Applied Mechanics and Materials Vol. 225

Abstract: A load cell is an important component in measuring thrust generated by rocket in rocket technology research and development. It aims to test the rocket thrust in achieving the targeted objectives of the project. A load cell is a transducer that is used to convert a force into electrical signal and it usually consists of four strain gauges assembled in Wheatstone bridge configuration. The strain gauge converts the deformation (strain) to electrical signals. This conversion occurs in two stages. First, the strain gauges on the load cell will detect the deformation of load cell structure (tension or compression) and second, the strain gauge will convert the changes in the load cell in terms of voltage readings. Before the load cell can be used as the thrust sensor in rocket testing, it must undergo a calibration process to determine the relation between Load (kg) and Voltage (V). LabVIEW is used as a platform for data logging interface which is connected to the National Instrument hardware. National Instrument hardware acts as a signal conditioning which allow the voltage readings acquired by load cell to be collected and analyzed by LabVIEW. Each load cell has its own equation that links between force and voltage. The equation is used as a reference to convert the voltage reading to thrust.

Abstract: The escalating number of occurrences of natural hazards such as landslides has raised a great interest among the geoscientists. Due to the extremely high number of point’s returns, airborne LiDAR permits the formation of more accurate DEM compared to other space borne and airborne remote sensing techniques. This study aims to assess the capability of LiDAR derived parameters in landslide susceptibility mapping. Due to frequent occurrence of landslides, Ulu Klang in Selangor state in Malaysia has been considered as application site. A high resolution of airborne LiDAR DEM was constructed to produce topographic attributes such as slope, curvature and aspect. These data were utilized to derive secondary deliverables of landslide parameters such as topographic wetness index (TWI), surface area ratio (SAR) and stream power index (SPI). A probabilistic based frequency ratio model was applied to establish the spatial relationship between the landslide locations and each landslide related factors. Subsequently, factor ratings were summed up to yield Landslide Susceptibility Index (LSI) and finally a landslide susceptibility map was prepared. To test the model performance, receiver operating characteristics (ROC) curve was carried out together with area under curve (AUC) analysis. The produced landslide susceptibility map demonstrated that high resolution airborne LiDAR data has huge potential in landslide susceptibility mapping.

Abstract: Ionospheric layer plays an important role as the main medium for communication of wireless radio in the High Frequency (HF) band. Critical frequencies are important parameters of the ionosphere. Critical frequencies vary diurnally following the pattern of day and night due to the activities of the sun. The critical frequency for Parit Raja station is determined using an ionosonde at latitude 1° 52' N and longitude 103° 48' E, which are close to the geomagnetic equator at geographic latitude 5° N. This work analyses the dependence of the critical frequency during the solar minimum of Solar Cycle 23. From the observations, the critical frequency observed in 2005 was the highest, corresponding to a higher sunspot number of between 11 and 192. The general trend of the daily critical frequency was 6.8 MHz to 12.0 MHz from 00:00 to 17:30 Coordinated Universal Time (UTC) and decreasing to 7.0 MHz from 18:00 to 23:00 UTC. The average value of the critical frequency for 2005 to 2007 was 7.5 MHz, with a minimum of 1.8 MHz and a maximum of 11.0 MHz. The results showed a slow decrease from 2006 to 2007 for the critical frequencies in 2006 and 2007.

Abstract: What it is like to sleep in zero gravity Is it ever occurred to you Sleep is actually a physical and mental resting state in which a person becomes relatively inactive, unaware of the environment, and is partially detachment from the world. It is a challenge for architects to design in a very extreme environment, which has different gravity, radiation exposure to avoid, the absence of basic needs (water, oxygen, etc.), sense of orientation (where is the top and where is the bottom) etc. The lack of ability for human to stand straight in zero gravity environment – fetal position – leads to the choosing of that position for designing sleeping compartment in space – mimicking a sleeping baby, which is, in fact, the healthiest sleeping position. This idea becomes our guideline in proposing the design of a sleeping compartment in zero gravity, particularly in space station. It gives potential advantage for reducing the payloads of habitat module; size and weight, which is a common problems in space travel; mainly for reducing fuel and cost. But on the other hand, the quality of a good sleep should be considered, which is the main aspect of this design. What is a feasible sleeping compartment design for optimizing those needs This research uses a design exploration approach to solve the problems and to find a suitable solution. The end result from this activity is S.H.E.E.P; Safe Haven with Ergonomics and Effective Performance. This sleeping compartment design is a private space for crew to rest comfortably without any interference from the external environment. This compartment is also equipped with necessary tools.

Abstract: In this paper, the Proportional-Derivative (PD) based attitude control algorithm of the gravity gradient stabilized satellite has been developed. The satellite is equipped with 3 magnetic torquers where each of the magnetic torquer is placed along the +x, +y, +z axes. The control torque is generated when the magnetic field generated by the magnetic torquers couples with the geomagnetic fields, whereby the vector of the generated torque is perpendicular to both the magnetic fields. The developed control algorithm was simulated using the complex and simplified geomagnetic field models for a Low Earth Orbit (LEO) satellite mission in a nominal attitude operation. Results from simulations exhibit the effectiveness of the attitude control torque generation that fulfills the mission attitude control requirements.

Abstract: The paper focuses on applying optimal control solutions to combined energy storage and attitude control system (CEACS) under different reference missions. In previous researches, the proportional-integral-derivative (PID) control method, the PID-active force control method and H₂ control were tested for CEACS and achieved its mission requirement. However, problems such as the in-orbit system uncertainties affect the PID control performances. Thus, two optimal control methods, H₂ and H_∞ controls are proposed and tested on CEACS under different mission scenarios to improve its pitch attitude accuracy. Results show that both H₂ and H_∞ are able to achieve the reference mission requirement even under the influence of uncertainties (non-ideal). Moreover comparison between H₂ and H_∞ shows the H₂ is a better control option for CEACS in terms of disturbance rejection.

Abstract: In an unprecedented experimental investigation, a binary, a ternary and a four-component hydrocarbon mixture at different pressure have been studied in a nearly convection free environment to understand the thermodiffusion process. Experimental investigations of the mixtures have been conducted in space onboard the spacecraft FOTON-M3. The experiment objective was to measure the thermodiffusion coefficient for multi-component hydrocarbon mixtures. Then the experimental results have also been used to test a thermodiffusion model that has been calibrated based on the results of previous experimental investigations. Results showed a good agreement with current theoretical results except for the four-component system where discrepancies were found and discussed.

Abstract: Ground operation software (GOS) plays an important role in satellite operations. The software need to be able to retrieve, decode, display and archive the telemetry data as well as send command to control the satellite. These are mandatory functions which will allow satellite operators to communicate and command the satellite in ensuring its mission is executed as designed. Researchers in Agensi Angkasa Negara (ANGKASA) are currently developing a picosatellite as a research project using various Commercial Off-The-Shelf (COTS) components. Even the software algorithm and coding are being developed from scratch. Compared to bigger sized satellites, the picosatellite has a much simpler architecture, modules and mission, thus the required functions on GOS are greatly reduced. The communication protocol used is unique yet simple, which means the GOS will not require any additional modules to understand and interpret either the telemetry data or payload data received as it is already in an easy-to-understand format. GOS was developed using .Net platform with several modules for easy maintenance and expansion of the system. Closed-loop simulation was applied to test the functionalities of GOS as well as for debugging purposes. Results of the simulation are presented at the end of the paper. In conclusion, the GOS may require a few upgrades due to a change of hardware. However, it will still remain as the main reference for future development of GOS.

Abstract: Total electron content (TEC) is a highly non-linear ionospheric parameter that is strongly affected by changes in the solar activity. Reliability of space-based systems is affected by TEC and hence requires the development of a good model to nowcast and forecast its variability. Therefore, the aim of this paper is to present a Neural Networks (NN) model to predict the TEC variability. Slant TEC (sTEC) from the GPS Ionospheric Scintillation and TEC Monitor (GISTM) receiver is calculated and converted to vertical TEC (vTEC) based on the Single Layer Model (SLM). As a preliminary study, only one variable is considered as an input parameter for the NN, which is the hourly vTEC values and this is used to train the network with feed forward back propagation (BP) algorithm. The data set is the observed TEC for April and May 2005. Absolute maximum error and root mean square error (RMSE) are then calculated for each trained NN to evaluate the performance of the model. Analysis of the results reveals that, on average, the NN model is capable to predict TEC values but however extended input data set is needed to improve the generalization capability and reliability of the model. The highest absolute maximum error is 17 TECU and the smallest absolute maximum error is 6 TECU. The RMSE values for May 27 to May 30 are 1 TECU, 4 TECU, 5 TECU and 1 TECU, respectively.

Abstract: In recent years, the growth of urban populations in hazardous areas has increased the impact of natural disasters in both developed and developing countries. The purpose of the current study is to assess the landslide susceptibility in Kalaleh township of Golestan province, Iran. In this study the Shannon’s entropy approach was applied. A total of 82 landslide locations were identified primarily from aerial photographs and field surveys. Then eighteen landslides conditioning factors were prepared in GIS. These landslide conditioning factors are: slope degree, slope aspect, altitude, plan curvature, profile curvature, tangential curvature, surface area ratio (SAR), lithology, land use, soil texture, distance from faults, distance from rivers, distance from roads, fault density, road density, topographic wetness index (TWI), stream power index (SPI), and sediment transport index (STI). Using these conditioning factors, landslide susceptibility index was calculated using Shannon’s entropy. For model validation, the results of the analyses were then compared with the field-verified landslide locations. Additionally, the receiver operating characteristics (ROC) curves for landslide susceptibility maps were drawn and the area under curve values was calculated. Verification results showed 82.15% accuracy. According to the results of the AUC (area under curve) evaluation, the map produced exhibits satisfactory properties.