Hybrid neural network models for hydrologic time series forecasting

The need for increased accuracies in time series forecasting has motivated the researchers to develop innovative models. In this paper, a new hybrid time series neural network model is proposed that is capable of exploiting the strengths of traditional time series approaches and artificial neural networks (ANNs). The proposed approach consists of an overall modelling framework, which is a combination of the conventional and ANN techniques. The steps involved in the time series analysis, e.g. de-trending and de-seasonalisation, can be carried out before gradually presenting the modified time series data to the ANN. The proposed hybrid approach for time series forecasting is tested using the monthly streamflow data at Colorado River at Lees Ferry, USA. Specifically, results from four time series models of auto-regressive (AR) type and four ANN models are presented. The results obtained in this study suggest that the approach of combining the strengths of the conventional and ANN techniques provides a robust modelling framework capable of capturing the non-linear nature of the complex time series and thus producing more accurate forecasts. Although the proposed hybrid neural network models are applied in hydrology in this study, they have tremendous scope for application in a wide range of areas for achieving increased accuracies in time series forecasting.     

Frequency comparison of blast-induced vibration per delay for the full-face millisecond delay blasting in underground opening excavation

Responses and damage to the structures subjected to blast-induced vibration are highly dependent on vibration frequency. Understanding the vibration frequency characteristics and its formation mechanism is essential for the safe and economic design of mining and construction blasts. When millisecond delay blasting is used in excavation, a global frequency value of all of the delays of vibrations fails to present a true picture of the vibration frequency characteristics. In the present study, comparisons of frequency characteristics for the blast-induced vibration per delay were first conducted via an underground opening case excavated by the full-face millisecond delay blasting sequence. The results show that if the blasthole geometry and charge structure are kept the same in each blast delay, the frequencies of single-delay vibration signals will decrease as the dimensions of the equivalent blasting vibration sources increase. However, the cutting blast used for the headmost holes inside is an exception, and its vibration frequency is lower than that of the breaking blast outside. It is the authors’ belief that this counter-intuitive phenomenon is caused by the free faces created by the cutting blast for the breaking blast. A small-scale blasting test and the related numerical simulation were subsequently performed to demonstrate this belief. It is found that the vibration frequency from the holes in the free-face blast is higher than that in the confined blast. In terms vibration frequency, therefore, the vibration from the breaking blast is less harmful to structures compared to the cutting blast for a certain velocity, and decreasing the burden of breaking blastholes is beneficial to reduce the vibrational damage of structures.     

Methodologies for the exploration of computer and technology transference

Transference, a term used in a variety of psychotherapeutic approaches especially psychoanalysis, has recently been applied to relationships people have with modern technologies, especially computers. Methods will be outlined which operationalize this notion and illustrative case studies will demonstrate the diversity of response resulting. The implications of these distinctions have yet to be explored, but it is suggested that they may have important consequences for the introduction of new technologies, as well as situations where people's relationships with computers are considered problematic.     

Systems modelling of the electric power objects

In order to carry out the complex researches of the influence of the different factors on the object-system operation efficiency in the electric power system (EPS), the multi-level systems models which represent the connections and relations between the elements of an object modelled are required.As an example of the systems approach to the modelling of the EPS one may consider the experience of developing the set of the model and program modules united into the system which describes the electromagnetic and heat processes in the turbogenerators; the characteristics of the assemblies connected to the electric power station, the static & dynamic operation conditions of the EPS and the distribution of the active & reactive power in the EPS units. The program modules are united by the common data base. The control programs provide for the systems analysis of a problem in question in the dialogue man-machine mode of operation.     

Structural performance of buried prestressed concrete cylinder pipes with harnessed joints interaction using numerical modeling

Broken prestressing wire wraps are the main cause of failure in buried prestressed concrete cylinder pipes (PCCP), which form the backbone of water and wastewater infrastructure networks in North America. Advanced numerical modeling using non-linear finite elements is used to model the effect of the number and location of broken wire wraps on the structural performance of Class 125-14, 96-in. PCCP. The modeling technique used is unique in that it considers full interaction between adjacent pipes with harnessed joints, as well as combined internal and external loading with full soil–pipe interaction. Performance indicators in the various components of PCCP are monitored as internal pressure is increased. A sensitivity analysis is presented for how manipulating the severity of the damage affects the failure pressure of the pipe. The results show that the internal fluid pressure required to cause failure can be as much as 34% lower when the damage is at the barrel of the pipe, and that the internal pressure that causes yielding of the wire wraps decreases by 66% as the damage worsens from 5 to 100 wire breaks.     

水库生态调度研究的若干思考

传统的水库调度方式在保障防洪安全的基础上力求最大限度发挥河流水资源的经济效益,对库区及下游的生态环境考虑较少,在防洪兴利的同时危及了河流健康。改变传统的水库调度方式,将生态目标纳入到水库调度中来,开展以维护或改善河流健康为重要目标的水库生态调度是十分必要和迫切的。从水库修建运用的生态效应出发,在国内外相关研究的基础上系统分析了水库生态调度的概念、内涵及研究热点,并重点讨论基于生态水文模拟的水库生态调度方式及其研究中的一些关键技术问题,以期能够对水库生态调度研究提供参考。     

Interval risk analysis for gravity dam instability

Fuzziness and randomness are two inseparable uncertainty attributes of most factors influencing stability of gravity dam. Moreover, there is a fuzzy transition from stability status into failure status. Risk analysis and fuzzy mathematics are conducted to evaluate the stability problems of gravity dams, where the process of stability failure is studied as a fuzzy event. Membership functions are used to describe the extent of stability failure risk for gravity dams. The fuzziness of both the design parameters and failure criterion are accordingly eliminated through a transformation by use of the concept of the Level Set. Corresponding analysis procedures are then provided to calculate the fuzzy risk and its probability of the stability failure for gravity dams. Based on a real dam section, a detailed example is further provided to illustrate the proposed risk analysis approach. The results show that it is feasible to apply the present method to analyze the fuzzy risk of stability failure for gravity dams. The modeling approach is sound and the findings do improve the current understanding of this important problem. The conventional risk is a determinate value but the proposed fuzzy risk is an interval value. The obtained conclusions can reflect more reasonably the actual dam engineering.     

Tunnel design considering stress release effect

In tunnel design,the determination of installation time and the stiffness of supporting structures is very important to the tunnel stability.This study used the convergence-confinement method to determine the stress and displacement of the tunnel while considering the counter-pressure curve of the ground base,the stress release effect,and the interaction between the tunnel lining and the rock surrounding the tunnel chamber.The results allowed for the determination of the installation time,distribution and strength of supporting structures.This method was applied to the intake tunnel in the Ban Ve Hydroelectric Power Plant,in Nghe An Province,Vietnam.The results show that when a suitable displacement u0 ranging from 0.0865 m to 0.0919 m occurrs,we can install supporting structures that satisfy the stability and economical requirements.     

Hydro-mechanical interaction analysis of high pressure hydraulic tunnel

The reinforced concrete lining of hydraulic tunnel cracks under high internal water pressure and the high pressure water will leak off from the crack surface, which is a typical hydro-mechanical interaction problem. Unfortunately, the analytical and numerical methods used in current engineering practice for simulating the hydro-mechanical interaction of the lining and surrounding rock do not adequately account for the effects of the cracking of lining as well as the conditional cooperation between them. When lining cracks under high internal water pressure, the tensile strain of concrete and reinforcement presents to be nonuniformity and the lining would detach from the surrounding rock in a certain condition. In this paper, the nonuniformity coefficients of reinforcement strain and concrete strain are introduced to compute the secondary permeability of cracked lining and a water-filled joint (WFJ) element is developed to simulate the conditional cooperation between the reinforced concrete lining and surrounding rock. Thus an equivalent coupling method is adopted to calculate the hydro-mechanical interaction in hydraulic tunnel. The results show that the reinforcement stress obtained by the new method and the observed data match well. The phenomenon that the reinforcement stress stays at a lower value in the reinforced concrete tunnel with high internal water pressure is verified.     

Possible glitch in next generation smart cards

New research has shown that smart card vendors could be developing next-generation processors that are vulnerable to cache-based ‘side channel’ attacks.This is a short news story only. Visit www.compseconline.com for the latest computer security industry news