Advanced Multiphysics Research Articles

Harvesting 3D Multiphysics Modeling Techniques for Smart and Sustainable University Campus

The EcoCampus Initiative is a novel flagship RD&D programme built on applied research and test-bedding of innovative technologies. The initiative covers the whole of Nanyang Technological University’s (NTU) 200-hectare campus and adjoining 50 hectares JTC Corporation’s CleanTech Park. The initiative was launched with a mission to achieve an impactful target of a 35% reduction in energy, water and waste intensity by 2020 (baseline, 2011), while leading the development and adoption of innovative technologies.The initiative has successfully collaborated with more than 20 industries and provided them the campus as testbed. The challenge ahead is to scrutinize the tested technologies, determine the best performing ones and find out the most optimum scale and location for their deployment.To aid such decision making, EcoCampus has collaborated with IES (Integrated Environmental Solutions) to exploit their IESVE™ technology. The project aims at developing a Multiphysics 3D Virtual Model of the campus that can virtually simulate the technologies through advanced Multiphysics modelling techniques. In addition to the technology performance analysis, IES’ innovative process solution, Ci2 (Collect, Investigate, Compare, Invest), is deployed to optimize the building performance in NTU Campus. The process focusses on Collecting historical data and identifying data gaps. This is followed by Investigating data using advanced IESVE™ analytics. This stage provides insights that may be hidden within the existing data. Once the story behind the data is known, the data is Compared against a calibrated model. Benchmarking analysis, decisions on refurbishing etc. are made during this stage. ROI, payback periods, NPV etc., prediction is also made in ‘Compare’ stage. Lastly, the Invest stage helps the decision makers to determine and prioritise the most attractive investment solutions for a sustainable and energy efficient operational building. This paper focuses on requirements for setting up a design model and modifying it to understand building behaviour.

Multiphysics coupled modeling of light water reactor fuel performance

A fuel performance code for light water reactors called CityU Advanced Multiphysics Nuclear Fuels Performance with User-defined Simulations (CAMPUS) was developed. The CAMPUS code considers heat generation and conduction, oxygen diffusion, thermal expansion, elastic strain, densification, fission product swelling, grain growth, fission gas production and release, gap heat transfer, mechanical contact, gap/plenum pressure with plenum volume, fuel thermal and irradiation creep, cladding thermal and irradiation creep and oxidation. All the equations are implemented into the COMSOL Multiphysics finite-element platform with a 2D axisymmetric geometry of a fuel pellet with cladding. Comparisons of critical fuel performance parameters for UO2 fuel using CAMPUS are similar to those obtained from BISON, ABAQUS and FRAPCON. Additional comparisons of beryllium doped fuel (UO2-10%volBeO) with silicon carbide, instead of Zircaloy as cladding, also indicate good agreement. The capabilities of the CAMPUS code were further demonstrated by simulating the performance of oxide (UO2), composite (UO2-10%volBeO), silicide (U3Si2) and mixed oxide ((Th0.9,U0.1)O2) fuel types under normal operation conditions. Compared to UO2, it was found that the UO2-10%volBeO fuel experiences lower temperatures and fission gas release while producing similar cladding strain. The U3Si2 fuel has the earliest gap closure and induces the highest cladding hoop stress. Finally, the (Th0.9,U0.1)O2 fuel is predicted to produce the lowest fission gas release and a lower fuel centerline temperature when compared with the UO2 fuel. These tests demonstrate that CAMPUS (using the COMSOL platform) is a practical tool for modeling LWR fuel performance.

Advanced Multiphysics Modeling of Solar Tower Receivers Using Object-oriented Software and High Performance Computing Platforms

Abstract This paper presents an advanced methodology for the detailed modeling of the heat transfer and fluid dynamics phenomena in solar tower receivers. It has been carried out in the framework of a more ambitious enterprise which aims at modeling all the complex heat transfer and fluid dynamics phenomena present in central solar receivers. The global model is composed of 4 sub-models (heat conduction, two-phase flow, solar and thermal radiation and natural convection) which are described. Results of the numerical model obtained so far are also presented and discussed

Computational Analysis of Scalable Three-Dimensional Electrode and Device Architectures

3-D architectures are electrode and battery configurations that are non-planar configurations and offer the potential for greatly improved performance, particularly in terms of volumetric energy density, compared to traditional planar (1-D along the cell-sandwich and 2-D along the plane of the electrodes) configurations (or their derivatives).1, 2 In this work, we present computational analysis of a novel 3-D electrode and device architecture that we introduced earlier.3 This can potentially provide significant enhancements in energy density. These designs are expected to be scalable and to operate over length scales that exhibit rapid electron and ion transport. One of the electrode designs we have explored is shown in Fig. 1 and is based on a photonic crystal design.4 The local current collector framework arranged in a 3-D configuration is shown in the bottom right-hand corner of Fig. 1a. We refer to this structure as a 3-D scaffold and these structures can be fabricated from carbon-based or metallic materials. The scaffold is coated conformally with a redox-active electrode material. The resulting porous 3-D electrode is shown in the cut-away sections of Fig. 1a and the entire electrode is shown more clearly in Fig. 1b. The continuous pore volume (Fig. 1b) is a key element for this electrode and is purposely designed to not only be interconnected but also to be minimized. Liquid electrolyte, which fills the pores, will thus have access to all of the redox-active material at a suitable length scale. A detailed view of how the electrolyte is arranged within a given electrode element is shown in Fig. 1c. This figure also indicates how the electrolyte is continuous through the well-structured electrode architecture leading to low tortuosity. In this paper, we will present the detailed computational analysis of the transport properties of the 3D cathode architecture described above and also relevant electrochemical/electrical/thermal behavior of a cell composed of this cathode. We will utilize the recent 3D battery simulation software (AMPERES - Advanced MultiPhysics for Electrical and Renewable Energy Storage)5for detailed analysis of power/energy density performance of this architecture. We also compare these results with theoretical limits of such 3D structures for a few standard battery chemistries such as LiCoO2 and LiFePO4 and compare with respect to standard planar slurry based electrodes. Acknowledgements This research is sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy. Additional support is provided by the Vehicle Technologies Program of EERE office within U. S. Department of Energy.

A parallel multi-domain solution methodology applied to nonlinear thermal transport problems in nuclear fuel pins

This paper describes an efficient and nonlinearly consistent parallel solution methodology for solving coupled nonlinear thermal transport problems that occur in nuclear reactor applications over hundreds of individual 3D physical subdomains. Efficiency is obtained by leveraging knowledge of the physical domains, the physics on individual domains, and the couplings between them for preconditioning within a Jacobian Free Newton Krylov method. Details of the computational infrastructure that enabled this work, namely the open source Advanced Multi-Physics (AMP) package developed by the authors is described. Details of verification and validation experiments, and parallel performance analysis in weak and strong scaling studies demonstrating the achieved efficiency of the algorithm are presented. Furthermore, numerical experiments demonstrate that the preconditioner developed is independent of the number of fuel subdomains in a fuel rod, which is particularly important when simulating different types of fuel rods. Finally, we demonstrate the power of the coupling methodology by considering problems with couplings between surface and volume physics and coupling of nonlinear thermal transport in fuel rods to an external radiation transport code.

Safer Batteries through Coupled Multiscale Modeling

Batteries are highly complex electrochemical systems, with performance and safety governed by coupled nonlinear electrochemical-electrical-thermal-mechanical processes over a range of spatiotemporal scales. We describe a new, open source computational environment for battery simulation known as VIBE - the Virtual Integrated Battery Environment. VIBE includes homogenized and pseudo-2D electrochemistry models such as those by Newman-Tiedemann-Gu (NTG) and Doyle-Fuller-Newman (DFN, a.k.a. DualFoil) as well as a new advanced capability known as AMPERES (Advanced MultiPhysics for Electrochemical and Renewable Energy Storage). AMPERES provides a 3D model for electrochemistry and full coupling with 3D electrical and thermal models on the same grid. VIBE/AMPERES has been used to create three-dimensional battery cell and pack models that explicitly simulate all the battery components (current collectors, electrodes, and separator). The models are used to predict battery performance under normal operations and to study thermal and mechanical response under adverse conditions.

Advanced multiphysics coupling for LWR fuel performance analysis

Even the most basic nuclear fuel analysis is a multiphysics undertaking, as a credible simulation must consider at a minimum coupled heat conduction and mechanical deformation. The need for more realistic fuel modeling under a variety of conditions invariably leads to a desire to include coupling between a more complete set of the physical phenomena influencing fuel behavior, including neutronics, thermal hydraulics, and mechanisms occurring at lower length scales. This paper covers current efforts toward coupled multiphysics LWR fuel modeling in three main areas.The first area covered in this paper concerns thermomechanical coupling. The interaction of these two physics, particularly related to the feedback effect associated with heat transfer and mechanical contact at the fuel/clad gap, provides numerous computational challenges. An outline is provided of an effective approach used to manage the nonlinearities associated with an evolving gap in BISON, a nuclear fuel performance application.A second type of multiphysics coupling described here is that of coupling neutronics with thermomechanical LWR fuel performance. DeCART, a high-fidelity core analysis program based on the method of characteristics, has been coupled to BISON. DeCART provides sub-pin level resolution of the multigroup neutron flux, with resonance treatment, during a depletion or a fast transient simulation. Two-way coupling between these codes was achieved by mapping fission rate density and fast neutron flux fields from DeCART to BISON and the temperature field from BISON to DeCART while employing a Picard iterative algorithm.Finally, the need for multiscale coupling is considered. Fission gas production and evolution significantly impact fuel performance by causing swelling, a reduction in the thermal conductivity, and fission gas release. The mechanisms involved occur at the atomistic and grain scale and are therefore not the domain of a fuel performance code. However, it is possible to use lower length scale models such as those used in the mesoscale MARMOT code to compute average properties, e.g. swelling or thermal conductivity. These may then be used by an engineering-scale model. Examples of this type of multiscale, multiphysics modeling are shown.

Hydrodynamics Computation of Jet Formation and Penetration for Micro-shaped Charges

Understanding the hydrodynamic mechanisms in millimeter size shaped charges and smaller, is important for defence- related applications but also for material processing, remote sensing and potential biological applications. Our current focus is to perform a high-fidelity computational study to investigate micro-shaped charge jet formation and penetration depth. We seek to develop an understanding of the limits of our current ability to predict the formation and penetration characteristics of micro-shaped charges by simulation. The LLNL's advanced multiphysics hydrodynamics code, ALE3D, is used as the computational framework. Results obtained for a series of multi-material computations using very small charges and cones will be discussed. The typical thickness of the metal liner is 0.0254cm (0.01 in) at a stand-off distance of approximately 2.6 Liner Diameters. A complimentary experiment was performed with a very small shaped charge based on a detonator, to generate a representative realization for a simple baseline computational validation/comparison. Various Equation of State (EOS) models have been invoked including JWL, Mie-Gruneisen and γ-law gas with a programmed burn capability. It was found from the experimental data that the penetration depth corresponds to 3.3 Liner Diameter.

Multiphysics processes in partially saturated fractured rock: Experiments and models from Yucca Mountain

The site investigations at Yucca Mountain, Nevada, have provided us with an outstanding data set, one that has significantly advanced our knowledge of multiphysics processes in partially saturated fractured geological media. Such advancement was made possible, foremost, by substantial investments in multiyear field experiments that enabled the study of thermally driven multiphysics and testing of numerical models at a large spatial scale. The development of coupled‐process models within the project have resulted in a number of new, advanced multiphysics numerical models that are today applied over a wide range of geoscientific research and geoengineering applications. Using such models, the potential impact of thermal‐hydrological‐mechanical (THM) multiphysics processes over the long‐term (e.g., 10,000 years) could be predicted and bounded with some degree of confidence. The fact that the rock mass at Yucca Mountain is intensively fractured enabled continuum models to be used, although discontinuum models were also applied and are better suited for analyzing some issues, especially those related to predictions of rockfall within open excavations. The work showed that in situ tests (rather than small‐scale laboratory experiments alone) are essential for determining appropriate input parameters for multiphysics models of fractured rocks, especially related to parameters defining how permeability might evolve under changing stress and temperature. A significant laboratory test program at Yucca Mountain also made important contributions to the field of rock mechanics, showing a unique relation between porosity and mechanical properties, a time dependency of strength that is significant for long‐term excavation stability, a decreasing rock strength with sample size using very large core experiments, and a strong temperature dependency of the thermal expansion coefficient for temperatures up to 200°C. The analysis of in situ heater experiments showed that fracture closure/opening caused by changes in normal stress across fractures was the dominant mechanism for thermally induced changes in intrinsic fracture permeability during rock mass heating/cooling and that fracture shear dilation appears to be less significant. Significant effort was devoted to predicting the long‐term stability of underground excavations under (mechanical) strength degradation and seismic loading, perhaps one of the most challenging tasks within the project. We note that such long‐term strength degradation is actually an example of a chemically mediated process governed by underlying (microscopic) stress corrosion and chemical diffusion processes. In the Yucca Mountain Project, such chemically mediated mechanical changes were considered implicitly through model calibrations against laboratory and in situ heater experiments at temperatures anticipated to be experienced by the rock. A possible future research direction would be to simulate such processes mechanistically in a complete coupled THMC framework where C denotes chemical processes.

The AMP (Advanced MultiPhysics) Nuclear Fuel Performance code

The AMP (Advanced MultiPhysics) Nuclear Fuel Performance code is a new, three-dimensional, multi-physics tool that uses state-of-the-art solution methods and validated nuclear fuel models to simulate the nominal operation and anticipated operational transients of nuclear fuel. The AMP Nuclear Fuel Performance code leverages existing validated material models from traditional fuel performance codes and the Scale/ORIGEN-S spent-fuel characterization code to provide an initial capability that is shown to be sufficiently accurate for a single benchmark problem and anticipated to be accurate for a broad range of problems. The thermomechanics foundation can be solved in a time-dependent or quasi-static approach with any variation of operator-split or fully-coupled solutions at each time step through interoperable interfaces to leading computational mathematics tools, including PETSc, Trilinos, and SUNDIALS. A baseline validation of the AMP Nuclear Fuel Performance code has been performed through the modeling of an experiment in the Halden Reactor Project (IFA-432) that demonstrates the integrated capability and provides a baseline of the initial accuracy of the software.

Dynamic Decision and Data-Driven Strategies for the Optimal Management of Subsurface Geo-Systems

Effective geo-system management involves understanding of the interplay between surface entities (e.g., locations of injection and production wells in an oil reservoir) and appropriately effecting subsurface characteristics. This in turn requires efficient integration of complex numerical models of the environment, optimization procedures, and decision making processes. The dynamic, data-driven application systems (DDDAS) paradigm offers a promising framework to address this requirement. To achieve this goal, we have developed advanced multi-physics, multi-scale, and multi-block numerical models and autonomic systems software for dynamic, data-driven applications systems. This work has enabled a new generation of data-driven, interactive and dynamically adaptive strategies for subsurface characterization and management. These strategies have been applied to different aspects of subsurface management in strategically important application areas, including simulation-based optimization for the optimal oil well placement and the data-driven management of the Ruby Gulch Waste Repository. This paper summarizes the key outcomes and achievements of our work, as well as reports ongoing and future activities focused on uncertainty estimation and characterization.

Numerical investigation of active porous composites with enhanced acoustic absorption

The paper presents numerical analysis – involving an advanced multiphysics modeling – of the concept of active porous composite sound absorbers. Such absorbers should be made up of a layer or layers of poroelastic material (porous foams) with embedded elastic inclusions having active (piezoelectric) elements. The purpose of such active composite material is to significantly absorb the energy of acoustic waves in a wide frequency range, particularly, at lower frequencies. At the same time the total thickness of composite should be very moderate. The active parts of composites are used to adapt the absorbing properties of porous layers to different noise conditions by affecting the so-called solid-borne wave – originating mainly from the vibrations of elastic skeleton of porous medium – to counteract the fluid-borne wave – resulting mainly from the vibrations of air in the pores; both waves are strongly coupled, especially, at lower frequencies. In fact, since the traction between the air and the solid frame of porous medium is the main absorption mechanism, the elastic skeleton is actively vibrated in order to adapt and improve the dissipative interaction of the skeleton and air in the pores. Passive and active performance of such absorbers is analyzed to test the feasibility of this approach.