System-Level Requirements Generation

Once the goals and hazards have been identified and a conceptual system architecture has been selected, system-level requirements generation can begin. Usually, in 

18 TCAS shall provide collision avoidance protection for any two aircraft closing horizontally at any rate up to 1200 knots and vertically up to 10,000feet per minute. 

1 TCAS shall operate in enroute and terminal areas with traffic densities up to 0.3 aircraft per square nautical miles (i.e., 24 aircraft within 5 nmi). 

Assumption Traffic density may increase to this level by 1990, and this will be the maximum density over the next 20 years. 

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The system-level requirements represent how the system should perform and behave, but often these requirements are not specific enough to determine how the subsystems are developed. For example, a surgical robot may have a top-level system requirement that requires it to generate 5 N of force. This top-level requirement must be decomposed into lower-level subsystems. A typical methodology is to use the concept of functional block... 

A power system is connected to a number of power supply machines that determine the fault level of that. system (e.g. generators and transformers). The impedances of all such equipment and the impedances of the interconnecting cables and overhead lines etc. are the parameters that limit the fault level of the system. For ease of calculation, when determining the fault level of such a system it is essential to consider any one major component as the base and convert the relevant parameters of the other equipment to that base, for a quicker calculation, to establish the required fault level. Below we provide a few common formulae for the calculation of faults on a p.u. basis. For more details refer to a textbook in the references. 

Top spray systems During top-spray cooling of an overheated core, the wall temperature is usually higher than the Leidenfrost temperature, which causes water to be sputtered away from the wall by violent vapor formation and then pushed upward by the chimney effect of the steam flow generated at lower elevations (as shown in Fig. 4.25). A spray-cooling heat transfer test with BWR bundles was reported by Riedle et al. (1976). They found the dryout heat flux to be a function of spray rate and system pressure. The collapsed level required to keep the bundle at saturation for various pressures compared reasonably well with that in the literature (Duncan and Leonard, 1971 Ogasawara et al., 1973). 

The power needs for MEMS devices are diverse— and batteries may not be the best choice to provide power to systems based on various types of MEMS drives. For example, magnetic drives operate at less than 1 V, but they require generating hundreds of milliamperes, which becomes a difficult challenge for batteries sized on the subcentimeter scale. The required micro- to nanoampere current levels for electrostatic and piezoelectric MEMS are feasible for batteries, but the tens to hundreds of volts that are needed will present difficulties for batteries with nominal voltages of 3 V. However, there may be a niche for batteries that would be used to power 10— 15 V drives. 

Analysis of complex genomics-based data in systems biology requires multivariate data-analysis methods to obtain useful information. The variation observed in these data sets occurs simultaneously on different levels, such as variation between organisms and variation in time. In conventional two-way methods like PCA, the different types of variation present in these data sets is mathematically confounded. A new method called multilevel component analysis (MCA) was recently introduced to separate these different types of variation [69]. The method was recently demonstrated using a data set containing II NMR spectra of urine collected from 10 monkeys at 29 time points during a 2-month study. In this application, MCA was used to generate different submodels for different types of variation that are easier to interpret. 

The testing system (Fig. 1) was a 1.2 volume pressure apparatus made of metaplex (1). The har support covered with the membrane (2) of an effective surface area of 49.2 cm was fixed in the lower part of the apparatus. To maintain the dye concentration on the level required, continuous circulation of the permeate between the feeding tank (5) and the apparatus was applied. The solution was mixed with a magnetic stirrer (3) which prevents excess concentration of dye on the membrane surface. Pressure was generated by feeding the apparatus with an inert gas (nitrogen) from a cylinder (8). Samples for flow rate measurements and determinations of dye concentration in the permeate were taken through a stub pipe (4). 

The two key performance requirements that determine whether a membrane technology is suitable for application in a power generation facility are performance capabilities and cost. Performance requirements of a membrane-based system are defined at the system level and often involve target purities for several components in filtered fluid streams. Other performance requirements include reliability and footprint targets. 

The Level 4 SSA is at the aircraft level and is the responsibihty of the aircraft integrator. For a modification (e.g. STC), it is scoped to consider the performance of the new system as well as the interaction between all affected aircraft systems. Safety requirements are functionally decomposed in a hierarchical structure from product (i.e. aircraft) level to subsystem (e.g. altitude display system) to components (e.g. Altitude Display Unit). At Level 4 the safety requirements are those requirements generated from the aireraft Functional Hazard Analysis (FHA) based on required aircraft functions... 

Component designers (i.e. System Level 2 in Fig. 1.1) may be required by the system integrator to develop a piece-part FTA with a top-level event for particular failure modes of a unit. The piece-part FTA would then develop through layers of logic gates until individual component failures (resistors, capacitors, etc.) are identified. This is often supported by a Failure Modes and Effects Analysis (FMEA) from which a Eailure Modes and Effects Summary (FMES) (see Chapter 5) can be generated for the individual next or end effects. 

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