Prescription and Effect of Orthokeratology Lenses

Orthokeratology (OK) is the way to correct the myopia or astigmatism by flattening or the central cornea with specialty lenses. The range of correction is from -2.50 to -4.00 diopters after 10 days of fitting. The designs are constructed with flat base curve radius, steep reverse curve, flat alignment curve, and peripheral curve. This multi-curve design enabled the OK lenses to stay on the cornea stably and effectively. Recently, the application of OK is extending to hyperopia and presbyopia. In the future, the amount of correction and the application of OK will increase more and more.

Minimum contact stress modification for profile curve design defects in the beam-spring-cone docking mechanism

A minimum contact stress modification method for profile curve design defects in a beam-spring-cone docking mechanism (BSCDM) based on genetic algorithm is presented in this paper, the profile curve and contact position of BSCDM are optimized. Under low-speed conditions, an improved elastic contact model of semi-space elastic bodies is established to modify and optimize the elliptic profile envelope curve based on Hertz contact theory and two kinds of complete elliptic integral, the improved contact model is used to solve elastic contact problems with the geometric characteristics of the ellipse surface, the optimal profile curve of the docking joint and the optimal docking contact point position are obtained. The results of numerical simulation and the experiment demonstrate the feasibility and validity of above models and methods.

A Review on Studies Based on Vehicle Stability and Safety on Rural Horizontal Curves

All over the world India bangs the top most position in crash deaths. Nearly 1.2 lakh people die every year on Indian roads. Crashes involving rolloverand lateral skidding are now responsible for almost 1/3 of all highway vehicle occupant fatalities. So, rollovers and skidding are more serious than other types of crashes. One of the major reasons for such incidents is vehicle instability at curves due to its inconsistent geometric design. This necessitates a review on current design guidelines followed in India. Many researchers have pointed out drawbacks of current design approach and a few have identified various influential factors which are significant in curve design to reduce rollover and lateral skidding. When some researchers conducted field studies to measure vehicle stability at selected curves, some carried out computer simulations. There are efforts to incorporate vehicular characteristics in curve design which is much appreciable. This paper aims to project efforts made by researchers to reduce vehicle instability at horizontal curves. Moreover, gaps in these research works and scope for further research are highlighted.

Two-Lane Highways Crest Curve Design. The Case Study of Italian Guidelines

The main purpose of the research is to evaluate the crest vertical curves radii Rv, not considering a conventional value of the opposing vehicle height h2, but the average vehicle heights h2(m) and the value of the 15th percentile of the height distribution h2(15) of the passenger car population. The study only considered car models with more than 20,000 registered vehicles in Italy. One hundred and fifteen car models belonging to different brands were taken into consideration, for a total of over 9 million vehicles. For the statistical sample analyzed, the following vehicle heights were estimated: h2(m) = 1.48 m and h2(15) = 1.39 m. The deviations between the crest radii calculated with the Italian standard (h2 = 1.10 m), and those obtained for h2(m) = 1.48 m and h2(15) = 1.39 m are up to 12%. The differences ΔHv between the values of the visible vehicle body height Hv = Hv(t) calculated using, respectively, h2(15) = 1.39 m and h2(m) = 1.48 m are modest. The value h2(m) = 1.48 m could be adopted in order to reduce the highways construction costs. In fact, the research shows that the value h2 = 1.10 m is too conservative and leads to oversizing of the crest vertical curves. Therefore, it would be necessary to make an appropriate choice of h2 value in order to take into account the current heights of passenger cars.

Investigating Automobile Passengers’ Comfort and Safety on Scenic Road Using Sideway Force Coefficient

To satisfy passengers’ experiential demand in scenic roads, a study on passengers’ comfort in the aspect of horizontal curve design is stated in this study. A new indicator sideway force coefficient (SFC) describing passengers’ comfort is introduced, which differs from lateral acceleration. The mechanism of SFC is provided depending on the dynamic balance condition of the vehicle on horizontal curve and S F C c representing passengers’ comfort tolerance limitation is investigated. A large scale naturalistic driving experiments along a park road are conducted, and the S F C c value from naturalistic driving experiments is verified through numerical simulation of 15 horizontal curves from 5 scenic roads from the perspectives of both passengers’ comfort and driving safety. The statistical analysis on data collected in field tests indicates that age and gender have no effect on S F C c , and the value of S F C c is determined as 0.291. The corresponding minimum radius limits under 20–60 km/h and superelevation 6%, 8%, and 10% are proposed. The numerical simulation denotes, when satisfying the comfort demand of passengers (SFC less than 0.291), the lateral distance path is in a safe range, which could also satisfy the safe driving requirements. Thus, S F C c and minimum radius limits proposed in this study are proved to be credible and appropriate for the curve design of horizontal alignment in scenic roads.