Warren Distinguished Lecture Series

Mark Borchardt
U.S. Dairy Forage Research Center

ABSTRACT: Human enteric viruses are well-known contaminants of groundwater supplies, and yet the level of illness risk associated with drinking virus-contaminated groundwater is not fully understood. This seminar will report the level of acute gastrointestinal illness in communities that use non-disinfected groundwater as their municipal drinking water source. In addition, absent a chlorine residual in these non-disinfecting systems, it was possible to estimate the level of illness solely related to virus contamination events in the drinking water distribution systems. Also presented will be a ground waterborne virus outbreak investigation that led to surprising findings.

Tomasz Hueckel
Civil and Environmental Engineering Department
Mechanical Engineering and Materials Science Department
Duke University

Abstract

A multi-scale, multi-physics sequence of processes is discussed as developing during drying of non-clayey soils. Two variables are believed to be central in drying: suction resulting from the evaporation and effective stress associated with external constraints imposed on drying shrinkage. These two variables are tracked across the scales, both in experiments and simulations. The effective stress is critical as leading eventually to soil drying-cracking. Cracking is a most unwanted development in soil undergoing dewatering. Drying - cracking is shrouded by two paradoxes. First, it takes place when the effective stress is compressive, and second, it occurs when soil is still almost entirely saturated. Drying cracks often arise in the apparent absence of external forces. Hence, a tensile eigen-stress pattern resulting from stiff inclusions, or (relatively weak) tensile total stress produced by reaction forces at the external boundary constraints need to be contemplated to reach cracking criteria. An earlier tubular micro-scale model of porous drying medium indicates that transport of water toward evaporating surface during saturation phase induces a high suction. As a result the effective stress is compressive, which is consistent with widely observed drying shrinkage. This paradox has been solved by George Scherer (1992), who postulated that in the presence of any surface imperfection, a total stress amplification is expected, which despite high suction yields a tensile effective stress locally. A critical suction value is reached at which water body boundary is penetrated in an unstable manner by air. We postulate that at the meso- scale such air penetration indeed constitutes a surface imperfection, and a tensile total stress amplification near its tip, and a rapid increase in local tensile effective stress and crack propagation. Recent experimental results from a configuration of a cluster of grains provide geometrical data suggesting that an imperfection resulting from of air entry penetrates deep into the granular medium over 4 - 8 radii of the typical pore. Percolation studies indicate that capillary fingers can penetrate over tens to several hundreds grain radii forming a drying front prompting formation of discrete cracks at the point of maximum tensile stress. Further evolution entails separation of grain clusters by funicular bridge instabilities, and in the last stage formation of two-grain pendular capillary bridges. The final phase is associated with a gradual decrease of the micro-scale suction within these elementary bridges, which eventually evolve into a positive pressure before the bridge rupture.

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Raj Dongre
Dongre Laboratory Services, Inc.

Abstract

The State Departments of Transportation (DOTs) asked the Federal Highway Administration (FHWA) to develop a simple and portable test method that may be used as a QC/QA tool for asphalt binders. FHWA along with Laser Technology Inc. (LTI) of Norristown PA has developed a QC/QA test method for asphalt binders. This device uses an air jet to produce creep and recovery loading, Figure 1. The resulting creep and recovery deformation is measured using a method that is based on laser technology. A first version of the QC/QA device has now been developed by Laser Technologies Inc. (LTI). Further testing was conducted at FHWA and LTI using the working prototype to further evaluate the technology and to study the long term steric hardening behavior of unaged and RTFO aged asphalt binders. This presentation will discuss the status of the ongoing QC/QA test method development under taken by FHWA and LTI, Figure 2. A demonstration of the test method will also be presented using various asphalt binders.

Biography

Dr. Raj Dongre is currently a consultant to the Federal Highway Administration (FHWA). For the past 16 years, he has been involved with the refinement of various Superpave specifications and development of standards. He has published numerous papers on material testing and specifications. Dr. Dongre received his MS and Ph.D. degrees from The Pennsylvania State University and his BSCE degree from the Maharaja Sayajirao University of Baroda, India. His background has varied aspects of asphalt highway engineering ranging from academic to research and consulting engineering. He owns the consulting engineering firm and testing laboratory Dongre Laboratory Services Inc. He is a member of the Transportation Research Board, The Association of Asphalt Pavement Technologists, The Canadian Technical Asphalt Association, and past Chairman of ASTM subcommittee D4.44.

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Satish Nagarajaiah
Professor of Civil and Mechanical Engineering
Rice University, Houston, TX
Satish.Nagarajaiah@rice.edu

Abstract

Traditionally researchers have focused on supplemental damping systems for earthquake protection. Nagarajaiah group has focused on the development of adaptive/variable stiffness systems and smart tuned mass dampers for response control. This seminar presents various stages of development of the concept of adaptive/variable stiffness structural systems. Recently NSF NEES-Adapt-Struct team with Satish Nagarajaiah as PI has focused on the development of supplemental adaptive stiffness systems for stiffness shaping in structures and apparent weakening for seismic protection. This webinar presents various stages of development of the concept of adaptive passive stiffness shaping achieved through the introduction of supplemental negative and positive tangential stiffness, and the design procedure for implementing it in various structures. The team at Rice University, University at Buffalo, RPI & UCLA funded through the NSF NEES program have developed practical and true negative stiffness system. The aim of the current project was to develop a true negative stiffness system and mimic “yielding” while retaining the main structure either in the elastic range or in the mildly inelastic range with reduced inelastic excursions—leading to a new concept called “apparent weakening”. The webinar presents the invention of the Negative Stiffness Device (NSD) and process that lead to the invention of the NSD—a creative process of innovation by a team of researchers. The innovation of apparent weakening concept is presented. Detailed analytical and shake table test results are presented to show the effectiveness of the new and innovative concept of adaptive negative-positive tangential stiffness which allows stiffness shaping in structures and apparent weakening for earthquake protection. Effectiveness of NSD in base isolated structures, inelastic single and multistory buildings, and based isolated bridges is demonstrated using experimental and analytical results obtained in the NEES-Adapt-Struct project. (Proj. site www.ruf.rice.edu/~dsg). View videos of NEES-ADAPT(ive)-STRUCT(ures) project in YouTube RiceDSNG channel

Biography

Nagarajaiah Satish Nagarajaiah is a Professor of Civil and Mechanical Engineering at Rice University, Houston. He obtained his Ph.D. (1987-1990) from University at Buffalo, where he was a post-doctoral researcher before he started his academic career in 1993. He has published extensively and presented several keynote lectures at international conferences. For full details visit his website satishnagarajaiah.rice.edu. Dr. Nagarajaiah currently serves as the managing editor of the journal of structural engineering [ASCE], editor of the structural control and health monitoring international journal [Wiley] and editor-in-chief (North America) of the structural monitoring and maintenance international journal [Techno-press]. He is an elected inaugural fellow of Structural Engineering Institute (SEI) of ASCE since 2012. He was awarded the NSF CAREER award in 1998 for his research on Adaptive Stiffness Structures. He has founded and chaired numerous committees in SEI, EMI, and IASCM on Structural Control and Monitoring.

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Yuri Bazilevs
University of California, San Diego

Figure 1. Left: FSI of a 5MW offshore wind turbine. Right: FSI of a Berlin Heart pediatric ventricular assist device

Abstract

Basics of Isogeometric Analysis are presented and the overview of this new computational technique and its application to a diverse set of problems of contemporary engineering interest and importance is shown. A framework for computational fluid-structure interaction based on the Arbitrary Lagrangian-Eulerian formulation is presented. The fluid—structure interface discretization is assumed to be nonmatching allowing for the coupling of standard finite-element and isogeometric discretizations for the fluid and structural mechanics parts, respectively. FSI coupling strategies and their implementation in the high-performance parallel computing environment are discussed. Simulations of engineering systems at vastly different spatial scales, including cardiovascular medical devices and wind turbines are presented, and the corresponding computational challenges are addressed.

Biography

Dr. Bazilevs received his PhD from the University of Texas at Austin in 2006, and he is currently an Associate Professor in Department of Structural Engineering at University of California, San Diego. He has published over 80 archival journal papers on computational fluid and structural mechanics, and fluid—structure interaction. He coauthored a book on isogeometric analysis, a technique that is now widely used in computational mechanics. He also coauthored a book on computational fluid—structure interaction. He is an Assistant Editor of Springer journal Computational Mechanics for the manuscripts on computational fluid mechanics and fluid—structure interaction. 

Stefano Gonella
Department of Civil Engineering
University of Minnesota

Abstract

Nonlinear phononic crystals owe their appeal to their ability to behave as flexible mechanical filters, which is due to the inherent nonlinearity-induced tunability of their wave propagation and attenuation zones. The main motive of this study is to understand the wave propagation characteristics that are intimately responsible for this macroscopic bandgap modulation. In parallel, we wish to provide a complete map of the complex packet distortion phenomena that appear in nonlinear phononic chains as a result of the tight interplay between nonlinear and dispersive mechanisms. These objectives are pursued by monitoring the spectro-spatial features of the wave profiles that are established in the chains through the excitation of tone bursts with variable frequency content. The first characterization is conducted on two benchmark mono-atomic chains, involving springs with cubic and quadratic hardening, respectively. For the cubic case, it is shown that the interplay between nonlinearity and dispersion can be recognized in the sustained motion of bi-modal wave packets with solitary-wave-like features and certain nonlinearity-insensitive energy propagation characteristics. For the quadratic case, the nonlinear behavior manifests as a non-symmetric modulation of the linear dispersive response by a long-wavelength sigmoidal profile. These observations are used to construct a set of simple inverse problems which can be used to distill the signature of the nonlinear effects from the dispersive response and consequently estimate the nonlinearity of systems with arbitrary complexity. The generality and versatility of the analysis is finally demonstrated though the inverse characterization of granular chains governed by different Hertzian power laws.

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Jia-Liang Le
Department of Civil Engineering
University of Minnesota

Abstract

Modern engineering structures are often made of quasibrittle materials, which are brittle heterogeneous materials such as concrete, composites, toughened ceramics, etc. The salient feature of quasibrittle structures is that the failure behavior is strongly dependent on the structure size, which further leads an intricate scale effect on the structural strength. Un- derstanding this scale effect is critical for extrapolating the results of small-scale laboratory tests to predict the response of a full-scale structure. So far, two independent scaling theories have been developed for quasibrittle fracture: 1) statistical scaling derived from the weakest link model, and 2) energetic scaling derived from fracture mechanics. The statistical scaling theory is generally applicable to structures with a smooth boundary whereas the energetic scaling theory is applicable to structures with a large pre-existing crack. Nevertheless, many engineering structures are designed to have complex geometries and material mismatch, which could introduce stress singularities that are weaker than the conventional "-1/2" crack-tip singularity. To derive the scaling model for such structures, it is critical to understand how the weak stress singularities modify the classical energetic and statistical scaling theories. In this study, a new scaling model for quasibrittle fracture is derived, which explicitly relates the nom- inal structural strength to the structure size and the magnitude of the stress singularity. The theoretical analysis is based on a generalized weakest link model that combines the energetic scaling of fracture with the finite weakest link model. The model captures the transition from the energetic scaling to statistical scaling as the strength of the stress singularity diminishes. To verify the proposed scaling model, we perform finite element simulations of the size effect on fracture of both homogenous and bimaterial quasibrittle structures exhibiting different magni- tudes of stress singularities. It is shown that the new scaling law is in close agreement, for the entire range of stress singularities, with the numerically simulated size effect curves. In closing, extension of this model to scaling of fatigue lifetime is outlined.

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Martin Schanz
Institute of Applied Mechanics
Graz University of Technology

Abstract

A lot of applications, especially, in geomechanics require the computation of waves in porous media [5], e.g., earthquake waves in soil. Soil is a partial saturated poroelastic material which sometimes can be modelled by a saturated theory, however, sometimes a partial saturated theory is necessary. Having waves in semi-infinite domains in mind a boundary element formulation for such materials seems to be preferable. But, this works only if a linear theory for partial saturated poroelasticity is used.

The partial saturated continuum consists of an elastic solid skeletton and a wetting and non- wetting interstitial fluid. A theory for such a three phase material can be derived based on the mixture theory [1]. Transforming the time dependent set of partial differential equations to Laplace domain allows to reduce the unknowns to the physical necessary set of solid displace- ments and both pore pressures (see [2]).

The fundamental solutions of such an elliptic coupled set of partial differential equations can be found using the method of Hörmander. Their singular behavior is determined by developing the exponential functions in these solutions in a power series. This shows that the fundamental solutions are at most weakly singular and the singular behavior is similar to elastostatics and acoustics [3].

The integral equations can be deduced based on the weighted residual technique. Obviously, for the final integral equations not only the weak singular fundamental solutions are required as well their co-normal derivatives and respective traction representations are needed. The latter ones cause strong singular integrals. These can be regularized by partial integration [4]. The final weak singular integral equation is discretized with standard polynomial shape functions in the spatial variable. Applying the convolution quadrature for time discretisation yield, finally, a time stepping procedure for dynamic processes in partial saturated poroelastic media.

The validation of this method is done with the help of a 1-d semi-analytical solution for a column [2]. The sensitivity on the spatial as well as on the temporal discretisation is presented. Finally, waves in a poroelastic half space are studied as well as the mode of action of an open trench for vibration isolation.

References

[1] Lewis, R. W.; Schrefler, B. A.: The Finite Element Method in the Static and Dynamic Deformation and Consolidation of Porous Media. John Wiley and Sons, Chichester, 1998.

[2] Li, P.; Schanz, M.: Wave Propagation in a One Dimensional Partially Saturated Poroelastic Column. Geophys. J. Int., 184(3), 1341-1353, 2011.

[3] Li, P.; Schanz, M.: Time Domain Boundary Element Formulation for Partially Saturated Poroelas- ticity. Eng. Anal. Bound. Elem., 37(11), 1483-1498, 2013.

[4] Messner, M.; Schanz, M.: A Regularized Collocation Boundary Element Method for Linear Poroe- lasticity. Comput. Mech., 47(6), 669-680, 2011.

[5] Schanz, M.: Wave Propagation in Viscoelastic and Poroelastic Continua: A Boundary Element Approach, Vol. 2, Lecture Notes in Applied Mechanics. Springer-Verlag, Berlin, Heidelberg, New York, 2001.

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Ning Lu
Civil and Environmental Engineering
Colorado School of Minesone

Abstract

Slope-stability analyses are mostly conducted by identifying or assuming a potential failure surface and assessing the factor of safety (FS) of that surface. This approach of assigning a single FS to a potentially unstable slope provides little insight on where the failure initiates or ultimate geometry and location of a landslide rupture surface. A unified effective stress framework for variably saturated porous media and a scalar field of factor of safety are employed to account for effective stress variations under rainfall conditions. The scalar field of FS is based on the concept of the Coulomb stress and the shift in the state of stress towards failure that results from rainfall infiltration. The FS at each point within a hillslope is called the local factor of safety (LFS) and is defined as the ratio of the Coulomb stress at the current state of stress to the Coulomb stress of the potential failure state under the Mohr-Coulomb criterion. Comparative assessment with limit-equilibrium and hybrid finite-element limit-equilibrium methods show that the proposed LFS is consistent with these approaches and yields additional insight into the geometry and location of the potential failure surface and how instability may initiate and evolve with changes in pore-water conditions. Quantitative assessments demonstrate that the LFS has the potential to overcome several major limitations in the classical FS methodologies such as the inherent underestimation of slope instability. Comparison with infinite-slope methods, including a recent extension to variably saturated conditions, shows further enhancement in assessing shallow landslide occurrence using the LFS methodology. The LFS provides a new means to quantify the potential instability zones in hillslopes under variably saturated conditions using stress-field based methods.

Biographical Sketch

Ning Lu is professor of civil and environmental engineering at Colorado School of Mines (CSM) and the director of the joint CSM/USGS Geotechnical Research Laboratory in Golden, CO. He is a recipient of ASCE 2007 Norman Medal and the recipient of ASCE 2010 Croes Medal, and an elected fellow of Geological Society of America and American Society of Civil Engineers. His current research focuses on developing a unified coupled hydro-mechanical framework for variably saturated porous media and applying it to rainfall-induced landslide analysis. He is the senior author of widely used textbook Unsaturated Soil Mechanics (John Wiley and Sons, 2004) and Hillslope Hydrology and Stability, (Cambridge University Press, 2013). He can be reached via ninglu@mines.edu.

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Douglas Blankenship
Sandia National Laboratories

Abstract

In the broader public, geothermal energy is the often the forgotten source of renewable energy but it has the potential to have a substantive impact on our Nation’s future energy portfolio. As a base load provider of electricity, geothermal derived power is an excellent complement to intermittent sources of renewable power such as solar and wind. Today, geothermal derived electricity is obtained from exploiting naturally occurring hydrothermal systems and as such it is limited in geographic extent. However, the heat resource is vast and if methods can be developed to economically “mine” this heat it will expand the impact of geothermal energy. However, exploiting geothermal energy requires accessing the subsurface through drilling to both confirm and develop the resource. Drilling is expensive and can easily exceed 50% of the capital costs associated with a development project. While there are similarities between oil & gas and geothermal drilling, there are differences and these differences adversely impact the economics of geothermal development. Sandia National Laboratories is pursuing applied research aimed at reducing the cost of geothermal energy development, particularly with regard to hard rock drilling technology, harsh environment monitoring, and novel reservoir stimulation methods — without such cost reductions geothermal energy will be a bit player in the power generation sphere.

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