Flexible Boundary Research Articles

A Quantitative Study of Micro and Macro Mechanical Parameters Based on the PFC3D Flat-Joint Model.

The flat-joint model, which constructs round particles as polygons, can suppress rotation after breakage between particles and simulate more larger compression and tension ratios than the linear parallel-bond model. The flat-joint contact model was chosen for this study to calibrate the rock for 3D experiments. In the unit experiments, the triaxial unit was loaded with flexible boundaries, and the influence of each microscopic parameter on the significance magnitude of the macroscopic parameters (modulus of elasticity E, Poisson’s ratio ν, uniaxial compressive strength UCS, crack initiation strength σci, internal friction angle φ and uniaxial tensile strength TS) was analysed by ANOVA (Analysis of Variance) in an orthogonal experimental design. Among them, Eƒ, kƒ has a significant effect on E; Cƒ and kƒ have a significant effect on ν; Cƒ, σƒ and kƒ have a significant effect on UCS; Cƒ; σƒ and Eƒ have a significant effect on TS; Rsd has a significant effect on σci; and φf, Eƒ, kƒ, μƒ, and σƒ have a significant effect on φ. Regressions were then carried out to establish the equations for calculating the macroscopic parameters of the rock material so that the three-dimensional microscopic parameters of the PFC can be quantitatively analysed and calculated. The correctness of the establishment of the macroscopic equations was verified by comparing the numerical and damage patterns of uniaxial compression, Brazilian splitting, and triaxial experiments with those of numerical simulation units in the chamber.

Probabilistic Operation of the Microgrids Including Active Loads and Distributed Generation Constrained to Flexibility and Reliability Indices

This paper presents a flexible-reliable operation strategy for clean microgrids (MGs) consisting of power sources, energy storage systems (ESSs), and responsive loads. The proposed strategy attempts to provide the minimum expected operating cost for the MG, power sources, predicted pollutant emission, and expected energy not-supplied (EENS) because of an N − 1 event considering different applications. The objective function of the problem is subject to several constraints including AC optimal power flow equations, flexibility and reliability boundaries, and model of power sources and active loads. The Pareto optimization based on the weighted sum method is then incorporated to obtain a single-objective model. Probabilistic programming is also used to model the uncertainties of load, renewable energy, electrical energy price, and MG equipment accessibility. The ant-lion and crow search algorithms are merged to solve the problem and find a reliable optimal solution. A standard MG is employed to test the proposed strategy and indicate its capability in enhancing technical and economic indicators of the MG while ensuring that the MG is clean.

Viscoacoustic wave simulation with the lattice Boltzmann method

The lattice Boltzmann method (LBM), widely used in computational fluid mechanics, is introduced as a novel mesoscopic numerical scheme for viscoacoustic wavefield simulation. Through mathematical derivation, a mapping model between the relaxation time of LBM and the quality factor based on the Kelvin-Voigt model is established, which provides a theoretical background for the comparison of the viscoacoustic wavefields obtained, respectively, by LBM and finite-difference method (FDM) formulated on the traditional wave equation. By defining the transmission and reflection coefficients and adopting a Newton interpolation algorithm to modify the streaming process of the LBM, we have extended the conventional LBM to simulate the wavefields in complex media with acceptable accuracy. A 2D homogeneous model, two 2D layered models, and the modified Marmousi model are tested in the numerical simulation experiments. The simulation results of LBM are comparable to those of FDM, and the relative errors are all within a reasonable range, which can verify the effectiveness of the forward modeling kernel. The modified LBM offers a new numerical scheme in seismology to simulate viscoacoustic wave propagation in complex media and even in porous media considering its flexible boundary condition and high discrete characteristic.

A pragmatist perspective on front-end project organizing: The case of refurbishment of the Palace of Westminster

This study examines how actors organized collective efforts to initiate the project and navigated their way forward, even though the ultimate outcome was not clearly defined. To address this question, we explore the potential of the philosophical tradition of pragmatism. This approach foregrounds duality, recursiveness and temporality of collective activities and offers a new and compelling way to understand and address the challenges actors face in organizing and managing the front-end. By accounting for both the situatedness of actions in the wider social and relational contexts, and by connecting the flow of present experience to the interpretations of the past and future, pragmatism holds the potential for integrating theory the actuality of lived experience in its continuous unfolding while accounting for actors’ transformative agency. By drawing on a real-time longitudinal study of conception of the program of the Restoration and Renewal (R&R) of the Palace of Westminster, we show how participants face the challenge of understanding and managing complex tensions that continually arise due to a duality of mobilization (between seeking consensus and expanding divergent possibilities) and a duality of transformation (between forming a bold vision of the future and translating abstract goals into concrete actions). To tackle the challenges, participants create strategic accounts that are stable enough to be practically feasible in current circumstances, but also sufficiently adaptable to pursue future possibilities in ways that challenge prevailing approaches. By showing how participants cope with these challenges by creating spaces of experimentation and constructing flexible boundaries this study contributes to the literature on management of project's front-end.

Efficient contour-based annotation by iterative deep learning for organ segmentation from volumetric medical images

PurposeTraining deep neural networks usually require a large number of human-annotated data. For organ segmentation from volumetric medical images, human annotation is tedious and inefficient. To save human labour and to accelerate the training process, the strategy of annotation by iterative deep learning recently becomes popular in the research community. However, due to the lack of domain knowledge or efficient human-interaction tools, the current AID methods still suffer from long training time and high annotation burden.MethodsWe develop a contour-based annotation by iterative deep learning (AID) algorithm which uses boundary representation instead of voxel labels to incorporate high-level organ shape knowledge. We propose a contour segmentation network with a multi-scale feature extraction backbone to improve the boundary detection accuracy. We also developed a contour-based human-intervention method to facilitate easy adjustments of organ boundaries. By combining the contour-based segmentation network and the contour-adjustment intervention method, our algorithm achieves fast few-shot learning and efficient human proofreading.ResultsFor validation, two human operators independently annotated four abdominal organs in computed tomography (CT) images using our method and two compared methods, i.e. a traditional contour-interpolation method and a state-of-the-art (SOTA) convolutional network (CNN) method based on voxel label representation. Compared to these methods, our approach considerably saved annotation time and reduced inter-rater variabilities. Our contour detection network also outperforms the SOTA nnU-Net in producing anatomically plausible organ shape with only a small training set.ConclusionTaking advantage of the boundary shape prior and the contour representation, our method is more efficient, more accurate and less prone to inter-operator variability than the SOTA AID methods for organ segmentation from volumetric medical images. The good shape learning ability and flexible boundary adjustment function make it suitable for fast annotation of organ structures with regular shape.

How can urban administrative boundary expansion affect air pollution? Mechanism analysis and empirical test

As a momentous policy tool for spatial management, urban administrative boundary expansion (UABE) significantly impacts resource reorganization and development modes. However, the environmental effects of UABE are easily ignored. Whether UABE can also impove the environmental quality in addition to its economic effects remains to be answered. To fill this gap, we took the city-county merger policy (CCMP) in China as quasi-experimental evidence and empirically investigated the impacts of CCMP on air pollution based on the difference-in-difference method. The impact mechanisms were also analyzed from a whole-process perspective. The results demonstrate that, apart from expanding the urban scale, UABE can improve urban air quality as well. Further analysis shows that the positive effect is mainly realized by source control and process management, rather than end-of-pipe treatment. Besides, the impacts of UABE on air pollution exhibit obvious spatial heterogeneous characteristics. We also reported that the environmental effects of UABE are largely dependent on governmental control, rather than market factors. According to the results above, flexible administrative boundary adjustment, strict government regulations, and effective market systems are required to realize the dual goals of environmental improvement and space optimization.

Discrete element analysis of the influence of compaction quality on mechanical properties of rockfill materials

To evaluate the influence of compaction quality on the mechanical properties of rockfill materials, conventional triaxial compression tests are numerically carried out based on the convex polyhedron Discrete Element Method (DEM). A DEM model of rockfill materials considering compaction quality and particle shape is proposed together with a flexible boundary algorithm. After the validity of the model is verified with laboratory test results, a series of numerical experiments are carried out for rockfill materials with different compaction qualities to determine the distribution and variation of mesostructure parameters, e.g., the particle rotation, the contact number, and the contact force. The results show that increasing the compaction quality of rockfill materials can strengthen the interlocking among the rockfill particles, reduce the proportion of floaters, improve the supporting role of small particles in the force chain, and restrict the rotation of small particles, which are macroscopically characterized by the enhancement of the strength and stiffness. It is also found that although the compactness exhibits a non-negligible effect on the variation and distribution rules of the rotation, the contact number, and the contact force, these impacts are gradually weakened with the loading process and almost disappear when the critical state is reached.

Mode-matching analysis of flexural trifurcated waveguide with porosity effects

The strong potential of porous media to absorb and change an incident sound wave interacting with a fluid that fills the pores of the material has sparked interest in their acoustic properties. Therefore, the current study describes the energy distribution and absorption mechanism of a dominating acoustics wave mode traveling out of the mouth of a semi-rigid waveguide. The underlying structure is tuned due to a trifurcated inlet region with flexible outer boundaries. In the outlet region of the duct, porosity effects for different porous materials are encountered. The continuity of pressure and velocity through the interface is used to match the scattering orthogonal and non-orthogonal duct modes. Mode matching techniques are used to compute the reflection and transmission coefficients. The resulting infinite linear algebraic systems are truncated and numerically solved. Of particular interest, the effects of considering different porous materials are observed and analyzed thoroughly. The obtained solution is confirmed to satisfy all geometrical conditions as well as the law of conservation of energy by mathematical and graphical representation.

Research on the Macro-Mesoscopic Response Mechanism of Multisphere Approximated Heteromorphic Tailing Particles

Abstract The shape of tailing particles is essential factors of their macroscopic mechanical properties. Scholars have studied the effects of controllable factors, such as loading method, confining pressure, and strain rate, on the strength of tailing sand. However, research on the tailing particle structure and shape through laboratory tests has proved to be difficult due to the uncertain and discrete tailing particle distribution. Thus, the macro-mesoscopic response of heteromorphic tailing particles is rarely investigated. In this paper, the macro-mesoscopic response of heteromorphic tailing particles is studied using multisphere approximation, and numerical simulation of triaxial tests on the particles is conducted. Nonlinear evolution patterns of porosity, internal friction angle, and cohesion of heteromorphic tailing particles with the variation of angularity were investigated using the flexible boundary program developed in this study, which revealed the intrinsic relationship between the mesostructure evolution mechanism and the macroscopic engineering characteristics of heteromorphic tailing particles. The research results showed that (1) changes in angularity led to tailing particle rearrangements and, in turn, porosity changes. With increased angularity and confining pressure, particle sphericity decreased, and the deviatoric and peak stress increased accordingly. In the meantime, the softening was more significant as the peak stress was exceeded, while the cohesive force generally increased. (2) With fixed particle shape and angularity, the internal friction angle decreased slightly as the effective confining pressure increased. (3) In the shearing process, the simulated contact force chain evolution of tailing particles with different shapes was similar. The disordered contact force chains gradually undergo directional connection, i.e., the increased confining pressure reduced the number of free tailing particles and increased the number of stressed particles. (4) The triaxial stress-strain and peak stress in rigid boundary simulations under different confining pressures were slightly lower than those in the flexible boundary simulations. However, the difference was insignificant, indicating the good feasibility and reasonability of rigid boundary simulations for the macroscopic mechanical behaviors in triaxial tests. The research results could offer more direct insights into the macro-mesoscopic response and mechanical mechanisms of nonspherical particles and provide references for the simulation of tailings at the microscopic levels.

Numerical Computation of the Vibroacoustic Behaviour of an Oil-Immersed Power Transformer

This paper presents a numerical calculation method that allows for the simulation of the mechanical and acoustic behaviour of a transformer tank. In order to simulate the vibroacoustic behaviour of an oil-immersed power transformer, an acoustic-mechanical coupled three-dimensional finite-element method model of a transformer was setup. The simulation is performed in the frequency domain at frequencies adjacent to the driving frequency. A vibration source closely resembling the actual active part of the transformer is placed within the oil-filled tank that mechanically represents an acoustic cavity with flexible steel boundaries. Via a fluid-structure interface the vibration source generates acoustic waves in the oil medium which partly transmit through the tank wall structure and partly reflect within the steel transformer tank again via a fluid-structure interface. The vibrating tank is then coupled with the external acoustic air medium and the corresponding sound field is calculated and evaluated according to IEC 60076-10. This numerical computation allows for the direct calculation of the complete vibrational and acoustic behaviour of a transformer.

Style-Guided and Disentangled Representation for Robust Image-to-Image Translation

Recently, various image-to-image translation (I2I) methods have improved mode diversity and visual quality in terms of neural networks or regularization terms. However, conventional I2I methods relies on a static decision boundary and the encoded representations in those methods are entangled with each other, so they often face with ‘mode collapse’ phenomenon. To mitigate mode collapse, 1) we design a so-called style-guided discriminator that guides an input image to the target image style based on the strategy of flexible decision boundary. 2) Also, we make the encoded representations include independent domain attributes. Based on two ideas, this paper proposes Style-Guided and Disentangled Representation for Robust Image-to-Image Translation (SRIT). SRIT showed outstanding FID by 8%, 22.8%, and 10.1% for CelebA-HQ, AFHQ, and Yosemite datasets, respectively. The translated images of SRIT reflect the styles of target domain successfully. This indicates that SRIT shows better mode diversity than previous works.

Stability conditions of multiple-relaxation-time lattice Boltzmann model for seismic wavefield modeling

In general, the wave equation can be taken to characterize the seismic wavefield propagation from a macroscopic perspective. The lattice Boltzmann method (LBM) is an alternative strategy to model seismic wavefields on mesoscopic scale. Due to its fully discrete nature and flexible boundary processing, LBM therefore has attracted increasing attention in seismology. The stability problem of LBM is a critical aspect in its seismic wavefield simulation. We give the steps of employing LBM for seismic wavefield modeling and some comparisons between LBM and the wave equation. Further, we derive theoretically the stability conditions of Bhatnagar-Groos-Krook (BGK) LBM and multiple-relaxation-time (MRT) LBM. Although the stability adjustment of MRT-LBM is more flexible, it is rather difficult to obtain an analytical solution concerning its relaxation parameters and other factors. In view of this, we first demonstrate that the stability and accuracy of MRT-LBM is superior to BGK-LBM to a certain extent by means of seismic wavefield modeling. Then, we investigate the individual effect of each relaxation parameter of MRT-LBM on the seismic waveforms. Most significantly, we construct the stability models for MRT-LBM only related to the relaxation parameters, based on the stability results of a large number of wavefield simulations in the homogeneous medium. Our stability models can well guide MRT-LBM for stable seismic wavefield modeling without considering other factors. Finally, we verify the correctness as well as the wide applicability of the proposed stability models by some simple layered media and modified Marmousi and BP models. The stability models may play a nice guiding role for further wavefield simulations based on MRT-LBM, especially for low-viscosity media.

Peristaltic mechanism of hydromagnetic Jeffrey fluid having variable thermal conductivity and slip conditions

In this study, we focus on the slip effects on the peristaltic unsteady flow of magnatohydromagnetic Jeffrey fluid in a flow passage with non-conducting and flexible boundary walls. The effect of the magnetic field with varying thermal conductivity is taken under the influence of heat transfer analysis. The dimensionless system of PDEs is solved analytically, and the obtained results are computed for the temperature, pressure drop, the axial pressure gradient, axial velocity, and then these results are discussed for different values of the physical parameters of our interest. For the stream functions, the contour plots are also obtained which indicates the exact flow behavior within the flow channel, and the effects of the physical parameters on Jeffery fluid within the flow channel are discussed briefly. Our results indicate that the heat transfer coefficient decreases with an increase in thermal slip and velocity slip parameters. Furthermore, it shows that the size of the trapped bolus is greater for the inclined magnetic field as compared to the transverse magnetic field.

PINN-FFHT: A physics-informed neural network for solving fluid flow and heat transfer problems without simulation data

In recent years, physics-informed neural networks (PINNs) have come to the foreground in many disciplines as a new way to solve partial differential equations. Compared with traditional discrete methods and data-driven surrogate models, PINNs can learn the solutions of partial differential equations without relying on tedious mesh generation and simulation data. In this paper, an original neural network structure PINN-FFHT based on PINNs is devised to solve the fluid flow and heat transfer problems. PINN-FFHT can simultaneously predict the flow field and take into consideration the influence of flow on the temperature field to solve the energy equation. A flexible and friendly boundary condition (BC) enforcement method and a dynamic strategy that can adaptively balance the loss term of velocity and that of temperature are proposed for training PINN-FFHT, serving to accelerate the convergence and improve the accuracy of predicted results. Three cases are predicted to validate the capabilities of the network, including the laminar flow with the Dirichlet BCs in heat transfer, respectively, under the Cartesian and the cylindrical coordinate systems, and the thermally fully developed flow with the Neumann BCs in heat transfer. Results show that PINN-FFHT is faster in convergence speed and higher in accuracy than traditional PINN methods.

Dynamics identification and stability analysis in turning of slender workpieces with flexible boundary constraints

The exact implementation of the turning stability analysis mainly depends on the realistic prediction model and reliable dynamical parameters. However, the workpiece located in the chuck-workpiece-tailstock dynamical system is generally regarded as a combination of a cantilever and a simply-supported beam. The effect of boundary conditions is ignored in the prediction of structural dynamics and stability limits. Hence, in this paper a model for slender workpieces with flexible boundary constraints is first built to improve the prediction accuracy of the turning stability. In this model, a two-dimensional (2D) compliance of the tool and part as well as the effect of the tool nose radius are incorporated in the dynamic force modeling, and the dynamical characteristic of slender workpieces in the chuck-workpiece-tailstock dynamical system is calculated according to the continuum theory. Then a novel strategy is proposed to identify the connection stiffness acting on the joint interface of the turning machine. According to the mathematical relation of workpiece dynamics induced by boundary conditions, a further theoretical derivation for the best selection of characteristic parameters, which is the critical part of the identification strategy, is developed on this basis. The optimal connection stiffness is determined by minimizing the deviation between the experimental and simulated values of characteristic parameters. The measured results of structural dynamics indicate that the connection stiffness identified from partial working conditions is also applicable to other working conditions. Finally, a series of turning experiments are conducted on this basis to verify the position-dependent stability limits considering flexible boundary constraints. The prediction result shows a good agreements with the experimental result. It proves that the proposed method has a unique advantage for the dynamics identification and stability analysis of the slender workpiece.

Flexible Boundary Multi-Microgrids Power Distribution Systems with Internet of Thing for System Efficiency Enhancement

Multi-microgrid power distribution systems are gaining attention in the smart grid era. Distributed energy resources, energy storage, as well as energy sharing and scheduling has a great potential to enhance multi-microgrid systems’ performance. This research develops an algorithm for optimal operation of various distributed energy resources in a flexible boundary multi-microgrid power distribution network, considering internet of things (IoT). The proposed algorithm used in this research can reduce power system operating costs, power, and energy losses and emissions, and ultimately increase the systems’ efficiency. A hybrid Particle Swarm Optimization-Tabu Search algorithm is developed for optimization purposes.

Examining Differences in the Binding Sites of Succinyl Transferases DapD and TabB

TabB and DapD are N‐succinyl transferases that succinylate tetrahydrodipicolinic acid (THDPA) during the biosynthesis of the natural product tabtoxin and lysine, respectively. Although TabB and DapD catalyze identical reactions, and are predicted to form homologous, trimeric left‐handed β‐helical structures, close examination of their sequences reveal that the three‐dimensional arrangements of functionality within their respective active sites diverge significantly. Further examination of the sequences and modeled structures of DapD and TabB suggest that they are representatives of distinct classes of THDPA N‐succinyl transferases, with a small number of amino acids that appear to distinguish “TabB‐class” from “DapD‐class” enzymes. The goal of this work was to test whether it was possible to “swap” one active site for the other within a single three‐dimensional scaffold. In total, we created sixteen DapD and TabB mutants. Four swapped amino acids in DapD for amino acids in TabB and vice versa with the goal of morphing one binding site into the other. The other twelve mutations replaced one amino acid for other similar, yet structurally distinct amino acids. The mutated plasmids were then transformed into E. coli and the corresponding TabB and DapD mutants were overexpressed and isolated. We tested the activities of these mutants via a colorimetric Ellman assay that detected the formation of the reaction coproduct CoASH. Initial results suggest that there is some plasticity within the TabB and DapD active sites, and future efforts are directed to exploring the boundaries of this catalytic flexibility.

ECO routing based on network flow method

In this paper, a new ECO routing approach to the problem of resolving pin inaccessibility on standard cells is presented. The conventional ECO routing approaches conceptually divide the rerouting path search problem for a set of target nets to rip-up and reroute into two interdependent tasks: (i) (Off-cell routing) repairing the routing path between the net terminal outside of the cell and the cell boundary and (ii) (On-cell routing) repairing the routing path between the cell boundary and the pin on the cell where they have conventionally performed tasks (i) and (ii) iteratively for each target net. Yet, there is no easy way to accurately predict the final result of task (ii) for all nets during task (i). In our approach, we place the primary importance on resolving pin inaccessibility on cells. Consequently, we perform on-cell routing for all ripped-up nets simultaneously to resolve the pin inaccessibility first by utilizing flexible cell boundary access points and then to adjust the sub-paths outside of the cell. For a number of benchmark circuits, it is shown that our approach of early consideration of entire on-cell routing is very effective, resolving the pin inaccessibility of 71.09% out of all nets for which a commercial ECO router has failed to find legal routes.

Placemaking of the dead in urban Rome

ABSTRACT The aim of this paper is to shed new light on the religious placemaking of the dead in the very dense and diverse metropolis of Rome in order to understand the role of the urban in the burial of the deceased in antiquity. In the Republican and Imperial periods in Rome, there is ample evidence of the impressive variety of sites and practices by which the dead were buried. However, the location of burial sites and the practices changed dynamically as they had to adapt not only to the growth of the city but also to new civic regulations, which were particularly focused on controlling public hygiene. The tension between the location of burial sites and their place biographies is made even more complex by the pomerium (sacred boundary) in Rome, an intangible and flexible boundary within which burials were forbidden. However, illegal and legal exceptions do exist. Therefore, the aim of this paper is not to provide an overview or classification of burial types, but to shed light on the role of the urban in influencing burial sites and rituals in order to identify where and how urban actors had to negotiate spaces and practices.

Land space optimization of urban-agriculture-ecological functions in the Changsha-Zhuzhou-Xiangtan Urban Agglomeration, China

Evaluating urban-agriculture-ecological space is useful in optimizing land space and high-quality socio-economic development. This study evaluated urban development and ecological protection in an urban agglomeration and delineated the ecological security pattern for the sustainable use of land spaces. Using the Changsha-Zhuzhou-Xiangtan (CZT) urban agglomeration as study area, system dynamics (SD) model, cellular automaton (CA), and artificial neural network (ANN) were utilized to simulate the variation trends of urban development space, ecological space, and urban agricultural space for 2019–2035 under different development scenarios (status-quo, economic-centric, environment-centric, and coordinated equilibrium). The highlights of results are as follows: (1) The combined effects of the economy, nature, accessibility, and spillover effects exerted significant impact on urban land expansion. Socio-economic variables and spillover effect constitute the main controlling factors of land space expansion. (2) The urban construction space of the CZT urban agglomeration would vary for the different development scenarios. During the simulation period, urban construction space in the study area would be 1572.06 km2 for the status-quo scenario, 1763.27 km2 for the economic-centric scenario, 1634.13 km2 for the environment-centric scenario, and 1668.69 km2 for the coordinated equilibrium scenario. (3) The growth boundary of the urban agglomeration was demarcated based on the spatial attributes, land-use functions, and clustering. The rigid growth boundary was estimated at 3686 km2, while the flexible growth boundary was estimated to be 1794.53 km2. These values can be used to guide planning, policies, and strategies for the orderly expansion of urban land in future development.