Exploring Temporal Preservation Networks for Precise Temporal Action Localization

Temporal action localization is an important task of computer vision. Though a variety of methods have been proposed, it still remains an open question how to predict the temporal boundaries of action segments precisely. Most works use segment-level classifiers to select video segments pre-determined by action proposal or dense sliding windows. However, in order to achieve more precise action boundaries, a temporal localization system should make dense predictions at a fine granularity. A newly proposed work exploits Convolutional-Deconvolutional-Convolutional (CDC) filters to upsample the predictions of 3D ConvNets, making it possible to perform per-frame action predictions and achieving promising performance in terms of temporal action localization. However, CDC network loses temporal information partially due to the temporal downsampling operation. In this paper, we propose an elegant and powerful Temporal Preservation Convolutional (TPC) Network that equips 3D ConvNets with TPC filters. TPC network can fully preserve temporal resolution and downsample the spatial resolution simultaneously, enabling frame-level granularity action localization. TPC network can be trained in an end-to-end manner. Experiment results on public datasets show that TPC network achieves significant improvement on per-frame action prediction and competing results on segment-level temporal action localization

DYNAMIC EFFECTS OF EQUIVALENT TRUNCATED MOORING SYSTEMS FOR A SEMI-SUBMERSIBLE PLATFORM

Physical model tests of floater with full-depth mooring system present obstacles because no tank is sufficiently large to perform model testing in reasonable scale. This paper presents numerical simulation on design method of equivalent truncated mooring systems for model testing of offshore platforms in wave basin. Based on static and dynamic equivalent, two approaches are used to design the truncated mooring systems, respectively. Considering a semi-submersible platform with full-depth and corresponding two equivalent truncated mooring systems, the floater responses and mooring line tensions are compared. The feasibility of model test with equivalent truncated mooring systems is discussed

Mooring Line Damping Estimation for a Floating Wind Turbine

The dynamic responses of mooring line serve important functions in the station keeping of a floating wind turbine (FWT). Mooring line damping significantly influences the global motions of a FWT. This study investigates the estimation of mooring line damping on the basis of the National Renewable Energy Laboratory 5 MW offshore wind turbine model that is mounted on the ITI Energy barge. A numerical estimation method is derived from the energy absorption of a mooring line resulting from FWT motion. The method is validated by performing a 1/80 scale model test. Different parameter changes are analyzed for mooring line damping induced by horizontal and vertical motions. These parameters include excitation amplitude, excitation period, and drag coefficient. Results suggest that mooring line damping must be carefully considered in the FWT design

Comparative Analysis on Coupling Effects between an Innovative Deep Draft Platform and Different Mooring Models

In global responses analysis for an innovative deep draft multi-spar platform, three different types of the mooring system are considered, namely a catenary, a semi-taut and a taut mooring system. These three types of mooring systems have the same arrangements with similar static restoring force characteristics. In this paper, the platform motions and mooring responses in three different water depths ranging from 500 m to 1500 m are analyzed. The coupling effects between the spar platform and its mooring lines are investigated through a numerical simulation method. Free-decay and three hours simulations under certain sea state conditions in the South China Sea are executed. The specifi c numerical results and analysis conclusions would be helpful for mooring system selection and motion performance study in the preliminary design

Rethinking SIGN Training: Provable Nonconvex Acceleration without First- and Second-Order Gradient Lipschitz

Sign-based stochastic methods have gained attention due to their ability to achieve robust performance despite using only the sign information for parameter updates. However, the current convergence analysis of sign-based methods relies on the strong assumptions of first-order gradient Lipschitz and second-order gradient Lipschitz, which may not hold in practical tasks like deep neural network training that involve high non-smoothness. In this paper, we revisit sign-based methods and analyze their convergence under more realistic assumptions of first- and second-order smoothness. We first establish the convergence of the sign-based method under weak first-order Lipschitz. Motivated by the weak first-order Lipschitz, we propose a relaxed second-order condition that still allows for nonconvex acceleration in sign-based methods. Based on our theoretical results, we gain insights into the computational advantages of the recently developed LION algorithm. In distributed settings, we prove that this nonconvex acceleration persists with linear speedup in the number of nodes, when utilizing fast communication compression gossip protocols. The novelty of our theoretical results lies in that they are derived under much weaker assumptions, thereby expanding the provable applicability of sign-based algorithms to a wider range of problems

Dynamic responses analysis of submerged floating tunnel under impact load

Submerged floating tunnel (SFT) may be subjected to sudden impact loads such as submarine and shipwreck. Besides the local damage caused by impact, the overall transient dynamic response may also affect its driving safety. Based on the dynamic impact finite element software, the full-length model and the locally truncated accurate model with solid element of the SFT are established respectively. By applying different spring stiffness constraints on the boundary of the truncated model, its first three modes are consistent with the full-length model, thus their dynamic characteristics are basically the same. The truncated model is further used to simulate the impact of a massive object on the SFT under different impact velocities, impact mass, impact angles and impact positions. The velocity and mass of the impact object have positive influences on the peak contact force, the displacement amplitude of the tube and the length of the damaged area. When the impact angle is perpendicular to the SFT tube, the contact force, displacement amplitude and the damaged area are the largest. The change of the impact position has little effect on the contact force and the damage area, but it will affect the distribution of displacement amplitude

Modified p-y curves for monopile foundation with different length-to-diameter ratio

The soil reaction of the monopile foundation subjected to lateral loading in offshore wind turbines is typically assessed relying on p-y curves advocated by API. However, this method is inadequate for gradually increasing monopile diameters and significantly underestimates the lateral soil confinement. In the present works, a 3D pile-soil interaction finite element model was first established, considering the soil suction and strain hardening characteristics for the normally consolidated clay in China’s sea. Modifications to the p-y curves in API were accomplished in the comparative process between the lateral soil resistance-displacement curves retrieved from the finite element model and the representative expression. Furthermore, the prediction accuracy for the corrected p-y curves has been proved by forecasting the monopile lateral bearing capacity with varying length-to-diameter ratios, which also demonstrates that the modified p-y curves could successfully reflect the lateral soil confinement of the normally consolidated clay and flexible piles. It also provides an approach to assess the deformation response and horizontal ultimate bearing capacity of monopiles with different length-to-diameter ratios

Sealing of oil-gas reservoir caprock: Destruction of shale caprock by micro-fractures

The sealing ability of caprock is affected by many factors, such as cap thickness, displacement pressure, fracture development, and lithology of caprock. Shale is one of the ideal materials for oil and gas sealing cap formation due to its low porosity and permeability. Microfractures can destroy the sealing property of shale caprock. When buried deep enough, shale will change from toughness to brittleness. In general, the greater the brittleness of shale, the more developed the fractures will be. In areas with high tectonic stress, such as the anticline axis, syncline axis and stratum dip end, the strata stress is high and concentrated, and it is easier to generate fractures. When the stress state of the caprock changes, new micro-cracks are formed or previously closed cracks are re-opened, reducing the displacement pressure of the caprock. These micro-fractures are interconnected to form microleakage spaces, which reduces the sealing capacity of the caprock