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In this paper, the natural supercavitys are studied both experimentally and numerically. A series of supercavitating vehicle water-entry test are carried out at different speeds, where it is found that the minimum pressure in the cavity gradually reduced with the increase of water-entry speed. The cause for the evolution progress of natural supercavitation is difficult to get from the experiment,...
Developing a new sonar for side-scan imaging can be a complicated and expensive proposition. Sonar models and simulations can be used to alleviate some of the expense and time required for development by providing some early simulated imagery of proposed designs. This paper describes a modeling approach where inverse imaging techniques are applied in order to generate simulated stave-level sonar data...
We propose a swarm control algorithm for unmanned vehicles that adapts to unexpected environments while making the optimal formation. Our proposed algorithm, “autonomous and adaptive control”, is inspired by the control mechanism of living organisms and reconciles adaptability under a complex and changing environment and optimality for the various purposes of the system. In this paper, we apply the...
In order to accurately control the portable AUV, a dynamic modeling method based on computational fluid dynamics (CFD) and a improved Generalized Predictive Control (GPC) method were presented. First, the whole modeling process was described from two aspects: dynamic model derivation and model parameter identification. Second, the validity of the model and modeling method were tested by comparing...
In this paper, a time reversal technique is proposed to enhance detection performance. When the time reversal technique is applied to the response of the clutter with strong time varying characteristic of shallow water, it is hard to obtain a high peak response. However, in the case that a cylindrical object is placed on the seafloor, However, in the case that a cylindrical object is placed on the...
Vision methods are very commonly used in underwater robotics. However, the cameras must be enclosed in a sealed housing for which flat-pane windows are the most economical and hence most popular solution. But they cause non-trivial refraction-based distortions at the air-glass-water interface. Recently, a new model for underwater cameras calibration called Pinax was introduced, which combines aspects...
In this study, the effects of fin stroke phase offset, fin position offset, and flapping frequency on thrust production are investigated for tandem pectoral fins. Two different fin geometries are considered, one rectangular and one bio-inspired. Experimental results are supported with computational fluid dynamics (CFD) simulations, validating the experimental methods as well as the computational modeling...
During an oil spill, an accurate assessment of the trajectory of oil is important for a quick and effective remediation response. In the remote Arctic, oil fate and transport models are critical; especially during winter months when darkness and ice presence hamper visual detection of oil. A set of equations to describe the transport of oil in ice-covered waters and an environmental database were...
Simulation of unmanned underwater vehicles (UUVs) plays an important role in the development of submarine robots. The test of controllers in different simulated scenarios is crucial in order to avoid the lengthy development on the real vehicle. Robot simulators like Gazebo have been extensively used for this purpose, even if off-the-shelf physic engines do not consider one of the main aspects of hydrodynamics:...
In this study, virtual planar-motion-mechanism (PMM) tests in pure sway motion at constant forward speed are carried out to determine the sway added mass values of a 6:1 prolate spheroid. Added mass values are obtained by solving the Euler equations and the Reynolds Averaged Navier-Stokes (RANS) equations across a range of frequencies and depths. The effect that distance from the surface and radiation...
Explosive naval mines pose a threat to ocean and sea faring vessels, both military and civilian. This work applies deep neural network (DNN) methods to the problem of detecting minelike objects (MLO) on the seafloor in side-scan sonar imagery. We explored how the DNN depth, memory requirements, calculation requirements, and training data distribution affect detection efficacy. A visualization technique...
This study investigates near-shore circulation and wave characteristics applied to a case-study site in Monterey Bay, California. We integrate physics-based models to resolve wave conditions (based on inputs from a global wave model, wind data from an operational weather platform, and predictions from a regional flow model) together with a linear machine learning algorithm that combines forecasts...
In this study, numerical investigations of flow characteristics of a pumpjet propulsor based on Computational Fluid Dynamics (CFD) method have been presented. The Zwart-Gerber-Belamri (Z-G-B) cavitation model based on the Reynolds Averaged Navier-Stokes (RANS) method is employed. The structured gird is applied. A four-blade skewed E779A propeller has been used to verify the numerical method. The comparison...
Modeling the spatial variation of resources is necessary because it gives an estimate of what to expect during their exploration and exploitation. We focus on the spatial modeling of polymetallic nodules found in the deep sea regions of the Clarion-Clipperton zone in the Pacific. The data from this region available in the open domain is sparse, which warrants modeling techniques that can efficiently...
A set of Matlab tools were developed to create seafloor mosaics from AUV photosurveys. The resulting mosaic products are used to guide instrument placement, ground-truth acoustic backscatter targets, and inspect sensor packages or other targets. Because of the positional sensitivity of these tasks, effort has been made to preserve the geographic distribution of the image content. After initial image...
A software tool has been developed to simulate the entanglement of leatherback sea turtles (Dermochelys coriacea) in fishing and aquaculture gear. Entanglements are well documented and are increasing in frequency due to greater fishing effort and with the use of synthetic materials in marine applications. However relatively little is known about how entanglements occur and how they might be prevented...
Autonomous underwater vehicles (AUV) are important resources to be used in the oil exploration industry in deep waters as well as a platform for scanning devices used in open sea regions of difficult human access. This work aims to analyze through computer simulations the influence of marine currents on the maneuverability of a flatfish shaped AUV. The 3D realistic scale simulations were performed...
The National Tsunami Warning Center (NTWC) and the Pacific Tsunami Warning Center (PTWC) collaborate to provide tsunami warning service and mutual backup to tsunami-threatened areas throughout the United States and many other countries throughout the world. With mostly home-grown analysis systems, NTWC staff rapidly locates, sizes, and otherwise characterizes major earthquakes. We determine each earthquake's...
In order to analyze the dynamic performance of a Remotely Operated Vehicle (ROV) during mission like ship hull inspection, it is necessary to establish the 6 degree-of-freedom equations of motion considering well modeled hydrodynamic force acting on a ROV. Typically, the hydrodynamic force is the model by polynomial functions and those coefficients are obtained by captive model tests or empirical...
A sequential space carving method has been developed for the 3-D reconstruction of objects from multitude of forward-look sonar images captured at known sonar poses [1]. The 3-D space within common viewing volume of several camera poses is divided into small volumetric pixels (voxels). Projecting each onto various images, all voxels satisfying certain consistency measure are maintained. Conversely,...
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