VTechWorks Repository :: Browsing by Author "Perumpral, John V."

Browsing by Author "Perumpral, John V."

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Analysis of a dynamic pressure measuring system
Blevins, Roger Allen (Virginia Tech, 1970-05-05)
A dynamic pressure measuring system composed of long connecting tube, transducer, D-C amplifier and galvanometer oscillograph were used in a wind study conducted by the Department of Agricultural Engineering, Virginia Polytechnic Institute. The instrumentation was used to measure and record dynamic pressures due to wind velocity. Data recorded in that study indicated velocity head pressure oscillations on some surfaces of the test structure in excess of 100 Hz. This investigation was undertaken to see if the recorded oscillations could have been generated in the measuring system or if they were truly windpressure variations. Components of the pressure measuring system were modeled by transfer functions. From these transfer functions, a system operational transfer function was determined and used to define system frequency response. The frequency analysis indicated the system was severely limited in response by the oscillating air column constrained within the interconnecting tube. The usable frequency range of the system (+ 10% tolerable amplitude error allowable) was found to go from zero to 34.2 Hz. By eliminating the air column this frequency range could have been extended to 99.4 Hz. Phase shifts in these frequency ranges were found to be negligible. Transducers were mounted rigidly to exterior walls of the test structure. The measured fundamental natural frequencies of these walls (transducer mountings) were found to be well within the usable frequency range of the instrumentation; and, therefore, a source of vibration pickup. To improve the measuring system reliability, recommendations were made to eliminate the air column and stiffen the transducer mountings.
Applying Probabilistic Risk Assessment to Agricultural Nonpoint Source Pollution
Buck, Sharon Perkins (Virginia Tech, 1997-01-30)
A probabilistic risk assessment (PRA) for the discharge of excessive nitrogen from nonpoint sources (NPSs) to a stream was performed for a small agricultural watershed in northern Virginia. Risk, by definition, is the product of the frequency of occurrence of an event and the consequences of that event. The purpose of this research was to determine the probability of occurrence of a nitrogen discharge event (i.e., frequency). The consequences of such a discharge event were not explicitly determined but were implicitly assumed to be negative in nature. An event tree was developed to show the basic hydrologic processes at work in a small watershed. However, the event tree could not be used to discover the causes for nitrogen loss from the watershed. Therefore, a fault tree was developed for excessive nitrogen discharge in surface runoff on any day from agricultural sources. The development of the fault tree was found to be a useful exercise in understanding the intricate cause and effect relationships between agricultural practices and NPS pollution. Based on the results, the fault tree methodology might be used as an effective teaching or communication tool. The fault tree was also evaluated quantitatively to determine a probability of occurrence for excessive nitrogen discharge to the stream on any day. Land use, fertilization, monitoring, and long-term weather records were used in conjunction with scientific judgment and expert opinion to establish the probabilities within the fault tree and to calculate the overall probability of nitrogen discharge to the stream on any day. The results obtained from the fault tree calculations tend to underestimate the importance of cropland best management practices (BMPs) over the long term, because the fault tree was developed on a daily basis (i.e., every day in a year has the same probability of a discharge event occurring). A more accurate depiction of the NPS pollution control problem was achieved by assuming the occurrence of a runoff event. A second fault tree was presented for the discharge of excessive nitrogen to the stream during a runoff event. The quantitative assessment of the new fault tree showed more clearly the impact of BMPs on reducing the likelihood of nitrogen discharge. A 0.15 decrease in the probability of nitrogen discharge during a runoff event was calculated for the Owl Run watershed from 1987 to 1993 due to the effects of BMPs installed during that time period. A 0.20 decrease was calculated for an Owl Run subwatershed for the same time period. This subwatershed isolated two major dairy operations and the effects of the BMPs installed for those dairies. Despite the success of the fault tree in mirroring changes within the watershed, the amount of data and time required to perform the quantitative assessment may limit its use in the NPS pollution control field. The basic nature of the fault tree technique also limits its usefulness in the field. One such limitation is that degrees of events cannot be expressed. For example, a BMP is either present or not present on a fault tree. There can be no indication of how effective the BMP is in preventing NPS pollution without substantially increasing the level of detail displayed by the tree. Another limitation is that the ultimate result of the fault tree calculations is a probability of occurrence. This value is not as easily understood as the output of NPS pollution computer models, for example, where the output has specific meaning and units (e.g., milligrams of nitrogen per liter of runoff). The qualitative fault tree, however, has the advantage over computer models when it comes to understanding the concepts behind the technique and being able to see the cause and effect relationships at work in the watershed. Laypersons can understand the fault tree more easily than the complex computer code and intricate equations of models.
Arthritis and Farming
Grisso, Robert D.; Perumpral, John V.; Ballin, Kirk; Mariger, S. Christian; Suttle, David E.; Funkenbush, Karen (Virginia Cooperative Extension, 2009)
This publication was developed primarily to familiarize farmers, ranchers, and farm workers with arthritis by providing general information about the disease. It provides information on the types of arthritis, symptoms, treatments, and steps that can be taken to avoid permanent damage to joints so individuals can continue farming activities without pain. It also provides sources for additional arthritis related information and types of assistance.
Assistive Technologies in Agriculture
Grisso, Robert D.; Perumpral, John V.; Pevarski, Kristen; Ballin, Kirk (Virginia Cooperative Extension, 2010-07-01)
Assistive technology can help farmers and ranchers who have disabilities or primary injuries to continue to be productive while reducing secondary injuries.
Auxiliary Procedures for the AGNPS Model in Urban Fringe Watersheds
Yagow, Eugene R. (Virginia Tech, 1997-02-28)
The Agricultural Nonpoint Source model (AGNPS) is a single-event grid-based model used for simulating runoff, sediment and nutrients from agricultural areas. This study involved using geographic information system (GIS) spatial data and functionality to improve the spatial and temporal assignment of parameter values for the AGNPS 5.0 model and incorporated methods for representing urban fringe land uses and their nonpoint source (NPS) pollution contributions in model inputs. Auxiliary procedures for modeling with AGNPS were developed both for enhancing input into the model and for enhancing modeled output. On an event basis, one procedure automated the creation of complex-formatted AGNPS 5.0 model input files using GIS as a spatial data manager. One pair of alternative procedures were developed to automate the assignment of parameter values on an event basis. One procedure used typical average annual parameter values, and the second assigned parameter values using adaptations of existing time-dependent relationships. On a monthly basis, a sequencing procedure was created to perform multiple runs with the model for a list of storms while updating parameters for each event and aggregating monthly modeled spatial output. Another pair of alternative procedures were developed to facilitate the simulation of monthly output from AGNPS modeled events. The first of these aggregated event output for all storms in each month, while the second supplemented the aggregated output with baseflow and septic system loads. The study area was the 6,500 ha urbanizing Bull Run watershed in northern Virginia, which was modeled as 14,621 cells. Databases were assembled and 109 selected storm events within a 16-year period were modeled using the above procedures. Event data were added together, where necessary, to correspond with observed data from composite-sampled intervals. Output from the two event parameterization procedures were compared with monitored loads calculated for 89 composite periods, while output from the two monthly simulation procedures were compared with monthly monitored data for 23 complete months. The monitored-modeled comparisons were considered inconclusive. Evidence strongly suggested that the rainfall records from a rain gauge outside the watershed did not correspond well with monitored runoff. The average runoff produced with the AGNPS model from the 109 selected storms amounted to 40.7% of rainfall, consistent with the calculated long-term average of 38% for the Bull Run watershed. A nonpoint source pollution index was developed to utilize monthly modeled total nitrogen, total phosphorus, and suspended sediment. Individual rating curves were developed to separately transform loads and concentrations of each pollutant into sub-index values. The maximum sub-index from each parameter was added together and averaged for the index. The index was calculated at the watershed outlet from monitored data, and in a spatially-distributed fashion along all streams from simulated output.
Bond graph modeling of hydraulic circuits on a sweet sorghum harvester
Rains, Glen Christopher (Virginia Tech, 1992)
A whole-stalk harvester was developed as part of a sweet sorghum-for-ethanol production system. Gathering chains grasped the stalks as they were cut at the base with a disk-cutter. These stalks were flipped onto a cross conveyor and deposited into an accumulator. Periodically the machine stopped and the accumulator was dumped. All the components on the harvester are powered hydraulically. Five pumps on the harvester supply flow to seven actuator circuits. Power is delivered to the pumps from the tractor PTO via a universal joint driveline. Each of the six existing circuits and one proposed circuit were modeled with bond graphs and implemented for computer analysis using TUTSIM. Model validation was done by comparing simulated and measured driveline torque, line pressure, and return line flow rate in each of the six existing circuits. Data collected on the gathering chains circuit was used to analyze the effect of driveline joint angles on transmitted torque and pump output. Torque measurements at three driveline angles showed a torsional vibration with a primary harmonic at driveline rpm and a secondary at twice driveline rpm. A combination of Cardan joint characteristics, mass unbalance, the secondary couple, and non-linear driveline and V-belt stiffness was used to model the driveline. Resulting simulated torque emulated the experimental very well. Measured pressure in the gathering chains circuit showed relatively low fluctuations at the highest amplitude torsional vibration (highest driveline joint angles). It was concluded that driveline vibration would not significantly affect the gathering chains circuit performance. The cross-conveyor motor circuit simulation showed close agreement to experimental results. Mean predicted flow, pressure, and torque were within 8.9, 7.3, and 7.7 percent of mean measured values. A simulation with a stalk load on the conveyor showed that power requirement increased only 8.0 percent. The accumulator dump circuit was analyzed to determine if the load on the motor would become over-running and cavitate the pump or motor as the stalks were being dumped. Simulation showed that a bundle up to 300 kg could be dumped without over-running the motor, and since this was a larger bundle than the bin could hold, a design modification was not necessary. The disk-cutter circuit was designed based on simulation results for several combinations of motor, pump, and sheave ratio. A 7.3 cm³/rad motor, 2.53 cm³/rad pump , and 2:1 sheave ratio produced the correct disk-cutter speed, and low torsional vibration when cutting the stalks, consequently this combination was selected for the design.
Collaborative Study and Paired Test Taking in Collegiate Level Linear Programming Instruction
Angel, N. Faye (Virginia Tech, 1998-09-16)
The purpose of this investigation was to examine the effects of collaborative learning strategies on formulating solutions to linear programming word problems that were designed to incorporate problem-solving skills. Forty-six students majoring in business at a small southwest college in Virginia participated in the study. After an instruction session, a study period, and a question and answer discussion, participants completed the test instrument based upon random assignment to three treatment groups. These included individual study with individual test taking (control), paired study with individual test taking, and paired study with paired test taking. All participants returned in 17 days to complete a posttest individually having received no further instruction in linear programming theory. The following null hypothesis was examined: No differences in treatment means measuring problem-solving abilities would be found based on students' test and posttest scores using two treatment groups of collaborative study, with collaborative or individual test taking, and a control group of individual study with individual test taking. After satisfying the assumptions of no difference in ability in the treatment groups, establishing significant influence of ability on test score and posttest score variables, and establishing homogeneity of regression, an analysis of covariance (ANCOVA) was used to test the null hypothesis. The null hypothesis was rejected. Treatment had a significant effect on the variance for the test score variable, F = 3.92, p < .05, and for the posttest score variable, F = 4.44, p < .05. Newman-Keuls post hoc test showed significant differences in the adjusted means of the test score variable between the individual study with individual test taking group (72.22) and the paired study with paired test taking group (87.86). For the posttest score variable, the Newman-Keuls post hoc test revealed significant differences between the adjusted means of the individual study with individual test taking group (36.25) and the paired study with individual test taking group (59.20), and between the adjusted means of the individual study with individual test taking group (36.25) and the paired study with paired test taking group (55.77). Implications of findings and recommendations for further research were discussed.
Combined Tension and Bending Loading in Bottom Chord Splice Joints of Metal-Plate-Connected Wood Trusses
O'Regan, Philip J. (Virginia Tech, 1997-05-01)
Metal-plate-connected (MPC) splice joints were tested in combined tension and bending to generate data that were used in the development of a design procedure for determining the steel net-section strength of bottom chord splice joints of MPC wood trusses. Several common wood truss splice joint configurations were tested at varying levels of combined tension and bending loading. The joint configurations were 2x4 lumber with 20-gauge truss plates, 2x6 lumber with 20-gauge truss plates, and 2x6 lumber with 16-gauge truss plates. All the joints tested failed in the steel net-section of the truss plates. The combined loading was achieved by applying an eccentric axial tension load to the ends of each splice joint specimen. Three structural models were developed to predict the ultimate strength of the steel net-section of the splice joints tested under combined tension and bending loading. The test data were fitted to each model, and the most accurate model was selected. Data from other published tests of splice joints were used to validate the accuracy of the selected model. A design procedure for determining the allowable design strength of the steel net-section of a splice joint subjected to combined tension and bending was developed based on the selected model. The new design procedure was compared with two existing design methods. The proposed design procedure is recommended for checking the safe capacity of the steel net-section of bottom chord splice joints of MPC wood trusses subjected to combined tension and bending.
Comparison of 1-D and 2-D modeling approaches for simulating runoff and sediment transport in overload areas
Hong, Seonggu (Virginia Tech, 1995-10-26)
One-dimensional and two-dimensional modeling approaches were compared for their abilities in predicting overland runoff and sediment transport. Both the I-D and 2-D models were developed to test the hypothesis that the 2-0 modeling approach could improve the model predictions over the 1-0 approach, based on the same mathematical representations of physical processes for runoff and sediment transport. Runoff processes were described based on the St. Venant equations and the sediment transport was based on the continuity relationship. The finite element method was employed to solve the governing equations. The nonlinear, time-dependent system of equations obtained by the finite element formulation was solved by the substitution method and the implicit method. The models were verified by comparing the analytical solutions presented by Singh and Regl (1983) and the solution by the Izzard method (Chow, 1959). The comparison showed that both the 1-0 and 2-D models provided reasonable estimations of runoff and sediment loadings. Evaluation of the models was based on four different hypothetical case studies and two experimental studies. The hypothetical case studies investigated the effects of the discretization level, cross slopes, and the size of the field area on the model predictions. The two experimental studies provided a comparison of model predictions with observed data. The results of the hypothetical case studies indicated that the maximum differences in the model predictions at the outlet were about 30% between the two modeling approaches. When the discretization level was sufficient to reasonably describe the shape of the surface, the 1-0 model prediction were almost the same as the 2-D model predictions. Even though cross slopes existed in the field, the differences in the model predictions at the outlet were not significant between the 1-0 and 2-0 models. The differences in the model predictions of runoff and sediment loading were not affected by the changes in the size of the field. Since the 2-D model resulted in 10 to 20% differences in model predictions when different boundary conditions were used and the 1-D model predictions were also affected by the choice of element length, the differences in model predictions at the outlet, shown in model application results, which were less than 30% in most cases, could not be considered significant. The model applications to the experimental studies also showed that no substantial differences existed in the model predictions between the I-D and 2-D models. Even though the spatial distributions of the flow depth and sediment concentration were significantly different, runoff volumes and sediment yields at the outlet showed less than 10% differences. Compared with the I-D model, the 2-D model required much more computational time and effort to simulate the same problems. In addition, convergence problems due to negative flow depths limited the 2-D model applications. The 2-D simulations required more than twice the computational time needed for the I-D simulations. As long as the model predictions at the outlet are concerned, the much greater computational costs and efforts could not justify the use of the 2-D approach. Based on the simulation results from the selected hypothetical case and experimental studies, the 2-D model provided better representations of spatial distribution of flow depths and sediment concentrations than the I-D model. However, no substantial differences in predictions of total runoff volume and sediment yield at the outlet area were found between the I-D and 2-D models.
Comparison of two hydrological models on a Virginia Piedmont watershed
Fu, Youtong (Virginia Tech, 1994-12-05)
KINEROS and PSRM-QUAL:J two distributed parameter event-based hydrologic models, were applied to Foster Creek Watershed, Louisa County, Virginia. The simulations of the two models were conducted using published data and a ten year database from the Foster Creek Watershed, Louisa County, Virginia. Data management and analysis was supported through the use of PC-VirGIS, a DOS based GIS package developed by the Information Support Systems Laboratory, Virginia Tech. The performance of the two models were based on the criteria established to compare the simulated and recorded peak discharge rates , total runoff volumes and time to peak. Goodness of fit criteria were based on graphic comparison relative error, model efficiency, linear regression, hypothesis testing and variance. Based on these measurements, the simulated results by both models were acceptable. KINEROS generally made better predictions of peak discharge rate and time to peak. Hydrograph shapes also generally matched the recorded sequence more closely. PSRM-QUAL simulated the total runoff volume slightly better than KINEROS. The sensitivity of KINER OS and PSRM-QUAL to the model input parameters was evaluated. For KINEROS, peak discharge rate and runoff volume were very sensitive to changes in rainfall amount, saturated hydraulic conductivity and effective capillary drive. For PSRM-QUAL, peak discharge rate and total runoff volume were very sensitive to changes in SCS CN, initial abstraction coefficient and rainfall amount.
A computer simulation model for investigating the effect of land application of sludge on runoff water quality
Deizman, Marcia McCutchan (Virginia Tech, 1989-04-22)
CREAMS-NT, a modified version of the field-scale model for Chemicals, Runoff, and Erosion from Agricultural Management Systems (CREAMS) model, was developed to simulate the nitrogen (N) transformations and subsequent nutrient transport processes which occur in the soil following organic waste applications. CREAMS-NT accounts for nutrient addition through fertilization and rainfall and losses of N by volatilization, denitrification, plant uptake, leaching, and overland flow. Data required by CREAMS-NT includes runoff volume, sediment yield, percolation, and soil environmental conditions which is generated by the hydrologic and erosion components of the original CREAMS model. The mineralization, nitrification, denitrification, ar1d volatilization processes are simulated using firstâ order knetic equations adjusted for the effects of soil environmental conditions including temperature, moisture, pH, soil/sludge contact, and soil cation exchange capacity. Prior to a runoff event, soil ammnonium-N (NH4 â N) is partitioned between adsorbed and desorbed phases. CREAMS-NT predicts the transport of organic-N, NH4 â N, and sediment=bound phosphorus (P3b) in runoff using enrichment ratios. The transport of soluble nutrients, nitrate-N (NO3 â N), NH4 â N, and soluble P (PTF), is estimated using extraction coefficients.
A computer simulation model for wastewater management in an integrated (fish production-hydroponics) system
Singh, Sahdev (Virginia Tech, 1996)
Intensive fish production in a recirculating aquaculture system facility is a complex bioengineering operation involving a sensitive balance among physiological, water quality, and management components of the overall system. Warm and nutrient-rich wastewater discharged from controlled-environment fish production facilities is a loss of heat energy and nutrients in addition to being potentially harmful to the environment. The operators of such systems need sophisticated management tools if the operation is to be both commercially successful and environmentally friendly. Effluent heat and nutrients can be recovered using hydroponics in a greenhouse attached to the recirculating aquaculture system facility. A computer model was developed to simulate system performance and to help determine design parameters for an integrated fish production-hydroponics system. The aquaculture component of the model predicts (a) fish growth-dependent feeding, (b) diurnal metabolic waste production/accumulation in the fish culture water, and (c) quality, quantity and frequency of wastewater discharge. The hydroponics component computes optimum greenhouse size and models the performance of vegetable plants in terms of nutrient-uptake, water use, and growth. SUCROS and TOMGRO, plant growth models with modifications for water use and nutrient uptake, were used to simulate lettuce and tomato performance, respectively. To validate the plant models, experiments were conducted in a greenhouse utilizing aquacultural wastewater as the hydroponic solution to produce lettuce and tomatoes. Plant growth, water quality (nutrient-uptake), water use, and environmental conditions were monitored. Lettuce and tomato growth was accompanied with significant reductions in nitrogen and phosphorus levels of the wastewater. Water use by plants strongly depended on solar radiation and plant growth stage. At harvest, nine-week-old lettuce weighed 160 g/plant (average) at a density of 40 plants/m². Tomato yielded 2.4 kg/m² after 17 weeks. However, the tomato fruits did not reach maturity during this time. After 20 weeks, the tomato yield was 3.1 kg/m² and some fruits showed maturity. The use of the model as a management tool for making decisions on optimum greenhouse area for a given recirculating aquaculture system size is demonstrated. The effect of fish stocking density and greenhouse heat loss factor on the optimum greenhouse size are also demonstrated. For an optimum greenhouse size, water use and nutrient-recovery from the effluent by lettuce and tomato plants are quantified.
Cover crop residue effects on machine-induced soil compaction
Ess, Daniel R. (Virginia Tech, 1994-07-05)
Crop production systems which utilize the biomass produced by rye (Secale cereale ) to suppress weed growth and conserve soil moisture have been developed at Virginia Tech. The success of alternative, reduced-input crop production systems has encouraged research into the potential for breaking the traffic-tillage cycle associated with conventional tillage crop production systems. The fragile residues encountered in agricultural crop production, whether incorporated into the soil or distributed on the soil surface, provide minimal protection against compaction by wheeled vehicles. The potential of an intact cover crop to reduce machine-induced effects on soil properties that affect primary crop growth was the subject of this study. A randomized complete block experiment was conducted at the Whitethorne Farm in Montgomery County, Virginia. One set of plots was arranged on a terrace adjacent to the New River in a fine, mixed, mesic, Aquic Argiudolls. Another set of plots was arranged on an upland site, a river terrace tread, in a fine-loamy, mixed, mesic, Typic Hapludults. Three rye cover crop treatments were examined. In one, a live cover crop was completely undisturbed prior to tracking by a wheel-type tractor. In another, the cover crop was chemically desiccated, and in the third treatment, all above-ground biomass was removed from plots prior to machine traffic. The treatments permitted investigation of the effects of crop condition on machine-induced soil compaction and the contribution of root reinforcement to the alteration of soil response to machine traffic. A fall-tilled fallow treatment served as an experimental control. Three levels of traffic were investigated: one pass, three passes, and five passes. Undisturbed soil core samples were analyzed to determine machine-induced effects on dry bulk density, pore size distribution, and saturated hydraulic conductivity. The treatments affected soil response to machine traffic. The cover crop treatments altered the soil-plant microenvironment, affecting soil parameters that influence compactibility. Soil compaction was attenuated by the reinforcing effect of a network of undisturbed roots within the soil. There was no convincing evidence that above-ground biomass contributed directly to the reduction of machine-induced compaction effects. Soil response to machine traffic was limited to the uppermost 15 cm of the soil profile.
Defining farm-safety research priorities and adjusting farm insurance premiums by a risk analysis approach
Zhao, Wei (Virginia Tech, 1992)
A risk analysis approach for farm work-related injuries was proposed. For this study, risk is defined as the Expected Injury Cost (EIC) index per farm worker per year. Four steps are involved in the risk assessment analysis of farm injuries: (1) determination of risk factors, (2) injury severity classification, (3) cost estimation, and (4) risk characterization. Farm variables were examined to determine their influences on the rates of occurrence as well as the severity of injuries. Farm injuries were correlated with the risk factors of employment status, gender of farm worker, age of farm worker, hours of exposure, type of agricultural operation, and various hazardous conditions on a farm. By combining the probability of injuries due to a particular risk factor with the estimated costs of injuries, the EIC indices were derived for farm workers and activities. Agricultural safety education and research priorities were defined based upon the risk model developed in this study. A sensitivity analysis was conducted to determine the impact of the assumptions on the research priorities established. It was found that the research priorities were not affected by the uncertainty on the magnitude of injury costs and other variables used in this study. The risk-based approach can also provide input to farm insurance ratings. By combining the EIC index for each worker with the number of workers employed on a farm, a composite risk factor could be obtained for the farm enterprise. This composite risk factor can be used as a basis for adjusting farm insurance premiums. Adjustment of insurance premiums or related benefits could be used as an economic incentive to encourage adoption of safer farming practices so that preventable farm accidents and human suffering can be reduced. Other potential applications of the risk model presented in this study include safety management and loss control for a farm enterprise, and serving as a guide for the systematic collection of farm injury data.
Development of a continuous, physically-based distributed parameter, nonpoint source model
Bouraoui, Faycal (Virginia Tech, 1994-04-18)
ANSWERS, an event-oriented, distributed parameter nonpoint source pollution model for simulating runoff and sediment transport was modified to develop a continuous nonpoint source model to simulate runoff, erosion, transport of dissolved and sediment-bound nutrients, and nutrient transformations. The model was developed for use by nonpoint source pollution managers to study the long-tenn effectiveness of best management practices (BMPs) in reducing runoff, sediment, and nutrient losses from agricultural watersheds. The Holtan's infiltration equation used in the original version of ANSWERS was replaced by the physically-based Green-Ampt infiltration equation. Soil evaporation and plant transpiration were modeled separately using the Ritchie equation. If soil moisture exceeds field capacity, the model computes percolation based on the degree of soil saturation. Nutrient losses include nitrate, sediment-bound and dissolved ammonium; sediment-bound TKN, and sediment-bound and dissolved phosphorus. A linear equilibrium is assumed between dissolved and sediment-bound phases of ammonium and phosphorus. Nutrient loss is assumed to occur only from the upper cm of the soil profile. The model simulates transformations and interactions between four nitrogen pools including stable organic N, active organic N, nitrate and ammonium. Transformations of nitrogen include mineralization simulated as a combination of ammonification and nitrification, denitrification, and plant uptake of ammonium and nitrate. The model maintains a dynamic equilibrium between stable and active organic N pools.
Development of a Virtual Reality Excavator Simulator: a Mathematical Model of Excavator Digging and a Calculation Methodology
Park, Borinara (Virginia Tech, 2002-10-31)
Virtual Reality (VR) simulators have become popular because of two distinctive merits. One is the capability to transfer data and information to users in an intuitive way by means of 3-D high-quality graphics output and real input devices. The other is the capability to represent physical systems in mathematical models so that meaningful responses of the systems can be predicted. Previous efforts in VR excavating machine simulator development, however, showed a lack of balance between the fidelity of the model of the physics and the visual representation of the simulated equipment. In order to ensure that a VR construction excavator simulator provides convincing operating results to users, the focus of simulator development needs to be shifted to interaction of physically valid soil and the excavator machine. This research aims to contribute to the development of a VR construction excavator simulator system by proposing a mathematical model of excavator digging and a calculation methodology. The mathematical model of excavator digging provides physically meaningful soil-bucket interaction information to a simulator. The calculation methodology provides systematic and efficient computation methods to ensure the seamless integration of the excavator digging model with a VR simulator system as well as adequate system speed. As a result, the simulator is realized as an engineering process tool equipped with real-time interactivity.
Development of phenomenologically-based distribution fitting procedures and spatial processes for mixed population soil properties
Cooke, Richard (Virginia Tech, 1993-11-08)
In the literature, two distinct flow phenomena, namely, flow through the main body of the soil, and flow through preferential flow paths, have been identified. Models which try to incorporate the effects of these two phenomena require either an explicit or an implicit knowledge of the probability distribution functions associated with the soil properties affecting flow. In keeping with the fact that these properties are influenced by two distinct phenomena, it is postulated that they should be represented by heterogeneous distribution functions. These distribution functions are, by design, suitable for representing mixed population data. Procedures were developed for fitting heterogeneous distribution functions to data. These procedures are encoded in Microsoft QUICKBASIC with some additional FORTRAN routines. The fitting procedures do not utilize any moment above the second order, and are markedly different from the use of regression methods for fitting multiple parameter distributions. Procedures were developed for two types of mixtures. One type is suitable for instances where a measured quantity is the sum of values from two populations, while the other is applicable when a measured quantity may be from one population or from another, but not from both at the same time or location. The procedures were applied to several data sets, including flow data, infiltrability data, and pH data. In many instances, the use of heterogeneous distributions resulted in an improvement in fit quality as compared to the fit quality for homogeneous distributions. The most dramatic improvement are observed in the fit to extreme data values. Procedures were also developed to incorporate heterogeneous distribution functions into three common processes in Soil and Water Engineering, namely, Monte Carlo simulation, stochastic field generation, and interpolation. In these procedures, data which are best represented by heterogeneous distributions are transformed to Gaussian space and existing Gaussian-based procedures are applied. In several validation efforts the modified processes were found to as good as, or better than, conventional procedures. In the process of developing the modified spatial processes mentioned above, a robust trend surface procedure and a new matrix decomposition procedure were developed. These ancillary procedures were shown to be useful in other engineering applications.
Development of root observation method by image analysis system
Kim, Giyoung (Virginia Tech, 1995-12-05)
Knowledge of plant roots is important for determining plant-soil relationships, managing soil effectively, studying nutrient and water extraction, and creating a soil quality index. Plant root research is limited by the large amount of time and labor required to wash the roots from the soil and measure the viable roots. A root measurement method based on image analysis was proposed to reduce the time and labor requirement. A thinning algorithm-based image analysis method was used to measure corn root length at the planar faces cut from a core sample. The roots were exposed by careful handling and contrasted from the soil by causing autofluorescence using long-wave ultraviolet light. The contrast-enhanced images were stored on the camcorder video tape and digitized by frame grabber. A binary root image was acquired from the digitized gray scale image by a thresholding operation. The binary root image was thinned until the roots were reduced to their basic structure. Root length was calculated from the number of pixels of the root's basic structure. This root length was divided by the removed soil volume of the profile of the core sample to estimate the root length density (RLD, cm root cm⁻³ soil). This estimated RLD was regressed on RLD, measured from washed roots in the same soil core sample, and a linear relationship (R² = 0.96) was obtained. This study indicated that the image analysis root measurement method can determine the length of corn root systems up to 2.5 times faster than by using the conventional method which incorporates a root washing procedure.
Driving Safely in Plain Communities
Ballin, Kirk; Grisso, Robert D.; Jepsen, S. Dee; Ohanehi, Donatus Chukwubueze; Perumpral, John V.; Pevarski, Kristen (Virginia Cooperative Extension, 2017-11-06)
Discusses traffic safety issues on roadways where there are both slow and high-speed vehicles.
Effects of forest harvesting best management practices on surface water quality in the Virginia coastal plain
Frazee, Joseph W. (Virginia Tech, 1996-09-09)
Three watersheds located in Westmoreland County, Virginia were monitored to evaluate effectiveness of forestry best management practices (BMPs) for minimizing hydrologic and water quality impacts associated with timber harvesting. One watershed was clear-cut without implementation of BMPs, one watershed was clear-cut with the implementation of BMPs and the third watershed was left undisturbed as a control. The 27 months of pre-harvest monitoring data and 17 months of post-harvest monitoring data were compared using the paired watershed regression analysis and the minimum detectable change (MDC) statistic. Analysis of the hydrologic data showed that peak discharge rates were not impacted by harvesting, regardless of whether BMPs were implemented. Harvesting with or without the implementation of BMPs resulted in no statistically significant change in stormflow volume. BMP implementation was found to be effective in minimizing harvesting impacts on stormflow total suspended solids (TSS), ammonia, total Kjeldahl nitrogen (TKN), total nitrogen (TN), sediment-bound nitrogen and total phosphorous (TP) concentrations and total flow TSS and TP concentrations. BMP implementation was also effective in minimizing harvesting impacts on stormflow TSS, TKN, sediment-bound nitrogen, TP and sediment-bound phosphorous loadings and total ammonia loading. The BMPs were not effective in reducing nitrate concentrations and loadings. The BROOK90 forest hydrology model was used to predict the site hydrology. Model predictions compared favorably with streamflow measurements from watersheds QN3 and QN4 until the time of harvest, but did not predict streamflows as accurately for the control watershed, QN5.

Browsing by Author "Perumpral, John V."

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