Stability Assessment of Rock Mass System under Multiple Adjacent Structures

Numerical modeling is important for exploring the fundamental processes occurring in rock and for evaluating the real performance of structures built on and in rock mass system, and thus for supporting the design of rock engineering problems. Estimating the stability of rock mass foundation systems entirely based on a theoretical approach is a complicated task if there exists overlapping of their potential collapse modes. This paper applies finite element limit analysis to evaluate the bearing capacity of equally spaced multiple strip footings resting on rock mass obeying the modified non-linear Hoek–Brown failure criterion. Numerical solutions are expressed in terms of the efficiency factor that is dependent on the spacing between footings, as well as the rock mass properties. In addition, the effects of surface surcharge and footing roughness are quantified. The maximum spacing at which the interfering effect of adjacent footings becomes disappeared is evaluated and an algebraic expression for approximating the maximum spacing is proposed. Failure mechanisms for a few cases of rock mass under multiple strip footings are examined.

Softball bat inertial considerations and their effects on female softball swing mechanics and estimated bat performance

This paper discusses the role of the inertial properties in the design and selection of the softball bat, and their interrelated effects on female softball swing mechanics and bat performance. The study was performed using 14 collegiate subjects whose swings were analyzed via a computer model, which included methods for estimating post-impact ball velocity. The model was driven kinematically by subject swing recordings using two different trial bats with markedly different inertial properties. Using this method, the following information was determined: subjects altered their linear kinetic inputs while applying consistent angular kinetic inputs to maintain nearly consistent trajectories; subjects compensated for increased bat inertia by modification of the bat instantaneous center-of-rotation trajectory ( ICR); and swing trajectory influenced the bat’s inertial feel, actual, and ideal impact locations, and batted-ball velocity. Subsequently, the mass properties of 27 collegiate level bats were input into the model for each subject trial. Using this information, the relative changes in kinetic inputs were quantified and the performance of the bats was estimated. Results showed that bat inertial properties varied considerably, and independent manipulation of individual properties was evident. In addition, subject kinetic inputs and bat performance measures were most affected by changes in mass center (CG) location, mass, and CG inertia. A modified definition of IGRIP based upon the ICR was presented, and practical implications for designers and practitioners were offered based upon these findings.

Ballistic Range Testing Data Analysis of Tianwen-1 Mars Entry Capsule

A typical blunt body such as Tianwen-1 Mars entry capsule suffers dynamic instability in supersonic regime. To investigate the unstable Mach range of flight and to confirm the design of aerodynamic shape and mass properties, a ballistic range test was carried out aiming at capturing supersonic dynamic characteristics of Tianwen-1. Aerodynamic coefficients of free-flight scaled models were derived by modified linear regression method based on position and attitude data, while the dynamic coefficients were established under the assumption of small angle linearization. The static moment coefficients and dynamic derivatives were identified thereafter. Results show that models in untrimmed configuration are dynamically unstable at certain Mach numbers, whereas models in trimmed configuration are dynamically stable at other Mach numbers tested. Both trimmed and untrimmed configurations are statically stable in all testing cases.

Moored Observations of Currents and Water Mass Properties between Talaud and Halmahera Islands at the Entrance of the Indonesian Seas

The currents and water mass properties at the Pacific entrance of the Indonesian seas are studied using measurements of three subsurface moorings deployed between the Talaud and Halmahera Islands. The moored current meter data show northeastward mean currents toward the Pacific Ocean in the upper 400 m during the nearly 2-yr mooring period, with the maximum velocity in the northern part of the channel. The mean transport between 60- and 300-m depths is estimated to be 10.1–13.2 Sv (1 Sv ≡ 106 m3 s−1) during 2016–17, when all three moorings have measurements. The variability of the along-channel velocity is dominated by low-frequency signals (periods > 150 days), with northeastward variations in boreal winter and southwestward variations in summer in the superposition of the annual and semiannual harmonics. The current variations evidence the seasonal movement of the Mindanao Current retroflection, which is supported by satellite sea level and ocean color data, showing a cyclonic intrusion into the northern Maluku Sea in boreal winter whereas a leaping path occurs north of the Talaud Islands in summer. During Apri–July, the moored CTDs near 200 m show southwestward currents carrying the salty South Pacific Tropical Water into the Maluku Sea.

Static Analysis of Wheel Rim Using Inventor Software

In this paper the 3D model of the real wheel rim was designed using Autodesk Inventor and finite element analysis is performed using Nastran software by applying restrictions and loads conditions. The materials taken for static analysis are steel, aluminum alloy, magnesium alloy and titanium alloy. Following the comparative study for the four models, it can be specified that the importance of the material for the construction of the rims depends on the mass properties and their design. Keywords: Wheel Rim, Static analysis, Autodesk Inventor Nastran

Development of a 6-DOF Testing Platform for Multirotor Flying Vehicles with Suspended Loads

The development of multirotor vehicles can often be a dangerous and costly undertaking due to the possibility of crashes resulting from faulty controllers. The matter of safety in such activities has primarily been addressed through the use of testbeds. However, testbeds for testing multirotor vehicles with suspended loads have previously not been reported. In this study, a simple yet novel testing platform was designed and built to aid in testing and evaluating the performances of multirotor flying vehicles, including vehicles with suspended loads. The platform allows the flying vehicle to move with all six degrees of freedom (DOF). Single or three-DOF motions can also be performed. Moreover, the platform was designed to enable the determination of the mass properties (center of mass and moments of inertia) of small multirotor vehicles (which are usually required in the development of new control systems). The applicability of the test platform for the in-flight performance testing of a multirotor vehicle was successfully demonstrated using a Holybro X500 quadcopter with a suspended load. The test platform was also successfully used to determine the mass properties of the vehicle.

Land-Ocean Interaction Affected by the Monsoon Regime Change in Western Taiwan Strait

The Taiwan Strait is a conduit between East China Sea (ECS) and South China Sea (SCS). Seasonal monsoon winds drive the southbound Zhejiang-Fujian Coastal Current and northbound SCS Warm Current through the strait. Water masses carried by these major current systems also carry fluvial signals from two major rivers, the Changjiang (Yangtze) River in ECS and the Zhujiang (Pearl) River in SCS through the strait. Here we show a switch occurred to signify the monsoon regime change on the western side of this conduit around 10:00 on May 8, 2015. Our data came from water mass properties and environmental proxies of N/P ratio in the surface water and 7Be and 210Pbex isotopes in surface sediments. The timings of the demarcation were identical in the water column and on the water-sediment interface. Our findings put a specific time point in the monsoon regime change in 2015.

A review on the prediction and assessment of powder factor in blast fragmentation

Powder factor can be defined as the quantity of explosives (kg) required to break a unit volume or tonne (t) of rock. The prospect of excavating rocks by blasting is characterized by a specific consumption of explosives. In the past decades, researchers have come up with several precise approaches to predict powder factor or specific charge in blast operations other than through trial blast. Research in this area has focused on the relationship between rock mass properties, blasting material and blasting geometry to establish the powder factor. Also, the interaction between specific energy and particle size embodied in the theory of comminution that is less dependent on local conditions has been studied. In this paper, the various methods for powder factor estimation based on empirical and comminution theory modelling as well as machine learning approaches in both surface bench blasting and underground tunnel operations have been reviewed. The influence of intact rock properties on powder factor selection and the influence of powder factor selection on post-blast conditions have also been discussed. Finally, the common challenges that have been encountered in powder factor estimations have been pointed out in this regard.