Actual Boundary Research Articles

Prescribed finite-time safe tracking control based on secure boundary protection method for nonlinear systems with unknown control gains

Aiming to the mutation of the actual output boundary, a prescribed finite-time safe tracking control problem is investigated for a class of nonlinear systems with unknown control gain in this paper. A secure boundary protection method (SBPM) and a new prescribed finite-time performance function (PFTPF) are proposed. The SBPM can construct automatically two adjustable secure boundaries, so that the system meets both the control performance prescribed by the PFTPF and the constraint of the secure boundaries. In order to solve the problem of the excessive jitter of control input caused by the mutation of the output constraint, a bidirectional filtering smoothing mechanism (BFSM) is proposed. The proposed method can effectively deal with the mutation of actual output constraint, and it is not necessary to predict the system output value to adjust the desired output trajectory. Finally, the effectiveness of this proposed method is verified by simulations.

Thermal transfer performance and flow instability analysis of direct steam generation for parabolic trough solar collectors

Parabolic trough solar direct-steam-generation (DSG) technology is the enabling technologies to achieve low carbon future. However, actual inlet boundary and flow boiling instabilities pose challenge to safe operation. In this paper, the coupled optical-thermal-flow pattern model for DSG loops is built utilizing conservation equations, separated flow model and Lagrangian method. The heat transfer performance, hydrodynamic characteristics and two-phase flow law of the loop are discussed under the coupled variation of direct radiation intensity (DNI), mass flow (m), inlet temperature (Tin) and inlet pressure (Pin). The correlation between multi-condition, thermodynamic characteristics and flow instability is analyzed. The results show that increasing Pin, Tin and DNI have almost no effect on the intermittent state. The percentage of annular flow only remained stable (about 84.8%) when the steam mass was 1. Increasing DNI and Tin did not effectively improve the flow heat transfer, while increasing Pin worsened the flow heat transfer and increased the probability that the annular flow would turn into stratified flow but could reduce the pressure drop and the fluid vapor-liquid density difference and stabilizes its hydrodynamic properties. The simultaneous increase in m not only weakens this effect and strengthens the heat transfer, but also permanently reduces the probability of stratified flow. The higher the Pin, Tin and DNI, the lower the flow instability of the DSG system. Manual operation is recommended to prevent the system having flow instability in the morning due to the lower solar radiation intensity and inlet temperature when the system is started in the morning.

The occurrence of coalbed methane in the depocentre of the Upper Silesian Coal Basin in the light of the research from the Orzesze-1 deep exploratory well

The Orzesze-1 exploratory well with a depth of 3708 m (TVD) was drilled in 2019–2020 in the depocentre of the Upper Silesian Coal Basin (USCB). The methane content in the coal seams has been tested to a depth of 2840 m and the sorption capacity of the coal to a depth of 2576 m. These are the deepest measurements in the USCB so far. The vertical distribution of methane content in the borehole shows two depth zones of interest, the first at a depth 883 m to about 1300 m (maximum methane content about 12 m3/t coaldaf) and another in the range of 1500–2840 m, that is, to the maximum measurement depth, so the actual lower boundary depth of this zone is unknown. The maximum methane content here exceeds 18 m3/t coaldaf at a depth of >2800 m. Both zones are separated by an interval of reduced methane content of about 5 m3/t coaldaf at a depth of approximately 1400 m. The gas composition is dominated by methane (∼90%), and the content of carbon dioxide increases to approximately 15% at a depth of >2300 m. The methane-bearing zone at ∼900–1300 m corresponds to the zone of high- and medium-volatile bituminous coal (second coalification jump), while the highest methane content at a depth of >2800 m was determined in anthracite. The methane sorption capacity of the coal seams oscillates between 16 and 40 m3/t coaldaf with a maximum in anthracite at a depth of >2800 m, where the temperature of the rock approaches 100 °C and the deposit pressure exceeds 28 MPa. The highest sorption capacity in anthracite results from its inner structure characterised by the predominance of ordered aromatic lamellas and the dominance of vitrinite macerals (>70%), which contain coal micropores accumulating adsorbed methane. The comparison of the sorption capacity of the tested coal and the measured methane content displays undersaturation of 11–59%, however, due to significant gas content in the deep zone (depth > 1500 m), the drilling area can be considered as a prospect for further exploration and development of coalbed methane (CBM).

A Convexity-Preserving Level-Set Method for the Segmentation of Tumor Organoids.

Tumor organoid cultures play a crucial role in clinical practice, particularly in guiding medication by accurately determining the morphology and size of the organoids. However, segmenting individual tumor organoids is challenging due to their inhomogeneous internal intensity and overlapping structures. This paper proposes a convexity-preserving level-set segmentation 4 model based on the characteristics of tumor organoid images to segment individual tumor organoids precisely. Considering the predominant spherical shape exhibited by organoid growth, we propose a level-set model that includes a data-driven term, a curvature term, and a regularization term. The data-driven term pulls the contour to the vicinity of the boundary; the curvature term ensures the maintenance of convexity in the targeted segmentation, and the regularization term controls the smoothness and propagation of the contour. The proposed model aids in overcoming interference from factors such as overlap and noise, enabling the evolving curve to converge to the actual boundary of the target accurately. Furthermore, we propose a selectable and targeted initialization method that guarantees precise segmentation of specific regions of interest. Experiments on 51 pancreatic ductal adenocarcinoma organoid images show that our model achieved excellent segmentation results. The average Dice value and computation time are 98.81±0.48% and 20.67 s. Compared with the C-V and CPLSE models, it is more accurate and takes less time.

Experimental Analysis of Heat Transfer Post Quenching of Medium Carbon Steel

<div>Transient temperature analysis is involved in the thermal simulation of the heat treatment process, in which the hot metal temperature changes with respect to time from an initial state to the final state. The critical part of the simulation is to determine the heat transfer coefficient (HTC) between the hot part and the quenching medium or quenchant. In liquid quenching, the heat transfer between the hot metal part and water becomes complicated and it is difficult to determine HTC. In the current experimentation a medium carbon steel EN 9 rod with a diameter of 50 mm and length 100 mm was quenched in water and ethylene glycol mixture with different concentrations. A part model was created; meshed and actual boundary conditions were applied to conduct computational fluid dynamics (CFD) analysis. In order to validate CFD analysis the experimental trials were conducted. Experimental results showed a reduced cooling rate for the specimen, and also a reduction in heat-carrying capacity of the mixture, which is attributed to the addition of ethylene glycol.</div>

Semi-analytic modeling and experimental verification of arbitrary aero-engine complex spatial pipeline

In-depth research is imperative for complex spatial pipelines with fluid-structure interaction. A comprehensive and universal three-dimensional semi-analytical modeling method is first established for complex fluid-conveying spatial pipelines under the base excitation with arbitrary connections and configurations under different boundary conditions. The virtual spring technology is used to connect the straight and curved pipeline segments with spatial angles and simulate boundary conditions. For a thorough analysis, the actual stiffness of the bracket-clamp system is experimentally measured for the first time. The multi-level coupling dynamic model of part, component, and system levels under actual boundary conditions is established. An efficient method for solving the fluid-structure coupling pipeline system dynamics considering the base excitation is proposed based on energy method. The mid-plane displacement function of the Fourier series is introduced and solved using the principle of modal superposition. Hammer impact modal experiments, ANSYS software and vibration response experiments are performed on spatial pipelines supported by flexible bracket-clamps; the numerical and experimental results support the semi-analytical results. The degenerate model is verified with the simple plane pipelines in other references, and the errors are less than 5 %. The proposed method exhibits broad applicability and generalizability, making it suitable for various configurations and boundary conditions.

Numerical and theoretical approach to evaluate the clamping force and the interlayer gap extent during drilling of stacked materials

In the aeronautical industry, one-shot drilling of stacked materials is a widely adopted and established solution. However, ongoing discussions persist, particularly regarding the issue of interlayer gap formation that arises when two or more unsealed materials are drilled together. This study aims to present a simplified and reproducible theoretical model based on the equation of the elastic curve applied to structural schemes that discretize and describe the interlayer gap phenomenon in the drilling process. The model is designed to estimate the extent of the interlayer gap phenomenon and predict the clamping force required for its reduction when an end-effector is employed as a clamping device during the drilling of stacked sheets. Experimental and finite element analyses were conducted to validate the results of the proposed theoretical model. Each model was developed and applied to a real structural unit of a fuselage panel, considering actual boundary conditions in terms of structural constraints and geometric features of the assembly. The results obtained in this study demonstrate that the proposed one-dimensional theoretical model consistently aligns with experimental and numerical observations obtained through finite element analysis. This offers an effective and readily implementable solution in an industrial context as a tool for sizing the clamping force exerted by a clamping device.

Numerical investigation on knock intensity, combustion, and emissions of a heavy-duty natural gas engine with different hydrogen mixing strategies

With the continuous development of hydrogen energy technology, mixing hydrogen has become a potential method to enhance the performance of natural gas engines and reduce emissions. Aiming to offer guidance for optimizing strategies for mixing hydrogen from the perspectives of knock control and thermal efficiency enhancement, a three-dimensional model of a commercial heavy-duty natural gas engine is constructed based on the actual boundary conditions from a high load bench test. In this study, simulations were conducted under conditions where the hydrogen volume fraction ranged from 0% to 40%. The study explored the effects of two injection strategies, port fuel injection of hydrogen-enriched natural gas (PFI) and port fuel injection of natural gas combined with direct injection of hydrogen into the cylinder (PFI + DI), on engine knocking, performance, and emissions. Results indicate that for various injection strategies, there is an increasing trend in knock intensity (KI) with the higher hydrogen mixing ratio. When the hydrogen volume fraction exceeds 20%, the timing of direct hydrogen injection significantly affects KI. This effect is mainly caused by the distribution of unburned hydrogen at the knock onset crank angle (KOCA). Compared to other injection strategies, the PFI + DI strategy when the direct hydrogen injection time at 120°CA BTDC results in a high concentration of hydrogen near the spark plug at the ignition moment, combined with good mixture uniformity in the cylinder. This leads to the shortest CA0-10 and CA10-90, and achieves a maximum indicated thermal efficiency (ITE) of 44.68% under 20% hydrogen volume fraction. Compared to the original natural gas engine, the ITE increased by 2.9% and the NOx emissions increased by 166%, while the HC and CO emissions decreased by 88% and 53%.

Lightweight steering equipment based on prestressed modal analysis

As the key component to control the driving direction of the vehicle, the steering device always bears large vibration and load. In order to improve structural performance and reduce costs, a multi-objective optimization method based on the results of prestressed modal analysis was proposed, which can achieve significant lightweight and cost-effectiveness improvement. Based on the principle and working characteristics of the steering device, the minimum value of mass, minimum value of maximum stress, maximum value of equivalent stiffness were set as optimization objectives. Through finite element analysis, the prestressed modal module was constructed, and the strength and modal characteristics of the steering device were obtained. In order to verify the accuracy of prestressed modal analysis, the vibration testing experimental platform was built in a non free state. The excitation and response signals can be obtained through sensors and data acquisition devices and used as input and output data. According to the comparative analysis of simulated vibration modes, it can be concluded that the coupling analysis of strength and mode is more in line with actual boundary conditions and has high reliability. The DOE (Design of Experience) method was adopted to construct discrete corresponding values between design variables and optimization objectives based on the results of prestressed modal analysis. In order to better evaluate the cost-effectiveness of lightweight, a comparative analysis was conducted on the results of primary and secondary lightweight. The results show that the prestressed modal analysis method can achieve good dynamic analysis accuracy. Without reducing strength and equivalent stiffness, the mass of the steering device can be reduced by 14 %, achieving high economic benefits.

Optimal surrogate boundary selection and scalability studies for the shifted boundary method on octree meshes

The accurate and efficient simulation of Partial Differential Equations (PDEs) in and around arbitrarily defined geometries is critical for many application domains. Immersed boundary methods (IBMs) alleviate the usually laborious and time-consuming process of creating body-fitted meshes around complex geometry models (described by CAD or other representations, e.g., STL, point clouds), especially when high levels of mesh adaptivity are required. In this work, we advance the field of IBM in the context of the recently developed Shifted Boundary Method (SBM). In the SBM, the location where boundary conditions are enforced is shifted from the actual boundary of the immersed object to a nearby surrogate boundary, and boundary conditions are corrected utilizing Taylor expansions. This approach allows choosing surrogate boundaries that conform to a Cartesian mesh without losing accuracy or stability. Our contributions in this work are as follows: (a) we show that the SBM numerical error can be greatly reduced by an optimal choice of the surrogate boundary, (b) we mathematically prove the optimal convergence of the SBM for this optimal choice of the surrogate boundary, (c) we deploy the SBM on massively parallel octree meshes, including algorithmic advances to handle incomplete octrees, and (d) we showcase the applicability of these approaches with a wide variety of simulations involving complex shapes, sharp corners, and different topologies. Specific emphasis is given to Poisson’s equation and the linear elasticity equations.

Method of virtual sources using on-surface radiation conditions for the Helmholtz equation

We develop a novel method of virtual sources to formulate boundary integral equations for exterior wave propagation problems. However, by contrast to classical boundary integral formulations, we displace the singularity of the Green’s function by a small distance h>0. As a result, the discretization can be performed on the actual physical boundary with continuous kernels so that any naive quadrature scheme can be used to approximate integral operators. Using on-surface radiation conditions, we combine single- and double-layer potential representations of the solution to arrive at a well-conditioned system upon discretization. The virtual displacement parameter h controls the conditioning of the discrete system. We provide mathematical guidance to choose h, in terms of the wavelength and mesh refinements, in order to strike a balance between accuracy and stability. Proof-of-concept implementations are presented, including piecewise linear and isogeometric element formulations in two- and three-dimensional settings. We observe exceptionally well-behaved spectra, and solve the corresponding systems using matrix-free GMRES iterations. The method is implemented for problems with known analytical solutions for comparison. We conclude that the proposed method leads to accurate solutions and good stability for a wide range of wavelengths and mesh refinements.

Performance of high-concentration photovoltaic cells cooled by a hybrid microchannel heat sink

The electrical performance and equipment lifetime of high-concentration photovoltaic cells depends heavily on efficient cooling. In this paper, we applied a hybrid configuration to the cooling of a high-concentration photovoltaic cell, an innovative pattern derived from a comprehensive study on the combination of oblique microchannel and micro pin fin. Results from this study found that an elliptical pin fin pattern conforming with streamlines most effectively removed heat flux with a Nusselt number of 65.44 at a Reynolds number 1250. Then, the performance evaluation of a photovoltaic cell with a concentration ratio of 1000 was carried out on the hottest day of each season in Shiraz under actual boundary conditions. With an average flow rate of 30 ml/min in the spring, the implementation of this hybrid design resulted in the photovoltaic cell achieving an electrical efficiency of 40.16 while still maintaining a constant surface temperature of 301 K. Unlike a straight microchannel, which failed to maintain a constant cell temperature throughout summer’s hottest hours, this hybrid configuration succeeded in sustaining cooling with an average flow rate of 90 ml/min. In the winter and autumn, the pump’s average power consumption required for cooling was about 25 and 38 mW, respectively. Moreover, the maximum output electrical power in the summer was 2.8 W, with pumping power contributing to 1500 mW.

Paleozoic Decollement Displaced the Surface Trace of Iapetus Ocean Closure in Northern Appalachians

AbstractThe northern Appalachians record accretion of Laurentia‐ and Gondwana‐derived terranes to Laurentian margin during the formation of Pangea. Terrane bounding structures, key to reconstructing this history, are poorly understood at depth. We use teleseismic receiver functions to probe the crust beneath Appalachian terranes in Québec and Maine. We identify an eastward‐dipping intra‐crustal boundary extending beneath the trace of the Iapetus Ocean closure that separates the peri‐Laurentian Dunnage and the peri‐Gondwanan Gander terranes. Systematic fabric in rocks is a likely cause of anisotropic seismic properties associated with it. Depth and position associate this boundary with a previously identified décollement separating authochtonous Laurentian basement from rocks emplaced during Pangea's assembly. Neither the décollement nor the crust‐mantle boundary under our profile change beneath the surface trace of the Iapetus Ocean closure, suggesting that it has been transported to the northwest relative to the actual boundary between mantle lithospheres of former Laurentia and Gondwana.

Thermodynamic analysis of Powell-Eyring-blood hybrid nanofluid through vertical stretching sheet with interface slip and melting heat

The present endeavor investigates the significance of entropy production due to stagnation point flow of hybrid nanofluid through a vertical stretchable surface. The system irreversibility arises due to fluctuation of temperature between mainstream and interface. At the surface of the sheet, the effects of slippage and melting are considered. The buoyancy-obsessed flow of hybrid mixture is exposed to Lorentz forces and thermal radiation. The mixture is created with the infusion of Iron and magnesium nanoparticles in Powell-Eyring fluid, which reassemble the blood features. The principal conservation equations (momentum and energy) are modified with the deployment of Tiwari-Das model. The resulting blood mixture demonstrates the features of shear thinning fluids. The prevailing boundary layer equations are turned into a system of ordinary differential equations by applying certain modifications, which are solved numerically by a Keller-Box approach for actual boundary conditions. Among the most intriguing results is that the volumetric loading of iron nanoparticles, melting phenomena, and slip provide a substantial thermal improvements. The flow of blood detract with escalation of melting and slippage at the boundaries. The effects of buoyancy assistance escalates the blood flow. Enlargement in viscosity parameter reduces the fluid viscosity and reduces the fluid drift. The effects of viscoelastic parameter are conflicting for velocity and temperature. The thermal profile escalates with increase in magnetic parameter. The production of entropy increases with enhanced Lorentz and buoyancy forces while diminished with slip and melting effects. The consequences of Bejan against theses parameters are conflicting. The frictional coefficient detract with high melting effects, while the results for energy transport coefficient are contrary. The influence of Iron are significant because of denser density.

Stability of Steel Columns with Concrete-Filled Thin-Walled Rectangular Profiles

This paper provides a numerical and experimental analysis of global stability of axially compressed columns made of thin-walled rectangular concrete-filled steel tubes (CFSTs), with the consideration of initial geometric imperfections. The presented work introduces the theory of stability and strength of composite structural members subjected to axial compressive force. Moreover, a numerical calculation method for the determination of column resistance under axial load is presented, taking into account the influence of second-order effects that are considered in the European standard for the design of such members. This paper also presents the method of creating 3D models using the ABAQUS software, numerical analysis, and comparison of the obtained numerical results with experimental tests. In addition to the actual boundary and load conditions, the real properties of the used materials were also taken into account during the creation of 3D models. The actual properties of the used materials were obtained experimentally. Based on the obtained results and their comparison, several new findings and proven facts about the design and assessment of axially compressed columns made of thin-walled rectangular steel tubes filled with concrete are presented in the conclusions of the paper.

A compatible boundary condition-based topology optimization paradigm for static mechanical cloak design

We propose a novel compatible boundary condition-based topology optimization formulation for realizing static mechanical cloaking of linear elastic structures. The key idea is to make the actual boundary conditions along the exterior of the cloaking region consistent with the reference boundary conditions, including the displacement and the nodal force, by designing the cloak structure solely. This compatible boundary condition-based optimization paradigm is not only applicable to various shaped voids (e.g., circle, ellipse, star, Mickey, square, “DUT” logo) and diverse loading conditions (e.g., pressure-sliding, biaxial-stretching, linear-stretching, random-stretching, stretching-sliding) but also demonstrates insensitivity to element quantities and slight variations of external load, ensuring consistent and robust elastostatic cloaking performance. Additionally, adopting the Moving Morphable Voids (MMV) method guarantees the optimized structures have the merits of explicit geometric boundaries and easy fabrication. Numerical examples and experimental validation demonstrate the effectiveness of the proposed approach. The present approach can be easily extended for cloak design in three dimensions and multiphysics.

Quantitative structural uncertainty analysis of composite honeycomb sandwich using a feedback neural network

The quantification of margins and uncertainty (QMU) method was applied using a neural network to inversely determine the strength boundary of a composite honeycomb sandwich structure considering the random uncertainty of its elastic modulus, shear modulus, tensile strength, compressive strength, and shear strength in the warp and fill directions, and panel thickness. An application framework for the deterministic quantitative analysis of strength was proposed based on margin design theory, combining the strength problem with the quantitative analysis of uncertainty. First, the failure criterion of the structure was modeled based on the progressive damage principle using ABAQUS. Next, Latin hypercube sampling was applied to simulate the stochastic uncertainty of the structural parameters, and the resulting sample sets were input into ABAQUS to calculate the corresponding structure lateral bearing capacities. These results were considered to collectively represent the actual strength boundary of the composite structure. A feedback neural network was subsequently trained on these ABAQUS data to obtain the functional mapping relationship between the parameters and capacity. The capacity obtained using this relationship was multiplied by an empirical safety factor to serve as the theoretical strength boundary. Finally, the QMU method was applied using cumulative distribution functions of the theoretical and actual strength boundaries to calculate the confidence factor and thereby evaluate the reliability of the composite honeycomb sandwich structure.

A regularized projection immersed boundary method for smooth boundary forces

The projection immersed boundary method calculates boundary forces (i.e., surface stresses) from velocity constraints without introducing additional timestep restrictions. However, the projection method generally fails to produce boundary forces that converge to the actual physical surface stresses when the grid is refined. In most cases, the boundary forces show spurious oscillation. This spurious oscillation is particularly violent when the Lagrangian-to-Eulerian grid spacing ratio is small. As a result, the traditional projection method may encounter problems in fluid-structural interaction (FSI) simulations where accurate boundary forces are needed. To address these challenges, we propose a regularized projection method using (generalized) Tikhonov regularization techniques. The regularized projection method yields smoother boundary force solutions that closely approximate the actual boundary force distributions for a wider range of Lagrangian-to-Eulerian grid spacing ratios. The boundary force shows first order convergence with properly chosen parameters. We demonstrate the effectiveness and accuracy of our approach through various test cases.

Thermal Field Simulation and Thermal Capacity Influence Factor Analysis of Disc Brake Based on Thermal-structure Coupling

The matching and heat dissipation capacity of the brake have an important impact on the braking performance of the vehicle. During braking, most of the driving kinetic energy of the vehicle is converted into the internal energy of the brake disc through friction heat generation, resulting in a quick rise in the temperature of the brake disc, thus causing a complex thermal-solid coupling problem. This paper takes the disc brake of a certain vehicle as the analysis object, establishes the finite element model of the disc brake through hypermesh, and analyzes the distribution characteristics of the contact pressure between the friction pad and the brake disc under clamping and torsion braking behaviors. A thermal-solid coupling simulation analysis method considering the actual heat flow and heat transfer boundary of the brake disc is proposed. Compared with the temperature field of the bench test, the simulation accuracy reaches 97%. Finally, three types of brake discs with point rib, rotation rib and straight rib are designed, and the influence of brake disc thickness, shape and number of ventilation rib on the thermal capacity of brake disc is analysed. It provides guidance for the structural design of brake discs and can replace partial tests and shorten the brake disc development cycle.

Coral reef applications of Landsat-8: geomorphic zonation and benthic habitat mapping of Xisha Islands, China

ABSTRACT Being one of the most significant and valuable coral reef systems in the South China Sea, the Xisha Islands has undergone rapid transformation due to increasing stressors from human impacts and climate change in recent years. However, as indispensable information for coral reef monitoring and management, the detailed reef extent, geomorphic zonation, or benthic composition of the Xisha Islands is not well documented. Considering limited access to the Xisha Islands, the rapid development of optical remote sensing technology provides us with a feasible mean for coral reef observation. This study adopted a water depth substitution index – probabilistic inundation (PI) – combined with depth-invariant index (DII) to achieve reef extent exploration, geomorphologic and benthic habitat types classification with unsupervised classification algorithms based on Landsat-8 time-series satellite data. Compared with two open-access datasets, the extent of each independent reef extracted from PI exhibited higher similarity with the actual boundary conditions displayed in RGB (Red-Green-Blue) composite images from Landsat-8. Based on PI and derived slope, we obtained geomorphic zonation classification results, and similarly benthic compositions were retrieved based on PI, DII, and reflectance. The overall accuracy of geomorphic zonation and benthic habitat classification results were 72% and 86%, respectively. We also interestingly discovered that corals of the Xisha Islands may be capable of an ability to resist chronic heat stress as a growth trend of reef area after two successive stress events in 2014–2015 were observed at most reefs. The proposed mapping framework of this study provides a repeatable and flexible scheme in depicting the comprehensive situation of coral reefs at Xisha Islands based only on publicly available remote sensing data without complicated pre-set parameters, which could be easily extended to coral reef research around the world. Simultaneously, the findings also provide requisite information supporting the sustainable management and conservation of coral reef ecosystems in the Xisha Islands.