Numerical Study of Fracture Characteristics of Deep Granite Induced by Blast Stress Wave

To study the characteristics of rock fracture in deep underground under blast loads, some numerical models were established in AUTODYN code. Weibull distribution was used to characterize the inhomogeneity of rock, and a linear equation of state was applied to describe the relation of pressure and volume of granite elements. A new stress initialization method based on explicit dynamic calculation was developed to get an accurate stress distribution near the borehole. Two types of in situ stress conditions were considered. The effect of heterogeneous characteristics of material on blast-induced granite fracture was investigated. The difference between 2D models and 3D models was discussed. Based on the numerical results, it can be concluded that the increase of the magnitude of initial pressure can change the mechanism of shear failure near the borehole and suppress radial cracks propagation. When initial lateral pressure is invariable, with initial vertical pressure rising, radial cracks along the acting direction of vertical pressure will be promoted, and radial cracks in other directions will be prevented. Heterogeneous characteristics of material have an obvious influence on the shear failure zones around the borehole.

ASESMEN KOROSI & ANALISIS RISIKO KUALITATIF PADA VERTIKAL BEJANA TEKAN

Keselamatan dan keamanan dalam penggunaan bejana tekan sangat penting dan hal utama dalam penggunaan bejana tekan, terlebih lagi jika bejana tekan tersebut sudah melewati umur desain nya. Penelitian ini bertujuan untuk menilai kelayakan kondisi terkini dari suatu bejana tekan vertikal (vertical pressure vessel) yang telah beroperasi sejak tahun 1970 tetapi berhenti beroperasi pada tahun 2011. Pendekatan penilaian pada bejana tekan vertikal ini berbasis pada metode penilaian korosi dan risiko secara kualitatif. Selain itu juga dipergunakan metode-metode lain dalam aspek penilaian nya seperti visual inspeksi, laju korosi (corrosion rate), Non-Destructive Examination (NDE), software calculation dan analisa risiko kualitatif (qualitative risk analysis). Dari hasil observasi dan inspeksi di dapat tekanan desain (design pressure) adalah 7 kg/cm2, Temperatur desain (design temperature) adalah 61°C dengan material konstruksi adalah SA-283 Gr. C dan standard & code yang dipergunakan adalah ASME Sect. VIII Div. 1 dan API 510 serta beberapa standard & code lainnya. Dari hasil kajian dan kalkulasi di lapangan, maka didapat faktor penyebab kerusakan yang kemungkinan terjadi adalah atmospheric corrosion & uniform corrosion dengan nilai laju korosi adalah sebesar 0,127mm/yr dan tingkat risiko dari bejana tekan vertikal ini masuk dalam kategori 2D yang artinya adalah medium-high dengan maksimal umur pakai sampai usia 27 tahun untuk top head dan 24 tahun dan bottom head serta 23 tahun untuk shell. Sehingga dapat disimpulkan bahwa bejana tekan ini masih aman dan layak dipergunakan dengan batasan-batasan di atas.

Optimization of the parameters for the molding process of small-size rice straw insulating blocks via response surface methodology

Rice straw, which is considered an excellent insulation material, can be filled into the hollows of concrete block after being pressed, thereby improving the thermal performance of the concrete block. This new type of straw-concrete composite block will have good mechanical and thermal properties. In this study, to explore the feasibility of this new type of block, the response surface method was introduced. The goal was to find the effects of processing parameters on the forming quality of straw blocks. The quadratic regression model was established, and the processing parameters were optimized. It was found that the forming density, vertical pressure, pressure-holding time, and the interaction between the forming density and pressure-holding time had significant effects on the forming quality of the straw blocks. The optimal conditions obtained by RSM optimization were a forming density, a vertical pressure, and a pressure-holding time of 319.7 kg/m2, 2.5 kN, 33.68 s, respectively. Under these conditions, the volumetric contractivity of straw blocks was 11.17%, the horizontal failure strength was 21.74 kPa, and the natural moisture content was 16.37%. The parameters calculated via the prediction model were highly consistent with the results produced via the actual measurements, which showed that the prediction model was reliable and potentially useful in guiding industrial production.

Study on Gas Enrichment Mechanism of Coal Seam Influenced by Vertical Stress on Mountainous Region Condition

The controlling effect of vertical stress of mountainous region on gas occurrence of the coal seam below it has always been ignored. In order to clearly express its influence mechanism, the change laws of depth, stress, and permeability of coal seam pressurised by the overlying mountain were studied based on the Winkler elastic foundation beam theory and seepage theory in the paper. At the same time, the enrichment mechanism of the coal seam pressurised by the overlying mountain was analyzed. The results showed the following: (1) There was a significantly strong correlation between the stress, permeability change rule of the coal seam, burial depth, and surface elevation under such condition. (2) Under the action of the vertical pressure of the mountain, the stress and permeability distribution of the coal seam showed significant nonlinear characteristics. The stress was the greatest under the peak, and the permeability was the smallest. (3) The initial gas content value was controlled by the permeability and the stress of the coal seam in the situation. Moreover, the field practice showed that under the action of vertical pressure of the mountain, the evaluation law of gas content was coupling with the surface elevation of the overlying mountain. In addition, the gas emission change law during the excavation of the driving face also showed the same characteristics. The results might be of great significance for the development and utilization of coal-bed gas and the safe exploitation of coal resources.

RANCANG TUGAL PUPUK JAGUNG TIPE VERTICAL

Alat tugal pupuk adalah alat yang digunakan untuk membagi/menabur pupuk. Untuk saat ini model pemupukanjagung paling banyak masih dilakukan dengan cara manaual. Kondisi ini sangat memberatkan bagi para petanikarena disamping proses pemupukan yang lambat juga harus membutuhkan tenaga manusia yang banyak untukmenyelesaikan pekerjaan tersebut. Disamping tenaga yang banyak, efek lainya seperti petani sangat kelelahanbekerja sebab badan terus membungkuk selama proses pemupukan. Pada penelitian ini bertujuan untuk mendesainalat tugal pupuk tipe vertical pressure yang tepat guna hingga mengetahui cara kerja alat dan mengetahui hasilpenaburan pupuk sesuai dengan level takaran. Adapun metode pada penelitian ini yaitu dilakukan tiga runingpengujian dengan menyetel level takaran kemudian dihitung berapa jarak yang ditempuh untuk waktu tertentu.Berdasarkan hail pengujian diperoleh bahwa runing satu dengan jumlah pupuk 15.7 gram memperoleh jarak 48m dengan waktu 6.12 menit dengan jumlah total pupuk 5 kg. Untuk runing dua dengan jumlah pupuk 30 grammemperoleh jarak 36 m membutuhkan waktu 4.59 menit dengan total pupuk yang sama. Sedangkan untuk raningtiga dengan jumlah pupuk 90 gram memperoleh jarak 23 m dengan waktu 2.15 menit dengan total pupuk yangsama. Alat ini sangat efektif digunakan oleh petani.

VALES

Context. Spatially resolved observations of the ionized and molecular gas are critical for understanding the physical processes that govern the interstellar medium (ISM) in galaxies. The observation of starburst systems is also important as they present extreme gas conditions that may help to test different ISM models. However, matched resolution imaging at ∼kpc scales for both ISM gas phases are usually scarce, and the ISM properties of starbursts still remain poorly understood. Aims. We aim to study the morpho-kinematic properties of the ionized and molecular gas in three dusty starburst galaxies at z = 0.12−0.17 to explore the relation between molecular ISM gas phase dynamics and the star-formation activity. Methods. We employ two-dimensional dynamical modelling to analyse Atacama Large Millimeter/submillimiter Array CO(1–0) and seeing-limited Spectrograph for INtegral Field Observations in the Near Infrared Paschen-α (Paα) observations, tracing the molecular and ionized gas morpho-kinematics at ∼kpc-scales. We use a dynamical mass model, which accounts for beam-smearing effects, to constrain the CO-to-H2 conversion factor and estimate the molecular gas mass content. Results. One starburst galaxy shows irregular morphology, which may indicate a major merger, while the other two systems show disc-like morpho-kinematics. The two disc-like starbursts show molecular gas velocity dispersion values comparable with those seen in local luminous and ultra luminous infrared galaxies but in an ISM with molecular gas fraction and surface density values in the range of the estimates reported for local star-forming galaxies. We find that these molecular gas velocity dispersion values can be explained by assuming vertical pressure equilibrium. We also find that the star-formation activity, traced by the Paα emission line, is well correlated with the molecular gas content, suggesting an enhanced star-formation efficiency and depletion times of the order of ∼0.1−1 Gyr. We find that the star-formation rate surface density (ΣSFR) correlates with the ISM pressure set by self-gravity (Pgrav) following a power law with an exponent close to 0.8. Conclusions. In dusty disc-like starburst galaxies, our data support the scenario in which the molecular gas velocity dispersion values are driven by the ISM pressure set by self-gravity and are responsible for maintaining the vertical pressure balance. The correlation between ΣSFR and Pgrav suggests that, in these dusty starbursts galaxies, the star-formation activity arises as a consequence of the ISM pressure balance.

Pressure balance in the multiphase ISM of cosmologically simulated disc galaxies

ABSTRACT Pressure balance plays a central role in models of the interstellar medium (ISM), but whether and how pressure balance is realized in a realistic multiphase ISM is not yet well understood. We address this question by using a set of FIRE-2 cosmological zoom-in simulations of Milky Way-mass disc galaxies, in which a multiphase ISM is self-consistently shaped by gravity, cooling, and stellar feedback. We analyse how gravity determines the vertical pressure profile as well as how the total ISM pressure is partitioned between different phases and components (thermal, dispersion/turbulence, and bulk flows). We show that, on average and consistent with previous more idealized simulations, the total ISM pressure balances the weight of the overlying gas. Deviations from vertical pressure balance increase with increasing galactocentric radius and with decreasing averaging scale. The different phases are in rough total pressure equilibrium with one another, but with large deviations from thermal pressure equilibrium owing to kinetic support in the cold and warm phases, which dominate the total pressure near the mid-plane. Bulk flows (e.g. inflows and fountains) are important at a few disc scale heights, while thermal pressure from hot gas dominates at larger heights. Overall, the total mid-plane pressure is well-predicted by the weight of the disc gas and we show that it also scales linearly with the star formation rate surface density (ΣSFR). These results support the notion that the Kennicutt–Schmidt relation arises because ΣSFR and the gas surface density (Σg) are connected via the ISM mid-plane pressure.