Local Pressure Loads Research Articles

Characterize the influences of hydraulic fracturing on preventing rock burst from the stress and vibration fields

The thick and hard roof (THR) is a significant factor that induces rock burst incidents. Traditional deep-hole blasting methods struggle to effectively relieve pressure for the high-level THR on a large scale. Although the horizontal staged hydraulic fracturing technology can crack high-level rock stratas, its impact on roof fracture still needs to be clarified, and there need to be more effective methods to evaluate its pressure relief effect. This paper conducted a comparative engineering test of local hydraulic fracturing pressure relief and load reduction on the working face to address this gap. The key layer theory and mine earthquake distribution were used to identify potential hazards of rock strata and the fracturing strata. Revealed the spatial and temporal evolution rules of microseisms induced by mining work, the failure mechanism of high-energy mine earthquakes, the evolution characteristics of source mechanical parameters, and the evolution characteristics of the stope stress field. The results indicate that after fracturing microseisms during mining presented exhibit a uniform distribution of high frequency and low energy. The fracture fragmentation of the roof rock was reduced, and the range of mining disturbance was minimized. High-energy mine earthquakes induced by mining are transferred to the goaf. Simultaneously, the corner frequency and stress decrease while the rupture radius and the shear component of the failure mechanism increase. The integrity of the THR is compromised, and fracture propagates and slips along the pre-crack. The roof of the working face experiences localized pressure, with decreased periodicity and intensity, reducing the overall static load level of the coal seam under the fracturing area. The research findings serve as a valuable reference for further investigations into the mechanism and risk assessment of hydraulic fracturing in preventing and controlling rock burst.

A Methodological Framework for Structural Reliability Assessment of Marine Structural Elements

The aim of this paper is to provide a robust framework to assist researchers in deciding which methods to use, depending on the problem at hand, in order to estimate the probability of failure of marine structural parts that are subjected to variable loads (both hull-girder and local pressure loads) that exhibit uncertainties in their material properties and that involve fabrication-related uncertainties. The limitations of analytical approaches both in deterministic mathematical modeling (strength formulas) and probabilistic estimation will be provided, and respective computational tools will be demonstrated (FEA and Monte Carlo simulation). The approach is showcased in flat and bow-defected rectangular plates through analytical and numerical approaches.

Hull Girder Ultimate Strength Analysis of 17500 LTDW Oil Tanker under the Combined Global and Local Load using Explicit Finite Element Analysis

This study investigates the hull girder’s ultimate strength of 17500 LTDW Oil Tanker. The explicit finite element analysis is carried out to estimate the hull girder longitudinal strength of the Oil Tanker. The numerical analysis starts with the longitudinal strength analyses that examine the ship’s structural response behavior due to sagging and hogging bending moment load. The structural strength analyses were conducted to determine the maximum structural response behavior for withstanding the operational load. Afterward, the hull girder’s ultimate strength is undertaken to reflect the progressive collapse behavior of the oil tanker structure under the combined global bending moment and local hydrostatic pressure load. The explicit finite element analysis is performed to estimate the ultimate strength behavior, considering the effect of the hydrostatic pressure load and the material nonlinearities. The typical 17500 LTDW oil tanker represents Indonesia’s common oil vessel that supports national fuel oil distribution. Furthermore, this study can recognize the oil tanker’s ultimate hull girder strength characteristics.

SIMULATION OF A MANEUVERING AIRCRAFT USING A PANEL METHOD

We present a method for numerical simulations of a maneuvering aircraft, which uses a first-order unsteady panel method as the only source of aerodynamic forces and moments. By using the proposed method, it is possible to simulate a motion of an aircraft, while the only required inputs are geometry and inertia characteristics, which significantly reduces the time required to start the simulation. We validated the method by a comparison of recordings of flight parameters (position, velocities, accelerations) from an actual aerobatic flight of a glider and the results obtained from the simulations. The simulation was controlled by deflections of control surfaces recorded during the actual flight. We found a reasonable agreement between the experimental data and the simulation. The design of our method allows to evaluate not only the integral kinematic quantities but also instant local pressure and inertia loads. This makes our method useful also for a load evaluation of an aircraft. A significant advantage of the proposed method is that only an ordinary workstation computer is requiredto perform the simulation.

Design of bridges against ship collisions

The paper outlines a rational design procedure for bridge piers and pylons against ship collision impacts. Firstly, a set of risk acceptance criteria are proposed. This is followed by a mathematically based procedure for calculation of the probability of critical ship meeting situations near the bridge, and the probability of ship collision accidents caused by human errors as well as technical errors. This first part of the paper leads to identification of the largest striking ship, “design vessels”, a given bridge pier must withstand without structural failure in order for the bridge connection to fulfil the risk acceptance criteria. The final part of the paper is devoted to an analysis of the needed impact capacity for the bridge pylons and piers exposed to ship bow impact loads from these “design vessels”. For a number of different ship types and different tonnage merchant vessels, load – displacement relations for ship bow collisions against rigid walls are derived. Based on these comprehensive numerical results, a new empirical relation is derived which is suited for design against bow collisions. This expression for maximum bow collision forces is compared with a previously published expression for ice-strengthened ships and with existing standards for assessment of bow crushing forces. It is shown that there is need for an update of these existing standards. For design of piers and pylons against local impact pressure loads, a pressure - area relation for bulbous bow impacts is derived.

Flow structure in the wake of a space-launcher model with propulsive-jet simulation

The flow around a space launcher is dominated by flow separation at the junction between the main body and engine and strongly influenced by the propulsive jet. The flow field is highly unsteady with strong local pressure and temperature loads. To conceive a means of mitigating these effects and allow for smarter launcher designs, a better understanding is necessary. The wake of a generic axisymmetric launcher model with and without afterexpanding propulsive jet was investigated at Mach 2.9, a Reynolds number text {Re}_D=1.3cdot 10^6 (model diameter D), and a nozzle exit velocity of the jet simulation of Mach 2.5. I observed the evolution of the flow and its spectral content with velocity measurements with particle image velocimetry and wall-pressure recordings. Coherent structures were analyzed based on a proper orthogonal decomposition. The propulsive jet has two major influences. First, the turbulent intensities in the shear layer are damped, and the larger structures in the wake contain less turbulent kinetic energy than in the baseline case without propulsive jet. Second, the reattachment process is modified and the wake instability phenomena change accordingly. Without propulsive jet, large-scale separation with reattachment on the nozzle fairing occurs and the low-frequency unsteadiness of the closed separation bubble/recompression-shock system is relevant. This phenomenon only has a minor influence under the influence of the jet plume, where the flow is displaced away from the surface and the reattachment process is incomplete. Here, shear-layer instabilities become more prominent.

Slamming load on trimaran cross section with rigid and flexible arches

In this paper, the mixed mode function–modified MPS method was adopted to simulate the water-structure dynamic interaction during slamming impacts on the cross deck of trimaran. The water was considered as an incompressible inviscid fluid and the “conceptual particle” model was used to enhance the stability of the intense free surface interaction during the “filling-up” process under the cross deck. The numerical model for the coupled rigid and flexible modal superposition model was derived for the dynamics of the trimaran hull with rigid and flexible arches, and the flexible arch was simplified by a beam structure. The fluid and structure solvers were coupled in a standard iterative way. The results for rigid-body arch cases obtained with the use of improved free surface condition show good improvement, in comparison to the experiment data. From the study of flexible arch cases with different flexibilities, it is found that the relatively soft structure can reduce the local pressure and slamming load.

Pressure distension in leg vessels as influenced by prolonged bed rest and a pressure habituation regimen.

Bed rest increases pressure distension in arteries, arterioles, and veins of the leg. We hypothesized that bed-rest-induced deconditioning of leg vessels is governed by the removal of the local increments in transmural pressure induced by assuming erect posture and, therefore, can be counteracted by intermittently increasing local transmural pressure during the bed rest. Ten men underwent 5 wk of horizontal bed rest. A subatmospheric pressure (-90 mmHg) was intermittently applied to one lower leg [pressure habituation (PH) leg]. Vascular pressure distension was investigated before and after the bed rest, both in the PH and control (CN) leg by increasing local distending pressure, stepwise up to +200 mmHg. Vessel diameter and blood flow were measured in the posterior tibial artery and vessel diameter in the posterior tibial vein. In the CN leg, bed rest led to 5-fold and 2.7-fold increments (P < 0.01) in tibial artery pressure-distension and flow responses, respectively, and to a 2-fold increase in tibial vein pressure distension. In the PH leg, arterial pressure-distension and flow responses were unaffected by bed rest, whereas bed rest led to a 1.5-fold increase in venous pressure distension. It thus appears that bed-rest-induced deconditioning of leg arteries, arterioles, and veins is caused by removal of gravity-dependent local pressure loads and may be abolished or alleviated by a local pressure-habituation regimen.

Blood pressure regulation V: in vivo mechanical properties of precapillary vessels as affected by long-term pressure loading and unloading

Recent studies are reviewed, concerning the in vivo wall stiffness of arteries and arterioles in healthy humans, and how these properties adapt to iterative increments or sustained reductions in local intravascular pressure. A novel technique was used, by which arterial and arteriolar stiffness was determined as changes in arterial diameter and flow, respectively, during graded increments in distending pressure in the blood vessels of an arm or a leg. Pressure-induced increases in diameter and flow were smaller in the lower leg than in the arm, indicating greater stiffness in the arteries/arterioles of the leg. A 5-week period of intermittent intravascular pressure elevations in one arm reduced pressure distension and pressure-induced flow in the brachial artery by about 50 %. Conversely, prolonged reduction of arterial/arteriolar pressure in the lower body by 5 weeks of sustained horizontal bedrest, induced threefold increases of the pressure-distension and pressure-flow responses in a tibial artery. Thus, the wall stiffness of arteries and arterioles are plastic properties that readily adapt to changes in the prevailing local intravascular pressure. The discussion concerns mechanisms underlying changes in local arterial/arteriolar stiffness as well as whether stiffness is altered by changes in myogenic tone and/or wall structure. As regards implications, regulation of local arterial/arteriolar stiffness may facilitate control of arterial pressure in erect posture and conditions of exaggerated intravascular pressure gradients. That increased intravascular pressure leads to increased arteriolar wall stiffness also supports the notion that local pressure loading may constitute a prime mover in the development of vascular changes in hypertension.

Research on Strength Calculation for Local Area under Pressure

Here individual anchored strength of prestressed end with local area under pressure was studied, the damaged mechanism of local area under pressure was discussed. The ferrule effect of peripheral concrete upon the concrete under local pressure loading is not obvious. For prestressed concrete members, especially scattered end anchorage of prestressed concrete member, the standard formula is not applicable.

Individual Anchored Strength Experimental Research for Prestressed End with Local Area Pressure

Here individual anchored strength of prestressed end with local area under pressure was studied through experiment, the damaged mechanism of local area under pressure was discussed. The ferrule effect of peripheral concrete upon the concrete under local pressure loading is not obvious.

Experimental Study on Local Compression of Concrete-filled Glass Fiber Reinforced Gypsum Wall Panel

The concrete-filled glass fiber reinforced gypsum wall panel is a kind of panel that the inside cavums of the glass fiber hollow gypsum panel is filled with concrete. The experimental results indicate that the concrete-filled glass fiber reinforced gypsum wall panel which has a better performance of the force and can be used to be the bearing wall of a building can form a novel structural system. When the beams supporting the wall panels, the wall panels which under the beams is in local state of compression. It were gained that when the wall panels are in the local compression state , local pressure loads are primarily borne by the concrete core columns and fiber gypsum board will damage in advance through the eighteen experimental wall panel specimens which in local compression. The test results show that the final destruction of the concrete is caused by being crushed and the contribution of the gypsum wall panel to local compression bearing is small. Compressive stress can only spread in the local loading on concrete core columns, cannot be expanded into an adjacent stud. Finally, the local compression bearing capacity calculation formula of the concrete-filled glass fiber reinforced gypsum wall panel is obtained by analysis of the test results.

Fatigue damage assessment of corroded oil tanker details based on global and local stress approaches

Fatigue damage assessment of double hull oil tanker structural details is performed, based on global and local structural finite element models. The wave-induced vertical and horizontal bending moments, as well as local pressure loads are accounted for in the fatigue damage calculations. Local stress analyses are considered based on the notch stress approach. Time-dependent stresses as a function of corrosion deterioration are analyzed based on nonlinear corrosion wastage during the design life of ship. The effective notch stress approach is applied for analyzing the stress distributions and the fatigue damage of the welded joint at two hotspots. The hotspots are located between the flat bar stiffener of a transverse web frame and the flange of a longitudinal stiffener at the side shell of a tanker ship hull. The details under consideration are modeled separately in a fine mesh employing the sub model techniques. Finally the fatigue damage assessment accounting for corrosion deterioration of the considered hotspots is analyzed.

Ultimate hull girder strength of a bulk carrier under combined global and local loads in the hogging and alternate hold loading condition using nonlinear finite element analysis

For bulk carriers in hogging, the most critical situation is the alternate hold loading (AHL) condition with odd numbered holds loaded with high density cargoes and even numbered holds empty. The effect of the local lateral pressure loads should be considered in the assessment of ultimate hull girder strength in the hogging and AHL conditions. In the present paper the ultimate strength of a Capesize bulk carrier hull girder under combined global and local loads in the hogging and AHL condition is extensively and systematically investigated using nonlinear finite element (FE) analysis with ABAQUS software. Since the bulk carrier used as a reference vessel in this study is an old design we also studied the effect of modified scantlings by multiplying the plate thickness in the bottom structure by a design modification factor (DMF). In particular, it should be noted that a DMF of 1.4 gives a design in accordance with the new CSR rules. Based on the results obtained by nonlinear FE analyses, a practical interaction equation is established between global hogging bending capacity and average external sea pressure over the bottom.

Reliability analysis of a bulk carrier in ultimate limit state under combined global and local loads in the hogging and alternate hold loading condition

The alternate hold still-water loading in hogging combined with wave loading is critical for the safe design of bulk carriers. The ultimate longitudinal strength of the hull girder of bulk carriers in this condition has been found to be considerably reduced by the action of local lateral pressure loads. In the present paper, an interaction equation based on the ultimate hull girder strength assessment obtained by nonlinear finite element analyses is adopted to consider the relationship between ultimate longitudinal bending capacity and average external sea pressure over the bottom. This interaction equation is used as the basis for the failure function. The annual probability of failure is obtained by FORM analysis considering two typical load cases, namely, pure longitudinal hogging bending moment and combined global hogging bending moment and local lateral pressure loads. The effect of heavy weather avoidance on the failure probability is evaluated. The results show that the local lateral pressure has a significant influence on the annual probability of failure of bulk carriers in the hogging and alternate hold loading condition.

Analytical model for characterizing the pear-shaped tribotest for tube hydroforming. Part 1

An analytical model to characterize the pear-shaped tribotest is presented. In this test, a tubular specimen is pressurized, forcing the material to flow towards the apex of a pear-shaped die. The height of the pear-shaped tube is a function of the magnitude of friction stress at the tube—die interface. Through a mechanistic approach, a closed-form solution for field variables die—tube contact pressure, effective stress/strain, longitudinal stress/strain, and hoop stress/strain can be computed as a function of input pressure loading. The model has been validated by finite element analysis. The closed-form solution can be used rapidly to establish the calibration curves for determination of friction coefficient in the pear-shaped tribotest. Of equal importance, the analytical model can be used to optimize both process and die geometric variables to suit specific needs such as die wear studies through monitoring local interface pressure loading, types of material to be tested, tube sizes, and so on. Details on the applications of the developed analytical model can be found in Part 2 of this paper.

Investigation of ultra violet (UV) resistance for high strength fibers

Ultra long duration balloons (ULDB), currently under development by the National Aeronautics and Space Administration (NASA), requires the use of high strength fibers in the selected super-pressure pumpkin design. The pumpkin shape balloon concept allows clear separation of the load transferring functions of the major structural elements of the pneumatic envelope, the tendons and the film. Essentially, the film provides the gas barrier and transfers only local pressure load to the tendons. The tendons, in the mean time, provide the global pressure containing strength. In that manner, the strength requirement for the film only depends on local parameters. The tendon is made of p-phenylene-2,6-benzobisoxazole (PBO) fibers, which is selected due to its high strength to weight ratio when compared to other high performance, commercially available, fibers. High strength fibers, however, are known to degrade upon exposure to light, particularly at short wavelengths. This paper reports the results of an investigation of the resistance of four commercial high strength fibers to ultra violet (UV) exposure. The results indicate that exposing high strength fibers in continuous yarn form to UV led to serious loss in strength of the fibers except for Spectra ® fibers. The adverse changes in mechanical behavior occurred over short duration of exposure compared to the 100 day duration targeted for these missions. UV blocking finishes to improve the UV resistance of these fibers are being investigated. The application of these specially formulated coatings is expected to lead to significant improvement of the UV resistance of these high performance fibers. In this publication, we report on the mechanical behavior of the fibers pre- and post-exposure to UV, but without application of the blocking finishes.

Pattern of injury in those dying from traumatic amputation caused by bomb blast.

Traumatic amputation of limbs caused by bomb blast carries a high risk of mortality. This paper describes 73 amputations in 34 deaths from bomb blast in Northern Ireland. The principal aim was to determine the sites of traumatic amputation to provide a biophysical basis for the development of protective measures. Few amputations were through joints; nearly all were through the bone shafts. The most common site in the tibia was the upper third. The distribution of femoral sites resulting from car bombs differed from that characterizing other types of explosion. For car bombs the principal site of amputation was the upper third; for other types of device it was the lower third. It is concluded that flailing is not a notable contributor to limb avulsion. The pattern of amputation is consistent with direct local pressure loads leading to bone fracture; the amputation itself is a secondary event arising from the flow of combustion products.

Mechanical passive and active models of the human basilar membrane

Simple three-dimensional passive and active models of the human basilar membrane were built, solved using the Finite Element Method and tested. In the active model an active mechanism connected with electromotility of outer hair cells was included. In the active model the active mechanism was incorporated in the form of additional, local pressure load. In the passive model the active mechanism was neglected. Hydrodynamic coupling between the cochlear partition and cochlear fluid was excluded in both models. Geometrical and physical parameters of the model were chosen to be adequate to those of humans in the best possible way. However, some of these parameters had to be estimated. The models were tested by calculation of typical curves known from cochlear measurements performed mostly on animals. For the passive model a linear input–output function and very small values of the basilar membrane velocities were obtained. This behaviour is to be expected for the passive model and for the basilar membrane in the poor physiological condition. For the active model the compressed input–output functions, tuning curves, isointensity curves and reasonable BM velocities were obtained. Possible inadequacies, which could explain the differences between numerical results and measurements were described.

Euler–Lagrange coupling with damping effects: Application to slamming problems

During a high velocity impact of a structure on a nearly incompressible fluid, impulse loads with high-pressure peaks occur. This physical phenomenon called ‘slamming’ is a concern in shipbuilding industry because of the possibility of hull damage. Shipbuilding companies have carried out several studies on slamming modeling using FEM software with added mass techniques to represent fluid effects. In the added mass method inertia effects of the fluid are not taken into account and are only valid when the deadrise angle is small. This paper presents the prediction of the local high pressure load on a rigid wedge impacting a free surface, where the fluid is represented by solving Navier–Stokes equations with an Eulerian or ALE formulation. The fluid–structure interaction is simulated using a coupling algorithm; the fluid is treated on a fixed or moving mesh using an ALE formulation and the structure on a deformable mesh using a Lagrangian formulation. A new coupling algorithm is developed in the paper. The coupling algorithm computes the coupling forces at the fluid–structure interface. These forces are added to the fluid and structure nodal forces, where fluid and structure are solved using an explicit finite element formulation. Predicting the local pressure peak on the structure requires an accurate fluid–structure interaction algorithm. The Euler–Lagrange coupling algorithm presented in this paper uses a penalty based formulation similar to penalty contact in Lagrangian analyses. Both penalty coupling and penalty contact can generate high frequency oscillations due to the nearly incompressible nature of the fluid. In this paper, a damping force based on the relative velocity of the fluid and the structure is introduced to smooth out non-physical high frequency oscillations induced by the penalty springs in the coupling algorithm.