On splitter plate coverage for suppression of vortex-induced vibrations of flexible cylinders

Experimental results show how vortex-induced vibration (VIV) amplitudes of flexible cylinders can be reduced up to a 90% by covering less than half of the length of the cylinder with splitter plates elastically mounted to the surface of the cylinder.The VIV amplitude reduction takes place along with drag coefficient reductions of up to a 50% for the reduced velocities investigated.     

Oyster patch reefs as indicators of fossil hydrocarbon seeps induced by synsedimentary faults

The Late Jurassic deposits of the Boulonnais area (N-France) represent the proximal lateral-equivalent of the Kimmeridge Clay Formation; they accumulated on a clastic-dominated ramp subject to synsedimentary faulting as a result of the Atlantic Ocean rifting. In the Gris-Nez Cape area, i.e., close to the northern border fault zone of the Jurassic basin, the Late Jurassic sequence contains small-dimensioned oyster patch reefs (<1 m) that are specifically observed at the base of an abrupt deepening trend in the depositional sequence induced by well-defined pulses of normal fault activity. Petrographic analysis of these patch reefs shows that they are exclusively composed of Nanogyra nana embedded in a microsparitic calcite matrix. ™¹³C measurements, carried out within both the matrix and the shells, display significantly lower values in the matrix compared to the oyster shells which suggests that the carbonate matrix precipitation was involving a carbon source different from marine dissolved inorganic carbon, most probably related to sulfate reduction, which is evidenced by light ™³⁴S in pyrites. Similarities but also differences with lucinid-rich bioconstructions, namely, the Late Jurassic pseudo-bioherms of Beauvoisin (SE-France) suggest that the patch reefs developed at hydrocarbon seeps are related to synsedimentary faults. The extensional block-faulting segmentation of the northern margin of the Boulonnais Basin in Late Jurassic times is thus believed to have induced a sort of small-dimension hydrocarbon seepage field, recorded by the patch reef distribution.     

Axial vibration analysis of the mud recovery line on deepwater riserless mud recovery drilling system

The series connection of multistage pumping module is the common concept of deepwater riserless mud recovery drilling system. In this system, the influence of the mass of pumping module on the vibration of mud recovery line cannot be ignored, and the lumped mass method has been utilized to discretize the mud recovery line. Based on the analysis of different boundary conditions, the paper establishes the axial forced vibration model of the mud recovery line considering the seawater damping, and the vibration model analysis provides the universal solution to the vibration model. An example of the two-stage pumping system has been used to analyze the dynamic response of mud recovery line under different excited frequencies. This paper has the important directive significance for the application of riserless mud recovery drilling technology in deepwater surface drilling.     

北京市电网雷害分布规律及风险评估

根据1996—2009年北京市逐日电网灾害资料分析了北京市电网雷害的发生规律, 结果显示:北京市电网雷害存在季节变化和日变化特征。结合同期气象观测站的雷暴日资料、北京市各区县的经济和人口密度特征提出了电网雷害概率、电网雷害频度、电网雷害密度、经济易损模数和生命易损模数作为北京市电网雷害风险评估指标。在此基础上,采用4级分区法对上述电网雷害易损性评估指标进行分级,并将北京市各区县按照5个电网雷害评估指标的所属等级值累加,得到电网雷害综合易损风险评估的评估系数。结果表明:北京地区电网雷害高风险区集中在北京城区中心附近,山区和山前迎风坡地带尽管电网雷害频次较高,但电网雷害风险却相对较低。     

UL-Isomap based nonlinear dimensionality reduction for hyperspectral imagery classification

The paper proposes an upgraded landmark-Isometric mapping (UL-Isomap) method to solve the two problems of landmark selection and computational complexity in dimensionality reduction using landmark Isometric mapping (LIsomap) for hyperspectral imagery (HSI) classification. First, the vector quantization method is introduced to select proper landmarks for HSI data. The approach considers the variations in local density of pixels in the spectral space. It locates the unique landmarks representing the geometric structures of HSI data. Then, random projections are used to reduce the bands of HSI data. After that, the new method incorporates the Recursive Lanczos Bisection (RLB) algorithm to construct the fast approximate k-nearest neighbor graph. The RLB algorithm accompanied with random projections improves the speed of neighbor searching in UL-Isomap. After constructing the geodesic distance graph between landmarks and all pixels, the method uses a fast randomized low-rank approximate method to speed up the eigenvalue decomposition of the inner-product matrix in multidimensional scaling. Manifold coordinates of landmarks are then computed. Manifold coordinates of non-landmarks are computed through the pseudo inverse transformation of landmark coordinates. Five experiments on two different HSI datasets are run to test the new UL-Isomap method. Experimental results show that UL-Isomap surpasses LIsomap, both in the overall classification accuracy (OCA) and in computational speed, with a speed over 5 times faster. Moreover, the UL-Isomap method, when compared against the Isometric mapping (Isomap) method, obtains only slightly lower OCAs.     

Mainstreaming local perceptions of hurricane risk into policymaking: A case study of community GIS in Mexico

This article suggests a framework for incorporating and communicating local perceptions of hurricane risk into policymaking through a case study conducted at El Zapotito commune in the State of Veracruz, Mexico. The authors constructed a geographical information system (GIS)-based model to quantify and spatially assess specific household-level vulnerabilities from information generated through interviews. This research developed a household vulnerability index applied to a participatory GIS to map vulnerability to hurricane hazard. The results indicate that infrastructural weaknesses are the most important factor contributing to vulnerability, explaining on their own 72.2% of the variation in the vulnerability patterns. These findings are corroborated by a vulnerability and capacity assessment (VCA), which shows that the community lacks strategies to cope with unsafe housing. It is suggested that linking community participation with modern techniques to analyse risk can empower communities and mobilise their capacities to address very specific vulnerabilities.     

An experimental study on using MR damper to mitigate longitudinal seismic response of a suspension bridge

In this paper, the seismic response reduction performance of magnetorheological (MR) damper is experimentally investigated for a suspension bridge. First, the force–displacement and force–velocity curves under a range of excitation frequencies, amplitudes and currents are obtained by mechanical behavior test of the RD1097 type MR damper. Then a new non-linear hysteretic model is proposed to model the mechanical behavior of the MR damper and the model parameters are identified from test data. An experimental method, as well as a set of testing setups with the MR damper for longitudinal seismic response reduction of a SDOF generalized system representing the fundamental longitudinal mode of suspension bridge, is developed. Finally, the seismic response reduction experiment subject to three kinds of earthquake excitations, including the Pingsheng Bridge earthquake wave, the El-Centro wave and the Taft wave, is carried out, and nine control cases, including uncontrolled, six passive control schemes with different input currents and two semi-active Bang–Bang control schemes, are tested. The results verify that the seismic response reduction experimental method is feasible and the good performance of seismic longitudinal response reduction of the suspension bridge can be achieved by MR damper. It is also shown that the passive control with optimum input current outperforms the semi-active Bang–Bang controls.     

Experimental study of the dynamic interaction between the foundation of the NEES/UCSD Shake Table and the surrounding soil: Reaction block response

An extensive experimental study of the dynamic interaction between the foundation block for the NEES/UCSD Large High Performance Outdoor Shake Table and the surrounding soil was conducted in 2003. The vibrations induced by the two NEES@UCLA large eccentric mass shakers were recorded at multiple stations within the reinforced concrete foundation block and on the surface of the surrounding soil up to distances of 270 m from the block. The present paper focuses on analysis of the data recorded within the reaction block including the average rigid body motion of the foundation and its dependence on frequency, and the deformation of the block for longitudinal (EW), transverse (NS), and torsional excitation. Comparison of the reaction block response during shaker induced vibrations with that for the much stronger actuator forces shows that linearity holds for the range of forces involved. Comparisons with analytical results for a simplified model of the foundation show good agreement between experimental and theoretical results.     

大跨连续钢桁拱桥动力系数影响因素研究

以南京大胜关长江大桥为研究对象,建立其车桥耦合动力分析模型,采用逐步积分法求解动力方程,以动力系数作评判标准,讨论行车速度、阻尼比、行车方向、车辆数、吊杆布置方式等参数对动力性能的影响.结果表明:动力系数随行车速度的提高而增大;吊杆索力的动力系数与无应力索长成反比;随着阻尼比的增大,各构件动力系数均有所降低;同向行驶时...