Derivation and validation of wind tunnel free-flight similarity law for store separation from aircraft
اشتقاق و اعتبار قانون تشابه پرواز آزاد تونل باد برای جداسازی فروشگاه از هواپیما-2020
This paper describes a design method for a similarity law for free-flight tests of aircraft load separation. The effect of the initial separation velocity on the motion similarity is considered. For the first time, the initial separation velocity is introduced into the equation of motion to identify similar trajectories. Finally, the model mass parameter characteristics and separation velocity equation are solved to determine similarity laws for wind tunnel tests, greatly improving the accuracy and applicability of test results from wind tunnels. The proposed derivation overcomes the problems faced by the traditional light model method and the traditional heavy model method, namely that they are limited in terms of ejection separation and cannot be realized in wind tunnel tests. The typical separation state under wind load scenarios is simulated using computational fluid dynamics (CFD). Separation data from real aircraft and previous test methods are compared with the simulation data obtained by the new similarity law design method. The improvement of the new similarity law in terms of trajectory simulation is verified through a comprehensive data comparison. The data show that the new similarity law greatly improves the accuracy of wind tunnel tests.
Keywords: Similarity law derivation | High-speed weapon delivery | Carrier and missile interference | Multi-body separation | Free-flight wind tunnel test
The size distribution of cities in China: Evolution of urban system and deviations from Zipf’s law
توزیع اندازه شهرها در چین: تکامل سیستم شهری و انحراف از قانون زیف-2020
How are urban residents distributed and agglomerated across different-sized cities? This question can be addressed by studying urban system or Zipf’s law. Using Chinese data for the period of 1990–2017, this paper contributes to the literature by exploring the evolution of urban system, and more importantly deviations from Zipfs law. It is found that (1) The size distribution of Chinese cities, as expected, did not follow Zipf’s law until very recently. Both large cities and small towns were under-sized relative to the Zipf’s law, implying possible loss of agglomeration economies; (2) When the top 10% large cities are excluded, the Chinese data fit the Zipfs law better, demonstrating the adverse role of government interference in containing the growth of mega-cities; (3) By and large, the distribution has been moving closer or further away from Zipf’s law, corroborating with policy directions in the relevant five-year plans of the central government; and (4) Government interferences helped enlarge while market forces helped reduce the numerical deviations of individual cities from Zipf’s law. The last three analytical findings are the first in the literature since no previous studies have focused on the issue of why urban system in China does not follow Zipf’s law. In particular, no earlier efforts have been made to model numerical deviations from Zipf’s law, as attempted in this paper. The results appeal for removal of government interferences and furthering market-based reforms in order to reap economies of agglomeration.
Keywords: Deviations from Zipf’s law | Agglomeration | Urban system | Urbanization | China
Nonlinear contact force law for spherical indentation of FGM coated elastic substrate: An extension of Hertz’s solution
قانون نیروی غیر تماس غیر خطی برای تورفتگی کروی بستر الاستیک روکش شده با FGM: گسترش راه حل هرتز-2020
This paper develops a nonlinear contact force law for the indentation of an elastic substrate with thin functionally graded material (FGM) coating by a rigid smooth sphere. The nonlinear contact force law is explicitly expressed in form of extended Hertz’s solution with a correction factor, which is related to the coating thickness, radius of the indenter, contact interference and the modulus ratio. The explicit expres- sion of the correction factor for arbitrary coating modulus gradation can be determined statistically with extensive numerical results. For computational efficiency and accuracy, an analytical contact model based on multilayered half space is developed and the associated mixed boundary value problem is converted to a Fredholm integral equation of the second kind. This model discretizes the thin FGM coating into n dissimilar and fully bonded sub-layers. Each sub-layer is a homogeneous elastic seam of finite thick- ness and constant elastic modulus and Poisson’s ratio. Variation of the coating elastic properties along the thickness direction is accurately approximated by the multilayered system. The non-linear contact force laws in closed-form are specifically given for both linear and exponential modulus gradations. The load-displacement relations predicted by these force laws are shown to be in exact agreement with the numerical results from the Fredholm integral equation. Additionally, this nonlinear contact force law for FGM coating is further incorporated into the Greenwood and Williamson model, which provides a feasible and effective way for modeling the contact of FGM coated rough surfaces.
Keywords: Contact force law | Coated materials | Functionally graded material (FGM) | Rough surface | Spherical indentation
Raman spectroscopy for forensic semen identification: Method validation vs. environmental interferences
طیف سنجی رامان برای شناسایی منی پزشکی قانونی: اعتبار سنجی روش در مقابل تداخل های محیطی-2020
Proper identification of body fluids at crime scenes is imperative to forensic investigations, as they yield crucial pieces of DNA evidence that lead to subsequent investigation resolution and criminal justice. Nevertheless, body fluid identification can prove a burdensome process, as several ubiquitous substances found at crime scenes often resemble the appearance of a specific body fluid. Therefore, it is extremely important to find a reliable method for body fluid discovery and differentiation among other potential environmental inferences (EIs). In this study, Raman spectroscopy was combined with advanced statistical analysis and used for semen identification. This method has already been proven to be a powerful tool for characterization of body fluid traces for forensic purposes. Twenty-seven EI substances that may (i) yield a false positive (FP) result on routine forensic tests for semen and/or (ii) resemble a semen stain at a crime scene were examined. Raman spectra of EI substances were compared to spectra of main body fluids: semen, blood, saliva, sweat, and vaginal fluid. The random forest algorithm was utilized for differentiating between body fluids and EIs commonly found for semen traces. Using the classification probability threshold of 70%, entire separation of classes was observed. None of the twentyseven EI substances was classified as any body fluid. This confirms a great potential of Raman spectroscopy for nondestructive and rapid identification of semen traces found at a crime scene.
Keywords: Raman spectroscopy | Chemometrics | Semen identification | Forensics | Biological fluids | Environmental interferences
Generalized laws of Snell, Fresnel and energy balance for a charged planar interface between lossy media
قوانین کلی شده Fresnel ، Snell و توازن انرژی برای رابط مسطح شارژ بین رسانه های از دست رفته-2020
The generalized laws of Snell, Fresnel and energy balance are derived for the harmonic inhomogeneous plane waves (HIPW) that are incident upon a charged plane interface between two absorbing media. Excess surface charges impact the Fresnel coefficients by the surface conductivity which is the ratio of the surface current to the tangential component of the electric field. The surface current introduces an extra term of Joule heat loss in the generalized energy balance besides the usual terms of reflection, transmission and interference. The reflection and transmission coefficients are calculated by the equations we derived, and the validity of the results is verified by comparison with those calculated by the finite- difference time-domain method. In addition, we identify a charge-induced increase of (pseudo) Brewster angle for the harmonic homogeneous plane waves (HHPW), a significant influence of the incident angles for amplitude propagation vector on optical properties for HIPW, and a strong increase of Joule heat loss due to the interaction between the incident HIPW and the surface charges.
Keywords: Harmonic inhomogeneous plane waves | Lossy interface | Charged plane | Surface conductivity | Reflection | Transmission
A PAPR reduction scheme combining superimposed O-OFDM and M-law mapping for VLC-OFDM systems
یک طرح کاهش PAPR ترکیبی از نقشه برداری O-OFDM و لایه برداری قانون برای سیستم های VLC-OFDM-2020
Due to the high peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals, the inherent nonlinearity of light emitting diodes (LEDs) is a challenge for optical OFDM (O-OFDM) schemes in visible light communication (VLC) systems. In order to reduce PAPR to mitigate the effects of the nonlinearity of LEDs, and avoid the asymmetric clipping interference in the conventional hybrid OOFDM schemes, a novel superimposed O-OFDM scheme is proposed in this paper, which reduce the PAPR by combining the ????-law mapping and the superposition modulation. Moreover, at the transmitter, the hybrid O-OFDM components are superimposed in an interference-free way, the receiver does not require the operation of interference cancellation, and the symbols of each branch can be demodulated independently. Simulation results verify that the proposed scheme can significantly reduce the PAPR. At the same time, the comprehensive performance of the proposed scheme outperforms other competing schemes under the constraints of the nonlinearity and limited dynamic range of LEDs.
Keywords: Visible light communications | Optical orthogonal frequency division | multiplexing | Peak-to-average power ratio | M-law mapping | LED nonlinearity
The Salak Field, Indonesia: On to the next 20 years of production
میدان سالاک ، اندونزی: تولید تا 20 سال آینده -2020
The Salak Geothermal Field is the largest producing geothermal field in Indonesia with an installed power generation capacity of 377 MWe. After more than 23 years of commercial operations and through vigilant resource management, the Salak Field is still performing well. Since 1994, when commercial production started, the net capacity factor has averaged about 91% annually. After the last turbine uprating in 2005, the net capacity factor has improved to an annual average of 95%. By 2019, a substantial injection realignment will be implemented which will move all condensate injection outside the field production boundary and shift most brine injection outside and to the southeast margin. This project will mitigate brine injection impact to the AWI 7 and 8 wells and hasten development of the steam cap in the western portion of the field. With this injection realignment, reservoir simulation forecasts show the Salak geothermal resource will likely be able to continue steam production at its current level in the foreseeable future. Similar to other long-producing geothermal fields, Salak has encountered resource management challenges, such as, injection breakthrough, influx of marginal recharge, wellbore scaling, and production of significant amounts of non-condensable gas (“NCG”), in response to commercial production. To address these challenges, an extensive reservoir monitoring program and integration of new make-up drilling results enabled updates and fine-tuning of the conceptual model of the field. Key updates include increased understanding of the distribution of the producing effective fractures and their permeability in the reservoir, identification of injection capacity outside the commercial field boundary in the Cianten Caldera, and improved understanding of NCG interference in the steam cap and injection and natural recharge impacts on the field. These insights and the updated conceptual understanding of the Salak geothermal system coupled with reservoir simulation have provided a credible forecast of the Salak reservoir’s future performance for decision-makers to have the necessary confidence to fund the injection realignment project. Additionally, the refined conceptual model provides the reservoir management team with a means to plan and target development make-up wells and effectively focus future data gathering and reservoir monitoring activities
Keywords: Salak | Injection breakthrough | Non-Condensable gases | Marginal recharge | Effective fractures | Wellbore scale
Derivation and verification of a similarity law for wind-tunnel free-flight tests of heavy-store separation
استخراج و تأیید قانون تشابه برای آزمایش های پرواز آزاد تونل بادی از تفکیک فروشگاه های سنگین-2020
Test-method research was carried out to consider the separation of a heavy store, and a similarity law for unsteady wind-tunnel free-flight tests of air-launch rockets was derived. The derivation of this similarity law considers the particular characteristics of a heavy store and aerodynamic interference with the carrier and focuses on solving the following problems: the separation of a heavy store causes a real carrier to have an acceleration and a velocity that cannot be ignored; the carrier in a wind-tunnel test is vertically fixed; and a wind-tunnel test cannot meet the Froude number (Fr) similarity condition. According to the special characteristics of heavy-store separation, a similarity law for wind-tunnel free-flight tests of heavy-store separation is derived. Computational fluid dynamics simulations are used to verify the new similarity law. The results show that the new similarity law can simulate the separation trajectory more realistically than existing methods, and the linear and angular displacement errors are decreased by an order of magnitude. The experimental accuracy of the new similarity law is even higher than that of a separation trajectory satisfying Fr matching. It is demonstrated that the new similarity law can be used to carry out unsteady experimental research on the separation of a heavy store such as an air-launch rocket, and this new law provides strong support for establishing the safety boundaries of heavy-store separation.
Keywords: Air-launch rocket | Similarity law derivation | Carrier and store interference | Multi-body separation | Wind-tunnel free-drop testing | Heavy-store airdrop
Semantic approach to compliance checking of underground utilities
رویکرد معنایی برای بررسی انطباق ابزارهای زیرزمینی-2020
Utility regulations stipulate the spatial configurations between underground utilities and their surroundings to avoid interferences and disruptions of utility services. Utility compliance checking aims to detect spatial noncompliances in underground utilities by examining geospatial data of utilities and their surroundings against textual data of utility regulations. However, the integration of heterogeneous utility geospatial and textual data for compliance checking remains a big challenge. This paper presents a semantic approach to integrate heterogeneous data and enable automated compliance checking of underground utilities through logic and spatial reasoning. The approach consists of the following key components: (1) four interlinked ontologies that provide the semantic schema for heterogeneous data relevant to utility compliance checking, (2) two data convertors for the conversion of heterogeneous data from proprietary formats into a common and interoperable format following the semantic schema, and (3) a query mechanism with spatial extensions for the detection of noncompliant utility instances. The approach was tested on a sample utility database, and the results demonstrate the success of the proposed approach in the integration of heterogeneous data from multiple sources and automated detection of spatial non-compliances in underground utilities. In addition to utility compliance checking, the approach can be extended to other application cases where both data integration from multiple sources and spatial reasoning are required.
Keywords: Ontology | Data integration | Semantic reasoning | Utility compliance checking
Workspace planning in construction: non-deterministic factors
برنامه ریزی فضای کار در ساخت : عوامل غیر قطعی-2020
Workspace interferences and collisions occurring on construction jobsites are products of unexpected spatiotemporal overlaps of resources. They affect the project performance and can create an unsafe environment. Current practices for workspace planning adopt a linear/mechanistic approach in modeling, which ignores uncertainties occurring during construction operations. Those methods do not account for the emergent behavior of crews, irreversibility of decisions made in the case of interferences, and bifurcation of those decisions over the project lifecycle. This paper presents the results of qualitative and quantitative analysis of the significance of such gaps. A software tool was developed to model workspaces probabilistically and detects interferences from 4D models. The impact of uncertainties on interference magnitudes was evaluated based on available models, and an industry survey was conducted accordingly. The results suggest that compounding effects of uncertainties may significantly affect the frequency and volume of overlapped workspaces in a project (volumes can increase for as much as 220%, for a 40% deviation in the inputs). Our findings also propose crew attributes for formulating a bottom-up approach, capable of capturing crews interactions and predicting their decision when managing collisions.
Keywords: Workspace management | Operational clash | Workspace interference | Spatial-temporal clashes | Construction planning uncertainties | BIM | 4D modeling | Agent-based modeling | Industry survey