J. C. Jofriet

A solution to vicinity problem of obstacles in complete coverage path planning

In real world applications there exist arbitrarily shaped obstacles in the workspace during complete coverage path planning of cleaning robots. A cleaning robot should be able to sweep in a variety of corners and in the vicinity of arbitrarily shaped obstacles in an indoor environment. Consequently, the robot is required not only to effectively avoid the obstacles, but also to delicately cover every area in the vicinity of obstacles. In the paper, a solution to vicinity problem of obstacles in complete coverage path planning is proposed using neural-neighborhood analysis. The path planner is a biologically inspired neural network. The proposed model is capable of planning a real-time path to reasonably cover every area in the vicinity of obstacles. The robot path is autonomously generated through the dynamic neural activity landscape of the neural network and the previous robot location. The effectiveness of the proposed approach is verified through computer simulations.

Analysis of strain and stress in the equine hoof capsule using finite element methods: comparison with principal strains recorded in vivo

Finite-element (FE) methods have great potential in equine biomechanics in evaluating mechanical stresses and strains in tissues deep within the hoof. In this study, we critically assessed that potential by comparing results of FE analyses of capsular strain with in vivo data. Nine FE models were developed, corresponding to the shape of hooves for which in vivo principal strain data are available. Each model had the wall, laminar junction, sole and distal phalanx (PIII). In a first loading condition (LC1), force is distributed uniformly to the bearing surface of the wall to determine reaction forces and moment on PIII. These reaction forces were subsequently applied to PIII in loading condition 2 (LC2) to simulate loading via the skeleton. Magnitude of the force resultant was equivalent to the vertical force on the hoof at midstance. Principal compressive strains epsilon2 were calculated at the locations of 5 rosette gauges on the real hooves and are compared with the in vivo strains at midstance. FE strains were from 16 to 221% of comparable in vivo values, averaging 104%. All models in this, and reports by other workers, show predominance of stress and strain at the toe to a greater extent than in the real hoof. The primary conclusion is that FE modelling of strain in the hoof capsule or deeper tissues of individual horses should not be attempted without corroborating experimental data.

Finite Element Prediction of Silage Temperatures in Tower Silos

ABSTRACT TEMPERATURE is an important factor affecting the quality of silage. Exposure to excessively high temperatures over long periods of time results in silage that is heat damaged. The objective of this report is to predict silage temperatures in tower silos over relatively long periods of time. Finite element heat transfer analyses were carried out on a 6.1 m diameter concrete tower silo filled with silage. The upper layers were selected for analysis because the highest temperatures occur there. Comparison of the finite element results with experimental measurements over a 50-day test period showed very good agreement. The effect of silo diameter, solar radiation and diffusivity of the silage were examined. The silage in smaller diameter silos cools much faster than in large diameter silos. In silos with a diameter greater than 7 m the temperature of the upper layer may be expected to remain around the initial temperature over 50 days after filling.

Structural loads on bunker silo walls: experimental study

Abstract An experiment to obtain wall pressures in a large bunker silo was carried out for 2 consecutive years. Normal wall pressures were measured with 18 pressure sensors mounted on a 3·7 m wide by 4·9 m high precast concrete wall panel of a 51 by 90 m bunker silo in Walker-ton, Ontario, Canada. The silo was filled with whole-plant corn silage both seasons. Wall pressures were measured during filling, during compaction with a 21 t bulldozer, and for about 3 months thereafter. Results from the 2-year experiment showed that the silage loading increases almost linearlywith depth measured from the silage surface. Thus, wall loading exerted by the silage can be expressed as a linear function of a pressure ratio and the silage density; the pressure ratio in this function would be the ratio of the normal wall pressure to the vertical stress in the silage. In the 1987 experiments, silage pressure was found to increase with depth at the rate of about 5·3 kPa/m and in the 1988 experiments at the rate of 6·8 kPa/m. The maximum pressure in 1988 was 28 kPa at the lowest sensor. In 1987, the top of the silage was flush with the top of the wall. In 1988, the silage was piled up well above the top of the wall with a surcharge angle of about 15°. The maximum values exceeded the 1983 Canadian Farm Building Code design load by afactor of 3·8 and 4·5 in 1987 and 1988, respectively. The maximum pressure in 1988 exceeded the new 1990 Canadian Farm Building Code by a factor of about 1·3. The maximum wall pressure due to the weight of the 21 t bulldozer used to compact thecorn was 10 kPa near the silage surface, 15% of the pressure under the tracks of the bulldozer.

Structural loads on bunker silo walls: Numerical study

The finite element method (FEM) of analysis was used to investigate wall pressures exerted by silage on bunker silo walls. Normal wall pressures determined by FEM analysis were in very good agreement with experimental values obtained in a field experiment on a large bunker silo. Both experimental and numerical results show that silage pressure increases linearly with depth and that an equivalent liquid pressure formula can be used for prediction. The density of the equivalent liquid can be calculated as the product of the silage bulk density and the pressure ratio (the ratio of the normal to vertical pressure). The pressure ratio is dependent on wall slope, silage surcharge angle and friction angle between wall surface and silage material. The pressure ratio increases by about 45% when the wall slope changes from 90 to 75 °, and by as much as 70% when the surcharge angle changes from 0 to 20 °. It is recommended that both the surcharge angle and the wall slope be taken into account in the design of bunker silos. Wall-silage friction reduces the pressure ratio by about 10% when the coefficient of friction increases from zero to 0·4. The effect of wall-silage friction is therefore of less importance in design calculations.

Computer-Aided Prediction of Silo-Wall Pressures

THE design equations for predicting the distributions of lateral pressures and friction forces in farm tower silos are described. Three cases are presented which take into account the mode of unloading operation and the wetness of the ensiled crop. A computer-aided design package is developed to expedite the numerical computations and the plotting of the pressure-depth curves. The package is comprised of three files: a program for performing the design calculations and graphing the pressure distributions on the monitor screen, a plotter program for hardcopy plots, and the reference manual. These programs are intended to be as self-explanatory and user-friendly as possible.

Deterioration of Reinforced Concrete in Farm Buildings Due to Sulfate and Sulfide Attack

Portland Cement (PC) concrete is generally a high durable structural material. Nevertheless, certain chemical actions and aggressive environments in a livestock building can cause deterioration and total collapses of structures have occurred long before they have reached their design life. The sulfide and sulfate resistance of three replicates of eight different reinforced concrete treatments were investigated in a laboratory study in which one half of the 48 specimens were half submerged in a sodium sulfate solution (20,000 ppm SO4 2-) and also exposed to hydrogen sulfide gas (1,000 ppm H2S). The other half of the 48 specimens was subjected to hydrogen sulfide gas only. The treatments included PC concrete with W/CM ratios of 0.4 and 0.5 and six treatments thereof, all with water/cementitious material (W/CM) ratio of 0.4. At the time of writing this paper one of the three replicates remains in the test chamber (16 specimens). Treatments PC with 0.5 and 0.4 W/CM ratio already stand out as the worst performers. So far all treatments containing silica fume, fly ash or slag perform better than PC with W/CM ratio of 0.4. Also, there is an indication that sulfate resistant cement is more resistant than type 10 Portland cement. The highest sulfur concentration occurred in the PC specimens with 0.5 W/CM ratio subjected to hydrogen sulfide only. The total sulfur measurements support the indication that the PC with 0.5 W/CM ratio does not perform as well as the treatments with a W/CM ratio of 0.4. Sulfate resistant cement concrete stands out again with very low sulfur concentrations, even near the surface of the cylindrical specimens. Concrete corrosion was most severe in PC40 specimens exposed to both hydrogen sulfide and sulfate; PC50 specimens also were badly corroded.

Measurements of the at-rest pressure ratio of silage and grains

A transducer was developed for measurements within the mass of the grain of the ratio of horizontal to vertical pressure (K) in grain bins. It recorded three normal stresses and the tilt of the device with respect to two reference axes in the horizontal plane; thereby, providing two independent values of the parameter K. This ratio was also determined for silage by measuring the frictional resistance caused by drawing two blades, one oriented horizontally and the other vertically, through the confined mass. For the granular materials, the pressure ratios were measured to be 0·39 for barley and 0·48 for wheat. These values appear to be directly related to the bulk density of the material, initially 690 and 780 kg/m 3 for barley and wheat respectively. For whole-plant corn silage the K ratio was influenced by the orientation of fibres relative to blade surfaces. The pressure ratios of the granular materials were essentially independent of the vertical stress level. Good agreement was found between the experimental results and code recommendations.

Breathing of Oxygen-Limiting Tower Silos

ABSTRACT BREATHING of oxygen-limiting silos interferes with the anaerobic conditions that must be maintained for optimum silage quality. The breathing is caused mainly by the diurnal fluctuation in ambient temperature and solar radiation. These fluctuations cause pressure changes in the head space above the silage and air exchange with the outside through pressure relief valves, cracks and joints. This reports presents estimates of air exchange between the head space and the outside for a severe condition of solar radiation in southern Ontario. The prediction is based on the results of a computer simulation. The behavior of a 6.1 x 22 m silo was illustrated in the analyses. Both concrete and steel silos were considered. The height of the head space was varied. Concrete silos were found to breathe less than steel silos. For the conditions considered, breather bags were not necessary for the concrete silos. A steel silo required an expansion volume of 7% of the total silo volume under the worst condition.

Lateral Pressures in Farm Tower Silos

ABSTRACT THE paper discusses two discrete pressure distributions which can occur in farm tower silos depending upon the wetness of the contained silage material. Formulas and graphs based on available data in the literature are presented for both cases. A new method is put forward to account for the effective fiber pressures developed by a saturated silage mass. An example is included illustrating the step-by-step approach to calculation of lateral wall pressures.