Contact Boundary Research Articles

Calculation of the destruction of ice structures by the grid-characteristic method on structured grids

Sea ice is a difficult object to study due to its heterogeneous structure and location near the melting point. This paper proposes a model of ice ridges as a heterogeneous structure with multiple water and air inclusions, free boundaries and free sliding contact boundaries. The dynamic growth of cracks in a given heterogeneous structure under intense dynamic influences is considered, which makes the considered boundary value problem nonlinear. The influence of explosion parameters (location of sources, frequency, number of periods) on the nature of the destruction of the ice ridges was investigated. The work also investigates the collision of an ice island with ice floes. For calculations, the grid-characteristic method is used on structured rectangular computational grids.

Stability for a boundary contact problem in thermoelastic Timoshenko’s beam

We demonstrate the existence of solutions to Signorini’s problem for the Timoshenko’s beam by using a hybrid disturbance. This disturbance enables the use of semigroup theory to show the existence and asymptotic stability. We show that stability is exponential, when the waves speed of propagation is equal. When the waves speed is different, we show that the solution decays polynomially. This result is new. We perform numerical experiments to visualize the asymptotic properties.

Effects of the rate of carbon dioxide injection at the initial gas-water contact on the recovery factor

The process of carbon dioxide injection into the initial gas-water contact with different rates of its injection, using a 3D model of a gas condensate reservoir, has been investigated. Calculations were carried out for one well injection rate of non-hydrocarbon gas: 40, 50, 60, 70, 80, 90 th.m3/day. According to the calculated results, it has been found that with an increased rate of the carbon dioxide injection into a productive reservoir, the operation duration of production wells decreases until the moment of the carbon dioxide breakthrough. Based on the techno-logical indicators’ analysis of the gas condensate reservoir’s development, it has been found that the introduction of the carbon dioxide injecting technology leads to a reduction in the production of formation water. Due to the injec-tion of non-hydrocarbon gases, a hydrodynamic barrier is created on the initial gas-water contact boundary, which decreases the water influx. Also, the introduction of carbon dioxide injection technology will additionally create an artificial barrier between water and natural gas, which blocks the selective water encroaching and thereby ensure stable waterless operation of production wells. Based on the conducted calculations, the main dependencies have been derived and the corresponding patterns between them have been established. According to the results of the statistical processing of the calculated data, the optimal carbon dioxide injection rate has been determined. At the time of the carbon dioxide breakthrough into the producing well, its optimal well injection rate is 58.17 th.m3/day. The ultimate gas recovery factor for the optimal carbon dioxide injection rate is 63.29 %. Under the same condi-tions during depletion, the ultimate natural gas recovery factor is 53.98%. The results of the carried out studies indicate the technological efficiency of carbon dioxide injection into the initial gas-water contact in order to slow down the formation water encroaching into productive reservoir.

Analysis results for dynamic contact problem with friction in thermo-viscoelasticity

We present a mathematical model which describes the dynamic frictional contact between a thermo-viscoelastc body and a conductive foundation. The contact is modeled using the normal compliance condition, the quasistatic version of Coulomb's law of fry friction. We derive the weak formulation and we prove the existence and uniqueness result. The proofs are based on the theory of first-order and second-order evolution inequalities and Banach fixed point theorem. We introduce a new problem on perturbation of the contact boundary condition and we establish its continuous dependence result. <br><br>Представлено математичну модель, що описує динамічний контакт тертя між термов’язкопружним тілом і основою-провідником. Контакт моделюється з використанням умови нормальної еластичності, квазістатичної версії закону фрикційного тертя Кулона. Пропонується означення слабкого розв’язку, доведена теорема існування та єдиності. Доведення базуються на теорії еволюційних нерівностей першого та другого порядків і теоремі Банаха про нерухому точку. Ставиться нова задача про збурення контактної граничної умови; отримана теорема про неперервну залежність.

НЕСТАЦИОНАРНОЕ ТРЕХМЕРНОЕ ТЕМПЕРАТУРНОЕ ПОЛЕ В МНОГОСЛОЙНОМ ЦИЛИНДРЕ

The problem of determining a non-stationary three-dimensional temperature field in a k-layer cylinder of length is solved. There is a symmetrically located cylindrical cavity in the center of this body. The absence of a cavity is a special case of the problem. In each layer, there are heat sources, depending on the coordinates and time. The initial temperature of the layers is a function of the coordinates. In the center of the body the symmetry condition is fulfilled. At the boundary of contact of the layers - ideal thermal contact: continuity of temperatures and heat flows. On the inner and outer side surfaces and ends, heat exchange occurs according to Newton's law with environments whose temperatures change over time according to an arbitrary law. The periodicity condition is set for the angle φ. The problem in this statement is solved for the first time. For the solution of the problem the following approach is used: by means of the method of finite integral transformations differential operations on longitudinal coordinate, angle and transverse coordinate are sequentially excluded, and the determination of time dependence of temperature is reduced to the solution of the ordinary differential equation of the first order.

Geometric nonlinear analysis of thin elastic paraboloid of revolution shaped shells with radial waves

From the old ancient types of roof and dome construction, various forms of shells have been discovered which attract special attention. A shell is a structure composed of sheet material so that the curvature plays an important role in the structural behaviour, realizing its spatial form. There are different types of shells, namely thick and thin shells. G. Brankov, S.N. Krivoshapko, V.N. Ivanov, and V.A. Romanova made interesting researches of shells in the form of umbrella and umbrella-type surfaces. The term nonlinear refers to a given structure undergoing a change in stiffness in its loaded state. There are basically three different types of nonlinearities: geometric, physical and contact (boundary condition nonlinearity). For further analysis of the stress-strain state, a paraboloid with an inner radius of 4 m and an outer radius of 20 m and the number of waves equal to 6 was considered. The test shell is made of reinforced concrete. The minimum load parameter at which the shell loses stability indicates a more than three times the margin.

Investigation of deformation of the cornea during tonometry using FEM

A three dimensional finite element model of the human eye is developed to evaluate the force which will be applied over the surface of cornea during tonometry and gonioscopy tests. The standard tonometers and gonioscopy experiences deformation from 0.5mm to 3mm of the cornea is adopted during both point contact and boundary contact on the surface of the cornea. The results demonstrate the maximum force experienced by the tonometer with point contact at the center of the cornea for the maximum possible deformation of the cornea during tonometry. The study also analyzes for the force experienced by the tonometer or goniolens with boundary layer contact for the defined deformation of the cornea along the direction from cornea towards the retina.

Evaluation of tensile strength of painted steel wi local corrosion at structural connections

Steel structures are often protected by paint coating, but the coating easily deteriorates at structural connections because moisture and dust accumulate at the contact. This leads to the local corrosion on the steel members near the contact and a reduction in tensile performance. The corrosion characteristics and tensile strength of steel plates with a concrete block are investigated. Four types of specimens were prepared, and each type had an unpainted area with different lengths away from the contact boundary. An accelerated cyclic corrosion test was conducted for 600 cycles using CCT-I test conditions specified in the ASTM D 6899–03 standard. To analyze the corrosion characteristics, the surface geometry of corroded specimens was measured in 1 mm × 1 mm intervals by an optical 3D measurement system. The average corrosion depth outside the concrete block was proportional to the unpainted area, and the average corrosion depth inside the concrete block was accelerated in unpainted areas. The two average corrosion depths have a power regression relationship, so the average corrosion depth inside the concrete block can be estimated from the average corrosion depth outside it. A simple method for quantitatively defining the residual thickness is proposed in terms of the effective thickness and the residual tensile strength, which can be evaluated using the effective thickness. Compared to previously proposed methods for this purpose, the effective thickness has higher accuracy.

High Speed Steel with Iron Addition Materials Sintered by Spark Plasma Sintering

Attempts were made to describe the effect of the sintering temperature and pure iron powder addition on the properties of high speed steel based materials produced by the spark plasma sintering technique. After sintering, their density, hardness, flexural strength, and tribological properties were determined. The sintered materials were also subjected to microstructural analysis in order to determine the phenomena occurring at the particle contact boundaries during sintering. Based on the analysis of the obtained results, it was found that the mechanical properties and microstructure were mainly influenced by the sintering temperature. Using the temperature of 1000 °C allowed materials with a density close to the theoretical density to be obtained, characterized by a high hardness of about 360 HB and a low wear rate of about 1E-07 g/s.

Stress waves in a cylindrical body interacting with external medium

The unsteady-state axisymmetric problem of longitudinal interaction of a cylindrical body with external elastic medium is considered in the paper. The condition of Coulomb friction is accepted at the contact boundary. The solution is implemented by the finite difference method. The results are shown in graphs and analyzed. The changes in stress, velocity, and displacement of particles at some points of a cylindrical body and external medium are presented. An increase in longitudinal stresses and particle velocities in the cylinder was determined when compared to a given load due to the outflow of strain energy from the external medium. The mechanism of strain energy redistribution and friction forces formation is shown, the changes in the direction of contact forces action are revealed. A significant violation of the uniform deformability of the medium, and possible maximum value that occurs in a cylindrical body, is determined. The established dependences of tangential stresses on relative displacements qualitatively coincide with experimental data obtained during the interaction of fragments of underground pipelines with soil.

Mathematical model of underground structure-soil interaction

Based on existing data of experimental studies of underground structure-soil interaction, a condition for boundary interaction between the underground pipeline and soil was developed. The proposed condition (a model) of interaction at the contact boundary takes into account the structural destruction of the contact soil layer and the cyclical nature of interaction process. The authors have shown by parametric analysis of the interaction model, that under cyclic interaction of the underground pipeline with soil, the structural disturbance of the soil contact layer does not reach the peak shear stress; the applicability of the problems of underground structure-soil interaction is also shown. The model of interaction on the contact structure-soil surface in particular cases passes into the existing conditions of interaction, including Coulomb friction.

Identities for droplets with circular footprint on tilted surfaces

Exact mathematical identities are presented between the relevant parameters of droplets displaying circular contact boundary based on flat tilted surfaces. Two of the identities are derived from the force balance, and one from the torque balance. The tilt surfaces cover the full range of inclinations for sessile or pendant drops, including the intermediate case of droplets on a wall (vertical surface). The identities are put under test both by the available solutions of a linear response approximation at small Bond numbers as well as the ones obtained from numerical solutions, making use of the Surface Evolver software. The subtleties to obtain certain angle-averages appearing in identities by the numerical solutions are discussed in detail. It is argued how the identities are useful in two respects. First is to replace some unknown values in the Young–Laplace equation by their expressions obtained from the identities. Second is to use the identities to estimate the error for approximate analytical or numerical solutions without any reference to an exact solution.

Research of the influence of the grid density of injection wells on the gas extraction coefficient when injecting carbon dioxide into reservoir

The object of research is gas and gas condensate reservoirs developed under the conditions of the manifestation of the water pressure mode of development and the negative effect of formation water on the process of natural gas production. In order to improve the existing technologies for the development of natural gas fields in the conditions of the manifestation of a water-driven mode of development of productive reservoirs, a study was carried out using the main tools of hydrodynamic modeling Eclipse and Petrel from Schlumberger (USA). On the basis of a three-dimensional digital model of gas condensate, the influence of the density of injection wells on the coefficient of natural gas extraction during the injection of carbon dioxide into productive reservoirs on the verge of a gas-water contact was investigated. The study was carried out for a different number of injection wells (4, 6, 8, 12, 16 wells), which are evenly spaced along the perimeter of the initial gas-water contact. According to the results of the calculations, it was found that the production of formation water decreases with an increase in the density of the well grid. In the case of using 4 wells to inject carbon dioxide into a productive reservoir, the accumulated production of formation water at the end of development amounted to 169.71 thousand m3. With an increase in the number of injection wells to 16 units, the accumulated production of produced water decreased to 0.066 m3. This result is achieved due to a more complete coverage of the perimeter of gas content with carbon dioxide and the creation of an artificial barrier between water and natural gas, which leads to a more effective blocking of the movement of produced water into productive reservoirs. According to the results of statistical processing of the calculated data, the optimal value of the number of injection wells was determined when injecting carbon dioxide into the reservoir. The optimal value of the number of injection wells at the time of the breakthrough of carbon dioxide into the first production well is 7.86 (8) wells. The maximum value of the number of injection wells according to the results of statistical processing is 6.8 (7) wells. The final gas recovery ratio for the given optimal injection value is 61.88 %. On the basis of the calculations, the technological efficiency of using as an agent for injecting carbon dioxide at the boundary of the gas-water contact was established in order to prevent selective watering of productive reservoirs and production wells.

Il disturbo autistico ad alto funzionamento: criteri per un modello integrato

The autism studies show a greater degree of scientific evidence. They derive from Applied Behavioural Analysis (Aba) and Cognitive-Behavioural orientation. Gestalt therapy deals with autism recently. The concepts of Gestalt psychotherapy, including the concept of contact boundary, the principle of creative adaptation and the phenomenological perspective of the organism-environment field, are central to the characteristics of autism. These concepts are important, in particular for autism high functioning. Gestalt therapists deal with the value of spirituality in the treatment of people with autism. This is of strong scientific significance. Health includes, in fact, the physical, social, psychological and spiritual aspects as represented by OMS in the 2004 Promoting Mental Health document. The purpose of this work is to produce a contribution in the direction of comparison and integration. The aim is to lay the foundations for the creation of an integrated model for the treatment of high functioning autistic disorder. In order to implement this integration logic, based on the study of scientific data and my clinical experience, the active ingredients present in these three approaches will be identified (Aba, Cognitive-Behavioral Psychotherapy and Gestalt Psychotherapy). The development of a mix of active ingredients allows to obtain a greater control of the possible limits and side effects present in each orientation. The next step is to conduct the assessment through these integration criteria. For this purpose, areas of intervention will be identified in which the examination of the specific characteristics will be described. Keywords Autism, intervention, integration Abstract in italiano Gli studi sull’autismo che mostrano un maggior grado di evidenza scientifica derivano dall’Applied Behavioral Analysis (Aba) e dall’orientamento Cognitivo-Comportamentale. La psicoterapia della Gestalt ha iniziato ad occuparsi di autismo recentemente. I concetti della psicoterapia della Gestalt, tra cui il concetto di confine di contatto, il principio di adattamento creativo e la prospettiva fenomenologica del campo organismo-ambiente, sono centrali per le caratteristiche dell’autismo e, in particolare, per la specificita dell’autismo ad alto funzionamento. Psicoterapeuti della Gestalt hanno, inoltre, evidenziato il valore della spiritualita nel trattamento delle persone con autismo. Cio e di forte pregnanza scientifica in quanto la salute comprende gli aspetti fisici, sociali, psicologici e spirituali come rappresentato dall’Oms nel documento Promoting Mental Health del 2004. La finalita di questo lavoro e produrre un contributo nella direzione del confronto e dell’integrazione. L’obiettivo e porre le basi per la costituzione di un modello integrato per il trattamento del disturbo autistico ad alto funzionamento. Al fine di attuare tale logica d’integrazione, sulla base dello studio dei dati scientifici e della mia esperienza clinica, saranno identificati i principi attivi presenti in questi tre approcci (Aba, psicoterapia Cognitivo-Comportamentale e psicoterapia della Gestalt). La messa a punto di un mix di principi attivi consente di ottenere un maggior controllo dei possibili limiti ed effetti collaterali presenti in ciascun orientamento. Il passo successivo e la conduzione dell’assessment mediante questi criteri d’integrazione. A tale scopo, saranno individuate delle aree d’intervento in cui sara descritto l’esame delle specifiche caratteristiche. Parole chiave: autismo, intervento, integrazione

Geometric design of rotary retractable plate structures based on parallelogram closed-loop chain linkages

For large-span retractable roof structures, the mechanism should be simple and efficient for the convenience of motion control. The kinematic characteristics of parallelogram closed-loop chain linkages (PCCL) show that a set of the angulated beams of PCCL rotates around the fixed points, which is suitable for retractable structures. This paper focuses on the geometrical design of the rotary retractable plate structures (RRPS), which evolves from PCCL by replacing the rotation angulated beams with cover plates. Each plate of RRPS has a fixed support and all the plates rotate simultaneously with a single DOF. The fixed points used as supports for cover plates to improve the stability and simplify the motion control of the system restrict the open area of the RRPS. By adjusting the contact boundaries of the cover plates, an optimisation method is proposed to increase the open area of the RRPS after fully deployed. The design approach is successfully extended to both symmetrical and asymmetrical RRPS. An example is carried out to demonstrate the feasibility of the approach and a simple physical model is manufactured to validate the design result in the example.

Analysis of Friction-Saturated Flutter Vibrations With a Fully Coupled Frequency Domain Method

Abstract Flutter stability is a dominant design constraint of modern turbines. Thus, flutter-tolerant designs are currently explored, where the resulting vibrations remain within acceptable bounds. In particular, friction damping has the potential to yield limit cycle oscillations (LCOs) in the presence of a flutter instability. To predict such LCOs, it is the current practice to model the aerodynamic forces in terms of aerodynamic influence coefficients for a linearized structural model with fixed oscillation frequency. This approach neglects that both the nonlinear contact interactions and the aerodynamic stiffness cause a change in the deflection shape and the frequency of the LCO. This, in turn, may have a substantial effect on the aerodynamic damping. The goal of this paper is to assess the importance of these neglected interactions. To this end, a state-of-the-art aero-elastic model of a low pressure turbine blade row is considered, undergoing nonlinear frictional contact interactions in the tip shroud interfaces. The LCOs are computed with a fully coupled harmonic balance method, which iteratively computes the Fourier coefficients of structural deformation and conservative flow variables, as well as the a priori unknown frequency. The coupled algorithm was found to provide excellent computational robustness and efficiency. Moreover, a refinement of the conventional energy method is developed and assessed, which accounts for both the nonlinear contact boundary conditions and the linearized aerodynamic influence. It is found that the conventional energy method may not predict a limit cycle oscillation at all while the novel approach presented here can.

Cooperativity Between Zirconium Dioxide Nanoparticles and Extreme Pressure Additives in Forming Protective Tribofilms: Toward Enabling Low Viscosity Lubricants

Realizing the efficiency benefits of low viscosity lubricants requires novel strategies to avoid failures resulting from increased boundary contact. Zirconium dioxide (ZrO2) nanoparticles (NPs) form protective tribofilms through tribosintering at lubricated contacts in pure hydrocarbon base oils, suggesting they hold promise for reducing boundary contact-induced failures. However, their tribological behavior alongside co-additives found in fully formulated oils has not been examined in depth. Here, the macroscopic tribological performance of dispersed ZrO2 NPs (1 wt% loading; 5 nm diameter nearly spherical ZrO2 tetragonal phase NPs with organic capping ligands for oil solubility) with and without the presence of co-additives found in fully formulated commercial gear oils was studied using a mini-traction machine (MTM). The results show that ZrO2 NPs reproducibly develop surface-bound ~ 100 nm thick tribofilms on both contacting surfaces under a wide range of rolling-sliding contact conditions, from 0 to 100% slide-to-roll ratio. Steady-state traction coefficient values of ZrO2 tribofilms formed alongside co-additives (0.10–0.11) do not substantially differ from ZrO2 tribofilms formed in neat polyalphaolefin base oils (0.10–0.13). However, there is improvement in the tribological performance of the contact, with at least a twofold reduction of wear of the steel. This behavior is proposed to be a result of cooperating mechanisms, where the extreme pressure additives adsorbed on the steel surfaces protect them against early adhesive wear, during the time that a protective ZrO2 tribofilm incorporating the co-additives forms on the steel surfaces, preventing further wear.

Unraveling the limitations of solid oxide electrolytes for all-solid-state electrodes through 3D digital twin structural analysis

Abstract Solid oxides are attractive electrolyte materials for all-solid-state lithium batteries (ASSLBs) owing to their high stability and pure Li-ion conductivity. Nevertheless, the electrochemical performance of ASSLBs employing solid oxide-based electrolytes cannot compete with ASSLBs with sulfide or polymeric electrolytes due to poor interfacial contact and high boundary resistance between the active materials and solid oxide electrolytes. To overcome this hurdle, elaborate microstructural analysis of the interface of the active material/solid oxide electrolyte in ASSLBs is essentially required since the interfacial contact area dominantly acts as the ion pathway and the electrochemical reaction site in the electrode. Although recent attempts on interfacial structure analysis of ASSLBs have provided simple 2D or semi-3D microstructural features, the results have not yielded deep insights. Herein, we investigated the interfacial defects in an all-solid-state electrode with a solid oxide electrolyte via a 3D digital twin technology combining 3D structural quantification and physico-electrochemical simulations to unravel the intrinsic limitations of solid oxide electrolytes. The in-depth results can be used to design materials and optimize electrode design parameters for ASSLBs.

Numerical Model for Hydration-Lubricated Contact and Its Friction Behavior at Nanoscale

In this study, we propose a numerical model to investigate the contact and friction behaviours of hydration lubricated contact in an aqueous solution confined in a gap of several molecular diameters. A force–distance curve was obtained under different surface forces, and friction behaviour was determined using the modified Eyring thermal activation model. The results showed that the normal boundary contact pressure and contact gaps were obtained using the proposed numerical model. In addition, friction force increased with the logarithm of sliding velocity. Hence, the Eyring model could predict the friction behaviour of hydration lubrication. Moreover, it could capture the underlying physical principles of the contact and friction behaviours of hydration lubrication.

Spherical indentation creep characteristics and local deformation analysis of 310S stainless steel

To estimate the creep properties of 310S stainless steel reasonably, its spherical indentation creep characteristics and local deformation behaviour during vacuum indentation creep tests are analysed in this study. The influence of creep load, temperature, and indenter diameter on the indentation depth – time curve is discussed. The results indicate that the spherical indentation depth rate decelerates before becoming approximately constant. With an increase in creep load and temperature, there is an apparent increase in the creep depth rate. Along with the increase of creep deformation, the hardness value increases. Compression deformation can be observed at the specimen center under the indenter. With an increase in the distance from the specimen centre, the value of stress triaxiality on the upper surface of the specimen increases gradually. Unlike that at the specimen centre, a pile-up phenomenon along with tensile deformation feature is observed at the contact boundary. When the indentation creep depth is small, changes in the microstructure of the specimen are not obvious. Overall, the local deformation has an apparent influence within a distance of approximately twice the indenter radius from the contact boundary.