• International Journal of Control, Automation, and Systems
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• v.5 no.2
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• pp.117-127
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• 2007

Many real world control systems usually track several control objectives, simultaneously. At the moment, it is desirable to meet all specified goals using the controllers with simple structures like as proportional-integral (PI) and proportional-integral-derivative (PID) which are very useful in industry applications. Since in practice, these controllers are commonly tuned based on classical or trial-and-error approaches, they are incapable of obtaining good dynamical performance to capture all design objectives and specifications. This paper addresses a new method to bridge the gap between the power of optimal multiobjective control and PI/PID industrial controls. First the PI/PID control problem is reduced to a static output feedback control synthesis through the mixed $H_2/H_{\infty}$ control technique, and then the control parameters are easily carried out using an iterative linear matrix inequalities (ILMI) algorithm. Numerical examples on load-frequency control (LFC) and power system stabilizer (PSS) designs are given to illustrate the proposed methodology. The results are compared with genetic algorithm (GA) based multiobjective control and LMI based full order mixed $H_2/H_{\infty}$ control designs.

• Asian-Australasian Journal of Animal Sciences
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• v.10 no.6
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• pp.621-628
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• 1997

This study aimed to quantify the impact of crossbreeding at farm level, in mixed farm systems in Gujarat. Households with crossbred cattle did not differ from households without crossbreds in terms of farm resources, crop gross margins and off-farm income. The use of crossbred animals did increase livestock gross margins by 64% and household income by 22%. The three agro-ecological zones included in this study differed considerably according to farm system and household income. However, in all three zones, households with crossbreds had higher livestock gross margins than households without crossbreds. There was no real difference in work load and labour division between households with and without crossbreds. There was also no difference in the use of bullocks for draught purposes between the two types of households. In particular buffaloes are being replaced by crossbred cattle. There was a large variation in farm income, largely because of land area. The milk offake per average cow and the number of buffaloes also related positively to farm income in both types of households. Crossbreeding has proved technically and financially viable in different Gujarat mixed farming systems. It can be concluded that crossbreeding is an important development option for landless farmers.

• Tribology and Lubricants
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• v.30 no.2
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• pp.116-123
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• 2014

The objective of this study is to model and simulate the nonlinear lubrication performance of the sliding part between the piston and cylinder wall in a hydrostatic swash-plate-type axial piston pump. A numerical algorithm is developed that facilitates simultaneous calculation of the rotating body motion and fluid film pressure to observe the fluid film geometry and power loss. It is assumed that solid asperity contact, so-called mixed lubrication in this study, invariably occurs in the swash-plate-type axial piston pump, which produces a higher lateral moment on the pistons than other types of hydrostatic machines. Two comparative mixed lubrication models, rigid and elastic, are used to determine the reaction force and sliding friction. The rigid model does not allow any elastic deformation in the partial lubrication area. The patch shapes, reactive forces, and virtual local elastic deformation in the partial lubrication area are obtained in the elastic contact model using a simple Hertz contact theory. The calculation results show that a higher reaction force and friction loss are obtained in the rigid model, indicating that solid deformation is a significant factor on the lubrication characteristics of the reciprocating piston part.

• Structural Engineering and Mechanics
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• v.75 no.5
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• pp.559-569
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• 2020

In the present study, the fracture toughness of U-shaped notches made of aluminum alloy Al7075-T6 under combined tension/out-of-plane shear loading conditions (mixed mode I/III) is studied by theoretical and experimental methods. In the experimental part, U-notched test samples are loaded using a previously developed fixture under mixed mode I/III loading and their load-carrying capacity (LCC) is measured. Then, due to the presence of considerable plasticity in the notch vicinity at crack initiation instance, using the Equivalent Material Concept (EMC) and with the help of the point stress (PS) and mean stress (MS) brittle failure criteria, the LCC of the tested samples is predicted theoretically. The EMC equates a ductile material with a virtual brittle material in order to avoid performing elastic-plastic analysis. Because of the very good match between the EMC-PS and EMC-MS combined criteria with the experimental results, the use of the combination of the criteria with EMC is recommended for designing U-notched aluminum plates in engineering structures. Meanwhile, because of nearly the same accuracy of the two criteria and the simplicity of the PS criterion relations, the use of EMC-PS failure model in design of notched Al7075-T6 components is superior to the EMC-MS criterion.

• Journal of Korean Institute of Industrial Engineers
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• v.35 no.1
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• pp.92-100
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• 2009

Today international trade through maritime transportation is significantly increasing. Due to this increase, shipping companies are faced with problems concerning the repositioning of empty containers from import dominant ports. The liner shipping service network has been provided to transport containers which load customers' freights. Container ships are moved on the liner shipping service network by observing the predetermined route and transportation time. This research deals with the empty containers distribution problem considering the container ship route. A mathematical model based on the mixed integer program has been introduced in this study. The objective is to minimize the total relevant costs of empty containers such as handling, leasing, and inventory holding, etc. Due to the complexity of the problem, a genetic algorithm has been suggested to solve large sized problems within a reasonable time. Numerical experiments have been conducted to show the efficiency of the genetic algorithm.

• Journal of Institute of Control, Robotics and Systems
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• v.5 no.3
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• pp.363-369
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• 1999

In this paper, we design the robust $H_{\infty}$ controller for water level control of steam generator using a mixed $H_{\infty}$ optimization with model-matching method. Firstly we choose the desired model which has good disturbance rejection performance. Secondly we design a stabilizing controller to keep the model-matching error small and also provide sufficiently large stability margin against additive perturbations of the nominal plant. Simulation results show that proposed robust $H_{\infty}$ controller at specific power operation has satisfactory performances against the variations of load power, steam flow rate, primary circuit coolant temperature, and feedwater temperature. It can be also observed that the proposed robust $H_{\infty}$ controller exhibits better robust stability than conventional PI controller.

• Journal of Mechanical Science and Technology
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• v.19 no.2
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• pp.567-577
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• 2005

Several methods for improving the interlaminar strength and fracture toughness of composite materials are developed. Through-the-thickness stitching is considered one of the most common ways to prevent delamination. Stitching significantly increases the Mode I fracture toughness and moderately improves the Mode II fracture toughness. An analytical model has been developed for simulating the behavior of stitched double cantilever beam specimen under various loading conditions. For z-directional load and moment about the y-axis the numerical solutions are compared with the exact solutions. The derived formulation shows good accuracy when the relative error of displacement and rotation between numerical and exact solution were calculated. Thus we can use the present model with confidence in analyzing other problems involving stitched beams.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.1
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• pp.87-107
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• 2015

Considering the localization estimation issue in mixed line-of-sight (LOS)/non-LOS(NLOS) environments based on received signal strength (RSS) measurements in wireless sensor networks, a grid-based correlation method based on the relationship between distance and RSS is proposed in this paper. The Maximum-Likelihood (ML) estimator is appended to further improve the localization accuracy. Furthermore, in order to reduce computation load and enhance performance, an improved recursively version with NLOS mitigation is also proposed. The most advantages of the proposed localization algorithm is that, it does not need any prior knowledge of the propagation model parameters and therefore does not need any offline calibration effort to calibrate the model parameters in harsh environments, which makes it more convenient for rapid implementation in practical applications. The simulation and experimental results evidence that the proposed localization algorithm exhibits good localization performance and flexibilities for different devices.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2006.06a
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• pp.37-42
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• 2006

The paper discusses the combined use of softwood and eucalyptus kraft pulps in the production of printing and writing papers. Looking for process and paper quality optimization, refining pilot plant trails were carried to identify the effects of refining type (mixed or separate) and intensities (specific edge load), and also furnish composition (amount of each pulp in mixture) on final paper quality and process costs. The basic effects on pulp fibers were evaluated against paper quality properties, such as physical strengths, bulk, vessel picking, opacity and porosity, as well as the interactions with papermaking process, such as estimates of paper machine runnability, paper breaks and industrial refining control. The results show that the furnish composition and the type of refining has a significant effect on properties related with both final paper quality and total costs. The best alternative for printing and writing papers was identified for mixed refining, under the lowest refining intensity, and with the highest dosage of eucalyptus pulp.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.7
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• pp.1155-1162
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• 2001

Sihs minimum strain energy density criterion(SED) often used in the mixed mode problem has the ambiguity of the choice of minimum values. In this paper, as the method to solve the problem of SED, maximum minimum strain energy density criterion is proposed that the crack propagates in the direction of having the maximum among the minimum values of modified strain energy density factor(MS), i.e., sign($\sigma$(sub)$\theta$).Smin.