Unique Design Parameter Research Articles

Finite-Time Stabilization Procedures for Discrete-Time Nonlinear Systems in Feedback Form

New control procedures for finite-time stabilization of discrete-time nonlinear systems in the strict-feedback form are proposed. The proposed designs enjoy the properties of being dependent on one design parameter and the ability to bring the state vector to the origin in finite time. Moreover, the settling-time functions are estimated in terms of the initial state vector and the unique design parameter that regulates the rate of the finite-time convergence. Finally, a trajectory-tracking control algorithm is presented and approved by numerical simulations. The simulation results have shown the excellent performance of the closed-loop system for different values of the free design parameter.

Seismic retrofit solutions using base isolation for existing RC buildings: economic feasibilty and pay-back time

The existing reinforced concrete buildings typical of the Mediterranean area commonly have poor seismic performance and high vulnerability to the seismic events. As demonstrated by recent post-earthquake reconstruction processes, they commonly exhibited significant damage to structural components and to infills and partitions resulting in very high repair costs. This suggests that effective seismic strengthening interventions should aim at both improving the safety and reducing the expected annual losses. Nowadays, the seismic retrofitting of existing RC buildings by using base isolation is becoming popular because of the high effectiveness as seismic protection strategy. However, the high costs of installation are limiting the widespread in the common design practice. In this context, a unique design parameter capable of combining the increasing seismic safety, the cost of installation and the reduction of the expected losses can be useful to draw simple cost-benefits considerations. This research work proposes a PBEE-based methodology to quantify the Pay-Back Time (PBT) of seismic retrofit solutions for existing RC buildings. The non-linear response of base isolated building is assessed and a comparison with different strengthening solutions is proposed to show the applicability of the PBT as a unique design parameter to select the most effective retrofit solution. A database of 59 RC buildings retrofitted by using base isolation during the L’Aquila reconstruction process, where actual retrofit costs are available, is used for the validation. Finally, these data are used to calibrate a simple formulation of the PBT to be used in the design practice.

Adaptive Failure-Tolerant Control for Spacecraft Attitude Tracking

Abstract An intelligent failure-tolerant approach is proposed for attitude tracking control of a rigid spacecraft. To deal with the integrated troublesome of model uncertainties, external disturbances and subsystem faults and failures, ideas from artificial intelligence are used for integrating and parameterizing the system model. Furthermore, the adaptive control technique is employed to estimate the unique design parameter extracting from the reconstructed model under bounded disturbances. With the help of Lyapunov theory, we show that the proposed method guarantees the failure-tolerance capability of the closed-loop systems. Finally, the feasibility of the proposed method is illustrated through numerical examples.

Local Optoelectronic Characterization of Solvent-Annealed, Lead-Free, Bismuth-Based Perovskite Films.

Traditional organolead-halide perovskite-based devices have shown rapid improvements in their power conversion efficiency in less than a decade, yet challenges remain for improving stability and film uniformity, as well as the elimination of lead to address toxicity issues. We fabricated lead-free methylammonium bismuth iodide (MBI) perovskite films and studied the effect of solvent annealing with dimethylformamide (DMF) on both (1) the crystallinity and structure of the films with X-ray diffraction and scanning electron microscopy and (2) the local optoelectronic properties of the films as measured via (photo)conductive atomic force microscopy. We found that solvent annealing leads to improved crystallinity and increased grain size in the MBI films as compared to the thermally annealed films. Furthermore, solvent-annealed MBI films show significantly increased electrical conductivity in the out-of-plane direction. Photoconductivity in both solvent-annealed and thermally annealed MBI films was increased in the grain interiors versus the grain boundaries. It was observed that DMF-induced solvent annealing impacts charge transport through the film, which can be a unique design parameter for optimizing local optoelectronic properties. By studying how solvent annealing affects the MBI film structure and changes the ways in which charges are transported through the film, we have developed a better understanding of how local optoelectronic properties are affected by DMF annealing.

Scale-up of a Luminescent Solar Concentrator-Based Photomicroreactor via Numbering-up.

The use of solar energy to power chemical reactions is a long-standing dream of the chemical community. Recently, visible-light-mediated photoredox catalysis has been recognized as the ideal catalytic transformation to convert solar energy into chemical bonds. However, scaling photochemical transformations has been extremely challenging due to Bouguer–Lambert–Beer law. Recently, we have pioneered the development of luminescent solar concentrator photomicroreactors (LSC-PMs), which display an excellent energy efficiency. These devices harvest solar energy, convert the broad solar energy spectrum to a narrow-wavelength region, and subsequently waveguide the re-emitted photons to the reaction channels. Herein, we report on the scalability of such LSC-PMs via a numbering-up strategy. Paramount in our work was the use of molds that were fabricated via 3D printing. This allowed us to rapidly produce many different prototypes and to optimize experimentally key design aspects in a time-efficient fashion. Reactors up to 32 parallel channels have been fabricated that display an excellent flow distribution using a bifurcated flow distributor (standard deviations below 10%). This excellent flow distribution was crucial to scale up a model reaction efficiently, displaying yields comparable to those obtained in a single-channel device. We also found that interchannel spacing is an important and unique design parameter for numbered-up LSC-PMs, which influences greatly the photon flux experienced within the reaction channels.

Mathematical Consideration on a Robustness Index for Adjustable Control Factors

Due to increased diversity of user needs and market globalization, use application and environment of the products have diversified. This causes the products are difficult to be designed. In other words, it is difficult for designers to find a unique design parameter value (a unique design solution) which assures the fluctuant products performance to be satisfied the design requirements. In such cases, the designers derive several values (range) of design parameters which can be adjusted by users or manufacturers and enable to satisfy the product performance by the adjustment. Unfortunately, the kind of design problems have not discussed sufficiently in the conventional robust design researches. This paper describes a robustness index which is applicable to such design problems and a mathematical consideration on a calculating method of the index using the Monte Carlo method.

A Factorization Approach to Sensitivity Loop Shaping for Disturbance Rejection in Hard Disk Drives

This paper investigates a factorization approach to sensitivity loop shaping for disturbance rejection in hard disk drives (HDDs). The advantage of the factorization approach is that the system sensitivity function can be expressed explicitly in terms of a unique design parameter. This greatly simplifies the control design process to make the system sensitivity function match a chosen target sensitivity function with guaranteed stability. By decomposing the controller structure, the design parameter is revealed to behave as a plug-in disturbance filter, the design of which is then presented to suppress the dominant disturbances at some specific frequencies. It is also shown that based on the nominal control system the proposed disturbance filter can reduce the sensitivity gains at specific frequencies without worsening the neighbouring sensitivity gains. Simulation together with implementation results demonstrate that the proposed method can effectively suppress the disturbances around the servo bandwidth and accordingly offers a superior tracking accuracy in comparison with other existing filters.

ON THE USE OF DYNAMIC INVERSION FOR THE IMPROVEMENT OF PID CONTROL

In this paper we discuss the use of a noncausal approach for the improvement of PID control, according to a method presented in (Piazzi and Visioli, 2004). In particular we verify that, despite the proposed methodology is based on an estimated first-order plus dead time (FOPDT) model of the process, different identification procedure can be employed for this purpose yielding in any case to a good result. Further, the role of the unique design parameter is analysed.

Effect of channel shape on gas/liquid catalytic reaction performance in structured catalyst/reactor

This paper presents an experimental study on the impact of channel shape to gas–liquid catalytic reactions inside small reaction channels (1–2 mm size). The channel shape is a unique design parameter offered by a structured catalyst/reactor. Comparative reaction testing of square channels vs. circular channels is conducted under various flow conditions in a gas/liquid co-current down flow mode. Hydrogenation of olefins and toluene saturation over the Ni/ γ -alumina monolith catalyst module are used as model reactions. The gas/liquid feed is directly delivered into one, single channel in the monolith catalyst module in order to eliminate any gas/liquid distribution problem. It is found that for the 2-mm channel size, the circular shape gives a catalytic conversion activity two to five times higher than the square-shaped channel. The dramatic activity enhancement is believed resulting from better gas/liquid/catalyst contacting in the circular channel than in the square channel. The degree of activity enhancement due to the channel shape decreases as the channel size is reduced from 2 to 1 mm, because the catalyst utilization is increased with decreasing the channel size. This finding suggests that catalyst utilization in the three-phase reactor can be largely affected by the non-uniformity of flow structure at particle size scale.

A Determination Method of Intermediate Die Surface in Multi-Step Forging by Means of an Optimization Technique

In forging operations, an appropriate die-shape determination is of vital importance. This paper presents a new method for automatic determination of the intermediate die surface in multi-step forging based on an optimization technique. In the first stage of the process, using a unique design parameter which generates the shape lying between the pre-form and the final product, a preliminary die surface, which gives the lowest forging load within the design space, is determined. In the second stage, further detailed optimization by local search is performed around thus obtained solution at the first stage. Constraints for avoiding material defects such as folding and cracking during forging are considered. The validity of this method has been confirmed by applying it to the die design for an axisymmetric backward extrusion problem.

Studies on a new type of silencer for air ducts

The research work deals with a study of a specific type of silencer previously designed and tested by Shenoda. It consists of a rectangular duct, which is treated at its side walls with a gradually variable flow resistance. It was realized by increasing the perforated area along the duct wall combined with an homogeneous sound absorbing material. Based on the assumptions that only plane waves propagate in the duct, ignoring the effect of the mean flow velocity (very low) and applying linear acoustic equations, the sound propagation in such a silencer was studied. Therefore the wave impedance, the sound reflection coefficient at the input of the silencer, and the transmission loss introduced by it were calculated, measured, and compared with a silencer of comparable dimensions which is treated with a constant flow resistance along its length. To optimize the design different configurations were theoretically studied, computed, and compared. An important result: The silencer performance depends on a unique design parameter, namely, the silencer characteristic area. The methods of realizing a variable wall flow resistance were introduced. The effect of using different kinds of sound absorbing materials and changing the graduality of the variable flow resistance were measured.