Theory of Economic Life Prediction and Reliability Assessment of Aircraft Structures

The theory of economic life prediction and reliability assessment of aircraft structures has a significant effect on safety of air-craft structures.It is based on the two-stage theory of fatigue process and can guarantee the safety and reliability of structures.According to the fatigue damage process,the fatigue scatter factors of crack initiation stage and crack propagation stage are given respectively.At the same time,mathematical models of fatigue life prediction are presented by utilizing the fatigue scatter factors and full scale test results of aircraft structures.Furthermore,the economic life model is put forward.The model is of sig-nificant scientific value for products to provide longer economic life,higher reliability and lower cost.The theory of economic life prediction and reliability assessment of aircraft structures has been successfully applied to determining and extending the structural life for thousands of airplanes.

Economic Life Assessment of Power Transformers Using an Improved Model

The electric power enterprise devotes considerable attention to the reliability of power transformers particularly when it decides to either maintain these transformers or decommission them altogether from operation.Although this process has reduced the risk of transformer faults,the attendant dilemma is of excessive maintenance of transformers,or retiring them prematurely,leading to high economic waste.This paper is inspired by real-time engineering applications,and proposes an improved model to assess the economic life of power transformers.The new model offers a more efficient approach than previous methods of assessment,with a specific focus of using the annual net income as separate criteria for determining the economic indices of continuous operation,overhaul,and retirement strategies of transformers.The economic life of power transformers is divided into three sections according to different strategies to better resolve the quantification problem in this field.A case study is provided to prove the feasibility and validity of the proposed economic life model.The case study achieves the fine management goal when the electric power enterprise is required to make the maintenance and retirement strategy decision.

A Valid Method for the Forecasting Economic Life Circle of Equipment

In this paper, the degrading regularities for quipment reliability and performance are discussed. Based on the isodegrading model, the characteristics of the cost and benefit in the equipment life circle are studied. Using the principle of getting maximum Net Annual Value(NAV), a valid method for forecasting economic life circle is proposed.

Research on Innovation of Floating Production Storage and Offloading Unit’s Rent Mode under Low Oil Price

After many years of exploitation,onshore oil and gas resources are about to enter a recession period.Oil and gas will mainly come from oceans in the future.Generally speaking,the exploration and production(E&P)cost of oil from offshore is much higher than that of oil from onshore,so it is more sensitive to oil price.However,in recent years,oil price has been hovering at a low level for a long time,almost close to or even lower than the E&P cost of oil,which directly affects the development of oilfields.Besides the influence of oil price,some oilfields present the characteristics of marginal reserve scale,short peak production period and output rapidly declining.There leads to short economic life period and makes the economic benefit close to or lower than oilfield’s hurdle rate,which increases the difficulty of offshore oilfield development.As an important part of oilfield development,Floating Production Storage and Offloading unit,its investment mode and rent mode directly affect overall oilfield’s rate of return and the economic life.This paper chooses lease mode as the research object based on the analysis of investment mode,and further puts forward rent mode related with oil price through the analysis of traditional rent mode,and illustrates the advantages and disadvantages of various rent modes and their applicability so that the lessor chooses the right mode to achieve Win-Win with Oil Company and promotes the development of oilfields under low oil price.

The Optimum Replacement of Weapon

The theory of LCC (Life Cycle Cost) is applied in this paper. The relation between the economic life of weapon and the optimum replacement is analyzed. The method to define the optimum replacement time of weapon is discussed.

Several issues to be considered for long-term better behavior of concrete gravity dams

Along with economic,social quick development and urbanization,dams and reservoirs are of strategic importance for flood control,water supply,electricity production,irrigation,etc.,both for developed countries and for developing countries.Climate change is a new challenging issue to be considered which will speed up the development of hydropower in developing countries.More and more attention will be paid on the long-term better behavior of dams to guarantee the safety of the people involved and the better development of the world.There are about 50000 old dams in the world and a lot of them have been completed and operated for more than 50 years.However,how do we evaluate the dams’safety?How do we make the decision to do rehabilitation work or to rebuild a new dam based on evaluation results?The life span and the real safety status of old dams becomes a challenging task for the dam society,especially for China because it has more than 6000 dams to be evaluated and rehabilitated within the next few years.Based on the investigation of the Fengman gravity dam,which is 91.7 m high,operated since 1943 and suffered uplift pressure,freeze and thaw problems,etc.,discussions on the life span evaluation of old concrete gravity dams have been made.The reasonable coefficient of dam safety has been discussed.The social decision for the final choice after comprehensive studies has been introduced.