Announcements

Thesis Defense: Jiaxin Zhang, “Uncertainty Quantification from Small Data: A Multimodel Approach”

THE DEPARTMENT OF CIVIL ENGINEERING

AND

ADVISOR MICHAEL SHIELDS, ASSISTANT PROFESSOR

ANNOUNCE THE THESIS DEFENSE OF

Doctoral Candidate

Jiaxin Zhang

Tuesday, August 7, 2018

9:00am

Hodson 311

“Uncertainty Quantification from Small Data: A Multimodel Approach”

As a central area of computational science and engineering (CSE), uncertainty quantification (UQ) is playing an increasingly important role in computationally evaluating the performance of complex mathematical, physical and engineering systems. UQ includes the quantification, integration, and propagation of uncertainties that result from stochastic variations in the natural world as well as uncertainties created by lack of statistical data or knowledge and uncertainty in the form of mathematical models. A common situation in engineering practice is to have a limited cost or time budget for data collection and thus to end up with sparse datasets. This leads to epistemic uncertainty (lack of knowledge) along with aleatory uncertainty (inherent randomness), and a mix of these two sources of uncertainties (requiring imprecise probabilities) is a particularly challenging problem.

A novel methodology is proposed for quantifying and propagating uncertainties created by lack of data. The methodology utilizes the concepts of multimodel inference from both information-theoretic and Bayesian perspectives to identify a set of candidate probability models and associated model probabilities that are representative of the given small dataset. Both model-form uncertainty and model parameter uncertainty are identified and estimated within the proposed methodology. Unlike the conventional method that reduces the full probabilistic description to a single probability model, the proposed methodology fully retains and propagates the total uncertainties quantified from all candidate models and their model parameters. This is achieved by identifying an optimal importance sampling density that best represents the full set of models, propagating this density and reweighting the samples drawn from the each of candidate probability model using Monte Carlo sampling. As a result, a complete probabilistic description of both aleatory and epistemic uncertainty is achieved with several orders of magnitude reduction in Monte Carlo-based computational cost.

Along with the proposed new UQ methodology, an investigation is provided to study the effect of prior probabilities on quantification and propagation of imprecise probabilities resulting from small datasets. It is illustrated that prior probabilities have a significant influence on Bayesian multimodel UQ for small datasets and inappropriate priors may introduce biased probabilities as well as inaccurate estimators even for large datasets. When a multi-dimensional UQ problem is involved, a further study generalizes this novel UQ methodology to overcome the limitations of the independence assumption by modeling the dependence structure using copula theory. The generalized approach achieves estimates for imprecise probabilities with copula dependence modeling for a composite material problem. Finally, as applications of the proposed method, an imprecise global sensitivity analysis is performed to illustrate the efficiency and effectiveness of the developed novel multimodel UQ methodology given small datasets.

Post-Doctoral Fellowship in Optimization of Energy and Food Systems

Post-Doctoral Fellowship in Optimization of Energy and Food Systems

Applications are invited for a full-time postdoctoral position at the Department of Civil Engineering and the Center for Systems Science and Engineering at Johns Hopkins University under the supervision of Sauleh Siddiqui at the Mathematical Optimization for Decisions Lab (MODL). The postdoc will spend 50% of their effort on existing projects involving equilibrium problems, bilevel optimization, and machine learning with applications to energy and food systems. The other 50% of the postdoc’s effort will be spent on a project of the postdoc’s choosing, for which a one-page application will be required. The details of the one-page application are below, but the proposal must be highly creative, original, and pertain to at least one of the topics mentioned in this paragraph.

The postdoc will work closely with an international multidisciplinary team of faculty and Ph.D. students from a number of institutions. In addition, the PI will make every effort to mentor the postdoc for transition into a faculty position. This includes guidance on grant-writing, teaching opportunities, and translation of research. Women and Underrepresented Minorities are highly encouraged to apply. This is a year-long postdoc which can potentially be extended up to two years upon satisfactory performance and availability of funding.

Requirements:

– PhD degree in applied or computational mathematics, computer science, engineering, economics, or a closely related field.

– Research experience in one or more of the following fields: optimization, equilibrium, machine learning.

– Experience with GAMS, MATLAB, Python, or other programming languages.

– Demonstrated ability to work independently as well as collaboratively with excellent written and oral communication skills.

– Interdisciplinary research experience is preferred

– A record of research accomplishment as reflected in publications in peer-reviewed journals and conferences and presentations at scientific meetings.

Anticipated start date is September 1, 2018. Review of applications will begin July 10th, 2018 and continue until the position is filled. Complete applications should include the following (in a single pdf file) to Siddiqui@jhu.edu:

(1) A cover letter

(2) A full curriculum vitae

(3) Up to two research publications and/or preprints

(4) The names and contact information for three references

(5) (Optional) A one-page original research proposal with the following headings: Motivation, Research Questions, Research Approach, Methods, Data Sources, Timeline. Proposals will be judged on creativity and originality, so think big!

Thesis Defense: Hwanpyo Kim “Simulation of non-Gaussian/non-stationary stochastic processes: beyond second-order orthogonality”

THE DEPARTMENT OF CIVIL ENGINEERING

AND

ADVISOR MICHAEL SHIELDS, ASST. PROFESSOR

ANNOUNCE THE THESIS DEFENSE OF

Doctoral Candidate

Hwanpyo Kim

Tuesday, April 24, 2018

12:00pm

Malone 107

“Simulation of non-Gaussian/non-stationary stochastic processes: beyond second-order orthogonality”

The theory of stochastic processes and their generations are indispensable to characterize wind fluctuations, ocean waves, and earthquake excitations among other quantities in engineering. To computationally analyze and simulate these stochastic systems, practical realization of samples of stochastic processes is essential. The object of this thesis is to introduce new state-of-the-art methodologies for the generation of stochastic processes with non-Gaussianity/non-stationarity possessing higher-order properties than the second-order orthogonality.

A new type of Iterative Translation Approximation Method (ITAM) using the Karhunen-Loève expansion was developed for simulating non-Gaussian and non-stationary processes utilizing translation process theory. The proposed methodology enhances the accuracy of simulated processes in matching a prescribed autocorrelation, maintains the computational efficiency, and resolves limitations caused by utilizing evolutionary power spectra for non-stationary processes.

A new generalized stochastic expansion, the bispectral representation method (BSRM), expanded from the traditional spectral representation method is introduced to simulate skewed nonlinear stochastic processes. With new orthogonal increments to satisfy the conditions of the Cramér spectral representation up to third order orthogonality, the BSRM generates samples that match both the power spectrum and bispectrum of the process by modeling complex nonlinear wave interactions.

A model of phase angle distributions to characterize phase coupling in higher-order stochastic processes is presented. Relationships between the trigonometric moments of circular distributions of phase differences and higher-order cumulant spectra are derived. The prescribed properties are shown to accurately model quadratic and cubic phase couplings in simple stochastic processes and can easily be extended to general n-wave couplings.

Lastly, as applications of the prescribed methods, wind pressure and turbulent wind velocity time histories are generated with SRM, ITAM, and BSRM and applied to two different nonlinear dynamic structural systems. For structures having material and geometrical nonlinearities, performance of an elastic perfectly-plastic structure and the buffeting response of a long-span bridge with coupled aerodynamic forces are examined. The structures are investigated to observe the effect of higher-order properties of the excitations on the response when compared to conventional second-order Gaussian and non-Gaussian excitations.

Thesis Defense: Wei Jang, “Machine Learning and Optimization for Healthcare and Energy Systems”

The Department of Civil Engineering
and
Advisor Sauleh Siddiqui, Assistant Professor
Announce the Thesis Defense of
Doctoral Candidate

 

Wei Jiang

Thursday, March 22, 2018

2:00-4:00pm

Latrobe 106

 

“Machine Learning and Optimization for Healthcare and Energy Systems

 

Abstract:

Healthcare and energy systems provide critical service to our society. Recent advancement in information technology has enabled these systems to keep retrieving and storing data. In this dissertation, we used machine learning, optimization techniques, and data from healthcare and energy systems to build predictive models and discover new knowledge to guide decision-making and improve the efficiency and sustainability of these systems. We also used optimization techniques to improve the efficiency of hyperparameter tuning for machine learning algorithms. Specifically, we built a dynamic daily prediction model for predicting heart failure patients’ 30-day readmission risk. We built a prediction model to predict xerostomia (dry mouth) for head and neck cancer patients treated with radiotherapy and identified the influence pattern of radiation dose across head and neck on xerostomia. Using an economic equilibrium model combined with optimization techniques for calibration, we built the first global trade model for wood chip and analyzed how local renewable energy policy in the United States could affect the global wood chip trade and lead to deforestation in other world regions. Finally, we created a new method for tuning the hyper-parameter for support vector machines by solving the problem as a bilevel optimization problem using stochastic gradient descent combined with dual coordinate descent method. We showed that the new method is more efficient than ad hoc empirical approaches. In summary, we demonstrated how machine learning and optimization techniques can improve the efficiency of healthcare and energy systems, and how optimization techniques can advance machine learning algorithms.

 

 

Spring 2018 Graduate Seminar Speaker Series

Below is a listing for the speakers being showcased during the Spring 2018 Civil Engineering Graduate Seminar Series. All civil engineering graduate seminars are FREE and open to the public. Attendance is required for all enrolled Civil Engineering graduate students. For information on individual seminars, please refer to the Events Calendar.

For directions and information on parking please see Maps & Directions link at www.jhu.edu and select information on Homewood Campus.

Thesis Defense: Reza Yaghmaie, “Multi-Temporal Multi-Physics Computational Framework For Fully Coupled Electric, Magnetic and Mechanical Systems With Evolving Damage”

THE DEPARTMENT OF CIVIL ENGINEERING

AND

ADVISOR SOMNATH GHOSH, PROFESSOR

ANNOUNCE THE THESIS DEFENSE OF

Doctoral Candidate

Reza Yaghmaie

Monday, December 18, 2017

1:00pm

Latrobe 106

“Multi-Temporal Multi-Physics Computational Framework For Fully Coupled Electric, Magnetic and Mechanical Systems With Evolving Damage”

 

 

MSE Essay Presentation: Johnpatrick Connors – “Variability in the Experimental Response of Thermally Excited Aluminum Alloys”

The Department of Civil Engineering

and

Advisor Michael Shields, Asst. Professor

Announce the Essay Presentation of

M.S.E. Candidate

 

Johnpatrick Connors

Monday, December 4, 2017

3:00-4:00pm

Latrobe 106

Variability in the Experimental Response of Thermally

Excited Aluminum Alloys”

 

The use of aluminum alloys for load bearing elements continues to expand rapidly across the marine, aviation, and commercial building industries, among others. Some factors driving this expansion are aluminum’s low density, good formability, and high corrosion resistance when properly alloyed and tempered. These properties give aluminum a number of competitive advantages, especially for light-weight structures such as airplanes and ships, as compared with other structural metals.

 

However, one factor hindering the expansion of aluminum alloys, especially in high temperature applications, is that is has a relatively low melting point. This, combined with a lack of knowledge regarding the uncertainty of aluminum’s performance at high temperatures often counteracts the weight savings provided by aluminum’s low density.

 

Existing studies of aluminum alloys have omitted discussion of the uncertainty in aluminum’s response to high temperature environments. In order to address this lack of data, this thesis presents experimental results of 100 tension tests and 54 plane strain tests of the most commonly used structural aluminum, 6061-T651 aluminum alloy.

 

Key results of the study include engineering stress-strain curves and statistics of mechanical properties obtained using digital image correlation. These statistics show the variation in the mechanical behavior of aluminum under two different stress states, six different temperatures, and between different batches of material.

Thesis Defense: Abdullah Mahmoud, “Analysis and Design of Spirally Welded Thin-Walled Steel Tapered Cylindrical Shells Under Bending with Application to Wind Turbine Towers”

THE DEPARTMENT OF CIVIL ENGINEERING

AND

ADVISOR BENJAMIN SCHAFER, PROFESSOR

ANNOUNCE THE THESIS DEFENSE OF

Doctoral Candidate

Abdullah Mahmoud

Monday, October 16, 2017

3:15pm – 5:15pm

Malone G33/35

“Analysis and Design of Spirally Welded Thin-Walled Steel Tapered Cylindrical Shells Under Bending with Application to Wind Turbine Towers”

Seeking Applicants for Tenure-Track/Tenured Faculty Positions with Emphasis in Systems Engineering

The Johns Hopkins University’s Department of Civil Engineering seeks applicants for tenure-track/tenured faculty positions at all levels and across all areas of Civil Engineering. While emphasis is in the area of Systems Engineering with particular interest in healthcare and/or infrastructure resilience, all qualified applicants in any area of Civil Engineering will be considered.

The Department of Civil Engineering has 11 faculty whose research broadly covers the areas of Structures, Systems, and Mechanics of Materials. Current enrollments in the Department are approximately 50 undergraduate students and 60 graduate students, the majority of which are Ph.D. candidates. The department maintains laboratories and major facilities for research. Strong links to JHU institutes and centers such as the Malone Center for Engineering in Healthcare, the Center for Systems Science and Engineering, the Center for Integrated Structures-Materials Modeling and Simulation, the Hopkins Extreme Materials Institute, and the Cold-formed Steel Research Consortium expand the footprint of the Department both within and outside of the University. More information about the Department of Civil Engineering can be found at http://www.ce.jhu.edu.

The Whiting School of Engineering comprises over 200 full time tenure-track, research, and teaching-track faculty in nine academic programs with a total annual research budget of over $100 million. Research partnerships with the Johns Hopkins School of Medicine, Applied Physics Laboratory, Bloomberg School of Public Health and the Krieger School of Arts and Sciences make the Whiting School of Engineering a unique research and educational environment. Student enrollment exceeds 1800 at the undergraduate level with over 1000 full time MS and PhD students. The Engineering for Professionals program enrolls over 2000 part time continuing education students and is the largest program of its kind in the country.

Applicants must hold an earned doctorate in an appropriate field by the time their appointment begins. Candidates must have a demonstrated record of outstanding independent research and excellence in teaching, professional service and translation. Applications at all levels will be considered; salary and rank will be commensurate with qualifications and experience. Applicants should submit a curriculum vitae, a research statement, a teaching statement, three recent publications, and complete contact information for at least three references. Applications must be made on-line at https://apply.interfolio.com/45609.

Candidates applying for associate or full professor positions should not provide any information for references. Candidates applying for the position of Assistant Professor should provide names and contact information of at least three (3) references. Review of applications will begin immediately.  While candidates who complete their applications by November 15, 2017 will receive full consideration, the Department will consider exceptional applicants at any time.

The Johns Hopkins University is committed to active recruitment of a diverse faculty and student body. The University is an Affirmative Action/Equal Opportunity Employer of women, minorities, protected veterans and individuals with disabilities and encourages applications from these and other protected group members. Consistent with the University’s goals of achieving excellence in all areas, we will assess the comprehensive qualifications of each applicant.

The Whiting School of Engineering and the Department of Civil Engineering are committed to building a diverse educational environment.

Fall 2017 Graduate Seminar Speakers Announced

Below is a listing for the speakers being showcased during the Fall 2017 Civil Engineering Graduate Seminar Series. All civil engineering graduate seminars are FREE and open to the public. Attendance is required for all enrolled Civil Engineering graduate students. For information on individual seminars, please refer to the Events Calendar.

For directions and information on parking please see Maps & Directions link at www.jhu.edu and select information on Homewood Campus.

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