Design of variable-stiffness conical shells for maximum fundamental eigenfrequency

Fiber-reinforced composite conical shells with given geometry and material properties are optimized for maximum fundamental frequency. The shells are assumed to be built using an advanced tow-placement machine, which allows in-plane steering of the fibers, resulting in a variable-stiffness structure. In this paper, different path definitions for variable-stiffness shells are provided and used to optimize conical shells for maximum fundamental frequency, while manufacturing constraints that apply for tow placement are taken into account in the process. The influence of manufacturing constraints on the performance is shown; and improvements of variable-stiffness conical shells over conventional, constant-stiffness shells are demonstrated.     

A generalized analysis for cascading single fluid vapor compression refrigeration cycles using an entropy generation minimization method

This paper focuses on cascading an ideal vapor compression cycle and determining the optimal intermediate temperatures based on the entropy generation minimization method. Only superheating and throttle losses of the cycle are considered since they are inherent to the ideal vapor compression refrigeration cycle. The second law equations have been developed in terms of specific heats and temperature ratios with the intent of reducing involved property modeling. Also the entropy generation was expressed in terms of a single independent variable and minimized to develop an advanced rule for selecting optimum intermediate temperatures. Results for a cascade system operating between reduced temperatures of 0.684 and 0.981 with R-134a as the working fluid are presented. The approximate method presented here predicted the optimum intermediate reduced temperature for a two-stage system to be 0.88, a difference of 2% from the optimum. The method presented was a much better predictor of the optimum temperature than the geometric mean method which was 0.82, a difference of 5% from the optimum. The entropy generation distribution of the optimum solution was investigated. For a two-stage system, the lower stage and higher stage entropy generation was 44% and 56%, respectively. In comparison to the single stage, the two-stage reduced losses by 78%.     

基于主成分分析法的炮兵目标威胁度评估

为提高作战指挥员对炮兵目标实施火力分配的量化决策水平，首先运用主成分分析法对炮兵目标威胁度的多项指标进行了聚集，其次在理想点的基础上建立综合优化决策模型，并进行实例分析，所得结果合理且符合客观实际，从而为作战指挥员提供了一种合理的决策依据和决策方法。     

A Monte Carlo methodological approach to plant availability modeling with maintenance, aging and obsolescence

In this paper we present a Monte Carlo approach for the evaluation of plant maintenance strategies and operating procedures under economic constraints. The proposed Monte Carlo simulation model provides a flexible tool which enables one to describe many of the relevant aspects for plant management and operation such as aging, repair, obsolescence, renovation, which are not easily captured by analytical models. The maintenance periods are varied with the age of the components. Aging is described by means of a modified Brown–Proschan model of imperfect (deteriorating) repair which accounts for the increased proneness to failure of a component after it has been repaired. A model of obsolescence is introduced to evaluate the convenience of substituting a failed component with a new, improved one. The economic constraint is formalized in terms of an energy, or cost, function; optimization studies are then performed using the maintenance period as the control parameter.     

Well Loss Estimation: Variable Pumping Replacing Step Drawdown Test

An optimization method is presented for simultaneous estimation of aquifer parameters and well loss parameters utilizing all the drawdowns observed during a variable rate pumping or multiple step pumping test. The proposed method does not require any graphical analysis. It is shown that a variable rate pumping test is a better substitute for the conventional step drawdown test to estimate well loss parameters. It suggests that the pumping rate may be changed frequently without waiting for a near steady state to be reached (or a selected duration, say 60 min) in each step of a conventional step drawdown test. This can result in a substantial saving of time and money involved in conducting a step drawdown test with a view to estimate well loss parameters. This gives a greater number of distinct discharges, which improves the estimates of the well loss parameters. Application of the method is demonstrated on published data sets, the results of which show that the parameters estimated using the new method are more reliable as compared to those obtained using prior methods.     

Computer simulation of gas generation and transport in landfills. III: Development of lanfills’ optimal model

In Parts I and II of this series a 3D model was developed for transport and reaction of gaseous mixtures in landfills, and was utilized, through computer simulations, to investigate the effect of various factors on the gases’ concentrations and the landfill's total pressure, under quasi-steady state and dynamic conditions. A fundamental problem with modelling of landfills is the severe shortage of publicly available experimental data for their static and dynamical properties, which hinders the development of accurate models for them. In the present paper we address this problem by formulating it as one of optimization, whereby the optimal spatial distributions of the porosity, permeability, tortuosity factor, and the total potential of various types of wastes for producing the gases in a landfill are determined, given some limited experimental data for a property of the landfill, such as the amount of methane which is extracted from it over a period of time. The numerical simulator developed previously is coupled to the Genetic algorithm in order to optimize the parameter space that characterizes the landfill's morphology and the reaction properties of the wastes. Since the parameter space can be very large, containing thousands of parameters to be optimized, we utilize massively parallel computations with message-passing interface technique in order to develop the optimal model. It is shown that, not only does the optimization technique reproduce accurately the data based on which the optimal model is developed, but also provides accurate predictions for the future behavior of the landfill's properties.     

Optimization opportunities in mining, metal and mineral processing

This paper examines the opportunities arising from the use of optimization in the fields of mining, metal and mineral (MMM) processing. A brief overview of optimization is given. Our main goal in this paper is to raise awareness to the use of optimization as a key enabling technology in the MMM field.     

Optimization and Analysis of Advective Travel Times beneath Hydraulic Structures

Steady, 2D Darcian seepage in a homogeneous isotropic porous medium under an impervious structure is studied by the methods of complex analysis. The geometry of the structure is studied focusing on the travel time of a marked (neutral tracer) particle from the upper pool to the tailwater. In the Verigin problem, the angle of inclination of a sheetpile resulting in minimal time along the bounding streamline is π/2. If the maximum of the minimum of the travel time is searched between all streamlines originated in the upper pool, then the optimal angles are found to be 0.404π and 0.596π. The minimization of the total volume of fluid that arrives from the upper pool to the tailwater during a prescribed time span is also considered. For arbitrary geometry, structure optimization with respect to travel time is carried out explicitly for the bounding streamline with a constraint on the wetted perimeter of a depressed structure. The minimal-time shape is found to be the Voshinin semicircular structure, which is mathematically generated by a line vortex.     

Assignment and Allocation Optimization of Partially Multiskilled Workforce

Multiskilling is a workforce strategy that has been shown to reduce indirect labor costs, improve productivity, and reduce turnover. A multiskilled workforce is one in which the workers possess a range of skills that allow them to participate in more than one work process. In practice, they may work across craft boundaries. The success of multiskilling greatly relies on the foreman’s ability to assign workers to appropriate tasks and to compose crews effectively. The foreman assigns tasks to workers according to their knowledge, capabilities, and experience on former projects. This research investigated the mechanics of allocating a multiskilled workforce and developed a linear programming model to help optimize the multiskilled workforce assignment and allocation process in a construction project, or between the projects of one company. It is concluded that the model will be most useful in conditions where full employment does not exist; however, it is also useful for short term allocation decisions. By running the model for various simulated scenarios, additional observations were made. For example, it is concluded that, for a capital project, the benefits of multiskilling are marginal beyond approximately a 20% concentration of multiskilled workers in a project workforce. Benefits to workers themselves become marginal after acquiring competency in two or three crafts. These observations have been confirmed by field experience. Extension of this model to allocation of multifunctional resources, such as construction equipment, should also be possible.     

Ship Detection and Characterization with Generalized Optimization of Polarimetric Contrast Enhancement

A Generalized optimization algorithm of polarimetric contrast enhancement （GOPCE） is proposed to find optimal polarimetric states and coefficients to max-imize the received power ratio of ship to ocean clutter, which facilitates ship detection. The method is validated with a real SIR-C/X image. The results indicate that, rather than optimal polarimetric contrast enhancement, GOPCE apparently improves the contrast of ship to sea by introducing the polarimetric feature vector.