Response of Damped Oscillators to Cycloidal Pulses

In this paper, the transient response of a damped oscillator subjected to cycloidal pulses is investigated. The response is computed analytically by considering viscous and friction damping, and response spectra for relative and absolute quantities are presented for the linear viscous and sliding oscillator. The study complements the list of numerous shock spectra mostly published for the undamped linear oscillator. Subsequently, a numerical procedure based on a state-space formulation is developed to compute the response of damped oscillators when subjected to ground motions recorded near the source of strong earthquakes. It is found that although in several occasions such motions resemble to cycloidal pulses, the response of structures with low to moderate periods is substantially affected by the high-frequency fluctuations that often override the long duration pulse.     

Gender stereotyping over instant messenger: The effects of gender and context

Researchers have observed that contrary to the high expectations for online communications, gender stereotyping has not disappeared in this medium, and is sometimes even accentuated. This study aimed to understand the effect of gender over instant messenger, a relatively new and unexplored medium. Instant messenger was chosen because it is a medium that is used most by youth who have grown up communicating online. Participants were interviewed over instant messenger about a potential online support service and were then asked to judge the effectiveness of their interviewer. The interviewer was identified only by a masculine or feminine name and was computer-simulated so as to remove any bias. The topic of discussion was stereotypically masculine or stereotypically feminine. Male participants were found to employ a male superiority heuristic, whereby they judged the male interviewer as more competent, regardless of the context. Female participants were hypothesized to judge the female interviewer as more competent in the feminine context, and the male interviewer as more competent in the masculine context (the context-gender match heuristic), but this hypothesis was not supported. The findings are discussed in the context of previous research on gender stereotyping in online communication.     

KnowBaSICS-M: an ontology-based system for semantic management of medical problems and computerised algorithmic solutions

In this paper, an ontology-based system (KnowBaSICS-M) is presented for the semantic management of Medical Computational Problems (MCPs), i.e., medical problems and computerised algorithmic solutions. The system provides an open environment, which: (1) allows clinicians and researchers to retrieve potential algorithmic solutions pertinent to a medical problem and (2) enables incorporation of new MCPs into its underlying Knowledge Base (KB). KnowBaSICS-M is a modular system for MCP acquisition and discovery that relies on an innovative ontology-based model incorporating concepts from the Unified Medical Language System (UMLS). Information retrieval (IR) is based on an ontology-based Vector Space Model (VSM) that estimates the similarity among user-defined MCP search criteria and registered MCP solutions in the KB. The results of a preliminary evaluation and specific examples of use are presented to illustrate the benefits of the system. KnowBaSICS-M constitutes an approach towards the construction of an integrated and manageable MCP repository for the biomedical research community.     

Proactive fault‐tolerant model predictive control

Fault‐tolerant control methods have been extensively researched over the last 10 years in the context of chemical process control applications, and provide a natural framework for integrating process monitoring and control aspects in a way that not only fault detection and isolation but also control system reconfiguration is achieved in the event of a process or actuator fault. But almost all the efforts are focused on the reactive fault‐tolerant control. As another way for fault‐tolerant control, proactive fault‐tolerant control has been a popular topic in the communication systems and aerospace control systems communities for the last 10 years. At this point, no work has been done on proactive fault‐tolerant control within the context of chemical process control. Motivated by this, a proactive fault‐tolerant Lyapunov‐based model predictive controller (LMPC) that can effectively deal with an incipient control actuator fault is proposed. This approach to proactive fault‐tolerant control combines the unique stability and robustness properties of LMPC as well as explicitly accounting for incipient control actuator faults in the formulation of the MPC. Our theoretical results are applied to a chemical process example, and different scenaria were simulated to demonstrate that the proposed proactive fault‐tolerant model predictive control method can achieve practical stability and efficiently deal with a control actuator fault. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2810–2820, 2013     

Rocking Response of Free-Standing Blocks under Cycloidal Pulses

This paper examines in depth the transient rocking response of free-standing rigid blocks subjected to physically realizable trigonometric pulses. First, the expressions for the dynamic horizontal and vertical reactions at the pivot point of a rocking block are derived and it is shown that the coefficient of friction needed to sustain pure rocking motion is, in general, an increasing function of the acceleration level of the pulse. Subsequently, this paper shows that under cycloidal pulses a free-standing block can overturn with two distinct modes: (1) by exhibiting one or more impacts; and (2) without exhibiting any impact. The existence of the second mode results in a safe region that is located on the acceleration-frequency plane above the minimum overturning acceleration spectrum. The shape of this region depends on the coefficient of restitution and is sensitive to the nonlinear nature of the problem. This paper concludes that the sensitive nonlinear nature of the problem, in association with the presence of the safe region that embraces the minimum overturning acceleration spectrum, complicates further the task of estimating peak ground acceleration by only examining the geometry of free-standing objects that either overturned or survived a ground shaking.     

Minimizing energy consumption in reverse osmosis membrane desalination using optimization-based control

This work focuses on the design and implementation of an optimization-based control system on an experimental reverse osmosis (RO) membrane water desalination process in order to facilitate system operation at energy optimal conditions. A nonlinear model for the RO process is derived using first principles and the model parameters are computed from experimental data. This model is combined with appropriate equations for reverse osmosis system energy analysis to form the basis for the design of a nonlinear optimization-based control system. The proposed control system is implemented on UCLA’s experimental RO desalination system and its energy optimization capabilities are evaluated.     

Rocking Response of Anchored Blocks under Pulse-Type Motions

This paper examines the transient rocking response of anchored blocks subjected to physically realizable horizontal pulse-type motion. Restrainers with elastic-brittle and elastic-plastic behavior are considered. Under one-sine pulse, anchored blocks can overturn with two distinct modes of overturning: (1) by exhibiting one impact; and (2) without exhibiting any impact. It is found that restrainers are more efficient in preventing overturning of small slender blocks subjected to low frequency pulses. This study uncovers that, although for most of the frequency range anchored blocks survive higher accelerations than free-standing blocks, there is a finite frequency range where the opposite happens. This paper examines this counterintuitive behavior and explains the destructive effect that increased strength and increased ductility of restrainers have on the rocking stability of rigid structures when excited by certain ground motions.     

Model-predictive control of feed flow reversal in a reverse osmosis desalination process

Model-predictive control algorithms are applied to a high capacity reverse osmosis (RO) membrane desalination process simulation that utilizes feed flow reversal in order to prevent and/or reverse scale crystal formation on the membrane surface. A dynamic non-linear model which incorporates feed concentration and membrane properties is used for simulation and demonstration of optimally controlled feed flow reversal. Before flow reversal can take place on a high capacity RO plant, the flow into the membrane unit must be carefully reduced to eliminate the risk of membrane module damage and unnecessary energy consumption. A cost function is formulated for the transition between the normal high flow steady-state operating point to a low flow steady-state operating point where it is safe to reverse the flow direction. Open-loop and closed-loop simulations demonstrate non-linear model-predictive control strategies that induce transition from the high-flow to low-flow steady-states in an optimal way while subjected to plant-model mismatch on the feed concentration, actuator magnitude and rate constraints, and sampled measurements.     

Dimensional Analysis of Rigid-Plastic and Elastoplastic Structures under Pulse-Type Excitations

In this paper, the inelastic response of rigid-plastic and elastic-plastic systems subjected to pulse-type excitations is revisited with dimensional analysis. Starting from Newmark’s result on the maximum displacement of a sliding mass resting on a base that is subjected to a rectangular acceleration pulse, the paper introduces an energetic length scale of the excitation and the relevant dimensionless Π-products that govern the response of yielding structures. The introduction of Buckingham’s Π-theorem reduces the number of variables that govern the response of the elastic-plastic system from five (5) to three (3). The proposed dimensionless Π-products are liberated from the associated elastic system response and are consistent with the incremental evolution from the rigid-plastic to the elastic-plastic system. When the response is presented in terms of the dimensionless Π-terms remarkable order emerges. It is shown that for a given value of dimensionless yield displacement the response curves (maximum relative dimensionless displacements) become self-similar and follow a single master curve. The self-similar solutions show clearly how the inelastic response amplifies as the normalized yield displacement increases and that an increase in strength may lead to an increase in inelastic displacements. The main advantage of the analysis presented in this paper is that it brings forward the concept of self-similarity—an invariance with respect to changes in scale or size—which is a decisive symmetry that shapes nonlinear behavior.