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141.
142.
Maneuvering modeling and simulation of AUV dynamic systems with Euler-Rodriguez quaternion method 总被引:1,自引:0,他引:1
The purpose of this study is to develop maneuvering models and systems of a simulator to improve the motion performance of autonomous underwater vehicles (AUVs) at the preliminary design stages in advance. The AUVs simulation systems based on the standard submarine equations of motion in six-degree-of-freedom (6-DOF) integrated with the Euler-Rodriguez quaternion method for representing singularity-free AUV attitude and time-saving calculation, and with a nonlinear control model for maneuvering and depth control simulations, time-marching in the fourth-order Runge-Kutta scheme. For validation of the simulation codes, results of the ISiMI AUV open-loop tests including turning test and zigzag test as well as an AUV simulator on the basis of Euler-angle method were used to compare with the quaternion-based AUV simulator. The computational results from the proposed simulator agree well with those from both the ISiMI AUV experiments and the Euler-angle based simulations. Additionally, a new maneuvering procedure, namely "put-out" was implemented to test directional stability for a large-scale AUV in the proposed AUV simulator that can be considered for vehicles in space as well as in constrained planes. 相似文献
143.
144.
In conventional modal analysis procedures, usually only a few dominant modes are required to describe the dynamic behavior
of multi-degrees-of-freedom buildings. The number of modes needed in the dynamic analysis depends on the higher-mode contribution
to the structural response, which is called the higher-mode effect. The modal analysis approach, however, may not be directly
applied to the dynamic analysis of viscoelastically damped buildings. This is because the dynamic properties of the viscoelastic
dampers depend on their vibration frequency. Therefore, the structural stiffness and damping contributed from those dampers
would be different for each mode. In this study, the higher-mode effect is referred to as the response difference induced
by the frequency-dependent property of viscoelastic dampers at higher modes. Modal analysis procedures for buildings with
viscoelastic dampers distributed proportionally and non-proportionally to the stiffness of the buildings are developed to
consider the higher-mode effect. Numerical studies on shear-type viscoelastically damped building models are conducted to
examine the accuracy of the proposed procedures and to investigate the significance of the higher-mode effect on their seismic
response. Two damper models are used to estimate the peak damper forces in the proposed procedures. Study results reveal that
the higher-mode effect is significant for long-period viscoelastically damped buildings. The higher-mode effect on base shear
is less significant than on story acceleration response. Maximum difference of the seismic response usually occurs at the
top story. Also, the higher-mode effect may not be reduced by decreasing the damping ratio provided by the viscoelastic dampers.
For practical application, it is realized that the linear viscous damping model without considering the higher-mode effect
may predict larger damper forces and hence, is on the conservative side.
Supported by: Science Council, Chinese Taipei, grant no. 88-2625-2-002-006 相似文献
145.
146.
147.
In gravel-bedded streams where bed material of a tributary differs distinctly in lithology from that of the main stream, rock-type percentages can be used to estimate bed-load contributions of the two streams. The rock type that shows the greatest difference in abundance between the two streams is selected as the indicator lithology. Percentages of this lithology are estimated in both the main stream and tributary stream above their junction, and also in the main stream at a distance sufficiently downstream from the junction to allow complete mixing. The fraction of bed load contributed by the main stream, p,is estimated by
,where
is an estimate of the proportion of indicator rock fragments in the bed of the main stream above the junction,
is an estimate of the proportion in the bed of the tributary above the junction, and
is an estimate of the proportion in the bed of the main stream below the junction. The variance of
is obtained as var (
)= [p1q1(pr – p2)2/n(p1 – p2)4] + [p2q2(pr – p1)2/n(p1 – p2)4] + [prqr/n(p1 – p2)2].Although no estimate of actual quantity of bed load is provided, the indicator rock technique supplies data that can serve as a check on data obtained by means of empirical formulas or actual transport measurements. 相似文献
148.
The variation of the oxygen content in olivines, (Fe
x
Mg1−
x
)2SiO4, with 0.2 ≤ x ≤ 1.0, was investigated by thermogravimetric measurements. Mass changes occurring upon oxygen activity changes were measured
as a function of oxygen activity and cationic composition at 1130 and 1200 °C. During the measurements the samples were in
direct contact with gases containing CO, CO2 and N2 and, at a few spots at the bottom of the sample stack, also with SiO2. By fitting experimental data of mass changes to equations derived using point defect thermodynamics, it was shown for olivines
with 0.2 ≤ x ≤ 1.0 at 1130 °C and 0.2 ≤ x ≤ 0.7 at 1200 °C within the oxygen activity ranges investigated that the observed variations in the oxygen contents are compatible
with cation vacancies and Fe3+ ions on M sites and Fe3+ ions on silicon sites as majority defects if it is assumed that only three types of point defects occur as majority defects.
Different cases were considered, closed systems, taking into account that ξ=[Si]/([Si]+[Fe]+[Mg]) is not necessarily equal
to 1/3, and olivines in equilibrium with SiO2 or pyroxenes. The oxygen content variations observed in this study are significantly smaller than those reported previously
in the literature. It is proposed that these differences are related to the dissolution of Fe into noble metal containers
used as sample holders in earlier studies and/or to the presence of secondary phases.
Received: 1 November 1995 / Accepted: 15 September 2002
Acknowledgements This work was supported by the Cornell Center for Materials Research (CCMR), a Materials Research Science and Engineering
Center of the National Science Foundation (DMR-0079992). The authors thank Mr. Daniel M. DiPasquo and Mr. Jason A. Schick
for helping in experimental work. 相似文献
149.
A numerical searching procedure to find the optimum tuning frequency and damping ratio of the tuned-mass damper which can reduce the steady-state response of damped main systems to a minimum level is developed and applied to the two different harmonic excitation sources, support motion of fixed-displacement amplitude and support motion of fixed-acceleration amplitude. The explicit formulae for these optimum parameters are then derived through a sequence of curve-fitting schemes. It has been found that, as the error of the explicit formulae is negligible, they provide a convenient tool to compute the optimum parameters in engineering applications. The numerical results show that the tuned-mass damper is less effective in reducing the system's response when there is a high level of damping incorporated into the system. It is also found that the optimum tuning frequency is strongly influenced by the damping level of a system, especially in regard to the fixed-acceleration support motion, but the optimum damping ratio of the tuned-mass damper is not sensitive to the damping level of a system. The response of the damped system using the undamped optimum value as the damping of the tuned-mass damper is not much different from the response using the damped optimum value. 相似文献
150.
Hsiang-Chuan Tsai 《地震工程与结构动力学》1993,22(11):975-990
A tuned-mass damper is a small damped spring-mass system which vibrates in resonance with the main structure to which it is attached so as to be able to dissipate vibration energy and reduce the structural response. In this paper, explicit forms of Green's function for the transient response of main structures equipped with the tuned-mass damper and subjected to support excitation are derived by perturbation techniques and provide an insight into the characteristics of the damper. It is found that there exists a critical damping level for the tuned-mass damper. If the damper damping is higher than this critical damping level, increasing the damper damping will enhance the structural response. When the damper damping is below this critical value, something called ‘beat phenomenon’ occurs where the structure will have a smaller response in the first beat cycle, but have a higher rebound in the following beat cycles. 相似文献