Robust motion control of nonlinear quadrotor model with wind disturbance observer

This paper focuses on robust wind disturbance rejection for nonlinear quadrotor models. By leveraging on nonlinear unknown observer theory, it proposes a nonlinear dynamic filter that, using sensors already on-board the aircraft, can estimate in real-time wind gust signals in the three dimensions. The wind disturbance is then treated as input to the PD controller for a quick and robust flight pathway in presence of disturbances. With this scheme, the wind disturbance can be precisely estimated online and compensated in real-time. Hence, the quadrotor can successfully reach its desired attitude and position. To show the effective and desired performance of the method, simulation results are presented in Matlab/Simulink and ROS-enabled Gazebo platform

New flood risk index in tropical area generated by using SPC technique

This study applied four hydrology parameters. The findings from Principal ComponentAnalysis confirmed that all selected parameters were significant to be taken as main tools forfurther analysis with result of R2> 0.7. SPC set up a new control limit for all selectedparameters in the study area. For those data within or beyond the Upper Control Limit value, itwas being considered as high risk for flood occurrence. New flood risk index within rangefrom 0-100 was calculated using a combination of new algebraic equation and control limitvalues obtained from SPC analysis as variable. The accuracy of FRI was tested using ANN.The result showed the accuracy of FRI was more than 90%. It can be stipulated that thecombination of chemometric techniques and SPC can produce a new standard FRI which iscost effective, accurate and flexible to be applied for the purpose of flood risk control intropical area.Keywords: flood risk index; statistical process control; chemometric technique; tropical area;control limit; prediction performance

Potential of sea level rise impact on South China Sea: a preliminary study in Terengganu, Malaysia

The effect of the sea level rise was involved the existence of sea water intrusion and coastal erosion phenomenon in the coastal of Terengganu. This study aim to determine fluctuation of high and low tides of the South China Sea in their relation to water quality value of Marang and Paka Rivers as well as from wells monitoring along the Terengganu Coast. Sampling was carried out twice during high and low tides, first in November 2012 and was repeated in November 2015. For the river quality study, it involves six parameters and involves nine parameters for well survey. Two-way t-test was used under statistical analysis to differentiate between two samplings. The result of the study can be assured that sea level rise resulting in decreased concentration of salinity, EC and TDS from upstream to downstream as a result of qualitatively rise of sea level at Terengganu beach as an impact of global warming events.Keywords: Marang and Paka Rivers; water quality parameter; well water quality; sea level rise; South China Se

Air quality modelling using chemometric techniques

The datasets of air quality parameters for three years (2012-2014) were applied. HACA gave the result of three different groups of similarity based on the characteristics of air quality parameters. DA shows all seven parameters (CO, O3, PM10, SO2, NOx, NO and NO2) gave the most significant variables after stepwise backward mode. PCA identifies the major source of air pollution is due to combustion of fossil fuels in motor vehicles and industrial activities. The ANN model shows a better prediction compared to the MLR model with R2 values equal to 0.819 and 0.773 respectively. This study presents that the chemometric techniques and modelling become an excellent tool in API assessment, air pollution source identification, apportionment and can be setbacks in designing an API monitoring network for effective air pollution resources management

Investigation of Low-Pressure Bimetallic Cobalt-Iron Catalyst-Grown Multiwalled Carbon Nanotubes and Their Electrical Properties

A bimetallic cobalt-iron catalyst was utilized to demonstrate the growth of multiwalled carbon nanotubes (CNTs) at low gas pressure through thermal chemical vapor deposition. The characteristics of multiwalled CNTs were investigated based on the effects of catalyst thickness and gas pressure variation. The results revealed that the average diameter of nanotubes increased with increasing catalyst thickness, which can be correlated to the increase in particle size. The growth rate of the nanotubes also increased significantly by ~2.5 times with further increment of gas pressure from 0.5 Torr to 1.0 Torr. Rapid growth rate of nanotubes was observed at a catalyst thickness of 6 nm, but it decreased with the increase in catalyst thickness. The higher composition of 50% cobalt in the cobalt-iron catalyst showed improvement in the growth rate of nanotubes and the quality of nanotube structures compared with that of 20% cobalt. For the electrical properties, the measured sheet resistance decreased with the increase in the height of nanotubes because of higher growth rate. This behavior is likely due to the larger contact area of nanotubes, which improved electron hopping from one localized tube to another

Metal concentration at surface water using multivariate analysis and human health risk assessment

This study defined the concentration of metals in Kerteh and Paka River water and their potential health risk towards human. 54 water samples were collected and analyzed using ICP-OES. Results revealed that most of the stations in Kerteh River gave the higher concentration of Cd, Cu, Zn, Co, Ni, As, Cr and Pb compared to Paka River. However As, Cr and Pb have exceeded the permissible limit of Malaysia standard for all stations in both rivers. Cd, Cu, Zn, Co and Ni were below than Malaysian standard permissible levels during the sampling period. The principal component analysis (PCA) revealed that both geogenic and anthropogenic sources were responsible to possible metals contamination in both rivers. Moreover, risk assessments for all metals were within the safe limits, except for As in the Kerteh River for both adult and child as well as to Paka River for both genders

Clustering Imputation for Air Pollution Data

Air pollution is a global problem. The assessment of air pollution concentration data is important for evaluating human exposure and the associated risk to health. Unfortunately, air pollution monitoring stations often have periods of missing data or do not measure all pollutants. In this study, we experiment with different approaches to estimate the whole time series for a missing pollutant at a monitoring station as well as missing values within a time series. The main goal is to reduce the uncertainty in air quality assessment. To develop our approach we combine single and multiple imputation, nearest neighbour geographical distance methods and a clustering algorithm for time series. For each station that measures ozone, we produce various imputations for this pollutant and measure the similarity/error between the imputed and the real values. Our results show that imputation by average based on clustering results combined with multiple imputation for missing values is the most reliable and is associated with lower average error and standard deviation

Wind gust estimation for precise quasi-hovering control of quadrotor aircraft

This paper focuses on the control of quadrotor vehicles without wind sensors that are required to accurately track low-speed trajectories in the presence of moderate yet unknown wind gusts. By modeling the wind disturbance as exogenous inputs, and assuming that compensation of its effects can be achieved through quasi-static vehicle motions, this paper proposes an innovative estimation and control scheme comprising a linear dynamic filter for the estimation of such unknown inputs and requiring only position and attitude information. The filter is built upon results from Unknown Input Observer theory and allows estimation of wind and vehicle state without measurement of the wind itself. A simple feedback control law can be used to compensate for the offset position error induced by the disturbance. The proposed filter is independent of the recovery control scheme used to nullify the tracking error, as long as the corresponding applied rotor speeds are available. The solution is first checked in simulation environment by using the Robot Operating System middleware and the Gazebo simulator and then experimentally validated with a quadcopter system flying with real wind sources