Applied Mechanics and Materials Vol. 771

Abstract: Since the Lusi Mud volcano erupts in Sidoarjo, East Java, on May 2006, soil embankments have been built to keep hot mud within the ponds. Unfortunately, since the embankments were sitting on a poorly weak ground, land subsidence intensively occurred around the embankments. These subsidences are mainly caused by water seepage penetrating the embankment. To observe the part of the embankment that is vulnerable to water seepage, DC Resistivity method, being a non-destructive and versatile method, is used to monitor the subsurface condition of the embankment. P.79 - P.82 embankment, which has collapsed on December 2010 is highlighted in this study because it has the lowest height of all part the embankment, directly adjacent with water from the mud volcano in the inside and field crop on the outside. The research will show the fluctuating results of the water seepage in the embankment during the timeline of February 2012 - October 2013 which, unlike the result of another area, is highly affected by the water level at each measurement. The embankment height during each DC Resistivity measurement is also measured to compare the subsurface result with the condition on the surface. The resistivity subsurface cross section shows increasing water seepage in each measurement (February 2012, July 2012 and October 2013). Alarming seepage level displayed in December 2012 which is presumably triggered by the increase of water level during rainy season is also followed by cracks occurred in the surface.

Abstract: It has been determined the best mother wavelet for stock prediction of SONY 2006 and BNI 2012 based on the Adaplet Method (The Adaptive Filter which is use wavelet as initial coefficients). The Mother Wavelets, which is used, are Coiflet 1-5, Daubechies 1-5, and Symlet 1-5. The prediction analysis includes overshoot, autocorrelation error and data pattern conformity, three days prediction, and segmentation. According to the overshoot analysis, it shown that for all the data, the overshoot at the beginning of data increased as its wavelet level increased. While using Daubechies 1 and Symlet 1 produced smallest overshoot among other wavelets (112.2%). The autocorrelation error of data pattern prediction indicates conformity with the original data. As its wavelet level increased, the autocorrelation error pattern also ramped (near zero). Coiflet 5 and Daubechies 1 produced the smallest mean square error (MSE), which is equal to 0.0147; meanwhile, Coiflet 1 shows the best result with an average error of 0.001 in next three days prediction analysis. On the other hands, Symlet 3 shows the best MSE of 1.213. Symlet offers the best result, according to best wavelet sequence assessment of each method.

Abstract: Vibration characteristic of a structure is unique due to mainly its material and geometrical properties. Hence, a variation imposed on either one or both the parameters can cause a different vibration response. This fact can be used to develop an alternative approach in testing the purity of gold particularly when the gold bar (Au) is no longer isotropic material due to the presence of other metals. A fake gold bar is commonly made by filling inside of the bar with other material for example Tungsten or Wolfram (W) which has density nearly the same as gold but its price is cheaper. This can not be identified easily without performing a testing as it has the same appearance as the pure gold bar. The purpose of this research is to develop gold bar purity testing method by observing natural frequencies and Frequency Response Function (FRF) of vibration response. For early development, the vibration response of gold bar and fake one are investigated. For this, numerical calculations are used rather than measurements. The results show that the natural frequencies and frequency response function (FRF) are useful information to detect whether a metal bar is pure gold bar or containing other metals. Higher natural frequency orders are required when the volume of tungsten in the bar reduces as the gap of lower order natural frequencies of pure gold bar and the fake become small. Moreover, the excitation point at corner and central of area of gold bar are suggested to be chosen during purity testing

Abstract: Study of EHD flow by using generator corona discharge with electrodes configuration of pin to multi concentric rings (MCR) and pin to single ring (SR) have been curried out. We measured the velocity of EHD flow and determined the comparison of velocity of EHD flow produced by pin to single ring electrodes. The pin needle was made by stainless steel with a length of 50 mm and a tip diameter of 0.14 mm. The multi-ring electrodes constracted by three concentric rings with a metal material connected to each other and each ring has a diameter of 24 mm, 16 mm and 8 mm in width and the same ring thickness is 2 mm and 3 mm. Single ring electrode has a diameter, width and thickness respectively 24 mm , 3 mm and 2 mm. EHD was generated by using a DC high voltage of 10 kV. Pin as an active electrode of corona discharge and concentric rings multi/single ring electrodes as ions collector and passive electrodes. The velocity of EHD flow was measured by a hot-wire anemometer. We found that the velocity of EHD flow with multi-ring concentric electrodes larger than a single ring electrode. The measurement of velocity for two cases of electrodes configuration were limited at the certain voltage due to breackdown and arc phenomena. The maximum velocity of the of EHD flow using a pin-multi rings concentric was 0.7 m/s at a voltage of 6 kV.

Abstract: Wood hardness is an important property for flooring, furniture products and structural utilization. Currently wood hardness can only be measured using destructive testing. As there is no suitable method for predicting wood hardness from standing trees, developing a non-destructive technique to predict wood hardness from plantations trees would provide significant benefits for evaluating optimal silvicultural treatments, and for selecting trees for tree improvement programs. It is proposed initillay that a possible non-destructive test may be developed using „crystallinity“ characteristics (degree of crystallinity (DC), crystalite width (CW) and length (CL) and microfibril angle (MFA)) determined using X-Ray diffraction. The aim of this study was to test the feasibility of using crystallinity as a non-destructive indicator of wood hardness. Experimentally, nine trees were taken representing small, medium and large diameter from five-year old fast growing teak plantation forest in Ciampea, Bogor, Indonesia. Wood hardness and crystallinity were determined following a standard testing regime. The results showed that MFA was negatively related to all hardness directions. Crstallite width only influenced side hardness with negative correlation, while degree of crystallinity only affected the end-grain hardness with positive correlation. Different vertical positions within tree only influenced the end-grain hardness value, while different radial positions had no effect on wood hardness. The optimum sampling height was found to be 80 cm, 130 cm, and 100 cm for radial, tangential and end-grain hardness, respectively. The relationship was based on the height that provided the highest correlation with the whole tree hardness values. Proposed models involving density and „crystallinity“ for predicting wood hardness are presented. While the R² from the proposed models was mostly less than 0.50, however, the approach described provides a new way to predict wood hardness from 10 mm increment cores at standing trees.

Abstract: In agriculture industry, natural produce classification is used in sorting, grading, measuring, and pricing. Currently, a lot of methods have been developed using computer vision to replace human expert in natural produce classification. However, some of the method used long features descriptor and complex classifier to obtain high classification rate. This paper proposes natural produce classification method using computer vision based on simple statistical color features and derivative of radius function. The k-nearest neighbors (k-NN) and artificial neural network (ANN) were used to classify the produce based on the extracted features. Preliminary experiment results show that the proposed method achieved best result with average classification accuracy of 99.875% using ANN classifier with nine nodes in hidden layer.

Abstract: The wave characteristics of horizontal annular two-phase flow in 16 mm diameter pipe were experimentally investigated using flush-mounted constant electric current method (CECM) sensors and visual observations. To examine the effect of surface tension on the wave velocity and frequency, air and three kinds of liquids with different surface tension were used, i.e., water, 2%-butanol solution, and 5%-butanol solution. The gas and liquid superficial velocities were varied from 12 to 40 m/s and 0.05 to 0.2 m/s, respectively. The liquid holdup was measured directly using CECM, while the wave velocity and frequency were determined using cross correlation and power spectral density functions of liquid holdup signals. Generally, combination of air and liquid with the highest surface tension gives the highest liquid holdup and wave frequency. Simple correlations for wave velocity and wave frequency were also developed.

Abstract: During the last decade Equal Channel Angular Pressing (ECAP) has emerged as a widely known procedure for the fabrication of ultrafine grained metals and alloys. This review examines recent developments related to the use of ECAP for grain refinement. In the current study the part of capsules wrapper for powder material to be compressed where the powder AA6061 was wrapped in copper sheet and heated at a temperature of 400 ^OC in hot pressed under the pressure of 400 MPa. Afterward the powder in solid condition was cooled in the air and then does analysis characterization. The sample results of AA6061 are ECAP as is and heat treatment with type Anneal and Artificial Aging (T6) where heat treatment is heated at a temperature of 530 °C for 1 h followed by heating at a temperature of 100 °C for one day and the other for heating at a temperature of 415°C for 2.5 hours followed by heating at a temperature of 177 °C for 8 hours. This paper explains the characteristics of each sample where analyses are based on the mechanism of properties to determine how much change of mechanical properties and microstructure. Heat treatment effect on grain coarsening so that the mechanical properties can be engineered.

Abstract: The spectral-element method (SEM) has been applied to simulate seismic wave propagation in 2D tentative geological model of Geothermal Area in Tiris, East Java Indonesia. we used 2-D model with 36 km x 5 km dimensions and discretized into 720 × 80 rectangular elements (mesh). We computed 8000 time steps with a sampling interval of 0.001 s using 10 Hz Ricker wavelet. The snapshots of seismic wave propagation along Tiris 2D geological model illustrate that SEM could accurately modeling seismic wave propagation. The seismic event that triggers a vibration in rock layers not only depend on the characteristics of the seismic earthquake source parameters and seismic wave propagation media, but also influenced by geometry of the media, such as topography and geological setting. The influence of ground topography, difference media, and structural geology were demonstrated by different time of wave arrival and different amplitudes. Therefore, SEM could be applied as preliminary study in geothermal exploration.