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"Thrust"
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Examining the tectono-stratigraphic architecture, structural geometry, and kinematic evolution of the Himalayan fold-thrust belt, Kumaun, northwest India
Existing structural models of the Himalayan fold-thrust belt in Kumaun, northwest India, are based on a tectono-stratigraphy that assigns different stratigraphy to the Ramgarh, Berinag, Askot, and Munsiari thrusts and treats the thrusts as separate structures. We reassess the tectono-stratigraphy of Kumaun, based on new and existing U-Pb zircon ages and whole-rock Nd isotopic values, and present a new structural model and deformation history through kinematic analysis using a balanced cross section. This study reveals that the rocks that currently crop out as the Ramgarh, Berinag, Askot, and Munsiari thrust sheets were part of the same, once laterally continuous stratigraphic unit, consisting of Lesser Himalayan Paleoproterozoic granitoids (ca. 1850 Ma) and metasedimentary rocks. These Paleoproterozoic rocks were shortened and duplexed into the Ramgarh-Munsiari thrust sheet and other Paleoproterozoic thrust sheets during Himalayan orogenesis. Our structural model contains a hinterland-dipping duplex that accommodates ∼541-575 km or 79%-80% of minimum shortening between the Main Frontal thrust and South Tibetan Detachment system. By adding in minimum shortening from the Tethyan Himalaya, we estimate a total minimum shortening of ∼674-751 km in the Himalayan fold-thrust belt. The Ramgarh-Munsiari thrust sheet and the Lesser Himalayan duplex are breached by erosion, separating the Paleoproterozoic Lesser Himalayan rocks of the Ramgarh-Munsiari thrust into the isolated, synclinal Almora, Askot, and Chiplakot klippen, where folding of the Ramgarh-Munsiari thrust sheet by the Lesser Himalayan duplex controls preservation of these klippen. The Ramgarh-Munsiari thrust carries the Paleoproterozoic Lesser Himalayan rocks ∼120 km southward from the footwall of the Main Central thrust and exposed them in the hanging wall of the Main Boundary thrust. Our kinematic model demonstrates that propagation of the thrust belt occurred from north to south with minor out-of-sequence thrusting and is consistent with a critical taper model for growth of the Himalayan thrust belt, following emplacement of midcrustal Greater Himalayan rocks. Our revised stratigraphy-based balanced cross section contains ∼120-200 km greater shortening than previously estimated through the Greater, Lesser, and Subhimalayan rocks.
Journal Article
Numerical study of the brash ice effects on propeller performance with different advance speeds
In this paper, the effects of brash ice on propeller performance with different advanced speeds are numerically analysed based on the CFD-DEM method. The results show that in the ice-water environment, the thrust and torque of the propeller oscillate violently due to the interaction between the ice and the propeller, and as the advanced speed increases, the oscillation becomes more and more intense. Moreover, under the blocking effect of sea ice, the average value of the thrust and torque of the propeller obviously increase and cause a large loss of propeller performance under high advance speed conditions, which would seriously affect the ice-breaking ability of polar ships.
Journal Article
Techniques of Fluidic Thrust Vectoring in Jet Engine Nozzles: A Review
Thrust vectoring innovations are demonstrated ideas that improve the projection of aerospace power with enhanced maneuverability, control effectiveness, survivability, performance, and stealth. Thrust vector control systems following a variety of concepts have been considered for modern aircraft and missiles to enhance their military performance. Short Take-off and Landing (STOL) and control effectiveness at lower aircraft speeds can be achieved by employing Fluidic Thrust Vectoring Control (FTVC). This paper summarizes a range of ideas for FTVC that have been designed and tested both computationally and experimentally to determine the thrust vectoring performance of supersonic propulsion system nozzles. The conventional method of thrust vectoring involves mechanical means to deflect the direction of flow of the exhaust gases, whereas the most recent method involves fluidic-based thrust vectoring techniques. Fluid-based thrust vectoring has the advantages of simplicity and low weight over mechanical-based thrust vectoring, which has complex geometry and adds extra weight to the aircraft. The fluidic vectoring control nozzles are divided into seven categories: shock vector, bypass shock vector, counterflow, co-flow, throat skewing, dual throat, and bypass dual throat nozzle control. This paper provides a summary of each fluidic thrust vectoring technique with its characteristics, design, classification, and different operational criteria developed to date and compares the intrinsic characteristics of each technique. Based on the present literature, it is concluded that among all the fluidic control techniques, the bypass dual-throat nozzle control can achieve better thrust vectoring performance with large vector angles and low thrust loss.
Journal Article
Pneumatic hammer characteristics of the aerostatic thrust bearing with central orifice and pressure-equalizing groove
The introduction of central orifice and central pressure-equalizing groove (PEG) greatly improves the load capacity of aerostatic thrust bearing. However, it is also easier to cause pneumatic hammer vibration which will degrade the bearing performance and requires to be studied urgently. In this paper, a dynamic model is developed to investigate this problem by coupling the bearing dynamic equation and the transient gas film Reynolds equation which is reduced by Galerkin weighted residual method and discretized through finite element method. The flexible sensor is creatively applied to measure the aerostatic force and gas film pressure distribution, which help verify the model correctness. The mechanism of pneumatic hammer is revealed by analyzing the molecular kinetic energy and the phase difference between variations of gas film thickness and aerostatic force. The characteristics of pneumatic hammer are analyzed under different structural parameters and supply pressures. The results indicate the pneumatic hammer vibration tends to happen when the mass and supply pressure are greater than the corresponding critical values.
Journal Article
Reduction in power loss and increased safety of thrust collar bearings through profiling of the treads – Application of rolling bearing profiles and crowning on thrust collar bearings
Thrust collar bearings can be used to increase the efficiency of megawatt-scaled turbo drivetrains by transferring the compressor thrust from the highspeed shaft to the low-speed shaft, where it can be efficiently supported in the low-speed bearings. This also allows the bearing on the high-speed shaft to be replaced by bearing types with lower power loss. In the following, measures to reduce the thrust collar power loss are investigated. In particular, the effect of different tread profiling is addressed. It is shown that the usual profiling of tribologically similar rolling bearings is no better suited to thrust collars than fully crowned profiles1.
Journal Article
Seismic interpretation of the Laga Basin; constraints on the structural setting and kinematics of the Central Apennines
The Messinian Laga basin is the largest foreland basin within the Central Apennines fold and thrust belt (Italy). This area, actively investigated in the 1980s and 1990s for hydrocarbon resources, is considered a valuable analogue for clastic reservoirs developed in confined structural settings. Furthermore, it represents a key area for understanding the evolution of the Apennines, as it links the internal, structurally uplifted Early Miocene fold and thrust belt of the western Central Apennines with the more external and recent belt to the east. Despite several papers published on this area, the only reconstruction of the substratum structure is an internal and classified industry report. During the present study, we had access to a seismic database comprising 200 km of seismic profiles that were collected between 1983 and 1990. These data allowed us to reconstruct the structural setting of the Laga basin substratum, define the lateral continuity of the main compressional structures within the basin, construct a balanced cross-section, and define the shortening values.
Journal Article
Study on the Characteristics of Axial Hydraulic Thrust of Ultra-high-head Pump-Turbines Considering the Clearance Flow
The clearance flow passage of a pump-turbine is a multi-stage thin-layer cavity composed of the impeller and the head cover or bottom ring. Since the clearance flow passage is extremely small in size and complex in shape, current research on the impeller hydraulic thrust often ignores its influence, making it difficult to fully reveal the unbalanced force on the impeller and the vibration mechanism of the unit. Therefore, it is essential to study the clearance flow of ultra-high-head pump-turbine impellers. In this study, numerical simulations of the impeller clearance flow in a pump-turbine at 3 different operating cases were conducted using CFX, based on the Navier-Stokes equations and the SST k-ω turbulence model. The internal flow state within the sealing clearance was analyzed through pressure distribution maps and velocity vector diagrams, thereby revealing the formation and distribution mechanism of vortices within the clearance. In addition, by using the preset clearance model and through the pressure contour maps, velocity vectors, and streamlines obtained from the simulation, the influence of the clearance flow on the axial hydraulic thrust under the pump condition was evaluated.
Journal Article
Experimental Study in Micro-drilling Mechanism on Heterogeneous Structure of Thermal Barrier Coated Inconel 718 Superalloy
Thermal barrier coated (TBC) superalloys are extensively used for manufacturing turbine blades to sustain high temperature zone while in operation. The production of cooling holes on these blades surface at various inclinations to the surface is essential to minimize the severe heat load experienced during working to achieve higher service life. Manufacturing of these holes is a main challenge in TBC superalloys due to combined metal and ceramic layers along the hole depth which effect on the thrust force generation, tool life and hole quality. Therefore, in this study mechanical micro-drilling is proposed to analyze the above highlighted difficulty. The experiments were performed on TBC Inconel 718 sheet having 3.3 mm thickness using 600 μm TiAlN coated carbide drill under dry environment. Three input parameters with their two levels are chosen for experimentations and each experiment is performed two times. Micro-drilling performance is assessed in terms of drilling thrust at different material layer with hole depth, taper of hole and distribution of thrust along the cutting edge of drill. Results show that magnitude of dynamic drilling thrust variation is observed at interface drilling irrespective of hole orientation. Whereas, maximum drilling thrust is observed before retraction of the drill. Magnitude of thrust force and fluctuation of thrust signal increases with depth of hole due to chip clogging in flute space. Minimum taper of a hole is observed in case of straight hole drilling than inclined hole whereas circular shape of hole is produced in straight hole drilling whereas elliptical hole is produced in case of inclined hole. Equal amount of thrust distribution along the cutting edge is observed in case of straight hole drilling but unequal amount of thrust distribution is seen in of case inclined hole due to drill-workpiece interaction.
Journal Article
Performance augmentation mechanism of in-line tandem flapping foils
The propulsive performance of a pair of tandem flapping foils is sensitively dependent on the spacing and phasing between them. Large increases in thrust and efficiency of the hind foil are possible, but the mechanisms governing these enhancements remain largely unresolved. Two-dimensional numerical simulations of tandem and single foils oscillating in heave and pitch at a Reynolds number of 7000 are performed over a broad and dense parameter space, allowing the effects of inter-foil spacing (
$S$
) and phasing (
$\\unicode[STIX]{x1D711}$
) to be investigated over a range of non-dimensional frequencies (or Strouhal number,
$St$
). Results indicate that the hind foil can produce from no thrust to twice the thrust of a single foil depending on its spacing and phasing with respect to the fore foil, which is consistent with previous studies that were carried out over a limited parameter space. Examination of instantaneous flow fields indicates that high thrust occurs when the hind foil weaves between the vortices that have been shed by the fore foil, and low thrust occurs when the hind foil intercepts these vortices. Contours of high thrust and minimal thrust appear as inclined bands in the
$S-\\unicode[STIX]{x1D711}$
parameter space and this behaviour is apparent over the entire range of Strouhal numbers considered
$(0.2\\leqslant St\\leqslant 0.5)$
. A novel quasi-steady model that utilises kinematics of a virtual hind foil together with data obtained from simulations of a single flapping foil shows that performance augmentation is primarily determined through modification of the instantaneous angle of attack of the hind foil by the vortex street established by the fore foil. This simple model provides estimates of thrust and efficiency for the hind foil, which is consistent with data obtained through full simulations. The limitations of the virtual hind foil method and its physical significance is also discussed.
Journal Article