Narrow Results

Tuned inerter damper (TID) has been introduced and investigated to improve the damping performance of the mid-story isolation system in this study. TID in this novel system is arranged into the mid-story isolation system to utilize its weak transition layer enhancing damping effects. To achieve the best results, the closed-form optimization solutions of TID based on vibration mode are proposed to present optimal design. As such, case studies have been conducted with the different arrangements of the isolation layer with TID and the damping effects of mid-story isolation system have been significantly improved. The presented random analysis results also show the superiority of the proposed novel system when compared with the traditional mid-story system in terms of multiple control indexes, e.g. the top displacement of the substructure, the relative displacement of the isolation layer and the top absolute acceleration of the superstructure. Mostly, the seismic peak responses of mid-story isolation system are significantly suppressed with the proposed optimal design parameters of TID, especially for the relative displacement of isolation layer.

Wind Turbine Towers (WTTs) are slender infrastructures for renewable energies, which are subjected to significant vibrations induced by wind and seismic hazards during their lifetime. In order to suppress these harmful vibrations, an Inerter-based Outrigger-Cable-Lever-Damping (IOCLD) system is proposed. It is composed of an outrigger, a lever, and a pair of cables and inerter-dashpot dampers. The outrigger is to convert bending rotation into vertical vibrations, which is transferred to the lever by the cables. The lever amplifies the inertial-damping force provided by the dampers. The inerter is beneficial to enhance energy dissipation. With these mechanisms, the vibration of WTTs can be effectively suppressed. In order to achieve optimal control performances, the tuning parameters of the IOCLD are analytically derived. Additionally, an equivalent inertance ratio is proposed to obtain the optimal parameters and evaluate the control performance. Finally, through practical numerical cases for wind- and seismic-induced vibration control, the effectiveness of the IOCLD is proved. Compared with existed Amplifying Damping Transfer System (ADTS) without inerters, IOCLD exhibits an excellent energy dissipation rate, which exceeds twice of ADTS for the investigated cases. Compared with conventional Tuned Mass Damper (TMD), IOCLD shows its advantages for lightweight, stability and in-situ adjustable feasibility.

Little, lightweight, low-power microelectromechanical system (MEMS) pressure switches offer a good development prospect for small, ultra-long, simple atmosphere environments. In order to realize MEMS pressure switch, it is necessary to solve one of the key technologies such as thermal robust optimization. The finite element simulation software is used to analyze the thermal behavior of the pressure switch and the deformation law of the pressure switch film under different temperature. The thermal stress releasing schemes are studied by changing the structure of fixed form and changing the thickness of the substrate, respectively. Finally, the design of the glass substrate thickness of 2.5 mm is used to ensure that the maximum equivalent stress is reduced to a quarter of the original value, only 154 MPa when the structure is in extreme temperature (80${}^{\circ }$C). The test results show that after the pressure switch is thermally optimized, the upper and lower electrodes can be reliably contacted to accommodate different operating temperature environments.

In this paper we proposed an approach for obtaining optimal stable modulator coefficients, which satisfy both SNR and stable input limit requirements. The empirical (3rd to 5th order) stable input limit formula is presented. Modulator examples are presented to demonstrate the usage of proposed method. The simulation results show that nearly 1-bit (6 dB) resolution is improved with the proposed method. The op-amp dc-offset influence on modulator performance is also discussed.

We study a generalized Gummel iteration for the solution of an abstract optimal semiconductor design problem, which covers a wide range of semiconductor models. The algorithm is to exploit the special structure of the KKT system and it can be interpreted as a descent algorithm for an appropriately defined cost functional. This allows for a convergence proof which does not need the assumption of small biasing voltages. The algorithm is explicitly stated for the (quantum) drift diffusion model, the energy transport model and the microscopic Schrödinger–Poisson model.

This paper is concerned with the following optimal design problem: find the distribution of two phases in a given domain that minimizes an objective function evaluated through the solution of a wave equation. This type of optimization problem is known to be ill-posed in the sense that it generically does not admit a minimizer among classical admissible designs. Its relaxation could be found, in principle, through homogenization theory but, unfortunately, it is not always explicit, in particular for objective functions depending on the solution gradient. To circumvent this difficulty, we make the simplifying assumption that the two phases have a low constrast. Then, a second-order asymptotic expansion with respect to the small amplitude of the phase coefficients yields a simplified optimal design problem which is amenable to relaxation by means of H-measures. We prove a general existence theorem in a larger class of composite materials and propose a numerical algorithm to compute minimizers in this context. As in the case of an elliptic state equation, the optimal composites are shown to be rank-one laminates. However, the proof that relaxation and small-amplitude limit commute is more delicate than in the elliptic case.

We consider a cantilever beam which possesses a possibly non-uniform permanent magnetization, and whose shape is controlled by an applied magnetic field. We model the beam as a plane elastic curve and we suppose that the magnetic field acts upon the beam by means of a distributed couple that pulls the magnetization towards its direction. Given a list of target shapes, we look for a design of the magnetization profile and for a list of controls such that the shapes assumed by the beam when acted upon by the controls are as close as possible to the targets, in an averaged sense. To this effect, we formulate and solve an optimal design and control problem leading to the minimization of a functional which we study by both direct and indirect methods. In particular, we prove that minimizers exist, solve the associated Lagrange-multiplier formulation (besides non-generic cases), and are unique at least for sufficiently low intensities of the controlling magnetic fields. To achieve the latter result, we use two nested fixed-point arguments relying on the Lagrange-multiplier formulation of the problem, a method which also suggests a numerical scheme. Various relevant open question are also discussed.

Accelerated degradation test (ADT) has been extensively applied to reliability assessment. To improve the efficiency–cost ratio of ADT, the optimal design method of ADT has become a research hot topic. An optimal design method based on acceleration factor, in which a Wiener degradation model and a step-stress ADT were considered, was proposed in the paper. In order to establish an accurate accelerated degradation model, acceleration factor constant principle was applied to derive the changing rules of Wiener process parameters with accelerated stress. Besides, the exact expression of acceleration factor was determined for a Wiener degradation model. The asymptotic variance of acceleration factor, which was considered as a measure of the consistency of failure mechanisms, was selected to be the objective function of optimal problem so as to ensure that the failure mechanism of products under accelerated stresses is probably consistent with that under the normal use stresses. A numerical example of designing an optimal ADT plan for a certain type electrical connector was studied, in which the effectiveness and feasibility of the proposed method were validated.

Most reliability models assume that components and systems experience one failure mode. Several systems such as hardware, however, are prone to more than one mode of failure. Past two-failure mode research derives equations to maximize reliability or minimize cost by identifying the optimal number of components. However, many if not all of these equations are derived from models that make the simplifying assumption that components fail in a statistically independent manner. In this paper, models to assess the impact of correlation on two-failure mode system reliability and cost are developed and corresponding expressions for reliability and cost optimal designs derived. Our illustrations demonstrate that, despite correlation, the approach identifies reliability and cost optimal designs.

In this paper we develop a pipeline processing system called NMR pipeline. In an NMR pipeline, processing elements at each stage are replicated to achieve high fault tolerance. Each stage of the pipeline is an N-Modular Redundant (NMR) System. This design combines the benefits of pipeline processing and NMR systems and is suitable for high speed safety-critical computing. Reliability analysis of this system is presented taking into account possible failures of processing and communication elements. The optimality of the system is defined in terms a suitably defined cost function that accounts for the component costs and the costs associated with system unreliability.

A distributed database system often replicates data across its servers to provide a fault-resistant application, which maximizes server availability. Various replication control protocols have been developed to ensure data consistency. In this paper, we develop optimal design methods for the quorum-consensus replication protocol, which (1) maximizes availability of the distributed database systems and (2) minimizes the total system cost by calculating the optimal read quorum and the optimal number of system servers. Several numerical examples and applications are provided to illustrate the results.

Many models and methods have been proposed in the literature to evaluate the reliability of fault-tolerant systems. In this paper, we study systems with one degradation mode. We introduce a static model and present efficient algorithms for the evaluation of the system performance and cost. For the special case of a system consisting of identical units we derive an efficient procedure for the determination of an optimal system design with respect to a minimum system cost.

Let Ω ⊂ ℝ^N be a bounded, smooth domain. We deal with the best constant of the Sobolev trace embedding W^1,p(Ω) ↪ L^q (∂Ω) for functions that vanish in a subset A ⊂ Ω, which we call the hole, i.e. we deal with the minimization problem for functions that verify u|_A = 0. It is known that there exists an optimal hole that minimizes the best constant S_A among subsets of Ω of the prescribed volume.

In this paper, we look for optimal holes and extremals in thin domains. We find a limit problem (when the thickness of the domain goes to zero), that is a standard Neumann eigenvalue problem with weights and prove that when the domain is contracted to a segment, it is better to concentrate the hole on one side of the domain.

An advanced technique for damage detection in beam structures, using a vibration characteristic tuning procedure is developed by an optimal design of piezoelectric materials. Piezoelectric sensors and actuators are mounted on the surface of the host beam to generate excitations for the tuning via a feedback process. The excitations induced by the piezoelectric effect are used to magnify the effect of the damage in the vibration characteristics of the damaged structure to realize an effective damage detection process. To describe the detection process, theoretical models of the cantilevered beams with and without tuning induced by piezoelectric effect are built first, while the damage is represented by a crack at the fixed end. From the established models, the natural frequencies of the tuned beams with and without the crack are obtained to study the sensitivity of the proposed technique. As a result of the tuning process, more obvious changes on the natural frequencies due to the existence of a crack are observed. The results also indicate a shorter distance from the piezoelectric actuators to the crack leads to a higher detection sensitivity. An optimal length of the piezoelectric actuators is also obtained for better detection.

Cables in cable-stayed bridges are subjected to the problem of multi-mode vibrations. Particularly, the first ten modes of long cables can have a frequency less than 3Hz and hence are vulnerable to wind-rain induced vibrations. In practice, mechanical dampers are widely used to mitigate such cable vibrations and thus they have to be designed to provide sufficient damping for all the concerned vibration modes. Meanwhile, the behaviors of practical dampers are complicated and better to be described by mechanical models with many parameters. Furthermore, additional mechanical components such as inerters and negative stiffness devices have been proposed to enhance the damper performance on cables. Therefore, it is increasingly difficult to optimize the damper parameters for suppressing multi-mode cable vibrations. To address this issue, this study proposes a novel damper design method based on the genetic algorithm (GA). The procedure of the method is first introduced where the damper performance optimization is formulated as a single-objective multi-parameter optimization problem. The effectiveness of the method is then verified by considering a viscous damper on a stay cable. Subsequently, the method is applied to optimize three typical dampers for cable vibration control, i.e. the positive stiffness damper, the negative stiffness damper, and the viscous inertial mass damper. The results show that the GA-based method is effective and efficient for cable damper design to achieve best multi-mode control effect and it is particularly useful for dampers with more parameters.

Tuned mass damper (TMD) is a type of energy absorbers that can mitigate the vibrations of the main system if its frequency and damping ratios are well adjusted. By adopting simple assumptions on the structure and loadings, many analytical and empirical relationships have been presented for the estimation of the parameters for TMDs. In this research, methods based on the artificial intelligence (AI) techniques are proposed for optimal tuning of the TMD parameters of the main damped-structure for three kinds of loadings: white-noise base acceleration, external white-noise force, and harmonic base acceleration. For this purpose, a dataset using the cuckoo search (CS) optimization algorithm is created. The performance of the proposed methods based on the radial basis function (RBF) neural network, feed-forward neural network (FFNN), adaptive neuro-fuzzy inference system (ANFIS), and random forest (RF) techniques are evaluated by some statistical indicators. The results show the proper performance of these methods for the optimal estimation of the TMD parameters. Overall, the ANFIS method results in best matching with the observed dataset. Moreover, the simulation results indicate that the TMD’s optimal frequency ratio is reduced, while its optimal damping ratio is increased, against the increase in the TMD mass ratio of the main structure subjected to harmonic base acceleration. This trend with a less slope is observed for the optimal frequency ratio of the TMD in the main structure subjected to external white-noise force; however, the optimal damping ratio of the TMD is independent of its mass ratio in this case. Similar results are obtained for the main structure subjected to white-noise base acceleration.

In the applications of supplemental dampers for seismic hazard mitigation, the supporting braces for the dampers are considered an important component for ensuring an efficient energy dissipation in the structure. Despite their importance, studies on the effects of the brace stiffness and the velocity exponent in the case of nonlinear viscous dampers are rather limited. In this paper, a numerical time-stepping method is developed for computing the seismic response of the structure with supporting braces and nonlinear viscous dampers. Using the proposed method, effects of the parameters of the nonlinear damper-brace systems are investigated, using first a single-story structure, followed by multi-story buildings. Results indicated that the design parameters for the dampers and supporting braces may be combined in numerous ways to satisfy a given set of structural performance objectives, but the brace stiffness can be minimized to achieve design efficiency in the range of velocity exponent commonly used for seismic applications of nonlinear viscous dampers. Results also indicated that for a set brace stiffness, if the dampers are optimally designed, the velocity exponent has an insignificant effect on the structural seismic performance objectives considered in this paper.

Atrium building is a common structural type that can be found in most of the big cities. For seismic vibration control of buildings with large atria, this paper proposes a novel approach of using a core structure inside the atrium building in combination with a truss-inertial mass damper (IMD) system to form a passive control mechanism. The proposed system utilizes the unsynchronized vibrations between the tops of the building and the core structure to activate the IMD for seismic energy dissipation. To evaluate the effectiveness of the proposed truss-IMD system, a numerical time-history method is first developed to compute structural response of the atrium building under an earthquake input, followed by parametric studies of the system. Effects of truss stiffness, inertance, and nonlinearity of the IMD on seismic performance of the atrium building are investigated. Results from a simple structural model and a six-story building indicate that the truss-IMD system can significantly alleviate the dynamic responses of the building, and the overall seismic performance improvement brought by the truss-IMD surpasses a truss-viscous damper system. Results also show that for a given set of truss stiffness and damper nonlinearity, there exists an optimal combination of inertance and damping coefficient for the IMD to achieve a maximum structural performance.

This paper presents the optimal designs of pinned supported funicular arches under equally spaced point loads for maximum in-plane buckling load. Under such loading conditions, the funicular arch shapes comprise straight arch members between the point loads, that is, following the shape of the bending moment diagram of an equivalent simply supported beam under the same loading condition. Two classes of funicular arch optimization problems are considered herein. The first class of funicular arches imposes a constraint on the cross-sectional area to be uniform throughout the entire arch length. The second class of funicular arches allows the cross-sectional area to be different from one straight arch member to another member. To facilitate the buckling analysis, the Hencky bar-chain model (HBM) is adopted. This discrete structural model simplifies the optimization process as the decision variables are the HBM rotational spring stiffnesses that define the cross-sectional areas and the horizontal force that controls the arch shape. Presented herein are new optimal funicular arch shapes under various numbers of equally spaced point loads. By increasing the number of point loads, the optimal solution approaches the solution of a parabolic arch under a uniformly distributed load.

This paper is devoted to the determination of the asymptotical optimal input for the estimation of the drift parameter in a partially observed but controlled fractional Ornstein–Uhlenbeck process. Large sample asymptotical properties of the Maximum Likelihood Estimator are deduced using Ibragimov–Khasminskii program and Laplace transform computations.