Conferences, Lectures, & Seminars
Events for October
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Peridynamics for multiscale materials modeling
Thu, Oct 01, 2009 @ 02:00 PM - 03:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Speaker: Dr. Richard B. Lehoucq, Sandia National Labs, Albuquerque, NM Abstract:
My presentation provides an overview of peridynamics, a continuum theory that employs a nonlocal model of force interaction. Specifically, the internal force density is given by an integral operator that sums forces separated by a finite distance. This integral operator is not a function of the deformation gradient, allowing for a more general notion of deformation than in classical elasticity that is well aligned with the kinematic assumptions of molecular dynamics. I also demonstrate that the peridynamic internal force density represents the statisical coarse-graining of molecular force as an ensemble average in phase space. This provides a statistical mechanical basis for peridynamics. Peridynamics effectiveness has been demonstrated in several applications, including fracture and failure of composites, nanofiber networks, and polycrystal fracture. These suggest that peridynamics is a viable multiscale material model for length scales ranging from molecular dynamics to those of classical elasticity.
Audiences: Everyone Is Invited
Contact: Evangeline Reyes
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Water Resources Workshop
Thu, Oct 08, 2009 @ 08:30 AM - 05:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Workshop GoalWater issues have been and will continue to exert challenges to communities and business in the West and in particular Southern California. By engaging in a discussion of these water challenges researchers from USC and Veolia believe that a common research-oriented collaboration can be developed. The action items that are identified through these focused discussion will provide the backbone of further work collaborations.Workshop Themes1. Water distribution systems including bio-films and sensors.2. Desalination including pre-treatment, post-treatment (brine management), and Red Tide.3.Water reuse of municipal and industrial wastewaters including technology and policy aspects.4.Construction management, including asset management, PPP and design, build, and operate.5.Robotics for inspection of collection systems.
Location: Ronald Tutor Hall of Engineering (RTH) - 526
Audiences: By Invitation Only
Contact: Evangeline Reyes
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RANDOM FIELD MODELS FOR POLYCRYSTALS AND TWO-PHASE MICROSTRUCTURES
Thu, Oct 08, 2009 @ 03:00 PM - 04:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Speaker: Mircea Grigoriu, Ph.D., Cornell UniversityAbstract:The presentation has two parts. In the first part, we use examples to illustrate the need for representing material microstructures by random fields and illustrate potential difficulties related to the estimation of the parameters of these felds. Common techniques for reconstructing microstructures are presented and critically examined. In the second part, we present (1) a Markov random field for aluminum polycrystals, calibrate the model to measurements of Euler angles giving the atomic lattice orientation, and generate virtual aluminum polycrystals, (2) an inhomogeneous non-Gaussian random field for inclusions of arbitrary geometry, calibrate the model to measurements, and generate virtual concrete aggregates, and (3) homogeneous/inhomogeneous level-cut filtered Poisson fields for two-phase microstructures. Filtered Poisson fields are sums of kernels with specied functional form and random amplitude/orientation that are located at Poisson points. The cuts of these fields above a level define the inclusions of two-phase microstructures.
Audiences: Everyone Is Invited
Contact: Evangeline Reyes
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NSF-ERC Workshop
Fri, Oct 09, 2009 @ 08:30 AM - 06:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Location: Kaprielian Hall (KAP) - 209
Audiences: By Invitation Only
Contact: Evangeline Reyes
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Characterization of EnvironmentalVariability in Identified Dynamic Properties of a Soil-Foundation-S
Tue, Oct 13, 2009 @ 03:00 PM - 05:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Ali Asghari, Ph.D. Student, Oral Defense
Abstract:
For more than thirty years, researchers have attempted to establish effective local and global methods for monitoring civil, aerospace and mechanical structures. The unpredictable nature of soil and the nonlinear behavior of civil structures, however, make monitoring rather complex. In fact, the combined soil-structure system can be influenced by environmental factors on daily to annual time scales. Identification of structural damage using vibration-based methodologies in the presence of such influences requires some data normalization to reduce uncertainties and variations introduced by environmental factors.
To better understand the correlation between environmental variations and the dynamics of soil-structure interaction, semi-continuous monitoring of a large-scale field test structure has been conducted. The analysis uses data from sensors placed at several locations on the NEES Soil Foundation Structure Interaction (SFSI) Test Structure, which is located on very well-characterized soil in southern California, as well as sensor arrays monitoring the soil response under the foundation. A network of sensors was designed and positioned to record temperature at various locations on the structure; some pertinent soil properties are also monitored.
The observations of measured environmental data and the identified structural system parameters demonstrated strong correlation between variations in the environmental features and in the dynamic properties of the structure; for example daily shifts in the structure's fundamental frequencies are as much as10% due to temperature change or seasonal shifts due to ground water table variation under the foundation. An example is given, based on novelty detection, of how "unusual" dynamic behavior can be indicated for the SFSI test structure in the presence of environmental variations.
To explain the effect of the soil saturation on the rocking frequency of SFSI systems, a predictive model based on Wolf's Cone Model approach was developed. The results from parametric study validated the observations from both the SFSI test structure and the scaled model of decreased natural frequency for dry soil. Further, the study shows that the opposite effectthat is, higher natural frequency with soil saturationoccurs for structures with different characteristics relative to the soil.
A 1/14 scale model of the SFSI test structure was constructed to validate the observed effect of the water level under the foundation on the rocking frequency of SFSI systems in a controlled laboratory environment. These experiments showed a similar correlation between the identified rocking frequency of the scaled prototype and the rise and fall of the water level under the foundation.
This work shows that understanding the environmental variability of an identified model is critical to developing methodologies for cleansing data and reducing uncertainty to allow more robust health monitoring in real civil structures.Location: Kaprielian Hall (KAP) - 209
Audiences: Everyone Is Invited
Contact: Evangeline Reyes
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PREDICTING DEBRIS YIELD USING ARTIFICIAL INTELLIGENCE MODELS
Thu, Oct 15, 2009 @ 02:00 PM - 04:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Zhiqing Kou, Ph.D. Candidate
Astani Dept. of Civil and Environmental Engineering Abstract:
Artificial Neural Network is a very powerful computational tool for modeling very complicated and highly nonlinear problems in various fields. In this study, it is first applied to estimate accumulated debris yield in 14 debris basins within Los Angeles County, California from 1984 to 2003 as a result of a series of storm events from watersheds partially or totally burned by wildfires. ANN models achieve very satisfactory modeling results when compared to a statistical model. The ANN technique is then applied to forecast unit debris yield resulting from a significant storm event collected from 36 small debris basins from 1938 to 1983 within the county. The same unit debris yield data is simulated by another two artificial intelligence models, Adaptive-Network-Based Fuzzy Inference System (ANFIS) and Generalized Dynamic Fuzzy Neural Network (GD-FNN) model. In addition to four basic input parameters: drainage area, watershed relief ratio, maximum one-hour rainfall intensity, and fire factor, six watershed morphological parameters including elongation ratio, drainage density, hypsometric index, total stream length, mean bifurcation ratio, and transport efficiency factor are included as input parameters and their relative importance are determined through sensitivity analysis. ANN models are also developed for modeling unit debris yield at 80 small debris basins which are classified into five groups based on the slopes of their upstream collection watersheds: mild slope, steep slope, steeper slope, extreme steep slope, and the steepest slope. In addition to four aforementioned basic input parameters, three soil properties such as soil erodibility factor, permeability rate, and liquid limit are included as input parameter one by one to study their impact on the simulation. Unit debris yield collected from large watersheds with area between 10 and 25 mi2, between 25 and 50 mi2, and between 50 and 200 mi2 are also simulated by neural networks. The modeling results show ANN models are able to reproduce most unit debris yield very close to their measured values and the accuracy of unit debris yield estimated by ANN models is significantly higher than those obtained from ANFIS, GD-FNN model, and empirical equations developed by US Army Corps of Engineers.Location: Kaprielian Hall (KAP) - 209
Audiences: Everyone Is Invited
Contact: Evangeline Reyes
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Modeling and Simulation of Multiphysical Processes in Particulate Media
Wed, Oct 21, 2009 @ 02:00 PM - 03:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Speaker: Dr. Tarek I. Zohdi,
Professor and Vice Chair for Instruction, The University of California, Berkeley Department of
Mechanical EngineeringABSTRACT: Ideally, in an attempt to reduce laboratory costs, one would like to make predictions of complex solid and fluid particulate material behavior by numerical simulations, with the primary goal being to minimize time-consuming trial and error experiments. A central objective of this presentation is to provide basic models and efficient numerical solution strategies for the direct simulation of complex particulate media that can be achieved within a relatively standard computing environment. Key corresponding laboratory experiments are also discussed. The topics to be touched upon are:(1) Electromagnetic Composites,
(2) Computational Bio-electromagnetics,
(3) Environmental Degradation of Composite Materials,
(4) Structural Fabric,
(5) Complex Particulate Flows and
(6) Generalizations to Modeling and Design of Collective Behavior.CONTEXT: Recently, several applications, primarily driven by micro-technology,have emerged where the use of solid, fluid and fabric materials with tailored mechanical, thermal and electromagnetic properties are necessary for a successful overall design. The "tailored" properties are achieved by combining an easily moldable base matrix with particles having material properties that are chosen to deliver overall macroscale (desired) effective properties. In many cases, the analysis of such materials requires the simulation of the strongly coupled, macroscopic and microscopic, mechanical, thermal and electromagnetic response,in order to identify possible failure at``hot spots'' within the microstructure. One of the key components in such composite systems are the microscale particulates, and their processing.External electromagnetic fields can be utilized to manipulate and control particulate flows during processing in order to achieve results that are not possible by purely mechanical means alone. Generally, industrial applications where this is important include electrostatic copiers, inkjet printers, powder coating machines, aerosol design, etc. For example, several industrial processes, such as Chemical Mechanical Planarization (CMP), involve using small-scale chemically-reacting particulates to ablate rough small-scale surfaces flat.These processes have become important for the success of many micro- and
nano- technologies. It is estimated that over 50 percent (by weight) of the materials used in high-end technology start out as particles or granulated material. Below a certain particle length-scale, approximately one millimeter, the dynamics of particles can be strongly affected inter-particle near-field forces, as well as external electromagnetic fields. During processing, whether intended or not, particulate agglomeration can occur.The dynamics of those clusters in the presence of an electromagnetic field are of high interest because they may lead to poor spray quality and inconsistent fabrication results, for example, of composite materials. Therefore, neglecting such near-field effects in an analysis can lead to a significant miscalculation of the characteristics of such flows. Thus, an issue of overriding importance to the successful characterization of such complex materials is the development of models and reliable computational techniques to simulate the response of composite particulate continua, as well as the dynamics and multiphysics of multibody particulate systems involving near-field interaction and contact simultaneously.
Location: Kaprielian Hall (KAP) - 209
Audiences: Everyone Is Invited
Contact: Evangeline Reyes
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Spatial correlation of earthquake ground motion intensities: ...
Wed, Oct 28, 2009 @ 02:00 PM - 03:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
...measurement and implications for regional infrastructure risk.Speaker: Dr. Jack W. Baker, Assistant Professor, Dept. of Civil and Environmental Engineering, Stanford UniversityAbstract:Risk assessment of spatially distributed building portfolios or infrastructure systems requires quantification of the joint occurrence of ground-motion intensities at several sites, during the same earthquake. This talk will present an overview of techniques to quantify the needed joint distributions using observations from past earthquakes, and describe how these distributions can be used in probabilistic seismic risk assessments of spatially-distributed lifelines. Lifeline risk assessment presents challenges related to describing ground-motion intensity over a region, and related to the computationally expensive task of repeatedly analyzing performance of a lifeline system under many damage scenarios. A simulation-based framework will be presented that develops a small but stochastically-representative catalog of earthquake ground-motion intensity maps that can be used for lifeline risk assessment. The approach dramatically reduces required computational expense, while also maintaining a set of simulations that is consistent with all conventional probabilistic seismic hazard analysis calculations. The feasibility of the proposed approach is illustrated by using it to assess the seismic risk of a simplified model of the San Francisco Bay Area transportation network. A catalog of only 150 intensity maps is generated to represent hazard at 1,038 sites from ten regional fault segments causing earthquakes with magnitudes between five and eight.
Location: Kaprielian Hall (KAP) - 209
Audiences: Everyone Is Invited
Contact: Evangeline Reyes