Estimation of Phases for Compliant Motion

Nowadays adding a skill to the robot that can interact with the environment is the primary goal of many researchers. The intelligence of the robot can be achieved by segmenting the manipulation task into phases which are subgoals of the task and identifying the transition between them. This thesis proposes an approach for predicting the number of phases of a compliant motion based manipulation task and estimating their corresponding HMM model that best fit with each segmented phase of the task. Also, it addresses the problem of phase transition monitoring by using recorded data. The captured data is utilized for the building an HMM model, and in the framework of task segmentation, the phase transition addressed. In this thesis, the concept of non-homogeneous HMM is used in modeling the manipulation task, wherein hidden phase depends on observed effect of performing an action (force). The expectation-maximization (EM) algorithm employed in estimating the parameters of the HMM model. The EM algorithm guarantees the estimation of the optimal parameters for each phase of the manipulation task. Hence the modeling accuracy of the forced based transition is significantly enhanced compared to position based transition. To see the performance of the phase transition detection a Viterbi algorithm was implemented. A Cartesian impedance controller defined by [6] for each phase detected is used to reproduce the learned task. The proposed approach is investigated with a KUKA LWR4+ arm in two test setups: in the first, we use parameter estimation for a single demonstration with three phases, and in the second experiment, we find a generalization of the parameter estimation for multiple demonstrations. For both experiments, the transition between phases of the manipulation task is identified. We conclude that our method provides a convenient platform for modeling and estimating of model parameters for phases of manipulation task from single and double demonstrations

Potential of Shallow Groundwater for Household Level Irrigation Practices in Tahtay Koraro Woreda, Tigray, Northern Ethiopia

This paper deals with the results of a pilot study conducted to estimate the shallow groundwater resource potential and irrigation capacity at the household level in Tahtay Koraro Woreda, northwestern zone of Tigray, Ethiopia. The potential evapotranspiration and actual evapotranspiration of the study area are estimated to be 1484 mm/year and 814 mm/year respectively. The runoff is approximately calculated to be 280 mm/year and the annual groundwater recharge is estimated to be 29 mm/year. The total annual groundwater abstraction for human, livestock, and irrigation is estimated to be 25 mm/year. It should be noted that the groundwater recharge rate is expected to remain constant while the total annual groundwater discharge is expected to increase from year to year. This relation when projected over a long period may result in a negative groundwater budget which can result in depletion of groundwater (lowering of groundwater levels), reduced baseflow to streams, and deterioration of water quality.  The computed values for hydraulic conductivity of the aquifers range from 1.63 m/day to 7.27 m/day with an average value of 4.9 m/day and transmissivity from 48.9 m2/day to 218.1 m2/day with an average value of 147.14 m2/day. The aquifers in the highly weathered basalt and highly weathered siltstone – sandstone intercalation have transmissivity values ranging from 99 m2/day to 218.1 m2/day with an average value of 157 m2/day and are grouped into the moderate potentiality aquifers category. The aquifers in the slightly weathered and fractured metavolcanics grouped under low potentiality based on the lower transmissivity values (<50 m2/day). The study area has low to moderate groundwater potentiality, hence, large-scale groundwater pumping is not possible. Therefore, the current activity of using hand dug wells for household-level irrigation is the best way of using groundwater for irrigation and other uses as well. Increasing the depth of the existing hand dug wells that are constructed in highly weathered basalt and highly weathered siltstone – sandstone intercalation can also enhance the yield of the hand dug wells. It is recommended to use water-saving irrigation technologies rather than increasing the number of wells. This will also help in increasing the irrigation area. Groundwater recharge enhancement structures such as trenches, percolation ponds, and check dams be constructed in scientifically selected localities to further enhance the groundwater potential

High-resolution Data Based Groundwater Recharge Estimations of Aynalem Well Field

Due to the ever-increasing demand for water in Aynalem catchment and its surrounding, there has been an increased pressure on the Aynalem well field putting the sustainability of water supply from the aquifer under continuous threat. Thus, it is vital to understand the water balance of the catchment to ensure sustainable utilization of the groundwater resource. This in turn requires proper quantification of the components of water balance among which recharge estimation is the most important. This paper estimates the groundwater recharge of the Aynalem catchment using high-resolution hydro-meteorological data. Daily precipitation and temperature measurement data for years 2001-2018; groundwater level fluctuation records collected at every 30 minutes; and soil and land use maps were used to make recharge estimations. In the groundwater level fluctuation, three boreholes were monitored, but only two were utilized for the analysis because the third was under operation and does not represent the natural hydrologic condition. Thornthwaite soil moisture balance and groundwater level fluctuation methods were applied to determine the groundwater recharge of the Aynalem catchment. Accordingly, the annual rate of groundwater recharge estimated based on the soil-water balance ranges between 7mm/year and 138.5 mm/year with the weighted average value of 89.04 mm/year. The weighted average value is considered to represent the catchment value because the diverse soil and land use/cover types respond differently to allow the precipitation to recharge the groundwater. On the other hand, the groundwater recharge estimated using the groundwater level fluctuation method showed yearly groundwater recharge of 91 to 93 mm/year. The similarity in the groundwater recharge result obtained from both methods strengthens the acceptability of the estimate. It also points out that the previously reported estimate is much lower (36 to 66 mm/year)

Evaluation of groundwater resources in the Geba basin, Ethiopia

This article presents an assessment of the groundwater resources in the Geba basin, Ethiopia. Hydrogeological characteristics are derived from a combination of GIS and field survey data. MODFLOW groundwater model in a PMWIN environment is used to simulate the movement and distribution of groundwater in the basin. Despite the limited data available, by simplifying the model as a single layered semi-confined groundwater system and by optimising the transmissivity of the different lithological units, a realistic description of the groundwater flow is obtained. It is concluded that 30,000 m(3)/day of groundwater can be abstracted from the Geba basin for irrigation in a sustainable way, in locations characterised by shallow groundwater in combination with aquitard-type lithological units

Evaluation of groundwater resources in the Geba basin, Ethiopia

This paper presents an assessment of the groundwater resources in the Geba basin, Ethiopia. Hydrogeological characteristics are derived from a combination of GIS and field survey data. MODFLOW groundwater model in PMWIN environment is used to simulate the movement and distribution of groundwater in the basin. Despite the limited data available, by simplifying the model as a single layered semi-confined groundwater system and by optimising the transmissivity of the different lithological units, a realistic description of the groundwater flow is obtained. It is concluded that 30,000 m3/d of groundwater can be abstracted in the Geba basin for irrigation in a sustainable way, in locations characterised by shallow groundwater in combination with aquitard type lithological units.status: publishe