Michael Latcha

An Efficient Monte Carlo Reliability Analysis using Global and Local Metamodels

*† ‡ An accurate and efficient computational method is presented for reliability analysis of engineering systems. The method can handle implicit, nonlinear limit-state functions, with correlated or non-correlated random variables, which are described by any probabilistic distribution. It uses a global and a local metamodel of the limit state. Both metamodels serve as an indicator to determine the failure and safe regions. Sample points close to limit state define a transition region between the safe and failure regions. An accurate local metamodel of the actual limit state is generated and used to evaluate all samples in the transition region. A Monte Carlo simulation calculates the probability of failure using the global and local metamodels. The cross-validated moving least squares method, and a robust maximin “space-filling” sampling technique, are used to construct the metamodels. Also, a Principal Component Analysis reduces the problem dimensionality making therefore, the proposed method attractive for problems with a large number of random variables. Three numerical examples highlight the accuracy and efficiency of the method.

A Monte Carlo Reliability Assessment for Multiple Failure Region Problems Using Approximate Metamodels

An efficient Monte Carlo reliability assessment methodology is presented for engineering systems with multiple failure regions and potentially multiple most probable points. The method can handle implicit, nonlinear limit-state functions, with correlated or non-correlated random variables, which can be described by any probabilistic distribution. It uses a combination of approximate or “accurate-on-demand,” global and local metamodels which serve as indicators to determine the failure and safe regions. Samples close to limit states define transition regions between safe and failure domains. A clustering technique identifies all transition regions which can be in general disjoint, and local metamodels of the actual limit states are generated for each transition region. A Monte Carlo simulation calculates the probability of failure using the global and local metamodels. A robust maximin “space-filling” sampling technique is used to construct the metamodels. Also, a principal component analysis addresses the problem dimensionality making therefore, the proposed method attractive for problems with a large number of random variables. Two numerical examples highlight the accuracy and efficiency of the method.Copyright

A self-contained, portable variable-pressure hydrostatic cell for use in low gauge pressure electromagnetic, ultrasonic, and photoacoustic studies

A simple, manually adjustable hydrostatic cell for electromagnetic, ultrasonic, and photoacoustic studies in absolute pressure ranges from 40 kPa to 5.5 MPa is described. The cell consists of two 3-mm-thick quartz windows enclosing a 1.3-cm-diameter hole bored through a 2.54-cm-long cube block of stainless steel. Four 3-mm-diameter counterbored and taper-threaded holes on the cube walls provide minimally intrusive, chemically inert ports for temperature and acoustical monitoring. Pressure is easily varied within the cell by means of a stainless steel threaded shaft with an O-ring seal at the end, situated inside a matched internally threaded housing. An example of photoacoustic waveforms acquired under conditions of varying hydrostatic pressure is provided.

Engaging Underrepresented Undergraduates in Engineering Through a Hands-On Automotive-Themed REU Program

Since the summer of 2006, the department of Mechanical Engineering at Oakland University (OU) has been organizing a research experience for undergraduates (REU) program that has been successful at recruiting underrepresented undergraduates in engineering — women in particular. Funded in 2006–2009 and in 2010–2013 through the National Science Foundation REU program and the Department of Defense ASSURE program, this summer REU program focuses on automotive and energy-related research projects. The main purpose of this paper is to share our 6-year experience of organizing and running a summer REU program and to report on the outcomes and short/medium-term assessment results of the program. Also included are some recommendations that we would make to further enhance the success of similar REU programs. We believe that this type of information could prove to be of value to other REU program directors and faculty seeking to organize similar programs.Copyright

To ship or not to ship: an engineering ethics case study

The authors have developed a numerical-based engineering ethics case study for use in engineering courses. It has been shown that ethics case studies that involve technical calculations and real-world situations appeal more to engineering students than do purely qualitative cases. The case is a fictionalized account of several incidents that the second author witnessed while employed at a steel manufacturing company. In this study, students are asked to evaluate several coils of steel and determine which ones meet certain minimum standards for yield strength. Statistical analysis is necessary to evaluate the strength of the steel. Test data is given for each of the steel coils, from one to five test samples per coil. After analysis, the students are presented with several scenarios and asked to decide which coils meet the minimum standards. In making the decision to approve coils for shipment, students must decide on the appropriate statistical measures to use and in particular how much of the confidence interval needs to be above the minimum standard.