Thin-walled Model Research Articles

Experimental Study on Static Pressure Sedimentation for a Thick-Walled Bucket Foundation in Sand

As an emerging foundation structure for offshore wind turbines, bucket foundations with superior bearing capacities and efficient construction procedures have attracted significant attention in China. Thick-walled bucket foundations with concrete skirts can effectively reduce the cost and prevent the buckling problem of steel skirts during construction, transportation, and installation. However, great challenges are encountered during the sinking process, and the accurate calculation of sinking resistance is a critical process. Static-pressure tests of thin-walled and thick-walled models in sand were performed to measure the penetration resistance and soil pressure at the sidewalls and ends. The horizontal-soil-pressure coefficients of different models were calculated, and the end and skin-friction coefficients in the cone-penetration test method are recommended. The drag-reduction effects of the anti-drag ring and pressure-pull-out loading method were examined, and the drag-reduction effect was evident for the bucket foundation. The drag-reduction effect of the pressure-pull-out loading method is mainly reflected in the end zone.

Inferring relative surface elastic moduli in thin-wall models of single cells

Inferring relative surface elastic moduli in thin-wall models of single cells

Dynamic characteristics of elastic ring squeeze film damper coupled high-speed ball bearings

This paper explores an elastic ring squeeze film damper (ERSFD) model incorporating high-speed ball bearings to study the journal dynamics at different rotor operating speeds and squirrel cage stiffness. Firstly, dynamic model of the ERSFD is established. The journal works under ball-outer raceway excitation rather than rotor unbalance force. Bearing high-speed characteristics including ball centrifugal force, contact angle change and heavy thrust-applied load are outlined in quasi-static model when deriving bearing force. Oil film pressure is governed by the Reynolds equation and solved iteratively using the central finite difference scheme. Flow performance through the orifice and its effect on the oil film pressure are analyzed using computational fluid dynamics (CFD) technique. Elastic ring deformation is addressed using a thin-walled ring model. Secondly, squirrel cage stiffness and rotor operating speeds were chosen as influence parameters to numerically examine the journal steady-state and transient dynamics, and finally the center orbit and vibration of the journal were experimentally measured. The results demonstrate that an increase in squirrel cage stiffness enables the journal to orbit at small size but leads to higher transmissibility. Small squirrel cage stiffness and rotor operating speed result in high amplitude and velocity oscillations and destabilize the journal; alternatively, higher squirrel cage stiffness is ineffective in transmissibility attenuation regardless of rotor operating speed. It was concluded that a small squirrel cage stiffness cooperating with high rotor operating speed contributes to stabilize journal and attenuate vibration effectively.

Thermoviscoelastic dynamics of composite thin-walled booms on spacecrafts subjected to solar radiation

Viscoelastic behavior of polymer-matrix composites depends very strongly on temperature. This paper presents a thermoviscoelastic dynamics modelling for fiber-reinforced polymeric composite structures with time-varying and nonuniform temperature field. It is used to investigate the thermally induced vibrations of spacecraft booms, for which a new anisotropic thin-walled beam model based on the generalized beam theory is also proposed. Furthermore, efficient evaluation of the thermoviscoelastic constitutive equations in hereditary integral form is performed by means of the derived recursion formula. A harmonic balance procedure in the circumferential direction of tubular booms is devised for both thermal and structural analyses. By comparing the results of viscoelastic and elastic models, the influence of thermoviscoelastic effects on dynamical responses of composite booms under thermal shock is illustrated. The results show that viscoelasticity may play a significant role in vibration suppression of on-orbit flexible structures, especially at high temperature. The work not only provides a novel model for thermal-structural dynamic analysis, but also develops thermoviscoelasticity theory oriented toward engineering and numerical applications.

Numerical study on energy absorption characteristics of bio-mimetic multi-cell thin-walled structures with different hierarchy

Horsetail plant is the most primitive terrestrial plant bred by spores. After hundreds of millions of years of evolution, the internal structure of horsetail plant stem is composed of multiple cavity which brings excellent impact resistance. The investigation of the internal thin-walled structure of horsetail plant can be used to improve the energy absorption property of the existing thin-walled structure, and has important significance and application potential for the design of anti-collision structure. In this study, four kinds of bio-mimetic thin-walled models with different shapes of cross-sections were proposed and established based on the horsetail plants, and the energy absorption values of the structures were calculated and analyzed by numerical method. The squ-3rd structure with the highest specific energy absorption value of 49.121 kJ/kg was obtained. Then the specific energy absorption value and crushing force efficiency of the structure under different parameters, including wall thickness, side length height ratio, and impact angle were calculated and discussed. Based on the numerical simulation results, we found that for the third-order form of structure with square cross-section, the structure with the wall thickness between 1 and 1.25 mm showed better crushing resistance. And, the energy absorption characteristics of the structure were found to have better performance when the side length height ratio is 1:1.

Elastic compressive buckling resistance for back-to-back double angle assemblies

The present study investigates the elastic buckling resistance of compression members consisting of non-slender hot-rolled double angles connected back-to-back with discrete interconnectors. Towards this goal, the study (a) formulates a thin-walled beam finite element buckling solution that treats both angles as independent members away from the intermediate connector locations while constraining the displacements for both angles at interconnector locations, and (b) develops an extension of the Vlasov thin-walled beam theory, originally intended for monolithic members, to determine the effective torsional/warping sectional properties for back-to-back double angle members. The validity of the thin-walled beam finite element model is then verified against experimental results and shell finite element models and its predictions are shown to asymptotically converge to the Vlasov theory extension developed in the present study as the number of interconnectors is increased. A systematic parametric study consisting of 1250 finite element runs is then conducted and the database of results generated is used to propose a simple equation to predict the elastic compressive buckling resistance of double angle compression members.

Effect of a “Slight” Curvature of the Axis of a Thin-Walled Nonprismatic Beam on its Free Vibration

This paper presents an analysis of the effect of a “slight” curvature of the axis of a thin-walled beam on its eigenfrequencies and forms. By “slight” we understand such a beam curvature at which no theory of curved beams (arches, horizontally curved girders), but classical beam theory is applied. The subject of the analysis is the open nonprismatic thin-walled beams with any geometrical parameters, and prismatic beams. The thin-walled beam model used in the analysis was derived on the basis of the momentless theory of plates, using the Vlasov assumptions. The free vibrations of the beams were analysed. Calculations were performed for four groups of beams. Each of the groups comprised two beams with the same configuration of flanges and identical geometrical cross section characteristics, but differing in web geometry. One of the beams had a symmetrical web (a beam with a rectilinear axis in the web plane), whereas the web of the other beam was asymmetrical (a beam with its axis curved in the web plane). The algorithm based on Chebyshev polynomials was used to solve the variable coefficient equations describing the model’s vibration. According to this algorithm, solutions are sought in the form of Chebyshev series and the closed analytical recurrence formulas generated by the algorithm are used to calculate the coefficients of the equations. It has been shown that even a “slight” curvature of the beam’s axis has a significant effect on its eigenfrequencies and forms, as confirmed by a comparison of the results with the ones obtained using Finite Element Method (FEM).

The influence of char particle morphology on char burnout behavior by atomistic simulation

Bituminous coal char particles will differ in morphology, porosity, reactivity, and behavior within the zone II regime (where most practical system operates) due to the influence of maceral, rank, and time–temperature-histories. Effective boiler design requires simulations that appropriately capture char behavior. Most simulations, however, assume solid spherical particles that have homogeneous physical and chemical properties. Unfortunately, coal and time–temperature-history variations make it impossible to make a direct comparison of morphologies alone using traditional experimental approaches. Thus, here the influences of coal char morphologies on its reaction behavior and physical structure were explored via small-scale atomistic simulations. Three (ash-free) chars of solid, thick-, and thin-walled morphologies were examined. The atomistic representations had ∼ 143000 carbon atoms, comprised of similar polycyclic aromatic hydrocarbons (PAH) sizes and stacking distributions. While these structures are far below the actual particle size, the approach permits a direct comparison with a level of control not possible via physical experimentation. The densities of the thick- and thin-walled char models were similar to literature observations (apparent and helium densities). The specific surface area for the solid, thick-, and thin-walled char models were 110, 368, and 509 m2/g, with the latter two being closer to experimental data. A simplified combustion simulation (diffusion and oxygen proximity calculations) demonstrated that the char morphology had a significant impact upon their relative reactivities. The thin-walled structure had the highest overall reactivity due to greater reactive surface access, while the solid and thick-walled structure was respectively 27 and 23% lower. The reaction rate profiles with char conversion for these three structures are close to the experimental observations for pulverized bituminous coal chars, where the rate peak occurs at ∼ 20% conversion. The changes in char size, density, and specific surface area (with char conversion) indicated the thick-walled structure was more similar to the literature data. These atomistic approaches have the potential to aid in exploring the reaction behavior of char particles with various morphologies and complicated structures. With scale-up additional behaviors such as particle fragmentation and ash behavior could be incorporated.

Joint modelling in advanced thin-walled beam models

A methodology for thin-walled frame analysis using displacement modes of beams at joint interfaces has recently been proposed. This paper introduces an implementation that uses a specific advanced beam element based on semi-analytical beam mode solutions of a generalised beam theory. The end cross-sections of the beam elements consist of wall elements with displacement degrees of freedom that can be joined to conventional finite shell element models of the joints. However, before joining the beam element and joint model at the interface, both beam and joint model are transformed into cross-section displacement mode degrees of freedom. This transformation enables the use of a reduced mode space at the interface as well as in the beam. The quadratic nature of the beam mode equations of the beam element leads to a non-unique number of beam displacement modes. However, this paper introduces an exact mode selection technique that leads to a unique set of modes. Necessary details of the beam element formulation are included in order to make a self-contained description of the mode selection technique. Mode reduction through a length scale dependent choice of the number of exponentially decaying distortional modes is investigated and discussed for three types of joint design in four examples. The three joint design types investigated are based on in-plane membrane action, flexural out-of-plane action and a combination of both membrane and flexural action.

A Comparative Study of the Mechanical Properties of FDM 3D Prints Made of PLA and Carbon Fiber-Reinforced PLA for Thin-Walled Applications.

This study focused on the analysis of the mechanical properties of thin-walled specimens fabricated by fused deposition modelling (FDM). Two materials were considered, i.e., polylactide (PLA) and polylactide with carbon fiber (PLA-CF). The article describes how the specimens with different thicknesses and printing orientations were designed, printed, measured to assess their geometric and dimensional accuracy, subjected to tensile testing, and examined using scanning electron microscopy. The data provided here can be used for further research aimed at improving filament deposition and modifying the base material by combining it with different components, for example carbon fiber. The investigations revealed that the properties of thin-walled elements produced by FDM varied significantly depending on the thickness. So far, this problem has not been investigated extensively. Research by analyzing the key parameter, which is the direction of printing that is important for thin-walled models, provides a lot of new information for designers and technologists and opens the way to further extended scientific research in the field of the strength analysis of thin-walled models produced by 3D printing, which is very applicable to structure optimization in the era of the industrial revolution 4.0 and progress in the LEAN manufacturing process.

An Analysis of the Effect of a Change in the Support Point Location on the Vibration of Thin-Walled Beams

This paper deals with an analysis of the free vibration of nonprismatic thin-walled beams, with a special focus on the effect of a change in the support point location on the eigenfrequencies of the systems. A change in the support point location is understood here as occurring within the same fixed cross-section of the beam where the latter is supported. The original elements of this study are a thin-walled beam model and a method of solving differential equations, not previously used by other authors. The equations describing the model used in this paper were derived using the momentless theory of shells and the Vlasov theory assumptions. The displacement equations were derived relative to an arbitrary rectilinear reference axis. In most works known to the authors the equations describing the vibration of the nonprismatic thin-walled beam do not take into account the effects due to the curvature of the axis formed by the shear centers. The recursive algorithm was used to solve the obtained differential equations with variable coefficients. The algorithm enables one to solve the analyzed displacement equations in the form of series relative to the orthogonal Gegenbauer polynomials. For special values of the parameter defining the order of the polynomials the Gegenbauer polynomials became Chebyshev or Lagrange polynomials. In the provided numerical example, the effect of a change in the support point location within the fixed cross-section is examined. It is also analyzed which of the approximation polynomials (Chebyshev or Lagrange polynomials) yield more precise results for a small approximation base. In order to verify the model and the effectiveness of the adopted solution method, the results obtained using this method are compared with the results yielded by FEM. The results obtained showed a significant effect of the position of the support point, within a fixed section, on the eigenfrequencies values of the thin-walled systems.

Investigation of Temperature Deformations and Burning of Models from Polymers

The usage of 3D printing technology SLA and DLP is promising for obtaining casting models. The article presents the results of a study of temperature deformations, developing during the burning of models from polymers “Fun to Do Castable Blend”, “Oh-All! Red” and “Orange Fluor”. In the performance of the experiments, photopolymer models were exposed to an impact of isothermal at temperatures from 50 to 330 °C, and their linear dimensions measured; changes developing on their surface were noted. It is shown that, with an increase of the isothermal holding temperature, the models expand first and narrow later. It has been linked to temperature expansion and subsequent decomposition of the photopolymer. It is shown that the casting molds ,obtained with the usied thin-walled hollow casting models from these photopolymers, are destroyed at the stage of their burning.

Analytical Calculation of Critical Anchoring Length of Steel Bar and GFRP Antifloating Anchors in Rock Foundation

Antifloating anchors are widely used during the construction of slab foundations to prevent uplift. However, existing methods for calculating the critical length of these anchors have limited capabilities and therefore require further research. As the mechanisms which govern the displacement and stability of antifloating anchors are closely related to those of piles subject to uplift, a simplified anchor model has been developed based on existing concentric thin-walled cylinder shear transfer models used for pile design. Analytical expressions for the critical length of the steel bar and GFRP (glass fiber reinforced polymer) antifloating anchors in rock are derived accordingly before demonstrating the validity of the method through engineering examples. The research results show that when the length of an antifloating anchor is less than a critical length, shear slip failure occurs between the anchor and surrounding material due to excessive shear stress. When the length of an anchor approaches the critical length, the shear stress gradually decreases to the undisturbed state. If the anchor length is larger than the critical length, the uplift loads are safely transferred to the ground without causing failure. The ratio of elastic modulus between the anchor and rock mass was found to be positively correlated with the critical anchoring length. Because the elastic modulus of GFRP bars is lower than that of steel bars, the critical anchoring length of GFRP bars is greater than that of steel bars under the same anchor-to-rock modulus ratio (Ea/Es). The results show that the proposed calculation method for the critical length of antifloating anchors appears valid and could provide a theoretical basis for the design of antifloating anchors after further refinement.

Measurement of mid-low order of magnitude of heat transfer rate using infrared thermography in rarefied flow

Based on the analysis of demand for measuring heat transfer of hypersonic vehicle at high attitude, aimed at the characteristic of mid-low order of magnitude of heat transfer rate at ground test for simulating rarefied flow, various factors of the influence on measurement accuracy of mid-low order of magnitude of heat transfer were analyzed. Firstly, the influence of model heating time on heat transfer measurement was analyzed from reducing lateral error of experiment model to controlling temperature rise of model surface, which was based on a steady heat transfer of model surface and one-dimensional and semi-infinite hypothesis. Secondly, model adiabat materials with low thermal diffusivity were put to use. Transient Plane Source Method was introduced so as to calibrate thermal physical parameter(density, specific heat ratio and thermal conductivity) of model material with high accuracy. Kinds of method, such as diffusing compensation and phase-locked method, were adopted to raise measurement accuracy of model surface emittance. Finally, when using thin-wall calorimetry to obtain model surface heat transfer rate, thermocouple was welded on the inner surface of test model to measure heat transfer rate such as MW/m2 order of magnitude, while one was done on the outer surface of model to measure that with several kW/m2 to several hundred kW/m2 by thermocouple or by infrared thermography. In order to compare these results, on the experimental condition of Mach number 12, total pressure 4.2 MPa and total temperature 700 K, heat transfer rate at different points of the double cone thin-wall model was measured by thermocouple and infrared thermography simultaneously. The results indicated that the heat transfer rate measured with infrared thermometry was approaching to that done with thermocouple on the outer surface of model, that heat transfer rate by thermocouple on the outer surface of model was greater than that by thermocouple on the inner surface of test model, and that the influence of model heating time on the measurement of heat transfer rate with different order of magnitude was different.

Research on GMAW based non-supporting thin-wall structure manufacturing

Purpose Additive manufacturing based on arc welding is a fast and effective way to fabricate complex and irregular metal workpieces. Thin-wall metal structures are widely used in the industry. However, it is difficult to realize support-free freeform thin-wall structures. This paper aims to propose a new method of non-supporting thin-wall structure (NSTWS) manufacturing by gas metal arc welding (GMAW) with the help of a multi-degree of freedom robot arm. Design/methodology/approach This study uses the geodesic distance on the triangular mesh to build a scalar field, and then the equidistant iso-polylines are obtained, which are used as welding paths for thin-wall structures. Focusing on the possible problems of interference and the violent variation of the printing directions, this paper proposes two types of methods to partition the model mesh and generate new printable iso-polylines on the split meshes. Findings It is found that irregular thin-wall models such as an elbow, a vase or a transition structure can be deposited without any support and with a good surface quality after applying the methods. Originality/value The experiments producing irregular models illustrate the feasibility and effectiveness of the methods to fabricate NSTWSs, which could provide guidance to some industrial applications.

Aeroelastic vibration analysis of wind turbine blade with Gurney flap

In this paper, based on the parametric design of 3 D blades including typical cross-section and natural frequency calculation of the equivalent model, an integral method for aerodynamic performance and aeroelastic vibration analysis of blade with Gurney flap is proposed. Parametric design and unstructured grid are used to pre-process the blades with/without the Gurney flap. The discrete aerodynamic performance parameters distribution including the lift, drag, and torsion coefficients calculated by Fluent is fitted by the nonlinear least square method based on the trust-region algorithm, and the natural frequencies of the rotating blade are accurately solved by the equivalent thin-walled beam model and Green’s functions. Based on the aerodynamic performance coefficients and natural frequencies obtained by the accurate calculation above, the aeroelastic response equation of typical cross-section considering local aerodynamic damping matrix is established, and the vibration response of blade in flap and torsion direction is further described. From the analysis results, it can be seen that the Gurney flap structure can not only bring higher lift performance to the blade, but also can reduce the amplitude and vibration range of aeroelastic vibration, improve the aeroelastic stability of the blade, and prove the effectiveness of Gurney flap.

Study on the similarity methods for the assessment of ultimate strength of stiffened panels under axial load based on tests and numerical simulations

Since the geometrical dimensions of stiffened panels including length and thickness are very different, considering fabrication, the complete similarity method is generally not realistic or economic to scale thin-wall models for testing. The present paper aims to figure out a partial similarity method to design testing small scale models for stiffened panels, which could consider the effects of buckling behaviours and dimensional distortions. The partial similarity method corresponding to different collapse modes is proposed to design small scale testing models according to the principal influential parameters of plate, column and torsional slenderness, instead of only geometrical dimensions. Seven specimens were tested for assessing the ultimate strength of the stiffened panels under in-plane compressive loads, which are used to verify the FE modelling technology. The influences of various partial similarity methods on the collapse behaviours are discussed by using experimental and numerical results. The strategy of proposed partial similarity method by considering different principle parameters combinations for various collapse modes could give close results between the full and small scale models, which would be a good option for designing testing models.

The impact of compliance on Stage 2 uni-ventricular heart circulation: An experimental assessment of the Bidirectional Glenn

The Bidirectional Glenn (BDG) or cavopulmonary connection is typically undertaken to volume unload the single ventricle in an effort to preserve ventricular and atrioventricular valve function. The geometry of this surgical palliation has been shown to influence the fluid energy loss as well as the distribution of flow that enters through the superior vena cava. In-vitro and in-silico studies to date have been performed on rigid wall models, while this investigation looks at the impact of flexible thin walled models versus rigid walls. Rigid and compliant models of two patient-specific Glenn geometries were fabricated and tested under various flow conditions, within a biosimulator capable of replicating patient specific flow conditions. It was found that the compliant models exhibit greater levels of energy loss compared to the rigid models. Along with these findings greater levels of turbulence was found in both compliant models compared to their rigid counterparts under ultrasound examinations. This shows that vessel compliance has a significant impact on the hemodynamics within hypoplastic left heart syndrome.

A nonlinear cross-section deformable thin-walled beam finite element model with high-order interpolation of warping displacement

In this paper, a new finite element model is developed for nonlinear analysis of thin-walled beams by introducing a high-order interpolation for the warping displacement field to better simulate actual cross-section deformation. It is discovered that, due to the significant coupling between bending and membrane deformations in each wall, it is crucial for a nonlinear thin-walled beam finite element to be capable to describe complex warping displacement distribution over the cross-section. In the geometrically exact beam element model developed, the warping displacement is expressed by using a higher-order interpolation scheme, while the distortion displacements are independently described by using a number of cross-section in-plane deformation modes. Numerical results are presented to demonstrate the effectiveness of the proposed model and investigate possible impacts of interpolation schemes for the warping displacement distribution on the solution accuracy under different problem settings. The results show that with an appropriate high-order warping displacement interpolation scheme, the proposed beam model can produce very accurate results even in the case of small wall thickness, outperforming many of the existing models. It is therefore concluded that special attention is needed on the warping displacement field for a finite element model to accurately simulate the cross-section distortional deformation of thin-walled beams. • A geometrically exact cross-section deformable thin-walled beam finite element model is developed. • The distortion and warping displacements are described by distortion modes and high-order interpolation, respectively. • Numerical examples are presented for a comprehensive investigation of the present finite element model. • The importance of warping displacement field for ensuring solution accuracy is pointed out.

Thin-walled composite beam cross-sectional analysis using the mechanics of structure genome

Quick and accurate predictions of cross-sectional properties are required in the preliminary design of thin-walled composite beams. Existing literature provides accurate analytical solutions to the problem, albeit limited to open and single cell sections with stress continuity constraints imposed. Mechanics of structure genome has been used to develop an asymptotically correct model for thin-walled open, closed, single and multi-cell cross sections consisting of any arbitrary anisotropic material without imposing any additional conditions. In this paper, Euler-Bernoulli thin-walled beam cross-sectional model is developed in a finite element framework and demonstrated using several examples, followed by a comparison with existing approaches.