• Smart Structures and Systems
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• v.5 no.1
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• pp.69-79
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• 2009

A non-clipped semi-active stochastic optimal control strategy for nonlinear structural systems with MR dampers is developed based on the stochastic averaging method and stochastic dynamical programming principle. A nonlinear stochastic control structure is first modeled as a semi-actively controlled, stochastically excited and dissipated Hamiltonian system. The control force of an MR damper is separated into passive and semi-active parts. The passive control force components, coupled in structural mode space, are incorporated in the drift coefficients by directly using the stochastic averaging method. Then the stochastic dynamical programming principle is applied to establish a dynamical programming equation, from which the semi-active optimal control law is determined and implementable by MR dampers without clipping in terms of the Bingham model. Under the condition on the control performance function given in section 3, the expressions of nonlinear and linear non-clipped semi-active optimal control force components are obtained as well as the non-clipped semi-active LQG control force, and thus the value function and semi-active nonlinear optimal control force are actually existent according to the developed strategy. An example of the controlled stochastic hysteretic column is given to illustrate the application and effectiveness of the developed semi-active optimal control strategy.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.17 no.4
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• pp.357-368
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• 1988

An application of thermal response coefficient method for obtaining thermal load on stud-frame walls in a typical house is presented. A set of stud-frame walls is two-dimensional heat conduction transients with composite structure. The ambient temperature on the right-hand face of the stud-frame walls is a typical day-cycle input and the room temperature on the left-hand face is a constant input. The desired output is thermal load at the left-hand face. The time-dependent ambient temperature is approximated by a continuous, piecewise-linear function each having one hour interval. The conduction problem is spatially discretized as 8 computer modelings by finite elements to obtain thermal response coefficients. The discretization and round-off errors can be neglected in the range of adequate number of nodes. A 60-node discretization is recommended as the optimum model among 8 computer modelings. Several sets of response coefficients of the stud-frame walls are generated by which the rate of heat transfer through the walls or some temperature in the walls can be calculated for different input histories.

• Computers and Concrete
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• v.20 no.6
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• pp.627-634
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• 2017

Predicting the compressive strength of concrete is important to assess the load-carrying capacity of a structure. However, the use of blended cements to accrue the technical, economic and environmental benefits has increased the complexity of prediction models. Artificial Neural Networks (ANNs) have been used for predicting the compressive strength of ordinary Portland cement concrete, i.e., concrete produced without the addition of supplementary cementing materials. In this study, models to predict the compressive strength of blended cement concrete prepared with a natural pozzolan were developed using regression models and single- and 2-phase learning ANNs. Back-propagation (BP), Levenberg-Marquardt (LM) and Conjugate Gradient Descent (CGD) methods were used for training the ANNs. A 2-phase learning algorithm is proposed for the first time in this study for predictive modeling of the compressive strength of blended cement concrete. The output of these predictive models indicates that the use of a 2-phase learning algorithm will provide better results than the linear regression model or the traditional single-phase ANN models.

• Ocean Systems Engineering
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• v.10 no.4
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• pp.373-397
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• 2020

Heave compensation is a vital part of various marine and offshore operations. It is used in various applications, including the transfer of cargo between two vessels in the open ocean, installation of topsides of an offshore structure, offshore drilling and for surveillance, reconnaissance and monitoring. These applications typically involve a load suspended from a hydraulically powered winch that is connected to a vessel that is undergoing dynamic motion in the ocean environment. The goal in these applications is to design a winch controller to keep the load at a regulated height by rejecting the net heave motion of the winch arising from ship motions at sea. In this study, we analyze and compare the performance of various control algorithms in stabilizing a suspended load while the vessel is subjected to changing sea conditions. The KCS container ship is chosen as the vessel undergoing dynamic motion in the ocean. The negative of the net heave motion at the winch is provided as a reference signal to track. Various control strategies like Proportional-Derivative (PD) Control, Model Predictive Control (MPC), Linear Quadratic Integral Control (LQI), and Sliding Mode Control (SMC) are implemented and tuned for effective heave compensation. The performance of the controllers is compared with respect to heave compensation, disturbance rejection and noise attenuation.

• The Journal of Asian Finance, Economics and Business
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• v.8 no.1
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• pp.271-283
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• 2021

This article provides empirical evidence on factors of internal audit (IA) characteristics affecting the internal audit effectiveness in steel enterprises in Vietnam. The study uses data from survey obtained from 114 responses representing owners, managers, and internal auditors from 38 steel enterprises in Vietnam for period from 2018 to 2019. Data collected is firstly checked with Cronbach's Alpha, then the EFA test, and the model linear regression is used to test the relationship between internal audit characteristics and internal audit effectiveness. Results reveal that internal audit effectiveness in steel enterprises in Vietnam is influenced by various internal factors, including the size of internal audit, the scope of internal audit, the capacity of internal auditors, the independence of internal auditor, and the operational bases and methods of internal audit. Based on the research results, the paper makes six recommendations: strengthening operational basis of IA; increasing the independence of IA; increasing the size and capacity of IA staff; expanding and not underestimate the scope of IA; and reforming the internal governance structure. These proposed recommendations could be applied, not only for steel companies in Vietnam, but also for other companies in Vietnam or other companies in jurisdictions that have similar conditions.

• The Journal of Asian Finance, Economics and Business
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• v.9 no.10
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• pp.201-214
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• 2022

Transformational leadership styles are seen as key to inspiring employees to embrace change, as well as to build a sense of responsibility and autonomy at work. This study aims to examine the impact of managers' emotional capacity on transformational leadership behavior in enterprises in Vietnam. Using quantitative research methodology, through exploratory factor analysis (EFA) and linear structure model (SEM), with survey data of 632 samples who are managers of different levels in the enterprise. Research results show that the emotional capacity of managers has both a direct and indirect impact on transformational leadership behavior through the intermediary factors of knowledge sharing at work and corporate social responsibility for employees. Based on that, the study proposes a number of recommendations to promote transformational leadership behavior in enterprises. The findings of this study have demonstrated the importance and impact of managers' emotional capabilities across multiple dimensions of transformational leadership behavior. These are both theoretical and practical contributions that provide managers with greater insight into their emotional capabilities and the need for transformational leadership behaviors. At the same time, the results of this study will also be an important foundation for further research.

• Current Optics and Photonics
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• v.6 no.4
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• pp.381-391
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• 2022

Two-photon-polymerization additive-manufacturing systems feature high resolution and precision. However, there are few reports on specific methods and possible problems concerning the use of small lasers to independently build such platforms. In this paper, a femtosecond-laser two-photon-polymerization additive-manufacturing system containing an optical unit, control unit, monitoring unit, and testing unit is built using a miniature femtosecond laser, with a detailed building process and corresponding control software that is developed independently. This system has integrated functions of light-spot detection, interface searching, micro-/nanomanufacturing, and performance testing. In addition, possible problems in the processes of platform establishment, resin preparation, and actual polymerization for two-photon-polymerization additive manufacturing are explained specifically, and the causes of these problems analyzed. Moreover, the impacts of different power levels and scanning speeds on the degree of polymerization are compared, and the influence of the magnification of the object lens on the linewidth is analyzed in detail. A qualitative analysis model is established, and the concepts of the threshold broadening and focus narrowing effects are proposed, with their influences and cooperative relation discussed. Besides, a linear structure with micrometer accuracy is manufactured at the millimeter scale.

• The Journal of Asian Finance, Economics and Business
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• v.9 no.9
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• pp.49-59
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• 2022

Based on assessing the impact of factors on the business efficiency of construction enterprises, the research team proposes policy implications to improve the business performance of listed construction enterprises in Vietnam in the coming time. The study used secondary data collected from the audited financial statements of 25 enterprises listed on Vietnam's stock market in the period 2015-2021 to estimate the factors affecting the business performance of construction enterprises. After collecting, the data will be encrypted and checked. The article uses a quantitative research method by using a linear regression model on Eviews 10 to analyze the data and analyze the impact of factors on the business performance of construction enterprises listed on Vietnam's stock market. The research result shows that firm size and growth rate positively affect business performance while capital structure, receivable management, fixed asset investment, and economic growth have a positive impact on the business performance of construction companies listed on the Vietnamese stock market. Based on this result, the paper also makes recommendations to the Vietnamese construction companies to enhance their business performance.

• Structural Engineering and Mechanics
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• v.85 no.6
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• pp.765-780
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• 2023

In this work, a novel combined logarithmic, secant and tangential 2D and quasi-3D refined higher order shear deformation theory is proposed to examine the buckling analysis of simply supported uniform functionally graded plates under uniaxial and biaxial loading. The proposed formulations contain a reduced number of variables compared to others similar solutions. The combined function employed in this study ensures automatically the zero-transverse shear stresses at the free surfaces of the structure. Various models of the material distributions are considered (linear, quadratic, cubic inverse quadratic and power-law). The differentials stability equations are derived via virtual work principle with including the stretching effect. The Navier's approach is applied to solve the governing equations which satisfying the boundary conditions. Several comparative and parametric studies are performed to illustrates the validity and efficacity of the proposed model and the various factors influencing the critical buckling load of thick FG plate.

• Advances in concrete construction
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• v.15 no.4
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• pp.215-228
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• 2023

The vibrational behavior of nanoelements is critical in determining how a nanostructure behaves. However, combining vibrational analysis with stability analysis allows for a more comprehensive knowledge of a structure's behavior. As a result, the goal of this research is to characterize the behavior of nonlocal nanocyndrical beams with uniform and nonuniform cross sections. The nonuniformity of the beams is determined by three distinct section functions, namely linear, convex, and exponential functions, with the length and mass of the beams being identical. For completely clamped, fully pinned, and cantilever boundary conditions, Eringen's nonlocal theory is combined with the Timoshenko beam model. The extended differential quadrature technique was used to solve the governing equations in this research. In contrast to the other boundary conditions, the findings of this research reveal that the nonlocal impact has the opposite effect on the frequency of the uniform cantilever nanobeam. Furthermore, since the mass of the materials employed in these nanobeams is designed to remain the same, the findings may be utilized to help improve the frequency and buckling stress of a resonator without requiring additional material, which is a cost-effective benefit.