共查询到20条相似文献，搜索用时 781 毫秒
1.
陈芸 《中国海洋大学学报(自然科学版)》1984,(4)
虽然迄今还没有发现有一个物理实验结果不符合狭义相对论,但v=c在洛仑兹变换中是个奇点。而狭义相对论正是把相对性原理从力学推广到电磁场(v=c)。 在狭义相对论中,空一时、电流密度-电荷密度、动量-能量等基本物理量均组成四维复矢量。即且其内积对不同惯性系具有不变性。由此得到启发,尝试以时-空整体性假设替代光速不变性假设,使在洛仑兹变换中不出现v=c这个奇点。 相似文献
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首先论述了航空矢量重力测量中科里奥利加速度的计算模型，给出了科里奥利加速度改正对水平、垂直速度要求的分析模型。数值表明，在低纬地区欲达到1mGal的科里奥利加速度的精度，要求速度的精度为5cm／s左右；依据实测数据，目前GPS测得的载体速度精度为0．3mm／s，完全能够满足航空矢量重力测量对科里奥利加速度改正的要求。 相似文献
3.
海洋重力仪是安装在船上用作海洋重力测量的。它在海上工作时必会遇到各种干扰加速度的干扰。重力仪在设计时采取了克服水平方向加速度干扰的措施,使质量只能在垂直方向上平动,仪器测量的视重力值为重力加速度与干扰加速度的垂直加速度之和,经数据处理把重力加速度分离出来。 为了检验重力仪探头在海浪作用下是否产生非线性变化,必须先在室内进行模拟海浪的试验,并要求模拟海浪的试验装置只产生垂直方向平动。同时,因为海浪近似于简谐振动,所以也要求这个装置产生较严格的简谐运动。据此设计了正弦振动台。 相似文献
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针对基于MEMS加速度传感器的空投波浪浮标存在采样频率与测波精度低的问题，根据频域衰减积分算法，提出一种相应的波浪测量算法，为了验证该算法测波的准确性，开展了多功能水槽试验研究。该算法旨在将MEMS加速度传感器输出的加速度与姿态角转化为浮标运动的波形，首先将加速度与姿态角信号进行竖向处理获得竖直方向的加速度，再利用离散傅里叶变换将竖向加速度转化为频域内的加速度复数序列，然后引入控制函数减弱低频噪声，经过频域积分、离散傅里叶逆变换、时域积分获得竖直方向的位移，最后通过后处理得到最终的波形。多功能水槽试验采取10中不同波高和周期的工况，对比空投波浪测量浮标与波高仪的测量结果，试验结果表明，浮标的测量误差在10%以内，达到测波标准。 相似文献
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本文总结了针对涠１１－４平台一年多时间的应变和加速度监测数据的处理分析工作，详细介绍了所用的数据处理方法，给出了应变数据的统计结果及长期分布规律。通过对应变和加速度信号进行频谱分析，揭示了平台在多种环境条件下的振动特性。 相似文献
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针对适合捷联式重力仪的AUV搭载平台的选型问题,基于国内AUV实际航行数据,分析了多推进器组合、推进器和浮力舱组合、推进器和鳍舵组合等3类AUV的定深航行运动特性;推导了AUV水下航行在3个坐标轴方向上对重力仪产生的运动加速度计算公式,得到运动加速度与AUV水下6个自由度运动要素的解析表达式;基于运动加速度分析,讨论了适用于水下移动重力测量的AUV平台和推进装置设计,进行了AUV搭载平台的优选,并给出了重力仪安装位置建议;选定的AUV实验平台实施移动重力测量验证试验重复线精度达到0.42mGal,验证了搭载平台优选的有效性。 相似文献
10.
北部湾潮波的数值模拟试验 总被引：6，自引：0，他引：6
北部湾是南海的一个主要海湾,湾内潮汐和潮流都以全日潮为主,是世界上典型的全日潮海区。为了摸清北部湾潮波的变化规律,我们于1983年对北部湾进行了初步的数值计算试验。但应当指出的是,我们在该项计算试验中,忽略了惯性(加速度)项的影响,并且将底摩擦也进行了线性化。实际上,北部湾平均水深约45m,其中大部分海区的水深为25m,而湾内日分潮的振幅大者可达1m。这也就是说,潮波运动方程中的惯性(加速度)项与局部加速度项一般只差一个量级,而在湾顶部分浅水海区,两者 相似文献
11.
Laboratory analysis of core samples from the western Alboran Sea slope reveal a large variability in texture and geotechnical properties. Stability analysis suggests that the sediment is stable under static gravitational loading but potentially unstable under seismic loading. Slope failures may occur if horizontal ground accelerations greater than 0.16g are seismically induced. The, Alboran Sea is an active region, on which earthquakes inducing accelerations big enough to exceed the shear strength of the soft soil may occur. Test results contrast with the apparent stability deduced from seismic profiles. 相似文献
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The overall performance of ships depends on the seakeeping performance in specified sea areas where the vessel is designed to operate. The seakeeping performance procedure is based upon the probability of exceeding specified ship motions in a sea environment particular to the vessel's mission. Given the operational area of the vessel, the percentage of time the vessel operates in a particular sea state can be determined from an oceanographic database through application of the response amplitude operators. The predicted motions are compared to the motion limiting criteria to obtain the operability indices. However, the operability indices are strongly affected by the chosen limiting criteria. This is particularly the case for passenger vessels where many conflicting criteria are used to assess the effect of motions and accelerations on comfort and well-being of passengers. This paper investigates the effect of seakeeping criteria on seakeeping performance assessment for passenger vessels. Conventional seakeeping performance measures are evaluated for various levels of vertical accelerations defined by the ISO 2631 standard. It is shown that the estimated seakeeping performance of a passenger vessel greatly depends on the level of limiting value selected as the seakeeping criteria. 相似文献
13.
Peter R. Payne 《Ocean Engineering》1997,24(3):235-263
For study purposes, a simplified model of a hydrofoil craft is constructed with the assumption that it has:
- • heave only motion;
- • no surface proximity effect on the foil;
- • no foil broaching.
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A comprehensive set of 456 monthly tide gauge records is analyzed for trend and acceleration over the same period that satellite altimetry was analyzed (1993 to 2011). Additionally, a 90 tide gauge record subset is analyzed for which GPS data are available. The selection criterion for the tide gauge data is 85% data completion. All measurements are adjusted for vertical land motion. Results from 456 pairs of tide gauges, adjusted for Global Isostatic Adjustment, and satellite recordings located within 1° root-mean-square latitude and longitude separation differences are compared. The tide gauge trends and accelerations are adjusted for spatial bias using the more globally dense satellite data.The average trends of the 456 and 90 gauge sets (3.26 and 2.68 mm/year, respectively) agree reasonably well with the global trend average of the satellite data (3.09 mm/year). Average trends for the 456 tide gauges are also in good agreement (within 95% confidence limits) with trends based on satellite data within the 1° satellite proximity criterion (3.26 and 3.31 mm/year, respectively). The trends for the 90 gauges with GPS nearby and qualifying satellite locations are 2.68 and 2.74 mm/year, respectively. For all datasets analyzed, the accelerations are quite strongly negative but the uncertainty is relatively large. Adjustment of the tide gauge trends for spatial bias modified both trends and accelerations significantly and decreased trend differences between the 456 and 90 gauge datasets. The spatially adjusted tide gauge trends (2.95 and 2.72 mm/year, respectively for the 456 and 90 tide gauges sets) are somewhat less than the 1° spatially adjusted satellite data (3.09 mm/year). Whether the increased sea level trend of approximately 3 mm/year measured by the satellites since the 1990's is a long-term increase from the 20th Century value of approximately 1.7 mm/year or part of a cycle will require longer records; however, the negative accelerations support some cyclic character. 相似文献
15.
Numerical simulations using a full-nonlinear BIM (Boundary Integral Method) potential-theory wave model are carried out to study the internal velocity and acceleration fields of an solitary wave overturning on a reef with vertical face (submerged breakwater) and their relation to breaker type. The simulations make it clear that the jet size normalized by the incident wave height is uniquely governed by the crown height of the reef, while the jet shape is similar and independent of the size. Further, they reveal that the overall internal kinematics of overturning waves is clearly related to the jet size. As the jet size increases and the breaker type changes from spilling to plunging, the kinematics thus become increasingly different from those of steady waves. Water particles with the greatest velocities or accelerations within the wave converge towards the jet. After the breaking, both of the velocities and accelerations almost simultaneously reach extreme values near locations beneath the jet. Some of the extreme values are closely related to the breaker type and can be uniquely determined by substituting the breaker type index into the regression equations suggested here. 相似文献
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The local and convective accelerations of steep irregular wave events have been investigated. These properties are measured by a two-camera PIV technique. Furthermore, the experiments are compared with two different theories including a fully nonlinear and a simplified analytical model. An important result is that the convective term is of the same order of magnitude and of opposite sign as the local acceleration. The convective acceleration term can therefore not be neglected in acceleration and force estimates. 相似文献
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应用理论推导及数值计算方法，对Stokes随机波的谱特性进行了分析。首先将波面方程，海水质点水平速度用一阶波面分量的非线性组合表示，应用平稳随机高阶短的降阶计算法则，得到了波面方程及海水质点水平速度与一阶波面分量的自相关函数之间的关系，从而确定了Stokes随机波浪的波浪谱密度及海水质点水平速度和加速度谱密度，进而求得有关波浪要素的均方根值。文章还应有数值计算方法，分析了波浪基本参数对均方根值的影响。 相似文献
18.
Heinrich Sding 《Ocean Engineering》2002,29(7):570-738
A number of ship safety problems involve flow computations. Most of them do not require involved CFD calculations, but can be solved by relatively simple means which, nonetheless, are not state of the art. The problems discussed here are, in order of increasing sophistication: cross-flooding of damaged compartments; evacuation of persons on board a ship; sinking of a damaged ship in still water; accelerations and loads on free-fall lifeboats and damaged ship survival time in a seaway. 相似文献
19.
Frank Chew 《Marine Geodesy》2013,36(1):103-116
Western boundary currents, such as the Gulf Stream, are often modeled as flows in near cross‐stream geostrophic balance with paths that are straight or nearly straight. The effect of planetary vorticity advection on the downstream sea‐level slope in these rectilinear flows is re‐examined and found negligible. Instead, the re‐examination reveals a much greater effect of the ageostrophic component of the horizontal divergence in determining the downstream slope. Overlooked in previous studies is the geostrophic component of the horizontal divergence because of a hidden assumption of parallel flow. To avoid this pitfall, we employ a natural coordinate system to follow precisely the downstream direction. Further, we differentiate between weak geostrophic flows with small accelerations and flows in cross‐stream geostrophic balance where downstream acceleration might be appreciable. Two Rossby numbers are employed: a small cross‐stream number (≤0.01) to describe the near cross‐stream balance, and a large downstream number (≤0.1) to describe the large downstream accelerations that are found in western boundary flows. Finally, by means of a scale analysis we show that over the whole range of possible Rossby numbers, the advection effect of planetary vorticity on downstream sea level slope is negligible compared to the effect of the ageostrophic component of the horizontal divergence. Some new data on the nearshore gradient of the Reynolds stress are also included. 相似文献
20.
Polarization relations for mesoscale stationary orographic waves (MSOWs) and formulas for calculating vertical profiles of the total vertical flux of wave energy and amplitudes of horizontal speed are obtained by taking account the rotation of the atmosphere. Expressions are derived for the total wave heat flux, accelerations of the mean flow, and heat influxes generated by MSOWs. Calculations of the characteristics of MSOWs propagating in the atmosphere from the surface to the lower thermosphere are made. It was shown that MSOWs may significantly affect the circulation and thermal regime of the middle and upper atmosphere. 相似文献