Economic Design Approach Research Articles

Pseudo-plastic moment resistance of continuous beams with cold-formed sigma sections at internal supports: An experimental study

Most thin-walled sections exhibit elastic-softening moment–rotation characteristics in bending, and therefore the elastic analysis/design method is usually recommended for continuous beams with this type of section. A more economical design approach, the pseudo-plastic design method, has been proposed to allow for the development of moment redistribution in the system. To facilitate this design method, pseudo-plastic moment resistance (PPMR) at the internal supports is required. This paper reports an experimental study of the structural performance of continuous beams with cold-formed sigma sections near the internal supports, based on which the PPMR was derived. To this end, only the part of the beam carrying a hogging moment near one of the internal supports was specifically studied. It was represented with a simply supported beam subjected to a central point load. The simple supports were placed at inflexion points and the concentrated load was a representation of the reaction. Research results include the behaviours of initial buckling, post-buckling and post-failure of sigma beams near the internal supports, the ultimate moment resistance under combined bending and shear, and the moment–rotation relationship. Four typical localised collapse patterns have been established and defined. The results of ultimate moment resistance obtained were compared with the theoretical predictions by using two codified methods, namely, the effective width method (EWM) and the direct strength method (DSM). Lastly, a semi-empirical approach has been proposed to find the pseudo-plastic moment resistance at the internal supports.

Economic design of exponential charts for time between events monitoring

The occurrence of defects or non-conformities in manufacturing processes can usually be modeled by a homogeneous Poisson process. However, the process parameter may change over time and it can be monitored with statistical process control techniques. Control charts based on an exponential distribution, called exponential charts in this paper, can be developed to monitor the occurrence rate of such events. For manufacturers, the economic objective of production is very important and has to be optimized. An economic approach is developed in this paper for the design of exponential charts. We compare and contrast the performances of statistical design, economic design and economic–statistical design. The usefulness of the proposed economic design approach is justified. The relationships among these designs are illustrated through numerical examples. In particular, the economic–statistical design approach is interpreted from a multi-objective optimization viewpoint. The limitations of the approach as well as future research are also discussed.

The effect of process adjustment error on?? chart design

The existing literature on economic design of X process control charts generally assumes perfect process adjustment, such that the process mean is returned to an exactly centered “in control” state following any real or false alarm control chart signal. This paper presents a model which demonstrates the effects of imperfect process adjustment on the economically designed control chart parameters. The model demonstrates that the optimal control limit width depends fundamentally on the precision with which the process can be adjusted. The greater the process adjustment error, all else constant, the wider will be the optimal control limits, in order to alleviate the potential for process overcontrol and tampering effects. By endogenously modeling these effects, the new model helps to rectify the problem of poor statistical properties for which the economic design approach has been criticized. © 1999 John Wiley & Sons, Inc. Naval Research Logistics 46: 597–612, 1999

Economic statistical design of S control charts using Taguchi loss function

An economic statistical design approach takes statistical properties into account while designing control charts economically. It improves both statistical design and economic design. In this paper, we present a statistically constrained economic model for the optimal design of S control chart for controlling process variability. In the model, the process quality can be affected by an assignable cause resulting in a shift of the variance of the distribution of output when it is operating according to its capability. The parameters are obtained by minimizing a total cost function proposed by Lorenzen and Vance, which is embellished with Taguchi loss function, subject to additional statistical constraints on average run length or average time‐to‐signal (ATS). Sensitivity analysis of the minimum cost will be performed to depict the effect of the choice of ATS bounds.

Economic design of dual-sampling-interval policies for X¯ charts with and without run rules

Recent studies show that the dual-sampling-interval (DSI) policies of X¯ control chart yield a smaller average time to signal (ATS) than Shewhart's classical fixed-sampling-interval (FSI) policy for off-target processes. An economic design approach for DSI policies has not been addressed in the literature. In this paper we develop a comprehensive cost model for DSI policies with and without run rules and steady-state performance. The expression for the unit cost of quality is used as the objective function in optimal design of DSI policy parameters. The design process and the sensitivities of some of the model input parameters are exposed through numerical examples.

Economic design of dual-sampling-interval policies for X¯ charts with and without run rules

Recent studies show that the dual-sampling-interval (DSI) policies of X¯ control chart yield a smaller average time to signal (ATS) than Shewhart's classical fixed-sampling-interval (FSI) policy for off-target processes. An economic design approach for DSI policies has not been addressed in the literature. In this paper we develop a comprehensive cost model for DSI policies with and without run rules and steady-state performance. The expression for the unit cost of quality is used as the objective function in optimal design of DSI policy parameters. The design process and the sensitivities of some of the model input parameters are exposed through numerical examples.

Economic, Statistical, and Economic-Statistical Design of Attribute Charts

We present a FORTRAN program that can be used to determine the economic, statistical, or economic-statistical design of a fraction defective or defects per unit chart. In the economic design approach, the general Lorenzen-Vance cost function is minimize..

Heat-transfer considerations for large liquefied-natural-gas storage tanks

Natural gas is used worldwide as a practical energy source. In order to have a concentrated form of energy, natural gas is liquefied and stored under a pressure slightly above atmospheric and at a corresponding temperature just above its normal boiling point (112 K). This investigation presents a general steady-state study of the heat transfers into such a storage tank. Two mathematical models are proposed in order to help improve the thermal design process for such a tank. It is concluded that the aspect ratio (i.e. height-to-radius) of such a tank for the minimum rate of heat gains should be approximately unity. This value differs from the economically most favourable aspect ratio, i.e. that leading to the least total financial expenditure over the lifetime of the tank. However, the two models allow a complete simulation of the thermal costs. As the unit cost of fuel rises relative to other costs (e.g. for the construction of the tank), the overall most economic tank design approaches that of the optimal thermal design of tank as deduced in this investigation.

Engineering Analysis of Potential Photosynthetic Bacterial Hydrogen Production Systems

Photosynthetic bacteria (PSB) are capable of generating hydrogen from organics in effluents from flod processing, pulp and paper, and chemical and pharmaceutical industries. Hydrogen evolution takes place under light in the absence of air. The rate of hydrogen production is expected to range between 300 to 600 scf of hydrogen per 1000 gallons of waste stream treated per hour. This hydrogen production system has been demonstrated at a bench-scale level and is ready for engineering development. A conceptual design for a PSB hydrogen production system is described. The system is expected to be sited adjacent to a waste stream source which will be pretreated by fermentation and pH adjustment, innoculated with bacteria, and then passed into the reactor. The reactor effluent can either be discharged into a rapid infiltration system, an irrigation ditch, and/or recycled back into the reactor. The gaseous products from the reactor are purified by removing water and carbon dioxide, compressed, and stored. The high fraction of system cost and the tight design constraints of the reactor make it the most crucial component of the PSB system. An effort to model the thermal, biological, and convective properties of the reactor is in progress. Several potential reactor designsmore » have been developed, analyzed, and costed. A large covered pond appears to be the most economical design approach.« less

HIgh-Power C-Band Multiple-IMPATT-Diode Amplifiers

The design considerations and performance characteristics of two high-power microwave reflection amplifiers that use multiple silicon IMPATT diodes are presented. The amplifiers employ microstrip hybrid-circuit-type power combiners to combine the individually matched IMPATT diodes. The first unit, a single-stage 4-diode amplifier, produced 8-W output with 6-dB gain while the second 12-diode amplifier gave 15.8-W output at about 9-dB gain. FM and AM noise added by these amplifiers has been measured with each amplifier driven to nearly full output. Use of microstrip hybrid-circuit power combiners appears to offer a simple and economical design approach for the implementation of microwave solid-state power amplifiers using multiple active devices.