Search results

Contemporary stochastic optimal control by synergy of the probability density evolution method (PDEM) and conventional optimal controller exhibits less capability to guarantee economical energy consumption versus control efficacy when non-stationary stochastic excitations drive hysteretic structures. In this regard, a novel multiscale stochastic optimal controller is invented based on the wavelet transform and the PDEM.

For a representative point, a conventional control law is decomposed into sub-control laws by deploying the multiresolution analysis. Then, the sub-control laws are classified into two generic control laws using resonant and non-resonant bands. Both frequency bands are established by employing actual natural frequency(ies) of structure, making computed efforts depend on actual structural properties and time-frequency effect of non-stationary stochastic excitations. Gain matrices in both bands are then acquired by a probabilistic criterion pertaining to system second-order statistics assessment. A multi-degree-of-freedom hysteretic structure driven by non-stationary and non-Gaussian stochastic ground accelerations is numerically studied, in which three distortion scenarios describing uncertainties in structural properties are considered.

Time-frequency-dependent gain matrices sophisticatedly address non-stationary stochastic excitations, providing efficient ways to independently suppress vibrations between resonant and non-resonant bands. Wavelet level, natural frequency(ies), and ratio of control forces in both bands influence the scheme’s outcomes. Presented approach outperforms existing approach in ensuring trade-off under uncertainty and randomness in system and excitations.

Presented control law generates control efforts relying upon resonant and non-resonant bands, and deploys actual structural properties. Cost-function weights and probabilistic criterion are promisingly developed, achieving cost-effectiveness of energy demand versus controlled structural performance.

This paper presents an optimal design method of number and placements of piezoelectric patch actuators in active vibration control of a plate. Eigenvalue distribution of energy correlative matrix of control input force is applied to determine optimal number of the required actuators. Genetic algorithms (GAs) using active vibration control effects, which are taken as the objective function, are adopted to search optimal placements of actuators. The results show that disturbance exerted on a plate is a key factor of determining optimal number and placements of actuators in active structural vibration control, and a global and efficient optimization solution of multiple actuator placements can be obtained using GAs.

In real life, excitations are highly non-stationary in frequency and amplitude, which easily induces resonant vibration to structural responses. Conventional control algorithms in this case cannot guarantee cost-effective control effort and efficient structural response alleviation. To this end, this paper proposes a novel adaptive linear quadratic regulator (LQR) by integrating wavelet transform and genetic algorithm (GA).

In each time interval, multiresolution analysis of real-time structural responses returns filtered time signals dominated by different frequency bands. Minimization of cost function in each frequency band obtains control law and gain matrix that depend on temporal-frequency band, so suppressing resonance-induced filtered response signal can be directly achieved by regulating gain matrix in the temporal-frequency band, leading to emphasizing cost-function weights on control and state. To efficiently subdivide gain matrices in resonant and normal frequency bands, the cost-function weights are optimized by a developed procedure associated to genetic algorithm. Single-degree-of-freedom (SDOF) and multi-degree-of-freedom (MDOF) structures subjected to near- and far-fault ground motions are studied.

Resonant band requires a larger control force than non-resonant band to decay resonance-induced peak responses. The time-varying cost-function weights generate control force more cost-effective than time-invariant ones. The scheme outperforms existing control algorithms and attains the trade-off between response suppression and control force under non-stationary excitations.

Proposed control law allocates control force amounts depending upon resonant or non-resonant band in each time interval. Cost-function weights and wavelet decomposition level are formulated in an elegant manner. Genetic algorithm-based optimization cost-efficiently results in minimizing structural responses.

The main purpose of this paper is to understand the impact on the United Arab Emirates (UAE) economy of the objective of reducing its dependence on oil, trying to achieve the Gulf Cooperation Council (GCC) fiscal convergence criterion and the inevitable depletion of oil resources.

An 18 equation compact macro‐econometric model is constructed and is evaluated and calibrated employing dynamic simulation techniques. Optimal control techniques are used to analyze the economic impact of the three objectives listed above.

Each of the optimal control experiments that has been carried out has served to reinforce the fact that the UAE is still critically dependent on oil. An increase in the share of the non‐oil sector, adhering to the GCC fiscal criterion and any reduction in oil output production will affect government finances adversely.

The macro‐econometric model developed is for the UAE and further research is needed to see if the conclusions can be generalized to the other oil exporting countries.

The estimated macro‐econometric model and the optimal control experiments indicate to the policy makers the need to continue the diversification of the economy and for government to actively explore and enhance non‐hydrocarbon sources of revenue.

This paper develops a compact macro‐econometric model of the UAE and uses optimal control techniques which go well beyond the standard simulation techniques and the routine counter‐factual experiments to understand the working of the economy.

The author developed a theory of optimal trajectories for air vehicles with variable wing area and conventional wings. He applied a new theory of singular optimal solutions and obtained the optimal flight in many cases. At first glance, the results may seem strange however, this is correct and this paper will show how this new theory may be used. The main idea of the research is in using the vehicle's kinetic energy for increasing the range of missiles and projectiles. The author shows that the range of a ballistic warhead can be increased 3‐4 times if an optimal wing is added to the ballistic warhead, especially a wing with variable area. If increased range is not needed, the warhead mass can be increased. The range of big gun shells can also be increased 3‐9 times. The range of aircraft may be improved 3‐15 percent and more. The results can be used for the design of aircraft, missiles, flying bombs and shells of big guns.

With a view to contributing to a better understanding of the interactions between design dimensions, the authors aim to present a formal model that analyzes the internal fit relationship between centralization and formalization, taking into account organizational technology and the “systems approach”.

Based on the study by Zeffane, the authors develop an alternative, formal model that introduces organizational technology and assumes that greater structural control does not necessarily lead to better organizational integration. The model equally considers the possibilities of underfit and overfit.

The proposed formal model provides a sound rationale on how organizational technology determines the contribution of centralization and formalization to the achievement of integration. The complementary interactions between design dimensions result in very clear patterns, with all the complementary choice variables tending to be done together at a comparable level. Also, it evidences that only a finite of feasible set of intermediate choices exists.

In the interests of simplicity, the model does not include other contingency factors, such as environment and strategy, nor does it address the question of non‐concavity of the objective function that allows equifinality. Questions such as whether the consequences of underfit are different from those produced by overfit should be addressed in further research and model developments.

This paper develops a rationale for better understanding the interactions between design dimensions, such as centralization and formalization and helps to fill the research gap related to the absence of analytical models that allow a rigorous analysis of the internal relationships between different organizational design dimensions.

In order to make sure of the safety of a long-span suspension bridge under earthquake action, this paper aims to study the traveling wave effect of the bridge under multi-support excitation and optimize the semi-active control schemes based on magneto-rheological (MR) dampers considering reference index as well as economical efficiency.

The finite element model of the long-span suspension bridge is established in MATLAB and ANSYS software, which includes different input currents and semi-active control conditions. Six apparent wave velocities are used to conduct non-linear time history analysis in order to consider the seismic response influence in primary members under traveling wave effect. The parameters α and β, which are key parameters of classical linear optimal control algorithm, are optimized and analyzed taking into account five different combinations to obtain the optimal control scheme.

When the apparent wave velocity is relatively small, the influence on the structural response is oscillatory. Along with the increase of the apparent wave velocity, the structural response is gradually approaching the response under uniform excitation. Semi-active control strategy based on MR dampers not only restrains the top displacement of main towers and relative displacement between towers and girders, but also affects the control effect of internal forces. For classical linear optimal control algorithm, the values of two parameters (α and β) are 100 and 8 × 10–6 considering the optimal control effect and economical efficiency.

The emphasis of this study is the traveling wave effect of the triple-tower suspension bridge under multi-support excitation. Meanwhile, the optimized parameters of semi-active control schemes using MR dampers have been obtained, providing relevant references in improving the seismic performance of three-tower suspension bridge.

Compiled by K.G.B. Bakewell covering the following journals published by MCB University Press: Facilities Volumes 8‐18; Journal of Property Investment & Finance Volumes 8‐18; Property Management Volumes 8‐18; Structural Survey Volumes 8‐18.