Load Solutions Research Articles

Sequential elastic adaptive NS-FE analyses for lower-bound limit load determination of plane-strain structures

The paper proposes the sequential elastic analyses run within the node-based smoothed finite element (NS-FE) framework incorporating an automatic adaptive mesh scheme to converge the lower-bound collapse load limit of plane-strain structures. The approach is familiar to practical designers as it solely involves a series of linear elastic analysis solves. Each of which performs a modified version of elastic compensation method that appropriately considers the modulus variations of some critical members. The nonlinear constitutive formulations describing intrinsic material properties can be directly accommodated. The NS-FE method simply adopts the low-order displacement functions, whilst the mesh adaptive algorithm employs the newest-bisection criteria with the novel modulus variation error indicators. A number of numerical examples and benchmarks involving the plane-strain structures with vertex and curve geometries illustrate the accuracy and efficiency of the proposed method. The approach overcomes the challenges associated with stress singularity and volumetric locking phenomena in an incompressibility condition. The collapse load solution converges to the lower-bound limit at modest computing efforts, where the final NS-FE layout (namely fine meshes over the areas developing high modulus variation rates and at the same time coarse meshes for those undergoing elasticity) depicts the failure lines of structures and hence mechanisms.

Automatic Adaptive Recovery Stress ES-FEM for Lower-Bound Limit Load Analysis of Structures

The paper proposes a novel automatic adaptive recovery stress edge-smoothed finite element method (ES-FEM) that determines the maximum load capacity of inelastic structures at plastic collapse. This approach performs solely a series of elastic ES-FEM analyses with systematic modulus variations (considering the influences of stress singularity) to converge the collapse load solutions. The smoothed [Formula: see text]-continuous recovery stress field ensures the satisfaction of static admissible stress and yield conformity conditions underpinning lower-bound limit analysis theorems. A modified modulus error function within the newest node bisection algorithm enables automatic mesh refining and coarsening constructions, and fast convergence to the lower-bound collapse limit.

Analysis Of 12- Level Cycloconverter To Minimize Thd (Total Harmonic Distortion) Level In 3-Phase Induction Motor

These harmonics are higher than essential frequencies and cause Total Harmonics Distortion (THD) which increases the rms current and generates more warmth in the load. Numerous techniques are used to suppress the harmonics to limit the warmth in the load. Another procedure is utilized in this work to limit THD and the method to beat the low exhibition of a traditional PWM (pulse width tweak) control. In this work, the desired output voltage is accomplished by contrasting the desired sinusoidal waveform (adjusting signal) with a high frequency three-sided waveform (transporter signal). Industrial applications demands high force and long life expectancy motor drives. Three phase motor drives have restricted force density consequently Multiphase motor drives are better solutions for high force density and substantial loads. In this work a 12 level cycloconverter is designed to drive three Phase load. The loads used in the industries almost nonlinear loads like motors. Thusly, because of these nonlinear loads extra harmonics incited at the output of the 12 level cycloconverter drive with major frequency. The harmonics and THD got using our proposed technique is thought about using Mat lab/Simulink

Particle Swarm Optimization for Load Balancing in Distributed Computing Systems – A Survey

Development of technology like Cloud Computing and its widespread usage has given rise to exponential increase in the volume of traffic. With this increase in huge traffic the resources in the network would either be insufficient to handle the traffic or the situation may cause some of the resources to be over utilized or underutilized. This condition leads to reduced performance of the system. To improve the performance of the system the traffic requires to be regulated such that all the resources are utilized conferring to their capacity which is known as load balancing. Load balancing has been one of the concerns in the distributed computing systems where the computing nodes do not have a global view of the network. There have been constant efforts to provide an efficient solution for load balancing through the approaches like game theory, fuzzy logic, heuristics and metaheuristics. Even though various solutions exist for balancing the load, the issue is challenging as there does not exist one best fit solution. The paper aims at the study of how Particle Swarm Optimization approach is used to achieve an optimal solution for load balancing in distributed computing system.

Dynamic Response of Offshore Wind Turbine on 3×3 Barge Array Floating Platform under Extreme Sea Conditions

Offshore wind farm construction is nowadays state of the art in the wind power generation technology. However, deep water areas with huge amount of wind energy require innovative floating platforms to arrange and install wind turbines in order to harness wind energy and generate electricity. The conventional floating offshore wind turbine system is typically in the state of force imbalance due to the unique sway characteristics caused by the unfixed foundation and the high center of gravity of the platform. Therefore, a floating wind farm for 3×3 barge array platforms with shared mooring system is presented here to increase stability for floating platform. The NREL 5 MW wind turbine and ITI Energy barge reference model is taken as a basis for this work. Furthermore, the unsteady aerodynamic load solution model of the floating wind turbine is established considering the tip loss, hub loss and dynamic stall correction based on the blade element momentum (BEM) theory. The second development of AQWA is realized by FORTRAN programming language, and aerodynamic — hydrodynamic — Mooring coupled dynamics model is established to realize the algorithm solution of the model. Finally, the 6 degrees of freedom (DOF) dynamic response of single barge platform and barge array under extreme sea condition considering the coupling effect of wind and wave were observed and investigated in detail. The research results validate the feasibility of establishing barge array floating wind farm, and provide theoretical basis for further research on new floating wind farm.

First yield in the Maugis‐adhesive contact of elastic spheres

AbstractWe analyze the onset of plastic yield in the Maugis‐adhesive contact of elastic spheres. Written in proper dimensionless variables, the problem solution depends on Poisson's ratio, the Tabor parameter and a non‐dimensional adhesion strength. The influences of adhesion range and strength are studied in detail. First yield can either occur inside the bodies on the axis of symmetry (for long range adhesion) or at the contact boundary (for short range adhesion). Adhesion significantly reduces the external load necessary to initiate plastic yield. A simple analytic solution for the critical load in the DMT‐limit of adhesion is being derived. Our results are quantitatively similar to previously published findings based on the double Hertz model of adhesion and can for example be applied to study an adhesive spherical microcontact in the contact of rough surfaces.

Analytical method for laterally loaded piles in soft clay considering the influence of soil outside the scour hole on the effective overburden pressure

Scour reduces the effective overburden pressure and the undrained shear strength of soil, thus affecting the lateral load-bearing capacity of pile foundations. Compared with general scour, local scour can decrease the reduction of the effective overburden pressure and the undrained shear strength around the pile due to the existence of soil outside the scour hole. To fully reflect the actual situation at a site, the behavior of laterally loaded piles in soft clay should consider both the scour-hole dimensions and the soil stress history. This paper proposes a closed-form analytical solution for laterally loaded piles in soft clay that can simultaneously account for the changes in effective overburden pressure and undrained shear strength caused by the scour-hole dimensions and the soil stress history based on the p–y curve proposed by Matlock. The average reduced stress is introduced according to Boussinesq’s point load solution. Case studies demonstrate that the analytical method is reliable with reasonable accuracy. According to the parameter study, the load eccentricity is the most sensitive factor compared with the changes in soil properties caused by the scour-hole dimensions and the soil stress history.

A unified theoretical solution of plastic limit load for the thin-walled pipeline with an incomplete welding defect

In this work, a unified theoretical solution of plastic limit load for thin-walled pipeline with an incomplete welding defect is proposed by the Net Section Collapse (NSC) criteria. The plastic limit torque of the thin-walled pipeline with an incomplete circumferential welding defect is calculated by the sand pile analogy method. The unified theoretical solutions of plastic limit loads for the pressure pipeline with a circumferential welding defect under combined tension, torsion and bending moment are deduced, and the influences of circumferential length and defect position on the plastic limit loads are discussed. The comparison with the finite element (FE) results show that the theoretical plastic limit loads of the pressured circumferentially defective pipeline based on the extended NSC criteria are reliable. The study can provide an important theoretical basis to establish the safety evaluations towards the pressure pipelines with incomplete welding defects.

Exact solutions for stochastic Bernoulli–Euler beams under deterministic loading

This study deals with two general solutions for a simply supported linear elastic Bernoulli–Euler beam with a stochastic bending flexibility, subjected to a deterministic loading. Two model problems are considered. The first problem is associated with a trapezoidally distributed load, whereas the second problem treats a sinusoidally distributed load. The importance of the solution for the trapezoidal load lies in its practicality. The derivation of stochastic characteristics for random beams under a sinusoidal load is useful due to the expandability to generally distributed loads by a Fourier sine series expansion. Numerical results are reported for various cases illustrating the effect of stochasticity of the beam’s properties on its flexural response.

A constraint correction method based on use of a single test specimen

Commonly, fracture toughness tests on deeply cracked specimens are used to assess defects in large-scale components. The paper presents a method for selection of test specimen type, size and crack length in order to obtain fracture toughness estimates relevant to defects in cracked pipes. The method uses available closed-form T-stress, stress intensity factor and limit load solutions to determine the required specimen dimensions. The paper reports elastic–plastic finite element analyses for single edge notched bend (SENB) and single edge notched tension (SENT) specimens and cracked pipes which demonstrate good agreement of the matching approach, although care is needed in selecting the appropriate limit load solution for SENT geometries.

Exact solutions for isothermal cyclic torsional loading of a circular SMA bar exploiting the shape memory effect

Two simple and fully analytical models are presented for a SMA bar or wire of circular cross section subjected to fully-reversed cyclic torsional loading, by taking into consideration the reorientation of the martensitic variants occurring during unloading and reverse loading. The process is assumed to take place at constant temperature between the start temperatures of the martensitic and austenitic transformations. In the first part of this work, the same shear modulus is taken both for Martensite and Austenite. In the second part, different elastic shear moduli are considered for the two phases. The volume fractions of both positive and negative twisted Martensite are assumed to evolve linearly with the shear stress. The bar is initially in a state of Austenite. As the applied torque is increased the martensitic transformation starts from the outer surface and then it extends inwards. If the maximum applied torque is large enough, then the complete Martensitic transformation takes place in the outer region of the cross section. During unloading and subsequent reverse loading the martensitic reorientation process may occur starting from the boundary between the fully martensitic outer region and the intermediate transforming region. Particular attention is focused on modeling the unloading and reverse loading processes. At each stage, the radial distributions of shear stress and Martensite variant are calculated analytically. A closed form relation between the applied torque and the angle of twist is presented for the entire process in the case of equal shear moduli, and only for the loading and elastic unloading stages in the case of different shear moduli. The approach is then validated against analytical, numerical and experimental results available in the literature for the direct loading–unloading process. Application to the seismic response of dissipative systems based on SMA helical springs is also envisaged.

Buckling analysis of nanoplates based on a generic third-order plate theory with shear-dependent non-isotropic surface stresses

In this paper, a general third-order shear deformation plate theory (GTSDPT) is employed to investigate the buckling behaviors of rectangular nanoplates. A new model with non-isotropic surface modulus that depends on in-plane and transverse shear strains, such as that for most crystalline faces, is established to analyze the significance of non-isotropic surface effects on buckling behaviors. The governing equations and the corresponding boundary conditions are established by using the principle of minimum potential energy. The analytical critical buckling load solutions are obtained for nanoplates with different boundary conditions. The proposed model is verified by comparing buckling results against the ones from existing plate theories. Using both Reddy’s third order shear deformation plate theory (TSDPT) and GTSDPT, the influence of plate thickness, length-to-thickness ratio, surface modulus, residual surface stress, bulk modulus and boundary conditions on the buckling behavior of nanoplates with surface stress effects is analyzed in detail. It is observed that the buckling results of the nanoplates from TSDPT and GTSDPT exhibit some differences due to the presence of shear stresses on the interface between surface layers and the bulk of the plates. The TSDPT theory may not be able to capture shear stress effect and the GTSDPT theory may need to be employed in this case. Finally, the influence of surface stresses on the buckling behaviors of nanoplates made of gold, nickel, silver and copper and subjected to uni- and bi-axial compressive loads is investigated using the GTSDPT theory.

Duck curve leveling in renewable energy integrated grids using internet of relays

Power grids are undergoing deregulation, privatization, and decentralization worldwide. The smart grid allows the integration of clean power renewable energy technologies to the utility grid through mini, micro, and nano grids. Conventional centralized power grids used to rely on fossil fuel-fired power plants which are being replaced worldwide with solar, wind, small hydro, geothermal, biomass, wave, and alternative energy technologies. Installed solar and wind power generation capacity has surpassed 1300 GW in 2020. Solar and wind powers rise during the day and fall during the evening. Consumer demand increases steadily during the evening and peaks after sunset when solar generation becomes zero and wind power falls substantially. Decentralized smart grid faces duck curve limitation on the integration of renewable energy technologies as centralized utilities used to face the peak-hours issue. Smart grid operators have no effective solution of load peaking after sundown except keeping fossil fuel-fired plants on standby to ride through the duck curve. We present a solution to the duck curve problem by integrating smart load shedding devices in micro and nano grids to adjust their demand frugally during peak hours to support the national grid. Information and communication (ICT) technologies that enabled the internet of things (IoT) have been attempted to facilitate smart load shedding in nano grids. ICT enabled voltage transformers (VT) and current transformers (CT) supply signals to heuristic rules based multifunction smart relaying system. Smart meters, instrument transformers, and status monitoring field devices generate a massive amount of data. The research designed an IoT and LabVIEW based software platform to carry out demand-side management. Under frequency (UF) and under-voltage (UV) relaying functions were used to conduct load shedding in nano grids. This nanoscale demand-side management experiment paves the way to ride through utility-scale duck curve setback. This PT/CT data based economic solution performs at nanoscale same as ABB PML 630 load shedding controller. This UF and UV relaying based multifunction relay starts shedding loads when frequency falls below <1% and voltage below 10% of rated values. Our load shedding scheme has successfully functioned on nanoscale 5 kW system. The future study section proposes to integrate big data technologies in-home energy management system (HEMS) through extract, transform and load (ETL) pipeline to import data from PT/CT and circuit breakers (CB) integrated smart meter to transform it according to requirement by loading data into Hadoop “big data” processing platforms for utility-scale load management with help of day-ahead load and weather-dependent renewable power generation forecasting techniques.

Strength Analysis of an Aircraft Sandwich Structure with a Honeycomb Core: Theoretical and Experimental Approaches

In this paper, the strength of aircraft sandwich structure with honeycomb core under bending load was evaluated theoretically and experimentally based on failure mode maps. A failure mode map for the loading under three-point bending was constructed theoretically to specify the failure modes and corresponding load. Three point bending test for aluminum honeycomb sandwich beam has been achieved to measure the peak load and maximum deflection. The obtained results elucidated a good agreement between the theoretical solutions and experimental tests, where the error ratio was not exceeded 12%. The core height, the cell size and the cell wall thickness were selected to explore the effect of honeycomb parameters on the strength of sandwich structure. In order to obtain the optimum solution of peak load and maximum deflection and energy absorption, Response Surface Methodology (RSM) was used. Results showed that the maximum bending load, minimum deflection, and maximum energy absorption were found at 25 mm core height, 10 mm size cell and 1 mm cell wall thickness. The optimal value of maximum bending load, minimum deflection and maximum energy absorption were 1975.3415 N, 1.0402 mm and 1.0229 J respectively.

Cloud Computing Demand Elasticity Algorithm based on Ant Colony Algorithm

Background: In the recent era of technology, the traditional Ant Colony Algorithm (ACO) is insufficient in solving the problem of network congestion and load balance, and network utilization. Methods: This paper proposes an improved ant colony algorithm, which considers the price factor based on the theory of elasticity of demand. The price factor is denominated in the impact on the network load which means indirect control of network load, congestion or auxiliary solution to calculate the idle resources caused by the low network utilization and reduced profits. Results: Experimental results show that the improved algorithm can balance the overall network load, extend the life of path by nearly 3 hours, greatly reduce the risk of network paralysis, and increase the profit of the manufacturer by 300 million Yuan. Conclusion: Furthermore, the results show that the improved method has great application value in improving network efficiency, balancing network load, prolonging network life and increasing network operating profit.

Elastic lateral-torsional instability of monosymmetric shear deformable fixed arches under a localized uniform radial load

This paper investigates the elastic lateral-torsional instability of shear deformable fixed arches having a monosymmetric cross-section when subjected to a localized uniform radial load. Hitherto, this topic has not been addressed in the open literature. The complex in-plane internal actions in a fixed arch with a monosymmetric section are produced by a localized uniform radial load and are affected by the arc length of localized load segment. When the in-plane internal actions reach certain magnitudes, the fixed arch may fail suddenly in a lateral-torsional instability mode. The lateral-torsional instability loads of such arches considering shear deformations under a localized uniform radial load are difficult to obtain and are investigated in this paper. The strain-displacement relationships for the longitudinal normal axial and shear strains in the arch with a monosymmetric section are derived. In-plane analyses for the internal forces produced by the localized uniform radial load are firstly carried out. The analytical solution for the lateral-torsional instability load accounting for shear deformations and monosymmetry is then obtained using the principle of stationary potential energy together with the Rayleigh-Ritz method and compared with ANSYS numerical results. It is found that the monosymmetry parameter, the shear deformations, the slenderness ratio and the arc length of the localized load segment have considerable effect on the lateral-torsional instability load of fixed arches with a monosymmetric section.

2.5D formulation and analysis of a half-space subjected to internal loads moving at sub- and super-critical speeds

The 2.5D dynamic response of a half-space to an internal point load moving at sub- and super-critical speeds is studied in Cartesian coordinates both analytically and numerically. Firstly, the partial differential equations of waves are converted to the ordinary differential equations by the Fourier transformation. Then, a multiplying factor is derived and added to the stiffness matrix to account for the dissipation of the load moving at different velocities, with or without self-frequency. Finally, the displacements of the half-space induced by the waves propagating upward and downward are obtained analytically for the specified boundary conditions. For comparison, the half-space is also analyzed by the 2.5D finite/infinite element method. The findings of the paper include: (1) the 2.5D solutions for a point load moving extremely fast are same as those for the line load by the 2D approach, (2) the dissipation of the moving load can be considered by adjusting the multiplying factor, (3) the attenuation of the half-space above the load level is reduced by the dissipation of the moving load, and (4) the displacement of the half-space increases with the self-frequency of the moving load.

Self-moments stiffening effect and buckling strength of periodic Vierendeel beams

This paper deals with the buckling phenomenon of periodic Vierendeel beams. Closed-form solutions for critical loads and deformed shapes are presented. They are built by exploiting several auxiliary solutions obtained for the discrete periodic girder and for a geometrically nonlinear micro-polar equivalent model. In particular, the girder when subjected to sinusoidal self-equilibrated systems of inner bending moments (self-moments) is analysed. The corresponding results are used for solving the large-deflection equilibrium problem of the continuous equivalent model by means of the eigenfunction expansion technique. Girder buckling conditions are then defined in terms of kinematics of the micro-polar model: more precisely, they are attained when special distributions of self-moments, able to bend the continuous system without violating compatibility of shear strains, act in the girder. It is shown that these systems, neglected in the theories presented so far, have a significant stiffening effect on the buckling girder behaviour. Moreover, they are governed by the continuity equation for micro-rotations that is solved in closed form by the Galerkin method, with the micro-polar model eigenfunctions as basis functions. The accuracy of the proposed solutions is verified by comparing them with those achieved by a series of finite element girder models.

New Approach to Drug Delivery in Ophthalmological Practice: Development of Composite Ophthalmological Solution for Drug Loading of Soft Contact Lenses

Introduction. This article provides a tentative justification of use of soft contact lenses as a carrier of ophthalmological solutions to eye tissues.Aim. The aim of the research is to develop the composition of the ophthalmic transport system for the treatment of glaucoma. Also, the proposed manufacturing algorithms were proposed for drug loading ophthalmological solutions.Materials and methods. Preparation of sodium hyaluronate solution was carried out based on the methodology described in EP 7.0 [01/2011:1472] (Sodium hyaluronate).Results and discussion. The conducted investigation with the purpose to justify a concentration of sodium hyaluronate helped to determine its concentration that gives the viscosity level as close to the upper limit stated in Russian Pharmacopoeia as possible. Buffer solution was chosen with criteria to use as less components in ophthalmological solution as possible. Also, it was found out that the more components are added to the viscous solution, the more viscosity level is decreased. Thus, initial viscosity of solution containing sodium hyaluronate was 149.59 mm2/s, and after addition of active pharmaceutical substance it dropped down to 88.49 mm2/s and 81.36 mm2/s for model solution number 1 and 2, respectively. After addition of citric acid and disodium hydrophosphate, the viscosity of model solution was found to be 78.11 mm2/s and 75.28 mm2/s for model solution number 1 and 2, respectively.Conclusion. As a result of the studies, two alternative model compositions of an ophthalmic solution for the saturation of soft contact lenses for the treatment of glaucoma were proposed. The choice of active pharmaceutical substances, and excipients has been justified. Technological procedure of preparation of model solution was described and explained, where the most attention was paid on dissolving of sodium hyaluronate in purified water.

Antiplane point load solution for a linear slot with rounded ends

Abstract An exact linear elastic solution is derived for a pair of opposing point loads, which act in the middle of a straight slot having rounded ends. This problem is analogous to the mode III crack problem where two concentrated forces act in opposite directions to open the surfaces of a finite-length crack. The corresponding path independent J integral for this slot problem is also determined.