Prediction of Ship Heave Motion Using Regularized BP Neural Network with Cross Entropy Error Function

Accurate prediction of ship’s heave motion can greatly enhance the safety of offshore operation. Due to its complexity and nonlinearity, however, ship’s heave motion prediction is a difficult task to be solved. In this paper, a new method for predicting ship’s heave motion is proposed based on an improved back propagation neural network (IBPNN). To overcome the gradient saturation phenomenon of traditional BPNN, the mean square error (MSE) loss function is replaced with a cross entropy (CE) loss function in IBPNN. Meanwhile, the weights of IBPNN is regularized by $$L_2$$ L 2 norm to enhance the generalization ability of traditional BPNN. Finally, conjugate gradient method is adopted to train IBPNN. The IBPNN is used to predict ship’s heave motion and the prediction results prove its effectiveness.

Remote Sensing of Tropical Rainforest Biomass Changes in Hainan Island, China from 2003 to 2018

The largest area of tropical rainforests in China is on Hainan Island, and it is an important part of the world’s tropical rainforests. The structure of the tropical rainforests in Hainan is complex, the biomass density is high, and conducting ground surveys is difficult, costly, and time-consuming. Remote sensing is a good monitoring method for biomass estimation. However, the saturation phenomenon of such data from different satellite sensors results in low forest biomass estimation accuracy in tropical rainforests with high biomass density. Based on environmental information, the biomass of permanent sample plots, and forest age, this study established a tropical rainforest database for Hainan. Forest age and 14 types of environmental information, combined with an enhanced vegetation index (EVI), were introduced to establish a tropical rainforest biomass estimation model for remote sensing that can overcome the saturation phenomenon present when using remote sensing data. The fitting determination coefficient R2 of the model was 0.694. The remote sensing estimate of relative bias was 2.29%, and the relative root mean square error was 35.41%. The tropical rainforest biomass in Hainan Island is mainly distributed in the central mountainous and southern areas. The tropical rainforests in the northern and coastal areas have been severely damaged by tourism and real estate development. Particularly in low-altitude areas, large areas of tropical rainforest have been replaced by economic forests. Furthermore, the tropical rainforest areas in some cities and counties have decreased, affecting the increase in tropical rainforest biomass. On Hainan Island, there were few tropical rainforests in areas with high rainfall. Therefore, afforestation in these areas could maximize the ecological benefits of tropical rainforests. To further strengthen the protection, there is an urgent need to establish a feasible, reliable, and effective tropical rainforest loss assessment system using quantitative scientific methodologies.

On the Positioning of a Piezoelectric Material in the Energy Harvesting From a Nonideally Excited Portal Frame

In this paper, we consider the application of the piezoelectric energy harvesting using a portal frame structure of two-degrees-of-freedom. The piezoelectric material is considered as a linear device using a capacitive mathematical model. The portal structure is of two-degrees-of-freedom considering with quadratic coupling between the first and second modes of vibration. 2:1 internal resonance between the first and second modes is set, which is a particular condition of this type of system due to the appearance of a saturation phenomenon. As this phenomenon causes the system to start vibrating from the second mode and, at steady-state, vibrates at the first mode, the objective of this work is to verify the energy uptake, considering the different positioning of a piezoelectric material, which is coupled to the supported beam and/or to the column. In addition, the structure is excited by a nonideal DC motor with a limited power supply. The results show a considerably nonlinear behavior due to the nonideal motor, and, with the saturation phenomenon, it is more efficient to collect energy by coupling the PZT to the column. The investigation of the stability of the system due to the piezoelectric coefficient Θ is also taken into account, which is carried out by numerical tools as phase planes, Poincare maps, bifurcation diagrams, and 0–1 test.

A commentary review on the use of normalized difference vegetation index (NDVI) in the era of popular remote sensing

The Normalized Difference Vegetation Index (NDVI), one of the earliest remote sensing analytical products used to simplify the complexities of multi-spectral imagery, is now the most popular index used for vegetation assessment. This popularity and widespread use relate to how an NDVI can be calculated with any multispectral sensor with a visible and a near-IR band. Increasingly low costs and weights of multispectral sensors mean they can be mounted on satellite, aerial, and increasingly—Unmanned Aerial Systems (UAS). While studies have found that the NDVI is effective for expressing vegetation status and quantified vegetation attributes, its widespread use and popularity, especially in UAS applications, carry inherent risks of misuse with end users who received little to no remote sensing education. This article summarizes the progress of NDVI acquisition, highlights the areas of NDVI application, and addresses the critical problems and considerations in using NDVI. Detailed discussion mainly covers three aspects: atmospheric effect, saturation phenomenon, and sensor factors. The use of NDVI can be highly effective as long as its limitations and capabilities are understood. This consideration is particularly important to the UAS user community.

INTEGRATED STATE VARIABLE OF PERSISTENT CONTACT JOINTS OF PARTS OF CUTTERS WITH BLOCK-MODULAR STRUCTURE

The increase in the health of block cutters when achieving the operational characteristics of persistent contact joints of their elements is considered. The results of changes in the regulated parameters of the surface profile of the block housing using the saturation phenomenon are presented. The operational characteristics of block cutters change their values during operation, due to wear of frequently replaced parts (for example, 100 changes of cutting blocks correspond to the operating mode of contacting surfaces when normal pressure is applied at Pn = 10 MPa and relative speed of 10 m/min per 1 minute), as well as elastoplastic deformations of their elements. By these characteristics we mean the performance (rigidity of the structure, the flexibility of its parts, etc.) tools. Their change causes deviations of the specified properties of the surfaces of the parts of the cutters from the set values. Preset properties include the state of contact when irregularities in the profile of the deformable surface fill the depressions of the contacted surface. In order to minimize such deviations, it is necessary to achieve a state of the surface layer of contact pairs of elements so that these parameters stabilize (reach equilibrium values) during operation. For this, it is proposed to use the complex state variable of the surface layer for contact compounds with saturation.