Element Displacement Research Articles

Clinical manifestations and neuroanatomical correlates of reversible impairment of cognitive functions in patients with normotensive hydrocephalus: Case Report

From a neuropsychological perspective, normotensive hydrocephalus NPH is characterized by cognitive impairment associated with the compression exerted by ventricular dilatation on the cingulate cortex and fronto-striatal circuits. The Rey-Osterrieth Complex Figure Test (ROCFT) is a neuropsychological assessment measure widely used by clinicians and researchers because of the wide variety of cognitive information it allows to estimate. We present the case of young male patient with refractory structural epilepsy secondary to a childhood brain injury resulting from a metastasis of a renal tumor. Referred to Neuropsychology for behavioral changes and cognitive impairment; presenting atypical performance in the copying phase of the ROCFT. Failures in visual integration and coding of the ROCFT copy show that, in cases of NPH, brain structures such as the cerebellum and posterior cingulum can also be compromised by the compression exerted by the cerebral hemispheres as they move due to ventricular dilatation. Failures in integration, planning, rotation and displacement of ROCFT elements have been reported in patients with secondary psychotic conditions and posterior cingulate tumors. Failures in visual integration associated with NPH may be related to the involvement of more postero-caudal brain structures such as the cerebellum and posterior cingulum or to secondary psychosis.

3D Modelling and numerical simulations of menisci in normal and osteoarthritic human knee joint

This paper presents 3D virtual modeling of the menisci in the human knee joint, based on CT sections performed on the human knee joint. CT images were processed using advanced modeling and simulation methods as Space Claim and Design Modeler integrated application under Ansys Workbench software package. By using Finite Element Analysis, the stresses and displacements from normal menisci, but also from those affected by osteoarthritis, are studied for the cases of 5 degrees valgus deviation of the mechanical axes of the knee. The study concludes with a comparison between the results obtained from the analysis performed for the healthy menisci, on the one hand, and for the damaged ones, on the other hand.

Comparison of microsurgical and endoscopic approaches to removing lumbosacral spine hernias

Degenerative and dystrophic changes of the spine rank first in the number of temporary disability days and second among the reasons for visiting a physician. (1) Disc hernia is a consequence of degenerative and dystrophic changes of the spine representing a local displacement of disc elements outside the disc. Herniated disc bulges are most common in the 30-50-year-old population. This paper describes in detail the aetiology and pathogenesis of intervertebral disc hernia development, provides classifications of degenerative and dystrophic changes of the spine according to Osna, Pfirrmann, and presents the classification of intervertebral hernias of the North American Spine Society. The authors also described the clinical picture: vertebrogenic pain syndrome, radiculopathy, urinary disorders, and cauda equina syndrome were characterised. The aim of the study was to compare the microsurgical technique of herniated discs removal with the endoscopic technique, as well as to identify the advantages and disadvantages of each approach. Using data from both domestic and foreign studies, the authors compared these methods and identified the features of each one of them. As an illustration of the microsurgical method, a detailed analysis of a clinical case of removing an intervertebral hernia of the lumbosacral spine was performed. As materials and methods, the authors used the data of the patient»s medical history and the surgery protocol.

Quantitative spatiotemporal evolution of large urban agglomeration expansion based on 1995–2020 nighttime light and spectral data

The spatial distribution of urban agglomerations is an essential component of urban agglomeration development planning. To obtain information regarding the expansion of urban agglomerations over large spatiotemporal scales and long periods, this research quantitatively assess the spatiotemporal evolution of the large urban agglomerations in the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) from 1995 to 2020 based on the multisource nighttime light and various spectral data. The results showed that, from 1995 to 2020, (i) the GBA expanded in a "northwest-southeast" pattern and showed a trend of slow expansion and then rapid expansion; (ii) the longest migration of the centroids of the cities in the GBA occurred in Foshan City (9965.22 m), which migrated at an angle of 37.88°to the west by north; the shortest migration distance of the centroid occurred in Macao (779.65 m), where it migrated at an angle of 33.96°to the south by the east; (iii) the GBA expanded in a "circle radiation" pattern, and the subcentre cities have more significant development potentia; (iv) the distribution of "hot and cold spots" of urban expansion in GBA remained stable; and (v) the aggregated autocorrelation of expansion in the GBA was not statistically significant but underwent continuous "decentralisation". Compared with previous studies, our work rapidly and accurately extracted the spatiotemporal evolution of GBA urban expansion from 1995 to 2020 at a spatial resolution of 30 m, which can effectively supplemented current socioeconomic statistics data lacking geospatial information, and detailedly discussed the geospatial displacements of the geographic elements for all cities to assess the differentiated information and agglomeration effects in the inner areas of large urban agglomeration. The results can provide valuable datasets, vital technical support and decision-making references for constructing sustainable development strategies in GBA and other large-scale urban agglomerations.

Research on eccentric-compressive behavior of steel stub columns with localized corrosion

To explore the impact of localized corrosion on the mechanical properties of hollow steel columns under eccentric loads, a specialized localized immersion-accelerated corrosion apparatus was developed. This device facilitated the creation of 17 locally corroded specimens, all subjected to eccentric loading. A systematic examination was conducted on various corrosion parameters including corrosion length, corrosion angle, localized corrosion rate, and corrosion location as well as loading conditions, which encompassed eccentricity and loading angle. Surface corrosion morphology and statistical parameters of the specimens were obtained using a 3D scanner. Subsequently, a nonuniform corrosion model, based on element displacement, was formulated through finite element analysis. Both experimental findings and numerical simulations indicate that localized corrosion does not alter the failure mode of locally corroded circular steel tubes (LCCSTs), which predominantly undergo local buckling in the compressed region. However, it was noted that localized corrosion leads to the elimination of the ascending segment in the load-displacement curve of the LCCSTs, thereby reducing both the ultimate load and ductility. Interestingly, the ultimate load of the LCCSTs was found to be relatively unaffected by variations in corrosion length and location but significantly influenced by factors such as localized corrosion rate, corrosion angle, eccentricity, and loading angle. Furthermore, through a comparative analysis of existing calculation models for the ultimate load of LCCSTs in major specifications, a practical model that accounts for localized corrosion is proposed. This model demonstrates high accuracy and is expected to enhance the understanding and prediction of the ultimate load capacity of LCCSTs in real-world applications.

Comparison of elements and state-variable transfer methods for quasi-incompressible material behaviour in the particle finite element method

AbstractThe Particle Finite Element Method (PFEM) is attractive for the simulation of large deformation problems, e.g. in free-surface fluid flows, fluid–structure interaction and in solid mechanics for geotechnical engineering and production processes. During cutting, forming or melting of metal, quasi-incompressible material behaviour is often considered. To circumvent the associated volumetric locking in finite element simulations, different approaches have been proposed in the literature and a stabilised low-order mixed formulation (P1P1) is state-of-the-art. The present paper compares the established mixed formulation with a higher order pure displacement element (TRI6) under 2d plane strain conditions. The TRI6 element requires specialized handling, involving the deletion and re-addition of edge-mid-nodes during triangulation remeshing. The robustness of both element formulations is analysed along with different state-variable transfer schemes, which are not yet widely discussed in the literature. The influence of the stabilisation factor in the P1P1 element formulation is investigated, and an equation linking this factor to the Poisson ratio for hyperelastic materials is proposed.

Об элементных фундаментах опор высоковольтных линий

Purpose: to substantiate the possibility of using the foundations of supports of high-voltage lines in the form of dispersed horizontal elements combined into a single structure for the perception of alternating loads. To determine by experimental and computational methods the effect of the mutual displacement of elements in the form of an increase in the bearing capacity of foundations and a decrease in their deformations under the influence of pressing and pulling loads. To show the possibility of replacing slab foundations of supports of high-voltage lines with structures made of prefabricated elements to reduce the volume and weight of products transported from the factory. Methods: application of the moire photogrammetric method to assess the development of soil compaction zones and angular deformations of the soil base in a tray with a glass wall under models of slab and elemental foundations. Using the method of boundary integral equations to obtain the dependence of precipitation on the step of elements for flexible and rigid foundations. Results: the effect of mutual influence of foundation elements during their convergence and dispersal in the form of a change in the stress-strain state in their base is illustrated. Differences in the depths of the distribution of compaction zones and areas of development of angular deformations are revealed. Quantitative data on the precipitation of slab and elemental foundations and the influence of the depth of the roof of the solid underlying layer on them have been obtained. Graphical dependences of the relationship of sediment elements with the distance (step) between them are presented. The effect of the division of the foundation on the rate of extinction of marginal tangential stresses in the base is shown. An illustration is made of an increase in the volume and surface area of the bulging body of the elemental foundation, which leads to an increase in its bearing capacity compared to the slab one when calculating for pulling out. Practical importance: the effectiveness of the use of an element foundation in comparison with the paid option in reducing the parameters of the stress-strain state of the base and facilitating logistical tasks during construction is shown. The experimental and computational methods used can be recommended for further refinement of the parameters of the elemental foundations.

Points of inflection of special eigenvalue functions as indicators of stiffness maxima/minima of proportionally loaded structures

The stiffness of a proportionally loaded structure may continuously increase or decrease. As a special exception, it may be constant. On the other hand, an initially stiffening (softening) structure may turn into a softening (stiffening) structure. At the load level of such a change the stiffness of the structure attains an extreme value. The task of this work is to present mathematical conditions for these load levels. Lack of them represents a void in the pertinent literature. The practical significance of the aforementioned changes is the one of indicators of the mechanical behavior to be expected after their occurrence. The second and the last author have recently presented a condition for the load level at which the stiffness of a proportionally loaded structure becomes a minimum value. It is given as d2(ℜ(χ1(λ)))/dλ2=0, representing the condition for a point of inflection of the real part of a complex eigenvalue function χ1(λ), where λ denotes a dimensionless load parameter. The underlying linear eigenvalue problem has two indefinite coefficient matrices, which is a necessary condition for complex regions of eigenvalue functions. These matrices are established with hybrid elements, available in a commercial finite element program. In the present work, d2(χ1(λ))/dλ2=0 is shown to be the condition for the load level at which the stiffness of a proportionally loaded structure attains a maximum value. The eigenvalue function concerned has no complex region. It is also shown that the displacement elements, which are the basis for their extension to the employed hybrid elements, are unable to indicate the load level at an extreme value of the stiffness.

Interfacial reaction mechanism between Y-containing DD5 alloy and Al2O3 ceramic during directional solidification process

This study systematically investigated the influence of varying yttrium(Y) additions on the interfacial reaction mechanism between the DD5 superalloy melt and Al2O3-based ceramic molds during directional solidification. The analysis revealed the formation of a complex multilayer reaction layer at the alloy-ceramic interface. The interfacial products changed from CaO·6Al2O3 to a mixture of various yttrium oxides after Y was added. As the reaction time increased, the sequence of interfacial reaction products observed on the surface of Y-containing alloys progressed as follows: Y2O3, Y4Al2O9, YAlO3, and ultimately Y3Al5O12. Increasing the Y additions promoted the formation of a reaction layer with a higher atomic percentage of Y. The interfacial reaction process between the DD5 superalloy and Al2O3-based ceramic molds involved ceramic decomposition and diffusion, Y element diffusion and displacement reactions, Al2O3 dissolution and further diffusion of the Al element. This process resulted in the formation of different yttrium-aluminum oxides and related to the bidirectional erosion of the Y2O3. These interfacial reactions significantly contributed to the consumption of Y element within the alloy.

A piezoelectric transducer for bone conduction implants designed using finite element analysis

AbstractThis study describes the design of a transducer for bone conduction implants that combines a piezoelectric element and a displacement amplifier. To develop a displacement amplifier with the maximum possible amplification ratio, theoretical analysis was performed to derive the parameters that affect the amplification ratio. Parametric sweep analysis was conducted to calculate the amplification ratio according to changes in the various parameters. The resulting optimal displacement amplifier afforded the maximum amplification ratio when the beam thickness, depth, inclination angle, and length were 0.15 mm, 1.2 mm, 6.5°, and 4 mm, respectively. The displacement amplifier with these optimal parameter values amplified the piezoelectric element displacement by approximately 7.7‐fold. Frequency characteristic analysis by weight was performed to derive a mechanical resonance location with frequency characteristics that appropriately compensated for hearing loss. As a result of this analysis, when a weight of 0.7 g was applied to the displacement amplifier, the mechanical resonance was that required for bone conduction implant transducers.

Study on the Interaction Propagation Mechanism of Inter-Cluster Fractures under Different Fracturing Sequences

Horizontal-well multi-cluster fracturing is one of the most important techniques for increasing the recovery rate in unconventional oil and gas reservoir development. However, under the influence of complex induced stress fields, the mechanism of interaction and propagation of fractures within each segment remains unclear. In this study, based on rock fracture criteria, combined with the boundary element displacement discontinuity method, a two-dimensional numerical simulation model of hydraulic fracturing crack propagation in a planar plane was established. Using this model, the interaction and propagation process of inter-cluster fractures under different fracturing sequences within horizontal well segments and the mechanism of induced stress field effects were analyzed. The influence mechanism of cluster spacing, fracture design length, and fracture internal pressure on the propagation morphology of inter-cluster fractures was also investigated. The research results indicate that, when using the alternating fracturing method, it is advisable to appropriately increase the cluster spacing to weaken the inhibitory effect of induced stress around the fractures created by prior fracturing on subsequent fracturing. Compared to the alternating fracturing method, the propagation morphology of fractures under the symmetrical fracturing method is more complex. At smaller cluster spacing, fractures created by prior fracturing are more susceptible to being captured by fractures from subsequent fracturing. The findings of this study provide reliable theoretical support for the optimization design of fracturing sequences and fracturing processes in horizontal well segments.

A Fireline Displacement Model to Predict Fire Spread

Most current surface fire simulators rely upon Rothermel’s model, which considers the local properties of fuel, topography, and meteorology to estimate the rate of spread, and utilises the concept of elliptical growth to predict the evolution of the fire perimeter throughout time. However, the effects of convective processes near the fireline, which modify fire spread conditions along the fire perimeter, are not considered in this model. An innovative fire prediction simulator based on the concept of fireline element displacement, which is composed of translation, rotation, and extension, rather than a point-by-point displacement, is proposed in this article. Based on the laws of convective heat fluxes across and along the fireline and on laboratory experiments, models to estimate the angular rotation velocity and the extension of the fireline during its displacement are proposed. These models are applied to a set of laboratory experiments of point ignition fires on slopes of 30° and 40° and, given the fact that the rate of spread of the head, back, and flank fire are known, the evolution of the fire perimeter can be predicted. The fire spread model can be applied to other situations of varying boundary conditions provided that the parameters required by the model are known.

A metaheuristic‐based method for analysis of tensegrity structures

SummaryTensegrity systems are construction system that offers solutions for lighter designs compared with a standard truss system consisting of tension and compression elements. Due to their structure, they are recommended in the design of space structures due to the use of lighter and easy‐to‐assemble structural elements such as cables, ropes, and similar to provide the desired durability. In this study, energy minimization was carried out to solve the structural element displacements. It is expected to reduce the total potential energy of the system with minimization. By minimizing the total potential energy of the tensegrity system models, the displacement of each building element is found for the equilibrium condition. Tensegrity models were analyzed by minimizing energy via the adaptive harmony search (AHS) algorithm. In this research, two distinct tensegrity structure specimens were employed. One comprised a cantilever beam, while the other adopted a cyclic model, forming eight equal octagons from eight nodes at both the base and the top. Additionally, an examination was conducted on a two‐layer iteration of the cyclic model. The method is robust for both space and planar tensegrity structures, allowing the determination of deformed shapes under various loads without design assumptions. The TPO/MA method demonstrates superiority in handling nonlinear and barely stable systems, as evidenced by examples illustrating its efficacy in maintaining structural form under increasing loads and challenging conditions.

Mesoscopic damage study of red sandstone considering initial defects under drying-wetting cycles

Abstract In order to study the mechanical properties and microscopic damage of red sandstone by dry and wet cycling, this paper establishes a 3-dimensional uniaxial compression model of red sandstone by using PFC3D software. On this basis, microscopic cracks were introduced to analyze the influence of different cracks on the mesoscopic cracking of the model. The results show that the error between the simulation results and the test results is less than 10% for the model established by PFC3D software. Based on the discrete element model, displacement and velocity maps were obtained, and the values are larger at the contact with the load and smaller at the distance from the load. With the increase of the initial crack angle, the peak stress gradually increases, and with the decrease of the crack size, the peak stress gradually decreases, and the contact force also decreases.

Kinematic and force parameters of an elastic wheel when rolling on a flat rigid surface

The implementation of forces and moments applied to the wheels of a vehicle occurs in the zone of contact of the wheels with the supporting surface, and therefore the analytical determination of their force and kinematic parameters should be based on consideration of the phenomena occurring in contact. One of the directions for solving these problems is based on a technique based on the theory of preliminary displacement of wheel surface elements in the contact zone with the supporting surface and dividing the contact area into adhesion and sliding zones, which makes it possible to take a new approach to the consideration of wheel rolling mechanics. The use of this technique makes it possible to obtain relatively simple equations for such power and kinematic parameters of the wheel as the coefficient of rolling resistance, the coefficient of tangential elasticity of the wheel, and hysteretic losses in the wheel material. The derived equations contain a small number of parameters that can be easily determined experimentally and are convenient for both theoretical and practical use. Comparison of theoretical and experimental results with studies of other authors shows their relatively small discrepancy, which confirms the validity of the research methodology used, as well as the assumptions made.

Finite element analysis and a pilot study of different fixation constructs for Danis-Weber A and B lateral malleolus fractures

BackgroundDisplaced lateral malleolus fractures are typically stabilised through open reduction and internal fixation. The biomechanically and clinically efficacy of locking plates and lag screws, particularly in Weber A and B distal fibular fractures remains a subject of contention. This study examines two locking plate designs for lateral malleolus fractures, evaluating their performance with and without interfragmentary screws using finite element models.MethodsUtilising CT images of a healthy adult male volunteer, a three-dimensional finite element model was constructed. The Fibula-specific Flank Multiaxial Locking Anatomic Plate (FMLP) and the Conventional Locking Plate (CLP) were subjected to stabilisation, both with and without an interfragmentary screw, mimicking the Danis-Weber A and B lateral malleolus oblique fracture fixation. Loads of 140 N and 70 N, equivalent to 20% of the body weight, were applied to simulate the single-leg and two-leg standing conditions in the axial direction. The von Mises stress (VMS) distributions and element displacements were subsequently analyzed.ResultsIn the Danis-Weber A fracture model group, the FMLP with an interfragmentary screw fixation exhibited the lowest peak VMS values: 51.9 MPa in the fibula, 89.0 MPa in the plate, and 61.3 MPa in the screws for simulating single-leg conditions. Under two-leg standing conditions, these peak VMS values decreased to 25.9 MPa in the fibula, 44.5 MPa in the plate, and 30.6 MPa in the screws, respectively. Furthermore, the overall structural peak displacements during single-leg standing for both Weber-A and B fractures with different implants ranged from 1.61 to 2.54 mm. While standing on two feet, the ranged was from 0.80 to 1.27 mm. An interfragmentary screw at the oblique fracture site resulted in reduced the peak value of VMS in the fibula, plate, screws, consequently decreased the overall structural displacement for FMLP and CLP fixation in lateral malleolus fractures.ConclusionsThe current finite element analysis (FEA) demonstrates that FMLP exhibits superior mechanical characteristics in Danis-Weber A and B lateral malleolus fractures compared to CLP. The inclusion of an interfragmentary screw, combined with locking plate design, enhances stability for simple oblique distal fibular fractures. The FMLP presents itself as potential as an alternative for lateral malleolus fractures from a biomechanical perspective. Nevertheless, further verification of these results is imperative through subsequent clinical studies.

Standalone Percutaneous Vertebroplasty for Hyperextension Injuries of the Ankylosed Thoracolumbar Spinal Kyphosis.

Hyperextension injuries of the ankylosed thoracolumbar spine, particularly those with preexisting kyphotic deformity, present significant therapeutic challenges. The authors viewed that such injuries without displacement or fractures of the posterior elements are reasonable candidates for standalone percutaneous vertebroplasty (PVP). In such cases, the posterior tension band is spared; thus, fractures are unstable not in the lateral direction, which would lead to the translation of the fracture, but in the vertical direction. Such vertical instability of the fracture can be stabilized if the open mouth-type vertebral cleft is adequately filled with a sufficiently large amount of polymethylmethacrylate (PMMA) cement. Our three patients receiving standalone PVP received injections of 12 mL, 16.5 mL, and 18 mL of PMMA cement. This minimally invasive surgical procedure achieved both short-term (immediate pain relief and mobilization) and long-term (fracture healing) goals.

Research of generalized mixed hexahedral finite element method based on volume coordinates

The sensitivity of isoparametric elements to mesh distortions has not been sufficiently addressed. Based on the generalized H-R variational principle, the formula of the hexahedral volume coordinate mixed method (HVMM) is derived which applies volume coordinates as local coordinates, maintaining a linear relationship with the Cartesian coordinate system. The influence of the stress boundary conditions on the stress results is also discussed. Numerical results demonstrate the superiority of the proposed element against mesh distortion, and the accuracy of stress results is higher than that of the hexahedral volume coordinate method element (HVCC8) and other displacement elements.

Phase field modeling of fatigue crack growth retardation under single cycle overloads

A zone-based crack retardation model that responds to single cycle overloads is applied to a phase field fatigue framework. Fatigue crack growth is incorporated through the degradation of fracture toughness in the phase field fracture model where a representative loading strategy is followed instead of explicit cyclic loading. The model is demonstrated to capture Paris-Erdogan law type behavior. Crack growth retardation following an overload cycle is simulated through a zone ahead of the crack tip taking inspiration from existing plastic zone-based retardation models. The retardation zone is described through a strain energy density limit, with the overload ratio controlling the extent to which the fatigue damage accumulation rate is slowed inside the retardation zone. The model is implemented utilizing user subroutines in Abaqus with coupled-temperature displacement elements where temperature acts as a stand in for the phase field parameter. The model is found capable of reproducing experimental levels of fatigue life gains and reduction in crack growth rate for compact tension and center-cracked tension panel specimens when various overload levels are applied. Furthermore, the model is demonstrated to be able to capture complex crack paths with great accuracy.

Analysis of Head Displacement during a Frontal Collision at a Speed of 20 km/h—Experimental Studies

The aim of the research is to compare the head displacements of volunteers with the head displacements of the KPSIT C50 dummy, taking into account the change of vehicle seat belts. Unfortunately, sudden braking or collisions between vehicles is becoming more and more common, especially during traffic jams. There is considerable ignorance in the literature on the behavior of the human body during a low-speed collision, which motivates the development of low-speed crash test procedures in order to reduce the risk of cervical spine injuries. The tests were carried out at a teaching station designed to measure the forces in seat belts and the displacements of individual body elements (dummy or volunteer) during a low-speed crash test. The article is part of extensive research on crash tests using volunteers and KPSIT physical dummies. The study involved 150 volunteers who were divided into specific percentile groups. The article compares the head displacements of the constructed KPSIT C50 dummy with the head displacements of volunteers representing the 50th percentile group of the male population. The study conducted with volunteers was under control and was completely safe for people participating in the study. The research shows that the use of a bucket sports seat equipped with four-point or five-point seat belts significantly reduces the movement of the head during a low-speed collision. This type of vehicle seat is safer and provides a reduced risk of injury from hitting the head on the steering column in a low-speed collision when the airbag has not deployed. Moreover, research shows that standard seat belts placed in passenger vehicles allow the head to move freely forward in the event of an accident or low-speed collision. Therefore, if the speed is too low to deploy the airbag, there is a high probability that the driver and passengers will hit their heads against the cockpit of the passenger vehicle during a collision at a speed of 20 km/h.