Prediction of the Collapse Region Induced by a Concealed Karst Cave above a Deep Highway Tunnel

The presence of a concealed karst cave above a deep highway tunnel may cause the collapse of the rock mass between the karst cave and tunnel during excavation. Rock mass collapse threatens the safety of tunnel construction personnel. A prediction method of the collapse region induced by a concealed karst cave above a deep highway tunnel is proposed on the basis of the upper bound theorem of limit analysis. An analytical expression of the collapse surface is derived from the variational principle. Using the analytical expression of the collapse surface, the shapes of the collapse surfaces are plotted for different rock mass parameters. Moreover, the minimum safe distance between the karst cave and tunnel is defined, and the computational equation of the minimum safe distance is derived. The proposed method is applied in a highway tunnel excavated in a karst terrain as a case study. Based on geological survey report parameters, the shape of the collapse surface and the minimum safe distance between the karst cave and tunnel are obtained. Finally, the collapse surface of the rock mass provided by the proposed approach is compared with that provided by numerical simulation, and the favorable result comparison shows that the proposed method is valid.

Experimental Characterization of an Embossed Capacitive Micromachined Ultrasonic Transducer Cell

Capacitive Micromachined Ultrasonic Transducer (CMUT) is a promising ultrasonic transducer in medical diagnosis and therapeutic applications that demand a high output pressure. The concept of a CMUT with an annular embossed pattern on a membrane working in collapse mode is proposed to further improve the output pressure. To evaluate the performance of an embossed CMUT cell, both the embossed and uniform membrane CMUT cells were fabricated in the same die with a customized six-mask sacrificial release process. An annular nickel pattern with the dimension of 3 μ m × 2 μ m (width × height) was formed on a full top electrode CMUT to realize an embossed CMUT cell. Experimental characterization was carried out with optical, electrical, and acoustic instruments on the embossed and uniform CMUT cells. The embossed CMUT cell achieved 27.1% improvement of output pressure in comparison to the uniform CMUT cell biased at 170 V voltage. The fractional bandwidths of the embossed and uniform CMUT cells were 52.5% and 41.8%, respectively. It substantiated that the embossed pattern should be placed at the vibrating center of the membrane for achieving a higher output pressure. The experimental characterization indicated that the embossed CMUT cell has better operational performance than the uniform CMUT cell in collapse region.

Core-polarization corrected relativistic energies and radiative data for one-electron spectra of Bi V through U XIV

The relativistic core-polarization corrected Dirac–Fock energy levels, oscillator strength, and lifetimes are predicted for highly ionized spectra of gold isoelectronic sequence from Bi V through U XIV. It is demonstrated that core polarization (core–valence electron correlation) strongly affects oscillator strengths and lifetimes of 6s–6p, 6p–5d, and 6d–5f transitions (the latter particularly in the vicinity of the collapse region) even for highly ionized systems of gold isoelectronic sequence.

Finite Element Analysis of Longitudinal Bending Collapse of Container Ship Considering Bottom Local Loads

The purpose of this research is to clarify the effect of bottom local loads on the hull girder collapse behavior of large container ship (8000TEU class) A 1/2+1+1/2 hold model of container ship is analyzed using implicit finite element method. The results reveal two major causes of reduction of hull girder ultimate strength due to local loads. One is biaxial compressive stresses induced at outer bottom. Thus, smaller hogging moment can induce a collapse of bottom panels. The other is a reduction of effectiveness of inner bottom that is on the tension side of local bending. As a result, the container ship attains hull girder ultimate strength with smaller spread of collapse region compared to that under pure bending.

Cosmic rays as regulators of molecular cloud properties

Cosmic rays are the main agents in controlling the chemical evolution and setting the ambipolar diffusion time of a molecular cloud. We summarise the processes causing the energy degradation of cosmic rays due to their interaction with molecular hydrogen, focusing on the magnetic effects that influence their propagation. Making use of magnetic field configurations generated by numerical simulations, we show that the increase of the field line density in the collapse region results in a reduction of the cosmic-ray ionisation rate. As a consequence the ionisation fraction decreases, facilitating the decoupling between the gas and the magnetic field.

Mechanical Properties and Energy Absorption Capability of Closed-Cell Al Alloy Foam

Based on compression tests of closed-cell Al alloy foam measured, mchanical properties and energy absorption capability had been investigated. The compressive stress-strain curve of closed-cell Al foam consists of three distinct regions, i.e., the linear elasticity region, the plastic collapse region or brittle crushing region, and the densification region. Formula on energy absorption capability of closed-cell Al alloy foam was presented, which could provide theoretical support for its engineering application.

Reliability Analysis of Defect-Containing Structures Using Partial Safety Factors

Some standards of structural integrity assessment such as BS 7910 and API 579-1/ASME FFS-1 recommend values of partial safety factor (PSF) applied to the deterministic engineering critical assessments of flaw-containing structures to achieve certain reliability levels. However, it is still uncertain as to whether the use of the PSFs can achieve the target reliability level specified in the codes, or excessively exceed the targets (un-conservative) or under-reach the targets (too conservative). This work was undertaken to make investigations into these issues raised from the use of PSFs through case studies involving deterministic fitness-for-service analysis incorporating PSFs and probabilistic fracture mechanics analysis. Two cases, a through-thickness crack and a surface-breaking elliptical crack in a plate subjected to tension, were considered. The results in terms of failure probability from the studied cases have shown a general trend that for each of the four PSFs recommended in BS 7910, the failure probability decreased as the assessments changed from the elastic fracture region to the plastic collapse region in the failure assessment diagram. Some over-conservatism has been found in certain situations from the use of PSFs recommended in BS 7910:2005. Cautions are given for application of the PSFs for integrity assessment of the structures and components containing flaws.