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2022 ◽  
Vol 4 (1) ◽  
Qianrong Li ◽  
Baoji Zhang

The resistance performance and motion stability of deep sea remotely operated vehicles (ROVs) subjected to underwater motion conditions are studied on the basis of the unsteady Reynolds-averaged Navier-Stokes method combined with the six-degree-of-freedom equation of motion to quickly and accurately predict them. In the modeling process, we consider the complexity of ROV geometry and thus reduce the model to a series of regular geometries to maximize the position and weight of the original components. The grid and value slots of an ROV are divided, and the surface is reconstructed. The forward, backward, transverse, floating, and submerged resistance of ROVs are simulated and compared with existing experimental forces to determine the accuracy of the calculation method. Then, the oblique navigation of the ROV on the horizontal and vertical planes is studied. Furthermore, the motion response of the ROV to direct horizontal motion, heave, pitch, and yaw are studied. The force, moment, and motion time curves are obtained. The stability of ROV motion is analyzed to provide technical support for the safety of ROVs.

2021 ◽  
Vol 105 (0) ◽  
pp. 3-33
E. Scalas ◽  
B. Toaldo

We consider plain vanilla European options written on an underlying asset that follows a continuous time semi-Markov multiplicative process. We derive a formula and a renewal type equation for the martingale option price. In the case in which intertrade times follow the Mittag-Leffler distribution, under appropriate scaling, we prove that these option prices converge to the price of an option written on geometric Brownian motion time-changed with the inverse stable subordinator. For geometric Brownian motion time changed with an inverse subordinator, in the more general case when the subordinator’s Laplace exponent is a special Bernstein function, we derive a time-fractional generalization of the equation of Black and Scholes.

Aidin Tamhidi ◽  
Nicolas Kuehn ◽  
S. Farid Ghahari ◽  
Arthur J. Rodgers ◽  
Monica D. Kohler ◽  

ABSTRACT Ground-motion time series are essential input data in seismic analysis and performance assessment of the built environment. Because instruments to record free-field ground motions are generally sparse, methods are needed to estimate motions at locations with no available ground-motion recording instrumentation. In this study, given a set of observed motions, ground-motion time series at target sites are constructed using a Gaussian process regression (GPR) approach, which treats the real and imaginary parts of the Fourier spectrum as random Gaussian variables. Model training, verification, and applicability studies are carried out using the physics-based simulated ground motions of the 1906 Mw 7.9 San Francisco earthquake and Mw 7.0 Hayward fault scenario earthquake in northern California. The method’s performance is further evaluated using the 2019 Mw 7.1 Ridgecrest earthquake ground motions recorded by the Community Seismic Network stations located in southern California. These evaluations indicate that the trained GPR model is able to adequately estimate the ground-motion time series for frequency ranges that are pertinent for most earthquake engineering applications. The trained GPR model exhibits proper performance in predicting the long-period content of the ground motions as well as directivity pulses.

2021 ◽  
Vol 27 (8) ◽  
pp. 770-772
Lei Ma

ABSTRACT Introduction: Phosphate (CP) its biosynthesis begins with the kidney. Glycocianine was synthesized from glycocianine, then methylated in the liver, and finally formed in each tissue. Objective: To study the effects of phosphatic acid in exercise training. Methods: This paper uses 50 pure male mice, 2 month old, weight at 22 ± 3 g, and mice per day, 5 minutes each time. After exercise training, dry dry with a towel and blow it with a hair dryer, and move it to the end of each other. Results: The average time of motion B mouse to give phosphate creatine is significantly longer than the average time of the non-administration of the A group, and the motion time is prolonged to extend 23.20%. Phosphate has improved motor endurance and promotes improvement in muscle microcirculation during exercise. Conclusions: Motion can be used to improve the maximum aerobic capacity of exercise in motion. Level of evidence II; Therapeutic studies - investigation of treatment results.

2021 ◽  
Vol 9 ◽  
Jiawei Li ◽  
Maren Böse ◽  
Yu Feng ◽  
Chen Yang

Earthquake early warning (EEW) not only improves resilience against the risk of earthquake disasters, but also provides new insights into seismological processes. The Finite-Fault Rupture Detector (FinDer) is an efficient algorithm to retrieve line-source models of an ongoing earthquake from seismic real-time data. In this study, we test the performance of FinDer in the Sichuan-Yunnan region (98.5oE–106.0oE, 22.0oN–34.0oN) of China for two datasets: the first consists of seismic broadband and strong-motion records of 58 earthquakes with 5.0 ≤ MS ≤ 8.0; the second comprises additional waveform simulations at sites where new stations will be deployed in the near future. We utilize observed waveforms to optimize the simulation approach to generate ground-motion time series. For both datasets the resulting FinDer line-source models agree well with the reported epicenters, focal mechanisms, and finite-source models, while they are computed faster compared to what traditional methods can achieve. Based on these outputs, we determine a theoretical relation that can predict for which magnitudes and station densities FinDer is expected to trigger, assuming that at least three neighboring stations must have recorded accelerations of 4.6 cm/s2 or more. We find that FinDer likely triggers and sends out a report, if the average distance between the epicenter and the three closest stations, Depi, is equal or smaller than log10 (Ma + b) + c, where a = 1.91, b = 5.93, and c = 2.34 for M = MW ≥ 4.8, and c = 2.49 for M = MS ≥ 5.0, respectively. If the data used in this study had been available in real-time, 40–70% of sites experiencing seismic intensities of V-VIII (on both Chinese and MMI scales) and 20% experiencing IX-X could have been issued a warning 5–10 s before the S-wave arrives. Our offline tests provide a useful reference for the planned installation of FinDer in the nationwide EEW system of Chinese mainland.

2021 ◽  
Vol 18 (13) ◽  
pp. 4059-4072
Toby D. Jackson ◽  
Sarab Sethi ◽  
Ebba Dellwik ◽  
Nikolas Angelou ◽  
Amanda Bunce ◽  

Abstract. Interactions between wind and trees control energy exchanges between the atmosphere and forest canopies. This energy exchange can lead to the widespread damage of trees, and wind is a key disturbance agent in many of the world's forests. However, most research on this topic has focused on conifer plantations, where risk management is economically important, rather than broadleaf forests, which dominate the forest carbon cycle. This study brings together tree motion time-series data to systematically evaluate the factors influencing tree responses to wind loading, including data from both broadleaf and coniferous trees in forests and open environments. We found that the two most descriptive features of tree motion were (a) the fundamental frequency, which is a measure of the speed at which a tree sways and is strongly related to tree height, and (b) the slope of the power spectrum, which is related to the efficiency of energy transfer from wind to trees. Intriguingly, the slope of the power spectrum was found to remain constant from medium to high wind speeds for all trees in this study. This suggests that, contrary to some predictions, damping or amplification mechanisms do not change dramatically at high wind speeds, and therefore wind damage risk is related, relatively simply, to wind speed. Conifers from forests were distinct from broadleaves in terms of their response to wind loading. Specifically, the fundamental frequency of forest conifers was related to their size according to the cantilever beam model (i.e. vertically distributed mass), whereas broadleaves were better approximated by the simple pendulum model (i.e. dominated by the crown). Forest conifers also had a steeper slope of the power spectrum. We interpret these finding as being strongly related to tree architecture; i.e. conifers generally have a simple shape due to their apical dominance, whereas broadleaves exhibit a much wider range of architectures with more dominant crowns.

2021 ◽  
Vol 54 (3) ◽  
pp. 503-509
Hicham Zatla ◽  
Bilal Tolbi ◽  
Fares Bouriachi

The aim of the present research is to find an optimal reference trajectory for an underactuated manipulator of type Xn-1Rp, where X is any type of joints and R is the last rotary joint, for n≥3. It is worth noting that in the case of absence of control of fully actuated manipulator, some second-order nonholonomic constraints may appear; these are known as acceleration constraints. The second-order nonholonomic constraint is a non-integrable differential equation. For this purpose, it was decided to combine two methods. The first one provides the open-loop control of the manipulator whatever the motion time is; in practice, the motion time should be minimal under the given geometric, technological, and dynamic constraints. To address this issue, a second method, based on the offline optimization approach, was used to achieve the time-optimal motion. It was revealed that the above combination gives an optimal control trajectory for an underactuated manipulator in which a reference trajectory can be utilized.

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