An official website of the United States government
This experimental project investigated the debris accumulation in front of structures during tsunamis (debris damming), which leads to an increase in the forces imposed by tsunami flow on structures. The study was conducted through the construction of a 1:20 geometric scale physical model. Tsunami-like waves were generated over an idealized slope and transported different shapes of multi-debris, representing shipping containers, over the flat test section to measure debris loadings on elevated column structures. The experiment optically measured the debris impact and damming process, along with the corresponding loads on the entire column structure using a Force Balance Plate and separately on an individual column in the front row using a load cell. This unique data set will help to understand the impact of various factors on debris-driven damming loads, including wave characteristics, specimen configurations, and debris shapes. This data will also help to develop and validate numerical models that predict the motion and dynamics of floating debris during extreme coastal events. This project is the outcome of “Collaborative Research: Experimental Quantification of Tsunami-driven Debris Damming on Structures” with collaborators from the University of Hawaii at Manoa, Louisiana State University, and Oregon State University.
more »
« less
Quantifying and Understanding Structural Loading from Wave-Driven Debris Fields
During a tsunami or storm surge event, coastal infrastructure and ports are subject to a series of disparate physical hazards that can cause significant damage and loss of life. Among these, debris impact loading during inundation events is chaotic, complex, and thus far minimally understood, especially when considering the accumulation of individual debris into a large debris field. This work provides the results of a comprehensive experimental study of the impact and subsequent damming of chaotic debris fields, including more than 400 individual trials; this scope of this paper describes the experimental design and initial analysis of wave-driven debris-induced loading for select configurations. These data include both the impact phenomena and subsequent damming by debris accumulation and find strong correlation between increasing debris field density and high impact forces. High frequency impact forces and low frequency damming signals are considered via fast Fourier transform methods. Overall trends in wave-induced debris forcing from large debris fields are presented.
more »
« less
- Award ID(s):
- 1933184
- PAR ID:
- 10366254
- Date Published:
- Journal Name:
- ASCE Ports 22
- Page Range / eLocation ID:
- 523 to 534
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract In the presented work, wave dynamics of 2D finite granular crystals of polyurethane cylinders under low-velocity impact loading was investigated to gain better understanding of the influence of lateral constraints. The deformation of the individual grains in the granular crystals during the impact loading was recorded by a high-speed camera and digital image correlation (DIC) was used to calculate high fidelity kinematic and strain fields in each grain. These grain-scale kinematic and strain fields were utilized for the computation of the intergranular forces at each contact using a granular element method (GEM) based mathematical framework. Since the polyurethane were viscoelastic in nature, the viscoelasticity constitutive law was implemented in the GEM framework and it was shown that linear elasticity using the strain rate-dependent coefficient of elasticity is sufficient to use instead of a viscoelastic framework. These particle-scale kinematic and strain field measurements in conjunction with the interparticle forces also provided some interesting insight into the directional dependence of the wave scattering and attenuation in finite granular crystals. The directional nature of the wave propagation resulted in strong wave reflection from the walls. It was also noteworthy that the two reflected waves from the two opposite sidewalls result in destructive interference. These lateral constraints at different depths leads to significant differences in wave attenuation characteristics and the finite granular crystals can be divided into two regions: upper region, with exponential wave decay rate, and lower region, with higher decay rate.more » « less
-
In current practice, debris-field impact loading for near-water structures is usually derived from (1) infrequent case histories, (2) simplified analytical equations, and (3) practitioner experience. Via advanced numerical simulation of tsunami-driven debris-field impacts at multiple scales and conditions, we are now forging a modeling approach to address a wider range of scenarios. Broadened cases are characterized, with chaotic natures expressed stochastically. The analytical tools have the potential to strengthen the basis of ASCE 7 guidelines and to encompass events not yet described in the code.more » « less
-
Abstract The core of this research is separated into three domains, the ultrahigh strain rate response of elastomeric polymers, laser‐induced shock waves , and terahertz time‐domain spectroscopy (THz‐TDS). Elastomers, e.g., polyurea, constitute an advance class of materials suitable for many applications, specifically in high impact loading scenarios, thus, a laser‐induced shock wave (LSW) experimental technique is used to investigate the mechanical response of shock‐loaded polyurea. LSW can submit samples to a strain rate exceeding 106s−1at low strains, enabling determination of material intrinsic failure modes. The large deformation induced during shock loading may alter the macromolecule structure, which can only be detected spectroscopically. Therefore, this research incorporated terahertz bulk spectroscopy to detect and report molecular conformational changes. Microscopy techniques were also used to elucidate changes in the microscale properties, morphology, and topography. The interpretation of the results explicated brittle failure in terms of partial and total spallation and, remarkably, ductile failure leading to plastic deformation, including plastic bulging and adiabatic shearing, not previously associated with LSW technique. Furthermore, spectral changes found in the terahertz regime substantiated the validity of terahertz spectroscopy in elucidating the underlying mechanism associated with the impact mitigating properties of dynamically loaded polyurea.more » « less
-
null (Ed.)Using electric fields to control crystallization processes shows a strong potential for improving pharmaceuticals, but these field effects are not yet fully explored nor understood. This study investigates how the application of alternating high electric fields can influence the crystallization kinetics as well as the final crystal product, with a focus on the possible difference between alternating (ac) and static (dc) type fields applied to vinyl ethylene carbonate (VEC), a molecular system with field-induced polymorphism. Relative to ac fields, static electric fields lead to more severe accumulation of impurity ions near the electrodes, possibly affecting the crystallization behavior. By tuning the amplitude and frequency of the electric field, the crystallization rate can be modified, and the crystallization outcome can be guided to form one or the other polymorph with high purity, analogous to the findings derived from dc field experiments. Additionally, it is found that low-frequency ac fields reduce the induction time, promote nucleation near T g , and affect crystallization rates as in the dc case. Consistency is also observed for the Avrami parameters n derived from ac and dc field experiments. Therefore, it appears safe to conclude that ac fields can replicate the effects seen using dc fields, which is advantageous for samples with mobile charges and the resulting conductivity.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1061/9780784484395.052
