Load Movement Research Articles

Investigation of incessant road failure in parts of Abeokuta, Southwestern Nigeria using integrated geoelectric methods and soil analysis

A flexible pavement devoid of discontinuities allows for smooth movement of a vehicle load on the roadway. This study involved the use of integrated geoelectric methods comprised of 1D and 2D Electrical Resistivity Tomography (ERT) as well as soil analysis to investigate causes of unceasing road failures along busy Camp—Alabata Road, Abeokuta, Southwestern Nigeria. Four road sections (two failed portions and one fair section and one good section) were identified along which four resistivity traverses were established along the investigated roadway. Four 1D Vertical Electrical Sounding (VES) points were also carried out on the 2D ERT lines. Apparent resistivity data were measured along the four traverses using Schlumberger and Wenner arrays with the aid of a Campus Ohmega resistivity meter. The VES and 2D resistivity data were processed and inverted using WinResist and RES2DINV softwares, respectively. Twenty soil samples at a sampling depth (0–1.0 m) with an interval of 0.2 m were also collected on all designated road sections and analyzed for selected hydraulic/geotechnical properties related to pavement durability. Penetration resistance (PR) was measured in situ by a penetrologger while other subgrade soil properties were evaluated in the laboratory. The VES results delineate three geoelectic layers comprising topsoil, weathered basement (clayey), and fractured/fresh basement with their corresponding resistivity values ranging between 71 and 282 Ωm, 12–76 Ωm, and 261–10,094 Ωm. The thicknesses range between 0.9 and 3.2 m for topsoil and 4.5–19.1 m for weathered basement. 2D resistivity inverted sections delineate two lithologic layers: topsoil with resistivity values > 200 Ωm, devoid of linear geological structures as competent topsoil on a stable road section while incompetent topsoil on failed road sections were characterized by resistivity values < 200 Ωm. The weathered layers as depicted by 2D inverted resistivity sections were generally of resistivity less than 100 Ωm while fractured/fresh basement were not depicted in the 2D model. Failed road sections are underlain by topsoil with a resistivity (< 200 Ωm), shallow weathered (clayey) layer, and differential settlement of saturated subgrade materials. Soil analyses results showed that the stable portion depicts lowest mean values of plasticity index (5.12%) and liquid limit (22.21%), uniform sandy-loam textural class, highest mean value (1.24 cm/h) of saturated hydraulic conductivity (Ksat); % sand content (73.2%) and Penetration Resistance (PR) values that increased within the sampling depth (0–40 cm). However, one of the failed sections had lowest mean value (0.81 cm/h) of Ksat, % sand content (64.9%) and PR values that decreased within the sampling depth (0–40 cm). Analysis of variance (ANOVA) showed that there were significant differences at the 5% level among all designated road sections with respect to percent silt and moisture content (MC). Adequate engineering construction approaches should be adopted considering the thick layer of incompetent formation (clay) observed across the area investigated. Integrated interpretations present a better resolution and detailed characterization of the substratum underlying the pavement.

Field study on axial behavior of instrumented post-grouted steel pipe micropiles in tropical lateritic soil

This paper presents a field study on the axial behavior of new configuration of steel pipe micropiles in tropical lateritic soil. The micropiles were installed following a two-step grouting process with high injection pressures at a new experimental site located at the University of Campinas (Unicamp). The main innovation of the micropiles relies on the use of high-strength steel pipes as a drilling tool, casing protection, structural component and injection device. Full-scale pile loading tests were performed under compression and tension loads to investigate the axial behavior of the micropiles. The micropiles were instrumented along the shaft with electrical extensometers, and they were monitored during the progress of the loading tests. The load–movement responses, elastic moduli, axial load transfer mechanism, and unit bond stress relating to the micropiles and their interactions with the tropical soil were measured and evaluated. The bearing capacity of the post-grouted micropiles was considerably improved by the proposed post-grouting technique. The ultimate load capacity of the grouted steel pipe micropile under a compression load is approximately the same under a tension load. The average ultimate bond strength was 99 kPa and 100 kPa for the micropile under compression and tension, respectively. The distribution of unit bond stress along the shaft of the micropile under compressive and tensile load presented a post-peak softening behavior. The average ultimate grout-to-ground strength at the soil–micropile interface was 2.4 and 1.7 times greater than other nongrouted and non-injected piles installed in the same soil conditions at Unicamp.

The Study for the Influence of Nonlinear Foundation on Responses of a Beam to a Moving Load Based on Volterra Integral Equations

The Study for the Influence of Nonlinear Foundation on Responses of a Beam to a Moving Load Based on Volterra Integral Equations

Trajectory Identification for Moving Loads by Multicriterial Optimization.

Moving load is a fundamental loading pattern for many civil engineering structures and machines. This paper proposes and experimentally verifies an approach for indirect identification of 2D trajectories of moving loads. In line with the “structure as a sensor” paradigm, the identification is performed indirectly, based on the measured mechanical response of the structure. However, trivial solutions that directly fit the mechanical response tend to be erratic due to measurement and modeling errors. To achieve physically meaningful results, these solutions need to be numerically regularized with respect to expected geometric characteristics of trajectories. This paper proposes a respective multicriterial optimization framework based on two groups of criteria of a very different nature: mechanical (to fit the measured response of the structure) and geometric (to account for the geometric regularity of typical trajectories). The state-of-the-art multiobjective genetic algorithm NSGA-II is used to find the Pareto front. The proposed approach is verified experimentally using a lab setup consisting of a plate instrumented with strain gauges and a line-follower robot. Three trajectories are tested, and in each case the determined Pareto front is found to properly balance between the mechanical response fit and the geometric regularity of the trajectory.

Investigation of Structure of Technology Cycle Time of Hydraulic Manipulators in the Process of Loading Forwarders with Logs

In the practice of using cut-to-length technology, hydraulic manipulators are widely used. Understanding manipulator cycle is important for improving existing logging technologies and developing new machine designs. The paper analyzes structure of technological cycle and operating time of manipulator in the process of loading forwarder on skid trails. Twenty-one loading processes were investigated. In the structure of technological cycle, the following elements were considered: empty movements, loaded movements, movements of manipulator links when performing operations inside load space of forwarder and special techniques such as re-grabbing logs and pulling of an incompletely closed log grip through the logs when the ends of the grabbed logs tilt and abut against the ground used during loading movement. Statistical processing of data showed that median values of samples consisting of time intervals of empty movements are in trange from 3.8 to 6 seconds, the median of samples of loaded movements is 6–16 seconds and median of samples of a pair of movements 5–9 seconds. With a 95% degree of probability, under the studied production conditions, the time of one loaded movement falls within the range of 4–14 seconds; one empty movement – in the range of 3–7 seconds. Total time of empty movements takes a share from 20 to 45% of the total loading time (on average 30%), the total time of loading movements is from 51 to 72% (on average 63%), the time of operations inside the load space is from 0 to 18% (on average 7%). Time of loaded movements, including use of special techniques, is from 13% to 64% of total time of loaded movements (or 10–53% of total number of loaded movements). The time, consisting of a pair of movements: empty and loaded, is somewhat influenced by forwarder size. Duration of one loaded movement is significantly affected by use of special techniques by the operator. Number and duration of loaded movements with these techniques is significantly influenced by: average size of loaded assortments and number of assortments carried in the grapple during one loaded movement. No significant influence of average size of assortments, number of assortments in grapple and size of the machine on empty movements was found. However, some influence on empty movements of number of loaded movements performed from one forwarder parking lot was observed. Duration and frequency of operations within the load space are weakly correlated with the size of assortments and forwarder size.

To the question of action on the rods lying on elastic foundation, inertial load with a variable speed of its movement

A method for calculating the rods on elastic foundation under the inertial load action when it moves at a variable speed is proposed. Test problems about a force or load movement with variable speeds along a hinged beam and about the movement with a high-speed railway car deceleration along a track section modeled by a hinged supported beam of great length on an elastic foundation are considered. The selection of the elastic foundation material of the rail track determines the dynamics of the high-speed railway car in different modes of its movement. To construct the methodology, the previously proposed by the author of the article solutions are used: a step-by-step procedure for solving the problems of unsteady dynamics of structures and the method of “nodal accelerations” to take into account the action on structures of a moving inertial load.

Allowing the Load to Swing Reduces the Mechanical Energy of the Stance Leg and Improves the Lateral Stability of Human Walking.

Loaded walking with typical rigid backpack results in a significant increase in the mechanical energy of the stance leg and a decrease in lateral stability. Allowing the load to swing, which has been applied in shoulder pole, a tool widely used in Asia for load carriage assistance, may attenuate these effects. This paper theoretically analyzes and experimentally validates the biomechanical and energetic effects of the swinging loads. When walking with a 30 kg load, allowing the load to swing reduces the fore-aft leg impulses by over 19% and further reduces the mechanical energy of the stance leg by 12.9% compared to the typical rigid backpack. The whole-body metabolic cost has no significant change, which may be attributed to the increase in the muscle work of the upper body and the leg swing. Moreover, the load movement out of phase to the human in the lateral direction reduces the lateral excursion of extrapolated center-of-mass by 27.2%, indicating an increase in the lateral margin of stability and implying an improvement in lateral stability. The results demonstrate that allowing the load to swing reduces the horizontal leg impulses and the mechanical energy of the stance leg, and improves the lateral stability of human walking.

Mechanical and mathematical modeling of the load movement on the thread wound on cylindrical drum with movable axis

A mechanical system, where the load in the form of material point is suspended on inextensible thread screwed on the rotating cylindrical drum, but the drum is connected to the boom rotating around fixed horizontal axis is considered. Using the Lagrange equation of the second kind, a mathematical model of the motion of the mechanical system is obtained. The system has three degrees of freedom, two of which are cylindrical. The investigation of the system motion is carried out using computer technology. As a result, the dependences of linear and angular coordinates and velocities in time at different values of the output data for two main modes of the system operation, namely – under the conditions of lifting and lowering the load are obtained. Appropriate graphs are constructed, including the trajectories of the cargo motion. The mathematical model takes into account nonlinearities of the system and allows you to find the amount of tension of the hoisting rope at any time. The analysis showed that vertical oscillations occur twice as fast as horizontal ones. The phase portrait of the generalized coordinate (angle of the rope with the vertical axis) is the focus, which is untwisted when lifting due to nonlinearity in the system, and when the load moves down, the focus, which twists and approaches the mathematical pendulum is obtained. The obtained results can be used in modeling of controlled pendulum motions for different mechanical systems. The methodology and program are recommended to the students and graduate students in terms of learning the principles of construction and analysis of complex nonlinear dynamical systems.

CONTROLLED VIBRATING MILL FOR GRINDING BULK MEDIUM

One of the advanced types of grinding equipment are vibrating mills, which provide high specific productivity at relatively low energy consumption, adjustable tone of grinding products. Vibration impact on the product significantly increases the shock-absorbing effect with the possibility of wide and separate variation of shock and abrasion factors. Significant speed of mechanical and heat and mass transfer processes, a high degree of homogeneity of the obtained products, the possibility of efficient fine grinding and dispersion of the product at relatively low energy consumption lead to the widespread use of vibratory grinding. The constructive scheme of the mill is developed, in which the flat vertical vibrating field provides lifting of a part of loading and by means of the transport-reloading device carries out its continuous adjustable movement from one grinding chamber to another, thereby circulating-spatial movement of the environment in which there is a grinding process. shock interaction of grinding bodies and material that is crushed. The priority direction of development of science and technologies at the modern level is the development, creation and implementation of new generation mechatronic systems. One of the most important rules for the construction of vibrating mills is the need to maximize the degree of their automation in order to increase productivity, improve the quality of grinding and reduce the cost of the process. Also in the article the structural model of the controlled vibromill with spatial-circulating loading movement which at change of weight of a working body in the course of separation and unloading of the crushed material from a grinding chamber constantly adapt to a resonant mode of work at the set technologically optimum parameters (productivity) and the minimum power consumption.

Large eddy simulation of sediment transport in high flow intensity by discrete particle method

The processes of sediment transport in high flow intensity are studied through numerical simulation using a coupled CFD (computational fluid dynamics)-DPM (discrete particle method) model with a focus on discussing the co-existence problem of bed load and suspended load and the corresponding sediment concentration distribution. It is shown that for the sediment-laden flows, the components of turbulence intensity decrease slightly as sediment concentration increases. The bed load and suspended load both coexist in a transition layer. Particle collision plays an important effect on the velocity of bed load movement. The total sediment transport rate obviously increases with the increase of flow intensity, but the bed load transport rate does not clearly increase. In the present study, the maximum value of suspended sediment concentration curve is about 7%, and increases with the increase of the flow intensity. The simulation results are generally consistent with experimental observation.

A Method of Adaptive Control of an Overhead Crane with Direct Tracking of the Load Movement

The paper proposes a method of automated control of an overhead crane aimed at direct tracking of horizontal movement of the load at a set height to the designated position under the conditions of continuous a priori uncertainty of the load parameters and external disturbances. The latter include wind effects, friction changes in the crane trolley movement, etc. The approach replaces two conventional problems: tracking of the crane trolley movement to a set position and damping of angular oscillations of the load. In addition, the proposed control method is based on an adaptive control approach with an identifier and an implicit reference model using simplified adaptation conditions. The latter are reduced to the requirement of convergence of the identification residual at applying an algorithm for continuous identification and the selection in a certain range of constant evaluation of the control coefficient. The said evaluation is chosen sufficiently large in its absolute value to provide the largest margin of stability of the closed control system in amplitude with the required quality of control. In order to implement continuous parametric identification, it is proposed to apply recursive least squares method with a forgetting factor. The reference model is chosen in the form of an oscillatory link with an eigenfrequency not exceeding that of a controlled object with a fixed base and falling within an experimentally set range. For closer definition of the reference eigenfrequency, an evaluation of the load suspension length with an accuracy of at least 30 % is required. The simplest algorithm for obtaining such an estimate is proposed. It is based on the average velocity of the vertical movement of the load, which is generally approximately known. The paper proposes a simple algorithm for obtaining such an evaluation and provides the results of model studies of the efficiency of the proposed adaptive control system on the basis of the performance of the developed experimental overhead crane unit, taking into account the characteristics of standard data sensors and drives. The proposed method has demonstrated its high efficiency in a wide range of loads and disturbance conditions. It can serve as a basis for development of functional control systems for any type of cranes for moving suspended loads.

Demountable Rod Structures with Flexible Connections Ensuring the Reliability and Safety of Construction Objects

Individual walls of structures based on wedge-type scaffolding can be different in height and are often used as enclosing structures for different cultural and sporting events. Usually, such structures are covered in the longitudinal direction with an awning cloth on both sides, which is why they take on the full wind load from the entire area of the awning. When calculating such structures, the wind load is the determining load. In practice, these structures are built according to the recommendations of the manufacturer’s catalog of scaffolding, and they are repeatedly statically indeterminate systems with a large number of unloaded elements. This increases the material consumption of the structure and increases the cost of transport and installation work. In structures made of modular scaffolding, diagonal elements are used to give spatial rigidity to the structure, to reduce the calculated length of vertical elements, and to perceive the shift movements of the cell caused by uneven vertical movements of adjacent posts and horizontal loads. A structure with a full set of diagonal elements has a large number of weakly loaded elements. In this regard, it is possible to perform the so-called «discharged» construction scheme for more efficient use, replacing rigid diagonal elements with cable ties and reducing the number of diagonal elements in the longitudinal direction. The main task of the work is to analyze the stress-strain states of both the original system with rigid diagonal elements and systems obtained by partially replacing standard diagonals with flexible connections in the form of pre-stressed and non-pre-stressed cable ties. In order to study the actual operation of elements of rod collapsible structures and improve their design solutions, an experimental study of a fragment of the Layher system with cable ties was performed. Based on the experiment, it was determined that the actual movements when using flexible connections differ significantly from the calculated ones. The reason for the discrepancy is the deformation of the elements in the attachment points. To increase the rigidity, the design of the attachment unit needs to be changed.

The effect of lubricant film on the dynamic response and signal transmission of moving load dynamic problems

Moving load dynamic problems with lubricant film are common in engineering. Previous studies of this kind of problem often ignored lubricating oil film, or regarded oil film as a simple linear system. To avoid errors caused by the nonlinearity of oil film, hydrodynamic equations are used to describe the oil film subsystem accurately in this paper. By coupling the kinematic systems (moving mass and elastic carrying mechanism), a comprehensive model of moving load dynamic problems with lubricant film is established, and a general numerical procedure of the problem is given. Then the dynamic response and the transmission law of load in the mechanism are studied by taking a reciprocating friction pair of a typical marine engine as an example. Results show that the load transmission is not sensitive to low-frequency harmonic signals, but has a strong filterability to the mid-high frequency harmonic signals. It is also found that the transfer rate of excitation signal through the oil film does not decrease smoothly as frequency increases, and there exist multiple peaks in the frequency domain.

Hydrodynamic modeling and radiotracer investigations in Kolkata Port Trust, Kolkata, West Bengal, India

In this study, hydrodynamic modeling and radiotracer investigations were conducted in Kolkata Port Trust, Kolkata, West Bengal, India to investigate the dispersion of sediments and to evaluate the suitability of three different dumping sites (Upper Auckland, Lower Auckland and Eden) for dredged sediments along a navigation channel. Scandium-46 (148-240 GBq) comprising scandium glass powder with a particle size distribution ranging from 75-100 μm was used as a radiotracer. The radiotracer was injected onto the seabed at the selected site using a remotely operated injection system and its movement on the seabed was tracked over a period of three months using waterproof NaI(Tl) scintillation detector. The tracer concentration curves were plotted on a site map of the area for different trackings and isocount contours were plotted. Qualitative information was obtained from the isocount contours such as the general direction of movement and spread of the radiotracer. The isocount contours showed that the sediment predominantly moved away from the navigation channel. From the isocount, a transport diagram was plotted based on isocount counter and sediment transport parameters such as the general direction of movement by sediments on the seabed, transport velocity, transport thickness and bed load movement rate were determined for all the sites. The dispersion patterns obtained for the sediments by modeling were compared with the experimental results and they were found to be similar. Thus, the model results were validated and the proposed sites were found to be suitable for dumping the dredged material because the sediments did not return to the navigation channel.

A New Insight to Vibration Characteristics of Spans under Random Moving Load: Case Study of 38 Bridges in Ho Chi Minh City, Vietnam

We propose a novel representative power spectrum density as a specific characteristic for showing responses of spans during a long operational period. The idea behind this method is to use the representative power spectrum density as a powerful tool to evaluate the stiffness decline of spans during their operation period. In addition, a new measurement method has been introduced to replace the traditional method of monitoring the health conditions of bridges through a periodic measurement technique. This helps to reduce costs when carrying out testing bridges. Besides, the proposed approach can be widely applied not only in Vietnam but also in many other underprivileged countries around the world. Obtained results show that, during the operational process of spans, there is not only a pure vibration evaluation such as bending vibration and torsion vibration tests but also a combination of various vibration types including bending-torsion vibration or high-level vibrations like first-mode bending and first-mode torsion. Depending on each type of structure and material properties, different types of vibrations will appear more or less during the operational process of spans under a random moving load. Furthermore, the representative power spectrum density is also suitable for evaluating and determining many different fundamental vibrations through the same measurement time as well as various measurement times.

Smart and Sustainable Logistics Ecosystem of Panama: A Conceptual Model

Greta Thunberg highlighted in her speech during the COP 2019 the lack of integrity about the goals of the countries in emission reduction when vessel and aircraft transportation has a great impact over pollution and none of them were addressed, that is the case of multimodal logistics systems in the world wide world. The question is What are Latin-American multimodal Logistics systems doing about it? Latin America has a great model in Pollution reduction and optimization of operations because Panama is working for decades to reduce emissions in the Panama Logistic ecosystem. For example, Panama Canal expansion increased the efficiency of movements in global commerce while reducing the impact of emissions. During the decade of 2010s, the Panama Canal took the risk to expand the canal to a third set of Locks and a new type of vessel arrived, the Neo-Panamax, which increased the capacity per vessel from 8,000 TEUS to 15,000 TEUs. Panama is increasing the awareness about the logistics impact over the emissions, but there are still challenges because of the increment of 87.5% of the load movement into the Logistic hub of Panama, and there is a need to address real-time information about the performance of the Distribution Centers, the ports, and the interaction with the Logistic ecosystem to increase efficiency and reduce CO2 emissions. Thus, the main objective of this research is to summarize the journey of the Panama Logistic Innovation path that results in a conceptual model of Smart and Sustainable Logistic Ecosystem (SSLE).

3D Spectral Element Solution of Multilayered Half-Space Medium with Harmonic Moving Load: Effect of Layer, Interlayer, and Loading Properties on Dynamic Response of Medium

Abstract The road pavement is a typical three-dimensional (3D) multilayered half-space medium, which consists of the surface courses, base courses, and soil subgrade/foundation. It is critical to u...

Аналіз пуску шарнірно-зчленованої стрілової системи при оптимальному ривковому режимі руху

This article presents the results of an analytical study of the kinematic and power parameters of the movement of the articulated boom system of the crane at the beginning of the movement. The study was carried out during the acceleration of the electric motor of the mechanism for changing the departure from the state of rest to the rotation frequency corresponding to the nominal operating speed of the load movement. In this case, the start of the electric motor occurs, provided that the entire boom system moves along with the load according to the law of jerking optimization. The using of this regularity allows you to completely smooth out the swinging of the load at the beginning of the movement. In addition, towards the end of the acceleration, the same speeds and accelerations are provided between the end point of the crane trunk and the load. This makes it possible to ensure high smoothness of movement of the boom system, and to avoid the load swinging after the rotor of the electric motor reaches the rated speed. Also, a study of static, dynamic and total force in the drive gear rack was carried out. These studies were carried out at different duration of the process of starting the electric motor according to the law of jerking optimization. This made it possible to establish the dependence of the studied kinematic and power parameters on the duration of the transient process. Based on the above, recommendations have been developed for choosing the duration of the acceleration of the electric motor in the mechanism for changing the departure. During of the study, graphs of changes in the studied parameters of the boom system in time were built. Graphical dependencies were obtained with the most acceptable duration of the acceleration mode from the point of view of reducing the dynamic loads on the links of the boom system, improving the technological process of the crane and its ergonomics.

Strengthening the 1960s UK Commonwealth Institute hyperbolic paraboloid roof

The Grade II*-listed 1960s roof to the former Commonwealth Institute consists of a central post-tensioned concrete hyperbolic paraboloid shell, typically only 75 mm thick, and is one of the few examples of large-scale concrete shell structures in the UK. After being unoccupied for a decade, in 2012, the Design Museum announced its plans to move into and redevelop the building. In order to make the space functional, the interior and foundations needed to be demolished and the entire 3100 m2, 2000 t roof held up 20 m above ground temporarily while the new structure was constructed underneath. This paper explores in detail the steps taken to assess the relatively delicate existing roof structure for the change in loading and future movements in both the temporary and permanent conditions and the resulting innovative strengthening, repair and temporary works required. Limited historical drawings and papers were available, and therefore, non-destructive testing and careful intrusive investigations were used to obtain more information on the as-built details. In order to determine the structural behaviour, hand calculations were conducted to back-calculate the original design intent, and computer modelling was used to conduct sensitivity analyses of the load paths.

Study on the influence of ecological vegetation revetment on river flow and sediment environment

AbstractThis paper studied the influence of vegetation cover on the river water flow environment and on sediment suspended load movement environment, closely combining the development and construction of new ecological water conservancy projects such as ecological embankments and ecological wetlands with ecological vegetation revetment cultivated on river bank slopes. The glass flume experiment was carried out in the vegetation-water flow-sediment environment. In the experiment, natural straight holly in the early growth stage was selected as the experimental vegetation, and erect type vegetation with uniform distribution of the upper and lower branches and leaves was simulated, and a total of 14 experimental groups were set in different combinations with fixed bed, movable bed, submerged and non-submerged conditions. The measured data of flow quantity, flow velocity and suspended load concentration were achieved in the experiment. The experimental results show that: (1) as to the influence of vegetation on the water flow environment, the vegetation canopy density directly affects the turbulent environment of the water flow, and the greater the density, the greater the disturbance to the water flow environment, and the flow velocity near the canopy will be decreased sharply; (2) in the fixed bed, under submerged conditions, the maximum turbulence intensity appears near z/h = 0.6; under non-submerged conditions, the turbulence intensity near the water surface is largest. In the movable bed, under submerged conditions, the maximum turbulence intensity reaches the maximum in the top and upper locations of the top of the plant, and the turbulence intensity reaches the maximum at the top of the plant under non-submerged conditions. (3) In terms of the influence of vegetation on the sediment suspended load movement environment, the concentration of suspended sediment decreases with the increase of plant height, the sediment content in the tail of the plant belt is reduced to some degree. When the relative water depth is z/h &amp;gt; 0.5, almost no suspended sediment exists. And the sediment-retaining effect under non-submerged conditions is better than that under submerged conditions.