Mountain Scholar :: Browsing by Author "Chen, Suren, committee member"

Browsing by Author "Chen, Suren, committee member"

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Open Access
A systems engineering approach to community microgrid electrification and sustainable development in Papua New Guinea
(Colorado State University. Libraries, 2019) Anderson, Alexander A., author; Suryanarayanan, Siddharth, advisor; Cale, James, committee member; Zimmerle, Dan, committee member; Chen, Suren, committee member
Electrification of remote communities worldwide represents a key necessity for sustainable development and advancement of the 17 United Nations Sustainable Development Goals (SDGs). With over 1 billion people still lacking access to electricity, finding new methods to provide safe, clean, reliable, and affordable energy to off-grid communities represents an increasingly dynamic area of research. However, traditional approaches to power system design focused exclusively on traditional metrics of cost and reliability do not provide a sufficiently broad view of the profound impact of electrification. Installation of a single microgrid is a life-changing experience for thousands of people, including both residents who receive direct electricity service and numerous others who benefit from better education, new economic opportunities, incidental job creation, and other critical infrastructure systems enabled by electricity. Moreover, an electrification microgrid must directly satisfy community needs, be sensitive to local environmental constraints, mitigate possible risks, and plan for at least a decade of sustainable operations and maintenance. These considerations extend beyond the technical and optimization problems typically addressed in microgrid design. An enterprise system-of-systems framework for microgrid planning considering technical, economic, environmental, and social criteria is developed in response to the need for a comprehensive methodology for planning of community electrification projects. This framework spans the entire systems engineering discipline and incorporates elements from project management, risk management, enterprise architecture, numerical optimization, and multi-criteria decision-making, and sustainable development theory. To support the creation of the systems engineering framework, a comprehensive survey of multi-objective optimization formulations for planning and dispatch of islanded microgrids was conducted to form a baseline for further discussion. This survey identifies that all optimizations studies of islanded microgrids are based on formulations selecting a combination of 16 possible objective functions, 14 constraints, and 13 control variables. A sufficient group of decision-making elicitees are formed from the group of nearly 250 publications surveyed to create a comprehensive optimization framework based on technical, economic, environmental, and social attributes of islanded microgrids. This baseline enables the formulation of a flexible, computationally lightweight methodology for microgrid planning in consideration of multiple conflicting objectives using the simple multi-attribute ranking technique exploiting ranks (SMARTER). Simultaneously, the identified technical, economic, environmental, and social decision criteria form a network of functional, operational, and performance requirements in an enterprise system-of-systems structure that considers all stakeholders and actors in the development of community electrification microgrids. This framework considers community capacity building and sustainable development theory as a hierarchical structure, where each layer of the hierarchy is mapped both to a set of organizational, financial, and physical subsystems and to a corresponding subset of the 17 SDGs. The structure presents the opportunity not only to integrate classical project management and risk management tools, but also to create a new lifecycle for planning, funding, executing, and monitoring multi-phase community infrastructure projects. Throughout the research, a case study of the Madan Community in Jiwaka Province, Papua New Guinea is used to demonstrate the systems engineering concepts and tools developed by the research. The community is the center of multi-phase community capacity building project addressing critical needs of the deep rural community, including electricity, education, water, sanitation, healthcare, and economic opportunities. The researcher has been involved as a pro-bono consultant for the project since 2013 and helped raise over $1M USD in infrastructure materials, equipment, and consulting. The structure of the community-based organization and numerical optimization of a series of islanded microgrids are used to illustrate both the system-of-systems hierarchy and microgrid planning techniques based on both single-objective optimization using linear programming and the SMARTER methodology for consideration of multiple qualitative and quantitative decision criteria.
Open Access
Airborne radar quality control and analysis of the rapid intensification of Hurricane Michael (2018)
(Colorado State University. Libraries, 2020) DesRosiers, Alexander J., author; Bell, Michael M., advisor; Barnes, Elizabeth, committee member; Chen, Suren, committee member
Improvements made by the National Hurricane Center (NHC) in track forecasts have outpaced advances in intensity forecasting. Rapid intensification (RI), an increase of at least 30 knots in the maximum sustained winds of a tropical cyclone (TC) in a 24 hour period, is poorly understood and provides a considerable hurdle to intensity forecasting. RI depends on internal processes which require detailed inner core information to better understand. Close range measurements of TCs from aircraft reconnaissance with tail Doppler radar (TDR) allow for the retrieval of the kinematic state of the inner core. Fourteen consecutive passes were flown through Hurricane Michael (2018) as it underwent RI on its way to landfall at category 5 intensity. The TDR data collected offered an exceptional opportunity to diagnose mechanisms that contributed to RI. Quality Control (QC) is required to remove radar gates originating from non meteorological sources which can impair dual-Doppler wind synthesis techniques. Automation of the time-consuming manual QC process was needed to utilize all TDR data collected in Hurricane Michael in a timely manner. The machine learning (ML) random forest technique was employed to create a generalized QC method for TDR data collected in convective environments. The complex decision making ability of ML offered an advantage over past approaches. A dataset of radar scans from a tornadic supercell, bow echo, and mature and developing TCs collected by the Electra Doppler Radar (ELDORA) containing approximately 87.9 million radar gates was mined for predictors. Previous manual QC performed on the data was used to classify each data point as weather or non-weather. This varied dataset was used to train a model which classified over 99% of the radar gates in the withheld testing data succesfully. Creation of a dual-Doppler analysis from a tropical depression using ML efforts that was comparable to manual QC confirmed the utility of this new method. The framework developed was capable of performing QC on the majority of the TDR data from Hurricane Michael. Analyses of the inner core of Hurricane Michael were used to document inner core changes throughout RI. Angular momentum surfaces moved radially inward and became more vertically aligned over time. The hurricane force wind field expanded radially outward and increased in depth. Intensification of the storm became predominantly axisymmetric as RI progressed. TDR-derived winds are used to infer upper-level processes that influenced RI at the surface. Tilting of ambient horizontal vorticity, created by the decay of tangential winds aloft, by the axisymmetric updraft created a positive vorticity tendency atop the existing vorticity tower. A vorticity budget helped demonstrate how the axisymmetric vorticity tower built both upward and outward in the sloped eyewall. A retrieval of the radial gradient of density temperature provided evidence for an increasing warm core temperature perturbation in the eye. Growth of the warm core temperature perturbation in upper levels aided by subsidence helped lower the minimum sea level pressure which correlated with intensification of the near-surface wind field.
Open Access
Analysis of multi-channel wind loading using proper orthogonal decomposition
(Colorado State University. Libraries, 2014) Adhikari, Rajendra, author; Bienkiewicz, Bogusz, advisor; Chen, Suren, committee member; Sakurai, Hiroshi, committee member
Wind tunnel testing utilizing multi-channel pressure measurement system leads to large volume of the acquired wind pressure data. In the presented research, use of Proper Orthogonal Decomposition (POD), to analyze such data, is described. Wind pressure time series acquired for a generic low-rise building were used in the analysis. First, the pressure covariance matrices were calculated. They were subsequently used to determine the pressure eigenvalues and the eigenfunctions. These quantities were next employed to calculate the POD principal coordinates. Finally, the eigenvectors and the principal coordinates were used to reconstruct the pressure time series. This analysis was carried out for pressures exerted on the whole building and on its distinct surfaces - side walls and roof. The convergence of the pressure time series reconstruction was inspected. The mean, standard deviation and the peak values of the reconstructed pressure were evaluated. The effects of wind direction on the original and reconstructed pressures were investigated. The POD modal contributions and the convergence of the pressure reconstruction were quantified. Overall, the obtained results were found to be consistent with findings of related POD studies reported by other researchers. High spatial and temporal resolutions of the wind loading data used in the present research made possible refined quantification of the effects of the studied parameters.
Open Access
Determining the items that structure bridge management components and their relative weights
(Colorado State University. Libraries, 2012) Johnson, Joshua F., author; Ozbek, Mehmet Egemen, advisor; Clevenger, Caroline, committee member; Atadero, Rebecca, committee member; Chen, Suren, committee member
Ensuring the optimal allocation of available resources between competing bridges is difficult, especially when considering a combination of factors such as continual age related deterioration, ever-increasing traffic demands, and limited resources to address preservation and improvement needs. Optimally allocating funding is crucial since bridges are an essential and expensive component of transportation networks. Bridge Management Systems (BMSs) are commonly used tools that aid managers and decision makers in establishing methods for optimizing available resources and determining how to distribute funds between competing bridges. Recently, NCHRP Synthesis 397 Bridge Management Systems for Transportation Agency Decision Making investigated how transportation agencies are using BMSs and the current state of bridge management practices. The report identified concerns of inadequacy and ineffectiveness with bridge management practices that base decisions solely on single value assessments such as Pontis' Bridge Health Index or the Sufficiency Rating, as found in the federally mandated National Bridge Inspection Standards. Given the critiques in the NCHRP report and other literature related to bridge management, it is evident there exists a need to pursue and develop alternative bridge management practices and systems. The overall purpose of this research is to investigate the concept of isolating the items used to make up a single rating or index in an effort to categorize them under distinct bridge management components such as structural condition, impact on public, and hazard resistance. Each bridge management component has a defined objective as follows: • Structural Condition - accurately access the structural adequacy of a bridge. • Impact on Public - evaluate how bridge attributes affect the traveling public. • Hazard Resistance - evaluate how bridge attributes and external factors affect the vulnerability of a bridge concerning the probability of an extreme event as well as the probability of failure during that event. The specific objectives of this research are (i) to identify the appropriate items that make up each of the aforementioned components and (ii) to determine the relative importance of those items as represented by weighting factors. To achieve these objectives, the researcher conducted a two-part survey seeking input from key bridge management personnel from State DOTs, the Federal Highway Administration (FHWA), and other industry professionals and experts. The first part of the survey identified the appropriate items and the second part determined the relative importance of those items using a mathematical method called the Analytic Hierarchy Process (AHP). The primary contribution of this research is to provide bridge management engineers and decision-makers with effective bridge management components, with well-defined objectives and related items, which clearly identify and distinguish differences in bridge attributes that may go unnoticed when using a single rating or index. This will especially be useful for State DOTs and local agencies, like the Wyoming Department of Transportation, from which the motivation for this research was adapted, who are developing BMSs and methods customized to their particular needs. Upon establishing the bridge management components, by determining the items that make up the components and their relative weights, transportation agencies may utilize them in a variety of ways to conduct multi-criteria decision analyses that complement their current bridge management practices, which in turn may better illustrate the operation of bridges in their system. The total number of respondents was 47, of which 32 were from 29 different State transportation agencies. Of the 47 participants, only 27 contributed to the second part of the survey. A major finding of this research was a result of several participant remarks about with quantifying preservation and maintenance demands through the addition of a fourth bridge management component. The preservation and maintenance component encompasses items that are bridge elements, but may not contribute to the structural capacity of a bridge. Given the degree of influence of adding a fourth component, further research is recommend to confirm these findings and conclusions with a refined two-part survey similar to this research study and possibly interviews or focus groups.
Open Access
Development of performance-based wind engineering for residential structures: from concept to application
(Colorado State University. Libraries, 2010) Dao, Thang Nguyen, author; Van de Lindt, John W., advisor; Chen, Suren, committee member; Bienkiewicz, Bogusz, committee member; Senior, Bolivar A., committee member
The majority of buildings and approximately 90% of residential structures in North America are light-frame wood construction. Many of these structures are subjected to high winds along the eastern seaboard and Gulf Coast and as a result routinely suffer damage resulting in significant financial losses. Losses for residential wood construction during hurricanes occur for a variety of reasons, i.e. from different sources. These include sources such as (a) the failure of structure due to high wind loading; (b) water intrusion as a result of high uplift pressures on the roof system resulting in gaps or as a result of a loss of roof coverings and/or roof sheathing panels; and (c) debris impact from windborne debris. A relatively new paradigm in earthquake engineering is performance-based design (PBD). PBD is, by and large, felt by most to be a system-level philosophy that allows inclusion of system level behavior including the improvement in performance as a result of this assertion. However, in wind engineering most failures are understood to be at the component and sub-assembly level. This study outlines and demonstrates the development of performance-based wind engineering for residential structures based on losses to the owner. To date, this is the first time a mechanistic model has been used to develop fragilities for performance expectations related to all levels of performance: occupant comfort, continued occupancy, life safety, structural integrity, and manageable loss.
Open Access
Effects of laboratory elevation on rolling thin film oven test results
(Colorado State University. Libraries, 2013) Wang, Haohang, author; Shuler, Scott, advisor; Chen, Suren, committee member; Valdes-Vasquez, Rodolfo, committee member
Asphalt is the most commonly used material for road pavement. Asphalt pavement provides low cost, high durability, superior waterproofing abilities, and rapid construction. Before laying down the actual pavement, a series of tests are performed to make sure the asphalt can meet the requirements on specifications. The tests are usually conducted twice. One is provided by the asphalt supplier, the other one is provided by the buyer to make sure the quality of the asphalt meets their requirements. The asphalt aging process is unavoidable and starts when the asphalt is produced. The Rolling Thins Film Oven test (RTFO) is used to simulate the aging from production to asphalt laydown. The Dynamic Shear Rheometer (DSR) is used to quantify asphalt's elastic and viscous properties, which can reflect asphalt's ability to resist deformation during its service life. The goal of this paper is to identify any trends with respect to elevation, including which binders are influenced by elevation change. The general hypothesis is that elevation can affect both test results from DSR and Ductility tests. If this is true, then the test results from specs might need to be adjusted when bringing asphalt from one elevation to another. E.g. If the supplier is at sea level and the buyer is at 6000 feet, the supplier's test results may perfectly match the specs at sea level, but when the asphalt is tested in the same way at 6000 feet, the result cannot meet the requirements. This means the supplier is at the risk of not getting paid. In this case, the specs need to be adjusted for a situation like this. By analyzing the test parameters from DSR and ductility test, my research showed that the elevation can affect the test results. The DSR test parameters are G*, δ, G*/sin δ, G*-6C, δ-6C, and G*/sin δ -6C. Complex modulus (G*) reflects the specimen's total resistance to deformation when repeatedly sheared. The bigger the G* value, the stiffer the asphalt binder is. Phase angle (δ) indicates the lag between the applied shear stress and the resulting shear strain. G*/sin δ is the rutting parameter. When DSR was conducted at -6C, it can achieve G*-6C, δ-6C, G*/sin δ -6C. The seven different performance grades of asphalt specimens were PG 64-22, PG 64-28, PG 64-34, PG 70-22, PG 70-28, PG 76-22 and PG 76-28. Results showed that test parameters of certain asphalt performance grades present linear regression as elevation goes up. E.g. G* value decreases as elevation goes up, in the corresponding asphalt binders PG 64-22, PG 64-34, PG 70-28, and PG 76-22. Parameter G*, δ, G*/sin δ, G* -6C, δ -6C, G*/sin δ -6C shows clear linear regression as elevation goes up. Ductility did not present obvious linear regression as elevation goes up, therefore, is omitted from the summary. The discrepancy may have resulted from insufficient test data. The recommendation is that the researchers continue collecting data on ductility properties test. When using PG 70-28 for DSR test, test parameters presented linear regression as elevation goes up. The test parameters are G*, δ, G*-6, δ- 6C. When using PG 76-22 in the DSR test, test parameters presented linear regression as elevation goes up. The affected test parameters are G*, δ, G*/sin δ, G*-6C, and G*/sin δ -6C. Logically, if δ is affected by elevation, then δ-6C should also be affected by elevation. Thus, the assumption that δ-6C does not present linear regression as elevation goes up was because of the insufficient data volume. If there had been three times more data pool than the data set in this paper, the assumption may be proved right.
Open Access
Efficiency modeling for neutron detectors
(Colorado State University. Libraries, 2014) Scallan, Lisa Marie, author; Brandl, Alex, advisor; Johnson, Thomas, committee member; Chen, Suren, committee member
Neutron detectors are used for various applications, such as for workplace monitoring in a neutron field, during nuclear incidents, and for the detection of contraband nuclear material. The Remote Sensing Laboratory has developed and employed several neutron detector designs, and characterization data have been collected with these detectors under varying environmental conditions. Using MCNP/MCNPX the neutron fluence rate and dose rate were evaluated during open-field deployment as a function of moisture content in air and soil, barometric pressure, and varying pavement and soil composition. The focus of this analysis was on the incident neutron spectra, detector efficiency and count rate at the detector location. The most prevalent parameters directly contributing to scattered neutrons into the active detector volume were evaluated. Experimentally observed functional dependence on the source-detector distance was compared to MCNP/MCNPX simulation data. This study provides detector efficiency data for a wide range of operational conditions beyond the current capacity for experimental detector characterization.
Open Access
Energy storage improvement through material science approaches
(Colorado State University. Libraries, 2013) Kelly, Brandon Joseph, author; Prieto, Amy, advisor; Kirkpatrick, Allan, committee member; Chen, Suren, committee member; Dasi, Prasad, committee member
A need for improved energy storage is apparent for the improvement of our society. Lithium ion batteries are one of the leading energy storage technologies being researched today. These batteries typically utilize coupled reduction/oxidation reactions with intercalation reactions in crystalline metal oxides with lithium ions as charge carriers to produce efficient and high power energy storage options. The cathode material (positive electrode) has been an emphasis in the recent research as it is currently the weakest link of the battery. Several systems of cathode materials have been studied with different structures and chemical makeup, all having advantages and disadvantages. One focus of the research presented below was creating a low cost and high performance cathode material by creating a composite of the low cost spinel structured LiMn2O4 and the higher capacity layered structure materials. Two compositional diagrams were used to map out the composition space between end members which include two dimensional layer structured LiCoO2, LiNiO2, LiNi0.8Co0.2O2 and three dimensional spinel structured LiMn2O4. Several compositions in each composition map were electrochemically tested and structurally characterized in an attempt to discover a high performance cathode material with a lower cost precursor. The best performing composition in each system shows the desired mixed phase of the layered and spinel crystal structures, yielding improved performance versus the individual end member components. The surrounding compositions were then tested in order to find the optimum composition and performance. The best performing composition was 0.2LiCoO2*0.7LiNi0.8Co0.2O2*0.1LiMn2O4 and yielded a specific capacity of 182mAh/g. Another promising area of chemical energy storage is in the storage of hydrogen gas in chemical hydrides. Hydrogen gas can be used as a fuel in a variety of applications as a viable method for storing and transporting energy. Currently, the storage of the hydrogen is one of the major obstacles to its use as a fuel, and is traditionally done in high pressure cylinders or cryogenic storage tanks. Chemical hydrides allow storage of hydrogen in a solid form with higher volumetric hydrogen storage density than both traditional options. These chemical hydrides however are not performing close to their theoretical values and need further improvement in order to be viable in mobile applications. In this study two complex chemical hydride materials (Li3AlH6 and LiNa2AlH6) with high theoretical storage values were studied and doped with catalysts in an attempt to increase the hydrogen yield. The successful improvement of both Li3AlH6 and LiNa2AlH6 with 2%LaCl3 catalyst was achieved improving the chemical hydrogen yield percent by 4.6% and 22.9% respectively.
Open Access
Evaluation of rapid scanning techniques for inspecting concrete bridge decks with asphalt overlay
(Colorado State University. Libraries, 2016) Vemuri, Sri Harsha, author; Atadero, Rebecca, advisor; Chen, Suren, committee member; Strong, Kelly, committee member
The average age of bridges in the USA is 42 years. The life expectancy of a majority of these bridges is 50 years. At the current rates of aging and replacement, almost half of the nation’s bridges will require major structural investment in the next 15 years as stated by the Federal Highway Administration. There is a severe deficiency in both time and resources available to address this problem, and methods to increase efficiency are needed. Bridge decks are the most critical elements of a bridge structure as they are directly and continuously exposed to harsh weather conditions and cyclic loading from traffic throughout their lifespan. This thesis attempts to improve management practices for bridge decks by addressing current challenges faced by the Colorado Department of Transportation (CDOT) in estimating the extent of damage on bridge decks. The current bridge deck inspection method being employed by CDOT is sounding and chipping. This procedure involves sounding the deck with chains, hammers and rotary percussion to detect the deteriorated areas followed by chipping. The issues with this procedure include its time-consuming nature, the requirement for traffic to be diverted for extended periods and the costs associated with the inspection and traffic diversion. Additionally, sounding is not adequate to provide a rough estimation of the class of damaged area and the resulting expenses. CDOT wants to take the advantage of newer alternative techniques to evaluate bridge decks. The alternative evaluation considered by CDOT involves using Ground Penetrating Radar (GPR) and Infrared Thermography (IR) thermography together for evaluating bridge decks. The major advantage of using GPR is that it is the only available method that can estimate the deterioration in concrete decks with asphalt overlay. Additionally, GPR can estimate the deterioration in early stages, unlike sounding which detects damage in advanced stages and GPR is also capable of detecting corrosion in rebars. Thus, GPR not only has the potential to address the disadvantages of sounding it also has additional advantages which can benefit the life of the bridge deck. This study attempts to understand the limitations that this newer evaluation method comes with and possibly solve some of these limitations to take complete advantage of this technology. This study took advantage of the available as-built data of four bridge decks rebuilt after sounding and chipping and the data available from GPR and IR scanning of the respective decks to study the limitations from using GPR and IR technologies. The scanned results from GPR and IR thermography are compared to the deck condition data from sounding and chipping. In two cases the damage detected by GPR and IR thermography did not correlate well with the damage detected from sounding and chipping. The two decks with reasonable correlation are compared to the decks with poor correlation in an effort to understand the possible causes for deviation in results. It was observed that for the decks with poor correlation the GPR showed areas with higher cover as deteriorated in the estimation. An improved data processing procedure to solve such miss-interpretation issue is suggested, and a coring strategy to assist future research in the direction of eliminating the depth-amplitude effects in GPR scans.
Open Access
Geometrically and materially nonlinear analysis using material point method
(Colorado State University. Libraries, 2022) Asiri, Abdullah N., author; Heyliger, Paul, advisor; van de Lindt, John, committee member; Chen, Suren, committee member; Cheney, Margaret, committee member
Computational engineering has become an effective tool for different engineering aspects. It provides suitable simulation models for complex problems. Also, the computational models are strongly recommended as alternatives to experiments due to the consumed cost and time. In addition, because this field has gotten attention earlier, the accuracy of computational models has been improved. The finite element method (FEM) is one of the famous computer simulations that has been adopted widely in scientific and technical fields. It considers an excellent tool for different engineering analyses; however, for the large deformation behavior, the FEM cannot withstand due to the finite discretization of the systems in which the accuracy would be lost as a result of the large distortion that occurred for the model. Thereby, the mesh-less methods are appropriate models for such problems. The material point method (MPM) is one of the improved mesh-less methods, which is an extension of the Particle In Cell (PIC) method used for fluid mechanics modeling. Both static and dynamic applications are intended to simulate the two-dimensional material point method model. The main objective here is to simulate and validate the material point method with the analytical solutions for different solid mechanics applications. Further, to examine the formulation of the nonlinear behavior using the MPM. The research can be achieved by studying two hypotheses: 1) Beam mechanics analysis using the material point method and 2) Damage mechanics analysis using the material point method. Both hypotheses consider different assumptions of the geometry and material constants. Material point simulation of the two hypotheses will be conducted through RMACC Summit Supercomputer using FORTRAN and MATLAB languages.
Open Access
Modelling the effective properties of magneto-electro-elastic three-dimensional cellular solids
(Colorado State University. Libraries, 2020) Kannan, Sandhya, author; Heyliger, Paul, advisor; Chen, Suren, committee member; Puttlitz, Christian, committee member
Cellular solid foams are increasingly used in various industries right from disposable coffee cups to crash padding of an aircraft cockpit. Hence it is important to understand the structure and properties of cellular solids and the ways their properties can be utilized in engineering design. Using the method of Finite Element analysis three-dimensional cellular solids made up of Magneto-Electro-Elastic (MEE) materials were studied. A FORTRAN code was written to implement the models in order to determine the effective mechanical properties for the solid under study. Computational model was created and properties such as elastic, piezoelectric and piezomagnetic and permittivity were studied as a function of relative density. Result obtained for purely elastic properties were plotted against the relative density. Different thickness of the three-dimensional foam under consideration was studied by varying the Poisson's ratio. The obtained results of the jack packed cellular foam analysis gave a similar behavior of other foam structures thus verifying the accuracy of the model.
Open Access
Multi-measure performance assessment of the divisions of the Wyoming Highway Patrol
(Colorado State University. Libraries, 2015) Jalili, Maral, author; Ozbek, Mehmet E., advisor; Unnithan, Prabha N., committee member; Chen, Suren, committee member; Senior, Bolivar, committee member
With many lives lost every year in traffic related crashes, traffic safety is a big concern all around the world. One way to advance traffic safety practices is to improve the overall organizational performance of agencies responsible for enforcing traffic safety. Internal benchmarking would be the first step to accomplish that goal, in order to compare the units of an organization, identify the best performing ones, and learn from their best practices so that other units within the organization can take advantage and improve their performance as well. Wyoming Highway Patrol (WHP) is a data-driven organization which uses multiple measures to assess its performance. These measures can be used by WHP to perform comparisons between its 17 divisions. However, this process involves the utilization of a single performance measure at a time and may result in difficulties in identifying the overall performance. Therefore, there is a need to develop a performance assessment framework that can identify the overall performance of these divisions in the presence of multiple measures. This research presents a performance assessment system developed for WHP using Data Envelopment Analysis. This system can incorporate multiple measures, enabling WHP to identify its best-performing divisions to be able to use those as benchmarks.
Open Access
Natural frequencies of twisted cables: a numerical and experimental study
(Colorado State University. Libraries, 2021) Alkharisi, Mohammed K., author; Heyliger, Paul, advisor; van de Lindt, John, committee member; Chen, Suren, committee member; Stright, Lisa, committee member
As the uses of cables have increased in different engineering applications, a better understating of their mechanical and dynamical behavior becomes more critical. Over the past several decades, many analytical, experimental, and finite element models have been developed to investigate vibrations of the cable structure. This attention explains the importance of such a structure, where it is more challenging than many ordinary structures because of the nonlinearity of the geometry and other combined effects. In addition, the twist along cable length leads to coupling behavior on the various kinematic variables of the cable system. This work is aimed at predicting and investigating the natural frequencies and the translations and rotations mode shapes occurring stimulatingly for both horizontal and inclined sagged cables, using both numerical and experimental methods. An efficient numerical procedure using elasticity-based finite elements is presented to generate the primary elastic stiffness coefficients of single-layered six-wire strands where the cables are subjected to axial and torsional loads in three-dimensional space. Cable models with lay angles varying from 5 to 30 degrees are then compared to eight different one-dimensional analytical models for the same range of angles. The finite element model gives stiffness coefficients that are in good agreement with the analytical models for angles below the maximum angle of the cable. The free vibration behavior of untwisted and twisted cables is then analyzed using the derived stiffness and mass matrices. When discretized over the horizontal span, the sagged cable is represented using transformed axial, coupling, and torsional characteristics where the resulting two-node cable element has three translational and three rotational degrees of freedom. A similar computational approach is used for inclined cables using inclination angles from 10 to 60 degrees. The natural frequencies and modal shapes are found to be in very good agreement in comparison with the results obtained using extensive experimental tests for identical cable geometries and materials. Where a harmonically time-varying support motion is employed, undergo different conditions. The acceleration and angular velocity time histories are then collected by sensors mounted on the mid and quarter span of the cables. In addition to the experimental results, the frequency spectrum and the translational and rotational mode shapes are analyzed and compared with the limited analytical model available from the literature and the computer finite element software ABAQUS. Practical examples are used to demonstrate the validity and applicability of the finite element model for untwisted and twisted cables. Then, the influence of the principal and microstructural parameters variation on the dynamics of the cable is investigated. This study shows that the elasticity, twist coupling, initial sag, inclination angle, and self-weight of the cable play a considerable role in the frequency and modal coupling behavior. It further suggests that some of the simple models available may not be adequate to fully understand the significant levels of modal coupling in the cable's dynamic behavior. The methods used in this study are finally extended to experimentally find the internal damping ratios and the reduction in the in-plane peak motions when a damper is used.
Open Access
Nonlinear free vibration of beams by one-dimensional and elasticity solutions
(Colorado State University. Libraries, 2018) Asiri, Abdullah N., author; Heyliger, Paul, advisor; Chen, Suren, committee member; O’Reilly, Mike, committee member
In this research, linear and nonlinear free vibration are examined. A three-dimensional rectangular parallelepiped free–free beam is studied based on the Ritz method. The equation of motion is derived depending on Hamilton's principle. A validation of the Ritz method formulation has been conducted by comparison with the Euler–Bernoulli beam theory. The impact of three-dimensional beam length has been investigated as well. In terms of nonlinear analysis, a two-dimensional clamped–clamped beam was studied. Total Lagrange formulation is adopted for the elasticity method based on the Green–Lagrange strain tensor and second Piola–Kirchhoff stress tensor. The outcomes of the approximated method have been compared by using the nonlinear Euler–Bernoulli theory depending on the Hermite and Lagrange interpolations. The solutions of both theories are computed according to the direct iteration method. Poisson's ratio effect is studied with two assumptions, as well as the impact of the Gauss evaluations.
Open Access
One-dimensional effective continuum mechanics models of braided and trapezoidal wires
(Colorado State University. Libraries, 2017) Alkharisi, Mohammed K., author; Heyliger, Paul, advisor; Chen, Suren, committee member; Weinberger, Chris, committee member
As the use of wires in different engineering applications increases, investigation into and better understanding of the wire's behavior become more important. Over the past years, heavy work has been done to study the mechanical and dynamical behavior of wires using analytical, experimental, and finite element models. This attention explains the importance of such a structure. However, studying such a structure is more challenging than with other ordinary structures, due to the nonlinearity of the geometry. In this work, the axial elastic behavior was studied using linear three-dimensional finite element Fortran 77 code. The wire was discretized, element matrices were built, and varying boundary conditions were applied to find the four elastic coefficients of the global matrix: pure tensile stiffness, two coupling terms between the tensile and torsional stiffness. Couple action appears when there is a twist in the wire, for that varying twist angles (0°, 5°, 10°, 15°, 20°, 25°, and 30°) were used to check their effect on the stiffness. To validate the model used, a simple straight wire rope (1+6) of known behavior was tested using same approach and twist angles, and then compared with 7 existing analytical models available in literature. Results showed a good agreement with the finite element model, which indicates that the approach used to solve for the trapezoidal wire was reliable and valid. The results showed that the trapezoidal wire is stiffer than the simple straight wire rope and exhibited extensional and torsional coupling behavior values, which can be critical in the design process of these structures. This model can also be used to decrease the high costs associated with experimental tests needed to determine its behavior. The method was extended, as, to evaluate the integrity of such a structure, it was essential to conduct a free vibration analysis using a one-dimensional finite element approximation for the trapezoidal wire as well as for the simple straight wire rope, which had not been done before, to investigate the extensional and torsional behavior of the motion of these wires. First, an aluminum straight bar was tested by solving the mass and stiffness matrices using 2-, 4-, 8-, and 16-element approximations, and the convergence was checked against the known exact axial and torsional frequency solutions. The 16-element approximation was applied to both the trapezoidal and the simple straight wire rope with all the lay angles considered. The coupled extensional and torsional vibration for these wires was solved using closed-form equations for the mass matrices; with these and the stiffness matrices constructed, the eigenproblem was solved to find the frequencies and the corresponding mode shapes. The two types of displacement, axial and torsional, were found in each frequency while having coupled stiffness. The simple straight wire rope behaved similarly to the trapezoidal wire, but with relatively lower frequencies. Which conclude that it is important to the design, safety, and monitoring, depending on the application for which these wires are used, that the coupled frequencies suggested be considered and studied carefully.
Open Access
Optimizing resilience decision-support for natural gas networks under uncertainty
(Colorado State University. Libraries, 2019) Ameri, Mohammad Reza, author; van de Lindt, John W., advisor; Chen, Suren, committee member; Jia, Gaofeng, committee member; Shields, Martin, committee member
Community resilience in the aftermath of a hazard requires the functionality of complex, interdependent infrastructure systems become operational in a timely manner to support social and economic institutions. In the context of risk management and community resilience, critical decisions should be made not only in the aftermath of a disaster in order to immediately respond to the destructive event and properly repair the damage, but preventive decisions should to be made in order to mitigate the adverse impacts of hazards prior to their occurrence. This involves significant uncertainty about the basic notion of the hazard itself, and usually involves mitigation strategies such as strengthening components or preparing required resources for post-event repairs. In essence, instances of risk management problems that encourage a framework for coupled decisions before and after events include modeling how to allocate resources before the disruptive event so as to maximize the efficiency for their distribution to repair in the aftermath of the event, and how to determine which network components require preventive investments in order to enhance their performance in case of an event. In this dissertation, a methodology is presented for optimal decision making for resilience assessment, seismic risk mitigation, and recovery of natural gas networks, taking into account their interdependency with some of the other systems within the community. In this regard, the natural gas and electric power networks of a virtual community were modeled with enough detail such that it enables assessment of natural gas network supply at the community level. The effect of the industrial makeup of a community on its natural gas recovery following an earthquake, as well as the effect of replacing conventional steel pipes with ductile HDPE pipelines as an effective mitigation strategy against seismic hazard are investigated. In addition, a multi objective optimization framework that integrates probabilistic seismic risk assessment of coupled infrastructure systems and evolutionary algorithms is proposed in order to determine cost-optimal decisions before and after a seismic event, with the objective of making the natural gas network recover more rapidly, and thus the community more resilient. Including bi-directional interdependencies between the natural gas and electric power network, strategic decisions are pursued regarding which distribution pipelines in the gas network should be retrofitted under budget constraints, with the objectives to minimizing the number of people without natural gas in the residential sector and business losses due to the lack of natural gas in non-residential sectors. Monte Carlo Simulation (MCS) is used in order to propagate uncertainties and Probabilistic Seismic Hazard Assessment (PSHA) is adopted in order to capture uncertainties in the seismic hazard with an approach to preserve spatial correlation. A non-dominated sorting genetic algorithm (NSGA-II) approach is utilized to solve the multi-objective optimization problem under study. The results prove the potential of the developed methodology to provide risk-informed decision support, while being able to deal with large-scale, interdependent complex infrastructure considering probabilistic seismic hazard scenarios.
Open Access
Predicting ductile fracture in steel connections
(Colorado State University. Libraries, 2016) Wen, Huajie, author; Mahmoud, Hussam N., advisor; Atadero, Rebecca A., committee member; Chen, Suren, committee member; Ellingwood, Bruce R., committee member; Puttlitz, Christian M., committee member
Separation of material, known as fracture, is one of the ultimate failure phenomena in steel elements. Preventing or delaying fracture is therefore essential for ensuring structural robustness under extreme demands. Despite the importance of fracture as the final stage during inelastic response of elements, the underlying mechanisms and the factors influencing the onset and progression of fracture have not been fully investigated. This is particularly the case for ductile fracture where significant pre-crack deformations are present. Existing approaches geared at predicting brittle fracture, marked by little to no plastic deformation, have been proven inadequate for capturing ductile fracture. Ductile fracture is dependent on two stress state parameters, the stress triaxiality and Lode parameter, which correspond, respectively, to two kinds of work hardening damage – that is hydrostatic and deviatoric stress components. The role of stress triaxiality on ductile fracture has been well defined and implemented in various models over the past several decades. Only until recently, however, has the role of Lode parameter been identified as an important factor for accurate prediction of ductile fracture. In general, no reliable fracture prediction methods are present that are consistent throughout the whole range of stress states, where the stresses are dominated by either tension loading, shear loading, or a combination of both. In this study, a new ductile fracture criterion based on monotonic loading conditions is first developed based on analysis and definitions of the two stress state parameters and subsequently extended to the reverse/cyclic loading conditions. The extension from monotonic to cyclic loading is based fundamentally on the fact that as long as large pre-crack plastic strain fields exist, the inherent mechanism in both loading cases can be viewed to be the same. Although the inherent mechanism is the same for both loading cases, extending the model to the reverse loading conditions required the inclusion of the effects of nonlinearity of the damage evolution rule as well as the loading history. The two criteria, monotonic and cyclic, are then validated on the coupon specimen level through comparisons between predicted fracture strains and their experimental equivalents for various metal types and steel grades that are available in the literature. The newly developed models offer improvements to existing known ductile fracture criteria in terms of both accuracy and practicality. Following the validation of the fracture model on the coupon specimen level, the model is employed on the connection level, up to and including failure, to evaluate block shear failure for gusset plate and coped beam connections under monotonic loading and shear links under cyclic loading. The chosen connection types are dependent on stress triaxiality (tension) and Lode parameter (shear) and are therefore appropriate for the validation of the ductile fracture model. For the block shear failure, prediction accuracy is verified through comparisons with results from corresponding laboratory tests, in the perspective of load versus displacement curves, fracture profiles, and fracture sequences. Some underlying mechanism of block shear is also explored and explained for the first time. Following the same modeling procedure, parametric studies on geometric effects on block shear failure is conducted. Three different block-shear failure modes and one bolt hole tear out mode are captured in the simulations and suggestions on design code changes are provided. For the shear links, which are typically employed in Eccentric Braced Frames, simulation of fracture under reverse/cyclic loading is also conducted and verifications are performed through comparisons with their previous experimental results. The fracture-associated variables are included in the cyclic loading analysis through deriving an implicit integration algorithm for the material constitutive equations with combined hardening, which was integrated in the simulation using a user-defined material subroutine VUMAT.
Open Access
Simple made continuous bridges with steel diaphragms: tension and compression transfer mechanisms
(Colorado State University. Libraries, 2015) Johnson, Robert I., author; Atadero, Rebecca, advisor; Chen, Suren, committee member; Clevenger, Caroline, committee member; Heyliger, Paul, committee member; Mahmoud, Hussam, committee member
Simple-made-continuous (SMC) steel bridges are a relatively new innovation in steel bridge design. The SMC concept has been used for quite some time in the construction of precast concrete bridges and based on current statistics, precast concrete bridge construction is outpacing steel bridge construction by a factor of two to one. The SMC concept is a viable solution for steel bridges to recover market share of the bridges constructed in the United States. The majority of SMC bridges currently in use are constructed with concrete diaphragms. This dissertation presents the results of numerical analysis and laboratory testing of an alternative simple-made-continuous connection scheme that uses steel diaphragms in lieu of concrete diaphragms. A bridge using steel diaphragms was constructed by the Colorado Department of Transportation in 2005 and the connections on this bridge serve as a basis for the research presented herein. Preliminary numerical analysis was performed by hand; this analysis discovered potential design flaws in the current bridge connection. Subsequent numerical analysis using Abaqus finite element analysis software provided results which were indecisive in regard to the flaws found in the hand analysis. The finite element analysis however, did provide valuable insight into some of the connection behavior, which was also verified with the physical test. Physical testing was subsequently performed on a full size model of the connection. The physical model consisted of double cantilever composite girders loaded at their ends with 300 kip actuators to simulate negative moments at the center connection. The physical test verified that there were design flaws in the original design. The results of analysis and physical testing provided information necessary to correct the design flaws and data required for the development of a design methodology based on the actual physical behavior of the SMC connection. Also, particular behaviors noted in the finite element analysis were corroborated with the physical test and the design methodology recognizes these behaviors. The research also compares the steel diaphragm SMC connection to concrete diaphragm connection and demonstrates that the steel diaphragm design has several desirable features. The steel diaphragm design provides for a more economical and quicker to construct steel bridge design and requires less total construction time than other SMC schemes. Additionally, since the girder ends are exposed, the girders are able to fully weather and they may be easily inspected.
Open Access
The impact of non-local elasticity factors on natural frequencies of a rectangular cantilever beam
(Colorado State University. Libraries, 2020) Bouzaid, Ibrahim F., author; Heyliger, Paul, advisor; Chen, Suren, committee member; Weinberger, Chris, committee member
The natural frequencies of a structural element are important factors in attaining a safe design. Natural frequency is the frequency at which an element tends to vibrate in the absence of any driving or damping force. When an object vibrates at a frequency equivalent to its natural frequency, its vibration amplitude increases significantly, which could lead to severe damage. A safe design would thus require having a different natural frequency compared to the frequency of the vibrating element. In some cases, obtaining accurate natural frequencies is challenging. In cases in which non-local elasticity, where the stress at a point is a function of the strain at the close region around that point, provides a better solution to the mechanical problems compared to other theories, natural frequencies should be studied. The non-local elastic solution to the non-local elastic natural frequencies of a rectangular cantilever beam problem was developed using a Fortran code, and the finite elements of non-local mesh were generated using a MATLAB code. The eigenvalue problem was solved, and the mode shapes were plotted using another MATLAB code. The results indicate that the natural frequencies for the non-local solution have dropped 25–30 percent. The non-local factors, mesh size, and slenderness influenced the drop in the natural frequencies. The non-local natural frequencies tended to match the local natural frequencies up to the third frequency, then start diverged. The mode shapes are similar to the local elastic mode shapes in all cases.
Open Access
Tritium uncertainty analysis for surface water samples at the Savannah River site
(Colorado State University. Libraries, 2012) Atkinson, Robert Frank, author; Brandl, Alexander, advisor; Johnson, Thomas, committee member; Chen, Suren, committee member; Kuhne, Wendy, committee member
Radiochemical analyses of surface water samples, in the framework of Environmental Monitoring, have associated uncertainties for the radioisotopic results reported. These uncertainty analyses pertain to the tritium results from surface water samples collected at five locations on the Savannah River near the U.S. Department of Energy's Savannah River Site (SRS). Uncertainties can result from the field-sampling routine, can be incurred during transport due to the physical properties of the sample, from equipment limitations, and from the measurement instrumentation used. The uncertainty reported by the SRS in their Annual Site Environmental Report currently considers only the counting uncertainty in the measurements, which is the standard reporting protocol for radioanalytical chemistry results. The focus of this work is to provide an overview of all uncertainty components associated with SRS tritium measurements, estimate the total uncertainty according to ISO 17025, and to propose additional experiments to verify some of the estimated uncertainties. The main uncertainty components discovered and investigated in this paper are tritium absorption or desorption in the sample container, HTO/H2O isotopic effect during distillation, pipette volume, and tritium standard uncertainty. The goal is to quantify these uncertainties and to establish a combined uncertainty in order to increase the scientific depth of the SRS Annual Site Environmental Report.