Non-uniform Loading Research Articles

Dynamic Stability Analysis of Square Isotropic/Laminated Composite Plates With Circular Cutout Subjected to Non-Uniform Follower Edge Load With Damping

The present investigation deals with the study of vibration and dynamic instability behaviour of square isotropic/laminated composite plates with circular hole subjected to partially distributed follower edge forces using finite element method. The first order shear deformation theory is used to model the plate, considering the effects of shear deformation and rotary inertia. The modal transformation technique is applied to the resulting equilibrium equation for subsequent analysis. Structural damping is introduced into the system in terms of equivalent viscous damping to study the significance of damping on stability characteristics. The effects of cutout size, load width, boundary condition, ply orientation, direction control of the load and damping parameters are considered for the stability behaviour of the plates. The results show that under follower loading, the system is susceptible to instability due to flutter alone or due to both flutter and divergence, depending on system parameters.

Theoretical modeling of the pre-cutting system performance for the tunnel face stability in very weak rock masses

By forming continuous pre-lining around the tunnel's perimeter, pre-cutting is a recognized tunneling technique that enables full-face excavation of a tunnel even in unfavorable ground conditions. In this study, a theoretical method is put out to simulate the performance of this kind of pre-support in squeezing conditions. The loading distribution on the pre-cutting shells is determined for this purpose using the LDP of an unsupported tunnel, and the non-linear stiffness of the pre-cutting shell is then determined using the shell theory. The convergence confinement method is used to calculate how much the pre-supported tunnel isdeformed. The non-uniform loading distribution also results in the tangential and longitudinal bending moments on the pre-cutting shell. To show the effectiveness of pre-cutting shells in extremesqueezingconditions, several examples are solved. As a result, a few graphs for the preliminarydesign of a tunnel using this technique are given. The graphs show the overall tunnel displacement for various pre-cutting shells under various geological conditions. The outcomes demonstrate good agreement between FALC 3D resultsand the ones by thesuggested analytical model. A preliminary design can be made using the assessment of the proposed methodonthe loads on the pre-cutting system.

Stability of a particle-laden planar jet in the dilute suspension limit

Particle laden flows are commonly seen in many industrial applications, such as fluidized beds in process industry, air laden with abrasive particles in abrasive machining, and particle laden plumes in chemical industries. In the present work, we perform local analysis of a particle laden planar jet in the dilute suspension regime. Unladen parallel planar jets have been extensively studied using normal modes and are shown to have two unstable modes, namely, sinuous and varicose modes. Sinuous modes are found to be more unstable compared to the varicose modes. In the present study, we investigate the effect of particles on the stability of planar jets. Addition of particles at low Stokes numbers (St) (fine particles) results in higher growth rates than that of the unladen jet. In the intermediate Stokes number regime, addition of particles has a stabilizing effect on both the sinuous and the varicose modes. Interestingly, for St∼10, the unstable varicose mode is completely damped. Increasing the Stokes number by increasing the particle size, both sinuous and varicose modes, shows increasing growth rates, while increasing the density ratio has a stabilizing effect on the flow. For non-uniform particle loading, additional modes apart from the sinuous and varicose modes are observed. These modes suggest the occurrence of compositional instability with an increased particle accumulation in the shear layer that is an order of magnitude higher compared to that of the sinuous and varicose modes.

Numerical analysis of transient heat and mass transfer for a water heat pipe under non-uniform heating conditions

Non-uniform loads are widely present in heat pipe applications and have significant effects on their performance. In this work, a transient 3D CFD model is developed to investigate the liquid–vapor flow and heat transfer for a water heat pipe under various non-uniform loads. The source terms are added to the governing equations using the User-Defined Function (UDF) to simulate the evaporation and condensation process. The model is verified using the experimental and simulated data under uniform and non-uniform loads in the literature. The effects of key parameters including adiabatic length, heating power, and heat distribution on the thermal performance of heat pipes are analyzed. The results show that the non-uniform conditions would shift the maximum axial velocity of vapor to the unheated side and induce a significant circumferential flow in the wick region, especially in the evaporator section. The short adiabatic length and high heating power could reduce the elapsed time of reaching the steady state. The heat distribution in the evaporator section exhibits little effect on the elapsed time reaching the steady-state and the average steady-state vapor temperature

The damage characteristics of a coal specimen and the associated constitutive model under nonuniform load

The damage characteristics of a coal specimen and the associated constitutive model under nonuniform load

Evaluating feasibility of field modeling of fire to calculate fire characteristics in buildings and premises

Introduction. The present paper describes application of a software package using a field model of fire dynamics to calculate fire characteristics in buildings and premises of nuclear power plants (NPP). The authors give necessary justifications for using the software package in performing fire calculations in multifunctional buildings and premises.Aim. To analyze different fire modeling methods, their application and use of the software package for field modeling of fire dynamics to determine the dynamics of fire hazards in complex premises, in facilities with non-uniform fire loads or complex gas exchange processes; to contribute solving the issue of safe distances ensuring that fire cannot spread between equipment elements.Materials and methods. The authors developed and verified a software package to perform calculations using the field model of fire dynamics. The paper presents the basics of the field method for fire modeling in multifunctional premises and the aspects of its application in fire simulation. The presented analytics is substantiated with examples of fire simulation results in real premises of NPPs.Results. Following the analysis of different methods of modeling the dynamics of development and spread of fire hazards, the present paper introduces the possibility of using various methods of fire modeling in the evaluation of fire hazards for buildings and premises. The authors describe the advantages of field modeling method for calculating local parameters of fire. The paper provides information on the software codes to calculate the dynamics of fire and evaluate the thermal effects of fire on building structures.Conclusion. It has been found possible to apply field model of fire dynamics for calculating fire hazards in various buildings, premises and open areas. Calculations using the presented field model enable the sufficiency of fire resistance of building structures and multifunctional premises to be substantiated due to preventing fire spread outside the fire zone during the estimated time of burnout of the total fire load.

Bearing Non-Uniform Loading Condition Monitoring Based on Dual-Channel Fusion Improved DenseNet Network

Misalignment or unbalanced loading of machine tool spindle bearings often results in skewed bearing operation, which makes the spindle more susceptible to failure. In addition, due to the weak impact signal of the bearing in skewed operation, a single feature information cannot accurately characterize the operation status of the bearing. To address the above problems, this paper proposes a method to monitor the uneven running state of bearing load based on a dual-channel fusion improved dense connection (DenseNet) network. First, the original signal is pre-processed by overlapping sampling method, and the dual-channel experimental data are obtained by frequency-domain and time-frequency-domain algorithms; then the processed data are input into the improved 1D-DenseNet and 2D-DenseNet models respectively for feature extraction; then the frequency-domain and time-frequency-domain features are fused by concat splicing operation, and the output belongs to each category The probability distribution is used to characterize the operating state of the bearings. Finally, the validity of the algorithm model is verified by using the Case Western Reserve University public rolling bearing data set, and an experimental bench is designed and built for experimental verification of the uneven bearing load operation. The comparative analysis of the experimental results in this paper shows that the algorithm can extract the features of the input signal more comprehensively and finally achieve 100% recognition accuracy.

Lateral Torsional Buckling Resistance and Design of High Strength Steel Beams Subjected to Nonuniform Temperature

The mechanical characteristics of high-strength steel (HSS) at high temperatures vary significantly from those of mild steel, so fire design regulations derived from mild steel cannot be transferred to HSS structures. Therefore, this paper investigates the fire resistance of beams made of HSSs, which will facilitate the design and application of HSS structures. Due to the heat dissipation of the concrete floor, steel beams are generally heated from three sides, and the temperature distribution in the steel beam cross-section is nonuniform. For such cases, the fire resistance of HSS beams is assessed using finite element models (FEMs) with nonuniform temperature distribution. A Ramberg–Osgood model was used to predict stress–strain relationships of Q460, Q690, and Q960 HSSs at elevated temperatures, and the model was verified by material tests. In the FEM, the proposed stress–strain relationships of HSSs at elevated temperatures, initial geometric imperfections and residual stress are considered for better accuracy. After verifying the established model against experimental results, the influence of nonuniform temperature distribution, load pattern, steel grade, and slenderness ratio on the resistance of HSS beams is investigated by conducting parametric analyses using the verified FEM. It is found that the critical bending moment of steel beams at elevated temperatures associated with lateral-torsional buckling highly depends on the reduction of elastic modulus of steel. By comparing FEM results with EN 1993-1-2, it is evident that EN 1993-1-2 is unsuitable for assessing the fire resistance of HSS beams. Therefore, the expression specified in EN 1993-1-2 is modified by fitting the finite analysis results to more accurately evaluate the fire resistance of HSS beams considering the nonuniform temperature distribution.

Failure analysis of an aero-engine inter-shaft bearing due to clearance between the outer ring and its housing

The inter-shaft bearing is a critical but vulnerable component of dual rotors, because of the severe operational conditions and loads. This paper investigates the failure mechanism of a fractured inter-shaft bearing belonging to a high thrust-weight ratio turbofan engine. Fractographic and microscopic analyses of the fracture surfaces were conducted, followed by vibration signal processing. Finite element analyses of the outer ring were also performed considering the centrifugal, thermal, and roller-raceway loads. What’s more, using the linear elastic fracture mechanics theory, the crack growth path simulation was obtained, whose result showed good agreement with the real fracture morphologies. The results indicated that due to the clearance between the outer ring and its housing during the operation, the anti-rotation tabs of the outer ring were subjected to non-uniform load, thus several tabs might suffer large stress concentrations at the root fillets, which could lead to the crack initiation. During the following operation of the aero-engine, the crack propagated through the outer ring and cause the fatigue fracture of tabs. The investigation provided herein suggests that the outer ring and its housing should be redesigned to eliminate the clearance during the operation, an outer ring formed integrally with the bearing housing flange is one of the failure preventions of this failure mode.

Two-scale concurrent topology optimization method of constrained layer damping structure subjected to non-uniform blast load

Two-scale concurrent topology optimization method of constrained layer damping structure subjected to non-uniform blast load

Buckling Behavior Analysis of Thin-Walled Cylindrical Shell Structure Under Localized Axial Compression Load Based on Initial Imperfection Sensitivity

In practical engineering, a thin-walled cylindrical shell structure is more easily subjected to localized axial compression loads caused by external adjacent structures or devices. However, until now there are few studies to reveal the buckling behavior of cylindrical shells under such nonuniform loading conditions based on initial imperfection sensitivity. Therefore, buckling analysis of cylindrical shell under localized axial compression loads is investigated in this paper. Based on the buckling test, the influence of the morphology and amplitude of measured initial geometric imperfection are studied using the finite element method. Meanwhile, the inherent reason for initial geometric imperfection affecting the buckling load is elaborated. The influence of amplitude, distribution range, and different combinations of local dent imperfections are also elucidated. In addition, the effects of inclined loading imperfection and uneven shell thickness distribution imperfection are analyzed in the form of deterministic numerical simulation. Finally, a new buckling load knockdown factor that can reasonably consider the influence of loading imperfection and shell thickness variation imperfection is proposed. This work elucidates the initial imperfection sensitivity of the thin-walled cylindrical shell structures under localized axial compression load and can provide useful guidance for the buckling design and preventing buckling failure of these structures.

Turbulent thermal convection in mixed porous–pure fluid domains

In this paper, we report on a direct numerical simulation (DNS) study of turbulent thermal convection in mixed porous–pure fluid domains. The computational domain consists of a cavity that contains a porous medium placed right above the bottom wall. The solid matrix is internally heated which, in turn, induces the convective motions of the fluid. The Rayleigh number of the flow in the pure fluid region above the porous medium is of the order of $10^7$ . In our study, we consider cases of different sizes of the porous medium, as well as cases with both uniform and non-uniform heat loading of the solid matrix. For each case, we analyse the convective structures in both the porous and the pure fluid domains and investigate the effect of the porous medium on the emerging flow patterns above it. Results for the flow statistics, as well as for the Nusselt number and each of its components, are also presented herein. Further, we make comparisons of the flow properties in this pure fluid region with those in Rayleigh–Bénard convection. Our simulations predict that, depending on the area coverage, the large-scale circulation above the porous medium can be in a single-roll, dual-roll or intermediate state. Also, when the area coverage increases, the temperatures inside it increase due to reduced fluid circulation. Accordingly, when the area coverage increases, then the Nusselt number becomes smaller whereas the Rayleigh number is increased.

Analytical investigation on the buckling of cylindrical shells under combined non-uniform axial compression and external pressure

This paper focuses on the buckling problem of cylindrical shells under combined non-uniform axial compression and external pressure. To obtain buckling loads, a completely new method called two-parameter perturbation method is established. Using this method, governing differential equations are solved and buckling loads expressed by load functions, load parameters, and shell dimensions are derived for the first time. Comparative studies show that buckling loads by the analytical formulas coincide with those for combined uniform loads or single wind load in literatures. Buckling of a cylinder subjected to combined bending and wind loads is analyzed, and confirmed by the Galerkin method for the case of small load variations. Therefore, the presented formulas are adequately validated. The numerical calculations are carried out to analyze the effects of non-uniform load parameters on buckling load coefficient. The obtained results in this paper can be applied to evaluate buckling loads for cylinders subjected to combined non-uniform loads in actual engineering.

Stress quantification in a composite matrix via mechanophores

Stress concentrations in polymer matrix composites occur due to non-uniform loadings which develop near the interface between the matrix and reinforcement in a stressed composite. Methods to better understand the evolution of this stress concentration are required for the development of advanced composites. Mechanophores, which are stress responsive molecules, can be embedded into the polymer matrix and used to quantify the local stresses in a loaded composite. In this work, single particle model composites were fabricated by combining functionalized glass particles embedded into a silicone/mechanophore matrix. Confocal microscopy was then used to measure the mechanophore activation in situ during mechanical loading. The fluorescence intensity was correlated to maximum principal stress values obtained from a finite element analysis (FEA) model of the system utilizing an Ogden hyperelastic model to represent the elastomer. By calibrating stress to fluorescence intensity spatially, quantitative stress measurements can be obtained directly from fluorescent images. To validate this technique, calibrated stress values for a two-particle composite system were compared to a FEA model and good agreement was found. Further experiments were performed on silicone matrix composites containing short cylindrical particles oriented with their major axis parallel or perpendicular to the stretching direction. To demonstrate the versatility of the single particle intensity/stress calibration approach, maximum principal stress values were mapped on the fluorescence images of the cylindrical experiments. This technique has potential to quantify stress concentrations quickly and accurately in new composite designs without the use of FEA models or differential image correlation.

Analysis of contact characteristics of ball screws under the combined loads considering non-uniform load distribution

Analysis of contact characteristics of ball screws under the combined loads considering non-uniform load distribution

3D printed biodegradable polymer reinforced concrete with high structural stability

The increase in the utilization of non-degradable polymers in the construction industry has raised reservations regarding eco-friendly and energy-efficient building solutions. The contemporary solution is the natural fiber reinforced concrete that registers low structural stability and high water absorption. The low strength is due to the non-homogenous distribution of fibers in composite causing non-uniform load distribution and water absorption is the result of hydrophilicity of natural fibers. This research proposes, for the first time, the manufacturing of biodegradable reinforcements for concrete in specific geometries using 3D printing (fused deposition modeling). The 3D printed reinforcements of polylactic acid concentrate the load in a uniform direction during compressive, flexure, and tensile testing. The reinforcements are tested with respect to different orientations and thicknesses in the concrete composite. The stability to water absorption is investigated using BS 1881 standard followed by post-water absorption compressive testing for concrete composites. The research presents in-situ image analysis for all mechanical characterizations that reveals true fracture behavior along with the validation of mechanical results. The flexure strength shows significant increase to 10.8 MPa as compared to the plain concrete samples. The water absorption test also shows prominent reduction of water absorption to 4.3 % as compared to 7.7 % of plain concrete sample. Overall, the novel reinforced concrete results in superior mechanical properties and moisture stability as compared to the plain (control) concrete and natural sisal fiber reinforced concrete composite.

Nonuniform load distribution of two-dimensional C/SiC z-pinned joints with four pins in a rectangular array prepared via chemical vapor infiltration

The design of ceramic matrix composite (CMC) mechanical joints takes into account the pseudoplastic mechanical behavior of CMC fasteners and the effect of the nonuniform microstructure. In this study, based on the linear correlation between the shear performance of two-dimensional (2D) C/SiC rivets and the rivet porosity, special z-pinned joints with four pins in a rectangular array with different porosities were prepared via the chemical vapor infiltration online gas-phase joining method, and a method is proposed to indirectly characterize the pin load distribution by measuring the strain distribution around the holes. The results show that the nonuniform distribution of the 2D C/SiC rivet density leads to an uneven distribution of the pin loads in the z-pinned joints with four pins in a rectangular array. The bearing ratio of the transversal rivets depends on the inverse of the ratio of the compliance coefficient of the two. The longitudinal rivets are capable to transfer the load; that is, the bottom transversal joint of the rivets is loaded first, and after the load limit is reached, the top transversal joint of the rivets starts to be loaded. Matrix cracking, crack deflection, interlayer sliding, fiber shearing, and fiber pull-out control rivet shearing. The dense rivets squeeze around the holes, leading to an uneven distribution of the pin loads. Oxidation at 700 °C leads to the fibers debonding from the matrix and cracking, which promotes crack deflection, interlayer sliding, and fiber pull-out; thus, the uneven pin load distribution tends to be uniform.

Rigorous plane-stress solution and buckling analysis of rectangular functionally graded plates subjected to non-uniform edge loads

In this article, analytical solutions for the buckling analysis of simply supported rectangular functionally graded (FG) plates subjected to various forms of non-uniform in-plane loads are presented. Both perfect and porous FG plates with power-law material property variation are considered. The analytical solution is obtained by adopting a two-step approach: First, a rigorous plane-stress solution is developed based on the superposition of Airy’s stress functions, and later, these stress solutions are used in the buckling load computation of the FG plate based on Galerkin’s technique. One key aspect of the proposed solution is that it can consider different non-uniform waveforms of the in-plane loads at two opposite sides of the plate. Results show that the nature of the edge load has a profound effect on the stress solution of the FG plates. Several tables and graphs are presented to obtain a qualitative and quantitative understanding of the buckling behavior of FG plates influenced by various plate design parameters which include plate aspect ratios, power-law exponent, and porosity index. Comparative studies are also presented to highlight some erroneous results published in the open literature. It can be emphasized that the analytical results reported here can be used as a reference to judge the accuracy of other numerical solutions such as the finite element method.

Comprehensive performance enhancement of conformal cooling process using thermal-load-based topology optimization

Conformal cooling technology is widely used in the thermal management for injection molding process. However, the overall design of cooling channel layout needs to be optimized due to non-uniform thermal load, limited design freedom and other factors. This paper presents a novel procedure for conformal cooling channel design by using thermal-load-based topology optimization. Unlike previous approaches that focused on optimizing the channel configuration or geometric parameters, the current work applies multiphysics topology optimization on the entire cooling area. The objective is to obtain the optimal channel layout with both low pressure drop and high heat transfer rate. A serious of optimized planar results are converted to three-dimensional channels that conform to the specific injection casting and are applied to injection molding process in a simulation software environment. For a given thin-plate casting, compared with the conventional parallel cooling process, the steady state average temperature and maximum temperature difference are decreased by 0.53 K and 2.20 K, respectively, and the pressure drop of coolant is decreased by 25.40%. For castings where non-uniform thermal loads are considered, the average temperature and pressure drop are decreased up to 1.45 K and 27.55%, respectively. The results for both sheet castings and cylindrical castings have demonstrated the stability, flexibility, and rationality of the proposed procedure. In addition, the conceptual design of cooling channels based on thermal load is expected to be applied to more potential thermal engineering fields.

Integrity assessment methodology of casing ovality deformation in shale gas wells

Casing deformation frequently occurs in shale gas wells during hydraulic fracturing. While the failure mechanism of casing ovality deformation is unclear due to the interweaving and compounding reasons from geological and engineering complexity. The multi-arm caliper tool can quantify the severity of casing deformation, and the spatial and temporal occurrence of casing deformations is analyzed. A finite element model of fractured shale squeezing casing is established to simulate the process of casing deformation. The simulated casing deformation is compared with logging data to validate the model with which the deformation mechanism would be revealed. Simulation results indicate that casing deformation in the Luzhou shale gas field belongs to compressive deformation. The length of casing deformation and the diameter shrinkage are local and small, and the deformation points are scattered along the horizontal well trajectory. The fracturing fluid pressure and fractured shale block generate a nonuniform load on the casing, which leads to stress yield and ovality deformation. The fluid pressure, formation degradation and cementing material are the key controlling factors to mitigate casing ovality deformation. This work provides a prompt & accurate assessment method and controlling measures for casing integrity in shale gas wells.