Experiments on thermo-hydro-mechanical behaviour of Opalinus Clay at Mont Terri rock laboratory, Switzerland

Repositories for deep geological disposal of radioactive waste rely on multi-barrier systems to isolate waste from the biosphere.A multi-barrier system typically comprises the natural geological barrier provided by the repository host rock e in our case the Opalinus Clay e and an engineered barrier system(EBS).The Swiss repository concept for spent fuel and vitrified high-level waste(HLW)consists of waste canisters,which are emplaced horizontally in the middle of an emplacement gallery and are separated from the gallery wall by granular backfill material(GBM).We describe here a selection of five in-situ experiments where characteristic hydro-mechanical(HM)and thermo-hydro-mechanical(THM)processes have been observed.The first example is a coupled HM and mine-by test where the evolution of the excavation damaged zone(EDZ)was monitored around a gallery in the Opalinus Clay(ED-B experiment).Measurements of pore-water pressures and convergences due to stress redistribution during excavation highlighted the HM behaviour.The same measurements were subsequently carried out in a heater test(HE-D)where we were able to characterise the Opalinus Clay in terms of its THM behaviour.These yielded detailed data to better understand the THM behaviours of the granular backfill and the natural host rock.For a presentation of the Swiss concept for HLW storage,we designed three demonstration experiments that were subsequently implemented in the Mont Terri rock laboratory:(1)the engineered barrier(EB)experiment,(2)the in-situ heater test on key-THM processes and parameters(HE-E)experiment,and(3)the full-scale emplacement(FE)experiment.The first demonstration experiment has been dismantled,but the last two ones are on-going.

Qinghai-Tibet Expressway experimental research

As one part of the National Highway Network Planning in China, the Qinghai-Tibet Expressway （QTE） from Golmud to Lhasa will be built in the interior of the Qinghai-Tibet Plateau （QTP） across about 630 km of permafrost lands. Due to the problematic interactions between the engineering foundations and permafrost, the frozen-soil roadbed of the QTE will be subjected to the more intense thermal disturbances due to the wider black surface. The design and construction for long-term thermal and mechanical stability will face more severe challenges than those in ordinary highways and railways in the same region. In order to provide scientific support for cold regions engineering practices, the QTE Experimental Demonstration Project （EDP） was constructed in situ in the vicinity of the Beilu＇he Permafrost Station in the interior of the QTP. In this paper, the anticipated problems of the proposed QTE project are enumerated, and the structures of the test sections for QTE EDP are described. Through numerical simulations, it was found that the heat transfer processes occurring in each specific road structure are significantly different. The heat accumulation in the highway embankment is mainly due to the black bituminous pavement, but in the railway embankment with its gravel surfaces, it mainly comes from the side slopes. As a result, the net heat accumulation of the highway embankment is three times higher than that in the railway. In expressway, the heat accumulation is further increased because of the wider pavement so that significantly more heat will be accumulated in the roadbed beneath the centerline area. Thus, the thermal stability of the fro- zen-soil roadbed and the underlying permafrost of the QTE can be seriously threatened without proper engineering measures protection against thawing. Based on research and practical experiences from the operating Qinghai-Tibet Railway （QTR） and the Qinghai-Tibet Highway （QTH）, combined with the predicted characteristics of heat transfer in an expressway embankment, nine kinds of engineering measures for mitigating the thaw settlement of foundation soils through the cooling the roadbed soils were built and are being tested in the EDP. The design of the monitoring system for the EDP and the observed parameters were also described.

Demonstration of a Shock-Timing Experiment in a CH Layer at the Shen Guang Ⅲ Laser Facility

Shock-timing experiments are indispensable to inertial confinement fusion mainly because the timing of multiple shock waves is crucial to understanding the processes of laser irradiation of targets. Investigations into shock waves driven by a two-step radiation pulse in polystyrene（CH） capsule targets are experimentally conducted at the Shen Guang Ⅱ laser facility. Differing from the traditional shock-timing implementation in which one shock wave could catch up with another one in solid CH, in this experiment, the second shock front in a rarefaction CH layer is observed through velocity interferometry. This second shock could also be made to converge with rarefaction waves within only a few micrometers of the CH capsule by designing the two-shock coalescence time. A shock-timing diagnostic technique to tune the multi-shock convergence in the CH capsule can thereby be achieved.The experimental results in the CH layer are quasi-quantitatively interpreted using streamlines simulated with the Multi-1 D program. The experimental results are expected to offer important information for target structure and laser pulse design, both of which are important for realizing inertial confinement fusion.

Far-field outdoor experimental demonstration of down-looking synthetic aperture ladar

Synthetic aperture imaging ladar （SAIL） has the capabil- ity of getting high-resolution and two-dimensional （2D）active imaging at a large distance in the side-looking mode, which has become an interesting area of research.

Numerical model and experimental demonstration of high precision ablation of pulse CO_2 laser

To reveal the physical mechanism of laser ablation and establish the prediction model for figuring the surface of fused silica, a multi-physical transient numerical model coupled with heat transfer and fluid flow was developed under pulsed CO2laser irradiation. The model employed various heat transfer and hydrodynamic boundary and thermomechanical properties for assisting the understanding of the contributions of Marangoni convention,gravitational force, vaporization recoil pressure, and capillary force in the process of laser ablation and better prediction of laser processing. Simulation results indicated that the vaporization recoil pressure dominated the formation of the final ablation profile. The ablation depth increased exponentially with pulse duration and linearly with laser energy after homogenous evaporation. The model was validated by experimental data of pulse CO2laser ablation of fused silica. To further investigate laser beam figuring, local ablation by varying the overlap rate and laser energy was conducted, achieving down to 4 nm homogenous ablation depth.

Experimental demonstration for 40-km fiber and 2-m wireless transmission of 4-Gb/s OOK signals at 100-GHz carrier

We experimentally demonstrate a 4-Gb/s radio-over-fiber （RoF） system with 40-kin fiber and 2-m wireless distance downstream at 100-GHz carrier. To the best of our knowledge, this is for the first time in China to realize optical wireless link at 100 GHz. In this letter, simple intensity modulator with direct detector （IM-DD） modulation is employed and optical power penalty afZer 40-kin single mode fiber （SMF）-28 and 2-m air link is 3.2 dB with bit-error-rate （BER） at 1 × 10- 9.

Experimental demonstration of underwater optical wireless power transfer using a laser diode

We experimentally demonstrate an underwater optical wireless power transfer （OWPT） using a laser diode （LD） as a power transmitter. We investigate the characteristics of a solar cell and a photodiode （PD） as a power receiver. We optimize the LD, the PD, and the solar cell to achieve the maximum transfer efficiency. The maxi- mum transfer efficiency of the back-to-back OWPT is measured as 4.3% with the PD receiver. Subsequently, we demonstrate the OWPT in tap and sea water. Our result shows an attenuation of 3 dB/m in sea water.

Design and Performance of an Improved Trapped Vortex Combustor

A trapped vortex combustor （TVC） has been a very promising novel concept for it offers improvements in lean blow out, altitude relight, operating range, as well as a potential to decrease NOx emissions compared to conventional combustors. The present paper discusses the improved designs of the new combustor over the prior ones of our research group, including that：a） the over-all dimensions, both axial and radial, are reduced to those of an actual aero-engine combustor; b） the air flow distribution is optimized, and especially 15% of the air is fed into the liner as cooling air; c） a straight-wall diffuser with divergence angle 9°is added. A series of experiments （cavity-fueled only, under atmospheric pressure） has been conducted to investigate the performance of the improved TVC. Experimental results show that at the inlet temperature of 523 K, the inlet pressure of 0.1 MPa, stable operation of the TVC test rig is observed for the Mach number 0.15-0.34, indicating good flame stability; the combustion efficiency obtained in this paper falls into the range of 60%-96%; as the total excess air ratio increases, the combustion efficiency decreases, while the increase of the inlet temperature is beneficial to high combustion efficiency; besides, the optimal Mach numbers for high combustion efficiency under different inlet conditions are confirmed. The outlet temperature profiles feature a bottom in the midheight of the exit. This paper demonstrates the feasibility for the TVC to be applied to a realistic aero-engine preliminarily and provides reference for TVC design.