Finite Element Analysis of Reinforced Concrete Beams with Corrosion Subjected to Shear

Finite element (FE) modeling techniques were developed to isolate the different contributions of corrosion damage to structural response of experimental reinforced concrete beams with shear-dominated behavior. Corrosion-damage parameters included concrete cover spalling due to the expansion of corrosion products; uniform stirrup cross-sectional loss from corrosion; localized stirrup cross-sectional loss due to pitting; debonding of corrosion-damaged stirrups from the concrete. FE analyses were performed including both individual and combined damages. The FE results matched experimental results well and quantitatively estimated capacity reduction of the experimental specimens

An Efficient Three-Dimensional FNPF Numerical Wave Tank for Large-Scale Wave Basin Experiment Simulation

This paper presents a parallel implementation and validation of an accurate and efficient three-dimensional computational model (3D numerical wave tank), based on fully nonlinear potential flow (FNPF) theory, and its extension to incorporate the motion of a laboratory snake piston wavemaker, as well as an absorbing beach, to simulate experiments in a large-scale 3D wave basin. This work is part of a long-term effort to develop a “virtual” computational wave basin to facilitate and complement large-scale physical wave-basin experiments. The code is based on a higher-order boundary-element method combined with a fast multipole algorithm (FMA). Particular efforts were devoted to making the code efficient for large-scale simulations using high-performance computing platforms. The numerical simulation capability can be tailored to serve as an optimization tool at the planning and detailed design stages of large-scale experiments at a specific basin by duplicating its exact physical and algorithmic features. To date, waves that can be generated in the numerical wave tank (NWT) include solitary, cnoidal, and airy waves. In this paper we detail the wave-basin model, mathematical formulation, wave generation, and analyze the performance of the parallelized FNPF-BEM-FMA code as a function of numerical parameters. Experimental or analytical comparisons with NWT results are provided for several cases to assess the accuracy and applicability of the numerical model to practical engineering problems. [DOI: 10.1115/1.4007597] Keywords: numerical wave tank, three dimensional, wave-basin experiment, fully nonlinear waves, potential flow, piston wavemaker, high-performance computing, boundary element method, fast multipole algorith

Rigid-Body Water–Surface Impact Dynamics: Experiment and Semianalytical Approximation

An experimental study of the dynamics of a generic rigid body during water impact and an equivalent-radius approximate analytical procedure is developed and calibrated in this study. The experimental tests in a wave basin covered a range of drop heights using a 1/6th-scale model of a practical water-landing object prototype for two drop mechanisms to determine the water impact and contact effects. The first mechanism involved a rope and pulley arrangement, while the second mechanism employed an electromagnetic release to drop the rigid body. Hydrodynamic parameters including peak acceleration and touchdown pressure were measured and the maximum impact/contact force was estimated for various entry speeds (corresponding to various drop heights) and weights of the rigid body. Results from the tests show that the impact acceleration and touchdown pressure increases approximately linearly with increasing drop height and the data provides conditions that keep impact accelerations under specified limits for the rigid-body prototype. The experimentally measured maximum accelerations were compared with classical von Karman and Wagner approximate closed-form solutions. In this study, an improved approximate solution procedure using an equivalent radius concept integrating experimental results with the von Karman and Wagner closed-form solutions is proposed and developed in detail. The resulting semianalytical estimates are calibrated against experimental results and found to provide close matching. [DOI: 10.1115/1.4025653

Rigid-Object Water-Entry Impact Dynamics: Finite- Element/Smoothed Particle Hydrodynamics Modeling and Experimental Validation

A numerical study on the dynamic response of a generic rigid water-landing object (WLO) during water impact is presented in this paper. The effect of this impact is often prominent in the design phase of the re-entry project to determine the maximum force for material strength determination to ensure structural and equipment integrity, human safety and comfort. The predictive capability of the explicit finite-element (FE) arbitrary Lagrangian- Eulerian (ALE) and smoothed particle hydrodynamics (SPH) methods of a state-of-the-art nonlinear dynamic finite-element code for simulation of coupled dynamic fluid structure interaction (FSI) responses of the splashdown event of a WLO were evaluated. The numerical predictions are first validated with experimental data for maximum impact accelerations and then used to supplement experimental drop tests to establish trends over a wide range of conditions including variations in vertical velocity, entry angle, and object weight. The numerical results show that the fully coupled FSI models can capture the water-impact response accurately for all range of drop tests considered, and the impact acceleration varies practically linearly with increase in drop height. In view of the good comparison between the experimental and numerical simulations, both models can readily be employed for parametric studies and for studying the prototype splashdown under more realistic field conditions in the oceans. [DOI: 10.1115/1.4027454

Case Study for Tsunami Design of Coastal Infrastructure: Spencer Creek Bridge, Oregon

The absence of tsunami load provisions in coastal infrastructure design has led to unchecked resistance capacity of bridges against one of the most eminent natural hazards on the U.S. west coast. The Spencer Creek Bridge, which was completely rebuilt on the Oregon coast in 2009, is a unique example to demonstrate development and implementation of site-specific tsunami loads during the design stage. Two tsunami models, the Cornell Multigrid Coupled Tsunami model (COMCOT) and the Finite-Volume Wave model (FVWAVE), defined the flow fields from three rupture configurations postulated for a Cascadia earthquake, which has a moment magnitude of 9.0 consistent with the seismic design of the bridge structure. Although both models produce comparable surface elevations at the site, the finite-volume formulation of FVWAVE provides higher flow speed because of its capability to conserve momentum and mass even with formation of tsunami bores. The FVWAVE results define the input to the computational fluid dynamic module of LS-DYNA. The computed time history of the horizontal and vertical loads on the bridge deck, in turn, provide the input to a finite-element model of the bridge structure for capacity comparisons and damage analysis. It is concluded that the earthquake design specifications used for this particular bridge provide more than sufficient strength to resist the maximum tsunami horizontal force. The margin of safety is much smaller for the uplift force, but still remains in an acceptable range.Keywords: Tsunamis, Tsunami load estimation, Bridge design, Bridge, Cascadia subduction zone, Finite-volume method, Finite-element method (FEM

Wave Energy Converter Modeling in the Frequency Domain : A Design Guide

Wave energy converter research continues to advance and new developers are continuing to emerge, leading to the need for a general modeling methodology. This work attempts to outline the design methodology necessary to perform frequency domain analysis on a generic wave energy converter. A two-body point absorber representing a generic popular design was chosen and a general procedure is presented showing the process to obtain first pass preliminary performance results. The result is a design guide that new developers can adapt to their particular design and wave conditions, which will provide the first steps toward a cost of energy estimate. This will serve the industry by providing a sound methodology to accelerate the new development of wave energy converters

Engineering design and economic analysis of offshore seaweed farm

As global demand for sustainable biomass and need to mitigate global warming begin to rise, cultivation of seaweed has gained significant attention in recent years due to its potential for carbon recycling. However, limited availability of suitable coastal areas for large-scale seaweed cultivation has led to exploration of offshore environments as a viable alternative. The nature of many offshore environments often exposes seaweed farming systems to harsh environmental conditions, including strong waves, currents, and wind. These factors can lead to structural failures, kelp losses, and significant financial losses for seaweed farmers. The main objective of this study is to present a robust design and numerical analysis of an economically viable floating offshore kelp farm facility, and evaluate its stability and mooring system performance. A numerical method of preliminary designs of the offshore aquaculture systems were developed using the OrcaFlex software. The models were subjected to a series of dynamic environmental loading scenarios representing extreme events. These simulations aimed to forecast the overall dynamic response of an offshore kelp farm at a depth of 50m and to determine the best possible farm design with structural integrity for a selected offshore environment. Furthermore, to assess the economic feasibility of establishing offshore seaweed farms, a comprehensive capital expenses analysis was conducted. The results revealed that, in terms of the kelp farms with the same number of the kelp cultivating lines, the cost of building kelp farms will be strongly affected by the cost of mooring lines. The present study may help to understand the dynamic response and economic feasibility of offshore kelp farms

Investigation of the Performance of the New Orleans Flood Protection System in Hurricane Katrina on August 29, 2005: Volume 1

This report presents the results of an investigation of the performance of the New Orleans regional flood protection system during and after Hurricane Katrina, which struck the New Orleans region on August 29, 2005. This event resulted in the single most costly catastrophic failure of an engineered system in history. Current damage estimates at the time of this writing are on the order of $100 to$200 billion in the greater New Orleans area, and the official death count in New Orleans and southern Louisiana at the time of this writing stands at 1,293, with an additional 306 deaths in nearby southern Mississippi. An additional approximately 300 people are currently still listed as “missing”; it is expected that some of these missing were temporarily lost in the shuffle of the regional evacuation, but some of these are expected to have been carried out into the swamps and the Gulf of Mexico by the storm’s floodwaters, and some are expected to be recovered in the ongoing sifting through the debris of wrecked homes and businesses, so the current overall regional death count of 1,599 is expected to continue to rise a bit further. More than 450,000 people were initially displaced by this catastrophe, and at the time of this writing more than 200,000 residents of the greater New Orleans metropolitan area continue to be displaced from their homes by the floodwater damages from this storm event. This investigation has targeted three main questions as follow: (1) What happened?, (2) Why?, and (3) What types of changes are necessary to prevent recurrence of a disaster of this scale again in the future? To address these questions, this investigation has involved: (1) an initial field reconnaissance, forensic study and data gathering effort performed quickly after the arrival of Hurricanes Katrina (August 29, 2005) and Rita (September 24, 2005), (2) a review of the history of the regional flood protection system and its development, (3) a review of the challenging regional geology, (4) detailed studies of the events during Hurricanes Katrina and Rita, as well as the causes and mechanisms of the principal failures, (4) studies of the organizational and institutional issues affecting the performance of the flood protection system, (5) observations regarding the emergency repair and ongoing interim levee reconstruction efforts, and (6) development of findings and preliminary recommendations regarding changes that appear warranted in order to prevent recurrence of this type of catastrophe in the future. In the end, it is concluded that many things went wrong with the New Orleans flood protection system during Hurricane Katrina, and that the resulting catastrophe had it roots in three main causes: (1) a major natural disaster (the Hurricane itself), (2) the poor performance of the flood protection system, due to localized engineering failures, questionable judgments, errors, etc. involved in the detailed design, construction, operation and maintenance of the system, and (3) more global “organizational” and institutional problems associated with the governmental and local organizations responsible for the design, construction, operation, maintenance and funding of the overall flood protection system

The final piece of the Triangle of U: Evolution of the tetraploid Brassica carinata genome

Background: Brassica carinata (Ethiopian mustard) is an ancient crop from the Ethiopian highlands with remarkable heat and drought tolerance that has potential as a sustainable oil source for biofuel production. The resilience of this species might be due to hybrid vigor, as B. carinata is a species derived from a hybridization between Brassica nigra (black mustard) and Brassica oleracea (kale, broccoli, etc.). Thus, the B. carinata genome is allotetraploid with two parental genomes, or subgenomes, merged in one nucleus. We present a high-quality, chromosome-scale reference assembly of the B. carinata genome, which is the last of six genomes comprising the classic Triangle of U model used to study hybridization and polyploid evolution. Question: Here, we compare B. carinata to the other Triangle of U genomes for insight into the remarkable heat and drought tolerance of this crop. We investigate the evolutionary trajectory of the B. carinata genome as it returns to the diploid state to elucidate the mechanisms that act on duplicated genes, such as functional divergence of gene families and the biased fractionation of one subgenome. Findings: The B. carinata genome is the largest among the Triangle of U with notable expansions in repetitive DNA sequences and gene families related to transcriptional regulation and stress tolerance. We characterized patterns of subgenome bias, finding that the subgenome derived from B. nigra is likely dominant over the subgenome from B. oleracea. Furthermore, we comprehensively characterize subgenomic bias in homoeologous exchanges, or meiotic crossover between subgenomes, in the Triangle of U allotetraploids. Next steps: The presented B. carinata genome is a crucial resource for its expanded use as a biofuel feedstock and insight into polyploid evolution. Unraveling the genomic basis of the stress resilience of B. carinata provides an opportunity to introgress these traits to other cruciferous vegetables, which are used worldwide as vegetable and oil sources.Ethiopian mustard (Brassica carinata) is an ancient crop with remarkable stress resilience and a desirable seed fatty acid profile for biofuel uses. Brassica carinata is one of six Brassica species that share three major genomes from three diploid species (AA, BB, and CC) that spontaneously hybridized in a pairwise manner to form three allotetraploid species (AABB, AACC, and BBCC). Of the genomes of these species, that of B. carinata is the least understood. Here, we report a chromosome scale 1.31-Gbp genome assembly with 156.9-fold sequencing coverage for B. carinata, completing the reference genomes comprising the classic Triangle of U, a classical theory of the evolutionary relationships among these six species. Our assembly provides insights into the hybridization event that led to the current B. carinata genome and the genomic features that gave rise to the superior agronomic traits of B. carinata. Notably, we identified an expansion of transcription factor networks and agronomically important gene families. Completion of the Triangle of U comparative genomics platform has allowed us to examine the dynamics of polyploid evolution and the role of subgenome dominance in the domestication and continuing agronomic improvement of B. carinata and other Brassica species.We gratefully acknowledge the support of the Nevada Agricultural Experiment Station (Grant No. NEV00384) and VPRI research funding (University of Nevada, Reno).The Pires lab is funded by the National Science Foundation (NSF IOS 1339156) and the Department of Energy Defense Threat Reduction Agency (HDTRA 1-16-1-0048). The Edger lab is funded by the National Science Foundation (NSF IOS 2029959). The Mason lab is partially funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy (EXC 2070 - 390732324). The Alvarez-Ponce lab is funded by the National Science Foundation (NSF MCB 1818288)