Strategies and challenges to facilitate situated learning in virtual worlds post-Second Life

Virtual worlds can establish a stimulating environment to support a situated learning approach in which students simulate a task within a safe environment. While in previous years Second Life played a major role in providing such a virtual environment, there are now more and more alternative—often OpenSim-based—solutions deployed within the educational community. By drawing parallels to social networks, we discuss two aspects: how to link individually hosted virtual worlds together in order to implement context for immersion and how to identify and avoid “fake” avatars so people behind these avatars can be held accountable for their actions

Improved Models of Cable-to-Post Attachments for High-Tension Cable Barriers

Computer simulation models were developed to analyze and evaluate a new cable-to-post attachment for high-tension cable barriers. The models replicated the performance of a keyway bolt currently used in the design of a high-tension cable median barrier being developed at the Midwest Roadside Safety Facility. Component tests of the keyway bolts were simulated and compared to the component test results. Accurate friction, fracture strain, and stress-strain material properties were determined for a solid element model of the keyway bolt by applying actual load curve measured from the test to a simulated pull cable. By simulating the material properties of the solid element keyway bolt in bending, torsion, and tension of a rod, load curves were developed for a simplified beam element model of the keyway bolt as well. When material properties were finalized, the solid and beam element models of the keyway bolt were inserted in bogie test models and simulated again. By analyzing the bogie testing results, it was determined that due to the very small size of the keyway bolt and potential contact difficulties, solid element models of the keyway bolt may be impractical for full-scale simulation purposes. However, the beam element models were determined to be advantageous and had a very small computational cost in comparison

Continued Development of a Non-Proprietary, High-Tension, Cable End Terminal System

A non-proprietary, cable guardrail system is currently under development for the Midwest States Pooled Fund Program. A cable guardrail end terminal was necessary to accompany the cable guardrail system. The objective of this research project was to develop design recommendations for the cable end terminal. Bogie testing that was previously completed on a design concept indicated delayed cable release, which was an undesired performance that led to vehicle instabilities. Several design changes were recommended for better end terminal performance and to reflect the changes made to the cable median barrier. An LS-DYNA model of the modified cable end terminal was developed. Simulations of 0- and 15-degree impacts on the end of the cable anchor bracket with a bogie model indicated that the cables would release easily and not induce vehicle instabilities. This behavior still needs to be verified through bogie and full-scale crash testing. Simulations of a 25-degree reverse impact between post nos. 2 and 3 with small car models indicated that cables did not release easily and may interlock around the car resulting in excessive vehicle decelerations or instabilities. Simulations of various line post designs found that the MWP and weakened MWP have lower forces and energies during impact than the S3x5.7 posts used in previous three-cable end terminals. This finding would suggest improved performance with respect to vehicle override and instability. However, vehicle simulations with multiple line posts impacted were inconclusive. Further design modifications, evaluation, and testing are recommended

Continued Development of a Non-Proprietary, High-Tension, Cable End Terminal System

A non-proprietary, cable guardrail system is currently under development for the Midwest States Pooled Fund Program. A cable guardrail end terminal was necessary to accompany the cable guardrail system. The objective of this research project was to develop design recommendations for the cable end terminal. Bogie testing that was previously completed on a design concept indicated delayed cable release, which was an undesired performance that led to vehicle instabilities. Several design changes were recommended for better end terminal performance and to reflect the changes made to the cable median barrier. An LS-DYNA model of the modified cable end terminal was developed. Simulations of 0- and 15-degree impacts on the end of the cable anchor bracket with a bogie model indicated that the cables would release easily and not induce vehicle instabilities. This behavior still needs to be verified through bogie and full-scale crash testing. Simulations of a 25-degree reverse impact between post nos. 2 and 3 with small car models indicated that cables did not release easily and may interlock around the car resulting in excessive vehicle decelerations or instabilities. Simulations of various line post designs found that the MWP and weakened MWP have lower forces and energies during impact than the S3x5.7 posts used in previous three-cable end terminals. This finding would suggest improved performance with respect to vehicle override and instability. However, vehicle simulations with multiple line posts impacted were inconclusive. Further design modifications, evaluation, and testing are recommended

Increased Span Length for the MGS Long-Span Guardrail System Part III: Failure Analysis

The objective of this research study was to review and analyze the system failure observed during crash testing of an increased span length for the MGS long-span guardrail system in test no. MGSLS-2. Test no. MGSLS-2 was a full-scale crash test conducted on the MGS long-span guardrail with a span length of 311⁄4 ft (9.5 m). This test utilized universal breakaway steel posts (UBSPs) adjacent to the long span in lieu of the controlled release terminal (CRT) wood posts used in previous long span systems. An engineering analysis was undertaken to review the downstream end anchorage failure observed in test no. MGSLS-2. The analysis also compared critical aspects of the barrier performance with previous full-scale crash tests that had similar features or increased anchor loading. The results of this analysis and conclusions regarding potential causes of the anchor failure suggested that there was no identifiable root cause for anchor failure, but the pocketing and deflection suggest that the barrier system may have been pushed near its limits. It was noted that certain factors may have contributed to the anchor failure, including increased span length, location of the impact point, differences in the breakaway post behavior adjacent to the unsupported span, and natural variation in wood strength. Following the analysis, several potential design modifications were noted for improving the barrier system and reducing the potential for end anchorage failure. However, it was noted that further analysis of these potential improvements, selection of a preferred design, and evaluation of the revised barrier system through full-scale crash tests will be required to fully evaluate the system to MASH TL-3 criteria

EVALUATION OF AN EXISTING STEEL POST ALTERNATIVE FOR THE THRIE BEAM BULLNOSE GUARDRAIL SYSTEM

Recently, the Minnesota Department of Transportation (MnDOT) funded a research project through the Midwest States Regional Pooled Fund to evaluate an existing steel post alternative for the thrie beam bullnose barrier system previously developed at the Midwest Roadside Safety Facility (MwRSF). MnDOT had an interest in the replacement of the wooden breakaway posts used in the current bullnose system with proprietary breakaway steel posts. The research project consisted of evaluation of current breakaway steel post designs, investigation and selection of a candidate post design, and full-scale testing of the bullnose system with a steel post alternative. The full-scale testing was to consist of two tests conducted according to the evaluation criteria of NCHRP Report 350: 1) Test 3-38, an impact of a 2000P vehicle on the Critical Impact Point (CIP) of the system at a speed of 100 km/h and an angle of 20 degrees, and 2) Test 3-31, an impact of a 2000P vehicle with the center of the vehicle aligned with the center of the nose of the system at a speed of 100 km/h and an angle of 0 degrees. The evaluation of the steel post alternative for the bullnose system project has been completed. A steel post alternative was selected followed by two full-scale crash tests. Unfortunately, both crash tests failed as the vehicle in each test ramped up the guardrail and vaulted the system. This letter summarizes the work completed

Length of Need and Minimum System Length for F-Shape Portable Concrete Barrier

Portable concrete barrier (PCB) systems are often used to redirect errant vehicles through a combination of inertial resistance, lateral friction loads, and tensile loads developed from the mass and friction of the barrier segments. State departments of transportation (DOTs) and other end users may wish to utilize minimal length PCB installations to shield a hazard or work zone or limit the number of barriers required on the upstream and downstream ends to reduce overall system length. However, concerns with the performance of shorter PCB installations include increased lateral deflections and working widths and barrier pocketing. Additionally, no impact testing has been performed near the upstream or downstream ends of the free-standing PCB system to determine the limits of the length of need (LON) of the system. These impacts may increase the potential for gating through the system, pocketing, rapid deceleration, and/or vehicle instability. The objective of this research study was to investigate and evaluate the safety performance of a previously developed F-shape PCB system to determine minimum system length and the number of barriers required for the beginning and end of the LON. LS-DYNA simulation modeling was applied to determine potential beginning and end of LON points on reduced system lengths to select a configuration for full-scale testing and evaluation of a minimum length PCB system. A 100-ft long PCB installation was selected, and full-scale crash testing was conducted on the beginning and end of LON of the reduced length system. Test no. NELON-1 was conducted to MASH test designation 3-35 criteria on the beginning of LON of the 100-ft long PCB installation, and the vehicle was safely redirected. Test no. NELON-2 was conducted to modified MASH test designation no. 3-37 criteria on the end of LON of the 100-ft long PCB installation, but the test was deemed a failure as the vehicle demonstrated a roll angle in excess of 75 degrees. Review of the crash test results suggested that a nine barrier or 112.5-ft long PCB installation would perform acceptably

Development of a Test Level 3 Transition Between Guardrail and Portable Concrete Barriers

Road construction often requires that work zones be created and shielded by portable concrete barriers (PCBs) to protect workers and equipment from errant vehicles as well as to prevent motorists from striking other roadside hazards. For an existing W-beam guardrail system installed adjacent to the roadway and near the work zone, guardrail sections are removed so a PCB system can be placed. A study was done to develop a crashworthy transition between W-beam guardrail and PCB systems. Design concepts were developed and refined through computer simulation with LS-DYNA. Additionally, a study of critical impact points was conducted to determine impact locations for full-scale crash testing. The design effort resulted in a new system consisting of a Midwest Guardrail System that overlapped a series of F-shape PCB segments placed at a 15:1 flare. In the overlapped region of the barrier systems, uniquely designed block-out supports and a specialized W-beam end shoe mounting bracket were used to connect the systems. Three full-scale vehicle crash tests were successfully conducted according to the Manual for Assessing Safety Hardware Test Level 3 safety performance criteria. Because of the successful test results, a Test Level 3 crashworthy guardrail-to-PCB transition system is now available for protecting motorists, workers, and equipment in work zones

Precipitation and Not Cover Crop Composition Influenced Corn Economic Optimal N Rate and Yield

The effects of single species cover crops on corn (Zea mays L.) N requirement and grain yield are well studied throughout the U.S. Midwest. However, comparing cover crop mixes that include different compositions of grass and broadleaf species is limited. Fourteen corn N response experiments were conducted in South Dakota from 2018 to 2021. Fall cover crops planted after small grain harvest were mixtures of dominantly grasses, broadleaves, a 50/50 grass/broadleaf mixture, and a no cover crop control. Compared to the control, including a cover crop led to no differences in economic optimal N rate (EONR) and yield at zero N (0N) and yield at EONR 44%, 62%, and 83% of the time, respectively. As spring cover crop/residue biomass and its C and N content increased, corn yield at EONR decreased and EONR increased when including cover crops (R2 = 0.36–0.56). Including cover crops reduced EONR and resulted in a similar yield when precipitation increased above 850 mm. When differences occurred with economic return from N, including a cover crop reduced economic return in 3 site-years (mean decrease of US$358 ha−1) and in only 1 site-year did including a grass cover crop increase economic return from N (+US$335 ha−1). Thus, in the first year of growing cover crops (i.e., grasses, broadleaves, or a grass/broadleaf mix) before corn, growers can normally expect some differences in EONR. However, with the appropriate rate of N, yield at EONR is maintained and any economic differences from N normally minimized