Concentrated Force Research Articles

QS21-Initiated Fusion of Liposomal Small Unilamellar Vesicles to Form ALFQ Results in Concentration of Most of the Monophosphoryl Lipid A, QS21, and Cholesterol in Giant Unilamellar Vesicles.

Army Liposome Formulation with QS21 (ALFQ), a vaccine adjuvant preparation, comprises liposomes containing saturated phospholipids, with 55 mol% cholesterol relative to the phospholipids, and two adjuvants, monophosphoryl lipid A (MPLA) and QS21 saponin. A unique feature of ALFQ is the formation of giant unilamellar vesicles (GUVs) having diameters >1.0 µm, due to a remarkable fusion event initiated during the addition of QS21 to nanoliposomes containing MPLA and 55 mol% cholesterol relative to the total phospholipids. This results in a polydisperse size distribution of ALFQ particles, with diameters ranging from ~50 nm to ~30,000 nm. The purpose of this work was to gain insights into the unique fusion reaction of nanovesicles leading to GUVs induced by QS21. This fusion reaction was probed by comparing the lipid compositions and structures of vesicles purified from ALFQ, which were >1 µm (i.e., GUVs) and the smaller vesicles with diameter <1 µm. Here, we demonstrate that after differential centrifugation, cholesterol, MPLA, and QS21 in the liposomal phospholipid bilayers were present mainly in GUVs (in the pellet). Presumably, this occurred by rapid lateral diffusion during the transition from nanosize to microsize particles. While liposomal phospholipid recoveries by weight in the pellet and supernatant were 44% and 36%, respectively, higher percentages by weight of the cholesterol (~88%), MPLA (94%), and QS21 (96%) were recovered in the pellet containing GUVs, and ≤10% of these individual liposomal constituents were recovered in the supernatant. Despite the polydispersity of ALFQ, most of the cholesterol, and almost all of the adjuvant molecules, were present in the GUVs. We hypothesize that the binding of QS21 to cholesterol caused new structural nanodomains, and subsequent interleaflet coupling in the lipid bilayer might have initiated the fusion process, leading to creation of GUVs. However, the polar regions of MPLA and QS21 together have a "sugar lawn" of ten sugars, the hydrophilicity of which might have provided a driving force for rapid lateral diffusion and concentration of the MPLA and QS21 in the GUVs.

Lubrication analysis of the piston ring for the two-stroke marine diesel engine based on modified radial tension

As the piston ring is inserted into the bore, it is forced against the liner by radial tension, thereby creating a seal. Radial tension not only affects the piston ring’s seal, but also significantly influences its tribological properties. To investigate the effect of non-uniform radial tension of piston ring on the lubrication properties, a contact finite element model of piston ring and cylinder liner tribo-pairs is constructed in this study. The contact pressure distribution between the tribo-pairs is determined based on this model. The obtained pressure is then regarded as the non-uniform radial tension of the ring, which is fitted to a formula. The formula is validated in two ways. Firstly, its generality is verified by simulating several different piston rings using the contact model and comparing their results with the formula. Second, a test rig was designed and set up to measure the piston ring’s circumferential tension. To verify the formula’s accuracy, an equivalent principle model of distributed pressure and concentrated force was proposed. This formula is used as an initial force to modify the piston ring mixed lubrication model. Based on this model, the lubrication performance of the piston ring with uniform radial tension and non-uniform radial tension into consideration is investigated. The findings demonstrate that the piston ring radial tension is of significance to its lubrication performance and can be modified to lessen local friction and wear issues, particularly those related to the piston ring gap, and thus improve the dependability of the piston ring.

Iterative decoupling procedure for the coupled 1D problems on example of closed cylindrical shell at static loading

The general iterative method of formal decoupling of two coupled 1D problems is suggested. Its essence consists in the alternative consideration of one of two problems as the main one, the aim of which is to produce the eigenfunctions. Then the other problem is considered as an auxiliary one, which is aimed to obtain the particular solution. The latter is presented as a linear combination of already known eigenfunctions, and then is substituted again into the first problem to refine the constants of main governing differential equation and to get the corrected eigenfunctions. The convergent iterative procedure of gradual refinement of the above constants is elaborated. The accuracy and technique of application is considered in details for the closed cylindrical shell problem, which is expanded in Fourier series with respect to circumferential coordinate. This actually leads to coupled 1D problems – one is the plane elasticity problem, and other – the plate problem. The results of calculation show the high accuracy of the method, which allows to get any required number of significant digits in eigenvalues. The comparison with known theoretical and FEM results for radial displacement and axial bending moment distribution at the vicinity of point of concentrated radial force application demonstrates the efficiency and accuracy of the method.

Mandibular Titanium Miniplates Change the Biomechanical Behaviour of the Mandible in the Case of Facial Trauma: A Three-Dimensional Finite Element Analysis.

Our study aimed to compare the biomechanical behaviour of mandibles with or without titanium miniplates when subjected to an impact after bone healing using a finite element model (FEM) of the human mandible. We simulated mandibular trauma on an FEM of a human mandible carrying or not two parasymphyseal miniplates and applying a concentrated force of 2000 N to four different areas, including the insertion area, the area straddling the edge of the miniplates and the adjacent bone, at a distance from the miniplates on the symphysis, and on the basilar border of the mandible below the miniplates. Then, we compared the Von Mises stress distributions between the two models. In the case of an impact on the miniplates, the maximum Von Mises stress occurred in two specific areas, on the cortical bone at the posterior border of the two miniplates at a distance from the impact, while in the model without miniplates, the Von Mises stresses were homogenously distributed in the impact area. The presence of titanium miniplates in the case of trauma affects the biomechanical behaviour of the mandible and could cause more complex fractures. We recommend informing patients of this potential risk.

Asymptotic solutions for large fractures growing parallel to a free plane

Straight 2D and disc-like cracks situated close to a parallel free plane are considered and asymptotic solutions for the stress intensity factors (SIFs) and crack opening are developed. Two asymptotic terms with respect to the small ratio of distance from the surface to the crack length/radius are derived. The derivation is based on considering the material between the crack and the free surface as an elastically supported beam or circular plate. The crack is considered to be opened either by uniform tensile stress or a pair of concentrated forces or moments representing the action of central defects (these represent for instance the crack growth from initial inclined crack or pore under compression acting parallel to the free surface). A crack with non-interacting surfaces (the conventional crack) and a crack with linear links between the surfaces are considered. Interaction with the free surface is shown to considerably increase the crack opening and SIFs, while the presence of the elastic links can reduce these crack parameters. In particular, the opening and SIFs of a crack with linear links under a pair of concentrated forces/moments exponentially vanish with the crack dimensions tending to infinity. The obtained asymptotic solutions provide a simple and accurate tool for investigating mechanisms of surface delamination and spallation (including thermal spallation and strain rockbursts).

Gradient elasticity solutions of 2D nano-beams

In this study, the exact analytical solutions of a two-dimensional linear homogeneous isotropic nano-beam in gradient elasticity are studied. Four different types of two-dimensional cantilever beams and related boundary conditions are considered. The cases are a cantilever beam under a concentrated force at the end, a cantilever beam under a uniform load, a propped cantilever beam under a uniform load, and a fixed-end beam under a uniform load. The two-dimensional stress gradient fields are investigated and obtained from the analytical solutions of a linear second-order partial differential equation written in terms of the classical and the gradient Airy stress functions. Additionally, the micro-size effects in the displacement components for different loads and support conditions for the two-dimensional cantilever beams by using strain gradient elasticity theory are investigated. Furthermore, for one-dimensional Euler–Bernoulli beam model, the associated stress and strain elasticity solutions are obtained from two-dimensional analytical solutions. The graphical presentations of the exact closed-form solutions are provided and discussed.

An isoparametric quadratic boundary element for coupled stretching-bending analysis of thick laminated composite plates with transverse shear deformation

Recently, we derived the Green's function for an infinite thick laminated composite plate subjected to concentrated forces and moments. By serving this Green's function as the fundamental solutions, in this paper for the first time we develop the associated boundary element method (BEM), which is applicable to general problems of thick laminated plates with various types of deformations. For example, the in-plane stretching and out-of-plane bending deformations may be coupled together, which occurs for the unsymmetric laminated composite plates. Besides, the transverse shear deformations are also incorporated based upon the first order plate theory. To complete the entire development of the proposed BEM, all the involved issues, such as the boundary integral equations, the fundamental solutions and their derivatives, the mathematical formulation for the selected isoparametric quadratic boundary element, and the treatments of singular integrals are elaborated in this paper. The calculations of complete solutions at boundary or internal points are provided as well. The accuracy and efficiency of the proposed BEM are demonstrated through numerical examples, which show that it outperforms the conventional finite element method and is applicable for general thick laminated plates with unrestricted coupling effects.

A generalized antiplane singularity within a semi-infinite wedge of arbitrary angle

The state of stress arising within an elastic wedge generated by an antiplane singularity present within it is studied. An analytical solution is derived with a unified generic approach. The singularity may represent either an anti-plane concentrated force or a screw dislocation. To validate the general solution, two degenerate cases are presented. Further, the image force present on the screw dislocation due to the wedge free boundary is obtained. It is found that when the screw dislocations are placed in the vicinity of the wedge surface, the image force will drive dislocations to the free boundary where they will be annihilated. This implies that a dislocation-free zone may exist along the free surface of the wedge. To demonstrate the application of the fundamental solutions, a formulation for a slip band under anti-plane loading with Green’s function method is provided. The solutions developed in this study may be used as building blocks to model the damage of material near a V-notch under versatile anti-plane load conditions or torsional loading.

To the Problem of Discontinuous Solutions in Applied Mathematics

This paper addresses discontinuities in the solutions of mathematical physics that describe actual processes and are not observed in experiments. The appearance of discontinuities is associated in this paper with the classical differential calculus based on the analysis of infinitesimal quantities. Nonlocal functions and nonlocal derivatives, which are not specified, in contrast to the traditional approach to a point, but are the results of averaging over small but finite intervals of the independent variable are introduced. Classical equations of mathematical physics preserve the traditional form but include nonlocal functions. These equations are supplemented with additional equations that link nonlocal and traditional functions. The proposed approach results in continuous solutions of the classical singular problems of mathematical physics. The problems of a string and a circular membrane loaded with concentrated forces are used to demonstrate the procedure. Analytical results are supported with experimental data.

INVERSE PROBLEM FOR A TIMOSHENKO BEAM WITH AN ADDITIONAL VISCOELASTIC SUPPORT UNDER NONSTATIONARY DEFORMATION

The non-stationary loading of a mechanical system consisting of a beam hinged at the edges and an additional support installed in the span of the beam is considered. The deformation of the beam is modeled on the basis of Timoshenko's hypotheses, taking into account the influence of rotatory inertia and shear. The deformation of the beam is described by a system of partial differential equations, which is solved analytically by means of expansion of the unknown functions into the relevant Fourier series and further use of the Laplace integral transformation. It is assumed that the additional support has linear-elastic and linear-viscous components, and the displacements coincide at the point where the additional support is connected to the beam. The reaction between the beam and the additional support is replaced by an external unknown concentrated force applied to the beam, which varies in time. The law of time variation of this unknown reaction is determined by solving the Volterra integral equation. The inverse problem of deformable solid mechanics is solved, that is, it is assumed that the deflection at a point of the beam with the additional support is known, whereas the law of time variation of the external impulse load causing the deflection is unknown. The application point of the external load and the point of the additional support connection are considered to be known and do not change in the process of deformation (when obtaining the solution of the problem it was supposed that these could be any points of the beam except for its ends). The described inverse problem is reduced to a system of two Volterra integral equations of the first kind with regard to the unknowns of the external disturbing load and reaction between the plate and the additional support, which is solved by analytical and numerical method. Analytical relations and calculation results for specific numerical parameters are given. The results obtained in this work can be used for indirect measurement of impulse and shock loads acting on beams with additional supports, for which not only elastic but also linear-viscous characteristics are taken into account.

MATHEMATICAL MODELLING OF DYNAMIC PROCESSES IN A LAYERED INCOMPRESSIBLE HALF-SPACE WITH INITIAL STRESSES UNDER THE ACTION OF A MOVING LOAD

This work is devoted to the study of the influence of the protective coating, initial stresses, mechanical characteristics of materials, movement parameters of the surface load on the stress-deformed state of the elastic base. The relevance of the research results is related to the possibility of their use in the creation of qualitatively new materials, structures and building structures. Two models of a layered incompressible half-space are considered and compared: 1) an elastic plate on an elastic half-space; 2) the top layer (protective coating) is modelled by concentrated masses. The concentrated force moves along the free surface of the protective layer at a constant speed at a certain angle to the surface of the half-space. The solution of the problem was obtained using the method of integral Fourier transformations. Analytical results are given in a general form for materials with an arbitrary elastic potential, for cases of unequal and equal roots of characteristic equations, for various conditions of combination of elements of a layered medium and for any speed of movement of the load. The material with the Bartenev-Khazanovich potential was considered for numerical analysis. The calculations were carried out within the framework of the theory of finite initial deformations. The impact of the moving load, initial stresses and mechanical parameters of the elements of the layered base on the main characteristics of its stress-strain state was studied.

The Thermal Stress Problem of Bimodular Curved Beams under the Action of End-Side Concentrated Shear Force.

A bimodular material is a kind of material that presents two elastic moduli in tension and compression. In classical thermoelasticity, however, the bimodular material is rarely considered due to its complexity in analysis. In fact, almost all materials will present, more or less, bimodular characteristics, and in some cases, the mechanical properties of materials cannot be fully utilized simply by ignoring the bimodular characteristics. In this study, the thermal stress problem of bimodular curved beams under the action of end-side concentrated shear force is analytically and numerically investigated, in which the temperature rise modes in a thermal environment are considered arbitrary. Using the stress function method based on compatibility conditions, a two-dimensional solution of thermoelasticity of the bimodular curved beam subjected to end-side concentrated shear force was obtained. The results show that the solution for a bimodular curved beam with a thermal effect can be reduced to that of a bimodular curved beam without a thermal effect. At the same time, the numerical simulation for the problem verifies the correctness of the theoretical solution. The results may serve as a theoretical reference for the refined analysis and optimization of curved beams in a thermal environment.

Lagrange multipliers at the boundary in the inextensional bending theory of thin elastic shells

The theory of inextensional deformations of shells is extended by introducing Lagrange multipliers at the boundary to supplement those operating in the interior. These are associated with a constraint on the metric on the closure of the shell midsurface. The additional multipliers allow for a richer set of external actions than those admitted by the conventional theory. In particular, they balance concentrated forces in the tangent plane of the surface applied at corners of the boundary.

Training on Sand or Parquet: Impact of Pre-Season Training on Jumping, Sprinting, and Change of Direction Performance in Professional Basketball Players

This study examined the effects of combined change of direction (CoD) and plyometric training on sand in basketball players’ jump, sprint, and CoD performances. In total, twenty-five male professional basketball players (age, 24.1 ± 4.2 years; height, 192.5 ± 8.0 cm; body mass, 92.6 ± 11.6 kg) participated in a pre-season intervention study over seven weeks, where two teams completed an identical speed training protocol, either on sand or on a hard surface, while a third team served as the control. All participants followed their regular pre-season training, while the intervention groups additionally performed the training protocol twice weekly. A repeated-measures ANOVA (rANOVA) showed significant interaction effects on the countermovement jump (F = 14.90, p &lt; 0.001), pivot–step–jump test (F = 8.09, p = 0.002), 10 m sprint time (ST) (F = 4.18, p = 0.050), and 20 m ST (F = 8.49, p = 0.002). Moreover, an rANOVA showed significant interaction effects for the CoD performance regarding total time (F = 5.70, p = 0.010) and average velocity prior to the CoD (F = 8.40, p = 0.002) and after the CoD (F = 3.89, p = 0.036). As such, the findings suggest that sand-based training elicits kinematic adaptations, increased muscle activation, and a shift towards concentric force development that all contribute to enhanced athletic capabilities.

Finite element analysis of the underslung carrier rocket effect on stress and strain distribution in a structure of the MiG-29 aircraft

The paper presents selected aspect of the analytical-conceptual research project entitled: Airborne-Rocket Launch System for Delivering Satellite Payloads into Low Earth Orbit – Feasibility Study. The aim of the project is to conduct series of aerodynamic, strength, and aeroelastic simulations of Polish aging combat aircraft (Mig-29 and Su-22) to explore applicability of both fighters as an airborne platform for carrying out carrier rockets with a detachable satellite payload. This work presents exemplary analyses in the area of airframe loads and structural strength and deformability of MiG-29 for predicted operational variants with carrier rockets put to the hardpoints under fuselage. The numerical simulations were conducted for a structural discrete model of the aircraft prepared for finite element analysis in MSC Software. Model development involved such aspects as precise discretization of geometric model, declaration of material constants, identification of structural properties, introduction of suitable merging connections for included airframe assemblies, and final validation of model mass and stiffness. The model was analyzed in MSC Nastran software with application of linear “Statics” solution. External flight loads introduced into the model were calculated for specific points of the flight envelope—the highest values of load factor were taken into consideration ( n=9). The counterpart aerodynamic force distribution in a form of a set of equivalent lumped forces was calculated. Then, the aerodynamic and weight loads were added to the model as a set of forces applied to specific structural nodes. Additionally, weights of applicable carrier rockets were taken into account as concentrated forces applied to under-fuselage suspension hardpoints. Calculations were performed for several rockets of mass values between 250 and 1200 kg. Parametric dependencies were investigated as an effect of missile mass and size on stress and strain distribution over the whole structure. The areas of stress cumulations were identified. On the basis of static structural deformation, maximum wing tip displacements were assessed.

An analytical Green’s function for Laplace operator in an infinite plane with two circular holes using degenerate kernels

In this paper, Green’s function problem of an infinite plane containing two circular boundaries is analytically studied by using the boundary integral equation method (BIEM). The original problem is decomposed into two parts by introducing the superposition technique. The first part is a free field caused by the concentrated force. The second part is a Laplace problem subjected to the corresponding boundary conditions. The second part can be solved by using the null-field boundary integral equation in conjunction with the degenerate kernel. Since the geometry of problem under study is composed by two circular boundaries, the kernel function is naturally expanded to series form in terms of the bipolar coordinates. The Green’s function is analytically expressed in three regions instead of two regions for the eccentric domain. To the authors’ best knowledge, this is the first time that the Green’s function of the problem is presented in this form. To show the validity of the present method, the contour result of the present method is compared with those obtained by the image method, the null-field BIE in conjunction with the adaptive observer of polar degenerate kernel.

Reinforcement determination for anchorage zones of post-tensioned concrete beams

In post-tensioned concrete beams, the high concentrated compressive forces are transmitted to the concrete zones at the beam ends through the anchorage devices. As a result, they can burst and split if the concrete is not adequately reinforced. The paper determines the reinforcement in anchorage zones with axially loaded post-tensioned tendons using the linear elastic analysis method, which involves computing the state of stresses as linearly elastic, and the equilibrium-based plasticity approach method as strut-and-tie models to provide prestressing force paths as a truss structure. Some numerical models are also analyzed to clarify the present methods.

Vibration Isolation Characteristics of Impedance-balanced Ship Equipment Foundation under Unbalanced Excitation

A new type of impedance-balanced ship equipment foundation structure based on the principle of impedance balancing using a “discontinuous panel-vibration isolation liquid layer-foundation structure” is proposed to solve the problem of poor low-frequency vibration isolation of the foundation under unbalanced excitation of shipboard equipment. Based on the finite element method, the influence of characteristic parameters of the foundation panel structure on its vibration reduction characteristics under unbalanced excitation is explored. The results show that the vibration isolation level of the impedance-balanced foundation is 10 dB higher than the traditional foundation in the low-frequency band of 10-500 Hz when subjected to combined excitation of concentrated force and moment. Increasing the thickness of the impedance-balanced foundation panel can enhance the isolation effect. Increasing the number of sub-panels can effectively reduce the vibration response of the foundation panel and enhance the isolation performance of the foundation. The connection stiffness between sub-panels has a small effect on the isolation performance of the foundation.

Receding of an elastic weighty strip from a rigid base under the action of a normal concentrated force

Receding of an elastic weighty strip from a rigid base under the action of a normal concentrated force

Effects of transverse normal strain on the deformation of laminated and sandwich arches under the action of concentrated force

It is well-known that the concentrated force develops high-stress concentration at the point of application which is one of the important parameters to be considered while designing the laminated composite structures under the action of concentrated force. The literature available shows that the study on static deformation of laminated sandwich shallow arches under the action of the concentrated force is limited. In the present study, static deformation of laminated sandwich arches under the action of concentrated loading is investigated using higher-order arch theory considering the effects of transverse normal strain. An exponential type higher-order arch theory is developed in this study which satisfies the traction-free boundary conditions at the top and the bottom surfaces of the arch using constitutive relations. Governing equations are derived within the framework of the principle of virtual work. An analytical solution for the static deformation of simply supported laminated and sandwich shallow arches are obtained using Navier’s technique. The effects of the lamination scheme, radius of curvature and aspect ratio on the deflection, and stresses of shallow arches are evaluated. The present results are compared with previously published results wherever possible for the verification of the present theory.