Engineering topics

Suich, Ronald C.

Publications and source records attributed to Suich, Ronald C..

7 records

NASA NTRS1993

Minimize system cost by choosing optimal subsystem reliability and redundancy

The basic question which we address in this paper is how to choose among competing subsystems. This paper utilizes both reliabilities and costs to find the subsystems with the lowest overall expected cost. The paper begins by reviewing some of the concepts of expected value. We then address the problem of choosing among several competing subsystems. These concepts are then applied to k-out-of-n: G subsystems. We illustrate the use of the authors' basic program in viewing a range of possible solutions for several different examples. We then discuss the implications of various solutions in these examples.

Suich, Ronald C.↗

NASA NTRS1991

Reliability and cost: A sensitivity analysis

In the design phase of a system, how a design engineer or manager choose between a subsystem with .990 reliability and a more costly subsystem with .995 reliability is examined, along with the justification of the increased cost. High reliability is not necessarily an end in itself but may be desirable in order to reduce the expected cost due to subsystem failure. However, this may not be the wisest use of funds since the expected cost due to subsystem failure is not the only cost involved. The subsystem itself may be very costly. The cost of the subsystem nor the expected cost due to subsystem failure should not be considered separately but the total of the two costs should be maximized, i.e., the total of the cost of the subsystem plus the expected cost due to subsystem failure.

Suich, Ronald C.↗

NASA NTRS1991

k-out-of-n:G systems - Some cost considerations

The authors provide a tool that an engineer designing a subsystem can use to decide between one subsystem and a more reliable but more costly one. The authors provide methods for selecting redundancy levels in k-out-of-n:G systems in order to minimize particular cost considerations where the k-out-of-n:G system is a subsystem of a major system. The n and k are chosen to minimize the total cost of the subsystem plus the average loss due to subsystem failure. A BASIC program is available to determine the n and k which find this minimum. Five loss functions are considered, and illustrations are given.

Suich, Ronald C.↗

NASA NTRS1991

Balancing reliability and cost to choose the best power subsystem

A mathematical model is presented for computing total (spacecraft) subsystem cost including both the basic subsystem cost and the expected cost due to the failure of the subsystem. This model is then used to determine power subsystem cost as a function of reliability and redundancy. Minimum cost and maximum reliability and/or redundancy are not generally equivalent. Two example cases are presented. One is a small satellite, and the other is an interplanetary spacecraft.

Suich, Ronald C.↗

NASA NTRS1991

Balancing reliability and cost to choose the best power subsystem

The justification of the increased cost of a more reliable power subsystem is discussed. A mathematical model is presented for computing total spacecraft subsystem cost including both the basic subsystem cost and the expected cost due to the failure of the subsystem. This is then used to determine the power subsystem cost as a function of reliability and redundancy. Minimum cost and maximum reliability and/or redundancy are not generally equivalent. Two example cases are presented. One is a small satellite, and the other is an interplanetary spacecraft.

Suich, Ronald C.↗

NASA NTRS1991

Reliability and cost analysis methods

In the design phase of a system, how does a design engineer or manager choose between a subsystem with .990 reliability and a more costly subsystem with .995 reliability? When is the increased cost justified? High reliability is not necessarily an end in itself but may be desirable in order to reduce the expected cost due to subsystem failure. However, this may not be the wisest use of funds since the expected cost due to subsystem failure is not the only cost involved. The subsystem itself may be very costly. We should not consider either the cost of the subsystem or the expected cost due to subsystem failure separately but should minimize the total of the two costs, i.e., the total of the cost of the subsystem plus the expected cost due to subsystem failure. This final report discusses the Combined Analysis of Reliability, Redundancy, and Cost (CARRAC) methods which were developed under Grant Number NAG 3-1100 from the NASA Lewis Research Center. CARRAC methods and a CARRAC computer program employ five models which can be used to cover a wide range of problems. The models contain an option which can include repair of failed modules.

Suich, Ronald C.↗

NASA NTRS1990

How much redundancy: Some cost considerations, including examples for spacecraft systems

How much redundancy should be built into a subsystem such as a space power subsystem. How does a reliability or design engineer choose between a power subsystem with 0.990 reliability and a more costly subsystem with 0.995 reliability. How does the engineer designing a power subsystem for a satellite decide between one power subsystem and a more reliable but heavier power subsystem. High reliability is not necessarily an end in itself. High reliability may be desirable in order to reduce the statistically expected loss due to a subsystem failure. However, this may not be the wisest use of funds since the expected loss due to subsystem failure is not the only cost involved. The subsystem itself may be very costly. The cost of the subsystem or the expected loss due to subsystem failure may not be considered separately. Therefore, the total of the two costs is minimized, i.e., the total of the cost of the subsystem plus the expected loss due to subsystem failure. A specific type of redundant system is considered, called a k-out-of-n: G subsystem. Such a subsystem has n modules, of which k are required to be good for the subsystem to be good. Five models are discussed which can be applied in the design of a power subsystem to select the unique redundancy method which will minimize the total of the cost of the power subsystem plus the expected loss due to the power subsystem failure. A BASIC computer program is available.

Suich, Ronald C.↗