Finite Loading Research Articles

Improving manufacturing lead time using holistic approach to planning and execution with integrated data structures: numerical simulation and comparison

Manufacturing planning and control (MPC) plays a significant role in effective planning of requirements and execution of those plans. It also influences various performance measures, in particular on-time delivery, which is dependent on many factors including manufacturing lead time. This paper aims to address key issues of infinite loading of resources, lack of forward planning, and limited simultaneous planning capabilities of MRP through a holistic approach to planning of various components and execution of those plans, based on integrated data structures. It is shown that integrated data structures, combining hierarchical single-level BOMs and sequential operations routings using a holistic approach to planning and execution enable reducing lead time by eliminating slack times associated with traditional methods. Furthermore, manufacturing lead time, based on integrated data structures is a true representation of operation times and is shorter compared with traditional lead time. Sensitivity analysis on lead-time with bills-of-materials (BOM) levels and floats shows that the holistic approach to planning and execution with integrated data structures is an effective way of improving lead-time, in particular when product structures involve many levels of BOMs and floats (slack times). The proposed holistic approach provides forward planning, simultaneous planning of components, and finite loading of resources. It is expected that the concept of integrated data structures be extended to model transaction data with process functions (e.g. production order cycle), which would improve overall cycle times by eliminating manual functions associated with current methods.

Effect of finite element model loading condition on fracture risk assessment in men and women: The AGES-Reykjavik study

Proximal femoral (hip) strength computed by subject-specific CT scan-based finite element (FE) models has been explored as an improved measure for identifying subjects at risk of hip fracture. However, to our knowledge, no published study has reported the effect of loading condition on the association between incident hip fracture and hip strength. In the present study, we performed a nested age- and sex-matched case–control study in the Age Gene/Environment Susceptibility (AGES) Reykjavik cohort. Baseline (pre-fracture) quantitative CT (QCT) scans of 5500 older male and female subjects were obtained. During 4–7years follow-up, 51 men and 77 women sustained hip fractures. Ninety-seven men and 152 women were randomly selected as controls from a pool of age- and sex-matched subjects. From the QCT data, FE models employing nonlinear material properties computed FE-strength of the left hip of each subject in loading from a fall onto the posterolateral (FPL), posterior (FP) and lateral (FL) aspects of the greater trochanter (patent pending). For comparison, FE strength in stance loading (FStance) and total femur areal bone mineral density (aBMD) were also computed. For all loading conditions, the reductions in strength associated with fracture in men were more than twice those in women (p≤0.01). For fall loading specifically, posterolateral loading in men and posterior loading in women were most strongly associated with incident hip fracture. After adjusting for aBMD, the association between FP and fracture in women fell short of statistical significance (p=0.08), indicating that FE strength provides little advantage over aBMD for identifying female hip fracture subjects. However, in men, after controlling for aBMD, FPL was 424N (11%) less in subjects with fractures than in controls (p=0.003). Thus, in men, FE models of posterolateral loading include information about incident hip fracture beyond that in aBMD.

Efficient and Accurate Methods for Characterizing Effects of Framework Flexibility on Molecular Diffusion in Zeolites: CH4 Diffusion in Eight Member Ring Zeolites

Molecular dynamics (MD) and transition state theory (TST) methods are becoming efficient tools for predicting diffusion of molecules in nanoporous materials. The accuracy of predictions, however, often depends upon a major assumption that the framework of the material is rigid. This saves a considerable amount of computational time and is often the only method applicable to materials for which accurate force fields to model framework flexibility are not available. In this study, we systematically characterize the effect of framework flexibility on diffusion in four model zeolites (LTA, CHA, ERI, and BIK) that exhibit different patterns of window flexibility. We show that for molecules with kinetic diameters comparable to (or larger than) the size of the window the rigid framework approximation can produce order(s) of magnitude difference in diffusivities as compared to the simulations performed with a fully flexible framework. We also show that simple recipes to include the effect of framework flexibility are not generally accurate. To account for framework flexibility effects efficiently and reliably, we introduce two new methods in which the flexible structure is approximated as a set of discrete rigid snapshots obtained from simulations of dynamics of an empty framework, using either classical or, in principle, ab initio methods. In the first method, we perform MD simulations of diffusion in a usual manner but replace the rigid structure with a new random snapshot at a certain characteristic frequency corresponding to the breathing motion of the window, while keeping positions of adsorbate molecules constant. In the second method, we directly compute cage to cage hopping rates in each rigid snapshot using TST and average over a distribution of snapshots. Excellent agreement is obtained between diffusivities predicted with these two new methods and direct MD simulations using fully flexible structures. Both methods are orders of magnitude more efficient than the simulations with the fully flexible structure. The new methods are broadly applicable for fast and accurate predictions of both infinite dilution and finite loading diffusivities of simple molecules in zeolites and other nanoporous materials, generally without the need for an accurate flexible force field.

Structural health monitoring of wind towers: residual fatigue life estimation

In a recent paper (Benedetti et al 2011 Smart Mater. Struct. 20 055009), the authors investigated the possibility of detecting cracks in critical sites of onshore wind towers using a radial arrangement of strain sensors around the tower periphery in the vicinity of the base welded joint. Specifically, the strain difference between adjacent strain sensors is used as a damage indicator. The number of sensors to be installed is determined by the minimum crack size to be detected, which in turn depends on the expected extreme wind conditions and programmed inspection/repair schedule. In this companion paper, we address these issues by investigating possible strategies for residual fatigue life assessment and management of onshore wind towers once the crack has been detected. For this purpose, fracture mechanics tests are carried out using welded samples to quantify the resistance to fatigue crack growth as well as the elastic–plastic fracture toughness of the welded joint at the tower base. These material strength characteristics are used to estimate (i) the critical crack size for structural integrity on the basis of fracture toughness tests, elastoplastic finite element analyses and loading spectra under extreme wind conditions, (ii) the residual life before structural collapse, applying a frequency-domain method to typical in-service wind actions and wind directionality.

Aircraft maintenance planning and scheduling: an integrated framework

PurposeThe purpose of this paper is to examine how certain limitations of the current approaches to planning and scheduling of aircraft heavy maintenance can be addressed using a single integrated framework supported by unified data structures.Design/methodology/approachThe “unitary structuring technique”, originally developed within the context of manufacturing planning and control, is further enhanced for aircraft heavy maintenance applications, taking into account the uncertainty associated with condition‐based maintenance. The proposed framework delivers the advanced functionalities required for simultaneous and dynamic forward planning of maintenance operations, as well as finite loading of resources, towards optimising the overall maintenance performance.FindingsExecution of maintenance operations under uncertainty involves materials changes, rectification and re‐assembly. It is shown that re‐scheduling of materials (spare‐parts), resources and operations can be taken care of by simultaneous and dynamic forward planning of materials and operations with finite loading of resources, using the integrated framework.Research limitations/implicationsAs part of adopting the proposed framework in practice, it needs to be guided by an overall methodology appropriate for application‐specific contexts.Practical implicationsThe potential direct benefits of adopting the proposed framework include on‐time project completion, reduced inventory levels of spare‐parts and reduced overtime costs.Originality/valueExisting approaches to aircraft maintenance planning and scheduling are limited in their capacity to deal with contingencies arising out of inspections carried out during the execution phase of large maintenance projects. The proposed integrated approach is, capable of handling uncertainty associated with condition‐based maintenance, due to the added functionalities referred to above.

Tracer diffusion in colloidal suspensions under dilute and crowded conditions with hydrodynamic interactions

We consider tracer diffusion in colloidal suspensions under solid loading conditions, where hydrodynamic interactions play an important role. To this end, we carry out computer simulations based on the hybrid stochastic rotation dynamics-molecular dynamics (SRD-MD) technique. Many details of the simulation method are discussed in detail. In particular, our choices for the SRD-MD parameters and for the different scales are adapted to simulating colloidal suspensions under realistic conditions. Our simulation data are compared with published theoretical, experimental and numerical results and compared to Brownian dynamics simulation data. We demonstrate that our SRD-MD simulations reproduce many features of the hydrodynamics in colloidal fluids under finite loading. In particular, finite-size effects and the diffusive behavior of colloids for a range of volume fractions of the suspension show that hydrodynamic interactions are correctly included within the SRD-MD technique.

Thermal Stress Simulation of Cooling Tube with Grid Plate Using Indirect Finite Element Method

Indirect finite element method was used to analyze the thermal - structural coupled field of cooling tube with grid plate, and the process of finite element modeling, loading and solution were given. Cooling grid tube deformation shape and node radial deformation curve were obtained by finite element analysis and the deformation increases gradually from pipeline inner wall to the outer wall, so the nonlinear performance is significantly. Deformation of grid plate increases linearly, and the maximum and minimum deformation are respectively for 0.32mm and 0.22mm. Diameter, axial and hoop stress distribution of cooling gate can be obtained, and the results show that heat transfer result in structure internal stress, radial stress is the state of compression at the place of cooling grid and pipeline Interchange, the axial stress is the state of compression in the middle of a cooling grid, the hoop stress is pressure at the wall of pipeline and tension at grid plate.

Stress and Strain Patterns of 1-Piece and 2-Piece Implant Systems in Bone

The transition from implant to abutment is solid in 1-piece (1P) and broken in 2-piece (2P) implant designs. This difference may affect occlusal load distribution and marginal bone response. To determine whether 1P and 2P implants with equivalent geometries exhibited stresses and strains differently under applied loading conditions. Design software simulated 1P and 2P implants restored with metal copings and embedded in 3 cylindrical bone block models that varied in dimensions, density, and percentage of bone-to-implant contact. Three-dimensional, finite element analysis simulated occlusal loading. Experiments evaluated stresses and strains relative to implant design and (1) periimplant bone thickness, (2) cortical bone thickness, (3) magnitude and direction of occlusal loading, and (4) % bone-to-implant contact. Implants with equivalent dimensions exhibited comparable stresses and strains in all experimental conditions. Implant diameter and periimplant bone thickness influenced stress levels. Only small-diameter (3.0 mm) 1P implants in low-density bone exhibited stress levels that might adversely affect marginal bone stability. Implant diameter and periimplant bone thickness influenced load distribution in bone, but the type of implant-abutment transition had no significant effect. Small-diameter 1P implants should be limited to dense bone to minimize stress concentrations.

3D-Modeling and Numerical Analysis of Fracture Behavior in AFM-Specimen on Mixed-Mode I-II Loading Condition

The computational analysis of a three-dimensional (3D) finite element model of all fracture modes (AFM) specimen on mixed-mode I-II fracture was presented in this paper. The separated energy release rates (SERRs) along the crack front of the AFM-model were calculated by the modified virtual crack closure integral (MVCCI)-method and commercially available software ANSYS. The influence of finite geometry and loading angles on mixed mode I-II fracture was investigated.

Application of Optimal Technique with Discrete Variables in Furnace Structure

Based on the characteristics of steel structure of the furnace, a generic finite element model, automatic loading, analysis and post-processing was achieved by ANSYS-APDL firstly. Then taking the sizes of profile as design variables and total mass as objective function, the size optimization design on steel structure was developed by means of two-level algorithm based on discrete variable.

Dermal penetration of propylene glycols: Measured absorption across human abdominal skin in vitro and comparison with a QSAR model

The dermal penetration of undiluted monopropylene glycol (MPG) and dipropylene glycol (DPG) has been measured in vitro using human abdominal skin under conditions of infinite dose application, and the results compared with predictions from the SKINPERM QSAR model (ten Berge, 2009). The measured steady-state penetration rates (Jss) for MPG and DPG were 97.6 and 39.3μg/cm2/h, respectively, and the permeability coefficients (Kp) were 9.48×10−5cm/h for MPG and 3.85×10−5cm/h for DPG. In comparison, the SKINPERM model slightly over-predicted Jss and Kp for MPG and DPG by between 2.6- and 5.1-fold, respectively. The model predictions of 254μg/cm2/h and 24.6×10−5cm/h for MPG, and 202μg/cm2/h and 19.8×10−5cm/h for DPG were in fairly good agreement with the measured values. Further, the model predicted a Jss of 101μg/cm2/h and a Kp of 9.9×10−5cm/h for the homologue tripropylene glycol. Assuming that the measured Jss was the same under conditions of finite dose application (taken to be 10μL/cm2) and was maintained over a 24-h period (both conservative assumptions), the relative dermal absorption of the applied dose was estimated to be 23% (0.96%/h) for MPG and 9% (0.39%/h) for DPG. However, the extrapolation for MPG may be further overestimated due to possible residence in the stratum corneum under infinite conditions of exposure that would not be applicable to a finite loading dose.

A Lagrangian model for hardening behaviour of materials at finite deformation based on the right plastic stretch tensor

In this paper a modified multiplicative decomposition of the right stretch tensor is proposed and used for finite deformation elastoplastic analysis of hardening materials. The total symmetric right stretch tensor is decomposed into a symmetric elastic stretch tensor and a non-symmetric plastic deformation tensor. The plastic deformation tensor is further decomposed into an orthogonal transformation and a symmetric plastic stretch tensor. This plastic stretch tensor and its corresponding Hencky’s plastic strain measure are then used for the evolution of the plastic internal variables. Furthermore, a new evolution equation for the back stress tensor is introduced based on the Hencky plastic strain. The proposed constitutive model is integrated on the Lagrangian axis of the plastic stretch tensor and does not make reference to any objective rate of stress. The classic problem of simple shear is solved using the proposed model. Results obtained for the problem of simple shear are identical to those of the self-consistent Eulerian rate model based on the logarithmic rate of stress. Furthermore, extension of the proposed model to the mixed nonlinear isotropic/kinematic hardening behaviour is presented. The model is used to predict the nonlinear hardening behaviour of SUS 304 stainless steel under fixed end finite torsional loading. Results obtained are in good agreement with the available experimental results reported for this material under fixed end finite torsional loading.

Comparison of analytical and inverse finite element approaches to estimate cell viscoelastic properties by micropipette aspiration

The viscoelastic properties of cells are important in predicting cell deformation under mechanical loading and may reflect cell phenotype or pathological transition. Previous studies have demonstrated that viscoelastic parameters estimated by finite element (FE) analyses of micropipette aspiration (MA) data differ from those estimated by the analytical half-space model. However, it is unclear whether these differences are statistically significant, as previous studies have been based on average cell properties or parametric analyses that do not reflect the inherent experimental and biological variability of real experimental data. To determine whether cell material parameters estimated by the half-space model are significantly different from those predicted by the FE method, we implemented an inverse FE method to estimate the viscoelastic parameters of a population of primary porcine aortic valve interstitial cells tested by MA. We found that inherent differences between the analytical and inverse FE estimation methods resulted in statistically significant differences in individual cell properties. However, in cases with small pipette to cell radius ratios and short loading periods, model-dependent differences were masked by experimental and cell-to-cell variability. Analytical models that account for finite cell-size and loading rate further relaxed the experimental conditions for which accurate cell material parameter estimates could be obtained. These data provide practical guidelines for analysis of MA data that account for the wide range of conditions encountered in typical experiments.

Multiple Stability of a Sparsely Encoded Attractor Neural Network Model for the Inferior Temporal Cortex

We study a neural network model for the inferior temporal cortex, in terms of finite memory loading and sparse coding. We show that an uncorrelated Hopfield-type attractor and some correlated attractors have multiple stability, and examine the retrieval dynamics for these attractors when the initial state is set to a noise-degraded memory pattern. Then, we show that there is a critical initial overlap: that is, the system converges to the correlated attractor when the noise level is large, and otherwise to the Hopfield-type attractor. Furthermore, we study the time course of the correlation between the correlated attractors in the retrieval dynamics. On the basis of these theoretical results, we resolve the controversy regarding previous physiologic experimental findings regarding neuron properties in the inferior temporal cortex and propose a new experimental paradigm.

A Wiener‐Hopf analysis of the parallel plate waveguide with finite length impedance loading

In the present work a rigorous Wiener‐Hopf approach is used to investigate the band‐stop filter characteristics of a parallel plate waveguide with finite length impedance loading. The representation of the solution to the boundary‐value problem in terms of Fourier integrals leads to two simultaneous modified Wiener‐Hopf equations which are uncoupled by using the pole removal technique. The solution involves four infinite sets of unknown coefficients satisfying four infinite systems of linear algebraic equations. These systems are solved numerically and some graphical results showing the influence of the waveguide spacing, surface impedances and the length of the impedance loading on the reflection coefficient are presented.

Geometrically Nonlinear Determination of Energy Release Rate and Mode Ratio in Single Leg Bending Tests

Geometrically linear and nonlinear finite element analyses are used to determine the energy release rate and mode ratio in simulated tests of unidirectional, symmetric, single leg bending (SLB) specimens. It is shown that the finite diameter loading rollers that are typically used in practical test set-ups cause this test to be inherently nonlinear. The differences between the linear and nonlinear results are presented parametrically as a function of material properties, specimen thickness, roller diameter, span length and crack length. These results are used, along with empirically derived equations, to develop an approach for designing SLB experiments where one will have a high degree of confidence in toughness values as obtained from conventional data reduction techniques, and for which relatively little specimen-to-specimen variation in mode ratio will be observed.

Bifurcational and dynamical analysis of a continuous biofilm reactor

A dynamical model of a continuous biofilm reactor is presented. The reactor consists of a three-phase internal loop airlift operated continuously with respect to the liquid and gaseous phases, and batchwise with respect to the immobilized cells. The model has been applied to the conversion of phenol by means of immobilized cells of Pseudomonas sp. OX1 whose metabolic activity was previously characterized (Viggiani, A., Olivieri, G., Siani, L., Di Donato, A., Marzocchella, A., Salatino, P., Barbieri, P., Galli, E., 2006. An airlift biofilm reactor for the biodegradation of phenol by Pseudomonas stutzeri OX1. Journal of Biotechnology 123, 464–477). The model embodies the key processes relevant to the reactor performance, with a particular emphasis on the role of biofilm detachment promoted by the fluidized state. Results indicate that a finite loading of free cells establishes even under operating conditions that would promote wash out of the suspended biophase. The co-operative/competitive effects of free cells and immobilized biofilm result in rich bifurcational patterns of the steady state solutions of the governing equations, which have been investigated in the phase plane of the process parameters. Direct simulation under selected operating conditions confirms the importance of the dynamical equilibrium establishing between the immobilized and the suspended biophase and highlights the effect of the initial value of the biofilm loading on the dynamical pattern.

Linear and nonlinear finite element analyses of unidirectional, symmetric single leg four-point bending tests

Geometrically linear and nonlinear finite element analyses are used to determine the energy release rate and mode ratio in simulated tests of unidirectional, symmetric, single leg bending specimens under four-point bending. It is shown that the finite diameter loading rollers that are typically used in practical test set-ups cause this test to be inherently nonlinear. The differences between the linear and nonlinear results are presented parametrically as a function of material properties, specimen thickness, roller diameter, crack length, and inner and outer span length. The perceived advantages and disadvantages of this test are compared to those of the more commonly used three-point single leg bending test. It is concluded that the four-point test provides an attractive alternative, as it can use the same type of test specimens and will produce toughnesses with essentially the same accuracy. Moreover, it allows non-precracked and precracked toughnesses, as well as R-curve data, to be obtained from each specimen tested.

Preliminary Parametric Study of Gurney Flap Dependencies

Introduction T HE Gurney flap1,2 is typically a small plate, which is attached at or near the trailing edge of an airfoil on the pressure side. The flap has been shown to be a highly effective small-scale (typically 0.5–1.5% of the chord) modification that can achieve significant lift and pitching-moment generation.1,2 The Gurney functions by essentially increasing the downward deflection of the trailingedge flow, facilitated through the formation of a series of counterrotating vortices similar to that of a von Karman vortex street. A subsequent effect is an apparent violation of the trailing-edge Kutta condition; experimental data show that finite loading is carried to the trailing edge. The Gurney flap increases the effective chord and camber of the airfoil, so by augmenting circulation. Liebeck3 suggested a flow pattern where a “virtual” cusped trailing edge is formed downstream of the Gurney from the shear layers merging downstream of the flap. The final pressure recovery would then occur off-surface, which is analogous to violation of the Kutta condition. Experimental and computational studies exploring the effect of Gurney flaps have been undertaken covering effects of flap height,4 angle,5 effects on multi-element airfoils,2 etc. In this Note, the database is increased through evaluation of the effects of flap porosity, inclination, and spacing from the surface. It would also be useful for experimental design and conceptual understanding to have correlations that relate Gurney-flap geometric parameters to performance. Consequently, such correlations are developed.

Numerical Analysis on Hybrid High Speed Sleeve Bearing

Hybrid sleeve bearing is widely used in high speed principal axis system. Numerical analysis on a spiral oil wedges hybrid sleeve bearing of high speed principal axis is investigated in this paper. The finite differential equations of Reynolds, film thickness and velocity in an oblique coordinate system are obtained. By means of the finite differential method, loading capacity, pressure distribution, and stream of lubricating oil of the hybrid sleeve bearing are computed and analyzed. The results show that spiral oil wedges can produce the flow separation between hot oil and cold oil, and avoid the oil heated repeatedly. With the increase of eccentricity and decrease of spiral angle, the loading capacity of the bearing increases.