Analysis of steel structures for first- and second-order element (displacement and force) solutions

Finite element method (FEM) relies on an approximate function to fit into a governing equation and minimizes the residual error in the integral sense in order to generate solutions for the boundary value problems (nodal solutions). Because of this FEM does not show simultaneous capacities for accurate displacement and force solutions at node and along an element, especially when under the element loads, which is of much ubiquity. If the displacement and force solutions are strictly confined to an element’s or member’s ends (nodal response), the structural safety along an element (member) is inevitably ignored, which can definitely hinder the design of a structure for both serviceability and ultimate limit states. Although the continuous element deflection and force solutions can be transformed into the discrete nodal solutions by mesh refinement of an element (member), this setback can also hinder the effective and efficient structural assessment as well as the whole-domain accuracy for structural safety of a structure. To this end, this paper presents an effective, robust, applicable and innovative approach to generate accurate nodal and element solutions in both fields of displacement and force, in which the salient and unique features embodies its versatility in applications for the structures to account for the accurate linear and second-order elastic displacement and force solutions along an element continuously as well as at its nodes. The significance of this paper is on shifting the nodal responses (robust global system analysis) into both nodal and element responses (sophisticated element formulation).

Socioeconomic differences in food choices : deficiencies in nutrition knowledge or simply too much on your plate?

Nutrition knowledge is associated with dietary choices in the general population and has been proposed to contribute to socioeconomic differences in food choices and corresponding socioeconomic gradients in mortality and morbidity for a number of diet-related illnesses. This paper explores current evidence regarding socioeconomic differences in nutrition knowledge, reviewing the components of nutrition knowledge that have been assessed, the dietary intake or food choice outcomes considered, and the socioeconomic indicators used. In addition, this paper considers how socioeconomic differences in nutrition knowledge may arise, and potential determinants of inequalities in the application of nutrition knowledge. It highlights issues to consider when developing strategies to improve nutrition knowledge and facilitate knowledge application among those of lower socioeconomic position.

A Matlab toolbox for parametric identification of radiation-force models of ships and offshore structures

This article describes a Matlab toolbox for parametric identification of fluid-memory models associated with the radiation forces ships and offshore structures. Radiation forces are a key component of force-to-motion models used in simulators, motion control designs, and also for initial performance evaluation of wave-energy converters. The software described provides tools for preparing non-parmatric data and for identification with automatic model-order detection. The identification problem is considered in the frequency domain.

Validation tool for traction force microscopy

Traction force microscopy (TFM) is commonly used to estimate cells’ traction forces from the deformation that they cause on their substrate. The accuracy of TFM highly depends on the computational methods used to measure the deformation of the substrate and estimate the forces, and also on the specifics of the experimental set-up. Computer simulations can be used to evaluate the effect of both the computational methods and the experimental set-up without the need to perform numerous experiments. Here, we present one such TFM simulator that addresses several limitations of the existing ones. As a proof of principle, we recreate a TFM experimental set-up, and apply a classic 2D TFM algorithm to recover the forces. In summary, our simulator provides a valuable tool to study the performance, refine experimentally, and guide the extraction of biological conclusions from TFM experiments.

Time- vs. frequency-domain identification of parametric radiation force models for marine structures at zero speed

The dynamics describing the motion response of a marine structure in waves can be represented within a linear framework by the Cummins Equation. This equation contains a convolution term that represents the component of the radiation forces associated with fluid memory effects. Several methods have been proposed in the literature for the identification of parametric models to approximate and replace this convolution term. This replacement can facilitate the model implementation in simulators and the analysis of motion control designs. Some of the reported identification methods consider the problem in the time domain while other methods consider the problem in the frequency domain. This paper compares the application of these identification methods. The comparison is based not only on the quality of the estimated models, but also on the ease of implementation, ease of use, and the flexibility of the identification method to incorporate prior information related to the model being identified. To illustrate the main points arising from the comparison, a particular example based on the coupled vertical motion of a modern containership vessel is presented.

Impact of the piston secondary motion on its slap force

A theoretical model is developed for the analysis of piston secondary motion. Based on this model, the slap force of a specific L6 diesel engine was compared when considering different boundary conditions, such as lubricating oil on cylinder liner, surface roughness, deformation of cylinder liner and piston skirt. It is concluded that it is necessary to consider the secondary motion of piston in the analysis of the inner excitation for an internal combustion engine. A more comprehensive consideration of the boundary condition (i.e., more close to the actual condition) will lead to a smaller maximum slap force, and among all boundary conditions considered in this paper, the structural deformation of the piston skirt and cylinder liner is the most influential factor. The theoretical model developed and findings obtained in this study will benefit the future analysis and design of advanced internal combustion engine structures.

Semiparametric estimates of the supply and demand effects of disability on labor force participation

This paper modifies and uses the semiparametric methods of Ichimura and Lee (1991) on standard cross-section data to decompose the effect of disability on labor force participation into a demand and a supply effect. It shows that straightforward use of Ichimura and Lee leads to meaningless results while imposing monotonicity on the unknown function leads to substantial results. The paper finds that supply effects dominate the demand effects of disability.

Assessment of revised recruitment standards for asthma in the Australian Defence Force

Objective To assess the impact of relaxed asthma recruitment standards adopted by the Australian Defence Force (ADF) in 2007. Methods A retrospective audit was conducted on clinical and administrative data for recruits, with and without mild asthma, in their first year of service. Results There was no evidence that mild asthmatics experienced worse outcomes than nonasthmatic recruits. Mild asthmatics had fewer illnesses and restricted duty days and were less costly compared to other recruits. There was no difference in the rate of discharge (attrition) between those with and without mild asthma. Conclusions The revised recruitment standards for asthma in the ADF have not resulted in unanticipated medical or administrative costs to the organisation. Health and administrative outcomes differed little between mild asthmatics and non-asthmatic recruits in their first twelve months of service.

Determination of strain-rate-dependent mechanical behavior of living and fixed osteocytes and chondrocytes using atomic force microscopy and inverse finite element analysis

The aim of this paper is to determine the strain-rate-dependent mechanical behavior of living and fixed osteocytes and chondrocytes, in vitro. Firstly, Atomic Force Microscopy (AFM) was used to obtain the force-indentation curves of these single cells at four different strain-rates. These results were then employed in inverse finite element analysis (FEA) using Modified Standard neo-Hookean Solid (MSnHS) idealization of these cells to determine their mechanical properties. In addition, a FEA model with a newly developed spring element was employed to accurately simulate AFM evaluation in this study. We report that both cytoskeleton (CSK) and intracellular fluid govern the strain-rate-dependent mechanical property of living cells whereas intracellular fluid plays a predominant role on fixed cells’ behavior. In addition, through the comparisons, it can be concluded that osteocytes are stiffer than chondrocytes at all strain-rates tested indicating that the cells could be the biomarker of their tissue origin. Finally, we report that MSnHS is able to capture the strain-rate-dependent mechanical behavior of osteocyte and chondrocyte for both living and fixed cells. Therefore, we concluded that the MSnHS is a good model for exploration of mechanical deformation responses of single osteocytes and chondrocytes. This study could open a new avenue for analysis of mechanical behavior of osteocytes and chondrocytes as well as other similar types of cells.

Computational strategies for surface fitting using thin plate spline finite element methods

Thin plate spline finite element methods are used to fit a surface to an irregularly scattered dataset [S. Roberts, M. Hegland, and I. Altas. Approximation of a Thin Plate Spline Smoother using Continuous Piecewise Polynomial Functions. SIAM, 1:208--234, 2003]. The computational bottleneck for this algorithm is the solution of large, ill-conditioned systems of linear equations at each step of a generalised cross validation algorithm. Preconditioning techniques are investigated to accelerate the convergence of the solution of these systems using Krylov subspace methods. The preconditioners under consideration are block diagonal, block triangular and constraint preconditioners [M. Benzi, G. H. Golub, and J. Liesen. Numerical solution of saddle point problems. Acta Numer., 14:1--137, 2005]. The effectiveness of each of these preconditioners is examined on a sample dataset taken from a known surface. From our numerical investigation, constraint preconditioners appear to provide improved convergence for this surface fitting problem compared to block preconditioners.

Improving the shear capacities of lipped channel beams with web openings using plate stiffeners

Cold-formed steel lipped channel beams (LCB) are used extensively in residential, industrial and commercial buildings as load bearing structural elements. Their shear capacities are considerably reduced when web openings are included for the purpose of locating building services. Past research has shown that the shear capacities of LCBs were reduced by up to 70% due to the inclusion of these web openings. Hence there is a need to improve the shear capacities of LCBs with web openings. A cost effective way of eliminating the detrimental effects of large web openings is to attach suitable stiffeners around the web openings and restore the original shear strength and stiffness of LCBs. Hence detailed experimental studies were undertaken to investigate the behaviour and strength of LCBs with stiffened web openings subject to shear, and combined bending and shear actions. Both plate and stud stiffeners with varying sizes and thicknesses were attached to the web elements of LCBs using different screw-fastening arrangements. Simply supported test specimens of LCBs with aspect ratios of 1.0 and 1.5 were loaded at mid-span until failure. Numerical studies were also undertaken to investigate the strength of LCBs with stiffened web openings. Finite element models of LCBs with stiffened web openings under shear, combined bending and shear actions were developed to simulate the behaviour of tested LCBs. The developed models were then validated by comparing their results with experimental results and used in further studies. Both experimental and finite element analysis results showed that the stiffening arrangements recommended by past research and available design guidelines are not adequate to restore the original shear strengths of LCBs. Therefore new stiffener arrangements were proposed based on screw fastened plate stiffeners. This paper presents the details of this research study and the results.

Colloidal drug probe : Method development and validation for adhesion force measurement using Atomic Force Microscopy

This study demonstrates a novel technique of preparing drug colloid probes to determine the adhesion force between a model drug salbutamol sulphate (SS) and the surfaces of polymer microparticles to be used as carriers for the dispersion of drug particles from dry powder inhaler (DPI) formulations. Model silica probes of approximately 4 lm size, similar to a drug particle used in DPI formulations, were coated with a saturated SS solution with the aid of capillary forces acting between the silica probe and the drug solution. The developed method of ensuring a smooth and uniform layer of SS on the silica probe was validated using X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM). Using the same technique, silica microspheres pre-attached on the AFM cantilever were coated with SS. The adhesion forces between the silica probe and drug coated silica (drug probe) and polymer surfaces (hydrophilic and hydrophobic) were determined. Our experimental results showed that the technique for preparing the drug probe was robust and can be used to determine the adhesion force between hydrophilic/ hydrophobic drug probe and carrier surfaces to gain a better understanding on drug carrier adhesion forces in DPI formulations.

Force-deformation properties of the human heel pad during barefoot walking

Introduction: The plantar heel pad is a specialized fibroadipose tissue that attenuates and, in part, dissipates the impact energy associated with heel strike. Although near maximal deformation of the heel pad has been shown during running, in vivo measurement of the deformation and structural properties of the heel pad during walking remains largely unexplored. This study employed a fluoroscope, synchronized with a pressure platform, to obtain force–deformation data for the heel pad during walking. Methods: Dynamic lateral foot radiographs were acquired from 6 male and 10 female adults (age, 45 ± 10 yrs; height, 1.66 ± 0.10 m; and weight, 80.7 ± 10.8 kg), while walking barefoot at preferred speeds. The inferior aspect of the calcaneus was digitized and the sagittal thickness and deformation of the heel pad relative to the support surface calculated. Simultaneous measurement of the peak force beneath the heel was used to estimate the principal structural properties of the heel pad. Results: Transient loading profiles associated with walking induced rapidly changing deformation rates in the heel pad and resulted in irregular load–deformation curves. The initial stiffness (32 ± 11 N.mm-1) of the heel pad was an order of magnitude lower than its final stiffness (212 ± 125 N.mm-1) and on average, only 1.0 J of energy was dissipated by the heel pad with each step during walking. Peak deformation (10.3 mm) approached that predicted for the limit of pain tolerance (10.7 mm). Conclusion: These findings suggest the heel pad operates close to its pain threshold even at speeds encountered during barefoot walking and provides insight as to why barefoot runners may adopt ‘forefoot’ strike patterns that minimize heel loading.

MIMO and SISO identification of radiation force terms for models of marine structures in waves

This paper presents a discussion on the use of MIMO and SISO techniques for identification of the radiation force terms in models for surface vessels. We compare and discuss two techniques recently proposed in literature for this application: time domain identification and frequency domain identification. We compare the methods in terms of estimates model order, accuracy of the fit, use of the available information, and ease of use and implementation.

Force controlled hexapod walking

This thesis is a study on controlling methods for six-legged robots. The study is based on mathematical modeling and simulation. A new joint controller is proposed and tested in simulation that uses joint angles and leg reaction force as inputs to generate a torque, and a method to optimise this controller is formulated and validated. Simulation shows that hexapod can walk on flat ground based on PID controllers with just four target configurations and a set of leg coordination rules, which provided the basis for the design of the new controller.