Optimal non-periodic inspection scheme for a multi-component repairable system using A search algorithm

This paper proposes an approach for finding an optimal non-periodic inspection scheme on a finite time horizon for a multi-component repairable system. The system consists of several components, each of which is subjected to soft failure. Soft failures of each component do not cause the system to stop functioning, but increase the system operating costs and are detected only if inspection is performed. Thus, the system is inspected at the scheduled inspection instances and if any of its components is found to have failed, the failed component is minimally repaired. The system’s expected total cost associated with a given inspection scheme includes inspection costs, repair costs, and the penalty costs that are incurred due to the time delay between the actual occurrence of a soft failure of the components and its detection at an inspection. The objective is to determine the optimal inspection scheme which minimizes system’s expected total cost.     

Sliding mode control of a shear-mode type ER engine mount

This paper presents feedback control characteristics of a shear-mode type electro-rheological (ER) engine mount. The field-dependent yield stress of an arabic gum-based ER fluid is obtained using a couette type electroviscometer, and it is incorporated into the governing equation of motion of the ER engine mount, which is derived from a bond graph model. A sliding mode controller which directly represents the field-dependent damping force is formulated by taking into account the stiffness and damping properties of the systems as parameter uncertainties. The controller is then experimentally realized by imposing a semi-active actuating condition. The effectiveness of the proposed ER engine mount is demonstrated showing capabilities of isolating the vibrations due to sinusoidal and random excitations.     

TRACKING DOMAINS FOR UNSTABLE PLANTS WITH SATURATING-LIKE ACTUATORS

In many mechanical systems, the tracking control is one of the most important issues. Therefore for the unstable system subject to actuator saturation, the domain of the initial states corresponding to an arbitrary reference signal, within which tracking condition can be achieved, is interesting to be considered. In this paper, an approximate tracking domain is derived analytically. First in Theorem 1, for simple case, it is constructed by using the partial Lyapunov function and the absolute stability theory. In the following Theorems 2 and 3, a new idea is used to obtain larger domains. Finally in the last section, a simple numerical example is given.     

Behavior of Pultruded Fiber-Reinforced Polymer Beams Subjected to Concentrated Loads in the Plane of the Web

Results of the behavior of pultruded fiber-reinforced polymer (FRP) I-shaped beams subjected to concentrated loads in the plane of the web are presented. Twenty beams with nominal depths from 152.4 to 304.8?mm were tested in three-point bending with a span-to-depth ratio of four. Load was applied to the top flange directly above the web—12 without bearing plates and 8 with bearing plates of varying width and thickness. All test specimens failed with a wedgelike shear failure at the upper web-flange junction. Finite-element results support experimental findings from strain gauge and digital image correlation data. Bearing plates increased beam capacity by 35% or more as a function of bearing plate width and thickness. Bearing plates increased average shear stress in the web at failure from 17.4 to 27.2?MPa—below the accepted value of in-plane shear strength (69?MPa). A design equation is presented, and predicted capacities are compared with experimental results. The average value of experimental capacity to predicted capacity is 1.12 with a standard deviation of 0.11 and coefficient of variation (COV) of 0.10 for sections up to 304.8?mm deep.     

1923 Gleno Dam Break: Case Study and Numerical Modeling

On the morning of December 1, 1923, the Gleno Dam (located in the Central Italian Alps) suddenly collapsed a few days after the first complete reservoir filling. Nearly 4.5×106??m3 of water was released. The consequent inundation caused significant destruction along the downstream valley and a death toll of at least 356 lives. This failure is the only historical case of dam break caused by structural deficiencies that has occurred in Italy. As a result, it has deeply influenced the evolution of Italian regulations regarding dam design and hydraulic risk evaluation. However, in spite of its relevance, this event has never been characterized from a hydraulic standpoint. This paper reports the main information obtained from the analysis of a vast amount of historical documents regarding the Gleno Dam break to set up a case study useful for validating dam-break models in mountain settings. Moreover, it presents the main results of one-dimensional (1D) modeling of the dam break wave propagation accomplished with a first-order finite volume numerical scheme recently proposed in the literature for field applications. The overall effectiveness and reliability of the model are evaluated for this case characterized by very irregular topography. Finally, the practical relevance of several choices that the numerical reconstruction of this kind of event demands is tested.     

浅谈机械产品可靠性试验技术的研究方向

可靠性是机械设备质量的核心与重要表征之一,为了对机械设备可靠性进行表达与评价,就需要进行试验。文章就机械可靠性试验及发展问题,进行了较为细致的探讨。     

Implication of unequal rivet load distribution in the failures and damage tolerant design of metal and composite civil aircraft riveted lap joints

Riveted lap joints are being used widely in civil aircraft structures. Conventional design procedures assume that the joint can be designed as if all rivets carry load equally. As found in literature associated with fatigue and fracture, forensic studies on structural failures, this assumption is not entirely valid. In this paper, the regulatory codes for civil aircraft as applicable to riveted joints in the form of FAR 25 regulations are briefly reviewed. The regulatory code discusses safety factors in an implied way, but has little specific recommendations for riveted joints. However, studies on the failures of specific aircraft illustrated in this paper add to the argument that both static strength and life are affected by the initial design procedures for the riveted joints. In this paper, finite element models for metal–metal, composite–metal, composite–composite lap joints are studied. A three row lap joint used in commercial aircraft and which was part of failure studies is also examined. Unequal rivet loads and in cases, nearly 50% more than conventional design has been seen in linear finite element analysis. Elasto-plastic analysis using rivet flexibility shows re-distribution of loads. Based on these observations, the effect of rivet loads on life estimation including the use of concepts such as by-pass stresses is discussed. These results have implications for static strength at ultimate load, damage tolerance and fail safety and are discussed in this paper. Next, in a composite–composite lap joint, the influence of ply-angle on the rivet loads is studied. Also, a composite–metal lap joint is studied for the rivet load distribution and life estimation. It is found that the load shared by the rivet rows in a composite–metal lap joint are not symmetric and therefore are more susceptible to cracking and subsequent failure as the unequal distribution can cause some of the rivet loads to be high. In conclusion, the issue of fail safe and damage tolerant design of civil aircraft structures with riveted joints are addressed, especially the implication of unequal load distribution on the failures of such joints and it is suggested that these unequal rivet load distributions be catered for at the early design stage itself via finite element analysis and the possibility of an over-arching safety factor could be considered that incorporates both ultimate load and damage tolerance conditions.     

Numerical investigation on stress concentration of corrosion pit

Localized (pitting) corrosion has been observed in steel and high-strength aluminium alloys in aqueous environments and has been identified as a potential origin for fatigue crack nucleation. In the present study, under uniaxial tension loading, stress distribution at the semi-elliptical corrosion pits has been investigated by conducting a series of three-dimensional semi-elliptical pitted models, systematically. Based on the finite element analyses, it is concluded that pit aspect ratio (a/2c) is a main parameter affecting stress concentration factor (SCF). An attempt has been made to construct simple equations to SCF depending on characteristic of pit parameters. At the bottom of hemispherical pit, contribution of secondary (premature) pit formation to SCF is very pronounced.     

数控系统故障间隔时间分布模型的研究

根据某型号数控系统 1年的故障数据,应用最小二乘法首次对其故障间隔时间分布模型进行了参数估计,并采用d检验法进行了假设检验,证明该数控系统故障间隔时间服从威布尔分布,并对此进行了简要的分析,为数控系统的可靠性改进设计提供了依据.     

What lessons have been learned in reforming the Renewables Obligation? An analysis of internal and external failures in UK renewable energy policy

Despite operating a delivery programme for RES-E since 1990, UK targets and policy goals have not been achieved. In response, the Government reformed the RO. This article re-examines UK renewable energy policy by analysing the internal and external failures of the various mechanisms to determine if Government has learnt from previous experience in reforming the RO. Government did not learn from their own actions during the NFFO/RO transition, evidenced by high-levels of similarity in internal/external failures. The reformed-RO is expected to significantly increase deployment, has provided a ‘renewables package’ by comprehensively addressing both internal/external failures but major internal failures (price/financial risk) still remain, resulting in contiguous failures over two decades and two mechanism changes (NFFO, RO, RO/reformed-RO). Success will again be heavily dependent on a select few technologies and new/untested measures to combat external failures. Mechanism-extension to 2037 is probably the single most important factor underlying potential deployment increases. However, introducing a FIT-like system via the sheer number of ‘bolt-on’ reforms to counter policy failures indicates loss of direction and clarity. Overall, although Government appears to have learnt some of its lessons from the past two-decades, significant doubt remains whether renewable energy policy objectives will be met via the latest mechanism change.