Detailed wheel/rail geometry processing with the conformal contact approach

Multibody System Dynamics - This paper proposes a new way of considering wheel–rail contact in multibody systems simulation that goes beyond the traditional planar constraint and elastic...     

Wheel/rail contact geometry on tight radius curved track: simulation and experimental validation

In this investigation, a numerical procedure for wheel/rail one and two-point contact geometry analysis is developed for predicting the location of contact points in curved negotiations on a tight radius curved track. The proposed method accounts for the change in the longitudinal location of contact point along the curved track as well as the circumferential contact point on the wheel flange. For the purpose of validation, simulation results for one and two-point contact scenarios are compared with those obtained using the experiment. The experiment is performed on a test track of R48 curve using an actual truck, and the location of contact points for given lateral and yaw displacements are measured on the tight radius curved track. It is demonstrated that good agreements are obtained between the simulation and experimental results in tread and flange contacts.     

Achieving privacy in trust negotiations with an ontology-based approach

The increasing use of Internet in a variety of distributed multiparty interactions and transactions with strong real-time requirements has pushed the search for solutions to the problem of attribute-based digital interactions. A promising solution today is represented by automated trust negotiation systems. Trust negotiation systems allow subjects in different security domains to securely exchange protected resources and services. These trust negotiation systems, however, by their nature, may represent a threat to privacy in that credentials, exchanged during negotiations, often contain sensitive personal information that may need to be selectively released. In this paper, we address the problem of preserving privacy in trust negotiations. We introduce the notion of privacy preserving disclosure, that is, a set that does not include attributes or credentials, or combinations of these, that may compromise privacy. To obtain privacy preserving disclosure sets, we propose two techniques based on the notions of substitution and generalization. We argue that formulating the trust negotiation requirements in terms of disclosure policies is often restrictive. To solve this problem, we show how trust negotiation requirements can be expressed as property-based policies that list the properties needed to obtain a given resource. To better address this issue, we introduce the notion of reference ontology, and formalize the notion of trust requirement. Additionally, we develop an approach to derive disclosure policies from trust requirements and formally state some semantics relationships (i.e., equivalence, stronger than) that may hold between policies. These relationships can be used by a credential requestor to reason about which disclosure policies he/she should use in a trust negotiation.     

Comparison of numerical and computational aspects between two constraint-based contact methods in the description of wheel/rail contacts

Multibody System Dynamics - The numerical and computation aspects of the Knife-edge Equivalent Contact (KEC) constraint and lookup table (LUT) methods are compared in this paper. The LUT method...     

SymROP: ROP protein with identical helices redesigned by all-atom contact analysis and molecular dynamics

Experience has shown that protein redesigns (using the backbone from a known protein structure) are far more likely to produce well-ordered, native-like structures than are true de novo designs. Therefore, to design a four-helix bundle made of identical short helices, we here proceed by an extensive redesign of the ROP protein. A fully symmetrical SymROP sequence derived from ROP was chosen by modeling ideal-geometry side chains, including hydrogens, while maintaining the "goodness-of-fit" of side-chain packing by calculating all-atom contact surfaces with the Reduce and Probe programs. To estimate the probable extent of backbone movement and side-chain mobility, restrained molecular dynamics simulations were compared for candidate sequences and controls, including substitution of Abu for all or half the core Ala residues. The resulting 17-residue designed sequence is 41% identical to the relevant regions in ROP. SymROP is intended for construction by the Template Assembled Synthetic Proteins approach, to control the bundle topology, to use short helices, and to allow blocked termini and unnatural amino acids. ROP protein has been a valuable system for studying helical protein structure because of its simplicity and regularity within a structure large enough to have a real hydrophobic core. The SymROP design carries that simplicity and regularity even further.     

A novel approach for analyzing dynamics in neural networks with saturated characteristics

Current theories about the dynamics of neural networks with nonlinear characteristics and parameterized by set of parameters are mostly based on approximations in one way or another. In this paper we first introduce a rigorous approach which allows us to check in which parameter region a given saturated state is an attractor of the dynamics: a saturated state w=(w _i , i=1,...,N){-1,1} ^N is an attractor of the dynamics if and only if there is a local field gap between neurons in J ⁺ (w)={i, w _i =1} and J ^- (w)={i, w _i =–1}. Then we apply the result to analyze several models in neural networks. In particular in the Hopfield model we calculate the capacity and give an exact relation between the capacity and the threshold.     

Mixed interpretation and extensions of the equivalent mass matrix approach for elastodynamics with contact

The present paper highlights the idea that the mass redistribution technique introduced by Khenous and co-workers (2006) [17], [18] for elastodynamics with impact, can be reinterpreted as a mixed formulation in displacements and velocities in which a special compatibility condition is enforced. Such a formulation opens the route to various extensions and to variational integrators for impact problems, potentially with variational time adaption. Those ideas are exemplified in the design of such integrators and various mass redistribution schemes.     

Inertia-driven enhancement of mixing efficiency in microfluidic cross-junctions: a combined Eulerian/Lagrangian approach

Mixing of a diffusing species entrained in a three-dimensional microfluidic flow-focusing cross-junction is numerically investigated at low Reynolds numbers, \(1 \le Re \le 150\), for a value of the Schmidt number representative of a small solute molecule in water, \(Sc = 10^3\). Accurate three-dimensional simulations of the steady-state incompressible Navier–Stokes equations confirm recent results reported in the literature highlighting the occurrence of different qualitative structures of the flow geometry, whose range of existence depends on Re and on the ratio, R, between the volumetric flowrates of the impinging currents. At low values of R and increasing Re, the flux tube enclosing the solute-rich stream undergoes a topological transition, from the classical flow-focused structure to a multi-branched shape. We here show that this transition causes a nonmonotonic behavior of mixing efficiency with Re at constant flow ratio. The increase in efficiency is the consequence of a progressive compression of the cross-sectional diffusional lengthscale, which provides the mechanism sustaining the transversal Fickian flux even when the Peclet number, \({Pe=Re \, Sc}\), characterizing mass transport, becomes higher due to the increase in Re. The quantitative assessment of mixing efficiency at the considerably high values of the Peclet number considered (\(10^3 \le Pe \le 1.5 \times 10^5\)) is here made possible by a novel method of reconstruction of steady-state cross-sectional concentration maps from velocity-weighted ensemble statistics of noisy trajectories, which does away with the severe numerical diffusion shortcomings associated with classical Eulerian approaches to mass transport in complex 3d flows.     

Soft sets combined with fuzzy sets and rough sets: a tentative approach

Theories of fuzzy sets and rough sets are powerful mathematical tools for modelling various types of uncertainty. Dubois and Prade investigated the problem of combining fuzzy sets with rough sets. Soft set theory was proposed by Molodtsov as a general framework for reasoning about vague concepts. The present paper is devoted to a possible fusion of these distinct but closely related soft computing approaches. Based on a Pawlak approximation space, the approximation of a soft set is proposed to obtain a hybrid model called rough soft sets. Alternatively, a soft set instead of an equivalence relation can be used to granulate the universe. This leads to a deviation of Pawlak approximation space called a soft approximation space, in which soft rough approximations and soft rough sets can be introduced accordingly. Furthermore, we also consider approximation of a fuzzy set in a soft approximation space, and initiate a concept called soft–rough fuzzy sets, which extends Dubois and Prade’s rough fuzzy sets. Further research will be needed to establish whether the notions put forth in this paper may lead to a fruitful theory.     

A combined reliability analysis approach with dimension reduction method and maximum entropy method

This paper presents a combined reliability analysis approach which is composed of Dimension Reduction Method (DRM) and Maximum Entropy Method (MEM). DRM has emerged as a new approach in this field with the advantages of its sensitivity-free nature and efficiency instead of searching for the most probable point (MPP). However, in some recent implementations, the Moment Based Quadrature Rule (MBQR) in the DRM was found to be numerically instable when solving a system of linear equations for the integration points. In this study, a normalized Moment Based Quadrature Rule (NMBQR) is proposed to solve this problem, which can reduce the condition number of the coefficient matrix of the linear equations considerably and improve the robustness and stableness. Based on the statistical moments obtained by DRM+NMBQR, the MEM is applied to construct the probability density function (PDF) of the response. A number of numerical examples are calculated and compared to the Monte Carlo simulation (MCS), the First Order Reliability Method (FORM), the Extended Generalized Lambda Distribution (EGLD) and Saddlepoint Approximation (SA). The results show the accuracy and efficiency of the proposed method, especially for the multimodal PDF problem and multiple design point problem.     

A rule dynamics approach to event detection in Twitter with its application to sports and politics

The increasing popularity of Twitter as social network tool for opinion expression as well as information retrieval has resulted in the need to derive computational means to detect and track relevant topics/events in the network. The application of topic detection and tracking methods to tweets enable users to extract newsworthy content from the vast and somehow chaotic Twitter stream. In this paper, we apply our technique named Transaction-based Rule Change Mining to extract newsworthy hashtag keywords present in tweets from two different domains namely; sports (The English FA Cup 2012) and politics (US Presidential Elections 2012 and Super Tuesday 2012). Noting the peculiar nature of event dynamics in these two domains, we apply different time-windows and update rates to each of the datasets in order to study their impact on performance. The performance effectiveness results reveal that our approach is able to accurately detect and track newsworthy content. In addition, the results show that the adaptation of the time-window exhibits better performance especially on the sports dataset, which can be attributed to the usually shorter duration of football events.     

A new residue and nodal error evaluation in h-adaptive boundary element method

An error indicator and evaluation of nodal error are proposed in the h-adaptive boundary element method. Error indicator is defined based on a new residue calculated at collocation points only. Nodal error is evaluated from the approximated residue by solving a matrix equation. Convergence of the solution is estimated with the nodal error. Efficiency of the proposed strategy is proved through numerical examples.     

A complete strategy for efficient and accurate multibody dynamics of flexible structures with large lap joints considering contact and friction

This paper deals with the dynamics of jointed flexible structures in multibody simulations. Joints are areas where the surfaces of substructures come into contact, for example, screwed or bolted joints. Depending on the spatial distribution of the joint, the overall dynamic behavior can be influenced significantly. Therefore, it is essential to consider the nonlinear contact and friction phenomena over the entire joint. In multibody dynamics, flexible bodies are often treated by the use of reduction methods, such as component mode synthesis (CMS). For jointed flexible structures, it is important to accurately compute the local deformations inside the joint in order to get a realistic representation of the nonlinear contact and friction forces. CMS alone is not suitable for the capture of these local nonlinearities and therefore is extended in this paper with problem-oriented trial vectors. The computation of these trial vectors is based on trial vector derivatives of the CMS reduction base. This paper describes the application of this extended reduction method to general multibody systems, under consideration of the contact and friction forces in the vector of generalized forces and the Jacobian. To ensure accuracy and numerical efficiency, different contact and friction models are investigated and evaluated. The complete strategy is applied to a multibody system containing a multilayered flexible structure. The numerical results confirm that the method leads to accurate results with low computational effort.     

Multibody dynamics simulation of thin-walled four-point contact ball bearing with interactions of balls,ring raceways and crown-type cage

Multibody System Dynamics - Computational speed and stability are two important aspects in the dynamics analysis of large-scale complex multibody systems. In order to improve both in the context of...     

Simulation of atomic quantum dynamics in combined intense laser and weak electric fields

Numerical simulations are presented for a two-dimensional model of a hydrogen-like nitrogen ion in such intense laser fields that the electron velocity becomes non-negligible to that of light. With increasing laser field intensity, the role of its magnetic field component becomes more significant and a notable magnetically induced electron drift in laser propagation direction occurs. We show that this drift can be controlled to some degree by applying additional static or oscillating electric fields polarized in the laser propagation direction.     

Parallel and distributed simulation of sediment dynamics in shallow water using particle decomposition approach

This paper describes the parallel simulation of sediment dynamics in shallow water. By using a Lagrangian model, the problem is transformed to one in which a large number of independent particles must be tracked. This results in a technique that can be parallelised with high efficiency. We have developed a sediment transport model using three different sediment suspension methods. The first method uses a modified mean for the Poisson distribution function to determine the expected number of the suspended particles in each particular grid cell of the domain over all available processors. The second method determines the number of particles to suspend with the aid of the Poisson distribution function only in those grid cells which are assigned to that processor. The third method is based on the technique of using a synchronised pseudo-random-number generator to generate identical numbers of suspended particles in all valid grid cells for each processor. Parallel simulation experiments are performed in order to investigate the efficiency of these three methods. Also the parallel performance of the implementations is analysed. We conclude that the second method is the best method on distributed computing systems (e.g., a Beowulf cluster), whereas the third maintains the best load distribution.     

Modeling and analysis of planar rigid multibody systems with translational clearance joints based on the non-smooth dynamics approach

The main purpose of this paper is to present and discuss a methodology for a dynamic modeling and analysis of rigid multibody systems with translational clearance joints. The methodology is based on the non-smooth dynamics approach, in which the interaction of the elements that constitute a translational clearance joint is modeled with multiple frictional unilateral constraints. In the following, the most fundamental issues of the non-smooth dynamics theory are revised. The dynamics of rigid multibody systems are stated as an equality of measures, which are formulated at the velocity-impulse level. The equations of motion are complemented with constitutive laws for the normal and tangential directions. In this work, the unilateral constraints are described by a set-valued force law of the type of Signorini’s condition, while the frictional contacts are characterized by a set-valued force law of the type of Coulomb’s law for dry friction. The resulting contact-impact problem is formulated and solved as a linear complementarity problem, which is embedded in the Moreau time-stepping method. Finally, the classical slider-crank mechanism is considered as a demonstrative application example and numerical results are presented. The results obtained show that the existence of clearance joints in the modeling of multibody systems influences their dynamics response.     

A hybrid approach using two-level SOM and combined AHP rating and AHP/DEA-AR method for selecting optimal promising emerging technology

Emerging technologies are playing an important role in establishing competitive advantage for technology based companies. Selecting an efficient and important emerging technology to invest in is significant to the companies also. In this study, we propose a method for selecting optimal emerging technology which is efficient, important and the most suitable to a company’s actual levels of input resource among various emerging technology alternatives. In order to select optimal emerging technology, the proposed method uses two-level-SOM to cluster the emerging technology alternatives based on alternatives’ required levels of input resource. For selecting efficient and important promising emerging technology, the proposed method calculates emerging technology alternatives’ efficiency score by using AHP/DEA-AR and their importance score by using AHP rating method in each technology cluster generated by two-level-SOM. Finally, the proposed method selects optimal promising emerging technology according to a company’s actual levels of input resource and each emerging technology alternative’s combined scores which is calculated by adding its efficiency score and importance score. A Korean company’s case of selecting optimal promising nanotechnology is employed to illustrate the proposed method. The result shows that the proposed method can provide an effective and reasonable selection of optimal promising emerging technology.