitry. Often, proteetion sehemes ean be easeaded to provide redundant proteetion in the event of a failure in a proteetion eireuit. A fuse or a eireuit-breaker usually provides sueh a baek-up funetion. 

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