bagus muljadi | University of Nottingham (original) (raw)

Papers by bagus muljadi

Jurnal Transportasi Multimoda

Kompleksitas lalu lintas barang di Provinsi Jawa Timur menunjukkan bahwa kebutuhan pangan di kabu... more Kompleksitas lalu lintas barang di Provinsi Jawa Timur menunjukkan bahwa kebutuhan pangan di kabupaten/kota cukup tinggi, termasuk di Kabupaten Tulungagung. Kabupaten Tulungagung merupakan satu dari lima kabupaten tumpuan lumbung pangan di Jawa Timur (Times Indonesia, 7 Juni 2020). Ketika produksi dan konsumsi masyarakat tinggi, diperlukan investasi untuk meningkatkan pasokan barang-barang kebutuhan pokok. Tujuan dari artikel ini adalah menganalisis pergerakan angkutan padi/beras di Kabupaten Tulungagung untuk memenuhi kebutuhan pokok. Pembahasan ada 4 yaitu bangkitan dan tarikan, distribusi, pemilihan rute dan evaluasi pengangkutan. Jumlah penduduk dan PDRB berpengaruh signifikan yang ditunjukkan dari persamaan regresi bangkitan dan tarikan. persamaan regresi bangkitan padi yaitu Ln Oi = 4406200,9 + 1,74 + (-40,3), bangkitan beras yaitu Ln Oi = 59822,4 + 0,62 + 25,1, dan tarikan beras yaitu Ln Dd= 2488310 + 0,1 + (-8,1). Dalam pendistribusiannya, bahan pokok didistribusikan di wil...

中文摘要氣體動力學理論歸類為二種，第一種方法，從巨觀空氣力學特性著手，將密度、質量與溫度視為獨立變數，並且考慮黏度、熱傳導係數等等。另一方面，第二種方法，則是由微觀的基本方程式層面下手，來探討氣... more 中文摘要氣體動力學理論歸類為二種，第一種方法，從巨觀空氣力學特性著手，將密度、質量與溫度視為獨立變數，並且考慮黏度、熱傳導係數等等。另一方面，第二種方法，則是由微觀的基本方程式層面下手，來探討氣體分子在巨觀表現下的一般特性，是現今最為被廣泛的接受，是為考慮單一粒子，在滿足波茲曼積分微方程下的分佈函數。本文著重的特色在運用新式的守恆算則，計算氣體動力流體，並建立在波茲曼方程式與局部熱力學平衡的假設下，配合分立坐標法的觀念，將一個原本在位置空間、時間及速度空間均連續的分佈函數的積分方程式，轉換為一在位置空間與時間連續。另一方面，經分立坐標法處理後之聯立微分方程組為一組念源項之雙曲線守恆律。進而由二階準確度，顯性算則稱著保守元素/解答方法，引入計算此方程式。積分捕捉SOD 震波管內流動結構的結果與Sjogreen 展開式問題，並且將其結果與Riemann’s Euler problem 比較程式的準確度為何。本文著重於將CE/SE算則引入分立坐標計算法，計算波茲曼方程式，這是先前研究都沒有使用過的。而在未來工作上，。本研究是著重於固態的基礎，將會把提高維度的計算，與引入碰撞項至波茲曼方程式中。ABSTRACThe dynamic theory of gases may be studied from two points of view. One may take as starting point the macroscopic equations of aerodynamics with the density, mass velocity, and temperature as independent variables and involving various coefficients, e.g., viscosity, heat conduction, etc. On the other hand, one may use a more fundamental and general microscopic formalism. The most fruitful of such formalisms available at present is that in terms of one particle distribution functions ...

AGU Fall Meeting Abstracts, Dec 1, 2018

University of Nottingham, UK Description One of the main difficulties in building numerical model... more University of Nottingham, UK Description One of the main difficulties in building numerical models with predictive capabilities for practical applications involving porous media is often the large disparity between the scale at which processes can be understood from first principles, and the scale at which practical predictions are needed and experiments are available. Multiscale techniques and models are therefore critically needed to fill this gap and provide ways to correctly interpret lab-scale data, connect them to microscale physics and upscale to field-scales. To this aim, it is imperative that any model, particularly the ones relying on multiscale assumptions, undergoes rigorous experimental validations. A consistent and systematic approach to calibrate and validate multi-scale models is still an open problem. The aim of the workshop is to bring together experimentalists, modellers, and computational scientists with interests in the flow and transport through porous material...

IOP Conference Series: Earth and Environmental Science, 2020

Industrial activities and the natural oxidation of metallic sulphide-ores produce sulphate-rich w... more Industrial activities and the natural oxidation of metallic sulphide-ores produce sulphate-rich waters with low pH and high heavy metals content generally termed Acid Mine Drainage (AMD). This is of great environmental concern, as some heavy metals are highly toxic. Within several possibilities, biochar and clamshell is an attractive option to treat AMD and to recover metals. This study aims to describe a simple method to utilized waste of both. Pyrolysis of waste material used to change waste to biomaterial biochar and clamshell. This research showed that biochar and clamshell are potentials material to reduce AMD impacts. This research will help and acceptable for rural areas to solve AMD problems.

A direct method for solving rarefied flow of gases of arbitrary particle statistics is presented.... more A direct method for solving rarefied flow of gases of arbitrary particle statistics is presented. The method is based on semiclassical Boltzmann equation with BGK relaxation time approximation. The discrete ordinate method is first applied to render the Boltzmann equation into hyperbolic conservation laws with source terms, then classes of explicit and implicit time integration schemes are applied to evolute the discretized distribution function. The method is tested on both transient and steady flow problems of gases of arbitrary statistics at varying relaxation times.

Accurate prediction of the macroscopic flow parameters needed to describe flow in porous media re... more Accurate prediction of the macroscopic flow parameters needed to describe flow in porous media relies on a good knowledge of flow field distribution at a much smaller scale---in the pore spaces. The extent of the inertial effect in the pore spaces can not be underestimated yet is often ignored in large-scale simulations of fluid flow. We present a multiscale method for solving Oseen's approximation of incompressible flow in the pore spaces amid non-periodic grain patterns. The method is based on the multiscale finite element method (MsFEM [Hou and Wu, 1997]) and is built in the vein of Crouzeix-Raviart elements [Crouzeix and Raviart, 1973]. Simulations of inertial flow in highly non-periodic settings are conducted and presented. Convergence studies in terms of numerical errors relative to the reference solution are given to demonstrate the accuracy of our method. The weakly enforced continuity across coarse element edges is shown to maintain accurate solutions in the vicinity of...

&lt;p&gt;Mathematical models of peatland growth have been developed for many purp... more &lt;p&gt;Mathematical models of peatland growth have been developed for many purposes, including understanding the effect of past or future climate change on peatland carbon accumulation. This is important because peatland contains a vast amount of carbon and has a significant role in the global carbon cycle through carbon dioxide and methane exchange with the atmosphere. In general, the models produced so far suffer from the fact that the mechanical process has an essential role in the peatland carbon stock resilience because they only focus on ecohydrological feedback. We propose a one-dimensional mathematical model that includes ecological, hydrological, and mechanical feedback on the peatland through the poroelasticity concept, which coupling between fluid flow and solid deformation. The formulation is divided into two categories, fully saturated and unsaturated, to accommodate peatland characteristics. We compare the numerical solution of the fully saturated case with analytical solutions of Terzaghi&amp;#8217;s problem for validation. We assume that peat is an elastic material with flat, impermeable, and stiff substrate properties. &amp;#160;Based on the initial simulation results,&amp;#160; we find that compression reduces the thickness of acrotelm, leading to the shorter residence time of plant litter, and consequently, higher cumulative carbon is obtained. Furthermore, mechanical deformation of the pore structure effectively maintains carbon stock in the peatland against climate change because it reduces water table depth fluctuations.&lt;/p&gt;

Science Advances

Termite nests have been widely studied as effective examples for ventilation and thermoregulation... more Termite nests have been widely studied as effective examples for ventilation and thermoregulation. However, the mechanisms by which these properties are controlled by the microstructure of the outer walls remain unclear. Here, we combine multiscale X-ray imaging with three-dimensional flow field simulations to investigate the impact of the architectural design of nest walls on CO2 exchange, heat transport and water drainage. We show that termites build outer walls that contain both small and percolating large pores at the microscale. The network of larger microscale pores enhances permeability by one to two orders of magnitude compared to the smaller pores alone, and it increases CO2 diffusivity up to eight times. In addition, the pore network offers enhanced thermal insulation and allows quick drainage of rainwater, thereby restoring the ventilation and providing structural stability to the wet nest.

Journal of Contaminant Hydrology

We present an experimental and numerical study of transport in carbonates during dissolution and ... more We present an experimental and numerical study of transport in carbonates during dissolution and its upscaling from the pore (∼ µm) to core (∼ cm) scale. For the experimental part, we use nuclear magnetic resonance (NMR) to probe molecular displacements (propagators) of an aqueous hydrochloric acid (HCl) solution through a Ketton limestone core. A series of propagator profiles are obtained at a large number of spatial points along the core at multiple time-steps during dissolution. For the numerical part, first, the transport model-a particle-tracking method based on Continuous Time Random Walks (CTRW) by [1]-is validated at the pore scale by matching to the NMR-measured propagators in a beadpack, Bentheimer sandstone, and Portland carbonate [2]. It was found that the emerging distribution of particle transit times in these samples can be approximated satisfactorily using the power law function ψ(t) ∼ t −1−β , where 0 < β < 2. Next, the evolution of the propagators during reaction is modelled: at the pore scale, the experimental data is used to calibrate the CTRW parameters; then the

Transport in Porous Media, 2016

Accurate prediction of the macroscopic flow parameters needed to describe flow in porous media re... more Accurate prediction of the macroscopic flow parameters needed to describe flow in porous media relies on a good knowledge of flow field distribution at a much smaller scale-in the pore spaces. The extent of the inertial effect in the pore spaces can not be underestimated yet is often ignored in large-scale simulations of fluid flow. We present a multiscale method for solving Oseen's approximation of incompressible flow in the pore spaces amid non-periodic grain patterns. The method is based on the multiscale finite element method (MsFEM [15]) and is built in the vein of Crouzeix-Raviart elements [10]. Simulations of inertial flow in highly non-periodic settings are conducted and presented. Convergence studies in terms of numerical errors relative to the reference solution are given to demonstrate the accuracy of our method. The weakly enforced continuity across coarse element edges is shown to maintain accurate solutions in the vicinity of the grains without the need for any oversampling methods. The penalization method is employed to allow a complicated grain pattern to be modeled using a simple Cartesian mesh. This work is a stepping stone towards solving the more complicated Navier-Stokes equations with a non-linear inertial term.

Multiscale Modeling & Simulation, 2015

The Multiscale Finite Element Method (MsFEM) is developed in the vein of Crouzeix-Raviart element... more The Multiscale Finite Element Method (MsFEM) is developed in the vein of Crouzeix-Raviart element for solving viscous incompressible flows in genuine heterogeneous media. Such flows are relevant in many branches of engineering, often at multiple scales and at regions where analytical representations of the microscopic features of the flows are often unavailable. Full accounts to these problems heavily depend on the geometry of the system under consideration and are computationally expensive. Therefore, a method capable of solving multiscale features of the flow without confining itself to fine scale calculations is sought after. The approximation of boundary condition on coarse element edges when computing the multiscale basis functions critically influences the eventual accuracy of any MsFEM approaches. The weakly enforced continuity of Crouzeix-Raviart function space across element edges leads to a natural boundary condition for the multiscale basis functions which relaxes the sensitivity of our method to complex patterns of obstacles exempt from the needs of implementing any oversampling techniques. Additionally, the application of penalization method makes it possible to avoid complex unstructured domain and allows extensive use of simpler Cartesian meshes.

Advances in Water Resources, 2015

The effect of pore-scale heterogeneity on non-Darcy flow behaviour is investigated by means of di... more The effect of pore-scale heterogeneity on non-Darcy flow behaviour is investigated by means of direct flow simulations on 3-D images of a beadpack, Bentheimer sandstone and Estaillades carbonate. The critical Reynolds number indicating the cessation of the creeping Darcy flow regime in Estaillades carbonate is two orders of magnitude smaller than in Bentheimer sandstone, and is three orders of magnitude smaller than in the beadpack. It is inferred from the examination of flow field features that the emergence of steady eddies in pore space of Estaillades at elevated fluid velocities accounts for the early transition away from the Darcy flow regime. The non-Darcy coefficient β, the onset of non-Darcy flow, and the Darcy permeability for all samples are obtained and compared to available experimental data demonstrating the predictive capability of our approach. X-ray imaging along with direct pore-scale simulation of flow provides a viable alternative to experiments and empirical correlations for predicting non-Darcy flow parameters such as the β factor, and the onset of non-Darcy flow.

Communications in Computational Physics, 2015

The adaptation of Crouzeix-Raviart finite element in the context of multi-scale finite element me... more The adaptation of Crouzeix-Raviart finite element in the context of multi-scale finite element method (MsFEM) is studied and implemented on diffusion and advection-diffusion problems in perforated media. It is known that the approximation of boundary condition on coarse element edges when computing the multiscale basis functions critically influences the eventual accuracy of any MsFEM approaches. The weakly enforced continuity of Crouzeix-Raviart function space across element edges leads to a natural boundary condition for the multiscale basis functions which relaxes the sensitivity of our method to complex patterns of perforations. Another ingredient to our method is the application of bubble functions which is shown to be instrumental in maintaining high accuracy amid dense perforations. Additionally, the application of penalization method makes it possible to avoid complex unstructured domain and allows extensive use of simpler Cartesian meshes.

An accurate and direct algorithm for solving the semiclassical Boltzmann equation with relaxation... more An accurate and direct algorithm for solving the semiclassical Boltzmann equation with relaxation time approximation in phase space is presented for parallel treatment of rarefied gas flows of particles of three statistics. The discrete ordinate method is first applied to discretize the velocity space of the distribution function to render a set of scalar conservation laws with source term. The high order weighted essentially non-oscillatory scheme is then implemented to capture the time evolution of the discretized velocity distribution function in physical space and time. The method is developed for two space dimensions and implemented on gas particles that obey the Maxwell-Boltzmann, Bose-Einstein and Fermi-Dirac statistics. Computational examples in one-and two-dimensional initial value problems of rarefied gas flows are presented and the results indicating good resolution of the main flow features can be achieved. Flows of wide range of relaxation times and Knudsen numbers covering different flow regimes are computed to validate the robustness of the method. The recovery of quantum statistics to the classical limit is also tested for small fugacity values.

Jurnal Transportasi Multimoda

AGU Fall Meeting Abstracts, Dec 1, 2018

IOP Conference Series: Earth and Environmental Science, 2020

Science Advances

Journal of Contaminant Hydrology

Transport in Porous Media, 2016

Accurate prediction of the macroscopic flow parameters needed to describe flow in porous media re... more Accurate prediction of the macroscopic flow parameters needed to describe flow in porous media relies on a good knowledge of flow field distribution at a much smaller scale-in the pore spaces. The extent of the inertial effect in the pore spaces can not be underestimated yet is often ignored in large-scale simulations of fluid flow. We present a multiscale method for solving Oseen's approximation of incompressible flow in the pore spaces amid non-periodic grain patterns. The method is based on the multiscale finite element method (MsFEM [15]) and is built in the vein of Crouzeix-Raviart elements [10]. Simulations of inertial flow in highly non-periodic settings are conducted and presented. Convergence studies in terms of numerical errors relative to the reference solution are given to demonstrate the accuracy of our method. The weakly enforced continuity across coarse element edges is shown to maintain accurate solutions in the vicinity of the grains without the need for any oversampling methods. The penalization method is employed to allow a complicated grain pattern to be modeled using a simple Cartesian mesh. This work is a stepping stone towards solving the more complicated Navier-Stokes equations with a non-linear inertial term.

Multiscale Modeling & Simulation, 2015

Advances in Water Resources, 2015

Communications in Computational Physics, 2015