Determination of the allowable maximum size of the obstacle while dragging a pipeline

In this article, the process of overcoming the stony obstacle while dragging pipeline through the channel is considered. Depending on the size of the duct and the pipeline itself the permissible size of the obstacle that the pipeline can overcome without resting against the upper part of the channel, is considered. To solve this problem, the pipeline is conditionally divided into two sections: the site located up to the obstacle and resting on it, and a free area that is after the obstacle. Directly on the process of dragging through an obstacle are acting the forces and moments which have influence on the pipeline. Starting from the equations of moment equilibrium for different points of the pipeline, and also from the equations of bending beams the value of the obstacle is evaluated.

Determining Optimal Gear Ratios of a Two-stage Helical Reducer for Getting Minimal Acreage of Cross Section

This article introduces a study on the optimal calculation of gear ratios of a two-stage helical reducer. In the study, the acreage of the cross section of the reducer was chosen as the objective function of the optimization problem. Also, the design equation for pitting resistance of a gear set was investigated. Furthermore, the equations on moment equilibrium condition of a two-stage helical reducer and their regular resistance condition were analysed. A computer program was performed to determine the optimal partial transmission ratios for getting the minimal acreage of the cross section of the system. From the results of the computer program, two models for determining the optimal gear ratios of a two-stage reducer were proposed. Using these models, the gear ratios can be calculated accurately in a simple way.

Design and Research of Electromagnetic Drive Pulley Type Downhole Blowout Preventer

A new electromagnetic drive rope and pulley type downhole blowout preventer is proposed. The moment equilibrium equation of downhole blowout preventer is established. The structural dimensions of the valve plate connecting position of blowout preventer and pulley rope location are optimized. The dynamic simulation of pulley type downhole blowout preventer is carried out to improve the parameters of this new blowout preventer and to improve its motion performance and mechanical properties.

A Study on Optimum Calculation of Partial Transmission Ratios of Coupled Planetary Gear Sets

This paper introduces a new and effective study on optimum calculation of the partial ratios of coupled planetary gear sets for getting minimum radial size of the gear sets. In the paper, basing on moment equilibrium condition of a mechanic system including two row planetary gear units and their regular resistance condition, an effective model for determining the partial ratios of coupled planetary gear sets was proposed. Especially, by giving this explicit model, the partial ratios can be calculated accurately and simply.

Active Thrust on an Inclined Retaining Wall with Inclined Cohesionless Backfill due to Surcharge Effect

A method based on the application of Kötter’s equation is proposed for the complete analysis of active thrust on an inclined wall with inclined cohesionless backfill under surcharge effect. Coulomb’s failure mechanism is considered in the analysis. The point of application of active thrust is determined from the condition of moment equilibrium. The coefficient of active pressure and the point of application of the active thrust are computed and presented in nondimensional form. One distinguishing feature of the proposed method is its ability to determine the point of application of active thrust on the retaining wall. A fairly good comparison is obtained with the existing solutions.

Aerodynamic Power of Geotechnical Centrifuge

The calculated aerodynamic power by using formulas in references is always much less than practical one. The reason was found through analyzing the transformation of mechanical energy output by the motor to heat energy of the whole system and motion energy of the air newly getting in based on the relations of moment equilibrium. New formula of aerodynamic power and equation of air following flow ratio were deduced for closed chamber and holed chamber geotechnical centrifuges. The aerodynamic powers of one constructed closed chamber geotechnical centrifuge and one constructed holed chamber geotechnical centrifuge were computed by using different formulas and the results were compared with each other as well as the practical values, respectively. The comparisons show that the new formulas are much more accurate than previous ones in references.

Testing the Commonality of Student Conceptual Explanations Across Institutions

To gain insight into the cognitive activities of students during an assessment task, students in Statics courses at three universities were asked to explain their answer to a multiple choice question about the equilibrium of bodies under given loads. Explanations were compared for similarity of terminology using Latent Semantic Analysis and then coded to determine if and when students invoked concepts of force and moment equilibrium. Both terminology and thinking was shown to be consistent across universities. Ideas related to equilibrium were invoked by nearly all students. Students differed principally on whether they applied both force and moment equilibrium consistently and correctly, and if they clearly differentiated between forces and moments. Different codings were sufficiently correlated with the different answer choices, so that one could make a reasonable guess as to a student’s thinking based on the answer choice alone.