Simple Analytical Model Research Articles

Design and Analysis of Reconfigurable Origami-Based Vacuum Pneumatic Artificial Muscles for Versatile Robotic System.

In this study, a vacuum-based modular actuator system named reconfigurable origami-based vacuum pneumatic artificial muscles (ROV-PAMs) is presented. The system consists of six types of actuating modules and three types of fluidic supporting modules each embedded with magnet-based connectors so that the modules can be assembled to modify the system behavior. The module can be used in a myriad of ways, including extending their working range, creating complex geometries upon deformation, and cooperating to improve overall performance. A simple analytical model for the actuating modules is derived based on the law of conservation of energy, and the model is verified experimentally which shows that this intuitive model can provide a reasonable prediction of performance. A block sorting robot is built using three different types of actuating modules with multiple fluidic supporting modules, and the robot shows that it is possible to flexibly and easily assemble modules to build a robot capable of completing diverse tasks. The ROV-PAM module and its concept can be applied to realize robotic designs, which can be altered on-the-fly to adjust its functionality to meet the evolving requirements required for truly flexible automation.

Elasto-Plastic Seismic Shear Distributions of Frame-Wall Structures

ABSTRACT In this study, theoretical and numerical methods were used to research seismic shear distributions of frame-shear wall structures under elasto-plastic conditions. The shear distributions of frame-shear walls were analyzed based on a simplified elasto-plastic analysis model of flexural shear. Based on a preliminary project, three groups of 2D models with different stiffness eigenvalues were designed and used to compare the shear distributions of whole structures and frames. The characteristics of the shear distributions of structures and frames and the development of plastic hinges were analyzed, and the rationality of shear adjustment based on Chinese standards was discussed from the perspectives of structural design, seismic performance and collapse resistance. The results revealed obvious differences between shear distributions of structures caused by strong vs. frequent earthquakes. For strong earthquakes, the shear distributions tended to be evenly distributed with respect to height, while the shear force of the bottom story was significantly larger than that of the upper stories. This was mainly caused by the redistribution of plastic internal forces due to the development of plastic hinges. The shear adjustment of the frame usually affected the reinforcement in the beams rather than in the columns, which contradicted the design concept of strong columns – weak beams. Additionally, shear adjustment had little effect on the seismic performance and collapse resistance of structures. This paper suggests that by ensuring the ability of strong columns, weak beams and plastic hinges to rotate, shear force adjustment can be prevented.

Simple analytical models for estimating the queue lengths from probe vehicles at traffic signals: A combinatorial approach for nonparametric models

This study develops a combinatorial approach for nonparametric short-term queue length estimation in terms of cycle-by-cycle partially observed queues from probe vehicles (PV). The method does not assume random arrivals and does not assume any primary parameters or estimation of any parameters but uses simple algebraic expressions that only depend on signal timing. For an approach lane at a traffic intersection, the conditional queue lengths given probe vehicle location, count, time, and analysis interval (e.g., at the end of the red signal phase) are represented by a Negative Hypergeometric distribution. The simple analytical estimators obtained are compared with parametric methods from literature and highway capacity manual methods using field test data and simulation data involving probe vehicles. The analysis indicates that the nonparametric models presented in this paper match the accuracy of the parametric ones used in the field test and simulated data for estimating queue lengths.

Shannon entropy of transport self-organization due to dissolution–precipitation reaction at varying Peclet numbers in initially homogeneous porous media

Abstract. Dissolution and precipitation processes in reactive transport in porous media are ubiquitous in a multitude of contexts within the field of Earth sciences. In particular, the dynamic interaction between the reactive dissolution and precipitation processes and the solute transport is of interest as it is capable of giving rise to the emergence of preferential flow paths in the porous host matrix. It has been shown that the emergence of preferential flow paths can be considered to be a manifestation of transport self-organization in porous media as these create spatial gradients that distance the system from the state of perfect mixing and allow for a faster and more efficient fluid transport through the host matrix. To investigate the dynamic feedback between the transport and the reactive processes in the field and its influence on the emergence of transport self-organization, we consider a two-dimensional Darcy-scale formulation of a reactive-transport setup, where the precipitation and dissolution of the host matrix are driven by the injection of an acid compound, establishing local equilibrium with the resident fluid and an initially homogeneous porous matrix, composed of a calcite mineral. The coupled reactive process is simulated in a series of computational analyses employing the Lagrangian particle-tracking (LPT) approach, capable of capturing the subtleties of the multiple-scale heterogeneity phenomena. We employ the Shannon entropy to quantify the emergence of self-organization in the field, which we define as a relative reduction in entropy compared to its maximum value. Scalability of the parameters, which characterize the evolution of the reactive process, with the Peclet number in an initially homogeneous field is derived using a simple one-dimensional ADRE model with a linear adsorption reaction term and is then confirmed through numerical simulations, with the global reaction rate, the mean value, and the variance of the hydraulic-conductivity distribution in the field all exhibiting dependency on the reciprocal of the Peclet number. Our findings show that transport self-organization in an initially homogeneous field increases with time, along with the emergence of the field heterogeneity due to the interaction between the transport and reactive processes. By studying the influence of the Peclet number on the reactive process, we arrive at a conclusion that self-organization is more pronounced in diffusion-dominated flows, characterized by small Peclet values. The self-organization of the breakthrough curve exhibits the opposite tendencies, which are observed from the perspective of a thermodynamic analogy. The hydraulic power, required to maintain the driving head pressure difference between the inlet and outlet of the field, was shown to increase with the increasing variance, as well as with the increasing mean value of the hydraulic-conductivity distribution in the field, using a simple analytic model. This was confirmed by numerical experiments. This increase in power, supplied to the flow in the field, results in an increase in the level of transport self-organization. Employing a thermodynamic framework to investigate the dynamic reaction–transport interaction in porous media may prove to be beneficial whenever the need exists to establish relations between the intensification of the preferential flow path phenomenon, represented by a decline in the Shannon entropy of the transport, with the amount of reaction that occurred in the porous medium and the change in its heterogeneity.

A Linear Theory for Periodic Convectively Forced Gravity Waves near a Coastline

Abstract This study presents a simple 2D linear analytical model aimed at investigating gravity waves forced by temporally periodic convection near a coastline. This investigation encompasses two distinct convective heating scenarios: deep convective heating and stratiform heating/cooling. Our model explores the intricate behavior of gravity waves in proximity to a time-dependent convective source and examines their propagation characteristics across diverse atmospheric conditions. Close to the convective source, gravity waves demonstrate nearly horizontal propagation with vertically aligned phase lines. The velocity of their propagation primarily depends on the vertical scale of the convective heating. The presence of a tropopause further extends their horizontal reach through partial wave ducting between the surface and the tropopause. However, the horizontal scale of the convective heating also plays a crucial role in determining the horizontal wavelength, and consequently, affecting the horizontal propagation speed of the gravity waves. If the heating horizontal scale is small compared to the horizontal scale of free waves at the forcing frequency, the heating vertical scale determines the vertical wavelength and thus the horizontal wavelength. However, if the heating horizontal scale is large, the horizontal wavelength determined by the heating vertical scale has little energy, so that the horizontal wavelength is mainly determined by the heating horizontal scale. Moreover, longer periods of convective heating and stronger background winds contribute to an increased downstream propagation distance of the gravity waves away from the source. Additionally, inertia-gravity waves generated by diurnal convection can propagate horizontally over greater distances at a higher latitude but become confined or trapped at latitudes exceeding 30°.

Prediction of crack initiation for notched concrete beam from FPZ at maximum load

The initial cracking load (Pi) of a notched concrete beam, difficult to measure, has been predicted from the maximum fracture load (Pmax) together with the notch-tip fracture process zone (FPZ) at Pmax. A simple analytical model is used to link Pi and Pmax together through the FPZ. The corresponding initiation and unstable fracture toughness, Ki and Kun, have also been determined. The model assumes that the lower limit of Pmax from a group of identical notched concrete beams corresponds to the lower limit of the FPZ length FPZL, so that the lowest limit Pmax = Pi is established for FPZL = 0. Detailed FPZ measurements before and at Pmax using a digital image correlation technique were analysed and used to predict the initial cracking load Pi. Six different specimens with various sizes (W = 40, 60 and 80 mm), initial notches (a0 = 12 to 48 mm) and FPZL (7 to 13 mm) at Pmax showed the average ratio of FPZL/(W – a0) was around 0.25, indicating the Pi/Pmax ratio was around 0.67 based on the analytical model. The crack growth resistance KR-curve between the crack initiation toughness Ki at Pi and the unstable fracture toughness Kun at Pmax was also established approximately by the simple model. Estimated intrinsic fracture toughness KIC was compared with Ki and Kun. The influence of average aggregate size dav on Pi and FPZL at Pmax was also discussed.

Numerical and experimental study of a suspension bridge with combined viscous-steel damping system under train and seismic loads

The longitudinal dynamic performance of long-span bridges with passive vibration control devices when subjected to vehicle and seismic loads has raised extensive attention of the civil engineering community. This study aims to provide numerical and experimental assessments of the dynamic performance of a railway suspension bridge with the Combined Viscous-Steel Damping System (CVSDS) under various excitations. The deck is simplified to a single-degree-of-freedom (SDOF) system according to the longitudinal vibration characteristics of the suspension bridge. The Dynamic Equation Method (DEM) and Fourier Expansion Method (FEM) are suggested for the equivalence of the spatiotemporal variable train loads to horizontal excitations. A simplified two-stage analytical model is proposed to simulate the restoring force characteristics and fuse-lock function of the CVSDS. Shake table tests are conducted to further illustrate the feasibility of the simplified model and evaluate the effectiveness of the CVSDS. The results indicate that the SDOF system is reasonable and satisfactory in simulating the deck displacement. The two-stage working mechanism of the CVSDS is verified by both the simulation and experiment, i.e. the viscous fluid damper works under train loads and the steel yielding damper operates under earthquakes. The vibration mitigation effectiveness of the CVSDS is remarkable.

The universal power spectrum of quasars in optical wavelengths

Context. The optical variability of quasars is one of the few windows through which we can explore the behaviour of accretion discs around supermassive black holes. Aims. We aim to establish the dependence of variability properties, such as characteristic timescales and the variability amplitude, on basic quasar parameters such as black hole mass and the accretion rate, controlling for the rest-frame wavelength of emission. Methods. Using large catalogues of quasars, we selected the g-band light curves for 4770 objects from the Zwicky Transient Facility archive. All the selected objects fall into a narrow redshift bin, 0.6 < z < 0.7, but cover a wide range of accretion rates in Eddington units (REdd) and black hole masses (M). We grouped these objects into 26 independent bins according to these parameters, calculated low-resolution g-band variability power spectra for each of these bins, and approximated the power spectra with a simple analytic model that features a break at a timescale, tb. Results. We find a clear dependence of the break timescale, tb, on REdd, on top of the known dependence of tb on the black hole mass, M. In our fits, tb ∝ M0.65 − 0.55REdd0.35−0.3, where the ranges in the exponents correspond to the best-fitting parameters of different power spectrum models. This mass dependence is slightly steeper than that found in other studies. Scaling tb to the orbital timescale of the innermost stable circular orbit (ISCO), tISCO, results approximately in tb/tISCO ∝ (REdd/M)0.35. In the standard thin disc model, (REdd/M) ∝ Tmax4, where Tmax is the maximum disc temperature, so that tb/tISCO appears to scale approximately with the maximum temperature of the disc to a small power. The observed values of tb are ∼10 longer than the orbital timescale at the light-weighted average radius of the disc region emitting in the (observer frame) g-band. The different scaling of the break frequency with M and REdd shows that the shape of the variability power spectrum cannot be solely a function of the quasar luminosity, even for a single rest-frame wavelength. Finally, the best-fitting models have slopes above the break in the range between −2.5 and −3. A slope of −2, as in the damped random walk models, fits the data significantly worse.

Carbon fabric-reinforced cementitious mortar composites for rehabilitation of continuous concrete beams with corroded reinforcement of various severity

Test results of 14 continuous concrete beams with corroded reinforcement of various severity are reported. Six corroded beams were tested to failure without repair. Carbon fabric-reinforced cementitious mortar (C-FRCM) repair solutions were applied to seven corroded beams. One virgin beam was used as a benchmark. Continuous beams with 20–40% sagging corrosion experienced 9–15% reductions in their load capacity. The beams with hogging corrosion experienced a maximum strength reduction of 9%. The C-FRCM repair solutions were successful in upgrading the response of the corroded beams. The corroded-repaired beams, except one, experienced a ductility index comparable to or higher than that of the virgin beam. The C-FRCM repair delayed yielding of the corroded steel and reduced the moments transfer after the occurrence of the first yielding. A simplified analytical model capable of predicting the load capacity of the tested beams was introduced and verified against the experimental results.

Urban Air Mobility Profitability and Operational Sensitivity to Battery and Charging Technology

Designs for electric vertical takeoff and landing (VTOL) aircraft deviate from traditional aircraft designs and include a wide variety of different configurations. Significant uncertainty also exists regarding the status of future battery technology, including energy density and charge rates. This paper presents a simple analytic model to estimate the profitability of an urban air mobility electric VTOL aircraft for a variety of vehicle configurations, battery technology parameters, and economic factors. Five main elements are considered by the framework: aircraft performance, battery technology, mission profile, mission economics, and electrical grid parameters. A sensitivity analysis is provided, comparing the operational performance and profitability of three electric VTOL concepts (lift plus cruise, quadcopter, and side by side), with respect to electrical grid and battery technology factors. The takeoff weight to maximize the number of completed routes or the overall profitability is also examined. Interestingly, results show that these two values do not coincide across the entire design space due to the nonlinearity of the battery life cycle with respect to the depth of discharge, which strongly affects battery replacement cost.

Pinning voltage model of vertical pinned photodiode for Dual-Pixel image sensor

This paper presents a simple solution for the pinning voltage of vertical pinned photodiode used in a dual-pixel configuration for phase-detection autofocus applications. Analytic solution of the conventional square deep photodiode has been presented elsewhere. However, this model cannot be adopted to dual pixel where a square pixel contains two rectangular photodiodes. Therefore, we propose a simple analytical model for the rectangular deep photodiode for dual pixels and validate its accuracy by TCAD simulations. The presented model accurately predicts the pinning voltage and potential inside the deep photodiode for dual pixels, thereby confirming its usefulness in the ab-initio design of the pixel as well as in the analysis of the photodiode design.

Stability analysis of heavy machinery moving on weak subsoil. 3D FEM model vs. analytical models

In this paper, the authors present an extension of the scope of the previously conducted research to the full three-dimensional computer simulation (using the finite element method), which takes into account the interaction between: heavy caterpillar tracks system – working platform – weak subsoil. The article presents a computer model considering two caterpillars, resting on elastic-plastic sub-soil, with standard Mohr-Coulomb yield conditions, allowing for computer simulation of the behavior of the system up to achievement of ultimate limit state. The results of the above model are treated as the reference for a simplified Analytical Models of estimating the limit state, which might be used in design procedures. In turn, these Analytical Models are enhancements of previously presented one. The most important results concluding form the Analytical Model are simple interaction formulas, in the space of moments acting on the machine-subsoil system, limiting a domain of safety in given soil conditions.

First Sagittarius A* Event Horizon Telescope Results. VIII. Physical Interpretation of the Polarized Ring

In a companion paper, we present the first spatially resolved polarized image of Sagittarius A* on event horizon scales, captured using the Event Horizon Telescope, a global very long baseline interferometric array operating at a wavelength of 1.3 mm. Here we interpret this image using both simple analytic models and numerical general relativistic magnetohydrodynamic (GRMHD) simulations. The large spatially resolved linear polarization fraction (24%–28%, peaking at ∼40%) is the most stringent constraint on parameter space, disfavoring models that are too Faraday depolarized. Similar to our studies of M87*, polarimetric constraints reinforce a preference for GRMHD models with dynamically important magnetic fields. Although the spiral morphology of the polarization pattern is known to constrain the spin and inclination angle, the time-variable rotation measure (RM) of Sgr A* (equivalent to ≈46° ± 12° rotation at 228 GHz) limits its present utility as a constraint. If we attribute the RM to internal Faraday rotation, then the motion of accreting material is inferred to be counterclockwise, contrary to inferences based on historical polarized flares, and no model satisfies all polarimetric and total intensity constraints. On the other hand, if we attribute the mean RM to an external Faraday screen, then the motion of accreting material is inferred to be clockwise, and one model passes all applied total intensity and polarimetric constraints: a model with strong magnetic fields, a spin parameter of 0.94, and an inclination of 150°. We discuss how future 345 GHz and dynamical imaging will mitigate our present uncertainties and provide additional constraints on the black hole and its accretion flow.

A simple analytical model for turbulent kinetic energy dissipation for self-similar round turbulent jets

This work presents a simple analytical model for the streamwise and radial variations of turbulent kinetic energy dissipation in an incompressible round turbulent jet. The key assumptions in the model are: similarity in the axial velocity profile with a Gaussian shape, axisymmetric flow and the dominance of radial derivatives of the mean velocity over axial direction derivatives (similar to boundary layer theory). Initially, a simplified eddy-viscosity relation for turbulent stresses is derived using the algebraic stress model by Gatski & Speziale (J. Fluid Mech., vol. 254, 1993, pp. 59–78). Subsequently, with this eddy-viscosity relation, the relation for variations of turbulent kinetic energy dissipation is formulated using the conservation of turbulent kinetic energy. To extract the necessary constants of the model, experimental velocity statistics for round jets are obtained through particle image velocimetry measurements. The experimental results of the mean entrainment coefficient for turbulent jets are also analysed. When comparing the radial variation of turbulent kinetic energy dissipation from the model with experimental results at Reynolds number $1.4\times 10^5$ and numerical results at Reynolds number $1200$ from the available literature, we observe a maximum error of $10\,\%$ and $15\,\%$ , respectively. Finally, using the validated model, we analyse the impact of mean velocity evolution parameters on the behaviour of turbulent kinetic energy dissipation and discuss its potential significance in future studies.

Absorption of collimated incident radiation in a semitransparent strongly scattering medium: Computational analysis and explanation of red algae blooming in snow

The study of directional radiation absorption in weakly absorbing and strongly scattering media is of interest for a variety of important applications, including laser hyperthermia of human tumors in a therapeutic window of transparency, determination of the optical and thermal properties of highly porous ceramics, and calculations of the deep solar heating of snow cover in polar regions and mountains. In such problems, multiple scattering of radiation can lead to a non-monotonic variation of the absorbed radiation power with distance from the illuminated surface of the medium and to the appearance of the absorption maximum at some depth below the surface. This effect has a known physical explanation and can be predicted using the suggested analytical solution based on the transport approximation for the scattering phase function and the two-flux approximation for the diffuse component of the radiation intensity. The range of illumination angles at which the absorption maximum inside an optically thick medium is observed is determined. The position and magnitude of this maximum are also obtained. In the present work, the verification of this approximate solution using reference numerical calculations is carried out for the first time. It is shown that the simple analytical model is acceptable for regular calculations. Computational results for pure snow illuminated by the Sun showed that red light gives the strongest absorption maximum at a small distance from the snow surface. This is a basis of the presented physical explanation for the intense photosynthesis of red microalgae responsible for the well-known ``snow blood'' phenomenon.

Mechanical Properties and Fracture Toughness Prediction of Ductile Cast Iron under Thermomechanical Treatment

Temperature has a great influence on the mechanical properties of ductile cast iron or nodular cast iron. A thermomechanical treatment was carried out at various elevated temperatures of 450 °C, 750 °C and 850 °C using a universal testing machine with a tub furnace. Specimens were held at these temperatures for 20 min to ensure a homogeneous temperature distribution along the entire length of the specimen, before a tensile load was applied. Specimens were deformed to various levels of uniform strain (0%, 25%, 50%, 75%, and 100%). These degrees of deformation were measured with a dial gauge attached to a movable cross plate. Three strain rates were used for each specimen and temperature: 1.8×10−4 s−1, 9×10−4 s−1 and 4.5×10−3 s−1. A simple analytical model was extracted based on the CT tensile test geometry and yield stress and a 0.2% offset strain to measure the fracture toughness (JIC). To validate the analytical model, an extended finite element method (XFEM) was implemented for specimens tested at different temperatures, with a strain rate of 1.8×10−4 s−1. The model was then extended to include the tested specimens at other strain rates. The results show that increasing strain rates and temperature, especially at 850 °C, increased the ductility of the cast iron and thus its formability. The largest percentage strains were 1 and 1.5 at a temperature of 750 °C and a strain rate of 1.8×10−4 s−1 and 9×10−4 s−1, respectively, and reached their maximum value of 1.7 and 2.2% at 850 °C and a strain rate of 9×10−4 s−1 and 4.5×10−3 s−1, respectively. In addition, the simple and fast analytical model is useful in selecting materials for determining the fracture toughness (JIC) at various elevated temperatures and different strain rates.

A bi-phasic numerical approach for non-linear response and stiffness recovery related to residual thermal stress in UHTCMCs

The tensile properties of sintered Cf-ZrB2/SiC UHTCMCs were investigated for different lamination sequences, revealing ultimate strengths of 570 MPa (0°/0°), 120 MPa (0°/90°), and 40 MPa (90°/90°). The results facilitated modeling the material’s non-linear tensile response, characterized by a remarkably prolonged plateau with pseudo-plastic behavior, followed by stiffness recovery before ultimate failure. A simplified analytical model was developed to predict this behavior originated by residual thermal stresses and inelastic phenomena. A complete constitutive law was then developed and implemented in a FE model, utilizing a bi-phasic approach including Drucker-Prager plasticity and orthotropic ductile damage. Two-step analyses were performed, starting with a thermal step to represent the buildup of a self-equilibrating RTS state in the material phases, followed by a mechanical simulation. This demonstrated the model's efficacy in capturing the non-linear response in both homogeneous and cross-ply lay-ups, contributing to advancements in materials engineering and the design of UHTCMCs-based hot structures.

Cost-Effectiveness of 2 Models of Pessary Care for Pelvic Organ Prolapse: Findings From the TOPSY Randomized Controlled Trial

ObjectivesPelvic organ prolapse is the descent of one or more reproductive organs from their normal position, causing associated negative symptoms. One conservative treatment option is pessary management. This study aimed to to investigate the cost-effectiveness of pessary self-management (SM) when compared with clinic-based care (CBC). A decision analytic model was developed to extend the economic evaluation. MethodsA randomized controlled trial with health economic evaluation. The SM group received a 30-minute SM teaching session, information leaflet, 2-week follow-up call, and a local helpline number. The CBC group received routine outpatient pessary appointments, determined by usual practice. The primary outcome for the cost-effectiveness analysis was incremental cost per quality-adjusted life year (QALY), 18 months post-randomization. Uncertainty was handled using nonparametric bootstrap analysis. In addition, a simple decision analytic model was developed using the trial data to extend the analysis over a 5-year period. ResultsThere was no significant difference in the mean number of QALYs gained between SM and CBC (1.241 vs 1.221), but mean cost was lower for SM (£578 vs £728). The incremental net benefit estimated at a willingness to pay of £20 000 per QALY gained was £564, with an 80.8% probability of cost-effectiveness. The modeling results were consistent with the trial analysis: the incremental net benefit was estimated as £4221, and the probability of SM being cost-effective at 5 years was 69.7%. ConclusionsResults suggest that pessary SM is likely to be cost-effective. The decision analytic model suggests that this result is likely to persist over longer durations.

The initial trajectory of a ball released from uniform circular motion

This short paper presents a simple analytical model for the abrupt termination of circular motion, as discussed in the ‘The Most Mind-Blowing Aspect of Circular Motion’. The model confirms that when a string is released, a ball at the far end of the string continues to move in a near-circular motion for a short time.

Assessing the Fate of Benzophenone-Type UV Filters and Transformation Products during Soil Aquifer Treatment: The Biofilm Compartment as Bioaccumulator and Biodegrader in Porous Media.

The fate of selected UV filters (UVFs) was investigated in two soil aquifer treatment (SAT) systems, one supplemented with a reactive barrier containing clay and vegetable compost and the other as a traditional SAT reference system. We monitored benzophenone-3 (BP-3) and its transformation products (TPs), including benzophenone-1 (BP-1), 4,4'-dihydroxybenzophenone (4DHB), 4-hydroxybenzophenone (4HB), and 2,2'-dihydroxy-4-methoxybenzophenone (DHMB), along with benzophenone-4 (BP-4) and avobenzone (AVO) in all involved compartments (water, aquifer sediments, and biofilm). The reactive barrier, which enhances biochemical activity and biofilm development, improved the removal of all detected UVFs in water samples. Among monitored UVFs, only 4HB, BP-4, and AVO were detected in sediment and biofilm samples. But the overall retained amounts were several orders of magnitude larger than those dissolved. These amounts were quantitatively reproduced with a specifically developed simple analytical model that consists of a mobile compartment and an immobile compartment. Retention and degradation are restricted to the immobile water compartment, where biofilm absorption was simulated with well-known compound-specific Kow values. The fact that the model reproduced observations, including metabolites detected in the biofilm but not in the (mobile) water samples, supports its validity. The results imply that accumulation ensures significant biodegradation even if the degradation rates are very low and suggest that our experimental findings for UVFs and TPs can be extended to other hydrophobic compounds. Biofilms act as accumulators and biodegraders of hydrophobic compounds.