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91.
Paul Mardikian 《International Journal of Nautical Archaeology》2004,33(1):137-148
The 12-m long submarine H. L. [Horace Lawson] Hunley was successfully recovered from the Atlantic in August 2000 after nearly 140 years of immersion, and immediately brought to the Warren Lasch Conservation Center to be excavated in a controlled environment. In 2001 a multi-disciplinary team excavated the crew compartment and uncovered numerous fragile artefacts and human remains. This paper describes the conduct of the excavation and technological advancements developed to work with this complex and unstable iron vessel. Impressed current technologies, automated tank controls and water monitoring systems; laser mapping; fibre-optics; database management; in situ x and gamma rays; moulding and protection of fragile archaeological features; and protocols for moving artefacts to the laboratory will also be discussed.
© 2004 The Nautical Archaeology Society 相似文献
© 2004 The Nautical Archaeology Society 相似文献
92.
It is well known that the soil-structure interaction (SSI) changes the dynamic response of a structure supported on flexible soil. The analysis of optimally controlled SSI systems has certain difficulties due to the nature of the SSI and the optimal control problem. In this paper, a two-step iteration-based numerical algorithm is proposed to handle optimally controlled SSI systems under earthquakes. First, the optimal control forces are obtained by using a fixed-base system. Then, the optimal control forces are converted to the frequency domain by the Fourier transform technique to be used in the equations of the SSI system. The lateral displacement and the rocking of the foundation are obtained from the equations of the SSI system containing the optimal control forces in the frequency domain. The lateral displacement and rocking of the foundation are then converted to the time domain by the inverse Fourier transform technique, and the lateral accelerations and the rocking accelerations of the foundation are obtained by the forward finite difference method. During the second step, the optimal control forces are calculated again by using the lateral acceleration and the rocking acceleration of the foundation along with the earthquake ground motion. Using the method explained above, the optimal control forces obtained in the time domain are used in the equations of the soil-structure system from which the behavior of foundation and structure is obtained. In the final section of the paper, a numerical study is conducted for a controlled structure supported on flexible soil. 相似文献
93.
Ian D. MacLeod Allison Selman Chris Selman 《Conservation and Management of Archaeological Sites》2017,19(4):269-287
The corrosion microenvironment of a dozen Second World War iron shipwrecks in Chuuk Lagoon, Federated States of Micronesia, was investigated to see if there were any measurable changes caused by a recent major typhoon. Seven previously inspected wreck sites were used for calibration to assess the environmental impacts. Five new wrecks, including the Fumitzuki, a destroyer of the Imperial Japanese Navy, were assessed at up to twice the depth of previous studies. The new data showed that the logarithm of the corrosion rate falls linearly with depth to 36 m. Measurements of corrosion potentials, concretion thickness and pH showed that many of the vessels suffered partial deconcretion during the typhoon Maysak in April 2015 with concomitant increases in the rate of decay. Regrowth of the colonising marine organisms are presently ameliorating the impact of the typhoon. 相似文献
94.
An approach to mitigate the seismic risk of existing structures by means of the creation of a continuous thin layer of grouted soil at a convenient depth is presented. A parametric numerical analysis is reported using different constitutive models with reference to two geometrical schemes. It is shown that if the grouted layer has a stiffness significantly lower than that of the surrounding soil, it may be effective in reducing the seismic demand. In the parametric analyses, the positive role of yielding is also observed, which indicates that the barrier is more effective with larger input amplitudes. 相似文献
95.
Worth Carlin Donald Keith Juan Rodriguez 《International Journal of Nautical Archaeology》2002,31(2):293-299
Historic shipwrecks frequently contain a large proportion of wrought-iron tools, fasteners, and other types of artefacts. Encrustations readily form around such objects in many marine environments. Depending on many factors, the iron objects inside these encrustations may be well preserved, completely disintegrated, or poorly preserved but still present. The latter type of encrustation is every conservator's nightmare because removing the encrustation yields merely a poorly preserved artefact still in need of extensive additional conservation. Neatly separating the artefact from its encrustation in order to obtain a natural mould for casting is generally impossible. Having encountered this problem many times, the authors began to experiment with the extraction of metallic iron from poorly preserved encrusted artefacts using galvanic dissolution. Data on rates of dissolution were gathered for three experimental configurations. The results of a test conducted on an encrusted artefact were promising, but inconclusive. 相似文献
96.
V. Salinas J. O. Caselles V. Pérez-Gracia S. Santos-Assunçao J. Clapes L. G. Pujades 《Journal of Earthquake Engineering》2014,18(1):90-112
Microzonation is widely used in seismic risk evaluations to define the predominant period values, which are usually associated with extended areas of a few hundred meters. However, the representative values corresponding to these areas are obtained from few measurements in each area. Thereby, results are accurate only in the case of depth-dependent soils. However, not detected narrow and sharp lateral changes in soil are potentially the cause of imprecision and could be a source of specific errors. This article aims to present several tests conducted in order to emphasise the importance of accurate selection of points, to underscore the necessity of more precise and detailed evaluations, and to suggest a possible methodology to select the most appropriate data acquisition points. Results highlight the need to divide microzonation areas into smaller zones for a precise evaluation in locations where sudden changes in soil characteristics exist. Therefore, in such sites the requirement of nanozonation appears; defining zones with the same soil response. Distance between vibration measurements could be the main problem for nanozonation; data acquisition in areas with irregular geology can be time consuming when a precise analysis is required. In the most complicated environments or in dense cities, it could even be unfeasible. Consequently, it is necessary to establish a functional methodology to adequately distribute the measurement points throughout the area. On this occasion, three sites in Barcelona city were studied. This city is surrounded by mountains at NW, W, and S, and by the Mediterranean Sea at N and E. As a consequence, the shallow geology is characterized by many paleochannels and streams that are currently buried. These geological structures most likely affect the soil response. Several tests were carried out to determine this dependence. The tests were based on Ground Penetrating Radar (GPR) surveys to define the paleochannels position and on vibration measurements in order to define properly the soil response. The results from both methods were compared to the known geology to accurately define the effect of the shallow geological structures in the predominant period and in the GPR images. Areas with the same geological unit but different materials were identified in the GPR images, allowing the selection of the most appropriate distance between vibration measurements in each place. As a final result, predominant periods that were measured over the same geological unit but over different material showed changes higher than the 40% in short distances. This procedure could improve the soil response maps, including nanozonation. 相似文献
97.
Mohammed Y. Fattah Mosa J. Al-Mosawi Abbas F. I. Al-Ameri 《Journal of Earthquake Engineering》2013,17(7):1158-1188
In this study, the response and behavior of machine foundations resting on dry and saturated sand was investigated experimentally. In order to investigate the response of soil and footing to steady state dynamic loading, a physical model was manufactured to simulate steady state harmonic load at different operating frequencies. Total of 84 physical models were performed. The footing parameters are related to the size of the rectangular footing and depth of embedment. Two sizes of rectangular steel model footing were tested at the surface and at 50 mm depth below model surface. Meanwhile the investigated parameters of the soil condition include dry and saturated sand for two relative densities 30% and 80%. The response of the footing was elaborated by measuring the amplitude of displacement by the vibration meter. The response of the soil to dynamic loading includes measuring the stresses inside the soil using piezoelectric sensors as well as measuring the excess pore water pressure using pore water pressure transducers. It was concluded that the maximum displacement amplitude response of the foundation resting on dry sand models is more than that on the saturated sand by about 5.0–10%. The maximum displacement amplitude of footing is reduced to half when the size of footing is doubled for dry and saturated sand. The final settlement (St) of the foundation increases with increasing the amplitude of dynamic force, operating frequency and degree of saturation. Meanwhile, it is reduced with increasing the relative density of sand, modulus of elasticity, and embedding inside soils. The excess pore water pressure increases with increasing the relative density of the sand, the amplitude of dynamic loading and the operating frequency. In contrast, the rate of dissipation of the excess pore water pressure during dynamic loading is more in the case of loose sand. 相似文献
98.
Ciro Visone Emilio Bilotta Filippo Santucci de Magistris 《Journal of Earthquake Engineering》2013,17(1):131-162
This article discusses how to calibrate some parameters of two-dimensional finite element models for numerical analyses in geotechnical earthquake engineering. The calibration was made through the simulation of the one-dimensional vertical propagation of S-waves in elastic layers, whose theoretical solutions are available in literature. The numerical results were compared with those obtained by frequency domain analyses. The influence of several sources of damping arising in the model, including that deriving from boundary conditions and numerical integration, was investigated. The proposed calibration procedure constitutes a useful preliminary step for performing advanced dynamic analyses of any geotechnical system. 相似文献
99.
山东青州香山西汉墓出土凝结铁器锈蚀特征分析及科学保护 总被引：1，自引：0，他引：1
在2006年发掘的山东青州香山西汉墓陪葬坑中发现了大量用于陪葬的铁质兵器,其中铁质矛头因锈蚀严重凝结在一起。采用显微共聚焦激光拉曼光谱、X射线衍射、X射线荧光、离子色谱对锈蚀产物进行了分析检测,并对其主要锈蚀产物α-FeOOH和γ-FeOOH的生成和特点做了陈述,阐述此件铁质文物的锈蚀特征。对此件铁质文物的保护过程没有采用以往常用的除锈剥离做法,而是利用先进的技术手段进行整体保护,灵活运用了文物保护原则,同样达到了保护要求的预期目标。 相似文献
100.
H.A. Waldron Ashok Khera Gayle Walker George Wibberley Christopher J.S. Green 《Journal of archaeological science》1979,6(3):295-298
Lead concentrations were measured in 41 rib samples from the Romano-British cemetery at Poundbury and in two sets of soil samples from the graves yielding up the bones. The levels of lead in the soil were in no way exceptional (means for the two series were 16·7 and 24·8 μg/g dry weight) and there was no correlation between soil lead and bone lead concentrations.Since bone lead concentrations vary independently of those in the soil, it is unlikely that the bones are contaminated by lead in the soil, at least under the conditions prevailing at this particular site. 相似文献