Bedside safety rails: assessment of strength requirements and the appropriateness of current designs

This second paper in a series of studies of the discomfort produced by multi-axis vibration is concerned with rotational seat vibration. The effects of level, frequency and direction of the roll, pitch and yaw vibration of a firm flat seat have been studied in two experiments. At octave centre frequencies in the range 1-31.5 Hz the first experiment determined the levels of roll, pitch and yaw seat vibration which caused discomfort equivalent to 0-5 and l.25m/s²r.m.s. 10 Hz vertical seat vibration. In the second experiment, comfort contours equivalent to 0.8 m/s² r.m.s. 10 Hz vertical seat vibration were determined from 18 males and 18 females at preferred third-octave centre frequencies from 1 to 31.5 Hz. In all cases the axis of rotation passed through the centre of the seat surface. There was no vibration of the feet and no backrest.

It was concluded that the shape of equivalent comfort contours need not normally depend on vibration, level. Both individual and group equivalent comfort contours are presented. Although there were significant correlations between subject size and subject relative discomfort it is not thought that these correlations have much practical application. In all three axes the median contours of vibration acceleration increase in proportion to vibration frequency. Sensitivity is greatest for roll vibration and least for yaw vibration of the seat.     

Automatic analysis of consistency between requirements and designs

Writing requirements in a formal notation permits automatic assessment of such properties as ambiguity, consistency, and completeness. However, verifying that the properties expressed in requirements are preserved in other software life cycle artifacts remains difficult. The existing techniques either require substantial manual effort and skill or suffer from exponential explosion of the number of states in the generated state spaces. “Light-weight” formal methods is an approach to achieve scalability in fully automatic verification by checking an abstraction of the system for only certain properties. We describe light-weight techniques for automatic analysis of consistency between software requirements (expressed in SCR) and detailed designs in low-degree-polynomial time, achieved at the expense of using imprecise data-flow analysis techniques. A specification language SCR describes the systems as state machines with event-driven transitions. We define detailed designs to be consistent with their SCR requirements if they contain exactly the same transitions. We have developed a language for specifying detailed designs, an analysis technique to create a model of a design through data-flow analysis of the language constructs, and a method to automatically generate and check properties derived from requirements to ensure a design's consistency with them. These ideas are implemented in a tool named CORD, which we used to uncover errors in designs of some existing systems     

NREC: risk assessment and planning of complex designs

Estimating the nonrecurring engineering (NRE) design cost constitutes an essential part of the investment-risk assessment and planning phases of new product development. A product's NRE design cost is the number of staff-months required to successfully complete its design. This information is essential in determining the human resources needed to meet a project's time-to-market constraints. For low-complexity development processes that target relatively stable products, relying on experienced managers to produce NRE design cost estimates is reasonable. But microprocessor design and other leading-edge product development processes often involve hundreds of designers, perhaps located at geographically distinct sites, and consist of a formidable number of tasks. These processes require a more systematic way of generating NRE design cost estimates. To that end, the authors have developed an NRE design cost estimation model and implemented it in a tool called NREC. NREC assists managers in making a fine-grained estimate of a project's NRE design costs, from requirements to final layout, as well as in tracking and assessing costs of completed projects. The tool also enables managers to systematically validate and tune the cost model's parameters according to the particular history of a project's design environment     

一款IP电话机的需求分析设计

需求分析与规格说明是嵌入式产品开发的一个重要环节。本文以一款IP电话机为例,通过"需求分析与概念性规格说明"以及"图形化规格说明"两部分来介绍这阶段工作要点。     

SafeSec Tropos: Joint security and safety requirements elicitation

The growing convergence of information technology with operational technology and the accordant proliferation of interconnected cyber-physical systems (CPSs) has given rise to several security and safety challenges. One of these refers to systematically identifying coherent, consistent, and non-conflicting security and safety requirements. This paper proposes an integrated method for safety and security requirements engineering for CPSs at the design stage of the system lifecycle. The method identifies security and safety objectives, it systematically elicits a comprehensive list of requirements, and it links these requirements to objectives, thus facilitating the process of resolving conflicts. To provide insight into the operations of the method, we demonstrate its use to the most vulnerable CPSs on board the Cyber-Enabled Ship (C-ES). By utilizing the proposed method, the safety and security objectives of these systems were defined, and their safety and security requirements were identified.     

Integrated safety analysis of requirements specifications

This paper describes an integrated approach to safety analysis of software requirements and demonstrates the feasibility and utility of applying the individual techniques and the integrated approach on the requirements specification of a guidance system for a high-speed civil transport being developed at NASA Ames. Each analysis found different types of errors in the specification; thus together the techniques provided a more comprehensive safety analysis than any individual technique. We also discovered that the more the analyst knew about the application and the model, the more successful they were in finding errors. Our findings imply that the most effective safety-analysis tools will assist rather than replace the analyst. A shorter version of this paper appeared in the Proceedings of the 3rd International Symposium on Requirements Engineering, Annapolis, Maryland, January 1997. The research described has been partly funded by NASA/Langley Grant NAG-1-1495, NSF Grant CCR-9396181, and the California PATH Program of the University of California     

Scenario-based assessment of nonfunctional requirements

This paper describes a method and a tool for validating nonfunctional requirements in complex socio-technical systems. The system requirements analyzer (SRA) tool validates system reliability and operational performance requirements using scenario-based testing. Scenarios are transformed into sequences of task steps and the reliability of human agents performing tasks with computerized technology is assessed using Bayesian belief network (BN) models. The tool tests system performance within an envelope of environmental variations and reports the number of tests that pass a benchmark threshold. The tool diagnoses problematic areas in scenarios representing pathways through system models, assists in the identification of their causes, and supports comparison of alternative requirements specifications and system designs. It is suitable for testing socio-technical systems where operational scenarios are sequential and deterministic, in domains where designs are incrementally modified so set up costs of the BNs can be defrayed over multiple tests.     

Means-ends and whole-part traceability analysis of safety requirements

Safety is a system property, hence the high-level safety requirements are incorporated into the implementation of system components. In this paper, we propose an optimized traceability analysis method which is based on the means-ends and whole-part concept of the approach for cognitive systems engineering to trace these safety requirements. A system consists of hardware, software, and humans according to a whole-part decomposition. The safety requirements of a system and its components are enforced or implemented through a means-ends lifecycle. To provide evidence of the safety of a system, the means-ends and whole-part traceability analysis method will optimize the creation of safety evidence from the safety requirements, safety analysis results, and other system artifacts produced through a lifecycle. These sources of safety evidence have a causal (cause-consequence) relationship between each other. The failure mode and effect analysis (FMEA), the hazard and operability analysis (HAZOP), and the fault tree analysis (FTA) techniques are generally used for safety analysis of systems and their components. These techniques cover the causal relations in a safety analysis. The causal relationships in the proposed method make it possible to trace the safety requirements through the safety analysis results and system artifacts. We present the proposed approach with an example, and described the usage of TRACE and NuSRS tools to apply the approach.     

Computer security: A current assessment

The basic question of computer vulnerability is initially explored, including disaster planning and computer fraud. Threat analysis is approached from the viewpoints of cost/benefit trade-offs as well as EDP auditing. A risk analysis approach is used in approaching a possible solution to the problems of vulnerability. Also included are such topics as managing the security function, physical and administrative controls, communications security, data integrity, interactive controls, post-processing procedures, training and qualifications of staff and software security.     

RTO: An overview and assessment of current practice

The practice of implementing real-time optimization (RTO) using a rigorous steady-state model, in conjunction with model predictive control (MPC), dates back to the late 1980s. Since then, numerous projects have been implemented in refinery and chemical plants, and RTO has received significant attention in the industrial and academic literature. This history affords us the opportunity to assess the impact and success of RTO technology in the process industries. We begin with a discussion of the role RTO serves in the hierarchy of control and optimization decision making in the plant, and outline the key steps of the RTO layer and the coordination with MPC. Where appropriate, we point out the different approaches that have been used in practice and discuss the success factors that directly relate to the success of RTO within an organization. We also discuss alternative approaches that have been used to alleviate some of the challenges associated with implementing RTO and which may be appropriate for those unwilling to commit to the traditional RTO approach. Lastly, we provide suggestions for improvement to motivate further research.     

Optimization of wing structures to satisfy strength and frequency requirements

In this investigation minimum weight design of wing structures with restrictions on strength, stability and frequency characteristics is attempted. The multiweb delta wing structure is idealized with three different kinds of finite elements. The constant stress triangular plate elements, the rectangular shear panels and pin jointed bar elements are used to represent, respectively, the cover skins, webs and the stringers of wing structures. A parametric study is made to reduce the number of design variables which in turn reduces the required computational effort. The feasibility of employing linearly approximated redesigns is investigated. Numerical results are presented to illustrate the feasibility. Off-design charts have been obtained by performing sensitivity analysis about the final optimum design point.     

Optimization of multi-cell wings for strength and natural frequency requirements

The present work determines the optimal number of cells for minimum weight design of an aircraft wing under strength and natural frequency constraints for the two cases (i) uniform loading and (ii) a tip moment. Two SUMT optimization algorithms with and without parameters have been used and suggestions for faster convergence for one have been given. The importance of different starting design points and convergence criteria in getting the constrained minimum has been shown. The variables considered are length, chord, skin thickness and various spar thicknesses. The natural frequency has been obtained by the use of exact continuum theory of cylindrical tubes, and comparison with elementary theory has been made. The optimization results indicate that increasing the number of cells beyond two does not lead to any substantial reduction or increase in weight. Also, stringent convergence criterion and more than one starting point are necessarry for better results.     

New trends and requirements for dynamic security assessment

This paper presents the main trends in the development of DSA tools, based on existing experience and following a questionnaire sent to more than 40 utilities world-wide. It is an abridged version of a Cigré brochure produced by the Task Force 38-02-13. It proposes a definition of DSA, and an overview of the current practices in this field, and it examines the general needs and requirements as well as the technical challenges ahead for DSA.     

Laptop displays performance: Compliance assessment with visual ergonomics requirements

The use of display devices such as smartphones, tablets, laptops is now massive and continuous in everyday life. It, therefore, becomes increasingly important to be aware of the performance of these devices, not only in terms of the tasks to be performed but also in terms of interaction with humans and therefore knows any possible effect on the ergonomics of vision. Following previous research activities conducted by the authors on the assessment of the visual ergonomics at video display terminal workstations, the aim of this study is to evaluate the ergonomics of human-system interaction of laptop displays. In details, a sample of 57 laptop displays is analyzed in accordance with the requirements of the EN ISO 9241-3xx series of international standards related to the display luminance, luminance ratio, contrast non-uniformity. An extensive luminance measurement campaign was carried out using a special pattern that allowed to measure the luminance in 13 different areas of the displays. The results obtained with this activity showed a great luminance variability between different displays. Almost all the displays are able to emit high levels of display luminance, and almost all the displays meet the requirement of contrast non-uniformity. However, several devices did not meet the recommended values of luminance ratio. Furthermore, the authors created a simplified graph to allow a rapid evaluation of the performance of the displays. This method could be periodically used in practice in order to evaluate the residual performance level.     

Visual requirements for safety and mobility of older drivers.

Efforts to assess visual deterioration with increasing age, coupled with new mechanisms proposed to limit the exposure of visually impaired drivers to driving risks, have emerged in response to the increase in older drivers. Visual functions discussed in this context include static acuity (photopic, mesopic, and in the presence of glare), dynamic visual acuity, visual field, contrast sensitivity, and motion perception. Exposure control mechanisms discussed include alternative periodic vision testing strategies, visual training, and environmental and vehicular modifications to accommodate the older driver. Finally, relevant research needs are addressed.     

Contract-based modeling and verification of timed safety requirements within SysML

In order to cope with the growing complexity of critical real-time embedded systems, systems engineering has adopted a component-based design technique driven by requirements. Yet, such an approach raises several issues since it does not explicitly prescribe how system requirements can be decomposed on components nor how components contribute to the satisfaction of requirements. The envisioned solution is to design, with respect to each requirement and for each involved component, an abstract specification, tractable at each design step, that models how the component is concerned by the satisfaction of the requirement and that can be further refined toward a correct implementation. In this paper, we consider such specifications in the form of contracts. A contract for a component consists in a pair (assumption, guarantee) where the assumption models an abstract behavior of the component’s environment and the guarantee models an abstract behavior of the component given that the environment behaves according to the assumption. Therefore, contracts are a valuable asset for the correct design of systems, but also for mapping and tracing requirements to components, for tracing the evolution of requirements during design and, most importantly, for compositional verification of requirements. The aim of this paper is to introduce contract-based reasoning for the design of critical real-time systems made of reactive components modeled with UML and/or SysML. We propose an extension of UML and SysML languages with a syntax and semantics for contracts and the refinement relations that they must satisfy. The semantics of components and contracts is formalized by a variant of timed input/output automata on top of which we build a formal contract-based theory. We prove that the contract-based theory is sound and can be applied for a relatively large class of SysML system models. Finally, we show on a case study extracted from the automated transfer vehicle (http://www.esa.int/ATV) that our contract-based theory allows to verify requirement satisfaction for previously intractable models.     

Performance requirements of physically strenuous occupations: validating minimum standards for muscular strength and endurance

Employment rights legislative mandates passed in the USA over the last three decades emphasize the importance of validating performance standards for physically strenuous occupations. This study validated minimally acceptable standards for the muscular strength and endurance necessary to perform fire suppression activities. Incumbent firefighters (n=153) selected for key demographic characteristics completed a simulated set of firefighting tasks (Fire Suppression Evolution) and then a Predictor Test Battery of physical abilities tests. Regression analysis revealed that three predictor test items (hose drag/high rise pack carry; arm lift; arm endurance) combined to significantly predict performance time of the Fire Suppression Evolution (p < or =0.01). Firefighters (n=41) rating videotaped performance times of the Fire Suppression Evolution determined that more than one-half a standard deviation slower than the mean time established by the incumbents reflected unacceptable performance. Approximately 80% of incumbent firefighters passed the minimally acceptable performance standard. Use of the 3-predictor test battery would correctly identify 89% of successful performers and 72% of unsuccessful performers. This study demonstrates that validation of minimal physical performance standards will identify a cohort of individuals with a high probability of not being able to perform critical fire suppression activities. This finding has important implications for examining the relationship between physical performance standards and medical and economic outcomes.