Verification Cases Research Articles

LODQuMa: A Free-ontology process for Linked (Open) Data quality management

For many years, data quality is among the most commonly discussed issue in Linked Open Data (LOD) due to the huge volume of integrated datasets that are usually heterogeneous. Several ontology-based approaches dealing with quality problems have been proposed. However, when datasets lack a well-defined schema, these approaches become ineffective because of the lack of metadata. Moreover, the detection of quality problems based on an analysis between RDF (Resource Description Framework) triples without requiring ontology statistical and semantical information is not addressed. Keeping in mind that ontologies are not always available and they may be incomplete or misused. In this paper, a novel free-ontology process called LODQuMa is proposed to assess and improve the quality of LOD. It is mainly based on profiling statistics, synonym relationships between predicates, QVCs (Quality Verification Cases), and SPARQL (SPARQL Protocol and RDF Query Language) query templates. Experiments on the DBpedia dataset demonstrate that the proposed process is effective for increasing the intrinsic quality dimensions, resulting in correct and compact datasets.

Application of the generalised fully Lagrangian approach to simulating polydisperse gas-droplet flows

In this paper, we demonstrate the application of a generalised fully Lagrangian approach to the simulation of polydisperse gas-evaporating droplet flows. The paper focuses on the proposed methodology for modelling the dispersed phase, droplets, in both steady and transient cases. To account for polydispersity, the set of Lagrangian variables is extended to include the droplet size, and the droplet size distribution function is introduced to the droplet parameter set. According to the Lagrangian approach, all the droplet parameters, including the distribution function, are found along the droplet trajectories. An interpolation scheme to convert droplet parameter fields from a Lagrangian to an Eulerian framework for visualising droplet distribution is proposed. The developed methodology was applied to simple 1D and 2D stationary cases for verification, after which it was incorporated into OpenFOAM to simulate steady and periodic flows around a cylinder. In the case of a steady flow, a region devoid of droplets is formed behind the cylinder. From the droplet distribution plots, it was observed that small and medium sized droplets reach a region near to the axis of the symmetry of the flow. In the case of periodic flow, the analysis of droplet distribution is based on instantaneous pictures of the droplet parameters rather than their values along droplet trajectories. In this flow, strongly influenced by vortices, a strong droplet segregation is shown; at various locations one can see a full droplet size spectrum, only small or large droplets, and/or droplets from a narrow size interval. In all cases, the effect of the evaporation is to decrease the maximum value of the droplet distribution function shifted towards smaller-sized droplets.

Springback Behaviour due to Die Deflection during Bending

The material strength of rolled steel sheet for car bodies is increasing considerably. It has been experientially known that the die deflection affects the springback, but there are few experimental verification cases. In this study, two bending dies with different rigidity but the same shape were manufactured. The springback of panels bended by each die was compared in detail. Using 590MPa class and 980MPa class steel sheets, the deformation of the dies due to bending also measured. The springback and deflection of the die were clearly large using the low rigidity die. From these results, it was suggested that it is necessary to consider the die deflection for accurate springback prediction of bending.

Analytical corrections for double-cantilever beam tests

Double-cantilever beams (DCBs) are widely used to study mode-I fracture behavior and to measure mode-I fracture toughness under quasi-static loads. Recently, the authors have developed analytical solutions for DCBs under dynamic loads with consideration of structural vibration and wave propagation. There are two methods of beam-theory-based data reduction to determine the energy release rate: (i) using an effective built-in boundary condition at the crack tip, and (ii) employing an elastic foundation to model the uncracked interface of the DCB. In this letter, analytical corrections for a crack-tip rotation of DCBs under quasi-static and dynamic loads are presented, afforded by combining both these data-reduction methods and the authors’ recent analytical solutions for each. Convenient and easy-to-use analytical corrections for DCB tests are obtained, which avoid the complexity and difficulty of the elastic foundation approach, and the need for multiple experimental measurements of DCB compliance and crack length. The corrections are, to the best of the authors’ knowledge, completely new. Verification cases based on numerical simulation are presented to demonstrate the utility of the corrections.

Better state pictures facilitating state machine characteristic conjecture

The mutual exclusion protocol invented by Mellor-Crummey and Scott (called MCS protocol) is used to exemplify that state picture designs based on which the state machine graphical animation (SMGA) tool produces graphical animations should be better visualized. Variants of MCS protocol have been used in Java virtual machines and therefore the 2006 Edsger W. Dijkstra Prize in Distributed Computing went to their paper on MCS protocol. The new state picture design of a state machine formalizing MCS protocol is assessed based on Gestalt principles, more specifically proximity principle and similarity principle. We report on a core part of a formal verification case study in which the new state picture design and the SMGA tool largely contributed to the successful completion of the formal proof that MCS protocol enjoys the mutual exclusion property. The lessons learned acquired through our experiments are summarized as two groups of tips. The first group is some new tips on how to make state picture designs. The second one is some tips on how to conjecture state machine characteristics by using the SMGA tool. We also report on one more case study in which the state picture design has been made for the mutual exclusion protocol invented by Anderson (called Anderson protocol) and some characteristics of the protocol have been discovered based on the tips.

A hybrid beam-column element for direct second-order nonlinear analysis of PFRP frame structures

In order to achieve accurate structural calculation of pultruded fiber reinforced polymer (PFRP) space frame structures by “a single element per member”, an imperfect nonlinear beam-column element considering the hybrid effects of component stiffness is proposed. Based on the unique characteristics of PFRP profiles, the equilibrium differential equations considering transverse shear effect and initial deflection were established. Afterwards, the stability functions, bending functions, force versus deformation equations and element tangent stiffness matrix were further derived. With the consideration of common connection system for PFRP profiles, the effect of joint stiffness, rigid arm and reinforcement segment were incorporated into the element formula without increasing the external degrees of freedom: The effect of joint stiffness is considered by the static condensation procedure; The rigid arm effect is considered based on the relationship between end points of the rigid vector; The effect of reinforcement segment is considered based on the idea of equivalence. Besides, a novel 3D co-rotational procedure allowing for large load step was proposed to update the local-global transformation matrix. The finally obtained hybrid beam-column element was used for calculation of several PFRP structure verification cases, which showed the advantages of easy structural modelling, good accuracy and high computational efficiency.

Polyphase uncertainty analysis through virtual modelling technique

A virtual model aided non-deterministic static analysis (including linear and nonlinear analyses) with polyphase uncertainty is presented in this paper. Within an uncertain system, the polyphase uncertainty integrates both probabilistic and non-probabilistic uncertainties, which is more sophisticated than the conventional uncertainty modelling through a single type. To further improve the computational stableness and robustness of the virtual model, a kernel-based machine learning technique, namely Twin Extended Support Vector Regression (T-X-SVR), is newly developed. The feature of auto-learning is fulfilled through the Bayesian optimization. The proposed approach is capable of providing sufficient statistical information, including the membership functions of mean and standard deviation, fuzzy-valued probabilistic density function (PDF) and cumulative distribution function (CDF) for the upper and lower bounds of the concerned structural response. To demonstrate the effectiveness and computational efficiency of the proposed approach, a verification case, where analytical solutions are available, is tested first. Then, two practically stimulated engineering applications are fully investigated.

Impact-induced twinning in a magnesium alloy under different stress conditions

We investigate deformation twinning in a highly textured magnesium alloy plate of Mg-3.1%Al-0.9%Zn-0.4%Mn under edge-on impact with in situ, synchrotron-based, ultrafast X-ray diffraction measurements, and corresponding stress states are simulated with the finite element method. Deformation twinning and its anisotropy under the triaxial stress condition are explained by a statistical analysis of resolved shear stress. The critical resolved shear stress criterion is applicable under complicated stress conditions induced by high strain rate impact loading. Three typical simple stress conditions are further explored as verification and application cases: uniaxial-stress, uniaxial-strain, and plane-stress. Extension twinning in the magnesium alloy is prone to occur for impact loading applied perpendicular to the crystallographic c-axis, regardless of the exact stress conditions.

Verification and test case development method based on civil aircraft operation scenario

Verification and test case development method based on civil aircraft operation scenario

Direct forcing immersed boundary methods: Improvements to the ghost-cell method

The ghost-cell immersed boundary methods (IBMs) are widely used to implement boundary conditions on non-body fitted grids. It has been previously shown that they have two major drawbacks. Firstly, these methods tend to have a maximum stencil size larger than 1, yielding non-band matrices. Secondly, for a maximum stencil size of 2 the ghost-cell linear IBM [1] have a first-order convergence rate for Neumann immersed boundary conditions. To address these two shortcomings and in the pursuit of increased accuracy and increased order of convergence the current article proposes the linear/quadratic square shifting methods for the ghost-cell IBM for Cartesian grids. The linear square shifting method guarantees a maximum stencil size of 1 and also improves the accuracy and convergence while the quadratic square shifting method improves the accuracy and convergence while maintaining the same stencil size of 2 as the original linear method [1]. The quadratic ghost-cell method [2,3] further improves the accuracy and convergence whilst maintaining a maximum stencil size of 3 while the currently proposed quadratic square shifting method makes it possible to increase the Lagrange polynomial interpolation order whilst maintaining a maximum stencil of 2 resulting in an improved order of convergence for Neumann immersed boundary conditions. The proposed methods are evaluated by considering their accuracy and convergence thanks to a comprehensive verification and validation process. Firstly, the canonical verification 2D and 3D Poisson test problems for various analytical solutions and immersed boundaries are considered and are followed by various verification and validation test cases for the Navier-Stokes governing equations, with and without heat transfer, in 2D and 3D.

Comparative Study of Physical Models for Particle Sedimentation Using SIMMER Code

Abstract In the context of improved safety requirements for Generation IV sodium-cooled fast reactors (SFR), an innovative severe accident mitigation scenario is being investigated. In the French frame of SFR research, the mitigation strategy consists of transfer tubes and a core catcher. The transfer tubes are dedicated to discharge molten fissile materials from the core center region and to guide them toward the core catcher where long-term cooling and subcritical state may be assured. The physical phenomena occurring during the discharge process are introduced in this paper. The current demonstration of the mitigation strategy uses best-estimate calculations with the reference computer code SIMMER. Previous analyses showed that the material discharge through the transfer tubes might be efficient; however, uncertainties of SIMMER approach are identified on the molten material mobility during the relocation process. It is related to a blockage formation due to particulate solid debris accumulation inside the transfer tube, in case of low energy accumulation in the degraded fuel, is believed to originate from the solid particle treatment in the code. As the performance of mitigation strategy strongly depends on the mobility of the relocating mixture, the most predictive behavior of particle flows is of great importance to SFR safety. Therefore, the SIMMER modeling of such flows is analyzed in this work. The first verification and validation test cases regarding the gravitational settling of particle clouds at varying volume fractions are presented. Recommendations for reactor calculations and first orientations for future research and development are highlighted.

A principled approach to design using high fidelity fluid-structure interaction simulations

A high fidelity fluid-structure interaction simulation may require many days to run, on hundreds of cores. This poses a serious burden, both in terms of time and economic considerations, when repetitions of such simulations may be required (e.g. for the purpose of design optimization). In this paper we present strategies based on (constrained) Bayesian optimization (BO) to alleviate this burden. BO is a numerical optimization technique based on Gaussian processes (GP) that is able to efficiently (with minimal calls to the expensive FSI models) converge towards some globally optimal design, as gauged using a black box objective function. In this study we present a principled design evolution that moves from FSI model verification, through a series of Bridge Simulations (bringing the verification case incrementally closer to the application), in order that we may identify material properties for an underwater, unmanned, autonomous vehicle (UUAV) sail plane. We are able to achieve fast convergence towards an optimal design, using a small number of FSI simulations (a dozen at most), even when selecting over several design parameters, and while respecting optimization constraints.

On the efficient modeling of generic source directivity in Gaussian beam tracing.

For large-distance sound propagation with complex obstacles, the Gaussian beam tracing (GBT) method is often applied. An omnidirectional source model is commonly implemented in GBT, which, however, neglects the influence of generic directivity patterns of practical acoustic problems. There have been efforts to synthesize or reproduce the target directivity pattern over an observation surface by using multiple distributed point sources. However, the efficiency and applicability of general applications still call for improvement. More specifically, rays from each of the point sources and their traces in the space should be computed and superposed to estimate the sound field, making the computational cost largely dependent on the complexity of the source directivity pattern. In this work, a complex-valued radiation function model is developed to realize the generic source directivity for GBT computation. One advantage of the method is that only one source is required such that computation cost can be greatly reduced. Rays are emitted from the source with direction-dependent amplitude and phase to realize the target directivity pattern. The development of the radiation function is associated with the GBT method. The verification cases show that this method can give good agreement with analytical or wave-based numerical solutions. Capabilities of modeling a complex source model of the spinning sound field to mimic the propeller noise are studied, and the result matches well with analytical solutions. Finally, a demonstration case of a four-propeller-powered drone in an urban region is conducted.

A clinical case of difficult determination of the treatment option for a patient with pulmonary embolism

The article presents a clinical case of difficult verification of pulmonary embolism severity and difficulty of choosing a treatment option for a patient with this disease.

Direct numerical simulation of evaporation and condensation with the geometric VOF method and a sharp-interface phase-change model

The paper describes a coupling of the geometric Volume-of-Fluid (VOF) method with a sharp-interface phase-change model for Cartesian and axisymmetric grids. Both the interfacial position and the temperature field are resolved with subgrid accuracy. Species transport with implicit diffusion is considered in the gas phase. The numerical implementation of the method developed here is described in detail, as well as its coupling with the incompressible Navier-Stokes solver PSI-BOIL, which features a hybrid, finite-volume/finite-difference approach based on a fixed, rectangular grid. Several verification cases have been undertaken to ensure correct implementation of the method in the code and to evaluate its performance. These include simulations of the Stefan problem, sucking problem and bubble growth in superheated liquid. In all cases, very good agreement with the analytical solution has been reached and grid convergence has been demonstrated. Simulations of evaporating and condensing rising bubbles, for which high-quality measured data are available, are also presented to serve as validation tests. Reasonable agreement of simulation results with experimental data has been recorded and applicability of the method to problems without inherent symmetry and featuring turbulence is shown. This work represents the first successful application of a geometric VOF method coupled with a sharp-interface phase-change model and species transport to non-trivial problems. The achieved performance of our algorithm in the verification and validation exercise represents an important step in the development of multiphase codes capable of accurately resolving complex three-dimensional multiphase flows.

The One-Way FSI Method Based on RANS-FEM for the Open Water Test of a Marine Propeller at the Different Loading Conditions

This paper aims to assess a new fluid–structure interaction (FSI) coupling approach for the vp1304 propeller to predict pressure and stress distributions with a low-cost and high-precision approach with the ability of repeatability for the number of different structural sets involved, other materials, or layup methods. An outline of the present coupling approach is based on an open-access software (OpenFOAM) as a fluid solver, and Abaqus used to evaluate and predict the blade’s deformation and strength in dry condition mode, which means the added mass effects due to propeller blades vibration is neglected. Wherein the imposed pressures on the blade surfaces are extracted for all time-steps. Then, these pressures are transferred to the structural solver as a load condition. Although this coupling approach was verified formerly (wedge impact), for the case in-hand, a further verification case, open water test, was performed to evaluate the hydrodynamic part of the solution with an e = 7.5% average error. A key factor for the current coupling approach is the rotational rate interrelated between two solution domains, which should be carefully applied in each time-step. Finally, the propeller strength assessment was performed by considering the blades’ stress and strain for different load conditions.

The Revelation Principle for Mechanism Design with Signaling Costs

The revelation principle is a key tool in mechanism design. It allows the designer to restrict attention to truthful mechanisms, greatly facilitating analysis. This is also borne out algorithmically, allowing certain computational problems in mechanism design to be solved in polynomial time. Unfortunately, when not every type can misreport every other type (the partial verification model) or—more generally—misreporting can be costly, the revelation principle can fail to hold. This also leads to NP-hardness results. The primary contribution of this article consists of characterizations of conditions under which the revelation principle still holds when reporting can be costly. (These are generalizations of conditions given earlier for the partial verification case [11, 21].) Furthermore, our results extend to cases where, instead of reporting types directly, agents send signals that do not directly correspond to types. In this case, we obtain conditions for when the mechanism designer can restrict attention to a given (but arbitrary) mapping from types to signals without loss of generality.

Topology-free immersed boundary method for incompressible turbulence flows: An aerodynamic simulation for “dirty” CAD geometry

To design a method to solve the issues of handling “dirty” and highly complex geometries, the topology-free method combined with the immersed boundary method is presented for viscous and incompressible flows at a high Reynolds number. The method simultaneously employs a ghost-cell technique and distributed forcing technique to impose the boundary conditions. An axis-projected interpolation scheme is used to avoid searching failures during fluid and solid identification. This method yields a topology-free immersed boundary, which particularly suits flow simulations of highly complex geometries. Difficulties generally arise when generating the calculation grid for these scenarios. This method allows dirty data to be handled without any preparatory treatment work to simplify or clean-up the geometry. This method is also applicable to the coherent structural turbulence model employed in this study. The verification cases, used in conjunction with the second-order central-difference scheme, resulted in first-order accuracy at finer resolution, although the coarser resolution retained second-order accuracy. This method is fully parallelized for distributed memory platforms. In this study, the accuracy and fidelity of this method were examined by simulating the flow around the bluff body, past a flat plate, and past dirty spheres. These simulations were compared with experimental data and other established results. Finally, results from the simulation of practical applications demonstrate the ability of the method to model highly complex, non-canonical three-dimensional flows. The countermeasure based on the accurate classification of geometric features has provided a robust and reasonable solution.

Research on Parametric Modeling and Digital Reproduction of Ancient Buildings on the Southern Silk Road

This paper takes the parametric modeling technology of ancient buildings on the Southern Silk Road as the research object, and conducts a more in-depth analysis of the types, forms, advantages, and shortcomings of parametric modeling in ancient building modeling with a wealth of cases to demonstrate profound theories in simple language. The parametric modeling of the dwellings of Bai ethnic group in Dali was used as a case for verification. This paper is a more in-depth research paper on the digital modeling of ancient buildings, which has positive reference significance for this kind of research and production.

Cross-code verification and sensitivity analysis to effectively model the electrothermal instability

This manuscript presents verification cases that are developed to study the electrothermal instability (ETI). Specific verification cases are included to ensure that the unit physics components necessary to model the ETI are accurate, providing a path for fluid-based codes to effectively simulate ETI in the linear and nonlinear growth regimes. Two software frameworks with different algorithmic approaches are compared for accuracy in their ability to simulate diffusion of a magnetic field, linear growth of the ETI, and a fully nonlinear ETI evolution. The nonlinear ETI simulations show early time agreement, with some differences emerging, as noted in the wavenumber spectrum, late into the nonlinear development of ETI. A sensitivity study explores the role of equation-of-state (EOS), vacuum density, and vacuum resistivity. EOS and vacuum resistivity are found to be the most critical factors in the modeling of nonlinear ETI development.