Second-order Code Research Articles

Development of a Fully-Implicit Second-Order system Thermal-Hydraulics analysis code for reactor modeling and simulations

There has been continuous advancement in numerical techniques and software engineering in the field of system thermal-hydraulics over the past decade. The current state-of-the-art involves the use of fully-implicit high-resolution schemes in conjunction with the Jacobian-Free Newton-Krylov (JFNK) method for both single-phase and two-phase flows. However, the application of these advanced schemes in system thermal-hydraulics codes is not a common practice. Given the opportunity and the need to develop a new modern system thermal–hydraulic code from scratch, there is no doubt that these recent advancements should be leveraged. In this work, we introduce a new modern object-oriented system thermal-hydraulics code named RETA. RETA is characterized by several key features, including: second-order temporal and spatial discretization schemes for both incompressible and compressible flows, as well as single-phase and two-phase flows; fully-implicit solution schemes utilizing both the Newton and PJFNK methods; and an object-oriented design of major fluid components and physical models, which allows for easy extension. A series of verification and demonstration studies are conducted to verify the implementation, demonstrate the accuracy improvement, and evaluate the performance of the new code. It is concluded that results from the second-order scheme are generally more reliable. Without the concern of a code stability issue, the second-order scheme should be the preferred and default choice for a code user or an analyst.

Marketing research agency, creative agency and client relationships: a study of relationship tensions

PurposeTo this date, research on tensions has been carried out on business networks and value co-creation, with no studies exploring tensions within the marketing services context. This study aims to use the three tension categories proposed by Toth et al. (2018) and Pressey and Vanharanta (2006) to address this gap by identifying the tensions experienced in the market research agency (MRA), creative agency (CA) and client relationship, as well as the processes that increase or minimize these tensions.Design/methodology/approachA total of 25 in-depth interviews were carried out with MRA, CA and client employees. NVivo 12 was used to conduct a thematic analysis to identify the overarching processes that influenced tensions.FindingsSix second-order codes were identified, designating processes that exacerbated or minimized each of the three tensions experienced. Two new processes were identified (“adopting governance processes” and “aspects of identity formation”) which have not been previously reported. An empirical framework was developed pinpointing processes that influenced each tension category, also highlighting complex interdependencies between behavioral, emotional and structural tensions.Originality/valueThis study presents the perspectives of all actors within the marketing services triad providing a more nuanced understanding of tensions at the triadic level, as previous literature predominantly focused either on dyads or on networks. Furthermore, this study highlights important interdependencies between tension categories, providing novel contributions, as well as directions for future research.

Removing Dust From the German Health Care System by Introducing Health Apps Into Standard Care: Semistructured Interview Study.

In 2019, Germany launched the Digital Healthcare Act. The reform enables physicians to prescribe health apps as treatments to their statutory-insured patients. We aimed to determine the extent to which the integration of health apps into standard care could be considered beneficial and which aspects of the regulation could still be improved. We conducted a semistructured interview study with 23 stakeholders in Germany and analyzed them thematically. We used descriptive coding for the first-order codes and pattern coding for the second-order codes. We created 79 first-order codes and 9 second-order codes following the interview study. Most stakeholders argued that the option of prescribing health apps could improve treatment quality. The inclusion of health apps into German standard care could improve the quality of treatment by expanding treatment portfolios. The educational elements of the apps might additionally lead to more patient emancipation through a better understanding of personal conditions. Location and time flexibility are the biggest advantages of the new technologies, but they also raise the most significant concerns for stakeholders because app use requires personal initiative and self-motivation. Overall, stakeholders agree that the Digital Healthcare Act has the potential to remove dust from the German health care system.

Mission Accomplished? Balancing Market Growth and Moral Legitimation in the Fair Trade Moral Market

Mission Accomplished? Balancing Market Growth and Moral Legitimation in the Fair Trade Moral Market

Resiliency-based adaptations used by primary care physicians during the COVID-19 pandemic.

The COVID-19 pandemic is a profound change event for U.S. primary care physicians and their medical practices. We examined how a group of U.S. primary care physicians and their medical practices used resiliency-based strategies, tactics, and mindsets to navigate pandemic-related change over the time period early 2020 through mid-2021. A 15-month longitudinal qualitative study of the same 10 physicians interviewed a total of 42 times at four time intervals during the 2020-2021 COVID-19 pandemic. Data were analyzed using a systematic coding approach consisting of first- and second-order code categories feeding into an overall interpretive framework of resiliency-based adaptations. Primary care physicians and their practices engaged in two main resiliency-based strategic adaptations during the pandemic. These adaptations were labeled "keeping the business afloat" and "keeping primary care relevant for patients." Each consisted of different strategies and tactics that shared common features including proactiveness, innovativeness, and pragmatism. Specific resiliency-based mindsets were identified that helped physicians both initially engage in needed strategies and tactics while continuing to engage in them over time. The results demonstrate how physicians use resiliency-based adaptation in response to profound change in their environments, defined by behavioral variety and motivated by self-interested and patient-centered imperatives. Physicians are proactive and possess multiple adaptive capabilities. Seen in this more positive light, health care organizations should focus on greater engagement of their physician-employees in implementing innovation in care delivery and managing change, that is, as responsible partners rather than resistors to meeting organizational imperatives.

Extreme springing response statistics of a tethered platform by deconvolution

The research examines the motion response and hydrodynamic wave loads of a deep-water Tension Leg Platform (TLP), emphasising the impacts of the wave sum frequency on the restrained modes of heave, roll, and pitch. The stochastic TLP structural reaction in a random sea state was precisely computed using a Volterra series representation of the TLP corner vertical displacement, which was selected as a response process. The wave loading was evaluated using the second-order diffraction code WAMIT and applied to a linear damped mass-spring model representing the dynamic system. Then, platform displacement response at the design low probability level has been determined using a novel deconvolution approach. Since the Volterra series represented the analytical solution, the exact Volterra and the approximated predictions have been compared in this study. The latter provided an accurate way to validate the effectiveness and precision of the proposed novel deconvolution method. Compared to existing engineering techniques, the most attractive advantage of the proposed deconvolution method is that it does not rely on any pre-assumed asymptotic probability distribution class. The latter may be an attractive point for practical engineering design. Thus the primary objective of this work was to validate a novel deconvolution approach using exact quasi-analytical solutions. This work also highlights the limitations of mean up-crossing rate-based extrapolation methodologies for the situation of narrowband effects, including clustering, which are often included in the springing type of response.

Relativistic second-order initial conditions for simulations of large-scale structure

Relativistic corrections to the evolution of structure can be used to test general relativity on cosmological scales. They are also a well-known systematic contamination in the search for a primordial non-Gaussian signal. We present a numerical framework to generate RELativistic second-order Initial Conditions (RELIC) based on a generic (not necessarily separable) second-order kernel for the density perturbations. In order to keep the time complexity manageable we introduce a scale cut that separates long and short scales, and neglect the “short-short” coupling that will eventually be swamped by uncontrollable higher-order effects. To test our approach, we use the second-order Einstein-Boltzmann code SONG to provide the numerical second-order kernel in a ΛCDM model, and we demonstrate that the realisations generated by RELIC reproduce the bispectra well whenever at least one of the scales is a “long” mode. We then present a generic algorithm that takes a perturbed density field as an input and provides particle initial data that matches this input to arbitrary order in perturbations for a given particle-mesh scheme. We implement this algorithm in the relativistic N-body code gevolution to demonstrate how our framework can be used to set precise initial conditions for cosmological simulations of large-scale structure.

On Decoding of Reed-Muller Codes Using a Local Graph Search

We present a novel iterative decoding algorithm for Reed-Muller (RM) codes, which takes advantage of a graph representation of the code. Vertices of the considered graph correspond to codewords, with two vertices being connected by an edge if and only if the Hamming distance between the corresponding codewords equals the minimum distance of the code. The algorithm uses a greedy local search to find a node optimizing a metric, e.g. the correlation between the received vector and the corresponding codeword. In addition, the cyclic redundancy check can be used to terminate the search as soon as a valid codeword is found, leading to an improvement in the average computational complexity of the algorithm. Simulation results for both binary symmetric channel and additive white Gaussian noise channel show that the presented decoder approaches the performance of maximum likelihood decoding for RM codes of length less than 1024 and for the second-order RM codes of length less than 4096. Moreover, it is demonstrated that the considered decoding approach outperforms state-of-the-art decoding algorithms of RM codes with similar computational complexity for a wide range of block lengths and rates.

Efficient goal-oriented mesh refinement in 3-D finite-element modelling adapted for controlled source electromagnetic surveys

SUMMARY We developed a 3-D forward modelling code, which simulates controlled source electromagnetic problems in frequency domain using edge-based finite elements and a total electric field approach. To evaluate electromagnetic data acquired across complex subsurface structures, software performing accurate 3-D modelling is required, especially for incorporation in inversion approaches. Our modelling code aims at finding a good compromise between the necessary solution accuracy at the points of interest and the general problem size by using a goal-oriented mesh refinement strategy designed for models of variable electric conductivity and magnetic permeability. To formulate an improved error estimator suitable for controlled source electromagnetic problems, we developed literature approaches of mesh refinement further targeting three aspects. First, to generate a roughly homogeneously fine mesh discretization around all receiver sites, our new error estimator weights the adjoint source term by the approximate decay of the electric field with increasing distance from the primal source using the expression for a homogeneous half-space. This causes almost no additional computational cost. Second, the error estimator employed in the refinement approach can be optimized for models with pronounced conductivity and magnetic permeability contrasts as often encountered in, for example, mineral prospecting scenarios by optionally including terms that measure the continuity of the normal component of current flow and the tangential component of the magnetic field across interfaces of abutting elements. Third, to avoid amplitude-dependent over-refining of the mesh, we formulate our element-wise error estimators relative to the local amplitude of the electromagnetic field. In this work, we evaluate the implemented adaptive mesh refinement approach and its solution accuracy comparing our solutions for simple 1-D models and a model with 3-D anomalies to semi-analytic 1-D solutions and a second-order finite-element code, respectively. Furthermore, a feasibility study for controlled-source electromagnetic measurements across ferrous mineral deposits is conducted. The numerical experiments demonstrate that our new refinement procedure generates problem-specific finite-element meshes and yields accurate solutions for both simple synthetic models and realistic survey scenarios. Especially for the latter, characteristics of our code, such as the possibility of modelling extended sources as well as including arbitrary receiver distributions and detailed subsurface anomalies, are beneficial.

Numerical computation of second-order vacuum perturbations of Kerr black holes

Motivated by the desire to understand the leading-order nonlinear gravitational wave interactions around arbitrarily rapidly rotating Kerr black holes, we describe a numerical code designed to compute second-order vacuum perturbations on such spacetimes. A general discussion of the formalism we use is presented in [N. Loutrel et al., Phys. Rev. D 103, 104017 (2021)]; here we show how we numerically implement that formalism with a particular choice of coordinates and tetrad conditions and give example results for black holes with dimensionless spin parameters $a=0.7$ and $a=0.998$. We first solve the Teukolsky equation for the linearly perturbed Weyl scalar ${\mathrm{\ensuremath{\Psi}}}_{4}^{(1)}$, followed by direct reconstruction of the spacetime metric from ${\mathrm{\ensuremath{\Psi}}}_{4}^{(1)}$, and then solve for the dynamics of the second-order perturbed Weyl scalar ${\mathrm{\ensuremath{\Psi}}}_{4}^{(2)}$. This code is a first step toward a more general purpose second-order code, and we outline how our basic approach could be further developed to address current questions of interest, including extending the analysis of ringdown in black hole mergers to before the linear regime, exploring gravitational wave ``turbulence'' around near-extremal Kerr black holes, and studying the physics of extreme mass ratio inspiral.

Unsteady anisotropic heat conduction in heterogeneous composite conical shells with temperature-dependent thermal conductivities: an analytical study

The present study proposes an exact analysis for unsteady anisotropic conduction heat transfer in heterogeneous composite conical shells. The fibers in the composite conical shell are wound in arbitrary directions so that a defined fiber angle changes between 0° and 90°. The cone’s base is considered to have a general linear boundary condition, while the effects of internal heat generation, thermal convection, and external radiation heat flux on the temperature distribution are investigated. The heterogeneity of the heat transfer problem is caused by a linear dependence of conduction coefficients on the temperature. To solve the governing equations, first, the Kirchhoff transformation followed by an appropriate finite integral transform is applied. The resulting nonhomogeneous equation is then separated into two equations, i.e., steady equation and unsteady equation. The solution of the steady case is derived using Green’s function, while the separation of variables method is utilized to solve the unsteady part. Eventually, the temperature distribution is achieved by applying the inverse transforms on the subsequent solutions. The verification of this solution is based on the comparison between the present analytical results and numerical computations with a second-order finite difference code. Applicability of the present solution is evaluated for resolving an industrial case problem.

Student experiences studying accounting in English as an additional language

Purpose This paper aims to explore the individual and social learning experiences of first-year accounting students studying in English as an additional language. The challenges of these students relating to listening, reading, speaking and writing in English, and the impact of these on their academic outcomes, are examined. Design/methodology/approach A qualitative case study design was used. Face-to-face semi-structured interviews were conducted with 14 students, both academically successful and unsuccessful, who had completed the first year. A thematic analysis of the data was conducted and a hybrid approach of deductive and inductive coding was used to interpret the data. This entailed the application of a language skills-based framework of teaching and learning to the first-order process of coding. An iterative and reflective process allowed themes to emerge from the data. These themes, in turn, triggered second-order codes that resonated with aspects of the interactionist approach to second language acquisition (SLA). Findings The themes that emerged indicated that students’ ability to interact with their study material, and their exposure to positive verbal interaction opportunities in both formal and informal contexts, may have contributed to their academic success. Practical implications It is recommended that an interactionist perspective be considered when designing curriculum resources and accounting language learning activities for first-year accounting students. Originality/value It is anticipated that the results will contribute towards building a bridge between accounting education and SLA research and provide a more informed linguistic foundation for incorporating language skills into the accounting curriculum.

On the solution of the slope beach problem in the context of shallow-water code benchmarking: Why non-linearization of the initial waveforms is essential

We detail a new semi-analytic solution for the slope beach problem in which linearization of the initial waveform is not carried out to provide the exact corresponding boundary condition for the transformed problem. Numerical code benchmarking requires the construction of exact solutions to check the convergence order and efficiently compare the simulations using fine meshes. We quantify the impact of the linearization assumption and compare two situations (linearized and non-linearized) with a second-order finite volume code. The accuracy of the shoreline velocity, maximum run-up, and maximum run-down situations, in particular, are of crucial importance in applications as they characterize the inundation and impact intensity of a wave on potential infrastructure. To this end, we provide two sets of spreadsheets, containing highly accurate approximations of the exact non-linearized solution for cases (c) and (d) of Carrier et al. (2003) study, for benchmarking purposes.

Estimation of seismic source parameters in 3D elastic media using the reciprocity theorem

We have developed a novel method based upon reciprocity principles to simultaneously estimate the location of a seismic event and its source mechanism in 3D heterogeneous media. The method finds double-couple (DC) and non-DC mechanisms of microearthquakes arising from localized induced and natural seismicity. Because the method uses an exhaustive search of the 3D elastic media, it is globally convergent. It does not suffer from local minima realization observed with local optimization methods, including Newton, Gauss-Newton, or gradient-descent algorithms. The computational efficiency of our scheme is derived from the reciprocity principle, in which the number of 3D model realizations corresponds to the number of measurement receivers. The 3D forward modeling is carried out in the damped Fourier domain with a 3D finite-difference frequency-domain fourth- and second-order code developed to simulate elastic waves generated by seismic sources defined by forces and second-order moment density tensors. We evaluate the results of testing this new methodology on synthetic data for the Raft River geothermal field, Idaho, as well as determine its applicability in designing optimal borehole monitoring arrays in a fracking experiment at the Homestake Mine, South Dakota. We also find that the method proposed here can retrieve the moment tensors of the space distributed source with data arising from spatially restricted arrays with limited aperture. The effects of uncertainties on the source parameter estimation are also examined with respect to data noise and model uncertainty.

Systematic study of accuracy of wall-modeled large eddy simulation using uncertainty quantification techniques

The predictive accuracy of wall-modeled large eddy simulation is studied by systematic simulation campaigns of turbulent channel flow. The effect of wall model, grid resolution and anisotropy, numerical convective scheme and subgrid-scale modeling is investigated. All of these factors affect the resulting accuracy, and their action is to a large extent intertwined. The wall model is of the wall-stress type, and its sensitivity to location of velocity sampling, as well as law of the wall’s parameters is assessed. For efficient exploration of the model parameter space (anisotropic grid resolution and wall model parameter values), generalized polynomial chaos expansions are used to construct metamodels for the responses which are taken to be measures of the predictive error in quantities of interest (QoIs). The QoIs include the mean wall shear stress and profiles of the mean velocity, the turbulent kinetic energy, and the Reynolds shear stress. DNS data is used as reference. Within the tested framework, a particular second-order accurate CFD code (OpenFOAM), the results provide ample support for grid and method parameters recommendations which are proposed in the present paper, and which provide good results for the QoIs. Notably, good results are obtained with a grid with isotropic (cubic) hexahedral cells, with 15 000 cells per δ3, where δ is the channel half-height (or thickness of the turbulent boundary layer). The importance of providing enough numerical dissipation to obtain accurate QoIs is demonstrated. The main channel flow case investigated is Reτ=5200, but extension to a wide range of Re-numbers is considered. Use of other numerical methods and software would likely modify these recommendations, at least slightly, but the proposed framework is fully applicable to investigate this as well.

On Redundancy Reduction of Non-Recursive Second-Order Spectral-Null Codes

The code design problem of non-recursive second-Order Spectral Null (2-OSN) codes is to convert balanced information words into 2-OSN words employing the minimum possible redundancy. Let $k$ be the balanced information word length. If $k\in \,\,2 {{I}}{{N}}$ then the 2-OSN coding scheme has length $n=k+r$ , with 2-OSN redundancy $r \in \,\,2 {{I}}{{N}}$ and $n\in \,\,4 {{I}}{{N}}$ . Here, we use a scheme with $r=2 \log k+\Theta (\log \log k)$ . The challenge is to reduce redundancy even further for any given $k$ . The idea is to exploit the degree of freedom to select from more than one possible 2-OSN encoding of a given balanced information word. To reduce redundancy, empirical results suggest that extra information $\delta _{k}=0.5 \log k+\Theta (\log \log k)$ is obtained. Thus, the proposed approach would give a smaller redundancy $r^{\prime }=1.5 \log k+\Theta (\log \log k)$ less than $r=2 \log k+\Theta (\log \log k)$ .

Numerical study of the cascading energy conversion of the reconnection current sheet in solar eruptions

Magnetic reconnection plays an important role in the energy conversion during solar eruptions. In this work, we present a resistive magnetohydrodynamical study (2.5D) of a flux rope eruption based on the Lin and Forbes model regarding cascading reconnection. We use a second-order Godunov scheme code, to better understand the physical mechanisms responsible for high reconnection rates and the internal structure, particularly in chaotic or turbulent regions, of the coronal mass ejection (CME)/flare current sheet (CS). Two sets of simulations with Lundquist numbers of 1.18 x 10(5) and 2.35 x 10(5) in the vicinity of the CS, generating a slow CME and a moderate one, show global dynamic features largely consistent with the flare model. Looking into the fine structure of the CS, magnetic reconnection employs simultaneously the Sweet-Parker mode and time-dependent small-scale Petschek patterns in the early stage. As the flux rope rises, the outflow region becomes turbulent, which further enhances the reconnection rates. Our results show that coalescence and fusion processes of plasmoids provide a large number of small, transient local diffusion regions to dissipate magnetic energy, and confirm that the dissipation starts at macro-MHD scales rather than ion inertial lengths. The two runs have the same range of the local reconnection rates (10(-4)-0.3) relevant to CMEs. The fast rates are closely proportional to the square of the aspect ratio of multiple small-scale CSs. The topology of the magnetic field and the turbulence spectrum of the energy cascade are statistically addressed as well.

Comparison of computational codes for direct numerical simulations of turbulent Rayleigh–Bénard convection

Computational codes for direct numerical simulations of Rayleigh–Bénard (RB) convection are compared in terms of computational cost and quality of the solution. As a benchmark case, RB convection at Ra=108 and Pr=1 in a periodic domain, in cubic and cylindrical containers is considered. A dedicated second-order finite-difference code (AFID/RBflow) and a specialized fourth-order finite-volume code (Goldfish) are compared with a general purpose finite-volume approach (OpenFOAM) and a general purpose spectral-element code (Nek5000). Reassuringly, all codes provide predictions of the average heat transfer that converge to the same values. The computational costs, however, are found to differ considerably. The specialized codes AFID/RBflow and Goldfish are found to excel in efficiency, outperforming the general purpose flow solvers Nek5000 and OpenFOAM by an order of magnitude with an error on the Nusselt number Nu below 5%. However, we find that Nu alone is not sufficient to assess the quality of the numerical results: in fact, instantaneous snapshots of the temperature field from a near wall region obtained for deliberately under-resolved simulations using Nek5000 clearly indicate inadequate flow resolution even when Nu is converged. Overall, dedicated special purpose codes for RB convection are found to be more efficient than general purpose codes.

Hybrid modeling of diffusive shock acceleration in collisionless shocks in multispecies plasma

Diffusive shock acceleration (DSA) is a very efficient mechanism of high energy particle acceleration in heliosphere, supernova remnants, stellar winds and gamma-ray bursts. We present microscopic simulation of particle injection and diffusive shock acceleration which is performed with 3D divergence-conserving second-order accurate hybrid code "Maximus". Hydrogen plasma with admixture of various heavy ions is considered. The injection process is found to start through shock reflection for both hydrogen and heavier ions. However, the reflection process depends on charge-to-mass ratio. While hydrogen ions reflection appears at shock ramp and is governed by the cross-shock potential, the reflection of ions with greater A=Z proceeds deeper down-stream via gyration in perpendicular magnetic field component. The heavy ions appear to inject into the DSA preferentially, but this chemical enhancement saturates with growing A=Z. The protons injection efficiency is estimated within various approaches, and it is shown that about 20% of initial flow energy goes into accelerated particles.

Computational modeling of blast exposure associated with recoilless weapons combat training

Military personnel are exposed to blast as part of routine combat training with shoulder-fired recoilless rifles. These weapons fire large-caliber ammunitions capable of disabling structures and uparmored vehicles (e.g., tanks). Scientific, medical, and military leaders are beginning to recognize the blast overpressure from these shoulder-fired weapons may result in acute and even long-term physiological effects to military personnel. However, the back blast generated from the Carl Gustav and Shoulder-launched Multipurpose Assault Weapon (SMAW) shoulder-fired weapons on the weapon operator has not been quantified. By quantifying and modeling the full-body blast exposure from these weapons, better injury correlations can be constructed. Blast exposure data from the Carl Gustav and SMAW were used to calibrate a propellant burn source term for computational simulations of blast exposure on operators of these shoulder-mounted weapon systems. A propellant burn model provided the source term for each weapon to capture blast effects. Blast data from personnel-mounted gauges during weapon firing were used to create initial, high-fidelity 3D computational fluid dynamic simulations using SHAMRC (Second-order Hydrodynamic Automatic Mesh Refinement Code). These models were then improved upon using data collected from static blast sensors positioned around the military personnel while weapons were utilized in actual combat training. The final simulation models for both the Carl Gustav and SMAW were in good agreement with the data collected from the personnel-mounted and static pressure gauges. Using the final simulation results, contour maps were created for peak overpressure and peak overpressure impulse experienced by military personnel firing the weapon as well as those assisting with firing of those weapons. Reconstruction of the full-body blast loading enables a more accurate assessment of the cause of potential mechanisms of injury due to air blast even for subjects not wearing blast gauges themselves. By accurately understanding the blast exposure and its variations across an individual, more meaningful correlations with physiologic response including potential TBI spectrum physiology associated with sub-concussive blast exposure can be established. As blast injury thresholds become better defined, results from these reconstructions can provide important insights into approaches for reducing possible risk of injury to personnel operating shoulder-launched weapons.