Y系列电动机过载范围浅析

通过对Y系列电动机一定范围内过载型式试验，结合理论分析，得出Y系列电动机超载运行将影响使用寿命的结论。     

Capacity Evaluation of a Severely Distressed and Deteriorated 50-Year-Old Box Beam with Limited Data

In 2005, 15 adjacent box-beam bridges were randomly selected and inspected to document their performance with consideration of the evolving design procedures. Longitudinal cracking along the soffit of several fascia beams was documented. After evaluating inspection data, the bridge engineer recommended the replacement of a severely distressed fascia beam from the Hawkins Road Bridge in Jackson County, Michigan. The beam was salvaged and the capacity was evaluated through load testing. The remaining prestress was 75% of the initial prestress, which is 5% less than the final prestress used for the design. Concrete modulus of elasticity was evaluated as 35.4?GPa and the nominal compressive strength as 54.4?MPa. Analysis of load test data indicated that a bridge with the beam in this distressed state is safe to operate. This is assuming that the transverse connectivity between the beams is sufficient for load distribution as envisioned in the design. The importance of identifying concealed corrosion, and quantifying material properties and load distribution is highlighted in this paper.     

Single machine scheduling with precedence constraints and positionally dependent processing times

In many real-life situations the processing conditions in scheduling models cannot be viewed as given constants since they vary over time thereby affecting actual durations of jobs. We consider single machine scheduling problems of minimizing the makespan in which the processing time of a job depends on its position (with either cumulative deterioration or exponential learning). It is often found in practice that some products are manufactured in a certain order implied, for example, by technological, marketing or assembly requirements. This can be modeled by imposing precedence constraints on the set of jobs. We consider scheduling models with positional deterioration or learning under precedence constraints that are built up iteratively from the prime partially ordered sets of a bounded width (this class of precedence constraints includes, in particular, series-parallel precedence constraints). We show that objective functions of the considered problems satisfy the job module property and possess the recursion property. As a result, the problems under consideration are solvable in polynomial time.     

EOQ inventory model for items with Weibull distribution deterioration,time-varying demand and partial backlogging

The paper presents an EOQ inventory model that is depleted not only by time-varying demand but also by Weibull distribution deterioration, in which shortages are allowed and partially backordered. The backlogging rate is variable and dependent on the waiting time for the next replenishment. Further, the optimal procedure was independent of the form of the demand rate. It is then illustrated with the help of four numerical examples. The sensitivity analysis is also studied.     

Multi-item integrated supply chain model for deteriorating items with stock dependent demand under fuzzy random and bifuzzy environments

In this paper, we have investigated multi-item integrated production-inventory models of supplier and retailer with a constant rate of deterioration under stock dependent demand. Here we have considered supplier’s production cost as nonlinear function depending on production rate, retailers procurement cost exponentially depends on the credit period and suppliers transportation cost as a non-linear function of the amount of quantity purchased by the retailer. The models are optimized to get the value of the credit periods and total time of the supply chain cycle under the space and budget constraints. The models are also formulated under fuzzy random and bifuzzy environments. The ordering cost, procurement cost, selling price of retailer’s and holding costs, production cost, transportation cost, setup cost of the supplier’s and the total storage area and budget are taken in imprecise environments. To show the validity of the proposed models, few sensitivity analyses are also presented under the different rate of deterioration. The models are also discussed in non deteriorating items as a special case of the deteriorating items. The deterministic optimization models are formulated for minimizing the entire monetary value of the supply chain and solved using genetic algorithm (GA). A case study has been performed to illustrate those models numerically.     

Service Life Assessment of Existing Highway Bridges with No Planned Regular Inspections

Safety of a highway infrastructure system depends very much on the proper maintenance of bridges. The level of required maintenance is, typically, determined through a series of regular field inspections with the guidance of safety–economy trade-off. In Turkey, bridge maintenance, repair, and rehabilitation are currently performed on an as-needed basis. Time-dependent reliability analysis cannot be utilized for Turkish bridges for the time being since the majority of the bridges are either not regularly inspected or not inspected at all. The purpose of this paper is to propose a simple method to assess the remaining service life of a bridge by defining a relationship between its current condition rating and its age by evaluating a set of bridges at different ages. In a case study, 28 bridges were inspected for the first time to assess the average life expectancy. The average life of a bridge was predicted to be 80?years, and for this set of bridges, the main body components were found to deteriorate more than earth retaining and serviceability components.     

Effect of Carbonation on Concrete Bridge Service Life

An increase in the number of distressed bridges and the limited financial resources emphasize the need for an efficient bridge management system (BMS) for India. Assessment of the remaining life of bridges becomes an essential step in BMS, which involves modeling of complex deterioration mechanisms in concrete due to chemical attacks, such as carbonation, chloride, sulfate, and so on. Lack of information on material properties used in bridge construction, construction techniques, exposure condition, and maintenance quality adopted make the remaining life assessment of bridges more complicated. Therefore, a parametric study has been carried out to understand the deterioration of concrete bridges due to carbonation. Effect of carbonation on the initiation and propagation time of corrosion was also included in the study. Based on the study, modifications are suggested in the clauses of Indian concrete bridge design standard IRC: 21 (2000) so as to enhance the service life of bridges.     

Adaptive Parametric Identification Scheme for a Class of Nondeteriorating and Deteriorating Nonlinear Hysteretic Behavior

The adaptive parametric identification of deteriorating and nondeteriorating nonlinear hysteretic phenomena is considered using a generalization of Masing model based on the observed memory behavior of distributed element models. The model permits a parametric identification to be performed using nonlinear optimization techniques for arbitrary response time histories. A changing objective function, defined as the normalized force estimation error over a shifting window of recent data, is employed so that classic nonlinear optimization techniques can be used for the adaptive identification problem. A variation of the steepest descent method is used with significant modifications. To achieve the best performance for any given problem, a set of a priori numeric tests are suggested to design the identification scheme. The design identification scheme exhibits a very good performance in identifying the correct values of the parameters and is rather robust in dealing with noise. The proposed approach has applications to adaptive identification of much wider types of nonlinear rate-dependent hysteretic behavior. Also, the set of guidelines proposed by the authors is a contribution toward having more effective autonomous identification schemes, using minimal information about the model and input.     

Joint production,inspection and maintenance control policies for deteriorating system under quality constraint

This paper studies the integration of production, sampling inspection and age-based maintenance planning for an unreliable production system subject to gradual deterioration. The deterioration process of the production unit has a twofold effect on its reliability and product quality. To mitigate the effects of such deterioration, an age-based major maintenance can be conducted, which denotes a perfect repair that restores the production unit to initial conditions. The quality control is performed through a sampling plan that inspects a fraction of the parts produced. The problem further considers that the optimal decision must be determined under a constraint on the outgoing quality required by the final customer. In this domain, standard sampling procedures are applicable only to production process that are statistically stable and under control. Nevertheless, such sampling plans disregard the interaction with production management and maintenance issues and they do not consider the effects of deterioration. In this paper a new joint control policy considering the interactions between production-quality and maintenance is proposed. A stochastic mathematical model is developed through specialized optimization techniques to solve such quality constrained problem. Numerical examples are provided to illustrate the usefulness of the proposed approach and to study the interactions between production-quality and maintenance strategies. An extensive sensitivity analysis and a comparative study are conducted to illustrate the effectiveness of the obtained joint control policy.     

The Durability of Alkali-Activated Materials in Comparison with Ordinary Portland Cements and Concretes: A Review

China is the largest producer and user of ordinary Portland cement (OPC), and the rapid growth of infrastructure development demands more sustainable building materials for concrete structures. Alkali-activated materials (AAMs) are a new type of energy-saving and environmentally friendly building material with a wide range of potential applications. This paper compares the durability of AAMs and OPC-based materials under sulfate attack, acid corrosion, carbonation, and chloride penetration. Different AAMs have shown distinct durability properties due to different compositions being formed when different raw materials are used. According to the calcium (Ca) concentration of the raw materials, this paper interprets the deterioration mechanisms of three categories of AAMs: calcium-free, low-calcium, and calcium-rich. Conflicts found in the most recent research are highlighted, as they raise concerns regarding the consistence and long-term properties of AAMs. Nevertheless, AAMs show better durability performances than OPC-based materials in general.