Applied Mechanics and Materials Vols. 166-169

Abstract: Jacket-type platforms may be the most common type of offshore structures, and damage localization and severity estimation is important for these structures. This paper employs a multi-hierarchical damage identification method based on BP neural network to detect damages in jacket platforms. Firstly, the damaged storey of the jacket is detected, and the numbers of the elements among the detected storey are then detected. According to this method, the learning samples can be more targeted and the number can be reduced largely. In the end, a jacket model is used to investigate the performance of this method, and the results indicate that this approach is more effective and has higher accuracy than direct diagnosis method.

Abstract: Based on the curvature modal damage identification of wavelet analysis principle, the finite element method was applied to analyze the vibration characteristics of the damaged deck arch bridge. Take Haar wavelet as the mother wavelet, through the continuous wavelet transform of curvature mode and then identified the damaged position by the maximum of wavelet coefficients. analyze the damage identification problem under three different damaged conditions (condition 1: only the arch 1 contained one damaged location; condition 2: the arch 1 and the arch 2 contained one damaged location respectively; condition 3: the arch 1 contained two damaged locations and the arch 2 contained one damaged location).This paper provided a valuable reference of damage identification and diagnosis for arch bridge.

Abstract: Wavelet packet coefficients carrying real signals have large amplitude but are in minority, while those carrying noise has lower amplitude but is of large number. In this case, the Basic principle of de-noising wavelet packet is to process signals carrying noise. A suitable threshold is chosen in different decomposition level. Wavelet packet coefficient of less than this threshold is set to equal zero, while wavelet packet coefficients of greater than this threshold is reserved and reconstructed into de-noising signals. MSE, SNR, PSNR are regarded as the standards of de-noising evaluation, some mathematical methods such as Shannon entropy, norm entropy, logarithm energy entropy, threshold entropy, Stein Unbiased Risk Estimate entropy are adopted to measure whether the wavelet packet basis is optimal , minimum Entropy function D value is the best base. Selecting threshold and threshold quantitative is the key to wavelet packet de-noising. And selection of threshold value abides standards such as Sqtwolog, Rigrsure, Heursure, Manimaxi, or Birge-massart. Wavelet packet de-noising method has been applied to tunnel vault sink and landslide monitoring data de-noising processing, which manifests itself being a more elaborate, flexible method compared to wavelet de-noising, since wavelet packet de-noising can even subdivided the low-frequency part and the high-frequency part of upper layer, thus entertains a more precise local analysis capabilities.

Abstract: Based on the concept of hydraulic damper energy dissipation, a passive Hydraulic Force Pulse Generator (HFPG) is presented. The design comprises a conical poppet valve inside a cylindrical hole without any seat. By virtue of aperture and orifice throttling, HFPG dissipates the kinetic energy of a rapidly moving object and cushions it to a halt to produce desired acceleration pulse. Prompt and easy adjustment can be achieved to the damping force by changing the size of the orifice set on cylinder. A mathematical model of the cushion process is developed by way of analyzing the internal fluid dynamic phenomenon of HFPG. And numerical simulation results of the model has exhibited the following features of HFPG: high-efficiency of energy dissipation; easy-regulation of acceleration waveform and being suitable in conditions with large momentum change, especially to be used as the negative pulse generator of dual-wave shock testing machines which can simulate the shock environment of underwater explosion.

Abstract: Taking Majiagou landslide which lies on the left side of the Three Gorges Reservoir as example, the relation between the shear strength c, values and the design parameters through the Janbu methods and sliding force transfer method is analyzed. After comprehensive analysis and comparison of the computing results, it is suggests that influence of the  value on the factor of safety and the residual sliding force is much apparent than that of c value.  value is the most critical factor to ensure the safety and invest of the slide controlling engineering. Therefore, it is significant to choose a reasonable  value in the stability analysis and the controlling design of landslides.

Abstract: Two-dimensional elastic thin plates are widely used in civil engineering structures. The plates deteriorate gradually under service conditions, which influence the safety of engineering structures. How to identify the damage of the plate is one of the hot issues in the civil engineering fields. The relevant theoretical analysis and numerical simulation are stressed, but the physical model experiments are few. There are some problems among the theory, methods and practical engineering applications. A method is presented for determining damage location and degree of civil engineering structures based on model testing of two-dimensional steel plates.

Abstract: The great effort for reducing emissions of CO2 to atmosphere will inevitably involve the carry-out process of Carbon Capture and Storage(CCS), a novel plan which intends to capture and store anthropogenic CO2 produced at many existing industrial sources, such as power stations and petrochemical works. In particular, anthropogenic CO2 pipeline transportation from the energy plant to the remote sequestration area(both onshore and offshore) is a fundamental issue regarding the feasibility of applying the CCS technology. CO2 pipelines have been in operation in USA, Europe and North Africa for almost three decades. However, the technical challenges for pipelines transporting CO2 due to the relevant effects of different impurities coming from flue gases, are still needed to get people to take up, especially for China which is focusing on the roll-out of CCS. This paper will address a FE-based method which can assess residual life of a supercritical CO2 transmission pipeline containing an inner defect induced crack. Specifically, a portion of welded round steel pipeline is selected as the object of our analysis and an ANSYS finite element procedure is generated to simulate the stress state of an element volume along the radial direction and hence to calculate the effective stress due to the effects of crack closure. Afterwards, combining the effective stress we get in the above numeric analysis, the Paris equation is modified to build an integral analysis method for the residual life evaluation of CO2 pipeline. Lastly, in order to verify the validity of the proposed method, a pipeline example in a published paper is used as the benchmark model, the full-scale test results of which are compared with those from our method. Based on this, a section of CO2 pipeline, with an initial defect (assumed as a crack source), is analyzed and its residual life is evaluated by using the presented method. The analysis of numerical results indicates that the method presented in this paper can give us a valuable reference to life-evaluation for CO2 pipeline in CCS.

Abstract: Wavelet analysis has the characteristics of timing and frequency adapting to each other. Two-dimensional wavelet analysis can rotate and amplify the signal in frequency domain. So, in this paper, two-dimensional wavelet analysis is used to detect the position of the injury of simply supported plate. This article simulates an injury and two injuries in a simply supported plate and the detection of the location of the injury. This article verifies that the feasibility of this method.

Abstract: This paper has studied the evaluation of bearing capacity of concrete piers exposed to the freeze-thaw cycles. In this paper, based on the mechanism of freeze-thaw process, several factors affecting the freeze resistance of concrete were considered, and a regression model including the interaction of loads and freeze-thaw was established according to experimental data. Besides, a wholly new concept - the effective depth of the freeze-thaw has been introduced into the analyzing, and it also considers of the area of cross section reducing, which results in the stress concentration. It calculates the maximal stress by using the limit state design method, and finally judges its rank of damage.

Abstract: This article from deformation characteristics of deep foundation pit which support by the pile anchor, then using neural network and Matlab software to establish the time series model to prediction and analysis the deep horizontal displacement of soil. The prediction results show that the overall shape of the curve is similar to "bow” ,and with the depth of excavation the maximum displacement occurred by the beginning of the location of 0.5 m from the surface to move to about half of the excavation depth That is the H/2 up and down position. The results have some reference to the practical engineering in a certain extent, this explain that the prediction is a kind of important means to realize information construction.