Nonholonomically Constrained Dynamics and Optimization of Rolling Isolation Systems

Rolling Isolation Systems provide a simple and effective means for protecting components from horizontal floor vibrations. In these systems a platform rolls on four steel balls which, in turn, rest within shallow bowls. The trajectories of the balls is uniquely determined by the horizontal and rotational velocity components of the rolling platform, and thus provides nonholonomic constraints. In general, the bowls are not parabolic, so the potential energy function of this system is not quadratic. This thesis presents the application of Gauss's Principle of Least Constraint to the modeling of rolling isolation platforms. The equations of motion are described in terms of a redundant set of constrained coordinates. Coordinate accelerations are uniquely determined at any point in time via Gauss's Principle by solving a linearly constrained quadratic minimization. In the absence of any modeled damping, the equations of motion conserve energy. This mathematical model is then used to find the bowl profile that minimizes response acceleration subject to displacement constraint.

An investigation of a two-stage nonlinear vibration isolation system

This paper investigates the most desirable configuration of a two-stage nonlinear vibration isolation system, in which the isolators contain hardening geometric stiffness nonlinearity and linear viscous damping. The force transmissibility of the system is used as the measure of the effectiveness of the isolation system. The hardening nonlinearity is achieved by placing horizontal springs onto the suspended and intermediate masses, which are supported by vertical springs. It is found that nonlinearity in the upper stage has very little effect and thus serves little purpose. The nonlinearity in the lower stage, however, has a profound effect, and can significantly improve the effectiveness of the isolation system. Further, it is found that it is desirable to have high damping in the upper stage and very low damping in the lower stage. © 2012 Elsevier Ltd.

On the Performance of a Two-Stage Vibration Isolation System Which has Geometrically Nonlinear Stiffness

Linear single-stage vibration isolation systems have a limitation on their performance, which can be overcome passively by using linear two-stage isolations systems. It has been demonstrated by several researchers that linear single-stage isolation systems can be improved upon by using nonlinear stiffness elements, especially for low-frequency vibrations. In this paper, an investigation is conducted into whether the same improvements can be made to a linear two-stage isolation system using the same methodology for both force and base excitation. The benefits of incorporating geometric stiffness nonlinearity in both upper and lower stages are studied. It is found that there are beneficial effects of using nonlinearity in the stiffness in both stages for both types of excitation. Further, it is found that this nonlinearity causes the transmissibility at the lower resonance frequency to bend to the right, but the transmissibility at the higher resonance frequency is not affected in the same way. Generally, it is found that a nonlinear two-stage system has superior isolation performance compared to that of a linear two-stage isolator.

Finite element code-based modeling of a multi-feature isolation system and passive alleviation of possible inner pounding

The existing seismic isolation systems are based on well-known and accepted physical principles, but they are still having some functional drawbacks. As an attempt of improvement, the Roll-N-Cage (RNC) isolator has been recently proposed. It is designed to achieve a balance in controlling isolator displacement demands and structural accelerations. It provides in a single unit all the necessary functions of vertical rigid support, horizontal flexibility with enhanced stability, resistance to low service loads and minor vibration, and hysteretic energy dissipation characteristics. It is characterized by two unique features that are a self-braking (buffer) and a self-recentering mechanism. This paper presents an advanced representation of the main and unique features of the RNC isolator using an available finite element code called SAP2000. The validity of the obtained SAP2000 model is then checked using experimental, numerical and analytical results. Then, the paper investigates the merits and demerits of activating the built-in buffer mechanism on both structural pounding mitigation and isolation efficiency. The paper addresses the problem of passive alleviation of possible inner pounding within the RNC isolator, which may arise due to the activation of its self-braking mechanism under sever excitations such as near-fault earthquakes. The results show that the obtained finite element code-based model can closely match and accurately predict the overall behavior of the RNC isolator with effectively small errors. Moreover, the inherent buffer mechanism of the RNC isolator could mitigate or even eliminate direct structure-tostructure pounding under severe excitation considering limited septation gaps between adjacent structures. In addition, the increase of inherent hysteretic damping of the RNC isolator can efficiently limit its peak displacement together with the severity of the possibly developed inner pounding and, therefore, alleviate or even eliminate the possibly arising negative effects of the buffer mechanism on the overall RNC-isolated structural responses.

Fuzzy logic intelligent system for gas turbine module and system fault isolation

A fuzzy logic intelligent system is developed for gas-turbine fault isolation. The gas path measurements used for fault isolation are exhaust gas temperature, low and high rotor speed, and fuel flow. These four measurements are also called the cockpit parameters and are typically found in almost all older and newer jet engines. The fuzzy logic system uses rules developed from a model of performance influence coefficients to isolate engine faults while accounting for uncertainty in gas path measurements. It automates the reasoning process of an experienced powerplant engineer. Tests with simulated data show that the fuzzy system isolates faults with an accuracy of 89% with only the four cockpit measurements. However, if additional pressure and temperature probes between the compressors and before the burner, which are often found in newer jet engines, are considered, the fault isolation accuracy rises to as high as 98%. In addition, the additional sensors are useful in keeping the fault isolation system robust as quality of the measured data deteriorates.

An experimental nonlinear low dynamic stiffness device for shock isolation

The problem of shock generated vibration is very common in practice and difficult to isolate due to the high levels of excitation involved and its transient nature. If not properly isolated it could lead to large transmitted forces and displacements. Typically, classical shock isolation relies on the use of passive stiffness elements to absorb energy by deformation and some damping mechanism to dissipate residual vibration. The approach of using nonlinear stiffness elements is explored in this paper, focusing in providing an isolation system with low dynamic stiffness. The possibilities of using such a configuration for a shock mount are studied experimentally following previous theoretical models. The model studied considers electromagnets and permanent magnets in order to obtain nonlinear stiffness forces using different voltage configurations. It is found that the stiffness nonlinearities could be advantageous in improving shock isolation in terms of absolute displacement and acceleration response when compared with linear elastic elements. Copyright (C) 2015 Elsevier Ltd. All rights reserved

Synthesis and properties of heterobifunctional photoaffinity reagents for the identification and isolation of receptors

A method employing isotopically- and photoaffinity-labeled probes and polyclonal and monoclonal antibody to the probes for the identification, isolation and recovery of protein receptors is described. Antibody was raised against N-(3-(p-azido-m-($\sp{125}$I) -iodophenyl)) propionate (AIPP) coupled to and photolyzed to BSA. The antibodies specifically bound AIPP-derivatized proteins. An isolation system was developed utilizing this probe and two antigenically identical reversible analogues. N-(3-((p-azido-m-($\sp{125}$I) -iodo-phenyl)propionyl)amidoethyl-1,3-dithiopropionyl) succinimide (Reversible $\sp{125}$I-AIPPS) reacts with primary amines and N-(((3-p-azido-m-($\sp{125}$I) -iodophenyl)propionyl)amidoethyl)dithiopyridine ($\sp{125}$I-AIPP-PDA) reacts with reduced thiols. The applicability of the system was established by derivatizing known ligands (Transferrin and Interferon-alpha) with one of the probes. The ligand-probe was then allowed to interact with its receptor by incubation with SS5 lymphoma cells and cross-linked by photolysis at 300 nm. The photolyzed ligand/probe/receptor preparation was then recovered with AIPP antibody. Utilization of N-(3-((p-azido-m-($\sp{125}$I) -iodo-phenyl-propionyl)-amidoethyl-1,3-dithiopropionyl) succinimide (Reversible $\sp{125}$I-AIPPS) allowed the components of the photolyzed complex to be separated by treatment with 2-mercaptoethanol in the SDS-PAGE solubilization buffer. Ligand and receptor labeling were then assessed by Coomassie staining and autoradiography. Results of receptor assays suggest that $\sp{125}$I-AIPP was, indeed, transferred to moieties that represent the receptors for both Transferrin and Interferon-alpha. ^

Program-level support for protecting an application from untrustworthy components

Many software applications extend their functionality by dynamically loading executable components into their allocated address space. Such components, exemplified by browser plugins and other software add-ons, not only enable reusability, but also promote programming simplicity, as they reside in the same address space as their host application, supporting easy sharing of complex data structures and pointers. However, such components are also often of unknown provenance and quality and may be riddled with accidental bugs or, in some cases, deliberately malicious code. Statistics show that such component failures account for a high percentage of software crashes and vulnerabilities. Enabling isolation of such fine-grained components is therefore necessary to increase the stability, security and resilience of computer programs. This thesis addresses this issue by showing how host applications can create isolation domains for individual components, while preserving the benefits of a single address space, via a new architecture for software isolation called LibVM. Towards this end, we define a specification which outlines the functional requirements for LibVM, identify the conditions under which these functional requirements can be met, define an abstract Application Programming Interface (API) that encompasses the general problem of isolating shared libraries, thus separating policy from mechanism, and prove its practicality with two concrete implementations based on hardware virtualization and system call interpositioning, respectively. The results demonstrate that hardware isolation minimises the difficulties encountered with software based approaches, while also reducing the size of the trusted computing base, thus increasing confidence in the solution’s correctness. This thesis concludes that, not only is it feasible to create such isolation domains for individual components, but that it should also be a fundamental operating system supported abstraction, which would lead to more stable and secure applications.

Girsanov Transformation-Based Reliability Modeling and Testing of Actively Controlled Structures

The problem of estimation of the time-variant reliability of actively controlled structural dynamical systems under stochastic excitations is considered. Monte Carlo simulations, reinforced with Girsanov transformation-based sampling variance reduction, are used to tackle the problem. In this approach, the external excitations are biased by an additional artificial control force. The conflicting objectives of the two control forces-one designed to reduce structural responses and the other to promote limit-state violations (but to reduce sampling variance)-are noted. The control for variance reduction is fashioned after design-point oscillations based on a first-order reliability method. It is shown that for structures that are amenable to laboratory testing, the reliability can be estimated experimentally with reduced testing times by devising a procedure based on the ideas of the Girsanov transformation. Illustrative examples include studies on a building frame with a magnetorheologic damper-based isolation system subject to nonstationary random earthquake excitations. (C) 2014 American Society of Civil Engineers.

固体力学进展及应用: 庆贺李敏华院士90华诞文集

《固体力学进展及应用：庆贺李敏华院士90华诞文集》收录了近代固体力学基础理论及其应用领域的重要科技成果和最新进展。作者是在同体力学领域工作多年的资深研究员，他们来自各行各业，有丰富的科研与丁作经验。他们提供的论文在相当程度上反映当前同体力学的发展现状与成就，并能看出发展趋势，对未来研究的课题选择有参考价值。《固体力学进展及应用：庆贺李敏华院士90华诞文集》还收集了李敏华院士的珍贵照片和纪念李敏华院士90华诞的庆贺和回忆文章，具有重要的史料价值。

Experimental Research On Fatigue Property Of Steel Rubber Vibration Isolator For Offshore Jacket Platform In Cold Environment

Jacket platform is the most widely used offshore platform. Steel rubber vibration isolator and damping isolation system are often used to reduce or isolate the ice-induced and seismic-induced vibrations. The previous experimental and theoretical studies concern mostly with dynamic properties, vibration isolation schemes and vibration-reduction effectiveness analysis. In this paper, the experiments on steel rubber vibration isolator were carried out to investigate the compressive properties and fatigue properties in different low temperature conditions. The results may provide some guidelines for design of steel rubber vibration isolator for offshore platform in a cold environment, and for maintenance and replacement of steel rubber vibration isolator, and also for fatigue life assessment of the steel rubber vibration isolator. (C) 2009 Elsevier Ltd. All rights reserved.

Detecção e isolamento de falhas em sistemas dinâmicos baseados em redes neurais

This master dissertation presents the development of a fault detection and isolation system based in neural network. The system is composed of two parts: an identification subsystem and a classification subsystem. Both of the subsystems use neural network techniques with multilayer perceptron training algorithm. Two approaches for identifica-tion stage were analyzed. The fault classifier uses only residue signals from the identification subsystem. To validate the proposal we have done simulation and real experiments in a level system with two water reservoirs. Several faults were generated above this plant and the proposed fault detection system presented very acceptable behavior. In the end of this work we highlight the main difficulties found in real tests that do not exist when it works only with simulation environments

Novel active and passive anti-vibration mountings

This paper investigates a novel design approach for a vibration isolator for use in space structures. The approach used can particularly be applicable for aerospace structures that support high precision instrumentation such as satellite payloads. The isolator is a space-frame structure that is folded in on itself to act as a mechanical filter over a defined frequency range. The absence of viscoelastic elements in such a mounting makes the design suitable for use in a vacuum and in high temperature or harsh environments with no risk of drift in alignment of the structure. The design uses a genetic algorithm based geometric optimisation routine to maximise passive vibration isolation, and this is hybridised with a geometric feasibility search. To complement the passive isolation system, an active system is incorporated in the design to add damping. Experimental work to validate the feasibility of the approach is also presented, with the active/passive structure achieving transmissibility of about 19 dB over a range of 1-250 Hz. It is shown here that the use of these novel anti-vibration mountings has no or little consequent weight and cost penalties whilst maintaining their effectiveness with the vibration levels. The approach should pave the way for the design of anti-vibration mountings that can be used between most pieces of equipment and their supporting structure. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.