Publications

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Solid particle receivers have the potential to provide high-temperature heat for advanced power cycles, thermochemical processes, and thermal storage via direct particle absorption of concentrated solar energy. This paper presents two different models to evaluate the performance of these systems. One model is a detailed computational fluid dynamics model using FLUENT that includes irradiation from the concentrated solar flux, two-band re-radiation and emission within the cavity, discrete-phase particle transport and heat transfer, gas-phase convection, wall conduction, and radiative and convective heat losses. The second model is an easy-to-use and fast simulation code using Matlab that includes solar and thermal radiation exchange between the particle curtain, cavity walls, and aperture, but neglects convection. Both models were compared to unheated particle flow tests and to on-sun heating tests. Comparisons between measured and simulated particle velocities, opacity, particle volume fractions, particle temperatures, and thermal efficiencies were found to be in good agreement. Sensitivity studies were also performed with the models to identify parameters and modifications to improve the performance of the solid particle receiver.

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This article is the second of two that consider the treatment of fluid-solid interaction problems where the solid experiences wave loading and large bulk Lagrangian displacements. In part-I, we presented the formulation for the edge-based unstructured-grid Euler solver in the context of a discontinuous- Galerkin framework with the extensions used to treat internal fluid-solid interfaces. A super-sampled L² projection was used to construct level-set data from the Lagrangian interface, and a narrow-band approach was used to identify and construct appropriate ghost data and boundary conditions at the fluid-solid interface. A series of benchmark problems were used to verify the treatment of the fluid-solid interface conditions with a static interface position. In this paper, we consider the treatment of dynamic interfaces and the associated large bulk Lagrangian displacements of the solid.We present the coupled dynamic fluid-solid system, and develop an explicit, monolithic treatment of the fully-coupled system. The conditions associated with moving interfaces and their implementation are discussed. A comparison of moving vs. fixed reference frames is used to verify the dynamic interface treatment. Lastly, a series of two and and three-dimensional projectile and shock-body interaction calculations are presented. Ultimately, the use of the Lagrangian interface position and a super-sampled projection for fast level-set construction, the narrow-band extraction of ghost data, and monolithic explicit solution algorithm has proved to be a computationally efficient means for treating shock induced fluid-solid interaction problems.

Here, this paper is the first of two that consider the treatment of fluid-solid interaction problems under shock wave loading, where the solid experiences large bulk Lagrangian displacements. This work addresses the issues associated with using a level-set as a generalized interface for fluid-solid coupling where unstructured overlapping grids are used for the fluid and solid domains. In part-I of this work, we outline the formulation used for the edge-based unstructured-grid Euler solver in the context of the discontinuous-Galerkin method. The identification of the fluid-solid interface on the unstructured fluid mesh uses a super-sampled L² projection technique, that in conjunction with a Lagrangian interface position, permits fast identification of the interface and the concomitant imposition of boundary conditions. The use of a narrow-band approach for the identification of the wetted interface is presented with the details of the construction of interface conditions. A series of computations are presented to demonstrate the validity of the current approach on problems with static interfaces. In part-II, we present the coupled dynamic fluid-solid system, and present an explicit monolithic algorithm for the treatment of the fully-coupled system. The interface conditions associated with moving interfaces is considered, and a comparison of moving vs. static reference frames is used to evaluate the dynamic interface treatment. Finally, a series of two and and three-dimensional projectile and shock-body calculations are presented.

The problem of understanding and modeling the complicated physics underlying the action and response of the interfaces in typical structures under dynamic loading conditions has occupied researchers for many decades. This handbook presents an integrated approach to the goal of dynamic modeling of typical jointed structures, beginning with a mathematical assessment of experimental or simulation data, development of constitutive models to account for load histories to deformation, establishment of kinematic models coupling to the continuum models, and application of finite element analysis leading to dynamic structural simulation. In addition, formulations are discussed to mitigate the very short simulation time steps that appear to be required in numerical simulation for problems such as this. This handbook satisfies the commitment to DOE that Sandia will develop the technical content and write a Joints Handbook. The content will include: (1) Methods for characterizing the nonlinear stiffness and energy dissipation for typical joints used in mechanical systems and components. (2) The methodology will include practical guidance on experiments, and reduced order models that can be used to characterize joint behavior. (3) Examples for typical bolted and screw joints will be provided.

In many applications, the thermal response of structures exposed to solar heat loads is of interest. Solar mechanics governing equations were developed and integrated with the Calore thermal response code via user subroutines to provide this computational simulation capability. Solar heat loads are estimated based on the latitude and day of the year. Vector algebra is used to determine the solar loading on each face of a finite element model based on its orientation relative to the sun as the earth rotates. Atmospheric attenuation is accounted for as the optical path length varies from sunrise to sunset. Both direct and diffuse components of solar flux are calculated. In addition, shadowing of structures by other structures can be accounted for. User subroutines were also developed to provide convective and radiative boundary conditions for the diurnal variations in air temperature and effective sky temperature. These temperature boundary conditions are based on available local weather data and depend on latitude and day of the year, consistent with the solar mechanics formulation. These user subroutines, coupled with the Calore three-dimensional thermal response code, provide a complete package for addressing complex thermal problems involving solar heating. The governing equations are documented in sufficient detail to facilitate implementation into other heat transfer codes. Suggestions for improvements to the approach are offered.

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The International Data Centre of the Comprehensive Nuclear-Test-Ban Treaty Organization relies on automatic data processing as the first step in identifying seismic events from seismic waveform data. However, more than half of the automatically identified seismic events are eliminated by IDC analysts. Here, an IDC dataset is analyzed to determine if the number of automatically generated false positives could be reduced. Data that could be used to distinguish false positives from analyst-accepted seismic events includes the number of stations, the number of phases, the signal-to-noise ratio, and the pick error. An empirical method is devised to determine whether an automatically identified seismic event is acceptable, and the method is found to identify a significant number of the false positives in IDC data. This work could help reduce seismic analyst workload and could help improve the calibration of seismic monitoring stations. This work could also be extended to address identification of seismic events missed by automatic processing.

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