Engineering Situations Research Articles

Practical guidelines for multivariate analysis and design in coastal and off-shore engineering

A frequent statistical problem in many coastal and off-shore engineering situations is to estimate the probability of structural failure expressed in terms of Return Period and Design Quantile. Usually, only the univariate approach is carried out to quantify the risk of failure. However, coastal and off-shore structures typically fail because of the occurrence of a critical combination of all the variables at play in a single sea storm: thus, it may be important to consider the joint occurrence of dangerous conditions. The present manuscript provides practical guidelines in order to carry out a sensible multivariate analysis of the available data, including a randomization procedure to cope with repeated observations. In addition, suitable strategies for performing multivariate design are presented and discussed. A practical case study is used to show the application of the techniques illustrated throughout the paper, and a preliminary rubble mound breakwater design is also carried out.

典型工程变形监测的一种新方法及应用研究

针对广州城市地铁、高支模工程和大型基坑变形监测实际，本文研究总结了一种基于测量机器人的变形监测新方法，即混合基点网法和多点强制自由设站边角交会法，并成功应用于多个典型工程。实践证明，该方法简单易行，自动化程度高，监测精度可满足多种典型工程的变形预警要求。According to the actual situation of high-formwork engineering and large deformation monitoring in Guangzhou subway, this paper studies the new method of monitoring based on measuring the deformation of a robot, that is a mixed base-point network method and multi-point & compulsory free-station linear-angular intersection method, and it was successfully applied to a number of typical projects. Practice has proved that the method is both simple with high degree automation. At the same time, monitoring accuracy can meet the requirements of a variety of typical deforma- tion warning works.

Repairing and Reinforcement of Bridge Structure

In order to make the damaged bridges continue to play a role in a short period of time, ensure the normal order of the bridge structure is used,and ensure the traffic safety, we carried out the bridge reinforcement and repair work. On the basis of the actual testing data in combination with the practical situation of engineering and the damage degree, we damaged parts of the bridge of grouting reinforcement, embedded, anti-corrosion treatment, eliminate the hidden trouble of the structures, to guarantee the normal operation of city traffic. This article mainly introduces the harm of main girder section and the reinforced repair way.

FINITE-VOLUME SOLUTION OF DIFFUSION EQUATION AND APPLICATION TO MODEL PROBLEMS.

In the present numerical study, the two dimensional diffusion equations are converted to a system of l inear equations using finitevolume method. The system of equations is solved by a direct method. For the entire process a computer code is developed in Matlab. In the second part of the present study, the comput er codes developed for solving diffusion equation i s then applied to a series of model problems. These problems contain features fou nd in more complicated engineering situations. The problems are distinguished by their different boundary conditions, and by the variation of the source term and diffusivity in the domain.

Stability of Liangshuijing landslide under variation water levels of Three Gorges Reservoir

Three Gorges Reservoir area of Yangtze River in China is a geological disaster-prone zone with frequent landslides. Liangshuijing landslide in Yunyang County in this area is just a case. The impoundment water level of Three Gorges Reservoir was 135 m in 2003, 156 m in 2006 and reached 175 m in 2009. The effect of such a large variation of reservoir level on the deformation and stability of Liangshuijing landslide is not negligible. It once suffered from a dangerous situation due to the influences of various factors such as water level variation and rainfall. Based on the geological exploration, a thorough analysis of the deformation status and geological engineering situation of Liangshuijing landslide is made, and the formation and instability mode of the landslide are also judged. Based on the limit equilibrium analysis method, the stability of axial profile of the landslide is studied under three kinds of extreme conditions (impoundment water level of 145, 175 m and drawdown of 175–145 m). Three-dimensional finite element numerical calculation is then adopted to study the deformation of the landslide under the above conditions based on the hydro-mechanical coupling numerical model. The quantitative calculations reveal that the variation of groundwater level caused by the variation of reservoir level is the main factor for the landslide resurrection, especially under the third condition of rapid drawdown. It is recommended to continue monitoring the landslide so as to further understand the deformation trend of the landslide under the influences of water storage.

The effect of nanotubes waviness on mechanical properties of CNT/SMP composites

In this paper, the effects of inclusion waviness and its distribution to the effective carbon nanotubes (CNTs)/shape memory polymer (SMP) composites stiffness is investigated. A micro mechanical model is developed to take into account the waviness effect of nanotubes, which are assumed as solid short fibers with a circular cross-section and exhibiting bow shape waviness. The mechanical properties of the composite are significantly increased by reinforcing with CNTs and the desired mechanical properties in addition to proper shape recovery behavior are obtained. The improvements in modulus are remarkably less than the micromechanical prediction assuming straight nanotubes. It is shown that the lack of fiber waviness distribution assumption was found to lead to inaccurate composite stiffness prediction. Since the effects of CNT waviness and aggregation in the composite frequently encountered in real engineering situation, in this study the effects of these defects on the overall properties of the CNT/SMP composite are simultaneously examined. The results indicate that both the waviness and aggregation can drastically reduce the stiffening effect of the CNTs and are two important factors influencing the reinforcing efficiency.

Unified semi-analytical solution for elastic-plastic stress of deep circular hydraulic tunnel with support yielding

A unified semi-analytical solution is presented for elastic-plastic stress of a deep circular hydraulic tunnel with support yielding under plane strain conditions. The rock mass is assumed to be elastic-perfectly plastic and governed by the unified strength theory (UST). Different major principal stresses in different engineering situations and different support yielding conditions are both considered. The unified solution obtained in this work is a series of results, rather than one specific solution, hence it is suitable for a wide range of rock masses. In addition, parametric study is conducted to investigate the effect of intermediate principal stress. The result shows the major principal stress should be rationally chosen according to different engineering conditions. Finally, the applicability of the unified solution is discussed according to the critical pressures.

Estimation of parameters in the state space model of stochastic RL electrical circuit

PurposeThe purpose of this paper is to consider the stochastic differential equation of the RL electrical circuit as the dynamic model of a state space system when the current in the circuit is hidden and corrupted by the measurement noise. Estimation of the corrupted current and the values of missing or unknown parameters (resistance, the observed current variance in the measurement model, the mean and variance of the current prior distribution) which are the main concern in electrical engineering is considered.Design/methodology/approachOptimal filtering is proposed for estimation of the hidden current from the noisy observations. Also, the problem of analyzing this model based on estimation of the unknown parameters is addressed from the likelihood‐based and Bayesian perspective.FindingsComputational techniques for parameter estimation are carried out by the Maximum likelihood (ML) approach using Expectation‐Maximization type optimization and Bayesian Monte Carlo perspective using Metropolis‐Hastings scheme. The explicit formulas for the ML estimator are obtained and it is shown that the smoothers, the filters and the predictions for the current have the best confidence intervals, respectively. Some numerical simulation examples which are performed by R programming software are considered to show the efficiency and applicability of the proposed approaches. Results show an excellent estimation of the parameters based on these approaches.Practical implicationsDue to the fact that in an empirical situation of electrical engineering, observing the current in the circuit regardless of the measurement noise and knowing the exact value of the parameters are unrealistic assumptions, this paper can be used in various types of real time projects.Originality/valueTo the best of the authors' information, the problem of analyzing the state space model of RL electrical circuit has not been studied before. Furthermore, the estimation of the hidden current as the state of the system and estimation of the unknown parameters of the model via both ML and Bayesian approaches have been investigated for the first time in the present study.

A new method for analyzing the stability of rock wedges

In the analysis of rock slope stability, the method of wedge analysis proposed by Hoek and Bray in their classic textbook Rock Slope Engineering (1981) [1] and the computer program SWEDGE (Rocscience, 2001) [18], which was developed based on this method, are widely applied, especially in practical engineering situations. In the Hoek–Bray method, wedge failure modes are identified by the effective normal forces that act on the two discontinuities forming the wedge. The effective normal forces obtained using this method may be distorted with respect to certain conditions since discontinuities usually cannot bear tensile stress. This may lead to inaccurate estimations of failure modes and incorrect solutions for safety factors. This paper establishes criteria for normal forces to identify failure modes according to kinematic conditions of wedge failure and proposes a modified Hoek–Bray method for the analysis of wedge stability. Considering the scattering in discontinuity orientation data, an optimization procedure for wedge stability is proposed. This involves a genetic algorithm (GA) for searching the critical failure surface with the minimum factor of safety and provides a low-limit solution with conservative advantages for engineering support design to ensure the stability and safety of the rock slope.

In Situ Measurement of Thermal Diffusivity in Anisotropic Media

A knowledge of thermal conductivity/diffusivity is essential in several situations in engineering. This material property serves also as a measure of the quality of the manufactured materials. The thermal conductivity and diffusivity are measured by specialized labs using commercially available equipment. Even though both the number of such sites and the available measurement techniques are quite large, non-destructive, fast, and reliable techniques are still demanded. The developed technique, due to its rapidity and nondestructive character, can be embedded in a manufacturing process. As opposed to most methods, it does not require preparation of samples of a special shape (e.g., a small cylinder, a thin foil, cuboid). Moreover, one measurement cycle of the proposed technique yields two principal components of the diffusivities of orthotropic materials.

Establishment of ‘Urban Tunnels’ in the Major ‘Civil Engineering’

Urban tunnels mainly include subway tunnels, street-passage tunnels and underground road tunnels etc. With the development and utilization of underground space, urban tunnels have developed rapidly in recent years. At the same time, development of urban tunnels faces new opportunities. However, related professionals are not sufficient to make it come true. This thesis discusses feasibility of establishing ‘Urban Tunnels’ in the major Civil Engineering, including employment situation of Civil Engineering, integration with the demands of Zhejiang Province and Hangzhou City, misplaced development with other colleges and universities and the features of students majoring in civil engineering. Besides, it makes sufficient preparation in aspects of hardware, software, teachers and social support, which makes the construction of new major be implemented successfully according to plans and steps.

Multivariate approach to design coastal and off-shore structures

ABSTRACT Salvadori, G., Tomasicchio, G.R.., D'Alessandro, F. 2013. Multivariate approach to design coastal and off-shore structures. A frequent statistical problem in many coastal and off-shore engineering situations is to estimate the probability of structural failure expressed in terms of Return Period and Design Quantile. Usually, an univariate analysis is carried out to quantify the risk of failure. However, coastal and off-shore structures typically fail because of the occurrence of a critical combination of all the variables at play in a sea storm: thus, it may be important to consider the joint occurrence of dangerous conditions. The present manuscript outlines an original approach, exploiting Copulas, in order to provide a consistent framework for the calculation of bivariate Return Periods and Design Quantiles, which can be generalized to the multivariate case.

An integrate information technology model during earthquake dynamics

Applying Information Technology (IT) in practical engineering has become one of the most important issues in the past few decades, especially on internal solitary wave, intelligent robot interaction, artificial intelligence, fuzzy Lyapunov, tension leg platform (TLP), consumer and service quality. Other than affecting the traditional teaching mode or increasing the inter-relation with users, IT can also be connected with the current society by collecting the latest information from the internet. It is apparently a fashion-catching-up technology. Therefore, the learning of how to use IT facilities is becoming one of engineers` skills nowadays. In addition to studying how well engineers learn to operate IT facilities and apply them into teaching, how engineers` general capacity of information effects the results of learning IT are also discussed. This research introduces the Combined TAM and TPB mode, to understand the situation of engineers using IT facilities.

The Current Situation and Future Prospect of Advanced Human-Machine Engineering’s Application in Coalmine

Coalmines’ productive activity demands safety, comfortability, efficiency and economy, which are just the features of advanced human-machine engineering. Then current situation of advanced human-machine engineering’s application in coalmine is summarized, including: operating devices of coalmine machinery are man-beneficial; “safe color” in coal mining machinery is applied; signals under coalmine are effectively released; noise environment in coalmine are improved. Finally, the future trends of advanced human –engineering are discussed: coalmine safe human-machine engineering, coalmine green human-machine engineering, coalmine virtual human-machine engineering, coalmine intelligentized human-machine engineering, and coalmine digital human-machine engineering, etc.

Practice and Study of the Effect of One-Household-One-Meter Conversion on NRW

In order to test the effect on NRW(None Revenue Water) of one-household-one-meter conversion, find out key factors to influence the water supply efficiency and propose ways to reduce the rate of NRW, this article was based on the current practical engineering situation in Chongqing, China, by selecting 5 representative controlled fields for a six-month testing period. It shows that: different installation qualities of one-household-one-meter act different influences on NRW. The individual customer’s domestic water can be measured effectively by installing the drip-proof valve. The rate of NRW can be decreased at the beginning in the fields with “drip-proof valve + meter”. Water supply efficiency rate of the fields with “meter only” keep stable during 6 months, and meanwhile the fields with “drip-proof valve + meter” decrease over time. The function of drip-proof valve is found to stop at 147 days after installation due to the rust and sand getting into the valve. “Drip-proof valve + meter” is a practical and effective one-household-one-meter conversion method. Relevant standard atlas is recommended to be developed and implemented timely. Maintenance of pipeline and guarantee of water quality in pipeline are very important to keep the contribution of “drip-proof valve + meter” on NRW.

A throttling mechanism sustaining a hole tone feedback system at very low Mach numbers

AbstractThis study investigates the sound produced when a jet, issued from a circular nozzle or hole in a plate, goes through a similar hole in a second plate. The sound, known as a hole tone, is encountered in many practical engineering situations. Direct computations of a hole tone feedback system were conducted. The mean velocity of the air jet was 10 m s−1. The nozzle and the end plate hole both had a diameter of 51 mm, and the impingement length between the nozzle and the end plate was 50 mm. The computational results agreed well with past experimental data in terms of qualitative vortical structures, the relationship between the most dominant hole tone peak frequency and the jet speed, and downstream growth of the mean jet profiles. Based on the computational results, the shear-layer impingement on the hole edge, the resulting propagation of pressure waves and the associated vortical structures are discussed. To extract dominant unsteady behaviours of the hole tone phenomena, a snapshot proper orthogonal decomposition (POD) analysis of pressure fluctuation fields was conducted. It was found that the pressure fluctuation fields and the time variation of mass flows through the end plate hole were dominantly expressed by the first and second POD modes, respectively. Integrating the computational results, an axisymmetric throttling mechanism linking mass flow rates through the hole, vortex impingement and global pressure propagation, is proposed.

Design of Optical Perfection of Flame Detector

This paper summarizes the current situation home and abroad of the detection technology of point flame detector. It briefly introduces the application situation of flame detector engineering and describes the problems exist in actual project application of the point flame detector. Based on the theoretical optics of flame detector, combining the optics testing platform, collection work on combustion flame of characteristic materials and characteristic source spectrum has been carried out. Through carrying out relevant experiments, relevant data has been collected and analyzed. Select automatic optical inspection focusing on flame detectors focusing on different wave bands. The optical perfection design scheme is put forward in the end based on point flame detector of reflecting light source.

A notch root radius to attain minimum fracture loads in plates weakened by U-notches under Mode I loading

The paper deals with the minimum value of a fracture load, with respect to the notch root radius, in plates weakened by U-notches under Mode I loading. It has been found that the fracture load has a minimum value at a critical value of the notch root radius (ρ), using four criteria, namely, Mean Stress (MS), maximum tangent stress or Point Stress (PS), Critical Strain-Energy (CSE) and Averaged Strain-Energy Density (ASED). Using a characteristic length (lch), which is a function of material properties, the results showed that the dimensionless critical notch root radius (ρ/lch)cr depended on w/a ratio (the specimen width to the notch depth), Poisson ratio, and loading condition (tensile or bending loading) under Mode I loading. In other words, according to these criteria, a notch root radius different from zero exists, providing a minimum fracture load. Therefore, a crack is not more dangerous rather than a U-notch under Mode I loading. This critical notch root radius is important for a quasi-brittle material, but may not be significant for brittle ones in practical engineering situations. Good agreement was found between theoretical predictions and experimental results on Al356-T6.

Simplified damage models applied in the numerical analysis of reinforced concrete structures

This work presents one and two-dimensional numerical analyses using isotropic and anisotropic damage models for the concrete in order to discuss the advantages of these modeling. Initially, it is shortly described the damage model proposed by Mazars. This constitutive model assumes the concrete as isotropic and elastic material, where locally the damage is due to extensions. On the other hand, the damage model proposed by Pituba, the material is assumed as initial elastic isotropic medium presenting anisotropy, plastic strains and bimodular response (distinct elastic responses whether tension or compression stress states prevail) induced by the damage. To take into account for bimodularity two damage tensors governing the rigidity in tension and compression regimes, respectively, are introduced. Damage activation is expressed by two criteria indicating the initial and further evolution of damage. Soon after, the models are used in numerical analyses of the mechanical behavior of reinforced concrete structures. Accordingly with comparison of the obtained responses, considerations about the application of the isotropic and anisotropic damage models are presented for 1D and 2D reinforced concrete structures modeling as well as the potentialities of the simplified versions of damage models applied in situations of structural engineering.

Break-up and droplet formation in shear thinning compound liquid jets

The break-up of a compound liquid jet into droplets has relevance to many practical situations in engineering and science. In this paper, we investigate the dynamics associated with the break-up of a non-Newtonian shear thinning compound liquid jet obeying the Carreau model. A long wavelength asymptotic expansion is used to reduce the governing equations of the problem into a set of 1D partial differential equations, which describe the evolution of the leading order axial velocity of the jet as well as the radii of both the inner and the outer interfaces. We solve these equations using a numerical method, based on finite differences, to investigate the effect of changing key parameters on break-up dynamics and droplet sizes.