Short Thrust Research Articles

The transition from salt diapir to weld and thrust: Examples from the Northern Flinders Ranges in South Australia

AbstractThe interactions between salt diapirs, thrust welds and thrusts in contractional belts are poorly understood due to, first, the inability of seismic data to distinguish between thrusts and welds or resolve associated sub‐resolution deformation, and second, the paucity of good field examples. The Warraweena area in the Northern Flinders Ranges of South Australia contains examples of Neoproterozoic to Early Cambrian squeezed diapirs linked by steep reverse faults formed during the Delamerian Orogeny. Benefiting from good field exposures, we use geological mapping, cross‐section construction and conceptual structural models to assess the three‐dimensional geometry and evolution of the structures, the lateral transition from diapirs to linking faults and the variability of associated meso‐ and small‐scale deformation. Three discrete diapirs consist of narrow outcrops of Callanna Group megabreccia (Willouran in age) up to 5‐km long. Their diapiric origin is confirmed by local development of caprock, steepening of flanking strata in composite halokinetic sequences and reworked diapir and roof debris in adjacent strata. The surrounding rocks display only background levels of small‐scale deformation. In contrast, the linking faults show no evidence of precursor diapirism, have fault‐related anticlines up to 100s of m in wavelength in their hanging walls, and an associated increase in small‐scale deformation (i.e. millimetre to metre scale folds, fractures and shear fabrics). The transitions from diapirs to faults occur within less than 200 m as short thrust welds at the diapir terminations. The exposed structures are analogous to those found on the subsurface of other salt basins such as the Gulf of Mexico and the South Atlantic conjugate margins. The results of this work can aid geoscientists evaluating three‐way traps against squeezed diapirs, welds or faults, and can help them to predict the style and abundance of both halokinetic and small‐scale structures that are below seismic resolution.

Growth of a thrust fault array in space and time: An example from the deep-water Niger delta

The temporal and spatial evolution of thrust fault arrays is currently poorly understood, and marine fold and thrust belts at the toe of passive margin gravitational systems, imaged by commercial 3D seismic reflection datasets, afford a unique opportunity to investigate this problem in three dimensions. Using an extensive 3D seismic data set and age data, the total cumulative strain (shortening) and interval strain rates have been calculated for 11 thrust-related folds mapped in the toe-thrust region of the southern lobe of the Niger Delta. For the first time, the sequence of thrust nucleation, propagation and linkage through time at a scale of 10 s km both along and across strike is documented. Short thrust segments had nucleated throughout the entire study area by 15 Ma. They then grew largely by lateral growth and linkage, increasing the fault trace length and generating asymmetric strain-distance plots, for the first 50% of their history. Thereafter, growth continued by shortening, with minimal along strike increase in fault length. Changes in shortening-distance data between adjacent structures across strike suggest that the change in growth mode occurred once the thrusts had linked in 3D through the common underlying detachment. Over the entire thrust array the strain rate varies through time, starting slowly (<200 m/Ma), then increasing between 9.5 and 3.7 Ma (200–400 m/Ma) before slowing down in the last ~ 4 Ma (<150 m/Ma). The variation in strain rate is attributed to a change in boundary conditions of the gravitational system. An increase in sediment supply to the delta occurred in the late Miocene-Pliocene, driving higher shortening rates in the toe area. A subsequent reduction in sediment supply in the last ~4 Ma led to a reduction in deformation rate and the cessation of activity on a number of the thrusts. Predictions of the critical taper wedge model are used to explain the near-synchronous growth of the entire thrust array over the last 15 Ma. Because sedimentation acts to lower the surface slope, the wedge can only continue to deform if shortening occurs over a wide area allowing the surface slope to build up. These new results suggest that models of piggyback fault propagation are not appropriate for deep-water fold and thrust belts.

How Many Impulses Redux

A central problem in orbit transfer optimization is to determine the number, time, direction, and magnitude of velocity impulses that minimize the total impulse. This problem was posed in 1967 by T. N. Edelbaum, and while notable advances have been made, a rigorous means to answer Edelbaum’s question for multiple-revolution maneuvers has remained elusive for over five decades. We revisit Edelbaum’s question by taking a bottom-up approach to generate a minimum-fuel switching surface. Sweeping through time profiles of the minimum-fuel switching function for increasing admissible thrust magnitude, and in the high-thrust limit, we find that the continuous thrust switching surface reveals the N-impulse solution. It is also shown that a fundamental minimum-thrust solution plays a pivotal role in our process to determine the optimal minimum-fuel maneuver for all thrust levels. Remarkably, we find that the answer to Edelbaum’s question is not generally unique, but is frequently a set of equal-Δv extremals. We further find, when Edelbaum’s question is refined to seek the number of finite-duration thrust arcs for a specific rocket engine, that a unique extremal is usually found. Numerical results demonstrate the ideas and their utility for several interplanetary and Earth-bound optimal transfers that consist of up to eleven impulses or, for finite thrust, short thrust arcs. Another significant contribution of the paper can be viewed as a unification in astrodynamics where the connection between impulsive and continuous-thrust trajectories are demonstrated through the notion of optimal switching surfaces.

52 cases of entrapment syndrome of superficial radial nerve treated with short thrust needling at Shànglián (上廉LI 9)

ObjectiveTo observe the clinical therapeutic effects on entrapment syndrome of superficial radial nerve treated with the short thrust needling at Shànglián (上廉LI 9). MethodsA total of 52 patients of entrapment syndrome of superficial radial nerve were treated with the short thrust needling at LI 9. Firstly, the needle was inserted gradually and deeply until the needle tip touched the radial periosterum. Secondly, the needle body was tilted to form an angle about 30° with the skin surface. Thirdly, the needle handle was lifted and trusted shortly and swiftly to induce the gentle rubbing of the needle tip on the periosterum. The stimulation intensity of this needling technique was determined by the obvious soreness and distention in the local area or the needling sensation radiated to the radial sides of the thumb, the index figure and the middle figure of the affected limb. Afterward, the needle was retained for 20 min. The treatment was given once a day, five treatments made one course and a total of 2 courses of treatment were required. ResultsOf 52 cases, 50 cases were cured, accounting for 96.2% and 2 cases remarkably effective, accounting for 3.8%. The mean conduction velocity of the superficial radial nerve was (49.38 ± 2.97) m/s after treatment, faster than (29.31 ± 5.94) m/s before treatment, indicating the significant difference (P < 0.05). ConclusionThe short thrust needling at LI 9 achieves the satisfactory clinical therapeutic effects on entrapment syndrome of superficial radial nerve. This therapeutic method is feasible to be promoted in clinical practice because of its less point selection and short treatment course.

Translation Dynamical Nonlinear Models in Perturbed Keplerian Conditions For a Geostationary Satellite

The dynamics of a GEO satellite will be studied in this work to obtain a dynamical model as accurate as possible. This model will be obtained in terms of Gauss' variation of osculating parameter (VOP) equations containing the environmental perturbing accelerations, which are traditionally used to plan the station keeping maneuvers. The idea is to implement a controller for geostationary station keeping purposes based on a model written in terms of osculating orbital elements instead of averaged elements. Such a controller plans in an automatic way the station keeping (SK) maneuvers and it could be integrated on board in view of autonomous station keeping control loop. The Geostationary Earth Orbit (GEO) satellites maintain an essentially fixed position with respect to the surface of the Earth. This is made possible by inserting the spacecraft into a circular, equatorial orbit at an altitude of roughly 36000 km. At this altitude, if the main environmental disturbing forces (the Earth's non-spherical gravity attraction, the Moon's and Sun's gravity attraction and the solar radiation pressure) are neglected except the Kepler attraction of the Earth, the geostationary motion is ideal. The satellite remains fixed with respect to the surface of the Earth. The mean motion n matches the Earth's rotation rate  of one revolution per 23 hours and 56 minutes. In presence of perturbations, it is a common practice to control a GEO satellite actively via station keeping maneuvers such that it stays confined in a box of 100-150 km width around a nominal geostationary longitude and latitude (1). Traditionally this is done with an open loop control technique based on a dynamical model of the satellite state vector subject to the only environmental perturbing forces and on a separate dynamical model taking into account the only thrust effects. Moreover, this latter model is derived supposing to use a chemical propulsion system characterized by high thrusts and very short thrust durations relative to the orbital period. These impulsive thrust hypotheses lead to assume that maneuvers induce jumps in the velocity part of the state vector but not in the position part. The GEO station keeping problem is thus dealt with in a discrete way, without considering spacecraft acceleration but only velocity and position vectors. With a view to substitute chemical propulsion systems with electrical ones, the solution approaches of the GEO station keeping problem should become continuous, in order to gain benefit from the technology change. A GEO satellite dynamics model has to be obtained taking into account all the perturbing forces (environmental or not) acting on the spacecraft. In this paper, we explain in detail the nonlinear dynamical model used to design the station keeping controller and the analytical approximations done to implement this

Characterization of Nanothermite Material for Solid-Fuel Microthruster Applications

Nanothermite composites containing metallic fuel and inorganic oxidizer have unique combustion properties that make them potentially useful for microthruster applications. The thrust-generating characteristics of copper oxide/aluminum nanothermites have been investigated. The mixture was tested in various quantities (9―38 mg) by pressing the material over a range of densities. The testing was done in two different types of thrust motors: one with no nozzle and one with a convergent―divergent nozzle. As the packing density was varied, it was found that the material exhibited two distinct impulse characteristics. At low packing pressure, the combustion was in the fast regime, and the resulting thrust forces were ∼75 N with a duration of less than 50 μs full width at half-maximum. At high density, the combustion was relatively slow and the thrust forces were 3―5 N with a duration 1.5―3 ms. In both regimes, the specific impulse generated by the material was 20―25 s. The specific impulse and short thrust duration created by this unique nanothermite material makes it promising for micropropulsion applications, in which space is limited.

Shock-Tunnel Experiments with a Mach 12 Rectangular-to-Elliptical Shape-Transition Scramjet at Offdesign Conditions

A shock-tunnel investigation of a scramjet with a rectangular-to-elliptical shape-transition inlet and an elliptical combustor has been conducted at conditions simulating flight at Mach 8.7. The inlet was designed using a quasistreamline-tracing method to have a design point of Mach 12.0 and operation down to Mach 6.0. The elliptical combustor began with a rearward-facing step around its perimeter and was followed by a constant-area and diverging section. The flowpath was completed by a short thrust nozzle. Gaseous hydrogen fuel was injected either through multiple portholes on the intake, a series of 48 portholes on the rearward-facing step at the combustor entrance, or a combination of the two. All fueling configurations resulted in a positive thrust coefficient at equivalence ratios above 0.3 without the use of ignition aids. Fuel injection in the intake produced robust combustion and good internal thrust levels, but led to inlet unstart at fuel equivalence ratios above 0.61. Stable mixing-limited combustion was observed for fuel injection at the step at all fuel equivalence ratios up to 1.23. Combined intake and step injection was observed to have the best performance. These experimental results demonstrate that rectangular-to-elliptical shape-transition scramjets designed for access-to-space applications can operate efficiently at conditions below the design Mach number.

Stress triggering in thrust and subduction earthquakes and stress interaction between the southern San Andreas and nearby thrust and strike‐slip faults

We argue that key features of thrust earthquake triggering, inhibition, and clustering can be explained by Coulomb stress changes, which we illustrate by a suite of representative models and by detailed examples. Whereas slip on surface‐cutting thrust faults drops the stress in most of the adjacent crust, slip on blind thrust faults increases the stress on some nearby zones, particularly above the source fault. Blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks. Short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults. We calculate that during a progressive thrust sequence in central California the 1983 Mw = 6.7 Coalinga earthquake brought the subsequent 1983 Mw = 6.0 Nuñez and 1985 Mw = 6.0 Kettleman Hills ruptures 10 bars and 1 bar closer to Coulomb failure. The idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events, in agreement with findings of prior investigations. Subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust‐faulting events on the periphery of the seismic rupture and its downdip extension. These features are evident in aftershocks of the 1957 Mw = 9.1 Aleutian and other large subduction earthquakes. We further examine stress changes on the rupture surface imparted by the 1960 Mw = 9.5 and 1995 Mw = 8.1 Chile earthquakes, for which detailed slip models are available. Calculated Coulomb stress increases of 2–20 bars correspond closely to sites of aftershocks and postseismic slip, whereas aftershocks are absent where the stress drops by more than 10 bars. We also argue that slip on major strike‐slip systems modulates the stress acting on nearby thrust and strike‐slip faults. We calculate that the 1857 Mw = 7.9 Fort Tejon earthquake on the San Andreas fault and subsequent interseismic slip brought the Coalinga fault ∼1 bar closer to failure but inhibited failure elsewhere on the Coast Ranges thrust faults. The 1857 earthquake also promoted failure on the White Wolf reverse fault by 8 bars, which ruptured in the 1952 Mw = 7.3 Kern County shock but inhibited slip on the left‐lateral Garlock fault, which has not ruptured since 1857. We thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales.

Biomechanics of knife stab attacks

Equipment, materials and methods for the measurement of the biomechanical parameters governing knife stab attacks have been developed and data have been presented that are relevant to the improvement of standards for the testing of stab-resistant materials. A six-camera Vicon motion analysis system was used to measure velocity, and derive energy and momentum during the approach phase of the attack and a specially developed force-measuring knife was used to measure three-dimensional forces and torque during the impact phase. The body segments associated with the knife were modelled as a series of rigid segments: trunk, upper arm, forearm and hand. The velocities of these segments, together with knowledge of the mass distribution from biomechanical tables, allowed the calculation of the individual segment energy and momentum values. The instrumented knife measured four components of load: axial force (along the length of the blade), cutting force (parallel to the breadth of the blade), lateral force (across the blade) and torque (twisting action) using foil strain gauges. Twenty volunteers were asked to stab a target with near maximal effort. Three styles of stab were used: a short thrust forward, a horizontal style sweep around the body and an overhand stab. These styles were chosen based on reported incidents, providing more realistic data than had previously existed. The 95th percentile values for axial force and energy were 1885 N and 69 J, respectively. The ability of current test methods to reproduce the mechanical parameters measured in human stab attacks has been assessed. It was found that current test methods could reproduce the range of energy and force values measured in the human stab attacks, although the simulation was not accurate in some respects. Non-axial force and torque values were also found to be significant in the human tests, but these are not reproduced in the standard mechanical tests.

An Investigation of High Performance, Short Thrust Augmenting Ejectors

The design of air-to-air, thrust augmenting ejectors having short curved wall diffuses utilizing boundary layer control is discussed. The design is achieved by an inverse method which uses the vorticity at the diffuser inlet as a flow parameter in the analysis. Three diffusers having ejector length-to-mixing chamber diameter ratios of approximately 6:1 and mixing chamber inlet area-to-primary nozzle area ratios of 20:1 and 40:1 were designed and tested. A new high level of performance was analytically predicted and achieved experimentally. Comparisons between predicted and observed performances, velocity distributions and pressure distributions are presented.

Supersonic hydrogen combustion with a short thrust nozzle

A shock tunnel was used to investigate the thrust produced by supersonic combustion of hydrogen in a simple, two-dimensional combustion chamber-exhaust nozzle combination, at stagnation enthalpies up to 15 MJ kg −1. The experiments demonstrated that one-dimensional flow concepts were not adequate to predict the thrust level, and that two-dimensional effects must be taken into account. An analysis was developed which allowed the internal thrust increment of the two-dimensional nozzle to be compared with that of an equivalent one-dimensional one. It was found that, up to combustor static temperatures of 2000K, measured thrust increments were approximately half of the value for premixed equilibrium flow through the equivalent one-dimensional nozzle. Ignition occurred at approximately 1000K, and values of internal specific impulse rose above 1000 s just above this temperature, but fell to 500 s as temperatures rose above 2000K.