Contact Boundary Research Articles

SIMPLIFIED ADAPTIVE TRIANGULATION OF THE CONTACT BOUNDARIES OF THE DAM MODEL

To numerically solve the system of integral equations, it is customary to establish a discrete grid within each integration area. In the context of 3D modeling, these areas correspond to surfaces situated in space. The standard discretization technique employed for the computational domain is triangulation. This study addresses the integral equation system pertinent to the electrical tomography of dams. The structural model encompasses an embankment dam, the upstream and downstream water bodies, the dam's base, and a potential leakage region on the upstream side. An alternative configuration may be encountered in specific scenarios with no water downstream. Consequently, the model may incorporate up to nine distinct contact boundaries. Accordingly, the system of integral equations comprises an equivalent number of equations. Effectively resolving this system through numerical methods necessitates applying triangulation techniques to these diverse surfaces. While mathematical packages like Matlab offer triangulation functions, they may not fully address the specific demands of the problem. Additionally, the grid resolution should be heightened in proximity to key elements such as the sounding line, the supply electrode, and the various contact lines within the medium. These considerations transform the triangulation task into a distinct subtask within the numerical simulation of the resistivity tomography problem. In this paper, we provide our specific approach to this problem. The simplification of the triangulation algorithm is rooted in the predominant utilization of the two-dimensional geometric properties inherent to the object under study. For most contact boundaries, the triangulation is constructed layer by layer with a gradual modulation in triangle dimensions as one progresses from one layer to the next, orthogonal to the axis of the dam. Concerning the surface corresponding to the leakage area, cylindrical coordinates are used for surface parameterization. This approach enables partitioning the surface into discrete strata, facilitating a systematic, layer-by-layer grid construction. Additionally, points at the intersections of contact boundaries are integrated into the pre-existing triangulation by applying a standard function within the Matlab package. In the future, the mathematical modeling based on the Integral Equation Method with adaptive discretization will help incorporate real-time computations into information systems related to monitoring hydraulic structures.

REDUCTION OF HEAT GAINS TO GEOTHERMAL HEAT EXCHANGERS IN LONG-TERM OPERATION

Link for citation: Polovnikov V.Yu., Shelemekhova S.D. Reduction of heat gains to geothermal heat exchangers in long-term operation. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 9, рр. 18-24. In Rus. The relevance of the research is caused by the colossal energy potential of geothermal and petrothermal energy. It is designed to stimulate research and development in the field of geothermal technologies. The development of technologies for the use of geothermal and petrothermal energy in the Russian Federation is reduced by some circumstances. These main reducing factors are competition from traditional energy, problems with the legal framework and the lack of relevant areas of research and development. Currently, there is a backlog of Russia in the field of development of geothermal resources from the world level. The main aim of the study is to evaluate the effect of condensation in the design of a geothermal heat exchanger on the change in heat inflows to it. The object of the research is a typical design of a geothermal heat exchanger consisting of a metal pipeline and a cement casing. Methods. Numerical analysis of heat and mass transfer was executed with rational values of the grid parameters and the time integration step. The assessment of the reliability of the results of the work was carried out by testing on the example of heat transfer problems, the numerical methods used and elements of the developed algorithms for solving boundary value problems of heat and mass transfer, checking the conservatism of difference schemes, and comparing with known data. The finite difference method and the implicit difference scheme were used. The peculiarity of problem solving was the discontinuity of the thermophysical characteristics at the contact boundaries between the layers and the presence of nonlinearity in the boundary condition. Results. The authors have carried out the numerical study of the effect of steam condensation in the design of a geothermal heat exchanger on the reduction of heat inflows in the system under consideration. It was found that steam condensation leads to a decrease in heat gain by 4,55–31,19 %. It is shown that the use of relatively simple heat transfer models makes it possible to predict the change in heat inflows to a geothermal heat exchanger under conditions of steam condensation in its structure during long-term operation.

Strategy for Patterning Titania Dendrites by Gas-Solution Interaction at Droplet Surfaces.

Interaction of the solution droplet surface with gaseous components of the environment can lead to the formation of highly ordered patterns, such as dendrites. Here, we show that these structures can be spontaneously created during the open-air interaction of aqueous solution drop of titanium(III) salt with gaseous NH3 at the contact boundary thereof. The conditions have been identified under which radially ordered dendritic patterns can form on the surface of the TiCl3 solution droplet. The formation of these self-organized dendrite patterns can be attributed to the surface instability manifesting in Marangoni thermal flows in a droplet occurring during open-air fabrication. The composition of as-synthesized structures corresponds to coprecipitated crystalline NH4Cl and amorphous TiO2nH2O. After thermal treatment at 450 °C, TiO2 with the anatase crystal lattice is formed; meanwhile, the ordered dendrite patterns are preserved.

정서·행동 문제 관심군 고등학생의 게슈탈트 접촉경계혼란 요인

This study investigated the difference and relationship between Gestalt contact boundaryconfusion in high school students with emotional and behavioral problems. For the study, 58 inthe interest group and 66 in the control group were selected. The results of the study showedthat the Gestalt contact boundary confusion factor had a more negative effect on emotionalbehavior problems in the students in the interest group than in the control group. As a factorcontact boundaries confusion, showed for retroflection, projection, and egotism in the interestgroup, and retroflection and projection in the control group. In particular, in the case of theinterest group, retoflection was found to affect anxiety, projection to psychological burden, andegotism to poor self-control. Therefore, as part of a counseling stratergy for interest group, aGestalt counseling treatment approach is required.

Finite element modeling of assembling rivet-fastened rectangular hollow flange beams in bending

The assembling rivet-fastened rectangular hollow flange beam (ARHFB) is a new type of cold-formed steel beam. The ARHFB section has two rectangular hollow flanges formed by U-shaped and C-shaped components that connected by self-locking rivets. A finite element model is developed to simulate 16 four-point bending experiments. Details of the modeling including finite element meshing, loading and boundary conditions, contact and analysis methods are presented. The accuracy of the developed finite element model is verified by comparing the ultimate moment capacity, applied load versus deflection curves, bending moment versus deflection curves, strain versus deflection curves and failure modes obtained from the tests and the finite element analysis. Based on the validated finite element model, a parametric analysis is carried out to discuss the effects of rivet spacing, section depth, flange thickness, and web thickness on the bending performance of ARHFB. The moment capacities of these sections obtained from the parametric study are compared with predictions from Australia and New Zealand, Chinese design standards for cold-rolled sections and the DSM (Direct Strength Method). It is found that GB50018 can conservatively predict the bearing capacity of ARHFB with a large error, while AS / NZS 4600 and DSM (Direct Strength Method) cannot provide reliable prediction results.

Space–time flow computation with boundary layer and contact representation: a 10-year history

In computation of flow problems with moving solid surfaces, moving-mesh methods such as the space–time (ST) variational multiscale method enable mesh-resolution control near the solid surfaces and thus high-resolution boundary-layer representation. There was, however, a perception that in computations where the solid surfaces come into contact, high-resolution boundary-layer representation and actual-contact representation without leaving a mesh protection opening between the solid surfaces were mutually exclusive objectives in a practical sense. The introduction of the ST topology change (ST-TC) method in 2013 changed the perception. The two objectives were no longer mutually exclusive. The ST-TC makes moving-mesh computation possible even without leaving a mesh protection opening. The contact is represented as an actual contact and the boundary layer is represented with high resolution. Elements collapse or are reborn as needed, and that is attainable in the ST framework while retaining the computational efficiency at a practical level. The ST-TC now has a 10-year history of achieving the two objectives that were long seen as mutually exclusive. With the ST-TC and other ST computational methods introduced before and after, it has been possible to address many of the challenges encountered in conducting flow analysis with boundary layer and contact representation, in the presence of additional intricacies such as geometric complexity, isogeometric discretization, and rotation or deformation of the solid surfaces. The flow analyses conducted with these ST methods include car and tire aerodynamics with road contact and tire deformation and ventricle-valve-aorta flow. To help widen awareness of these methods and what they can do, we provide an overview of the methods, including those formulated in the context of isogeometric analysis, and the computations performed over the 10-year history of the ST-TC.

Ironies of proximity: Intergroup threat and contact avoidance on neighbourhood interface areas

AbstractResearch on the dynamics of neighbourhood desegregation and diversity has identified a paradox. On the one hand, such processes may engender positive intergroup contact experiences, improving intergroup attitudes and relations. On the other hand, they may have the opposite effect, exacerbating negative intergroup relations and generating new forms of avoidance and exclusion. The present research explored one aspect of this paradox. Building on a field survey conducted with Indian residents (n = 364) of a suburb of Pietermaritzburg, South Africa, we demonstrate how their relative proximity to areas occupied by ‘incoming’ Black African residents has shaped their perceptions of intergroup threat and associated reactions such as contact avoidance, boundary fortification and support for policies resisting desegregation. At the same time, we demonstrate how such effects are moderated by residents' wider experiences of positive interracial contact. In conclusion, we emphasize the need to better integrate psychological work on the contact hypothesis with work in companion disciplines such as urban studies and human geography. Please refer to the Supplementary Material section to find this article's Community and Social Impact Statement.

A Multi-Scale Investigation to Predict the Dynamic Instabilities Induced by Frictional Contact

We propose a new variational formulation to model and predict friction-induced vibrations. The multi-scale computational framework exploits the results of (i) the roughness measurements and (ii) the micro-scale contact simulations, using the boundary element method, to enrich the contact zone of the macroscopic finite element model of rubbing systems with nominally flat contact boundaries. The resulting finite elements at the contact interface of the macroscopic model include (i) a modified normal gap and (ii) a micro-scale description of the contact law (i.e., pressure gap) derived by solving the frictionless contact problem on a rough surface indenting a rigid half-plane. The method is applied to a disc brake system to show its robustness in comparison with classical deterministic formulations. With respect to the traditional complex eigenvalues analysis, the proposed multi-scale approach shows that the inclusion of roughness significantly improves the results at low frequencies. In this panorama, any improvement of dynamic instabilities predictions should be based on an uncertainty analysis incorporating roughness combined with other parameters such as friction coefficient and shear moduli of the pads, rather than on roughness itself.

Characterizing postural balance on 2-dimensional compliant surfaces with directional virtual time-to-contact

BackgroundThis study aimed to (1) investigate postural balance control on 2-Dimensional (2D) compliant surfaces using directional virtual time-to-contact (d-VTC), a novel method for VTC calculation; and (2) compare d-VTC with conventional balance measures in this context. MethodsA dual-axis robotic platform was used to simulate 2D surfaces/grounds with varying compliance levels. Twenty healthy young adults stood on the platform with either open or closed eyes. Balance was evaluated using d-VTC in multiple aspects, including temporal (VTC mean), spatial (boundary contact - BC), and control aspects (switching rate – SR). Additionally, conventional balance measures, namely center-of-pressure (COP) area and COP root-mean-square (RMS), were employed for further comparisons with d-VTC measures. Normality checks were performed using Shapiro-Wilk tests. Two-way repeated measures ANOVA tests were used to examine the effects of surface compliance and vision on postural balance, followed by post-hoc pairwise comparisons across conditions with Bonferroni correction. ResultsThe results showed that increasing surface compliance and/or absence of vision caused a significant decrease in VTC mean (all p-values <0.001; all ηp2 > 0.816). Interaction effects between surface compliance and vision on 2D and ML VTC mean were also significant (all p-values <0.019; all ηp2 > 0.355). The AP and ML BC values indicated a converging trend to 50%. No vision effect was observed (p = 0.458), but both surface compliance (p = 0.001; ηp2 = 0.522) and interaction (p = 0.002; ηp2 = 0.492) effects were significant. Decreases in SR were significant due to the compliance of the standing surface (p = 0.01; ηp2 = 0.401) but not vision (p = 0.109). COP area increased due to both surface and vision conditions (all p-values <0.001; all ηp2 > 0.872). AP and ML RMS were altered by vision (all p-values <0.001; all ηp2 > 0.741), but not by surface condition (all p-values >0.06). No interaction effect was observed in the conventional measures (all p-values >0.07). ConclusionBalance control is compromised by 2D compliant surfaces, which is exacerbated when vision is absent. Among all balance measures, VTC mean measures demonstrated particularly high sensitivity in identifying decreased balance capabilities, while BC and SR provided new insights into fall risks and balance control mechanisms. These insights may facilitate the development of rehabilitation training or assistive devices for fall prevention.

The contact condition of viscoelastic contact problems

Three contact states in the viscoelastic contact deformation area between the rigid cylinder and the viscoelastic foundation are discussed based on various material mechanical properties between the rigid and the viscoelastic materials. On this basis, the relationship model between the node displacements and the node stresses in the boundary contact area is established, and the corresponding numerical analytical algorithms are used to simulate the viscoelastic contact deformation. Meanwhile, an example is given to simulate the contact deformation of the conveyor belt.

A finite element approach for nonlinear, transient heat conduction problems with convection, radiation or contact boundary conditions

Heat conduction problems with convection and/or radiation boundary conditions arise in nuclear and other engineering fields. This paper presents a finite element approach to solve transient, three-dimensional (3-D), nonlinear heat conduction problems using quadratic tetrahedral elements with area/volume coordinates and quadrature integrations. Boundary conditions modeled include surface convection, to-ambient radiation, and surface-to-surface radiation (using the radiosity matrix method, RMM). Instead of the commonly used hemi-cube method, L′Huilier’s theorem is used here to calculate view factors. Contact constraints are also imposed. Interface condition is set up for the interfaces of different material. The one- and two-step backward differentiation are used for time integration. Nonlinearities introduced by temperature-dependent material thermal properties and the Stefan–Boltzmann law for radiation are handled using the Picard and/or Newton–Raphson methods. The convergence rate of the numerical scheme is verified using an analytical solution obtained using the method of manufactured solutions (MMS). Several practical cases are simulated, including that of two spheres in contact with each other, and results are compared to those obtained using commercial codes.

Boundary contact problems with regard to friction of couple-stress viscoelasticity for inhomogeneous anisotropic bodies (quasi-static cases)

Abstract In this paper, quasi-statical boundary contact problems of couple-stress viscoelasticity for inhomogeneous anisotropic bodies with regard to friction are investigated. We prove the uniqueness theorem of weak solutions using the corresponding Green’s formulas and positive definiteness of the potential energy. To analyze the existence of solutions, we equivalently reduce the problem under consideration to a spatial variational inequality. We consider a special parameter-dependent regularization of this variational inequality which is equivalent to the relevant regularized variational equation depending on a real parameter, and study its solvability by the Galerkin approximate method. Some a priori estimates for solutions of the regularized variational equation are established and with the help of an appropriate limiting procedure, the existence theorem for the original contact problem with friction is proved.

Cast-rolling force model of multi-roll solid–liquid cast-rolling bonding process for fabricating metal cladding materials

Based on twin-roll casting technology and multi-roll groove rolling technology, a Multi-Roll Solid-Liquid Cast-Rolling Bonding (MRSLCRB) process was proposed to fabricate Cu/steel cladding bars, which processes the advantages of short flow and high-efficiency. However, it is a typical 3-D thermal-fluid-mechanics coupled problem, and determining cast-rolling force is difficult during the equipment design. Therefore, the geometrical evolution of the cast-rolling area was studied, laying the foundation to establish contact boundary equations and analyze mechanical schematics and metal flow. Then, a 3-D steady-state thermal-fluid coupled simulation model, including casting roll, substrate bar, and cladding metal, was established. The Kissing Point (KP) height, average outlet temperature, and process window were predicted, and simulation results of the three-roll layout indicate that the KP distribution along the circumferential direction can be considered uniform. Hence, the engineering cast-rolling force model was derived based on the differential element method and plane deformation hypothesis. The accuracy was verified by the 3-D finite element model, and the influences of process layouts and technological parameters on the cast-rolling force were analyzed. Through the indirect multi-field coupled analysis method, the temperature–pressure evolution and reasonable process window can be predicted, which provides a significant basis for guiding equipment design and improving product quality.

Ultrathin liquid film phase change heat transfer on fractal wettability surfaces

Surface wettability is significant for the liquid–vapor phase change heat transfer. In this paper, patterned wettability surfaces are constructed from the perspective of fractal theory to comprehensively investigate the microscopic mechanism of surface wettability patterns affecting evaporation and bubble nucleation. The evaporation heat transfer rates of the hydrophilic fractal wettability surfaces are close to that of the pure hydrophilic surface. The solid–liquid interfacial heat transfer dominates the evaporation heat transfer. In contrast, the liquid–vapor interfacial heat transfer’s effect is insignificant. The hydrophobic points of the hydrophilic fractal wettability surfaces provide stable and abundant nucleation sites for the bubble nucleation process. The nucleation times of the hydrophilic fractal wettability surfaces are earlier than that of the pure hydrophilic surface. Hydrophobic fractal wettability surfaces can improve bubble nucleation. With increased hydrophilic points, nucleation sites are mainly concentrated in hydrophobic regions near the hydrophilic/hydrophobic contact boundary. The expanding low potential energy region near the contact boundary is the main reason for improving bubble nucleation. Critical heat flux (CHF) increases as the area proportion of the hydrophilic part increases, and surface superheats decrease when CHF occurs. The fractal wettability surfaces improve CHF, and the CHF of the hydrophilic fractal wettability surface is close to that of the pure hydrophilic surface.

Performance degradation analysis and fabrication guidance of μ-TEG from material to device

Micro thermoelectric generator (μ-TEG) attracts more and more attention due to its small size and high power density. Many two-dimensional thermoelectric materials with high performance have facilitated the development of μ-TEG. However, the performance of μ-TEG fabricated by these great thermoelectric materials is significantly degraded due to size effect, interfacial effects (include contact effect and boundary effect) and structure effect. To accurately assess the performance degradation degree from material to μ-TEG and guide the device fabrication, an experiment-verified mathematical model considering interfacial and size effects is proposed. Firstly, the phonon/electron temperature distribution in thermoelectric leg of μ-TEG is analyzed to investigate the device-level thermoelectric properties of material. Then based on the device-level thermoelectric properties, the actual power generation performance model of μ-TEG is established to conduct the influence analysis of these effects (boundary, size, contact and structure effects) on material and device. Finally, the thermoelectric leg thickness (Hte) is optimized to realize optimal power generation. The study results reveal that boundary and size effects weaken the device-level thermoelectric properties, and the reduction trend is more obvious when Hte is smaller, especially when Hte ≤ 20 μm. The decrease from the material intrinsic figure of merit ((ZT)m) to the device figure of merit ((ZT)D) is owing to the boundary effect, structure effect and contact effect, and the dominant factor of this decrease changes from structure effect (Hte＜7 μm)to contact effect (Hte ≥ 7 μm) as Hte increases, which points to a main optimization direction for (ZT)D for different Hte. As for contact effect, the electrical contact resistivity (re,c) has a more significant impact on weakening the performance of μ-TEG than thermal contact resistivity (rk,c), and their optimization goals are explored (re,c ≤ 5.1 × 10−12 Ω·m2, rk,c ≤ 9.3 × 10−8 K·m2/W). At given electrical and thermal contact resistivity, there exists an optimal Hte for achieving the optimal power generation (Popt) and a large range of Hte for achieving 95%Popt, and the optimal Hte increases with increasing electrical and thermal contact resistivity. This study can reduce the processing difficulty and save time and economic costs of μ-TEG fabrication, which can avoid the blind fabrication of μ-TEG.

Determination of online thin film buckling configuration by parametric optimization for flexible sensor application

A mini basket type mapping catheter consists of thin film flexible sensors and is applied in the medical field to measure the electrocardiography (ECG) signals in order to localize and quantize the physiological condition/status of heart. The flexible nature of the thin film changes the configuration with respect to the contact boundary conditions when it contacts a target surface. Therefore, to accurately localize the flexible sensor, the thin film flexible sensor’s configuration must be determined accurately in an on-line fashion. As a study of localizing the thin film flexible sensor, this study proposes an on-line thin film buckling configuration determination method using parametric optimization and interpolation technique. With the specific modulus of elasticity and dimensions of the thin film flexible sensor of the mapping catheter prototype, the buckling configuration with two point boundary condition under axial load can be calculated in desktop environment. The proposed calculation method is validated by mapping catheter sensor prototype test. The calculation/test results showed that the maximum overall length L, x_{a}, and y_{a} value error between the calculation and experiment are approximately 0.16 mm, − 0.12 mm. − 0.10 mm in 50 ms calculation time. The calculation result of the proposed method is also compared with that of the numerical simulation by FEM, which has approximately 0.44 mm y_{a} value error compared with that of the experiment.

Building a model of the impact grinding mechanism in a tumbling mill based on data visualization

A mathematical model was built based on data visualization for the impact grinding mechanism in a tumbling mill, which is mainly implemented during coarse grinding. The determination of impulse interaction parameters is problematic due to the difficulty of modeling and the complexity of hardware analysis of the behavior of intramill loading. Conceptually, it was envisaged to identify the relative dynamic parameters of the impact action as components of the model, which are criteria for the similarity of the loading movement and the grinding process. Impact power was taken as an analog of grinding performance. The initial characteristic of the impact was considered to be the averaged vertical component of the speed of loading movement in the flight zone at the boundary of contact with the shear layer. The formalization of the model revealed the effect on the performance of the mass fraction of the flight zone and the reversibility of loading. The method of numerical modeling was applied, based on experimental visualization of the behavior of granular loading in the cross section of a rotating chamber. The influence of the rotation speed on the performance at a chamber filling degree of 0.45 and a relative particle size of a milling load of 0.0104 was estimated by experimental simulation. The maximum productivity value was found at the relative speed of rotation ψω=1–1.05. A rational condition for impact grinding at ψω=0.75–0.9 has been established. The test proved the effectiveness of using visualization to evaluate dynamic loading interaction analogs. Verification of modeling results was implemented by comparison with the data of the technical standard. The use of similarity criteria unifies approaches to modeling different mechanisms of destruction. The model built makes it possible to predict the rational parameters of the grinding processes by impact, crushing, and abrasion

Torsion crack in a bimaterial with different types of contact boundary conditions on interface

Torsion crack in a bimaterial with different types of contact boundary conditions on interface

Elastic-plastic torsion of a two-layer rod

We study the elastic-plastic torsion of a two-layer rod under the action of torque in this article. It is assumed that the rod consists of two layers. Each layer has its own elastic properties, but the plastic properties of both layers are the same. The contact boundary of the layers is located along the oh axis. The lateral boundary of the rod is stress-free, displacements and stresses are continuous at the interface. The components of the stress tensor at a point are calculated using contour integrals derived from conservation laws calculated along the lateral boundary. Next, the second invariant of the stress tensor is compared with the yield strength. At those points where the yield point is reached, the plastic state is realized, in the rest -elastic. This allows you to build a boundary between the plastic and elastic regions. This technique provides a way to calculate elastic-plastic boundaries for the main rolling profiles of rods. This is supposed to be done in subsequent works. We remind you that earlier, with the help of conservation laws, the main boundary value problems for a plastic two-dimensional medium, elastic-plastic torsion of isotropic rods and elastic media for bodies of finite dimensions were solved.solutions.

A finite volume penalty‐based implicit procedure for the treatment of the frictionless contact boundaries

AbstractThis article presents a new implicit coupling procedure for mechanical contact simulations using an implicit cell‐centred finite volume method. Both contact boundaries are treated as Neumann conditions, where the prescribed contact force is calculated using a penalty law, which is linearised and updated within the iterative solution procedure. Compared to the currently available explicit treatment, the implicit treatment offers better efficiency for the same accuracy. This is achieved with the proposed implicit linearisation, which replaces the explicit under‐relaxation of the contact force. The proposed procedure, intended for frictionless contact of Hookean solids, can handle non‐conformal contact interface discretisations and faces in partial contact. The accuracy and efficiency of the implicit approach are compared with the explicit procedure on four benchmark problems, where it is shown that the proposed method can significantly improve efficiency and robustness.